The effect a screen has on the projector's image and contrast ratio - AVS Forum
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post #1 of 39 Old 01-31-2011, 10:14 PM - Thread Starter
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I made this write up to clarify some of the misinformation and misunderstandings that exist with how projector screens affect lighting conditions and contrast ratio.

Example 1) A screen can only change both the black level and white levels together,
hence even if increasing the brightness by a factor of 2x, the difference between them (ON/OFF Contrast) are not changed from a ratio standpoint,
here we have a 2:1 ratio regardless (100|50 = 2:1, 200|100 still = 2:1).

This essentially means the contrast starts and ends at a different part of the contrast spectrum (a brighter or darker range), but the overall Total ON/OFF contrast ratio remained unchanged. So although the perceivable contrast will appear differently at different levels to our eyes, the total ON/OFF contrast ratio cannot be increased in this case. Also note that these levels should be calibrated to standards, not blown out to make some content look better, while making other content look worse.

One of the simplest definitions for contrast ratio that I have seen is shown below:
For instance, if a display claims a contrast ratio of "500:1," what this is saying is that the white areas
(the brightness when the video inputs are at their maximum value) are 500 times the brightness of the
"black" (all video inputs at their minimum).

Example 2) HOW a screen can help black levels without INCREASING ON/OFF contrast
If the black levels become darker from the beneficial effects of a screen, then this is only possible if the screen helped in making the room itself darker or redirected the ambient light to not hit the screen itself as much, fairly simple here. This is because of how our eyes work (the darker the room, the darker a black will appear). So since the screen made the room darker from less reflection, the whites will also be darker. That is what people really mean by perceivable contrast, it's just allowing you to lower the starting range of the total contrast range (the black level part of the contrast range) and still seeing it without the ambient light washing it out. When you did this, the maximum white level also decreased at exactly the same rate. Therefore, this did not increase the projector's TOTAL ON/OFF contrast by even a single number, what it did was allow you to see the lower levels in the contrast range visibly within the limitations of your eyes given a certain amount of light in the room, hence allowing your eyes to view lower levels of the contrast spectrum.

Getting Darker Blacks = ENHANCED PERCEIVABLE ON/OFF CONTRAST might just be called DARKER BLACK LEVELS and DARKER WHITE LEVELS at the same time.
So if a screen improves the appearance of how dark a black is in a given setup, it just demonstrates the fact that some people have their projectors calibrated incorrectly or are running them in a poorly light-controlled room (or a white ceiling or something is wrong). Keep in mind though that since no room can be considered a perfect bat cave, high gain or gray screens or any screen that changes light reflectivity characteristics could potentially improve the image, even in a room thought to be a bat cave. Howver, also note that overall what people are really seeing as far as improvements from a SCREEN are what could have otherwise been acheived simply by calibrating for maximum contrast in a perfect BAT CAVE on any screen regardless of the type of screen material or reflective nature (excluding the one exception being if their image is too bright or dim beyond what their projector can correct, then we need a + or - gain effect on the screen itself to correct the issue).

Reflectivity Characteristics of the Screen affect Contrast Passively not Actively
I have white ceilings like many, so any screen that can reduce reflections will help improve black levels and ANSI contrast overall, but that doesn't mean the screen did it directly, it means the screen did it only by reducing ambient light by redirecting some of the light to a better place or just absorbing / reflecting less light in the case of a gray screen. So in this case, contrast isn't improved directly by the screen ACTIVELY, but its only because the room is not as bright did the ANSI contrast improve, that is how we can still call the screen a passive device. Yet in this situation, the ON/OFF contrast did not improve at all, it just allows you to adjust it to a darker level and for your eyes to see the darker colors at the lower end of the spectrum. Hence the blacks and whites can now be darkened while still allowing you to comfortably view the image without the image appearing to be too dim (thanks to the now darker room).

The only time a Screen can assist the projector to INCREASE the Total On/Off Contrast is in this one scenario below
So the only situation where the screen can affect the ON/OFF contrast as opposed to just changing the white and black levels proportionately together, is by allowing your projector to be calibrated to get back to best mode when the lamp is not bright enough (or too bright), or possibly if your projector just has calibration issues at certain levels of brightness. This is where the HIGH POWER can help so much, or any high gain screen for that matter. Again, this is only referring to the screen allowing you to calibrate within the optimal range, but it is not the screen changing the actual contrast number, it simply allowing your projector to be adjusted at or near a BEST mode, when previously you purposefully had to use incorrect/non-BEST mode values to obtain the best possible picture either due to brightness limitiations of your lamp or the room conditions.

A High Power or High Gain Screen does NOT ruin black levels
As long as the high power does not raise the light so much that it makes the image too bright for your projector to compensate, then the HP will not cause a problem in black levels. On some projectors, sure it can cause a problem by making the black levels start too bright, but that means you need to move the projector off-axis or correct the problem so that the calibration range can be achieved. It is a falsehood that the HP screen will ruin black levels, in the case of white ceilings it may make them better by keeping the room darker overall from less reflected light off the ceiling. Now to acheive the best black levels in a bat cave with a high gain screen, the room has to be absolutely 100% perfectly dark, don't go watching the movie in a white jumpsuit or a silver leotard (don't ask), and your furniture better be black or close to it.

I believe the above issues are why people get so confused on this.

AMBIENT LIGHT
If you have a bunch of ambient light, then it just means you have to calibrate the black level / starting point of the ON/OFF range to a brighter point to compensate, hence the reason the black levels worsen or rise. Now you could have to make this so bright to compensate for the ambient light that the contrast is clipped at the upper ranges, so in this sense the contrast was changed, but this only applies to a non-optimal lighting scenario. The same goes at the lower scales, you could set the lower range of contrast starting so low that the black levels are clipped (at least from what our eyes can see), and the picture is washed out and too dim.

You should NOT try to create a VISIBLE increase in perceivable contrast without checking it against a calibration
This can be a problem because if you perceive an increase in constrast by your eyes alone, then you really have no idea how this affected all movies or scenes as a whole that you will be watching in the future. So the end result is that by trusting our eyes for contrast, we are now straying away from the optimal calibration standards which are there for a purpose, this is to keep movies looking their best on average and how the director intended. Keep this in mind if you are planning on "improving" perceivable contrast by fiddling with stuff or implementing a MAGICAL DIY screen without calibrating back to the correct ranges.

To demonstrate this, start from a THX or ISF mode and go watch Apollo 13, a Pixar cartoon, or Lord of the Rings, or something like this, and notice how most of the scenes are very contrasty looking. It's because the excellent camera work in these films kept most scenes within appropriate ranges to how a projector would optimally display it as an end result. Now go watch a TV episode from the 1970's, you could probably change your projector's settings away from ISF and make the 1970's TV series look better, but then go back and watch Apollo 13 with the new settings, it will usually look worse given all other factors are equal.

Now there is no harm in making an adjustment to the PJ settings temporarily on a really bad quality movie source or poorly lit transfer, but this is why projectors have user stored settings that you store as a calibration, or revert back to after you muddle them up for specific scenarios.

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post #2 of 39 Old 02-01-2011, 06:14 AM
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I agree there is nothing a screen or a room can do to improve contrast ratio beyond the capabilities of the projector. Contrast ratio is the ratio between the whitest white and the blackest black (or lack of light) when measured. What a screen and room can do is all you mentioned above and that is trying to preserve contrast ratio. The killer of CR is dilution with other light. Pointing a flashlight at a black and white ANSI checkerboard pattern will raise both measurements equally lowering the CR overall. Say white was 1000 lumens and black 10 lumens 1000/10 = 100 CR or 100:1 now add a 50 lumen flashlight 1050 white and 60 black 1050/60 = 17.5 CR or 17.5:1 That’s a five times drop in CR.

I also agree with your facts on how screens with gain can also direct ambient light away from the viewer as long as the source of the ambient is not closely inline with the projected beam. In the case of retro reflective screens the ambient is sent back to its source and in the case of angular reflective it skips off the screen at a angle equal to the angle it entered the screen. Neglecting that because these same coatings work similarly on white and neutral gray screens lets assume we have two screens of unity type dispersions one being a 1.0 gain white and the other a .5 gain neutral gray. We have a projector that has a range of calibration such that when calibrated on the white in the above example it produces the 1000 lumens of white and the 10 of black and to use the neutral gray screen it takes 2000 white and 20 black to get it to its best location. Both still produce 100:1 CR without ambient now adding in the flashlight 2050/70 = 29.3 CR or 29.3:1 So in this case we haven’t improved the projectors max CR but in real world terms we have preserved or some would say “improved” by almost doubling the outcome. The cost was having to double the lumens. That’s my take on gray screens when one is needed and that has something to do with perceived contrast but not all.

The thing you didn’t mention about the perception of contrast and ANSI contrast and when discussing some movies cinematography being better to showcase contrast than others is when a image is filmed the more ANSI like the image is, this being a overall bright image with areas of darkness. True ANSI test pattern is black and white equally. The white introduces rebound light into the room so that the effects on the black can be viewed and measured. And viewed and measured are two totally different things. Measured is an absolute number representing a brightness value, when viewed our eyes adjust and provide perception. The human eye can adjust around 22-f stops full range each f stop being a doubling of the one before. That range is huge in terms of vision, many times some really good cameras capability. But nonetheless a digital camera set to auto will take pictures showing this same perception and sometimes even improve on the contrast shown. The reason you hear all the time screen shots are worthless. (not completely true)

Perception is all about our eyes and brain as the overall image brightness goes up our iris closes and blacks become darker in our vision. The easiest way to compare this is by watching a high ANSI contrast movie and seeing those inky blacks and then go to the end credits mostly black with white text. Look at the blacks near the edge of the screen with no white near by. That is better than the best blacks you thought you had been seeing thru the movie. You will also think the blacks are a little better closer to the text. People that loved CRT projectors always loved the fade to black images because CRT had a huge on off number and the room would get as black as a coal mine. Digitals not quite as good but many more lumens on the other end that can be used to improve the perception of contrast.

Sorry for the long post, and a long way around to where I was getting. And that is my whole front projection world for me is built around perceived contrast and preserved contrast. With lots of lumens overdriving a dark screen. The end result is ambient light friendly setup with great ANSI picture quality, the trade off being not as good when on off contrast comes into play.

For what its worth that’s my thoughts on the matter and I could be wrong.
Thanks for taking the time to start an interesting thread topic.

edit:
Below are two screen shots taken by another member , and yes I know screen shots are not perfect examples but will show in a general way the math I put forward above. The two samples were made to try and have a similar reflective index. The image was projected as a split screen, and one photo was taken with all room lights off and the other on. And the trust factor here is the photos show close to what the eyes saw.

Room lights on


Room lights off


I have other photo examples that show more of the complexities of perception if anyone cares to see them.


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post #3 of 39 Old 02-01-2011, 07:30 AM
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Great write up. However I have to disagree a little. There is one screen I am aware of that tends to bend the rules a bit, or at least I think so, the SI Black Diamond screen. By reducing the light reflected off the screen to the sides it darkens the room. This is the key point here, by not allowing wash out (ambient light to brighten the black level) the residual light in the room does not affect the blacks as much as traditional screen. But by also having a 1.4 gain it really makes the whites brighter to the viewer, and the screen is dark gray to start with it really has increased blacks but because of the gain doesn't kill your gray levels. In this case I think the screen does help the contrast. If I take a meter to it my blacks are blacker because of the dark screen and no wash out effect and my whites are whiter because of the gain.

It follows your rules which I find sound but I do disagree with the phrase "there is nothing a screen or a room can do to improve contrast ratio beyond the capabilities of the projector" I think the technology in screens is going to start changing and the screen will have an effect on the contrast and overall picture.

However an important point every screen has it's good and bad point. I find it very important to match the screen to the projector and the room.

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post #4 of 39 Old 02-01-2011, 09:07 AM
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Quote:
Originally Posted by programmergeek View Post
It follows your rules which I find sound but I do disagree with the phrase "there is nothing a screen or a room can do to improve contrast ratio beyond the capabilities of the projector" I think the technology in screens is going to start changing and the screen will have an effect on the contrast and overall picture.
A big part of my post was trying to say I agreed with the OP insomuch as the CR of a projector cannot be improved thru any form of a passive device like a screen. That's just pure and simple laws of physics. But where most people go off in thinking of it as improving is really a case of loosing less with screen A than screen B. There is no perfect screen or theater room and there will always be losses, assuming the screen material is something reflective and in the range of the projectors calibration to correct it. The OP is correct in a black body room capsule that sucks away all light not going into our eyes.

In the real world there are no perfect rooms and the less perfect the more screen tricks can help minimize loss in some manner.

There are two different forms ambient light can take, first being light that's in the room from something other than the projectors beam. It can be the spill out the air vents in the projector or the rope lights on the floor or the kitchen that's behind the family room some people try and use FP in. The second is rebound light leaving the screen and striking something and being redirected back to the screen. That type light is not constant dilution of the image it is instantaneous with the image brightness on the screen so when the image gets bright as it should its also being washed out more as it shouldn't. Screens like the SI black diamond use a dark surface and also directional gain. The gain may be to overcome the attenuation of the dark surface and also to throw redirected projector light coming back to the screen away from the viewers and to a side wall to be absorbed. If the gain can be added to the screen without any of the adverse side effects such as sparkles or warm center image and the viewers are not seated outside the sweet spot of the image IMHO all this could work well to preserve some of the CR the projector is putting out. The only criticism I have had for this screen is how they market it in their videos etc. they show a image on a white high dispersive wide viewing angle screen that's not at the proper calibration for the dark screen they pull down in front and show a dramatic comparison based around apples and oranges.

I was reluctant to post the above pictures because of the gray white sample for the same reason because the image can only be gray scale calibrated to one of the samples at a time. In this case the difference was less dramatic because both samples were of high dispersion with none of the rebound light playing a major part. Those test were made really early on and later testing was done on samples that did hold the same calibration.


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post #5 of 39 Old 02-01-2011, 01:00 PM
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Quote:
Originally Posted by programmergeek View Post

Great write up. However I have to disagree a little. There is one screen I am aware of that tends to bend the rules a bit, or at least I think so, the SI Black Diamond screen.

No the BD screen is subject to exactly the same rules of physics, as set out in the OP.

Quote:
Originally Posted by programmergeek View Post

By reducing the light reflected off the screen to the sides it darkens the room. This is the key point here, by not allowing wash out (ambient light to brighten the black level) the residual light in the room does not affect the blacks as much as traditional screen.

That was already accounted for in the OP.

Quote:
Originally Posted by programmergeek View Post

But by also having a 1.4 gain it really makes the whites brighter to the viewer, and the screen is dark gray to start with it really has increased blacks but because of the gain doesn't kill your gray levels.

That's a bit garbled but seems to imply, falsely, that because the screen is dark gray it keeps the blacks low while the gain increases the whites. That would effectively be saying it increases the projector's contrast ratio, which it can not do.

Whether you are talking about a gray screen with gain or a white screen with gain, the gain will raise the black levels and white levels by precisely the same amount. It won't keep the black levels dark but raise the white levels. If you have a true 1.4 overall gain then whether the underlying screen is gray or white it shouldn't matter - overall black levels will rise the same.

But if you are ONLY talking about the wash out effect then, again, this was already addressed in the OP. The BD screen does not change the rules o' physics and other gray screens with gain react similarly (e.g. the Stewart Firehawk).
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post #6 of 39 Old 02-01-2011, 02:04 PM
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A gray screen will make the blacks darker, correct we both aggree.
But you are saying it will also lower the whites, again aggreed.

However you through a gain into the formula it will reflect more light back to the viewer making the white brigher.

Thus the gray is making the black darker, than refrence (matt white) but the gain is making the white brigher, thus increasing your contrast.

However this is not with out a down side if mesured off cone way to the side the oppsite happens since the light reflected back is concentrated in the cone the sweet spot of the screen if you will.

Now if you are talking a total room avarage and not the viewer position I aggree it can't reflect more light back than you are throughing at it but it can concentrate it where needed.

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post #7 of 39 Old 02-01-2011, 02:57 PM
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Quote:
Originally Posted by programmergeek View Post

A gray screen will make the blacks darker, correct we both aggree.
But you are saying it will also lower the whites, again aggreed.

However you through a gain into the formula it will reflect more light back to the viewer making the white brigher.

Thus the gray is making the black darker, than refrence (matt white) but the gain is making the white brigher, thus increasing your contrast.

No I'm afraid that is a common misunderstanding.

The gain coating increases the reflectivity (focusing light to viewer) of the whole spectrum. Light is light. It doesn't, and can't, just select which light to send back as in "only the brighter areas of the image."

So you've got a misunderstanding of how these specialty screens work to preserve contrast. In a screen like the 1.4 gain BD screen, the gray substrate of the screen material isn't there to make the projected blacks blacker (it could only do so by dimming the entire image). Rather it's there to dampen the effects of off-axis reflected light in the room.

What happens is the gain focuses the projector's light back toward the viewer, raising the brightness. But not all the light goes directly to the viewer (if it did the screen would look more like a mirror). Some of it still scatters in the room, hits the ceiling/floor/walls, much of it heading back to the screen from oblique angles. The darker gray substrate of the screen dims the light reflected back to it from off-axis angles - doesn't reflect it back to the walls as brightly as a white screen. So it better kills nearby surface reflections. Meanwhile the gain coating keeps light coming from the projector location focused toward the viewer to maintain brightness.

It's this combination of effects that allows a gray screen with gain to help preserve contrast in more challenging (read: light) room conditions.

But it doesn't increase the actual contrast ratio of a projector and it does not work by the gray "making the blacks blacker" and the gain "making the whites whiter."

Cheers,
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post #8 of 39 Old 02-01-2011, 03:10 PM
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Using some make believe numbers purely to illustrate my thinking.

The way I view it the screen can not improve on/off contrast ratio. Unless there is a source of ambient light

Ambient light is 1, projector light 100, white 1 gain screen. Screen reflects 100 projector light and 1 ambient light. 100 desired light vs 1 undesired light.

Ambient light is 1, projector light 125, gray 0.8 gain screen. Screen reflects 125 x 0.8 = 100 desired light, 1 x 0.8 = 0.8 undesired light. Higher contrast

Ambient light 1, projector light 40, high 2.5 gain retro-reflective screen with narrow viewing cone. If the ambient light source is off axis then it has a lower gain on the screen, so say 40 x 2.5 = 100 and 1 x 0.5 = 0.5 undesired light. Higher contrast

Ambient light is 1, projector light 1000, black 0.1 gain screen. Screen reflects 100 projector light and 0.1 ambient light. 100 desired light vs 0.1 undesired light. Higher contrast.



With no ambient light sources on/off contrast can not be improved but simultaneous on screen contrast can be improved by the screen if there are room reflections which there will be even in a bat cave.
Light hits screen, light bounces off towards viewer and around the room, the light bounces around the room including back on to and off the screen. So room reflections lower contrast.

Bat cave reduce the amount of light the room reflects to as little as possible.

Smaller screen surface area to room surface area means light bouncing around the room is less likely to hit the screen, the light is being reduced each time it hits a surface so the more surfaces it hits before hitting the screen the less room reflectance.

White screen 1 gain, you hit the screen with 100 light and 100 light is reflected back into the room, room reflections bounces some of that back to the screen say room reflectance is 10%, 10 light is reflected back on to the screen, and due to the screen gain 1, 10 light is reflected off the screen back to the viewer. 100 desired light vs 10 unwanted room reflections

Low 0.8 gain gray screen with higher lumen projector, you hit the screen with 125 light and 100 light is reflected back into the room, with room reflectance 10% then 10 light is reflected back on to the screen, and due to the screen gain 0.8, 8 light is reflected off the screen back to the viewer. 100 desired light vs 8 unwanted room reflections. Less washout by room reflections so higher on screen contrast.

High 2.5 gain retro-reflective screen with narrower viewing cone, and lower lumen projector. You hit the screen with 40 light and 40 x 2.5 = 100 light is reflected to the viewer in the viewing cone. But total light reflected into the room is only 40 light as the screen does not create extra light, room reflectance of 10% results in 40 x 0.1 = 4 light hitting the screen, but due to the screen reflecting light primarily back towards the source only say 50% of that light goes towards the viewer so 4 x 0.5 = 2 unwanted room reflections makes it back to the viewer. 100 desired light vs 2 unwanted room reflections. Less washout by room reflections so higher on screen contrast.

A angular reflective or retro reflective screen is best if you can use the correct projector - screen - viewer angles. A gray screen is also advantageous. In theory a high gain gray screen is most advantageous but unfortunately also has the disadvantages of both types of screen as well as the advantages.
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post #9 of 39 Old 02-01-2011, 07:54 PM - Thread Starter
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Rich is exactly correct on his posts.

This is why there is so much confusion on how a screen affects the projector.
The science of it really isn't that hard, people just wan't to believe that a screen has magical properties that improve the projector.

Also relating to some of the other issues people posted, ANSI contrast has a very small perceivable difference after getting it to a certain point in a bat cave. This can be noted of how the experts all say the JVC's have a better picture but also have much lower ANSI contrast. Many people would be suprised at how low ANSI they are actually viewing their image, your projector might do 500:1 ANSI, but without a bat cave you may be at around 50:1 or lower ANSI which isn't uncommon.

Once you get the room as bat cave status, whether or not your face just got a tan is going to have very little effect on the picture. Wearing white clothes will affect it some, but more importantly is the room. All the screen can do is help bad rooms look better, it cannot help perfect rooms look more perfect (at least not enough from an ANSI contrast spec to matter). Sure we can split hairs and talk about the screen itself or how hot spotting could affect ANSI as given one side of the screen to the other (or any number of other small variables that can affect stuff), but for explanation purposes this stuff is just splitting hairs and we have to assume BAT CAVE means a perfect 100% dark room.

Last I checked, bat caves just have a lot of bats and other dark scary things, not reflective surfaces


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post #10 of 39 Old 02-01-2011, 09:43 PM
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Quote:
Originally Posted by programmergeek View Post

A gray screen will make the blacks darker, correct we both aggree.

Much of this was already covered by the other guys, but just figured I would add another perspective. The gray makes the amount of light that comes off the screen on average darker than a 1.0 matte white screen, so it does make the blacks darker if you consider all possible viewing positions, but that does not mean it makes the blacks darker to a spot getting 1.4 gain. To that spot it makes the blacks brighter, just like it makes the whites brighter to that spot. But only for the places on the screen that have a higher than 1.0 gain. A screen can give you 1.4 gain in the hottest spot and .7 gain out at the edges. In that case it is making the blacks darker out at the edges, but also making the whites darker out there.
Quote:
Originally Posted by programmergeek View Post

However you through a gain into the formula it will reflect more light back to the viewer making the white brigher.

And the black brighter. The screen doesn't know whether it is reflecting black images or white images. The gain is the same for both other than color balance.

One thing a screen can do is have a very non-standard color balance (basically different gains for different wavelengths). If a screen has a push toward red that may be visible on white, but hard to notice on black because red can be hard for humans to see in dark images. So there the perceived contrast ratio may go up, but with a color shift to the screen. And if you have to calibrate differently because of that color shift it may help or hurt contrast ratio (where a reddish screen with a projector weak in red could help things).
Quote:
Originally Posted by programmergeek View Post

Now if you are talking a total room avarage and not the viewer position I aggree it can't reflect more light back than you are throughing at it but it can concentrate it where needed.

Yep, and it does that for absolute black (0% video level) as well as white.

As explained above, the gray can help retain ANSI CR in a room with reflections. A .5 gray layer can kill half the light hitting it, so half the light going to the walls and coming back, then kill half of that light again, for an effective 2x improvement over a 1.0 gain screen (assuming no directionality for either) from the first order reflections. A screen with directionality can do something similar, and a screen with both directionality and a gray layer (like I believe this BlackDiamond screen is) can help retain ANSI CR in both ways.

--Darin

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post #11 of 39 Old 02-01-2011, 09:46 PM
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Quote:
Originally Posted by coderguy View Post

Example 1) A screen can only change both the black level and white levels together, hence the difference between them (ON/OFF Contrast) are not changed (100-50 = 50, 200-150 still = 50).

First, I appreciate the writeup coderguy. I am confused about what your example here is supposed to show though. The screen (like a 2.0 gain) doesn't keep the absolute difference the same, it keeps the relative difference the same, so the numbers would seem like they should be 100-50 and 200-100. The screen would have changed the absolute difference, but not the relative difference, or ratio between the points (which is really what matters as far as that part goes).

Were you trying to say that a screen can't change 100-50 to 200-150?

--Darin

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post #12 of 39 Old 02-01-2011, 09:55 PM - Thread Starter
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Quote:
Originally Posted by darinp2 View Post

The screen (like a 2.0 gain) doesn't keep the absolute difference the same, it keeps the relative difference the same, so the numbers would seem like they should be 100-50 and 200-100. Were you trying to say that a screen can't change 100-50 to 200-150?

--Darin

I corrected it. I was using Psuedo math to show how it does not change the ON/OFF contrast differential. That's why I stated this is a difference and not part of a ratio. 100-50 becoming 200-100 is increasing by a factor of 2 is showing it as a ratio, whereas my original example was using an imaginary measuring system showing an addition/subtraction relationship from both sides of the equation. The 50 was sort of representing the contrast itself I guess you could say, but not a ratio. I have since corrected it since we think of contrast in terms of ratios, not measurement values.

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Originally Posted by darinp2 View Post

Much of this was already covered by the other guys, but just figured I would add another perspective. The gray makes the amount of light that comes off the screen on average darker than a 1.0 matte white screen, so it does make the blacks darker if you consider all possible viewing positions, but that does not mean it makes the blacks darker to a spot getting 1.4 gain.

I agree and you are one of the masters of the deep technical info on this stuff, however sometimes your technical knowledge on the topic is so far adept that it may confuse some people. I'm sure I don't even know all the exceptions, but for me I just learn what I can and move on. We also have to assume a comparison is done at a given level at a given condition using the same levels and same conditions. I mean we can always throw wrenches in it since most people don't even have near enough of a bat cave, which is why a gray or high gain screen can be good.

Some people are still hung up on how they think the screen itself will make enormous improvements in a bat cave given all other factors are equal (color balance, quality of the material, no sheen, etc...). If people have a bat cave, obviously just get the best material that calibrates best to their projector's brightness.

For me I tend to like to have the extra BRIGHTNESS that the HP gives me over a gray screen, and for the most part you can get the blacks close enough in a bat cave even with an HP, even given the light path and viewing angle exceptions. Although either way it does take some work. I just hate it when my lamp gets too dim too fast. The advantage being even if you don't have a bat cave, the HP does quite well if you are able to take advantage of the reflection paths. I'm sure in some cases a grey screen in a near-bat cave will fair better than the HP, but for me it looses too much "brightness play" and makes you kind of stuck with what you have left.

It will be nice when we have affordable LED projectors, because then I'm guessing an ISF calibration will hold closer to the calibration levels much better as the lamp ages.

I think first people need to understand the basic that BAT CAVES are the start to a better image, and that a high gain screen or a gray screen is a compromise (although not a bad one), but nothing beats a projector with super high intrascene ON/OFF contrast in a pure bat cave (not even a magical screen with a lesser projector). They also need to understand that if you finally get very close to a full bat cave, you don't have to go replacing your GRAY or HP screen, as the effects of the Hp can still be advantageous.

There is a lot of people that say "completely avoid the HP in a bat cave", to me that seems like a bad recommendation. I mean if someone has $xxx to spend, I doubt they will beat the overall quality of an HP screen by that much even if the screen is in a bat cave, as long as they compensate properly.


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Originally Posted by coderguy View Post

Also relating to some of the other issues people posted, ANSI contrast has a very small perceivable difference after getting it to a certain point in a bat cave. This can be noted of how the experts all say the JVC's have a better picture but also have much lower ANSI contrast. Many people would be suprised at how low ANSI they are actually viewing their image, your projector might do 500:1 ANSI, but without a bat cave you may be at around 50:1 or lower ANSI which isn't uncommon.

But ANSI checkerboard contrast and on screen simultaneous contrast are not the same thing. Native On/Off contrast is like a best case figure and ANSI checkerboard contrast is like a worst case figure. In most scenes I would expect the JVC projector to have a higher on screen contrast than other projectors.

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Once you get the room as bat cave status, whether or not your face just got a tan is going to have very little effect on the picture. Wearing white clothes will affect it some, but more importantly is the room. All the screen can do is help bad rooms look better, it cannot help perfect rooms look more perfect (at least not enough from an ANSI contrast spec to matter). Sure we can split hairs and talk about the screen itself or how hot spotting could affect ANSI as given one side of the screen to the other (or any number of other small variables that can affect stuff), but for explanation purposes this stuff is just splitting hairs and we have to assume BAT CAVE means a perfect 100% dark room.

Last I checked, bat caves just have a lot of bats and other dark scary things, not reflective surfaces

In my opinion there is no such thing as a perfect room. I am unaware of a completely non-reflective material you can coat the walls, ceiling, floor, furniture with.
When the projector is on can you see anything other than the image on the screen, if you can see the walls, floor, ceiling or furniture then they must be reflecting light.
If you turn the projector off and shine a torch around the room not at the screen, does the screen stay pitch black if not you have room reflections.
If you reduce the zoom on the projector or move the projector slightly so its projected image is not illuminating the whole screen, does the part of the screen not illuminated by the projector stay as black as the black velvet surrounding the screen if not there are room reflections.
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Originally Posted by dovercat View Post

But ANSI checkerboard contrast and on screen simultaneous contrast are not the same thing. Native On/Off contrast is like a best case figure and ANSI checkerboard contrast is like a worst case figure. In most scenes I would expect the JVC projector to have a higher on screen contrast than other projectors.

In my opinion there is no such thing as a perfect room.

We understand the differences between On/Off without an IRIS, On/Off with an IRIS, and ANSI contrast. The fact that in bright scenes the JVC looks about as good even with the lower ANSI is a good sign that ANSI contrast is not a very important measurement beyond a certain point, even for brighter scenes. ANSI is of course important still, but people have tested the effects of having 100:1 ANSI in a room vs 200:1 with almost no visual benefit.

Consider this scenario of a "perfect room" would be getting close enough or as close as is realistically possible using very dark materials.


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Quote:
Originally Posted by coderguy View Post

We understand the differences between On/Off without an IRIS, On/Off with an IRIS, and ANSI contrast. The fact that in bright scenes the JVC looks about as good even with the lower ANSI is a good sign that ANSI contrast is not a very important measurement beyond a certain point, even for brighter scenes. ANSI is of course important still, but people have tested the effects of having 100:1 ANSI in a room vs 200:1 with almost no visual benefit.

Consider this scenario of a "perfect room" would be getting close enough to the point where our eyes cannot make out a difference between that and a black hole. There are rooms that do that, or get darn close enough.

I was not saying ANSI is indicative of bright scenes, it is a checkerboard. I understand a checkerboard is the worst case scenario not typical scenes in movies be they dark or bright or somewhere in-between.

The increase in ANSI contrast could be indicative of reducing room reflections but a two fold increase is quite small. I believe white paint is around 85% reflectance, black paint around 5% and black fabric maybe half that 2.5%. So the difference between a light colored room and a bat cave could easily be 16 to 34 times less reflectance.

If you figure besides the screen wall a room has five surfaces, back wall, floor, ceiling and two sidewalls. A retro-reflective screen helps reduce reflections that are not on angle, so anything not from the back wall, so it might reduce room reflections by more than two fold.

I would expect using a retro-reflective screen in a non-perfect bat cave would noticeably improve the picture. At least it does in my room.

My room is light controlled, with no sources of light other than the projector, with the lights out and projector off, I can not see my hand in front of my face. It is also what I would call a bat cave, it is covered in black fabric, walls, floor, ceiling, furniture.

With a white matt screen although the screen wall remains pitch black with obvious expception of the screen, the rest of the room is illuminated by the screen and I can see the sidewalls, floor, ceiling.

With a retro-reflective screen the sidewalls near the screen join the screen wall in staying pitch black and the whole room stays darker, is less illuminated. The picture also appears to have more contrast. So the retro-reflective screen seems to help in my case.

Maybe my room is not big enough or the black fabric is not non-reflective enough but a retro-reflective screen was cheaper than trying to buy slightly darker fabric to cover the room, and I had more confidence that a retro-reflective screen might improve the picture than using slightly less reflective black fabric.
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post #16 of 39 Old 02-02-2011, 06:22 AM
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There is absolutely no question that the ideal environment for front projection in terms of picture quality would be a bat cave devoid of any light sources and draped in the best light absorbing black velvet and all items in the room including the viewers were equally light absorbing. Combine that with a projector of adequate lumens for the job and super high on off contrast and a screen that reflects evenly across its surface and is dead on neutral in its color shifting.

But! There are many more out there that are less than perfect ether by factors beyond the control of the person or more and more by choice. These are the people I believe are wrongly seeking screens that can improve contrast when what they really are seeking is something that preserves contrast given a baseline of a 1.0 gain white screen I could see how they might think the specialty screen had magical properties after all seeing is believing.

The problem is further compounded when selecting a projector for these vastly different environments. A 1,000,000:1 on off CR projector sounds impressive and may be perfect in the bat cave, but will do little for the guy with the sports bar setting when his ANSI contrast is reduced to 40:1 by ambient light and not enough lumens to overpower the ambient. By the same token 4000 lumens with 2000:1 CR projector wouldn't be something the bat cave owner would want but might really pop on a dark screen watching football in the sports bar setting. Many people read reviews based around near perfect environments want to boast a high CR number to their friends and then bring it home to a living room setting and start searching for a magical screen to pull it back.

High lumens not high contrast is the trick when dealing with ambient but no amount of lumens is going to help with making black after all black is projecting no lumens in theory. That's where shifting the gray scale equally on each end using a neutral gray surface works. Many people have the misconception that white can't be projected off of a gray surface, and you hear a lot that gray screens make muddy whites etc. neutral gray is white with the intensity turned down. The excess lumens makes up for the lower intensity.


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post #17 of 39 Old 02-02-2011, 06:46 AM
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Perceived/retained contrast from a Black Diamond in ambient conditions is a must see especially compared to all white and gray screens out there.
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post #18 of 39 Old 02-02-2011, 09:22 AM
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Personally in a room with ambient lighting I would rather play it safe and go the same route as Cine4home.de, using a 6000 Lumen projector with a black screen, or if the space is available using back/rear projection instead of front projection. Even then there are many situations where projectors just can not compete with the ambient light.

600 or less lumen projectors relying on specialist high gain gray screens like the Black Diamond to make the picture watchable in ambient light sound good in theory and look good in the publicity videos. But I would only go that route if I was using a custom installer. If I DIY and it fails to work in practice the postage plus 50% re-stocking fee for returns is a killer. If it was cheaper or they had a no quibble satisfaction guaranteed or your money back, no re-stocking fee, then I would be more willing to try it.
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post #19 of 39 Old 02-02-2011, 10:26 AM
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Didn't have time to read all the responses, and I'm sure Darin said this already, but even the BD can only minimize the room's damage to the pj's CR, not improve it.

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Oddly Screen Innovations marketing is the main deterrent to buying a Black Diamond Screen.
Seeing may be believing but listening to the hype just leads to disbelief.

"Black Diamond is the only screen that absorbs all unwanted ambient light in a room. Ambient light is absorbed above, below, and even in the path of the projector, allowing the screen to maintain and preserve the projectors contrast. Only the projectors light is reflected back into the viewers eyes creating over 300% more contrast compared to all other screens."

"With the lights on with no sacrifice in image quality"

"no need to do masking"

"It allows projection to exist with the lights on or off by increasing projector contrast over 900%"

"improves contrast by 900% even in black dark room"

"Black Diamond reduces light scatter by over 75%, increasing viewer immersion and contrast."
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post #21 of 39 Old 02-02-2011, 03:03 PM
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I'm glad Darinp2 posted in the thread.

I am acutely aware there is no perfect room. I've gone to a lot of effort to cut reflections in my own room: the ceiling is dark brown felt, the rug dark brown (and I sometimes put a roll of black velvet to cover even that), my side walls get covered with dark brown velvet, the sofa is dark brown etc.

Even with all this I can still see the room when watching a movie (at least the brown material portions) so I know the room isn't perfect. But drawing from long discussions and measurements performed by others it seems that doing what I've done goes most of the way to minimising room effects. But the "could it be better?" part of me doesn't always stay quiet.

That's why I do have some envy of the darker specialty screens. If I employed one in a room like mine I'd think I'd be losing very little contrast. But unfortunately I have yet to find a specialty screen that had compromises I could live with (screen texture, hot-spotting, problematic off-axis performance etc).

I currently have some samples of another specialty screen - the DNP supernova material. It's pretty wild. Like the BD screens the substrate is very dark gray. It's meant to maintain decent viewing angles horizontally, while rejecting light bounce vertically (from the ceiling/floor). It's pretty wild because from straight on the image looks normal and relatively bright, but the more you are looking down at the the material the darker it becomes and it goes almost black-looking from a vertical angle.
So it must really not be sending much light vertically (and rejecting light vertically).

But it's so hard to tell issues with just 12 x 12" samples. I have the impression, from the way the luminance changes with viewer position that it would hot-spot like crazy, but I don't even know if it's angular reflective or retroreflective.

Darin, I seem to remember you had checked out the DNP material at some point. Can you comment?

Thanks.
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post #22 of 39 Old 02-02-2011, 04:25 PM
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Quote:
Originally Posted by R Harkness View Post

Darin, I seem to remember you had checked out the DNP material at some point. Can you comment?

I checked it out very early and my memory is that I had a big problem with the sparkly effect. I think it was the main designer who told me that I shouldn't be seeing that from any normal viewing distance, but I did see it. And I saw it in a demo he was showing in a hotel room at one of the shows. He told me that it was called speckling and that the amount of it was dependent (at least somewhat) on the size of the chip in the display. So maybe this is a reason I didn't see the same kind of problem with a Vutec Silverstar with a CRT, but do with the digitals I've seen with it.

I think the Supernova may have been modified after my experience above and I'm pretty sure it was a screen that I saw at CEDIA later with a DLP projector (probably 3 chip) and didn't see this speckling effect. Looked like a nice screen in the environment it was in (open to the show floor). I don't remember whether it had any visible hotspotting. If you had a luminance meter you could measure for it by moving the sample to different locations. Or maybe put it up with a piece of white paper and test both at different locations to see how it compares to the paper. If it is brighter in the center of the screen, but dimmer than the paper when both are out to the side from a center seat this could be an indication that you will see some hotspotting. Not a perfect test, but might help give you some indication. If you have the ST130 you could try the same kind of thing to see how the gain compares to the ST130 at different locations.

--Darin

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post #23 of 39 Old 02-02-2011, 11:33 PM - Thread Starter
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If we can get a hold of the below material to cover our rooms with and grab the next-gen of projectors that can do higher ANSI and higher ON/OFF, then we're getting somewhere...
http://www.world-science.net/othernews/080123_black.htm

The material, a thin carbon coating, reflects less than 0.1 percent of incoming light. It absorbs the rest. Ordinary black paint reflects 5 to 10 percent. The darkest manmade material, prior to the Lin group’s discovery, reflected just under a fifth of a percent, Lin said. The new material has a total reflective index of less than a twentieth of a percent—in total, 0.045 percent, he said.

@Dovercat...
I should have clarified in that I meant a LITERAL giant bat cave for explanation purposes or as close as possible.
Good points, and I don't think we really disagree because we both agree the HP screen can still help most people's rooms since they don't really have as perfect of a bat cave as they think, that is unless their reflective paths are just not in agreement with the HP, then they may be better off with another screen. I guess I just didn't explain it right, but I think I covered all this in the original post.

With vaulted ceilings that were like 15' high and walls more than 25' away, it might be possible to get really really close to a perfect room (or at least it seemed that way to me). Air diminshes reflectivity because it allows the reflections to scatter, as air itself is the least reflective material on earth (although it doesn't absorb much either)... I used to have a room like this, and I sure do miss it, because I can't seem to get my PJ looking anywhere near as good as before.

Also, relating to ANSI I'm just saying we aren't there yet with the current equipment anyhow.

From my understanding, ANSI is more of a representation of how PJ's work in brighter scenes because that's generally where the contrast spectrum (or at least the projector's abilities) provides a narrower contrast range from the source material, which is why a white checkerboard square next to a black one is more representing of the projector's capabilities of displaying brightness and darkness at the same time in brighter scenes. Sure it is not a perfect representation since the way ANSI is measured is a bit extreme, but in bright scenes killing the ANSI definitely has a major effect if your room has too much ambient light, so it does tell us something. The reason I'm referring to ANSI is because that is what you are changing / preserving more of the projector's capabilities, whereas with On/Off your just altering the ranges.

If all this stuff is correct, then once I get my JVC I should be blown away even despite my non-perfect room conditions.

The point being is most people just have the ROOM so bright, or so bad, that they are FAR FAR away from even a non-perfect bat cave.


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Quote:
Originally Posted by coderguy View Post

With vaulted ceilings that were like 15' high and walls more than 25' away, it might be possible to get really really close to a perfect room (or at least it seemed that way to me). Air diminshes reflectivity because I believe (unless I am mistaken), air itself is the least reflective material on earth (although it doesn't absorb much either)... I used to have a room like this, and I sure do miss it, because I can't seem to get my PJ looking anywhere near as good as before.

Also, relating to ANSI I'm just saying we aren't there yet with the current equipment anyhow.

From my understanding, ANSI is more of a representation of how PJ's work in brighter scenes because that's generally where the contrast spectrum (or at least the projector's abilities) provides a narrower contrast range from the source material, which is why a white checkerboard square next to a black one is more representing of the projector's capabilities of displaying brightness and darkness at the same time in brighter scenes.

I would say it has more to do with distance and less to do with air. Light spreads out in two directions so it diminishes by the square of the distance as it returns into your room the greater the distance the lesser the intensity. The surface it strikes then has much more surface area to attenuate what light it can and the return trip back to the screen is a long distance with more expansion of the light beam.

Our eye is no different than a projector with a live variable iris. It can't be in two different stages of openness at the same time. So in terms of projectors our eyes can do close to a million to one on/off contrast, that's between the contrast perception and the iris changing size I have read. Likewise instantaneous contrast ratio abilities of our eyes I have read are not more than 500:1 in the best of eyes.

The best black any projector can do is during a total fade to black full screen black, because there is the least rebound ambient light returning to the screen diluting what is trying to be black. The worst black then would be a full white screen with a tiny black spot in the center, max rebound ambient. Fortunately or unfortunately our eyes see the two reversed, the blackest black is seen with the brightest image and that's because of the eyes iris closing and then our perception taking over.

For me the use of an ANSI test pattern is about what's going on in the room with reflections and how the screen is handling ambient light in the room. Dark screens and high lumen projectors and lower output CR might allow some ambient light when the image is high ANSI like contrast, sports, regular tv, and some movies will look pretty good. The drawback will be in very dark images where you are looking for shadow detail the true contrast will be what you are seeing and wont look so good.


Bud

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Quote:
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If we can get a hold of the below material to cover our rooms with and grab the next-gen of projectors that can do higher ANSI and higher ON/OFF, then we're getting somewhere...
http://www.world-science.net/othernews/080123_black.htm

By that point your skin, clothes, teeth, and whites of your eyes might be the dominant photon pollution sources.

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By that point your skin, clothes, teeth, and whites of your eyes might be the dominant photon pollution sources.

That's why I ban smiling in my home theater during movies, like any other
sane, careful AVS member who has read to many threads about projection screens.
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Quote:
Originally Posted by darinp2 View Post
I think the Supernova may have been modified after my experience above and I'm pretty sure it was a screen that I saw at CEDIA later with a DLP projector (probably 3 chip) and didn't see this speckling effect. Looked like a nice screen in the environment it was in (open to the show floor). I don't remember whether it had any visible hotspotting.

--Darin
Having just purchased a DNP Supernova Core screen, I can tell you there is no texture to it. I don't see any speckling effect (I'm assuming due to the texture of the gain material). I also don't see any hotspotting.

I think they may have all of their ducks in a row, so to speak.

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post #28 of 39 Old 02-03-2011, 05:29 PM - Thread Starter
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Quote:
Originally Posted by bud16415 View Post

Dark screens and high lumen projectors and lower output CR might allow some ambient light when the image is high ANSI like contrast, sports, regular tv, and some movies will look pretty good.

You explained it well. I agree that better ANSI of course makes everything look better (we can see that because if we turn the lights on, both dark scenes and bright scenes look washed out), but it is still dimenshing. I was speaking in terms of good setups though to where dark scenes already look good and the ANSI is around 100:1 or higher that you are acheiving, so sometimes bright scenes aren't as punchy because as the relectivity levels increase, the brighter image can be more washed out. So yes, as you said it's a catch 22, on the reverse brighter may look more punchier but then the blacks will look worse if you have too much brightness in your image. If you had a perfect room, both types of scenes would be much closer to their maximum punchiness (or maybe someone spiked my punch).


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post #29 of 39 Old 02-03-2011, 05:50 PM
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Originally Posted by coderguy View Post

According to DarinP and others who tested it, you need a fairly HUGE 10x+ increase in ANSI to make much difference.

coderguy,

I appreciate you explaining this stuff, but just wanted to mention that the above may be a misinterpretation of something I've said (at least the part attributed to me). I'm not sure how much it takes, but it can depend on where you start from of course. If you started with 30:1 then an improvement to 60:1 might make a nice visible improvement. People definitely reported nice improvements going from non-liquid coupled CRTs to liquid coupled CRTs and those may have been around 2x improvement.

It can also matter how much CR for real images is hurt by low on/off CR. I would love to find out whether the JVC projectors with high native on/off CR would look much better in a dark room with about 600:1 ANSI CR from the projector compared to about 300:1 from the projector. They might in some images.

One more thing to keep in mind is that high MTF at full resolution or close to full resolution can come with high ANSI CR and it may be this high MTF that is most visible and least affected by the room. I say least affected because a contrast ratio of 20:1 at full resolution would be very good and a room may take that down to maybe 18:1 even though the same room could take 1000:1 ANSI CR down to less than 200:1 off the screen. So, about the
same absolute reflections back to the screen during the ANSI CR test as a full resolution checkerboard of white and black, but with less relative washout effect during the full resolution test. Also, high ANSI CR from a projector doesn't necessarily mean that it has high MTF at full resolution or close to full resolution and it is possible to have high MTF at full resolution or close to full resolution without having the best ANSI CR.

--Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."
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post #30 of 39 Old 02-03-2011, 06:03 PM - Thread Starter
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Quote:
Originally Posted by darinp2 View Post

coderguy,

I appreciate you explaining this stuff, but just wanted to mention that the above may be a misinterpretation of something I've said (at least the part attributed to me). I'm not sure how much it takes, but it can depend on where you start from of course. If you started with 30:1 then an improvement to 60:1 might make a nice visible improvement.

I stated once you get beyond a certain point how ANSI affects brighter scenes (100:1+).
Wasn't that the point of the test comparing relatively high ANSI to even higher ANSI?


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