Objectively evaluating the Screen - AVS Forum
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post #1 of 26 Old 08-07-2014, 01:19 AM - Thread Starter
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Objectively evaluating the Screen

I do not proclaim to be an expert but I know alot about photography and in turn alot about imaging.

I've had a projector for some time now and was always annoyed by the poor black levels my budget LCD produced. Like a sheep I painted a grey screen which only served to reduce the brightness of the image.

I now know much more about imaging and a little bit about how your eyes work. Your eyes have the ability to adapt to dramatic changes to light. Just think about how you can see in the day and how when you wake up in the middle of the night you can still see too. Your eyes also adjust for light colour temperature very well too. Consider how skin looks in the sun and under florescent lighting and how similiar it looks.

A cheapo digital camera is a pretty decent objective measuring tool provided you know how to use it. To measure contrast and black levels all you need to do is look at the histogram. A screen or projector with high contrast will be able to create a histogram where the light and the dark are very far apart. so an absolute test would be to project an image with some dark black and some white and compare on the histogram how far apart the gap is.

If you want to measure shadow detail you project an image which grades from grey to black and compare what happens in the histogram.

There are alot of buzz words getting thrown about in this forum which sounds likes the silliness which happens in the "audiophile" forums. I think it's silly because I know your eyes adapt so well to changes in light.

I'm not convinced you need a strictly "neutral" colour to project on. If it looks whiteish enough in regular light it will certainly look white with a projector. I've projected onto a clearly beige sheet and really enjoyed the movie. I'ved used monitors on 9300K and 6500K and while using them didn't even notice what setting it was on.

I'm not convinced of the benefits of creating the darkest blacks because your iris will open up when the image gets dark.
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post #2 of 26 Old 08-07-2014, 07:40 AM
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You nailed it. Eyes adapt. It's a psychological phenomena. If you don't know, then you can't see it. But once you know, some of us have a brain disorder whig doesn't allow us to adapt and contact videophile syndrome.

It's similar to why cars tend to pull into motorcycles. You see them less so less attention is spent towards motorcycle identification compared to cars.

If you can't tell 9300 from 6500, you've got immunity from a sickness that consumes all free hours.
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post #3 of 26 Old 08-09-2014, 08:51 AM
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I'm just sorry, but anyone who professes to be a Photographer and claims to know about imaging yet states he cannot see the difference between a cooler image at 9300 and a warmer image at 6500 must have very little if no discerning ability to see colors as being accurate....at all.

I myself am no real advocate of the dire necessity of Calibration, but I have been spoiled for a long time by using applications that needed very little. But I'll be kicked in my _as if I cannot immediately see the color shifts between varying color temperatures. And the more accurate a screen / monitor is, the more obvious the differences are.

The fact that eyes can adapt relates only to the long term viewing of an image, not the instant evaluation of same. Certainly one can eventually get used to and accept wearing a patch over one eye, but why do so if both eyes are working? Just the same, why bother to have to adjust to a poorer image when one can simply start out viewing a better one? Unless one simply does not care.

This whole thing really seems to be more importantly directed to "CONTRAST"...and how "white" whites can look even though a Gray Screen makes then look Gray when compared to the same white shown on a reference white material. Yet take away the reference white, and watch an image long enough with deeper blacks present and the whites seem perfectly normal. Now that is "adjustment". But attenuate colors, or change their actual hue, and if one cannot tell the difference immediately, they need to go back to watching movies on a Black & White TV. Even in Digital Projection's infancy, when LCD PJs pushed Blue and DLP PJs pushed Red, I never heard / read anyone say there was no need to correct the imagery....if possible.

Now absolutely, some did take it to extremes. They would say, "If it's not absolutely, perfectly neutral, it isn't worthy of watching. So drawing a parallel between such Videophiles and the same type of Audiophiles is a valid point....in that respect. What make someone happy is what's important.

It is the fostering off on others the absolute purist beliefs one holds dear on those whom such refinement is lost, then stating that they are grossly wrong to not follow suit, that is perhaps what is behind the OPs postings. In that respect I cannot disagree.

But to advocate that one need not, should not bother to make at least some degree of an attempt to aspire to produce the best, BIG image they can.....that's just, well...myopic.

Lastly....if you are watching a Movie that contains content that has Blacks that should be BLACK...and seeing Gray seems like black, then there is a distinct lack of appreciative values going on, not any logical reasoning. There is a difference, adjusting of the eyes notwithstanding. Subtle differences in Gray scale....ok...that I can "see" to agree with, but BLACK is BLACK and Gray is Gray...and in digital projection where all Blacks are projected, not created by an absence of light, Blacks must start out Black, and that blackness maintained on screen or viewing quality will suffer across the spectrum. Contrast applies to every color...not just to Black & White. Shadow detail depends upon the subtle differences between very slight differences in brightness. You cannot see such detail without adequate contrast.

Poor contrast, be it caused by the PJ's lack thereof or the screen's surface's fallacies, and /or the room's lighting and /or Walls or Ceiling surface interaction, will always degrade the original image, and if one cannot discern that, it simply means they have had no real chance to see the difference. I know this...because between my own experience personally with many thousands of different people who got the chance to make just such a comparison, as well as all the many FP advocates on these Forums who will attest to the same, the issue at hand has been settled many, man times over.

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post #4 of 26 Old 08-12-2014, 11:09 PM - Thread Starter
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Inspiration of this thread came from this post. (The thread where you appear to have gotten schooled.)

Quality difference of Screen paints.


Quote:
Originally Posted by MississippiMan View Post
I'm just sorry, but anyone who professes to be a Photographer and claims to know about imaging yet states he cannot see the difference between a cooler image at 9300 and a warmer image at 6500 must have very little if no discerning ability to see colors as being accurate....at all.
Take a photo with mixed lighting, like window light and florescent light. It looks dreadfully awful. What usually happens is the auto colour temp of the camera picks one temp and makes the other light look bad. But the world we live in doesn't look this unphotogenic. It's because your eyes and brain seemlessly adapt to the differing light so well. The actual aesthetic impact of the colour temperature is pretty minimal compared to other photographic qualities, like sharpness and composition. In extremes the colour temperature can totally mess the tone of the movie.


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I myself am no real advocate of the dire necessity of Calibration,
End of conversation. You're not interested in contributing to impartial science.
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post #5 of 26 Old 08-12-2014, 11:23 PM - Thread Starter
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I pulled up a random camera test

http://www.dpreview.com/reviews/sony-alpha-a6000/11

This has one of those white to black bars in the THX calibration section that used to be on DVD's. This can be used to test if a screen actually does something to shadow detail. But depending on your eyes can be problematic. If you set your camera to manual then you can A/B test between different screen materials and use the histogram to compare. I doubt you can use the same exposure settings to compare the extreme white and black.
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post #6 of 26 Old 08-12-2014, 11:29 PM - Thread Starter
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Worth while reading on colour temperature.

http://strobist.blogspot.ca/2006/03/...o-correct.html

These are gels which are put in front of lighting equipment (flashes in this case). They are used to match overpowering existing light. Look at how deep the colour cast they will project, but in reality your eyes magically see white as white.

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post #7 of 26 Old 08-13-2014, 03:20 AM
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People who grab on sentence and use it out of context were never interested in having a conversation with anyone but themselves. I did not state I do not nor will not use calibration. I just do not find it to be arbitrarily a requirement.

You flip flop a lot...first you state a Camera can be a objective tool formeasurement, then you make the statement that a Camera cannot be counted upon* to accurately convey the appearance of a given subject, and then on the other hand state that the Camera's Historgram is a accurate tool of measurement.
When in fact all it is doing is conveying a listing of values it (the Camera) sees. Which is it? Is a Camera a accurate Tool...or happen-chance guesswork?
*(...not surprisingly one does have to "Know" how to use a Camera correctly")

Selectively choosing whichever aspect of a given circumstance that fits your opinion when one wants to use it to prove a point is something many who simply want to press an argument do often.

You cannot make either assumptions or determinations for anyone else but yourself, and even then that can be problematical.

Your welcome to post up opinions and commentary, helpful advice or almost anything of worth. But trying to create a one sided argument, or ladling out insults, veiled or otherwise isn't what this Forum represents.

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post #8 of 26 Old 08-14-2014, 01:46 AM
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Quote:
Originally Posted by Herc View Post
I'm not convinced of the benefits of creating the darkest blacks because your iris will open up when the image gets dark.
I can say that after a bit of experimenting with different flat greys in a very light-controlled room (both in the dark and with different lights-on situations), I agree pretty strongly with this above statement.

The dark and darker greys gave no real benefit toward black-level, after a couple seconds of eyes adjusting to the screen black bars were equally visible as they are on a flat-white screen. This surprised me because I'd read the light level at which we can detect nothing darker is roughly 0.00087 ftL and I'd made VERY sure to be darker than that by the end..even so, seconds later I could still see black wasn't pitch-black and so could others.

There ARE also problems with going darker. The eye can see more contrast variations within the brighter range, so a contrast figure that stays the same will actually look slightly higher-contrast if it is brighter.
While black levels aren't helped, shadow detail IS harder to make out on a darker surface. Once again, the visible contrast range is shrunk so your eyes perceive a flatter, less contrasty shadow detail.
Color perception can also be weaker on a darker surface which also hurts shadow details (dark scene made even darker..less visible contrast AND less visible colors).
Add to all this that you need to keep a certain level of brightness compared to your surroundings or else you'll end up noticing your projected whites are grey. I was working with a relatively dim projector so I had to black-out my walls and ceiling to get my eyes to stop noticing that the white walls were looking too bright compared to the lighter scenes on-screen.

So, in my case, the dark (low gain, flat) screens offered no benefits, but did have small disadvantages (lacking detail, less vibrant color, finicky perception of white depending on any bright surface in peripheral vision) especially as I went darker.

In the end I went back to flat white. I regret nothing and am happy for the experience.

This is all pertaining to flat, natural-gain screens. Ambient light rejecting screens are a completely different story.

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.

Last edited by Ftoast; 08-14-2014 at 02:00 AM.
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post #9 of 26 Old 08-14-2014, 08:06 AM
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Quote:
Originally Posted by Ftoast View Post
This is all pertaining to flat, natural-gain screens. Ambient light rejecting screens are a completely different story.
I suppose this last statement more correctly illustrates my position, because as I stated in a prior post, I'm spoiled by my experience with the screens I make. And Flat neutral Gray screens are not included in that designation....and certainly not dark neutral gray ones.

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post #10 of 26 Old 08-14-2014, 02:00 PM
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It does still mean something for light rejecting screens too though. I doubt going any darker helps them either, not unless it is just being used for bringing down peak ftL to a comfortable level (keeping lamp dimming and 3D in mind).
The only things a screen can do for ambient light is minimize how much ambient light it throws toward the viewer by strategically narrowing its viewing angles, and directing more of the projector's light toward the viewer by (once again) strategically narrowing its viewing angles.
The trick then is to find the balance between a super-effective screen that hotspots and becomes too dim off-angle for multiple viewers, and an ineffective screen with no hints of hotspotting nor limited angles that isn't being very efficient with projector light and isn't doing anything to redirect close-angled ambient light away from the viewer.
Dark or light makes little/no difference as long as the gain-boost over the shade's natural gain remains the same percentage (a dark 0.5 boosted to 0.8 should fight equally as well as a light 1.0 boosted to 1.6) and so long as viewing cone performance is equal.

Of course the best things anyone in a home-theater situation can do are keeping as much light as possible OFF the screen to begin with (curtains..curtains..and point that light away from the screen, please) AND use a projector with as many watchably accurate full-color lumens as possible without giving up too much native-on/off contrast (the 1000:1-2000:1 range is a good spot to be and will still look very theatrical). These two things will take you much further than any specialty screen could ever hope to.

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.

Last edited by Ftoast; 08-14-2014 at 02:27 PM.
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post #11 of 26 Old 08-14-2014, 02:12 PM
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No...actually a properly balanced DIY Ambient Light screen app can...and will be able to do much more to improve the viewing experience, including both noticeable improvement in perceived contrast and without any appreciable loss of viewing angle. It does not need to have observable Hotspotting tendencies, nor be a completely basic Flat Neutral Gray that is sub 1.0 unity gain.

It's been done, and shown being done so often on here it brooks no argument whatsoever, but as expected, those who have had no experience with such, or that will not take the comments of the very many DIY'ers who have had such experience, absolutely they will argue the point.

For instance, no screen actually rejects (ie: redirects) ambient light, it merely "resists" the effects of such light through one means or another.....Mfg Claims notwithstanding.

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post #12 of 26 Old 08-14-2014, 03:07 PM
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Quote:
Originally Posted by MississippiMan View Post
1. No...actually a properly balanced DIY Ambient Light screen app can...and will be able to do much more to improve the viewing experience, including both noticeable improvement in perceived contrast and without any appreciable loss of viewing angle.

2. It does not need to have observable Hotspotting tendencies,

3. nor be a completely basic Flat Neutral Gray that is sub 1.0 unity gain.

4.It's been done, and shown being done so often on here it brooks no argument whatsoever, but as expected, those who have had no experience with such, or that will not take the comments of the very many DIY'ers who have had such experience, absolutely they will argue the point.

5. For instance, no screen actually rejects (ie: redirects) ambient light, it merely "resists" the effects of such light through one means or another.....Mfg Claims notwithstanding.
1. I agree that there are many fine DIY apps that can boost perceived contrast against ambient light and do so without badly limiting viewing angles. I disagree if you are saying the screen is likely to make a bigger difference than simply keeping ambient light off the screen to begin with and/or significantly upping ftL with a brighter PJ or smaller screen.

2. Agreed. As I said, a good DIY app finds the proper balance where there is no bothersome hotspotting.

3. Agreed, as stated I don't believe there's any appreciable good to come from using a darker shade (especially flat) unless you really need to darken peak white to a more comfortable level. And I totally agree there is plenty of wiggle room between flat-natural and above unity/gain-boosted where you can simultaneously enjoy enhanced ambient light performance without causing the image to noticeably suffer.
I do still claim two downfalls that I think you agree with as well. The more reflective the mix is (specialty gain boosted..not naturally from changing to a lighter shade) the more finicky the application usually becomes as more reflective mixes show small imperfections in surface and application much more than simple flat paint does.
AND
The more reflective the mix is (taken too far) the more likely you are to experience hotspotting and visibly narrowed viewing angles.

4. I'll admit I'm prone to argue. I'll try to keep it reasonable and civil. I've certainly been wrong before and am happy to learn something new (though sometimes reluctant to admit it's because I was wrong).

5. I might disagree or we might simply be calling things different words and meaning something similar.
I say "redirects" because ambient light hitting a reflective screen from the side (or near angle) is mostly reflected toward the opposite side like a billiard ball against the wall or a light against a mirror while centered and high angled light from the projector is mostly reflected down and center toward the viewers..so more PJ light goes where it's needed and some ambient light gets directed toward the opposite angle instead of evenly spread throughout the image and seating.
"Redirect" seems like an accurate word, though I'd be happy to learn a more proper (technical?) one if it exists.

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.

Last edited by Ftoast; 08-14-2014 at 03:17 PM.
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post #13 of 26 Old 08-15-2014, 07:56 AM
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At best, the overt gain / directionality of most ambient light screens simply resists the intrusion / effect of non-direct ambient light. I know of no screen material that selectively redirects sideways incoming light back upon itself. If it did, the area around the screen would light up from such. Such screens can effectively attenuate such incoming indirect light, but only if that light is of considerably less amplitude than the projected light.

Even highly Retro Reflective screens do not look dark under indirect room lighting unless they also posses a dark surface to begin with.*
Case in point...a DaLite HP. A screen that will collect ambient light and dispense it back to the eye of a person unless it is reflecting the intense light coming from a projector. Yet that screen, and even Black Diamond types always show a marked lessening of contrast at the edges when light comes in from the sides and strikes them.
*...when such a screen starts out dark, and is also retro, the end result is a surface that at least maintains a darker appearance.

In truth, it is the Retro properties that only manage to prevent projected light from hitting walls and ceilings that are off axis to the screen. And that is all they manage to accomplish beyond any attenuation afforded by the darker surface itself....if the screen itself possesses such.

And BTW, no one can or ever accused me of not advocating the necessity of muting Room reflectivity, nor have I ever stated anything remotely akin to such. While I do not advocate Black as being necessary as a chosen color, I do insist that Flat Deep hues are the best to use, and Bright Fire colors or Light Pastels should be avoided.

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post #14 of 26 Old 08-15-2014, 04:20 PM
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I was talking about standard reflective "light gets reflected toward the opposite side" because most DIY retroreflective results (and many professional) are pretty lackluster. I believe glass bead is supposed to be retro..or maybe it's half-spheres of glass bead.

Think of it this way (unless you disagree, in which case please mention that right away), the extreme end of a reflective screen is essentially a mirror. Of course a mirror hotspots and has very narrow viewing angles, but that's why screens are made to diffuse light..and the most evenly diffuse surface is a flat-white (or maybe smooth titanium dioxide). The trick when you're dealing with ambient light is to get the best balance between these two extremes.

Think of a mirror in a room where the back wall and back halves of the ceiling and walls are black..what color is that mirror? Now apply the same scenario to a very high gain screen. With no light getting directed from a screen toward the viewer, the screen will look very dark even if it does otherwise look white with light hitting it at the proper angle that most of it is directed toward the viewer. A projector and high-gain reflective screen and audience is like a flashlight a mirror and a friend that you want to blind. In a black (in the back half) room, even shining a light on the mirror won't stop it from looking black unless the light is angled to reflect toward the viewer.

The sides look more washed-out because projected light hitting the edges gets reflected outward more than toward the middle where most viewers are. That's why viewing a blackdiamond from one side makes that side brighter and the far side dimmer.

Also the edge that's closest to a light coming in from a near side is at a less steep angle than the middle which results in more ambient light reflecting from the near-side than from the middle or farther side.

I don't think any of your screen mixes are reflective enough to worry so much about angle problems, brightness uniformity or sides lighting up more than middle or far-side..but more extreme gain-boosted screens like the BD have to be aimed to be worth anything and still need ambient light sources to be closer to the screen's side of the room to not interfere with the screen just as badly as if it were a flat-white.


I didn't mean to claim you're against good light control, sorry if it came out that way. I have heard you suggesting tips for painting surrounding walls/ceilings, so I know you know..ya know? :P

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.

Last edited by Ftoast; 08-15-2014 at 04:30 PM.
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post #15 of 26 Old 08-24-2014, 11:28 AM
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Quote:
Originally Posted by Herc View Post
A cheapo digital camera is a pretty decent objective measuring tool provided you know how to use it. To measure contrast and black levels all you need to do is look at the histogram. A screen or projector with high contrast will be able to create a histogram where the light and the dark are very far apart. so an absolute test would be to project an image with some dark black and some white and compare on the histogram how far apart the gap is.

Generally both the white and black will clip the camera. In other words, when I take a photo of my screen, the darkest parts of the screenshots are 0 in the histogram and the lightest are 255.
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post #16 of 26 Old 08-26-2014, 02:37 AM
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An interesting use of a camera for evaluating:
http://www.lagom.nl/lcd-test/contrast_ratio.php

Has obvious limits, but is world's better than relying on manufacturers specs and results seem to accurately match more professional measurement as well as visual results.
Fun as well as eye-opening.

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.
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post #17 of 26 Old 08-26-2014, 02:27 PM
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Quote:
Originally Posted by Debonaire View Post
You nailed it. Eyes adapt. It's a psychological phenomena. If you don't know, then you can't see it. But once you know, some of us have a brain disorder whig doesn't allow us to adapt and contact videophile syndrome.

It's similar to why cars tend to pull into motorcycles. You see them less so less attention is spent towards motorcycle identification compared to cars.

If you can't tell 9300 from 6500, you've got immunity from a sickness that consumes all free hours.
I completely agree with what the OP is saying. Side by side a white screen will look much better than any tinted screen. That is why you never see side by side comparisons with any screen and a white screen. People like grey screens and I,m sure they look good. Most screens look good once your eyes adjust but I want the one that looks best side by side with other screens and that will probably be a white screen. Next thing you know we will be changing power cords on our projectors.

Last edited by chambers1517; 08-26-2014 at 02:33 PM.
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post #18 of 26 Old 08-26-2014, 06:06 PM
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Not true 100%.,..which is why umbrage must be taken. A white screen in ambient light will look bad compared to a HCCV screen. A White screen beside a advanced metallic infused DIY screen that is properly mated with a appropriate projector.....neither in the dark or the light will it (White) measure up.

Now in the dark, with a N8.0 sub 1.0 gain Gray matched up 1.1 gain Matte White, absolutely many if not indeed most observers will point out the differences and opt to choose the Matte White.

Unless there is reflected light pouring back onto the screen from the nearby ceilings and wall. Then.....the Gray would rule the day.

And again, with a proper mated PJ, in the dark, the basic Neutral Gray can both equal and surpass the White in many important respects. Contrast being the paramount one to consider.


Basically, it's silly for anyone to speak in such definitive absolutes without first qualifying the context of their remarks, much as I have done above..

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post #19 of 26 Old 08-26-2014, 09:02 PM
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Actually for some time now...we're been displaying gray screens side by side with white screens in both ambient light and controlled lighting...

Such as this... of course it's obvious which are the white samples and which are the gray ones. Oh and to note..the pic was taken 30 to ,40 percent off axis... so the grey samples are at an obvious disadvantage...right...

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post #20 of 26 Old 08-27-2014, 10:08 AM
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Comparing any two screens side-by-side, unless one is showing enough noticeably terrible artifacts to distract the viewer, you will always prefer the brighter image because our eyes will see the dimmer image's whites/brights as dirty or off-white. Standing alone however any surface bright enough to not crush darks or lose shadow-detail will be fine as long as it isn't too much darker than surrounding walls/ceiling that may show a brighter reflection and once again make the eyes see the screen's whites/brights as dirty and dim by compare.
So the safest is the brighter or white.

If you compare two flat (aka natural gain) screens in a lit room, a darker screen holds no contrast advantage. Compare a 2000lumen projector on a screen getting hit with 20lumens of ambient light.. a white screen will show blacks around 20L and whites as 2000L; a contrast of 100:1.
What if you used a dark grey screen? The dark grey absorbs 50% of the light that hits it and that's why it looks grey and darker than white..that same 20L of ambient light now only appears as 10L! However the projector light is darkened as well by 50% so you end up with a difference of 1000L whites and 10L blacks; a contrast of 100:1. The overall image becomes darker but contrast remains the exact same.
However, your eyes are able to see more contrast variations on a brighter image so the lighter screen does have a perceived contrast advantage.

If you compare two screens where one is a dark-grey specialty screen (with gain boosted back up to 1.0) and the other is a flatwhite screen with natural 1.0gain they should appear the same in a dark room from the center seat with a long-throw(2:1/1.6:1) projector.
If you use a more common shorter throw-distance (or don't have a particularly long room) the highgain screen will suffer a certain amount of brightness non-uniformity where the edges will be dimmer than the center. .how noticeable this non-uniformity becomes is dictated by how much higher than natural the screen's gain is and can only be helped by lowering gain, increasing throw-distance, or curving the screen.
So the least finicky and least artifacted is the white screen.

Whether or not you achieve watchable uniformity, the high-gain screen will also dim a certain amount as you sit farther to one side. The brightness fall-off is once again dictated by how much higher than natural the screen's gain is. The off-angle brightness doesn't necessarily become too dim at extreme angles, but it will be darker than when viewed from center.

The positive side of this limited viewing angle is that it can be carefully tuned to only be a bother at angles of viewing that would never be used anyway..so you are essentially taking light from the extreme sides that wouldn't be viewed anyway and directing more of it toward the seating. It's using the light even more efficiently!
The problem is that brightness gains are typically small in modest cases and more extreme ones require either a curved screen (which lowers contrast and distorts the image) or using a longer throw-distance (not always possible with space and generally requires a projector in the $2000+ range).
Unless you are after only a tiny brightness gain or shopping in the $2000+range for a projector to be properly aimed in a long room, a white screen is the way to go.

Also, with today's projectors and in a darker room you won't really need that extra brightness. It's more of an ambient light fighting measure.
Then again, curtains over window are a cheaper, easier, less detrimental to the image ambient light fighting measure.

Simple <$250 dedicated black-fabric theater room, build in a day, takedown in an hour.
Easy $25-40 DIY black/dark-grey ambient-light rejecting screen, grab two things from a local store..mix..roll..done.

Last edited by Ftoast; 08-27-2014 at 10:25 AM.
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post #21 of 26 Old 09-08-2014, 09:59 PM - Thread Starter
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You flip flop a lot...first you state a Camera can be a objective tool formeasurement, then you make the statement that a Camera cannot be counted upon* to accurately convey the appearance of a given subject, and then on the other hand state that the Camera's Historgram is a accurate tool of measurement.
When in fact all it is doing is conveying a listing of values it (the Camera) sees. Which is it? Is a Camera a accurate Tool...or happen-chance guesswork?
I know you can use a digital camera to measure white crush or black crush. It is also useful to measure absolute brightness (err reflectivity) and reflective uniformity (ie hotspotting). I know if you're measuring contrast you can't directly compare differing cameras, particulairly from different manufacturers because of how they interpret the optical sensor. Some manufacturers will digitaly boost contrast (because its aesthetically pleasing).

However I don't know how to deal with colour. I don't understand the relationship between colour temperature, cameras, converting to RGB and your eyes.
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post #22 of 26 Old 09-08-2014, 10:05 PM - Thread Starter
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Basically, it's silly for anyone to speak in such definitive absolutes without first qualifying the context of their remarks, much as I have done above..
That's why I started the first post. When you measure correctly you don't have to qualify.
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post #23 of 26 Old 09-19-2014, 10:44 AM
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I haven’t posted in a while. Good to see the debates still rage on between the scientific types and the more artistic types.
If you want to dig back into the archives you can find quite a bit of tests done using photography as a measurement tool for DIY screen evaluation. We used to have a member Tiddler that constructed some very valid testing setups. Ideally testing is done with color sample slides projected but the more artistic types couldn’t stay focused to long so he made slides from photographs that had elements people liked to see along with that the slides had a clear window done in Photoshop or some similar program that would let 100% pure projected light thru as white. Those places on the screen were affixed photographic color charts of known values with gray scales and color palette. The white light would illuminate them for the photo so in the frame we could measure projector and an actual known sample and we even knew white value. We had split slides that could do A/B and A/B/C comparisons even with the exact same image on each sample of DIY paint. Camera settings were selected so no auto adjusting would happen to improve image quality. We also ran all samples in all locations across the screen.

I have written many times about how the eye interacts with our perception. The human eye has an ability of about 400:1 CR is all instantaneously but over 1,000,000:1 from time to time. If I remember right it can adjust about 25 f stops. In the middle of the range it can’t detect ½ f stop change in light level and barely can detect a full f stop. That’s a doubling of light intensity for the non-photographers. Keep in mind a candle will crush the CR of a 10,000:1 projector down to something less than 1000:1.

The major contributing factor to what we see in a projected image is perception of contrast and that’s what we love or hate about front projection. It’s not that some people have super vision and super hearing as someone posted above and require all this special stuff. All you need to do is go to the end credits of any movie where the image is 95% black and some white text in the center of the screen. That black never looks that good, kind of a gray. That same black is what you saw in every black in the movie that looked ink black because of the contrast in the image. It’s why a high contrast image like a sporting event looks so good in a sports bar setting the image is mostly light. As the brightness goes up the iris in our eye closes and the perceived contrast is there.

I have always taken all the factors together in my projection rooms. Very high lumens, dark screen, light absorbing nature to the room and light sources location to appear to light the room but not light the screen. The classic number thrown out for projection is 15 FL even off my dark screens I like a number closer to 30 FL if I can get it. It keeps the iris closed to all but the darkest parts of the viewing and then the dark screen helps by lowering the overall CR.
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post #24 of 26 Old 09-28-2014, 10:59 PM - Thread Starter
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fascinating post bud16415. What was the outcome of the discussion on colour saturation?

Cameras do not show colour the same. Amongst camera fanatics its widely known that Canon cameras pump a tiny bit more saturation than Nikon cameras. I suppose in their research this transform curve they select as default is more aesthetically pleasing.

I hope everybody is also aware of why measuring is so important, particularly when you're designing. Its an invaluable tool to help you refine and iterate your design. Equally important is that it helps to calibrate and tune your senses. That is it uncovers what your visual preferences are to tune your design towards.
Its unlikely that we will all have the same preferences towards, absolute black level, contrast, colour saturation, shadow detail, highlight detail, sharpness etc.

I'm realizing now that its the transform curve that we ought to be measuring and doing it with ordinary camera equipment is no small feat. One would have to capture in raw and create a custom transform curve calibrated against the original projected image. If the camera has a 9 stop dynamic range capability, you'ld have to take at least 3 photos at different shutter speeds to capture the entire visual range and then splice the transform curve together. For a complete descriptor of the screen you'ld also have to capture at least the center (for hotspotting), 2/3's from the edge (where the natural photographic focal point is) and the extreme edge (for light fall off). All of these shots should be from the seated positions.

You might also want to measure the off axis reflective light too. As this will impact how much light gets reflected back onto the screen.


Evaluating a static photograph is not enough because any given movie will have hundreds of photographic styles captured with different sensors/films/lenses/lightning conditions. That would be like auditioning speakers strictly listening to hip hop when you also listen to rock, folk, jazz and country.
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post #25 of 26 Old 10-01-2014, 01:01 PM
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I don’t remember all the conclusions anymore but I agree with your above assessment of what one would have to do to really pinpoint results. It was always an ongoing battle here to try and devise a method that was both simple enough and done with equipment anyone could get their hands on and then try and show it and convey the idea to a lot of people viewing on a bunch of different type and calibrated monitors. Even different nationalities have different preference to what they view as correct. I’m afraid the new super bright flat screen devices are even changing what most feel is normal. I have seen super images at friend’s houses and they claim they look more real than reality.

The distractors here always viewed a screen as more than a passive device and always felt the screen could expand and improve on what was sent to it. Quite a few of us gave up and went back to what we came here for in the first place. That is viewing an projected image so perfect that our eyes looked past the surface of the screen and enjoyed the 3D quality built into the images by the director of the movie. To me that 3D is the real 3D. Some of us called it an open window effect. We also had long debates over how things like surface texture, sheen and metallic draw the eye back to the 2D reality of the screen.

I stop back a few times a year just to see if my old friends are still around.


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Quote:
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A White screen beside a advanced metallic infused DIY screen that is properly mated with a appropriate projector.....neither in the dark or the light will it (White) measure up.
Someone better let the directors, cinematographers, and colorists who are actually producing the images and colors that we are attempting to reproduce at home that they should scrap their white screens if they want the ultimate experience.

Funny how the people actually making these movies, with their unlimited funds and their literally definitive take on what they "should" look like, choose white screens both for making their movies and for watching at home.

I will again repeat my never-to-be-granted request to MM to let me purchase a sample of his finest Silverfire from him -- say, 2' x 4' or thereabouts -- so that I might see how it looks for myself and report back to the forum with observations, photos, etc, using each of three projectors (Mits HC3000, Mits HC4000, JVS RS4810). I will extend this request to any other satisfied SF customer who has leftover paint that they can use to make a sample.
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