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AVS Contrast Thread - Now with Dynamic Contrast Results! - Page 5

post #121 of 200
Cliff,

I am not going to respond to your post. Either you are drunk or have some other problem.
post #122 of 200
Quote:
Originally Posted by odyssey View Post

Do you think that an 80 ANSI CR, especially in a good room, is not something to be concerned about and does not have a significant impact on overall image quality? In the case of the G90, it's also a very good proxy for MTF, which is very low at the higher spatial frequencies. In any case, the ANSI CR of the G90 without room effects, should be about 150-175:1.

Those numbers are NOT CORRECT. What was used to measure that high of a ANSI from a SINGLE G90? What were the conditions? What was the screen size? Do you have a link?

I think some of these numbers that are being posted right now in regards to performance are just plain flat out wrong and I bet that I could back it up.

Cliff
post #123 of 200
Quote:
Originally Posted by odyssey View Post

Cliff,

I am not going to respond to your post. Either you are drunk or have some other problem.

Are you kidding me? This has to be some kind of joke.

Your telling me that I should be more worried about ANSI performance than on/off and I'm telling you that IS NOT TRUE. Drunk or have some other problem doesn't come into this scenario.

Quote:
Originally Posted by odyssey View Post

No, that's not what I said. The G90 primaries are not accurate for either consumer SD or HD and are far off from DCI primaries, but those are different topics.

You really should not be concerned about sequential CR. If you want to be concerned about something, it should be ANSI CR and color accuracy. The measurements show problems with grey scale tracking...the 100 IRE blue is much too high and the low end much too red. How much of a problem this is depends on how far up the luminance scale this goes.

You also told me that the G90 primaries are NOT accurate for either consumer SD or HD and are far off from the DCI primaires and I'm calling you out now and telling you that you ARE WRONG.

You MIGHT THINK based upon your current KNOWLEDGE of the G90 that it cannot match those specs but I'm here to tell you that it can, can do it easily, and I WILL prove you wrong.

Cliff
post #124 of 200
Darin,

I don't really care what Cliff does and I am not making any recommendations. I know from my experience that both sequential and ANSI CR are important, with ANSI CR being more of a proxy for more typical intra-image CR and MTF than a useful absolute value. As Greg R. says, it's a figure of merit.

Although I have the right tools to do it, I have not measured the ANSI CR of my G90. I do remember credible measurements in the 150-175:1 range with methods that minimize the room effect, but don't know the actual source.
post #125 of 200
Thread Starter 
Guys, let's please not turn this into an ANSI cr vs On/Off debate or digital vs CRT. What I'm personally most interested in is learning about the low APL performance of CRT and I think Cliff is on the verge of adding a lot of useful information about that. We all know that CRT's have relatively low ANSI cr but I'd really like to learn more about CRT performance at the very bottom.

As far as the greyscale tracking goes, I assume it's very normal for CRT to deviate significantly from D65 in the off state, but does anyone know about where on the luminance curve one can expect it to start tracking better? With digitals it's mostly dependent on the native on/off cr. With low contrast digitals from 5 years ago they would fall apart below 10 IRE or so but I think something like an RS1 will go fairly low before going red (or is it blue?), maybe a few % stim or so.

What I'd really like to see is not the off state though, but rather intraimage contrast at the bottom of the scale. There has been suggestions that CRT can't do more than 1k:1 max intraimage contrast which seems way to low. I think CRT will be better than the best digitals at the bottom in this respect but how much better? I'm guessing that it won't be 10x better than the on/off differences would suggest. The results should be very interesting.

Another point is the comment about subtracting ambient. Ambient will only act to lower the measured on/off so if there is ambient (which doesn't sound like there is from Cliff's description), then the true on/off would be higher than the reported 200k:1 figure (all things being equal).
post #126 of 200
Sorry for borking your thread Mark. I apologize. I stand by my opinions though.......

Cliff
post #127 of 200
[quote=Mark Petersen;146 What I'd really like to see is not the off state though, but rather intraimage contrast at the bottom of the scale. There has been suggestions that CRT can't do more than 1k:1 max intraimage contrast which seems way to low. I think CRT will be better than the best digitals at the bottom in this respect but how much better? I'm guessing that it won't be 10x better than the on/off differences would suggest. The results should be very interesting. [/quote]

The problem with getting an accurate intra-image CR measurement with CRT projectors is eliminating the effect of the room. This is hard to do and more of a challenge than single lens units. It becomes easier if you measure each primary individually using the same techniques as single lens units.

I don't know which test pattern you are currently using to measure intra-image CR, but I expect the performance of the G90 to be relatively poor. There are many internal reflections in even the best LC CRT projectors. The halation effect is strong and there is only so much you can do with anti-halation coatings. The phosphors emit light in all directions and the lenses have much lower contrast performance compared to the best DLP projector lenses. The ANSI CR and MTF performance give a good indication of what will happen with an intra-image contrast pattern that more closely resembles typical content. The MTF of the G90 at the spatial frequency that corresponds to 1920x1080 is probably no better than 10-20%.

One of the issues with getting a meaningful sequential CR measurement is defining the performance of grey scale tracking and low luminance detail that's required. It's very easy to degrade these and get a very high number with the G90. What is the requirement for D65 accuracy and at what luminance levels? What is the requirement for gamma starting with digital value 17?

The issue with ambient is not that the CR will be even higher if ambient is subtracted, but that the CR measurement is inaccurate. The main source of ambient is the screen. The entire screen is focused on the phosphor screen by the lens. You can see this clearly if you shine a light on the screen and look into the lenses. If the red CRT was not capped during the green black measurement, it can easily account for the entire .002 fL reading. Even if it was capped, other small sources of light in the room will get back to the phosphor screen through the screen. I am very familiar with measuring luminance from the phosphor screen through the lenses and I suggested it's use with the G90s. I also understand the potential problems.

I have a G90, a Minolta LS-100, and a Photo Research PR-705 with cosine corrected receptor. I even have a fiber optic lens coupler for the LS-100 that came from one of your former colleagues at Hughes JVC, but I am not interested in making these measurements. I don't use the G90 for movies and I have a much better overall projector for that. Also, I will be replacing the G90 soon.
post #128 of 200
Quote:
Originally Posted by overclkr View Post

I would like to ask you a question if you dont mind and am curious if you have measured the ANSI performance of your HT5000 with Ken?

Cliffy

Ken measured it and it was under 200:1 as I recall.

Art
post #129 of 200
Quote:
Originally Posted by Art Sonneborn View Post

Ken measured it and it was under 200:1 as I recall.

Art

WOW!!!! Art, I think you have just proved a point in my mind in regards to what real world numbers actually show after real world measurement.

Quote:
Originally Posted by odyssey View Post

Do you think that an 80 ANSI CR, especially in a good room, is not something to be concerned about and does not have a significant impact on overall image quality? In the case of the G90, it's also a very good proxy for MTF, which is very low at the higher spatial frequencies. In any case, the ANSI CR of the G90 without room effects, should be about 150-175:1.
post #130 of 200
Quote:
Originally Posted by Art Sonneborn View Post

Ken measured it and it was under 200:1 as I recall.

Art

That must have been a measurement from the screen with room effects. The ANSI CR of the projector only is at least 500:1.
post #131 of 200
Quote:
Originally Posted by odyssey View Post

That must have been a measurement from the screen with room effects. The ANSI CR of the projector only is at least 500:1.

I'm not saying it isn't but how do you know that ?

Art
post #132 of 200
Quote:
Originally Posted by Art Sonneborn View Post

I'm not saying it isn't but how do you know that ?

Art

Because 200:1 is way too low for that projector when you eliminate the room effects. Was the anamorphic lens in the image path when the measurement was done? If yes, that would change my estimate to at least 400:1. It seems that what are considered to be very good rooms can drop ANSI CR to 40-50% that of the projector alone. Both measurements, the G90s and the HT5000, are consistent with that.
post #133 of 200
Quote:
Originally Posted by odyssey View Post

Because 200:1 is way too low for that projector when you eliminate the room effects. Was the anamorphic lens in the image path when the measurement was done? If yes, that would change my estimate to at least 400:1. It seems that what are considered to be very good rooms can drop ANSI CR to 40-50% that of the projector alone. Both measurements, the G90s and the HT5000, are consistent with that.

No I'm asking how you know my projector actually has ANSI CR of over 500:1.

Art
post #134 of 200
Quote:
Originally Posted by Art Sonneborn View Post

No I'm asking how you know my projector actually has ANSI CR of over 500:1.

Art

Unless it's defective, at least 500:1 without the anamorphic lens is consistent with measurements that have been posted. If it's defective or has dust or other contaminants on the optical surfaces, then I have no idea what the ANSI CR is. With everything in order, there is not much unit to unit ANSI CR variation in these designs.
post #135 of 200
Quote:
Originally Posted by odyssey View Post

Unless it's defective, at least 500:1 without the anamorphic lens is consistent with measurements that have been posted. If it's defective or has dust or other contaminants on the optical surfaces, then I have no idea what the ANSI CR is. With everything in order, there is not much unit to unit ANSI CR variation in these designs.

No one on this forum has shown HT 5000 measurements AFAIK. Lots of assumptions in your posts.

Art
post #136 of 200
Quote:
Originally Posted by Art Sonneborn View Post

No one on this forum has shown HT 5000 measurements AFAIK. Lots of assumptions in your posts.

Art

I have seen HT5000 ANSI CR measurements posted by at least Wolfgang and CM.

I usually (not always) say so when I am estimating something, using a term like probably. I also know these projectors well enough to be able to make good estimates.

My position that the G90 primaries are off, especially compared to DCI primaries, seems to irritate some. Same for the apparent grey scale tracking problem of the G90 stack being discussed. These are not assumptions. I have measured the G90 primaries and they were significantly off from both Rec709 and SMPTE C. It's possible to improve these with filters, but there is a trade off for both light output and ANSI CR and I don't think that you can get filters that will correct exactly. The grey scale tracking problem is also not an assumption. The 100 IRE blue measurement for one of the projectors shows a serious problem. I also question the low end tracking based on the red measurement. Some of this can be corrected, but the G90 will never have the color accuracy of some of the other projectors available. Isn't this one of the reasons why you changed projectors?
post #137 of 200
Quote:
Originally Posted by Art Sonneborn View Post

Ken measured it and it was under 200:1 as I recall.

As I've mentioned before, I wonder if there was some error in this from the meter. At first I didn't realize the problems measuring high ANSI CR with a Minolta LS110 and would expect an LS100 to have similar issues. Basically, all it takes is .5% of the light from white rectangles to get into the lens of the meter, bounce around, and register at the sensor of the meter, in order for a theoretical infinite ANSI CR off a screen to measure only 200:1. 200:1 is around the limit I found for the ANSI CR measurement of the LS110 without doing some things to limit the effect of the white rectangles on the meter. If you wanted to make sure the meter isn't the limiting factor, one thing you could do is make a black pipe for the front of the meter that kills most of the light from the white rectangles before it even gets to the lens for the meter. Another would be to get a black sheet or piece of black velvet and cut a hole in it and place it over part of the screen with the hole over a black rectangle and the black material covering the white rectangles just around the black rectangle being measured. If you just cover part of the screen it should reduce the reflections around the room some and make the ANSI CR measurement go up some, but if the ANSI CR measurement all of a sudden jump to a much higher value I would say that the meter was causing much of the problem. If the goal was to measure the ANSI CR of just the projector you could cover the whole screen except for part of the one black rectangle being measured. This isn't a problem when measuring the white rectangles because then the percentage it affects the reading is small.

ANSI CR of the projector is generally easier to measure with a meter that faces the projector in my experience.

--Darin
post #138 of 200
Thread Starter 
Quote:
Originally Posted by odyssey View Post

The problem with getting an accurate intra-image CR measurement with CRT projectors is eliminating the effect of the room. This is hard to do and more of a challenge than single lens units. It becomes easier if you measure each primary individually using the same techniques as single lens units.

Yes I understand and you're right, this is something that has to be guarded against even with a single lens projector but it's much more difficult with a CRT because of the physical separation of each gun and also the glow of the phosphor that is induced by ambient light that is discussed later in this post.

Quote:


I don’t know which test pattern you are currently using to measure intra-image CR,

The patterns are posted at the beginning of this thread. There are two sets of patterns the first set was developed by Wm Phelps and is designed to measure intra-image contrast using varying sized full white rectangles which sweep the APL region from very low to ANSI. I developed a second set designed to measure intra-image contrast using varying grey whites with a constant geometry. This second set allows direct comparison of projectors that use dynamic contrast mechanisms.

Quote:


but I expect the performance of the G90 to be relatively poor. There are many internal reflections in even the best LC CRT projectors. The halation effect is strong and there is only so much you can do with anti-halation coatings. The phosphors emit light in all directions and the lenses have much lower contrast performance compared to the best DLP projector lenses.

Yes this is exactly what makes this experiment so interesting. It seems as though a CRT would have many problems with intra-image contrast, but real world empirical tests seem to suggest there is more going on. As an example if we take a high native digital like an RS1 and project something like a star field image on it and compare that to a DI equipped projector like the VW50 the RS1 has noticeably more contrast in that scene. The reason for this is because that image requires more intra-image contrast than the DI can provide. If we take that same image and display it on a RS1 and a CRT, the CRT seems more contrasty. This suggests to me that the CRT is delivering more than the intra-image dynamic range of a DI and also an RS1 with that particular scene which is on the order of many thousands to 1. So this is the heart of what I find most intriguing about this experiment.

Quote:


The ANSI CR and MTF performance give a good indication of what will happen with an intra-image contrast pattern that more closely resembles typical content.

Yes but only at high APL. At low APL I think the CRT will perform much better and I think it will perform better than the best digitals. But the only way we will know for sure is if someone wants to invest the time and dedication into doing this work and why I really want to encourage Cliff to give it a shot.

Quote:


One of the issues with getting a meaningful sequential CR measurement is defining the performance of grey scale tracking and low luminance detail that’s required. It’s very easy to degrade these and get a very high number with the G90. What is the requirement for D65 accuracy and at what luminance levels? What is the requirement for gamma starting with digital value 17?

Yes, I can see this easily happening with the off state measurement with a CRT. I think it's also easy as an example for someone without a gamma tweak to sacrifice greyscale detail for blacks. Because the off state of CRT is so good, I know it will have huge on/off numbers but this doesn't really mean that much except for black out scenes. For intra-image contrast at low APL though it's not so easy to tweak the CRT to get astronomical contrast readings which is another reason I'm most interested in those measurements. We know all about the weaknesses of CRT in MTF and ANSI cr but very little about it's strengths.

Quote:


[font=Arial][size=3]The issue with ambient is not that the CR will be even higher if ambient is subtracted, but that the CR measurement is inaccurate. The main source of ambient is the screen. The entire screen is focused on the phosphor screen by the lens. You can see this clearly if you shine a light on the screen and look into the lenses.

Yup, I understand now. This is a similar effect to shining a laser at a phosphor or even a light bulb. For the measurements that I did in this thread, I placed a black sheet over the screen and also masked areas around the projector to eliminate reflected light off of the probe from hitting the projector and bouncing back into the probe. I can see how this can be even more important for CRT measurements.

The intra-image patterns used in this thread will likely have enough white so that the black reading will be many multiples above the ambient so that ambient will probably be less of a factor although it still should be carefully monitored and guarded against.

Quote:


but I am not interested in making these measurements. I don’t use the G90 for movies and I have a much better overall projector for that. Also, I will be replacing the G90 soon.

Even if you're not interested in using your G90 anymore, you'll have to admit that it's still an interesting exercise in seeing how the best attribute of a G90 compares to a digital (and arguably the worst attribute of digital). I never planned on using a DI equipped projector but went through a lot of time and effort just to understanding better how it compares with native projectors (and hopefully other dynamic technologies in the future, especially iris equipped LCD's). You have the knowledge and the equipment, it sure would be interesting to see your results if you decide to change your mind and spend a day or so on this
post #139 of 200
Quote:
Originally Posted by odyssey View Post

I have seen HT5000 ANSI CR measurements posted by at least Wolfgang and CM.


I'm not taking a position just looking for measured values not stated specs. I've not seen them so I was wondering how you specifically knew that it was higher than what we measured. I believe the mesured number Ken came up with is not correct,personally ,but it still was a measured value.

Art
post #140 of 200
Quote:
Originally Posted by odyssey View Post

the G90 will never have the color accuracy of some of the other projectors available. Isn't this one of the reasons why you changed projectors?

Pretty far down the list. I never really found subjective issues with the G90 color. I changed for full vertical and horizontal res, apparent sharpness, extreme uniformity,high APL pop, CIH option and light output. Quieting the room and opening it up architecturally was ahead of color actually.

art
post #141 of 200
Thread Starter 
Quote:
Originally Posted by Art Sonneborn View Post

I'm not taking a position just looking for measured values not stated specs. I've not seen them so I was wondering how you specifically knew that it was higher than what we measured. I believe the mesured number Ken came up with is not correct,personally ,but it still was a measured value.

Art

Here is an interesting anecdote. Alan G. was going to send me a HT5000 for a few days to measure for this thread but the timing didn't work out (I left for vacation when he was going to send it and when I returned he had already sold it). It would have been very interesting to get a really good 3-chip into the mix of projectors measured. My guess is that it will come in around 500:1 ANSI, but it's just a guess. So far we have an RS1, the ANSI king (Sharp 20K) and a good Sony DI implementation (VW50). It sure would be good to get a projector like the HT5000 into the mix.... hint... hint.... nudge....nudge...
post #142 of 200
Quote:
Originally Posted by Art Sonneborn View Post

I'm not taking a position just looking for measured values not stated specs. I've not seen them so I was wondering how you specifically knew that it was higher than what we measured. I believe the mesured number Ken came up with is not correct,personally ,but it still was a measured value.

Art

Ken did not measure the ANSI CR of the HT 5000. He measured the ANSI CR of the HT 5000 and your room.
post #143 of 200
Quote:
Originally Posted by odyssey View Post

Ken did not measure the ANSI CR of the HT 5000. He measured the ANSI CR of the HT 5000 and your room.

No $hit ,really.

Art
post #144 of 200
Quote:
Originally Posted by Art Sonneborn View Post

No $hit ,really.

Art

You asked how I knew that 200:1 was too low. I knew that 200:1 was too low for an HT-5000 only measurement, and knew that it was a measurement with the room effects. I don't think that 200:1 is too low with the room effects. I mentioned that the HT-5000 ANSI CR is at least 500:1. You seemed to be comparing the 200:1 and 500:1.
post #145 of 200
Quote:
Originally Posted by odyssey View Post

You asked how I knew that 200:1 was too low. I knew that 200:1 was too low for an HT-5000 only measurement, and knew that it was a measurement with the room effects. I don't think that 200:1 is too low with the room effects. I mentioned that the HT-5000 ANSI CR is at least 500:1. You seemed to be comparing the 200:1 and 500:1.

My point was you are still not using measured values of the 5000 only specs. You may well be entirely correct but I don't see how you could know.I should say you don't actually know.

art
post #146 of 200
Guys, looking foward to proving that yes it is possible to correct the G90 primaries without using filters and as well without sacrificing enough light or ANSI CR for it to be a discernable difference to the eye.

With that being said, I will keep in line with the requests and also look foward to posting the rest of the numbers down the road when time permits it.

Cliff
post #147 of 200
Thread Starter 
Quote:
Originally Posted by overclkr View Post

Guys, looking foward to proving that yes it is possible to correct the G90 primaries without using filters and as well without sacrificing enough light or ANSI CR for it to be a discernable difference to the eye.

With that being said, I will keep in line with the requests and also look foward to posting the rest of the numbers down the road when time permits it.

Cliff


I'm very much looking forward to it Cliff. Thanks for taking the time to do this. I'd also like to hear more about your measurement methodology so that I can have a leg up if I ever get the time and opportunity to measure a CRT myself.
post #148 of 200
Quote:
Originally Posted by Art Sonneborn View Post

My point was you are still not using measured values of the 5000 only specs. You may well be entirely correct but I don't see how you could know.I should say you don't actually know.

art

No. Both Wolfgang and CM posted measured ANSI CR for the HT 5000. I remember close to 500:1 for Wolfgang and 700:1 for CM. Based on these, I said at least 500:1. Later, I said that with the anamorphic lens, at least 400:1.
post #149 of 200
Quote:
Originally Posted by odyssey View Post

No. Both Wolfgang and CM posted measured ANSI CR for the HT 5000. I remember close to 500:1 for Wolfgang and 700:1 for CM. Based on these, I said at least 500:1. Later, I said that with the anamorphic lens, at least 400:1.

Link please? You keep talking about it but are not providing fact?

Cliff
post #150 of 200
Quote:
Originally Posted by overclkr View Post

Link please? You keep talking about it but are not providing fact?

Cliff

You can do the search. I remember well enough not to do it.
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