The Official ChromaPure thread - Page 122

I've seen such #'s for direct view tv's and projectors many times, but have always wondered why they are different.     If 35 ftL is desired coming off a lcd tv, why is it not desired coming off a screen from a projector?   It is light coming to the eye; I don't see why the mechanism of how it is generated should matter.     (My ignorance I'm sure!)

Sure Tom will chime in, but one reason I can think of is ambient light (or lack of). I can't watch my TV in the dark as it hurts my eyes at 35fL, but with the lights on it's fine. Equally my projector looks pale and washed out with the lights on, but perfect with them off.

The TV is often smaller as well if this makes a difference.

thxz Tom but what you mean exactly? Can I somehow measure how good the black level is in both possible configurations I made? Because like I said both (1. lamp mode LOW with manual iris on 75 and 2. lamp mode HIGH with manual iris on 13) give me 15ftl so there s no difference there.

You could use the contrast measurement section: My guess is that the high lamp low iris will have more contrast than the low lamp higher iris, though you are also at the mercy of the meter's sensitivity and accuracy for measuring the black level. You could try turning the meter to face the projector (and maybe move it towards the projector a little) with the diffuser in place and just measure which has the highest black level as you already know the peak white is the same.

In a dark room with a touch of ambient light behind the TV, I prefer 80cd/m2 (23 fL). I find that plenty bright enough and having the backlight lower helps with the blacks. To be completely honest, I settled on 80cd/m2 just to try and keep reasonably close to specs, I am perfectly happy with a lower max light output. I prefer black detail over maximum light output.
Edited by Audionut11 - 12/12/12 at 4:50pm

For example, with Sony's new 84" 4K lcd tv, is 35 ftL the desired brightness coming off of it?    If so, why is 14 ftL the desired value for a projector and a 84" screen?

Size matters.

Dark room, 51" plasma > 35 FtL, 75" DLP > 22 FtL, 120" front projector > 14-16 FtL. Brighter rooms will require brighter output.

Front projection values are based on SMPTE recommendations where it assumes black out conditions.
There is some science behind it, however it is not cast in stone. As technologies get better references and standards change to meet those developments.
Despite the recommendations actual levels can be typically alot lower as projector bulbs age, this is both for true theatre and home projection.
Human vision adapts a considerable amount.

Home TV is more generalised guidelines because the environments can be vastly different, with that the real factors are perceptual ratios of screen area, light output and ambient light. Where ambient light is typically more powerful of the ratio parts, light output is realtive perceptually to ambient light, screen area as it gets larger perceptually drops saturation(you will measure accurate values but perceptually lose saturation), like wise luminance perception changes with screen area.

The values that are typically quoted as guides, are just that, guides for where the ratios are more likely to create a visually balanced experience. They are neither right or wrong, just starting points.

The one caveat is two technologies; Plasma and projection when set accurately can typically be at maximum with nothing left in head room, meaning the user has to control the ambient light to meet the balanced viewing condition.

Yes, I appreciate the difference if the room has significant ambient light, and also how well the human eye can adjust to different light levels in a fully darkened room.    E.g., at the end of the life of my first lamp I was getting only ~ 6 ftL with my Sony1000; it was still watchable (in my blacked out room), but I did feel I was missing the dynamism.    With my new lamp I'm now getting 35 or more ftL; the eye adjusts to this level of brightness even in a fully blacked out room, and the dynamism is dramatically enhanced.  I suppose it's most dramatic for sports, e.g., NFL, NBA, MLB, etc.

 

And I'm not alone in this:   quite a few knowledgeable folks over the the >$20K forum extoll the virtue of > 30 ftL with their projectors, e.g., Art Sonneborn, Coldmachine, and others. 

That's the EBU standard. If I were to make a prediction it would be that the two standards will eventually converge at the middle point--100 cd/m2.

So far as I know, EBU has not made recommendations for theater projection. Its focus seems to be on studio reference monitors.
Edited by TomHuffman - 12/13/12 at 1:06am

This has nothing to do with knowledge. It is about resources and personal preferences. In the real world, this is almost never an issue. I see a lot of home theater projection installations in my work. In almost every case, the person has chosen a screen that is too big for the light output of the projector (this is human nature--maximum result for minimum input), so they are getting typically 20-35 cd/m2. The first thing I usually try to do is start playing with the available adjustments to try and get more light out of the thing. In the most extreme example I can recall, a guy had a really beautiful large, terraced home theater with a 135" Grayhawk screen (negative gain) and a old JVC projector. He was getting about 25 cd/m2. I could have waterboarded him, but he would not consider either a different screen or a new (expensive) projector.

These standards serve a purpose. They provide guidance as to what provides good results for the great majority of viewers. If you have the money, space, and inclination I suppose you can go as bright as you want, but for the vast majority of installations that never even comes up.

Also, the 48 cd/m2 standard for projectors assumes a dark environment. If you want to watch a projector screen with ambient light, then all bets are off. The 120 cd/m2 standard for direct view assumes a well-lit environment with neutral surround and minimal screen reflections.
Edited by TomHuffman - 12/13/12 at 1:07am

It is not about size. It is about viewing environment and the method of illumination. Projection screens are designed to operate under very low light conditions. If you assume a dark room, then the image can be much dimmer and still be pleasing to the eye. The standards for projection arose with commercial theaters in mind. It is prohibitively expensive to illuminate a 300" screen to 120 cd/m2; and, in a dark room it is simply unnecessary and would also be uncomfortable for a lot of people. Direct view displays are designed to be viewed under normal lighting conditions, so they have to be brighter. Also, it is relatively easy and inexpensive to manufacture a direct view display that outputs the requisite 120 cd/m2.

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I judt did a 3d calibration (with glasses attached to i1 display pro III meter) and the best result I think I can achieve is what you see in these reports. Overall (I think?) not bad but only the gamma looks not good. There s a major drop from 60-70ire and above. What could be the cause of this and can I fix that problem in some way?

Is it therefore fair to say that for an LCD, limiting Y except for personal preferences is not necessary and 120 cd/m2 should be seen as a minimum rather than optimum?

Your comments are (of course!) very true, Tom, and I agree with everything you say above.   It is indeed all about personal preference, and we all try to get what we like best within our constraints of space, budget, etc.   In a fully darkened room, with light absorbing material in critical areas, I find 14 ftL off a large screen very nice (certainly better than the 6 to 7 I was getting at the end of my first lamp's life).   However I find that  twice that is even more dynamic and engrossing (maybe my eyes are just growing dim!); this is entirely personal preference.     I'm sure I would find a 150" lcd tv in my same darkened room, giving 35 ftL, just dynamic and enjoyable, and it would have the advantage of degrading less when I do turn on a reading light by my chair;  but it would of course probably be more than I am willing to pay for, let alone getting it into the room.

Hi,

What is that actual gamma target for a TV (in a dark environment) ?
Is it still 2.22 ? Or is it 2.45 as some people say ?

Thank you.

I think that is the case because for a projector you use full field patterns but I could be wrong and the light output is lower compared to window patterns, but I could be very wrong just a guess.

PS   When I first thought about replacing my 19" Sony Trinitron about 10 yrs ago, I got a Samsung 61" RPTV (having read many of Arun Gupta's posts here on the Forum).    I loved it, but after ~ 6 months got hungry for something bigger, and after a yr or so went to a Mits 73" RPTV.    Liked it even better, but then the same story:  wanted something bigger, and realized that the only way this would be possible would be by going to a projector.   I read for over a yr, trying to decide whether or not this would work for me, and finally made the plunge just as the JVC RS1 came out.   That was my personal preference.

 

So for me, a projector, with its sensitivity to ambient light, etc., was the compromise I was willing to make and deal with in order to get the large screen experience I wanted.     As said, I would be happy to have a comparable size 4K lcdtv, but this is just not reasonable, at least for the present; maybe rolldown OLED, so some other technology, will make direct views displays of this size manageable (and affordable) in the future.  If I'm still around at that time, I would be delighted to go that route.   

I think 2.22 is for a room with ambient light, a dark room , no lights on is 2.4. Most program material is mastered for 2.2-2.3. It's a bit of a hairy subject a new standard has been developed but there is no way of knowing if some studios have adapted it or continue to use 2.22.

Either the contrast is set too high or you are using full field test patterns on a plasma.

As I said, nothing is "necessary." The standard is 120 cd/m2. If you want more and your eyes can tolerate it, then I see no harm.

2.22 is approximately the average gamma for sRGB, though the actual curve is higher at the top end and lower at the bottom end. I don't know where you heard 2.45? EBU uses 2.35 and many DVDs are mastered at 2.4 or 2.2.

This reminds me somewhat of the light output discussion above. In the vast majority of installations the display's gamma is too low, not too high. It is not uncommon to find gamma is the 1.5-2.0 range. The important thing is to get the gamma up to a reasonable level, and 2.22 is a good target. Other than that I would pick BT.1886 which, like sRGB, starts high in the 2.35-2.4 range and then drifts downwards at the low end. The JVC projectors in particular benefit from this. If you try to do a 2.4 gamma top to bottom you will get crushed blacks.

Ok thank you.

One more question. I got my gamma curve flat around 2.22 from 30% to 60%. Then I had to lower the contrast on my plasma TV in order to heighten the end of the curve that was falling down to 1.8 at 70%.
I had to set my contrast to 34 only (60 is maximum, 52 is the clipping limit), it gives me a 22FL output.
Is this not too low ?
Should I give the advantage to high contrast or a 2.22 gamma in this case.

Thanks.

Are you using window test patterns? The correct setting for contrast on Pioneer plasmas is 40.

This sounds like a case of the window being too large. I ran across this myself years ago on the Kuros. At the time 25% window size was being shown by my pattern generator and I couldn't get light output up into the 30's without gamma being reduced at the high end. After an update I was able to display smaller window sizes with my generator, which eliminated the problem.
If I were you I'd try to find some smaller window patterns.

The Gamut Calibration Disk, or GCD has 10% APL window patterns. Give them a try.

Actually, before you posted this I had actually done that yesterday. See here my results.
Gamut was calibrated at 75%stimulus, to give good results at 75% and 100% saturation. Linearity over saturation seems quite good for this panel.
I used the 10p white balance control to lower gamma at the low end for BT1886. But at the very low end (5% and 10%), 20p control would have been better but my Samsung 55ES8000 does not have that.

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Hi,

yesterday I did my first autocal with 125 point color correction. I am curious if the results are what is to be expected from autocal. The reason I ask is because when I do greyscale and gamme by hand, I can dail it in so that from 20 to 100 is below 1.0 dE. I expected the autocal feature to do the same, but it seemed to be really strugeling to get even below 2.0.
I used a display 3 (not Pro) profiled to a i1 spectro 2 with a radiance mini on a VT50. Before I did the autocal run I did a two point greyscale in the service menu to help things along. I used the THX brightroom preset and used windowed 100% patterns from the mini itself.

Wouter Panasonic 131212 first autocal 125 pt thx day.pdf 2484k .pdf file

Yes, I'm using the Windows patterns on the AVSHD DVD.
Most of the calibration settings around the web give 36 to 50 for contrast for a Panasonic V20.
Is 40 on Pioneer a low setting too ?
Hi, do you mean that depending on window size, you got different results with the same settings ?
You had that gamma curve falling down with bigger windows, then, with smaller, you got it up back to 2.22 ?
Thanks.

Tom, lowering my contrast did not help neither did raising the blue and red helped. However, lowering GREEN to -20 gave a good result. I ll post my new graph in a few hours (@work atm). The only questions is: I ve read a few times that changing the GREEN too much is not preferable. Does this apply for making a flat grayscale for 3D also?

ps. I m using the 'normal' (center screen) patterns from the AVS-HD709 disc (special CP patterns)