BIG Screen Brightness Survey/Questions - Page 3 - AVS Forum
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post #61 of 71 Old 10-25-2013, 08:21 AM
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Quote:
Originally Posted by coderguy View Post

Your post is just rambling...

ANSI Lumens is the standard method used unequivocally in this forum, by reviewers online, by calibrators that want to determine screen brightness, and this fact still applies EVEN if you have to apply a gain difference to it after you convert it to fL, for simplicity sakes.

AVS uses this method, we all use it. No-one said to ignore the non-uniformity of a severely non-uniform screen like an HP, you added that in. No-one has ever said to JUST factor in Ansi Lumens, the gain was included as part of the formula, how that is applied or calculated is a separate issue, but the simplest method was shown in the formula for simplicity sakes as to not confuse posters, otherwise it would have been a much longer and confusing formula.

It is best to apply the measurement commonly used (ANSI Lumens) which you can then apply the known gain spec to. The data he proposes of calculating exact screen uniformity and projector uniformity individually at each point on the screen is not as easily measured accurately, if it were, then we would be measuring off the screen in the first place instead of using ANSI lumens. Such a process is overly tedious for the purpose of this exercise. As noted, there are spreadsheets and other programs to aid with the calculation of non-uniform gain screens. It is better to completely remove one error in the results that is easily removed (PJ uniformity), rather than try to recommend that everyone also measure screen uniformity individually and factor that in.

Since I own the HP 2.4 gain screen, his assertion that I do not understand there was also a screen component is not only silly, but it was purely polluting to the thread for no reason other than to start trouble.


Time to stop enablement.. this thread is useless as it is now.. no need to continue. I feel bad for asking the question and starting this mess.

Doug

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post #62 of 71 Old 10-25-2013, 10:11 AM
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Quote:
Originally Posted by coderguy View Post

I will not respond.
Why keep claiming stuff like this and not do what you say? Interesting that you then went and modified your post way after the fact as if you didn't say that.
Quote:
Originally Posted by coderguy View Post

ANSI Lumens is the standard method used unequivocally in this forum, by reviewers online, by calibrators that want to determine screen brightness, and this fact still applies EVEN if you have to apply a gain difference to it after you convert it to fL, for simplicity sakes.
ANSI Lumens is for light from the projector. There is a simple principal involved where the average of the thing that is being measured is used. When calculating light from the screen the proper calculations applying the same principal would average the luminance (ft-lamberts) values. Averaging the illuminance values before applying non-uniform screen gain creates mathematical error. It is just mathematically wrong. If people want to take a shortcut for simplicity that is one thing, but to claim that it is mathematically correct to average the first non-uniformity out before applying the other is incorrect.
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Originally Posted by coderguy View Post

AVS uses this method, we all use it.
Who besides you would take the lux readings, average them out to determine ANSI lumens, then apply the non-uniformity of the screen gain to that ANSI lumens value? Taking shortcuts and realizing it is another matter, but you have claimed that averaging the lux values before taking the non-uniform screen gain into account is the correct mathematically way of getting ft-lamberts when taking non-uniform screen gain into account.
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Originally Posted by coderguy View Post

As noted, there are spreadsheets and other programs to aid with the calculation of non-uniform gain screens.
And if those spreadsheets first average the lux values to get ANSI lumens and then use that with the non-uniform screen gain values then they are doing the math wrong. If they are doing it because all they have is ANSI lumens and not the lux values then that is one thing (they don't have the data to apply), but when they have the data for the different lux values at different places and the screen gains for those places, then doing the math as you suggest and first converting to lumens is wrong.

If you or anybody else has a spreadsheet that takes in lux values and uses non-unformity of gain to calculate ft-lamberts they should not convert to ANSI lumens first to get the right value.

The most accurate way in general to get the ft-lamberts is to measure it directly. If a person has access to any measuring equipment they would want then this is the best way to go.

To be clear for everybody, by coderguy's logic, if a person has a Minolta L-100 luminance meter they cannot determine their ft-lamberts properly even if they measure 21 ft-lamberts for the brightest spot off their screen just below center and measure 9 points off their screen as:

12, 14, 13
15, 20, 16
13, 16, 14

Why do I say that? Because according to him the proper math for determining ft-lamberts after taking lux readings and wanting to take the screen non-uniformity into account is to first average those lux values out to ANSI lumens before taking the screen non-uniformity into account. That is different math than the actual ft-lamberts values for those spots on the screen, so if that were the correct math as he claims, then direct measurements of ft-lamberts would not provide the information needed. I already provided one example where his math differs from actual ft-lamberts measurements and where it isn't an accident since he is claiming that it is the proper math.

Is there anybody here besides coderguy who believes that the correct math for taking both screen and projector non-uniformity into account when determing ft-lamberts is to first convert lux values to ANSI lumens and then apply that ANSI lumens value to the non-uniform screen gain?

--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 #63 of 71 Old 10-25-2013, 11:08 AM
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Unbelievable you are still going on and would deny what everyone in here knows to be true, that we take fL and then apply a single gain to that as a general easy method. You still going on. No-one is reading your gibberish. There are all kinds of reasons we use ANSI Lumens instead of measuring off the screen, the main reason is most of us do not have the equipment nor patience to do it off the screen, both techniques have error margins and are flawed, but this method works fine for its use. I do not know the difference in error margin between the two techniques, but by far measuring from the screen with a regular colorimeter (as was discussed earlier) is the most flawed technique.

I never said they were mathematically exact, I even mentioned there are errors in every method, you sir, are not only acting like a jerk by twisting around everything I said, but you continue to insult me for something that everyone knows is a generally accepted practice, mathematically perfect or not.

You are being a complete pompass jerk IMO, stating the obvious repeating definitions and claiming "ONLY YOU", yah only me and everyone else posting in threads the last 5 years when we generalize lumens - fL - gain, as well as reviewers. Of course it's a generalization, the baselines of the measurements are not perfect enough for it to be anything else. You cannot just easily measure some points on the screen to determine screen non-uniformity so simply and then apply that either, it is a very tedious process.

Furthermore, I did not post the formula to take non-uniform gain into account, there are several variables involved, that is just a lie. I simply said it is approximated for simplicity sakes and there are some spreadsheets that can help. I also did not say if there formulas were exact or not, I have not diven into it enough to even look, nor could I care when it comes to non-uniform gain as it is all an approximation. You asked me a question about a screen that I did not even know had non-uniform gain.



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post #64 of 71 Old 10-25-2013, 11:25 AM
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Quote:
Originally Posted by coderguy View Post

I never said they were mathematically exact, I even mentioned there are errors ...
Of course there are errors, but we are talking about an error that you are purposely putting in for no good reason. I think I was pretty clear in spelling out that we were talking about the case where people have the lux values and are applying the non-uniform screen gain, so your examples of other people who were not trying to do those specific things do not apply.

To be clear, coderguy is wrong about this:
Quote:
Originally Posted by coderguy View Post

The average gain and factoring in the difference in seating position for any non-uniform or retro-gain screen should also be done to the post-converted fL measurement AFTER you measure the regular ANSI LUMENS, not from measuring fL points.
Ignorance is one thing, but willful ignorance quite another.

He has no problem correcting other people, but we can see how he reacts when he is wrong. And he is wrong about the proper way to do that calculation. Thinking that the best way to take non-uniform screen gain into account to determine ft-lamberts with lux measurements is to first convert to ANSI lumens and use that one number is just wrong. As I said, if he or any spreadsheet does it that way once they have the lux readings and screen gain points it is doing it incorrectly. Admitting that there are other errors in the system doesn't make it correct that the proper way is to convert to lumens first.

--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 #65 of 71 Old 10-25-2013, 11:29 AM
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Stop putting words in my mouth and partially quoting something out of context that 3 sentences later stated to take account the gain.
No-one said anything about the best way, I said it's the quick way we do it, it's the standard way. We don't sit and punch numbers all day to try to find a non-uniform gain average, we use a single gain number for simplicity and portability sakes.

I said it was the better and quicker way versus measuring with a colorimeter, because unless you are very careful, measuring from the screen method is easy to mess up. I stated this many times, that it is possible to do it other ways. I am not going to sit here and be privy to this ridiculous attack anymore.

I do not get mad when I am wrong, it was the method in which you worded it acussationally and baiting to intentionally start an argument and ruin the thread. I am sick of dealing with you.



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post #66 of 71 Old 10-25-2013, 11:32 AM
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post #67 of 71 Old 10-25-2013, 05:07 PM
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In my own experience, I have found that with a darker room I can get away with less lumens than normally sought after, because the light doesn't bounce around off all the white walls, even though there isn't more lumens, the perception changes if the only light being seen in the theater is the movie on screen. You'll notice many projectors have advertised in their promotional stuff or specifications screen sizes up to 25ft. I see them sometimes on projectors that are only 1000 lumens, which is way to dim for such a size. However, in a theater dark room after your eyes adjust to the dark, I suppose its doable, but not the best picture. I guess that's why they advertise them to such a big size, when they are really less than ideal. I'm sure shadow detail would decrease as well, but I can't say for certain. Anyway I've watched plenty of movies on lower than 12 lumens according to calculators and based off of what projector reviews have measured far as lumens in various modes by projecting giant screens. I definitely prefer brighter even at the expense of color accuracy. I think this goes for most non movie aficionado type people. I found it interesting that Art from Projectorreviews.com mentioned in a review that he had people over and were watching a football game on his 5020ub. Then during the break he switched pjs without telling them to the veiwsonic pjd7820HD and apparently everyone noticed the brightness change and really like that over the Epson, even though the Epson would have had a superior color accuracy. So my point is, even if you can get away with less lumens, you might lose some pop to the picture, something you may regret, especially as the lamp ages and loses light.

If I were you, I would project onto a white wall with different sizes and see how you like it, you may find that bigger trumps less brightness. I
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post #68 of 71 Old 10-26-2013, 01:36 PM
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Jvc x90. 150" 1.0 gain 16:9 screen. 14fl high lamp open aperture. Thats my max. I vary screen size/fl/aperture/lamp mode depending on content. Perfect ambient light control room and decor is blacked out quite well now.
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post #69 of 71 Old 10-29-2013, 04:47 AM - Thread Starter
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WOW and Thank You SoupD. This is the information I was looking for from the forum.

MOST people who are putting a screen that is larger than 150" have a professional calibrating their new room and projector, and have a good idea of the brightness of the image from the calibration professional. USUSALLY this is quoted to the user in fL. EXACTLY as SoupD commented. I was not asking for a soap box on calibration or measurement.

In another three weeks or so, I might ask the question again, and hope a poop throwing contest does not break out - for three pages.
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Jvc x90. 150" 1.0 gain 16:9 screen. 14fl high lamp open aperture. Thats my max. I vary screen size/fl/aperture/lamp mode depending on content. Perfect ambient light control room and decor is blacked out quite well now.
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post #70 of 71 Old 10-29-2013, 04:55 AM - Thread Starter
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Thanks James. I come from the CRT world for the past 15yrs, and truely appreciate a properly calibrated 12fL image. Only in the past 5yrs have the digital light cannons become acceptable in black level IMHO, and now I am faced with building out a new room.

Like CRT rooms of the past, I will have 100% light control, so in spite of the consumer draw of bright as the son, I think a very large 12fL image may be acceptable, but I wanted to hear from those out there.

Your comparison of an Epson to the Viewsonic is interesting. I have seen the 5020 in action, and agree it puts up a decently accurate color image, but still find the black levels lacking. I could never look at a Viewsonic image long term in a theater. NEVER, but the point is interesting.

Jeff in Detroit
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post #71 of 71 Old 10-31-2013, 01:37 PM
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What size screen would you like to achieve. It sounds like you could live with a slightly darker picture and just go big. I forgot to mention, my parents still use the old optoma hd70 on a 150 inch screen and that's on the original lamp, its definitely not the brightest picture, but after the eyes adjust, its not horrible. That pj is only 1000 lumens, I used to take it up to 20ft to play movies and games and only the real dark movies suffered where I didn't want to watch them at that size. My friends kids always wanted it bigger and didn't care about losing brightness either. OF course they are going to be less critical than adults. Coming from a CRT, I think it would be hard to settle with the some of the newer pjs far as blacks are concerned. Which pjs are you looking at.
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