Field of View (FOV) for meter profiling on direct view screens: i1 display pro vs i1 pro 2 - AVS Forum
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post #1 of 14 Old 02-26-2013, 11:37 PM - Thread Starter
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So here is what I think to know from reading around on AVS:-) the field of view is an imaginary circle and the size of this circle differs between meters. Put the meter further away from the screen, and the size of the circle increases. Thus, putting the above mentioned meters the same distance from the screen, will make the i1 display pro read a larger portion of the screen area than the i1 pro 2.

The primary reason the FOV needs to match for meter profiling, is display uniformity variance. Displaying, for instance, the pattern for full read on a LCD can show that the delta E is not constant over the entire screen surface. Meter profiling is meant correct the measurement error in the colorimeter so that it will measure the same as the more accurate spectrophotometer. The measurement error could be wrong (influenced by display variance) if both meters are measuring a different portion of the screen.

Now then, on my plasma moving the i1 display pro further away (1-15 cm) or closer (as close as possible = contact mode) does not change the x,y readings for red at 75% stimulus, 100% saturation significantly(I tried green and yellow too). Sure it fluctuates with 0.003 at the most but I understand this is within repeatability limits. What *does* fluctuate harder is the light reading (Y).

So, what if we would exclude Y from the correction matrix seeing colorimeters should already be better at reading it anyway? And why does Y vary harder?

My gear: Panasonic TH-42PF11EK pro plasma display. -- Iscan Duo video processor -- i1 display 3 colorimeter -- i1 pro 2 spectrometer
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post #2 of 14 Old 02-26-2013, 11:57 PM
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Here is the best information on field of view matching:
http://store.spectracal.com/article-why-viewing-angle-is-important


At high light levels spectro's and colorimeters aren't that different for measuring Y, in fact if anything I might give the edge to a spectro, because the filters on a colorimeter will always be imperfect.

Either way the NIST traceable prodcedure uses a four color matrix which includes the Y value.
http://www.spectracal.com/downloads/files/Website/Website%20Articles/Four-Color%20Matrix%20Method%2011-08-10.pdf

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post #3 of 14 Old 02-27-2013, 12:33 AM - Thread Starter
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Hi Sotti,

Yes, I've read that paper before indicating it is not so important for "transmissive illuminate displays". However, since Y varies a lot with distance, I consider it the most error prone component to profile another meter to. I'm going to try measure Y with both the i1 display pro and i1 pro and see whether I get any considerable difference when using the meters in close proximity of the screen (at most 10 cm distance).

If Y does not vary by much, the issue is probably a very small one indeed for the non-projector folks.
The problem is, can anyone define what a small, medium and large variance for Y is?

My gear: Panasonic TH-42PF11EK pro plasma display. -- Iscan Duo video processor -- i1 display 3 colorimeter -- i1 pro 2 spectrometer
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post #4 of 14 Old 02-27-2013, 04:23 AM
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Quote:
Originally Posted by Jeroen1000 View Post

Hi Sotti,

Yes, I've read that paper before indicating it is not so important for "transmissive illuminate displays". However, since Y varies a lot with distance, I consider it the most error prone component to profile another meter to.

You do realize when you are not in contact mode, you must adjust each of the meter on the tripod up down left right to get the Max Y and to get then to match between the 2 meters before you do the profile. Having both meters on the same tripod at the same time makes this father simple. I can get my i1pro and C6 to read the same light output within a couple of decimals when profiling my projector off the screen. If Y is bouncing and it is bouncing on both meters than there is some other problem with the software or display
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post #5 of 14 Old 02-27-2013, 08:08 AM - Thread Starter
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But that is the confusing part. Sorry if this sounds stupid (I'm really serious)

Only ONE of both meters has the correct reading for Y. So suppose the i1 display pro reads 90 cd/m² and your i1 pro 2 reads 80 cd/m². Moving the i1 display pro back (away from the display) will obviously make the 90 drop towards 80. Heck, moving the i1 pro 2 closer may even get its 80 up to 90.

At some point I'm sure you will able to get them to agree but whether that will ever be accurate? Would it not just make more sense to just stick them both in contact mode to the screen eliminating the distance variable*? That way both meters can get the maxiumum light output and you adjust the colorimeter to read what the spectro reads. This assuming the spectro is more accurate for reading Y to begin with (which it should be if you pick a pattern with 100% stimulus, right?)

Your method assumes both meters are already reading Y correctly and I thought profiling was about correcting the meter that does not read correctly. What's the point in taking Y into account when profling if you move meters back and forward until they agree on Y? Perhaps these are dumb questions as I have not tried profiling for myself just yet.

*but because of their different FOV they won't be reading an equal screen area which may or may not be an issue

My gear: Panasonic TH-42PF11EK pro plasma display. -- Iscan Duo video processor -- i1 display 3 colorimeter -- i1 pro 2 spectrometer
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post #6 of 14 Old 02-27-2013, 08:24 AM
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You can only split a hair some many times with a pick ax.

The main thing the matrix is correcting is how the target sees color ..
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post #7 of 14 Old 02-27-2013, 08:34 AM
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Greetings

Luminance readings are some of the last things I would care about in the profiling process. It doesn't really matter when you calibrate ... since we don't calibrate to luminance numbers.

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post #8 of 14 Old 02-27-2013, 08:52 AM - Thread Starter
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So it is not overly important because we calibrate relative to the luminance of white and hardly ever use absolute luminance.
My mistake for not remembering that. New to profiling is my excuse:d

My gear: Panasonic TH-42PF11EK pro plasma display. -- Iscan Duo video processor -- i1 display 3 colorimeter -- i1 pro 2 spectrometer
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post #9 of 14 Old 02-27-2013, 09:29 AM
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Greetings

It is more important to get the x, y coordinates right. You will determine if it is too bright for your eyes later. If it hurts your eyes, the contrast is too high. (or the backlight is too high).

Please read this article on contrast to get some perspective. smile.gif

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post #10 of 14 Old 02-27-2013, 09:30 AM
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No apologies needed we are all learning!
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post #11 of 14 Old 02-27-2013, 10:15 AM - Thread Starter
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Ok you got me. I feel my screen is a bit too dim after calibration. I used 10% window patterns because I have a plasma. I got 127 cd/m² if I'm not mistaken and I wanted to make sure that number is accurate. 127 cd/m² is theoretically enough but I still feel it looks a bit dim.
TBH, I'm not even sure what kind of pattern (as the size has a considerable impact on the light output number) I have to use to measure peak light output. I could probably go even higher when measuring a 5% window pattern:)

My gear: Panasonic TH-42PF11EK pro plasma display. -- Iscan Duo video processor -- i1 display 3 colorimeter -- i1 pro 2 spectrometer
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post #12 of 14 Old 02-27-2013, 10:30 AM
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Quote:
Originally Posted by Jeroen1000 View Post

Ok you got me. I feel my screen is a bit too dim after calibration. I used 10% window patterns because I have a plasma. I got 127 cd/m² if I'm not mistaken and I wanted to make sure that number is accurate.

Plasmas aren't that bright, if you want a bright image you're better off with an LCD.

That said, all you can do is try maximize contrast so that it doesn't clip or cause discoloration. After those are set, you're getting maximum calibrated output, if you aren't happy with that amount of light, then you chose the wrong display for your needs.

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post #13 of 14 Old 02-28-2013, 01:17 AM
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Two things I've found with both my plasmas, using a large window pattern or a field will get a darker picture due to the limiting circuits. I use a small window, 10%, and have also had good results from Chad's 4% patterns, not his apl's. The second thing is to keep your gamma no greater than 2.3.

One of my first calibrations cut the light output by more than half, I had used a larger window pattern, 25% I believe. Without changing anything on the set, just re-measurung with the smaller patterns, I found the gamma was reading 2.42 as opposed to 2.26 with the larger patterns.
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post #14 of 14 Old 02-28-2013, 01:31 AM
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Not sure if it has anything to do with it, but I found that with small patterns my contrast is set a lot lower because there is no ABL. When I ise medium patterns and set my contrast with those, the contrast is set a lot higher. That would account for a dimm picture.

So maybe set contrast using a medium window which triggers abl, then calibrate with a small window without abl?
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