The Official ChromaPure thread - Page 133

Projector used for 2 hrs before starting calibration. With the Lumagen XS pattern #2 I rechecked brightness and contrast. At bright 44 below black is invisible, and 4% above barely visible. I stayed with 84 on contrast. Above and below white are visible almost all the way to 100.

I set 75% intensity, full field test patterns, and the defaults for everything else. I am not sure what to make of the results other than they are not what I expected. I was in another room while it ran and have not looked at any program material since.




022102 Calibration Detail.pdf 2551k .pdf file

The problem with the grayscale at the low end is that you are not getting nearly enough light out of this PJ. You need to do something--put it in high lamp mode or maybe get a new bulb. Your light output is about 1/3 of what it should be, and that was with light artificially boosted with a 1.6 gamma. Post calibration with a good gamma response the light output is now 1/6 of what it should be.

In the short run, turn the meter around, place the diffuser over the lens, and point at the PJ's lamp. This will get more light into the probe and provide better results at the low end of the grayscale.

Would it be ok, on a projector with low light output, to profile a i1 display pro with the spectro pointing to.the screen and with the d3 facing the projector with the diffuser on?

Thank you. Slightly surprised about output since it seems bright at 100%. Will do manual adj for the moment and order a new lamp this weekend.

It would depend on the screen. A color neutral screen, yes. An exotic screen, probably not.

Hi Tom
I have a query, after doing an advaced autocal with a lumagen XS I've noticed that the lumagen has not asked me to save my changes (like it used to when i did non-advaced cals on older lumagen firmware). Is this because chromapure now tells XS to save the changes now, or hase something gone wrong?

Thanks
Chris

It saves automatically.

Phew, I thought I was in the embarrassing position of thinking I could see improvements when non had been made.

Placebo calibration, cheapest kind

Hi Tom and others,

Any tips on how to measure on/off contrast on a plasma?

Sure I can display a full black field (not a Window) and measure it (recollecting from memory, I believe I'm getting about 0.041 cd/m²). But for white, the peak output depends on the size of the white square. The smaller the white square (window), the better my contrast ratio. Showing a white field obviously yields the lowest number for the contrast ratio.

What I do to measure contrast :
I measure my white peak with a SMALL APL 100% White pattern.
Then, I put a 100% Black Window Pattern and take measurement.

For example, I have 109 cd.m² against 0.012 cd.m²; which gives me a ration of ~9000:1.

I use the Window checkboard pattern to measure ANSI contrast. Which in my case is a bit lower of course.

Never take your white peak level with a full screen on a plasma TV. The ABL will be working and your contrast ratio will be altered.
Edited by mlg33 - 2/26/13 at 1:20am

Frankly, I'm just trying to support my idea that my display is slightly too dim.This is to say, that the content I'm watching is being displayed too dimly.
I've got an option (called contrast) on my plasma that compresses dynamic range in order to obtain higher peak white output (the true contrast control is called input level). I'm not sure what bad things will ensue from compressing the dynamic range though. I do know (from just looking at the screen) the effect is a brighter picture:-).

Anyway, using an APL-pattern makes sense if you know what kind of cd/m² you should be getting for a certain APL. So if the APL (which I assume means the pattern + the background) equals 50%, you should be getting 60 cd/m², right? But on the other hand, using a larger pattern (meaning here the area you will actually measure becomes bigger) with the same APL for the background will again have an effect on the peak white output numbers in cd/m². It's like chasing your own tail. So how do you balance between the size of the pattern and the video levels used for the background to achieve a certain APL?

I appreciate the fact that a screen will rarely be 100% white (Ice hockey and snow sports broadcasting may come close, however). So I could guess on and conclude that if you are getting sufficient cd/m² in the 20% to 70% APL area you are good, even if you do not get 120 cd/m² for 100% APL because of the ABL on a plasma screen (= the same as a completely white screen).

Using Chromapure Deluxe and Accupel 5000 signal generator.

When running the Color Management module and you select 75% Rec.709, does the program change which patterns it selects in the Accupel or do you make the change in the Accupel's OSD under User/ color (selecting 075 for each RGB) and then chromapure selects the correct pattern(s)?

The application selects the correct colors automatically. No user intervention is needed.

So if you go back and forth between 709 and 75% of 709, there isn't something else you manually change in the Accupel OSD?

No user intervention is needed.

I am currently in the process of learning the ins and outs of ChromaPure and am curious about something I have noticed during a calibration. Why doesn't CP always pick the lowest measurement number?

Last night and previously I was running an auto-calibration using default settings; i.e. dE 1.75. For grayscale as an example, I noticed the dE go from something like 4.15 up to 21.03, then head down to a low of 1.89 with the final number something like 2.98 for the final dE number. I will be watching the measurements scroll on the screen and wonder why didn't it stop on the lower number? I suppose there could be other considerations 'under the hood' that I am not aware of.

I must stress I am very happy with ChromaPure and the results I am getting with it. The above is not a complaint, just wondering.

Regards,

Steve

It should pick the lowest number. If you can run this and copy/paste the text in the activity window and send it to CP support, I'll look into it.

Note: It won't "stop" on the lowest number if that number is above the selected target, as in your example. However, when it finishes trying to get a better number and fails, it should then apply the lowest dE achieved.

Thanks Tom, I will do that.

Just to reiterate, I am very happy with the results I am getting.

While I have you, if you recall we e-mailed recently about a totally different problem I was having with CP not giving me correct readings in any area and the color windows in the Duo not matching?. I am pretty sure it was my fault because oh how I installed the recent version update. Yesterday I deleted and then installed CP from scratch. Works fine now! So, was not CP. It was me.

Thanks for help.

Steve

So regardless of selecting either 75% or 100% signal intensity in the options/signal generators/device settings, it doesn't impact using Rec.709 or 75%Rec.709 in the Color Management module?

I am going to spend some time on this, not just to answer your question but because this is an issue that comes up often and obviously requires clarification.

1. The 75% of Rec. 709 option in Color Management refers only to 75% saturation of Rec. 709. That means that the target point is 75% of the distance from the white point to the Rec. 709 gamut boundary--a much reduced gamut. The spec for a Rec. 709 red and a 75% saturated Rec. 709 red have different xy coordinates.

2. The 75% and 100% Intensity selectors in the Signal Generator setup refer only to % of intensity. This has nothing to do with the size of the gamut. It only refers to the level of luminance, which is not represented on the CIE Chart at all. A 75% intensity Rec. 709 red and a 100% intensity Rec. 709 red have exactly the same xy coordinates: x0.640, y0.330. They even have the same Y specification: 0.2126. This is true even though they are different levels of luminance because the reference white changes along with the color, thus the ratio between the color's luminance and the luminance of the reference white point stays the same. What changes is the absolute luminance, measured in cd/m2 or ft-L.

3. As a matter of best practice I always recommend using 75% intensity test patterns for color management. You may or may not choose to use the 75% of Rec. 709 target gamut in color management. It helps with some displays and not with others, and it really makes reporting more difficult. However, the two (intensity selection and target gamut selection) really have nothing to do with one another.

I have found a discrepancy in the Advanced Color Management module. Please tell me what I'm doing wrong as I'm pulling my hair on this one.
I've added screenshots to accompany the below information. My pattern generator is an iScan Duo with v2.32 firmware. My meter is an i1 display pro (so with extra tables).

When I do a baseline run, I get x = 0.646 en y = 0.332 for red.
dE = 1.6 here. This was measured with a pattern with 75% amplitude (=stimulus) and 100% saturation.

Next, I'm going to the Primary Color Amplitudes screen.

For the red 75 measurement (meaning 75% amplitude 100% saturation?) I'm getting x = 0.647 en y = 0.332 for red. Which is expected as the amplitude does not alter the x,y coordinates. The small change for x does not matter. It is proably a repeatability issue or the plasma screen has a faint variance.

Yet the the dE = 13.6.

So, why is this? This is the exact same measurement as the baseline measurement and the dE error is much worse here.


baseline.PNG 29k .PNG file
75 amplitude 100 sat.PNG 151k .PNG file

Since x and y are the same, the problem should be with the Y, the luminance of what you are measuring.

Nope, all good too I think (0.209 vs 0.21)

I see some weirdness in Advance Color as well. You just finish a 125 point calibration and everything is under dE of 2 and yet you get numbers that don't match when you run all measurements in Advance Color Management.. You go in post cal gamut and rerun and the numbers match up quite closely with 125 point calibration. This funny business in Advanced Calibration is not always the case and never anything like your dE 13.6 but general weirdness seems to happen fairl often.

Looks to me like you are feeding it a 100% saturated red and it wants a 75% saturated red. x,y needs to be at 75% of the distance from red to white.

I had thought of that and unless I made a mistake or the Iscan Duo Control Panel did something funny, I tried 75 stim 75 sat. (which made the dE even worse) and also 100 stim. 75 sat. and also 75. stim 50 sat.
I'm not sure what the 'Set pattern intensity' drop down menu in the second screenshot is referring too: saturation of stimulus?

I can't repeat before Tuesday but perhaps I should have rebooted all the gear and CP too. That's about the only thing I "forgot" to take into account as the source of this error.

Tom: A question. My understanding is that new 4k (UHTV) TVs will be required to use the Rec. 2020 color gamut which covers ~ 76% of the 1931 gamut versus the ~ 35% covered by today's Rec. 709 space. Will we need new calibration software and meters to calibrate these TVs? Thanks

I think any decent meter should be able to measure almost any color in the IEE chart and the available programs should be ablle to report that measurement. Of course new signal generators will be needed to generate the required test patterns at 4HD resolution.

I have no clue as to whether existing 4K displays have wide enough primaries for the new color space. I think it will be quite some time until we see 4HD sources with the new space. 4K with DCI color space can be had and I think all present 4K displays can support that wider space (than rec 709).
Edited by mark haflich - 3/3/13 at 3:11pm

When measuring amplitudes, you must use 100% stimulus test patterns, because that is the baseline from which the other targets are calculated.