yCMS - Color Management System

[naomatrix]

I have an LCD monitor is calibrated program Atrise Lutcurve and I watch movies through MPC-HC + madVR. Look it very good. I also tried to use parameters color gamut of my display, that I have received from computer program - Monitor Asset Maneger via EDID, my tinctures such

# Parameters by Monitor Asset Maneger
# Default color space ...... Non-sRGB
# Display gamma ............ 2.20
# Red chromaticity ......... Rx 0,640 - Ry 0,334
# Green chromaticity ....... Gx 0,285 - Gy 0,599
# Blue chromaticity ........ Bx 0,153 - By 0,076
# White point (default ).... Wx 0,313 - Wy 0,328

I ordered a template string

Gamut_Measurements 0.640 0.334 0.285 0.599 0.153 0.076 0.313 0.328

and made the files 3DLUt, but I do not see any difference between the image without gamut correction and with correction. Where should I look at and whether there is some objective method of comparing images. Is it possible to make in yCMS use of parameters gamut through EDID automatically.
Sorry for my english I'm from Ukraine

[yesgrey]

Originally Posted by cyberbeing

So in other words you don't want to share what you are doing...

Please don't take it personally, but until yCMS be more stable and less bug affected I prefer to not discuss publicly some aspects of it. I consider it solely as some kind of protection...
Furthermore, I haven't yet implemented some of my ideas. The current clipping is only slightly better than the other two available modes...

[yesgrey]

Originally Posted by naomatrix

but I do not see any difference between the image without gamut correction and with correction.

The differences are more evident when the display gamut differs more from the source one, especially when it's wider, which isn't your case. In your case, the coordinates are so similar to the HD ones that you might not be able to detect any differences with real world images, probably only with some test patterns, where you could compare the primaries colors.
If you don't have any test patterns, go here and get them on the first post. Play the 100% color video and you should be able to detect some differences.

Originally Posted by naomatrix

Is it possible to make in yCMS use of parameters gamut through EDID automatically.

I don't know if that will ever be added, because the reliability of that info might not be very high...

[janos666]

Originally Posted by flanger216

Most importantly, when and how should one measure the primaries for use in yCMS?

There are three important components in your display:
- CCFL or LED back-light which has it's own color spectrum and it's own color temperature (and max/min luminance).
- LCD TFT panel with it's R, G, B pixels (made with color filters)
- (digital) driver/controller panel(s).

They are intended to match with various design parameters which can be a standard (like Rec709, sRGB, ect...) or any custom design. But they will be slightly unique (one by one) and they will change in time uniquely. (This is the reason why you need a colorimeter. You shouldn't think those instruments are perfect, but they are usually more than enough.)

The combination of the back-light and the TFT panel will determine the native characteristics of your display.
You have different options to push your display closer to the desired standard characteristics:
- It can be done with the internal electronic controllers, fully or partially.
- You can use software calibration, like VGA LUT or yCMS, ect.
- They can be used together.

Your possibilities will be limited by the supported hardware calibration features. Some professional displays will allow you to upload your 3D LUTs (made by an automated software) and make a complete hardware calibration. Some display will let you change a few things only (nothing like 2D LUT or IRE list for gamma or sliders for huye and saturation, but luminance and contrast only...)

There is no universal rule here but the general suggestion that you should change any possible setup in your hardware settings first and fine-tune it with software calibration. (Of course, you should omit any hardware features if you find them defective. And this applies to software bugs as well.)

And the basic idea behind this calibration:
- You have ** output characteristics but you want ## like ones. - You know the desired ## and you can measure the representative values of the ** state.
- You can make a matrix with math functions or pre-calculated tables of any possible values to manipulate your input signal to get ## through your ** output distortion.

Of course, the number of the lost color tones will be (nonlinearly) scaled by the distance between your display's native characteristics and the desired standard.
But this is another hardware factor. We usually have 8 bit/color materials and some displays will support higher bit depth. For example it will process the 10 bit input signal with 12 bit accuracy for 10 bit visualization, so there can be some room for image manipulation without losing details. But the other side is when you have 8 bit input with 8 bit processing and 6+2 bit visualization (like 6 bit TN or c-PVA panels with dithering) and you are far from the standard.

yCMS creates 16 bit 3DLUTs but MadVR will convert it back to 8 bit with dithering (I do not know but may be fake 10 bit quality is a good estimation - but there will be some dithering noise as a side effect...). But this number can be increased in the future with deepcolor support.

So, this is a deep hole, filled by eternal questions, desinformations, and a lot of shit. But the achievable result is much better than it was without calibration.

And to answer to your question (if you didn't figured it out already): You should use the measures which you make after the hardware or VGA LUT calibration. (Because that is your current display characteristic.)

You can see hexagonal CIE diagrams when you measure the primaries and secondaries after you manipulated the primaries only. This is not a standard behavior for HDTVs or consumer PC monitors. May be this function can be used for better CMYK simulation (which is used by printers).

[cyberlolo]

But how are the chromaticity primaries (Rx Ry Gx Gy Bx By Wx Wy) measured? Yesterday, an ISF certified calibrator came home to calibrate my KRP-500A, and he didn't know how to get those values.

He used his calibration equipment, and he saw that in Pure mode, using Bumtious' settings, my set was already perfectly calibrated. He only had to tweak the color temperature to reach 6500K, but nothing else. And then, I showed him the yCMS manual and asked him to give me the chromaticity coordinates of my TV so I can enter them to create a custom 3dlut, but he didn't know how to get those values.

Any help here, please?

[Mark_A_W]

Measure Primaries with HCFR and export values to a spreadsheet. Is this what you want?

Measure Red Green Blue Yellow Cyan Magenta
X 14.10174 9.465929 4.771986 22.703403 14.206526 18.559078
Y 7.40095 20.656126 2.066542 27.544523 22.373522 9.33258
Z 0.631434 5.138814 25.99736 5.800269 31.580687 26.514742
R 34.007427 -3.639539 -0.67371 28.340027 -4.099868 32.5783
G 0.242164 29.789465 0.331876 29.909027 29.515242 0.621179
B -0.05774 1.744957 27.324909 1.775425 29.609224 27.156624
Rc 7359 1014 280 7929 1312 7477
Gc 911 6691 943 7526 7520 1842
Bc 317 2897 5284 3202 8234 5577


My friend is an ISF Calibrator, he went to the US to do the course. He only did it because he needed it as a "qualification" as a professional calibrator.

He said the course is a complete joke. It's like calibration for 5 year olds. So being an "ISF Calibrator" as such is almost meaningless, it bears no reference to their actual competence.

[cyberlolo]

Not exactly. What I want is something like this (values are not mine) for my display:

# Red chromaticity ......... Rx 0,640 - Ry 0,334
# Green chromaticity ....... Gx 0,285 - Gy 0,599
# Blue chromaticity ........ Bx 0,153 - By 0,076
# White point (default ).... Wx 0,313 - Wy 0,328

So with that info I can create a 3dlut with this line:

Gamut_Measurements 0.640 0.334 0.285 0.599 0.153 0.076 0.313 0.328

So my question is: how can I get this values that belong to my display?

[Mark_A_W]

Is this closer? I just picked xyY instead of RGB. (Sorry the columns get all mixed up).

Measure Red Green Blue Yellow Cyan Magenta White
x 0.637104 0.268454 0.145328 0.405069 0.208427 0.341119 0.316547
y 0.334368 0.585809 0.062935 0.491444 0.328246 0.171535 0.330533
Y 7.40095 20.656125 2.066542 27.544523 22.373521 9.33258 29.550847
delta E 9.6 15.6 5.3 8.7 11.6 17.1
delta xy 0.50% 3.50% 0.60% 2.00% 1.60% 0.027
delta luma 17.80% -2.30% -3.10% 0.50% -3.80% 10.90%

[cyberlolo]

Yes, Mark, I think you got it! With that info, your values are:

# Red chromaticity ......... Rx 0.637 - Ry 0,334
# Green chromaticity ....... Gx 0.268 - Gy 0.585
# Blue chromaticity ........ Bx 0.145 - By 0.062
# White point (default ).... Wx 0.316 - Wy 0.330

And now, can you PLEASE explain me how have you done it?

[Mark_A_W]

With my DIY HCFR probe, and the HCFR software.

There are cheap probes you can buy instead of build....probably cheaper than your ISF calibration..

http://www.homecinema-fr.com/colorimetre/index_en.php


I think I just answered half of my questions to Yesgrey myself (the other part being "how to get a custom gamma curve").

[Mark_A_W]

Oh, and these aren't my "real" measurements. These numbers come from some quick and dirty measurements on my 24" Sony CRT monitor, not my projector.


But I know how now

Just need to break out the tripod and measure the projector again (it's been a while).


Actually, my colour filtered CRT projector is very close to Rec 709. The reds a bit more saturated, but I kinda like that. I will try the Gamut cropping with the 3DLUT, but I will need a new videocard, the 2600XT stutters on bluray with the 3DLUT enabled.

[cyberlolo]

Cheers Mark, you've been of great help to me. I think I'll call the calibrator to see if he can come home again to use his probe with HCFR and get the values. Thank you!

[Mark_A_W]

If he saved the measurements, then he already has the values. He just has to find the values in xyY format, like I did.

[yesgrey]

Originally Posted by cyberlolo

Not exactly. What I want is something like this (values are not mine) for my display:
# Red chromaticity ......... Rx 0,640 - Ry 0,334
# Green chromaticity ....... Gx 0,285 - Gy 0,599
# Blue chromaticity ........ Bx 0,153 - By 0,076
# White point (default ).... Wx 0,313 - Wy 0,328

You're right, the manual is not clear enough. I will add that the coordinates must be in xyY format. Sorry for the trouble.

Originally Posted by Mark_A_W

(the other part being "how to get a custom gamma curve").

What do you mean with that?
(1) How to measure your display's gamma curve or
(2) How to use yCMS to let you create your favorite gamma curve

[Mark_A_W]

"(2) How to use yCMS to let you create your favorite gamma curve "

There is an application on AVSforum called Video Equalizer.

http://www.avsforum.com/avs-vb/showthread.php?t=1042160
http://archive2.avsforum.com/avs-vb/...d.php?t=777353

You can drag the curves around to create a custom gamma curve. All together, or one colour at a time.

It's used to create a custom gamma curve, but you have to run it each time you boot to load the custom gamma curve (a big limitation).


If this kind of interface, combined with the ability to call series of standard gamma curves (say 2.2, 2.3, etc), was combined with a colourimeter greyscale measurement, and yCMS, then we'd have a closed-loop custom gamma curve solution.

Combine this with the gamut correction, and it's perfect (isn't it?). You get a correct gamut and your desired gamma curve (standard or custom).

Mark

[yesgrey]

Originally Posted by Mark_A_W

"(2) How to use yCMS to let you create your favorite gamma curve "

That's on my todo list too.

To be honest, with the Grayscale_Measurements command it's already possible to do it, but it's not very user friendly... I already have some ideas on how to do it in a more friendly way, but we'll discuss it after I release the next yCMS version.

[Mark_A_W]

VideoEqualizer looks like this:




And it kinda does "standard" gamma curves (LH lower sliders), but the numbers use the PC style numbers (which are backwards), not the "video" way of describing gamma.

[janos666]

Originally Posted by cyberlolo

But how are the chromaticity primaries (Rx Ry Gx Gy Bx By Wx Wy) measured? Yesterday, an ISF certified calibrator came home to calibrate my KRP-500A, and he didn't know how to get those values.

LOL. If that happened as I imagine, I would say: "Stop! Do not touch anything! Leave my house now, please."

ISF means nothing in my country. We just use the instruments. There are some barbarians who want to sell their half job for big price but others have EyeOne or ColorMunky and they know what they are doing and their price is good. (I bought an own colorimeter because I would like to test different settings. And I could do a favor for friends, as they did other favors for me in exchange, so it was not an expensive instrument at all.)

[flanger216]

My experiences with ISF 'technicians' have also been subpar at best. Not as bad as the yokels at the cable company, mind you --- I once had some cable tech, standing in my apartment, staring at a huge purple 60hz hum-bar wobbling down my TV, and he actually argued that the problem was caused by my speakers. He was, of course, referring to the magnetically shielded speakers that were sitting five feet from my LCD screen. I could only stare at him gape-jawed and politely observe that I'm pretty sure magnetic distortion looks nothing like that, that I'm pretty sure there are no magnetic fields in an LCD screen that could become improperly biased, and that I'm pretty sure it's just a ground loop caused by the oxidized bird's nest of coax cabling installed haphazardly on the roof of the apartment building. He stared at me like I was speaking Chinese. I swear to god, the cable guy didn't know what a freaking ground loop is.

So yeah, teaching yourself is the way to go

And thanks for the write-up on colorimetry, janos666... extremely helpful stuff!

P.S. I almost forgot the capper to the story: eventually I got so fed up that I went out and bought a big roll of coax cable, went up to the roof in the middle of the night, ripped out the cable company's mess and just reinstalled the whole stupid thing myself --- and I actually bothered to loop the cabling properly and (gasp!) put it in an enclosure so it wouldn't get rained on. Finally, no more ground loop. A few days later I overheard a few neighbors wondering if the cable company had done something to make their TVs look better

[sepheas]

hello,

I would like to have more information about the custom gamma curve. In fact, I really don't understand the values : lv av pv threshold ?

The only thing I understood is pv= 1/gamma.

Is there a way to create a custom gamma curve with something like videoequalizer and then save it with the values ( lv/av/ap/threshold)

I mean, to adjust it graphically and then catch the values to paste into ycms.

sorry for my english, if there's errors