Kodak Q-13 color target

ggc · August 19, 2018, 3:31pm

Hello everyone,

i have obtained a Kodak Color Separation Guide and Gray Scale (Q-13).

Can i use it for color profiling my cameras?

Or at least to male a “rough” profile ((even a lut) to make colors from my phone’s dng similar or not too far from, for example, my Fuji X-T20 that should have a good profile?

I’ve seen in How to create DCP color profiles - RawPedia that unfortunatly this profile isn’t supported.

Thank you in advance.

ggc · August 19, 2018, 9:01pm

Found out something in this thread @ dpreview

I repost what Iliah Borg wrote:

Q13 consists of two cards, gray scale and colour separation. The numbers refer to gray scale card Q13. Is it the colour control portion of that card that you want? That one is not designed for exposure control, it is for old CMYK separation process. I can give its numbers for AdobeRGB, of course:

Name R G B

"Light_Blue" 243.473 240.670 229.074

"Blue" 113.479 100.212 151.237

"Light_Cyan" 232.292 237.325 222.258

"Cyan" 39.255 157.842 200.724

"Light_Green" 222.769 227.829 192.470

"Green" 83.448 156.321 78.440

"Light_Yellow" 246.280 236.952 163.699

"Yellow" 248.129 222.480 52.150

"Light_Red" 234.436 201.450 155.827

"Red" 191.807 67.359 70.052

"Light_Magenta" 242.981 222.436 193.704

"Magenta" 186.805 24.702 90.269

"White" 247.637 245.723 237.539

"Light_Brown" 195.278 184.085 132.714

"Brown" 106.988 89.230 80.456

"Light_Gray" 233.699 231.318 215.430

"Black" 53.318 50.971 50.392

ggc · August 20, 2018, 6:40am

I have seen the new feature in g’mic 2.3.4 Add filter Colors / CLUT from after-before layers *. This filter is able to recover the color transformation that has been applied between a pair of images, as a HaldCLUT. This HaldCLUT can then be applied afterwards to a bunch of other images.

Maybe it could be useful. I’ll need to create e.g. with gimp a syntetic grid of colors, and fill it with with colors taken from the images, then try what happens with this g’mic filter.

Unfortunatly the weather here isn’t that great.

Morgan_Hardwood · August 20, 2018, 9:44am

@ggc using G’MIC’s Colors / CLUT from after-before layers, I think the process would be:

Photograph the Q-13 under whatever light you most-frequently shoot under (D50 daylight and StdA incandescent).
Process the raw in RawTherapee without any color manipulation other than white-balance. Use the white balance picker on a gray patch. Next, make the gray patches match the reference brightness values using curves in the Exposure tool. Remember to use the same working color space as used for the reference values. Save the image as reference.tif
Make the color patches match the reference values, you’ll probably want to use the H=f(H) curve in the L*a*b* tools. Remember to use the same working color space as used for the reference values. Save the image as tweaked.tif. You might also want to save a partial profile with the tools you used to adjust the colors, named something like make_model_light.pp3
Open both images as layers in GIMP and use the CLUT filter in G’MIC to create a HaldCLUT mapping the difference between them. Now you should be able to use that CLUT in RT/GIMP/etc to map the colors.

In the end, you should be able to apply either make_model_light.pp3 or the HaldCLUT to an image to get better colors.

It’s an interesting project, let us know how it goes.

Morgan_Hardwood · August 20, 2018, 11:48am

In fact, you don’t even need to leave RT to create the HaldCLUT.
Instead of step 4, open the HaldCLUT identity image in RT and apply make_model_light.pp3 to it (only the color adjustments, not the white balance adjustments and not the gray patch adjustments). Save the CLUT, done.

ggc · August 20, 2018, 11:51am

I’ve been able to take pictures with the sun. Trying now. A big thank you

ggc · August 20, 2018, 11:52am

Forgot to copy and paste grayscale values.

ggc · August 20, 2018, 11:57am

Now i need to convert 0-100 Raw Therappe luminance values to 0-255 Adobe Rgb values. Should i choose Adobe RGB as a working space AND as the output color space?

ggc · August 20, 2018, 12:05pm

Here are translated values, from 0-255 to 0-100, hope they are ok

|243|95,29412|
|217|85,09804|
|194|76,07843|
|178|69,80392|
|157|61,56863|
|142|55,68627|
|128|50,19608|
|115|45,09804|
|104|40,78431|
|93|36,47059|
|84|32,94118|
|75|29,41176|
|68|26,66667|
|61|23,92157|
|55|21,56863|
|50|19,60784|
|45|17,64706|
|41|16,07843|
|37|14,5098|
|34|13,33333|

Morgan_Hardwood · August 20, 2018, 12:12pm

You don’t need to convert [0-255] to [%]. Just click on the values in the Navigator panel to change the notation to [0-255].
http://rawpedia.rawtherapee.com/The_Image_Editor_Tab#Navigator

Edit - but yes, you would need to convert them if you want to use the “edit node in/out values” button.

Morgan_Hardwood · August 20, 2018, 12:25pm

I just found this, won’t have time to read it until this evening but seems worth sharing right away:

ggc · August 20, 2018, 12:30pm

I came across that rawdigger page yesterday, but is a bit too complex for me…

Now the problem is that B gray isn’t that different from 17 gray, so i loose 1 point (raw therapee doesn’t create another point, if it’s too near too another in terms of value). I bet i can skip one point without troubles.

ggc · August 20, 2018, 12:36pm

The curve

ggc · August 20, 2018, 12:47pm

For now i’m lost with color correction… i don’t understand how to use h=f(h) in lab.

Can i use rgb curves? (i have to click 3 times, for r g and b, with maybe alignment and little differences).

ggc · August 20, 2018, 12:58pm

Meanwhile, 0-100 values for colors.

|Name|R|G|B||R|G|B|
|---|---|---|---|---|---|---|---|
|||||||||
|Light_Blue|243473|240670|229074||95,48|94,38|89,833|
|Blue|113479|100212|151237||44,502|39,299|59,309|
|Light_Cyan|232292|237325|222258||91,095|93,069|87,16|
|Cyan|39255|157842|200724||15,394|61,899|78,715|
|Light_Green|222769|227829|192470||87,36|89,345|75,478|
|Green|83448|156321|78440||32,725|61,302|30,761|
|Light_Yellow|246280|236952|163699||96,58|92,922|64,196|
|Yellow|248129|222480|52150||97,305|87,247|20,451|
|Light_Red|234436|201450|155827||91,936|79|61,109|
|Red|191807|67359|70052||75,218|26,415|27,471|
|Light_Magenta|242981|222436|193704||95,287|87,23|75,962|
|Magenta|186805|24702|90269||73,257|9,687|35,4|
|White|247637|245723|237539||97,113|96,362|93,153|
|Light_Brown|195278|184085|132714||76,58|72,19|52,045|
|Brown|106988|89230|80456||41,956|34,992|31,551|
|Light_Gray|233699|231318|215430||91,647|90,713|84,482|
|Black|53318|50971|50392||20,909|19,989|19,762|

ggc · August 20, 2018, 1:02pm

Using rgb curves seems to create too strong discontinuitess, already with the first 4 boxes…

age · August 20, 2018, 1:53pm

Very informative!
From what I understand it says that Adobe apply some hidden exposure compensation at different iso and it shows how to neutralize that with the Kodak grey card, the most important patch is M because it is the middle gray 18% in linear gamma( 45 in 8 bit, 11654 in 16 bit, 116 in 8 bit and 2.2 gamma, and so on)

Morgan_Hardwood · August 20, 2018, 2:27pm

Yes, as do most raw converters. They apply a baseline exposure value and use a non-linear tone-curve.

To see the “unmodified” raw image, just open a raw file in RawTherapee and apply the “Neutral” profile.

Morgan_Hardwood · August 20, 2018, 2:39pm

I recorded this screencast to show how to use the HH curve (hue according to hue) to adjust the colors in the image to match some reference values:

ggc · August 20, 2018, 3:11pm

Thank you @Morgan_Hardwood .

I’ve tried, but seems to me it’s impossible to reach the suggested values…

E.g. in the upper left box, i should reach 243 240 229