GIMP 2.9 color picker values


(Gabriele ) #1

Hi,
I’m a little confused about color picker.
I understand ( I think)

Pixel : pixel value in RAM
RGB % : ?? about what
RGB (0…255) : ?? about what

i.e an image in ProPhoto I have RGB(0…255) R=255;G=0;B=0 RGB% R=115.9%;g=0.1%;B=0.0% Pixel R=216;G=85;B=32

What is the correlation?

and more… in the color box on the right I have e little magenta triangle … what does it mean??

I think I wrong something because I have wrong colors


(Elle Stone) #2

Hi @dafrasaga,

I was planning to attach a screenshot to help explain what the various items are, but alas I triggered a crash. In the meantime:

  • “Pixel” shows the floating point channel values in the image’s actual assigned RGB color space, in this case ProPhotoRGB.

  • For default GIMP, the magenta areas mean “these colors are out of gamut with respect to GIMP’s built-in sRGB color space”.

When I have a chance to redo the screenshot, I’ll explain the other items. In the meantime, which version of GIMP are you using? The reason I ask is that what the color picker shows will depend on whether you are using my patched version of GIMP, or default GIMP. And if you are using default GIMP, what the color picker will show depends on what version of default GIMP, as the color picker dialog has changed recently.

Also which ProPhotoRGB profile are you using? When I redo the screenshot, I’ll try to use the same ProPhotoRGB profile.


(Elle Stone) #3

The % values are channel values for GIMP’s internal sRGB color space, on a scale from 0 to 100. The values from 0 to 255 are channel values for GIMP’s internal sRGB color space on a scale from 0 to 255. So these values don’t match the pixel values.


(Gabriele ) #4

Hi Elle,
I use GIMP from git
image

but when you say “internal sRGB color space” what do you refer ?
built in sRGB or the “Working” profile??

The test image with embedded profile was


(Gabriele ) #5

I created with Argyll a profile for my printer…EPSON_MPHW2.icc (1.5 MB)

Then I created a proof image with timage 16 bit
Imported in GIMP and converted from default sRGB ( it was without profile) to my profile EPSON_MPHW2.icc for printing.
The “Pixel” values are changed and if I feed they into xicclu -ff I have % and 0-255 values as before. These “Pixel” values should be the RGB value to send to printer for correct printing, right?

But the print come yellowish…image
instead image

Display image with sRGB imported (color picker into gray surround)

Display image converted to EPSON_MPHW2.icc (color picker into gray surround)

If I feed the values converted to xicclu

gabriele@darkstar:~/profilazione/EPSON/Matte Paper Heavy Weight/Profilo/profilo2$ xicclu -ff -s65536 EPSON_MPHW2.icc
31675 28541 22364
31675.000000 28541.000000 22364.000000 [RGB] -> Lut -> 56.696596 -0.039016 0.123453 [Lab]

I have a neutral tone of 56.696596 -0.039016 0.123453 but not in print :confused:

What can I do for a correct print???
I miss something, I know…

Cheers


(Elle Stone) #6

Hi @dafrasaga - I downloaded your printer profile and plan to see what I can figure out. It might take a day or two. I’m looking into how GIMP handles ProPhotoRGB images.

Can you provide your actual ProPhotoRGB profile?


(Gabriele ) #7

Hi Elle,
thanks for your time…
However I have the same behaving with this test image with no profile and therefore GIMP assigns sRGB built in …
The ProPhoto profile I extracted with GIMP from image and is ProPhoto RGB.icc (940 Bytes)

Because in GIMP printing there isn’t the choose for printer profile I do:

  • Open image in GIMP
  • Convert it to destination printer profile
  • Print it

Is it right??

Cheers
A presto :slightly_smiling_face:


(Gabriele ) #8

:neutral_face:
I have a doubt…
because I created a calibration file with printcal… and applied it to printtarg with the -K option which modified the patches…

Do I have to apply the calibration file to the ICC profile too??:thinking:

Now I’m not at PC +printer … but what do you think about??


(Elle Stone) #9

Hi @dafrasaga - I don’t have a printer or any practical experience with making printer profiles or with using GIMP or any other software to make prints. So I’m just not qualified to answer questions about printing.

You might try posting to the ArgyllCMS mailing list for information about making/using/modifying/etc a printer profile.

Also, I think there are other softwares that people do use for printing - maybe darktable? Have you tried printing using software other than GIMP?


(Gabriele ) #10

Hi,
I used Photoprint which is a dead project I am no able to compile on the new OS…
I’ll try DT…
The statement I said before is come when today I found a thread on Argyll mail list
This evening I’ll try and I’ll make you know something…

Thanks for now
Gabriele


(Elle Stone) #11

Hi Gabriele,

I did try soft proofing your timage image (assigning GIMP’s built-in sRGB profile) to your printer profile, and then doing the conversion using GIMP. I also did the conversion using cctiff from the command line, using this command:

$ cctiff -c -p -k -ir sRGB-elle-V2-srgbtrc.icc -ip EPSON_MPHW2.icc -e EPSON_MPHW2.icc default.tif default-to-printer.tif
Worst error = 1324 bits, average error = 37.033435 bits
Worst error = 2.020294%, average error = 0.056509%

Both conversions produced visually the same result, which also matched the results of soft proofing using GIMP.

I didn’t see such strong colors in the converted or soft proofed image as your print screenshot shows, neither with perceptual intent nor with relative colorimetric and not using black point compensation. But you already know that :slight_smile:

So maybe the problem is that the profile really doesn’t describe the printer-paper combination? Or maybe the problem is in the software that’s being used to make the print? Or in the settings/drivers/etc that you are specifying? In other words I have nothing helpful to suggest. All I can do is confirm that it doesn’t look like the print should be so yellow or so saturated in the color areas.


#12

Ciao Gabriele!

Two questions:

  1. Did you use the same paper and the same ink when creating the profile as when you made your test print?

  2. Do you have Darktable installed?

Cordiali saluti,
Claes a Lund, Svezia


(Gabriele ) #13

Hi Elle,Claes
the culprit was me :pensive::sweat:
I didn’t apply the calibration curve to icc profile as Argyll creator says…

Now the print is almost perfect, it lacks of deep black but I think is because I did reduce the density because with the default driver setting (Gutenprint) the patches were bleeding each other…

I’ll investigate…
However I’m very happy for the result which I thought wouldn’t be done possible for my little knowledge in color management…
I must say this “not working” let me discover in more deep the color management and ICC profiles structure.
I think GIMP would have to make choose the printer profile into printing process but for now it is good as it is.
I hope to improve more in the future :slightly_smiling_face:

Cheers, Ciao
Gabriele


Yellowish print - SOLVED -
#14

Good morning!

Good that you have solved your problem.
The reason why I asked if you have darktable installed was
that dt has a print module, in which you can select a printing profile.
See more here: https://www.darktable.org/2015/01/print-module/

Have fun!
Claes a Lund, Svezia


(Gabriele ) #15

Thanks for the informations Claes.

Have fun!

Gabriele