How to use white balance card with specific RGB values in gimp

[Liese]

Hello,
I have a white balance card that has specific RGB values, 219, 220, 220. I am trying to adjust my photo in gimp so that the area of the picture with that white balance card matches its actual numbers and thereby correcting all colors in the photo. I appreciate any help I can get on this! Thank you.

[Krikor]

(11-19-2021, 12:12 AM)Liese Wrote: Hello,
I have a white balance card that has specific RGB values, 219, 220, 220. I am trying to adjust my photo in gimp so that the area of the picture with that white balance card matches its actual numbers and thereby correcting all colors in the photo. I appreciate any help I can get on this! Thank you.

Good question.

I did a quick search and found almost nothing on the subject related to Gimp (most use PS or Lightroom).

A post that might shed some light on this question:
https://www.gimp-forum.net/Thread-Noob-q...20question% 20about%20white%20balance%20calibration,-New%20Reply

[sallyanne]

ok I have looked at this thread for a couple days now. I have an idea since no one else has said what you 'may' do - I could be wrong.
Have you tried adding an extra area to your photo that you can crop out after?
Fill it with the same white as your card - You can make that colour in Gimp by just clicking on your foreground colour. That will open the colour dialogue where you can change the RGB values.
When you have the extra colour with your photo try color > levels and click on the white point dropper and pick your white in the photo.

May be a long way to do it. Maybe one of our script writers could shorten the process for you if you have a lot of photos to do.

[rich2005]

That R=219, G=220, B=220 is a grey point.

To match that, use a sample point see: https://docs.gimp.org/2.10/en/gimp-sampl...ialog.html

Split a example for before / after   The color match card shows R=165 G=169 B=196

   

Adjust the colour curves. There are separate curves for each of RGB  Get the value R=219, G=220, B=220

   

You can save that curve and use it with other photos taken at the same session.
Of course, it can be a lot more complicated than this to match a complete range of colours.

[Liese]

(11-20-2021, 09:25 AM)rich2005 Wrote: That R=219, G=220, B=220 is a grey point.

To match that, use a sample point see: https://docs.gimp.org/2.10/en/gimp-sampl...ialog.html

Split a example for before / after   The color match card shows R=165 G=169 B=196



Adjust the colour curves. There are separate curves for each of RGB  Get the value R=219, G=220, B=220



You can save that curve and use it with other photos taken at the same session.
Of course, it can be a lot more complicated than this to match a complete range of colours.

Thank you so much for this helpful answer, I would have never figured it out on my own!