How to Color-Balance Field Photos for Accurate RGB Analysis in Photoshop

[kianmcdonough]

I’m working in a lab studying how fruit color influences herbivory, and I need accurate RGB values from fruit photos to use as standardized data points. Each photo includes a color checker alongside the fruit specimen, but the photos were taken in the field under varying lighting conditions, causing slight differences in exposure and contrast. Photos are .jpgs

How can I color-balance these photos in Photoshop (or Lightroom, if necessary) to ensure the RGB values of the fruit are as scientifically accurate as possible? Is there a way to set RGB values of colors in the image to true the values on the card? I understand that exposure and contrast can impact these values, so I’m looking for a way to standardize these variables across all the photos.

I know that it would have been ideal to make sure the orginal photos were shot in the same light/contrast environement, but I unfortunetly have no control over that. So looking to make do with what I can in post processing.

Once the colors are corrected, I plan to determine fruit color by selecting a representative area of the fruit using the rectangular marquee tool and applying a blur > average filter.

Could someone provide a detailed, step-by-step explanation for this process? I’m new to this and would really appreciate any guidance.

Note: Examples of the photos are attached for reference.

 

[thebestcpu]

Hi @kianmcdonough
For that color checker please check the following link and in particular the instructional videos: https://dgkcolor.tools/
You need to in particular listen to the second half of the video
That will get you awfully close.
Here is a link to the guide of that color checker: https://dgkcolor.tools/wp-content/u...te-Guide-to-the-DKC-Pro-Color-Chart_Final.pdf
I bet that answers most if not all of your questions.
I am not the expert here yet in that instruction guide it gives you want the Lab color space values should be for each of the colors on the color checker. Its in the guide and here is a copy right here:





The colors correspond to the numbers in the chart below
If you do not have an automated way to match them up, then you can convert the image into Lab color mode (space), put color sampler dots in a variety of locations, and then use the Curves adjustment Layer to use to get the tones and colors to match. Just doing a few of the grayscale colors will get you real close because the a and b values should be zero in the color samplers.

Just using the curves adjustment Layer and sampling four of the ray tones and adjusting the L, a, b channels separately, here was a very rough result:



Hope this gets you started
John Wheeler

 

[ushere]

exactly as john wheeler suggests. however, i would try to make your life easier by suggesting that you try to 'white balance' your camera exposure in the first place, as explained in this (and many other youtube videos):

also, use a plain, evenly lit background - i would suggest white, but this may throw your cameras' exposure off. a light / medium grey might be better.

using a wooden, plastic ruler might also avoid mis exposure from reflections off the steel one.

good luck ;-)