Colour analysis

This post is not travel related.
Does anyone here know of a way to norm digital images, so you can analyse the change of colour from one image to another in terms of RGB or Lab readings? I'm trying to monitor colour changes in scar tissue over time. When taking the images we used a Kodak Colour Control Patch to attempt to have a baseline. I tried adjusting the images (using Adobe Photoshop CS2) so white on the Kodak Patch reads RGB 255/255/255 (Lab 100/0/0), but the other normative colours are still out after this (and to the human eye the image then looks overexposed). I don't know enough about colour analysis to work out why this happens and if there is any way to norm images to a standard. Any ideas?

As you've discovered, just using the white point is insufficient.

Depending on the exact exposure of the image that may result in shifts in the black-point and or histogram expansion/compression; which means even adjusting for the black-point as well may well result in all the midtones being out of whack still.

Unfortunately you'll have to use all the target patches if you want accurate results.

I've never tried to do this, but it looks like the Silverfast AI scanning software may have the option to automate colour correction from a Kodak IT8 target: Silverfast. I think it might be worth dropping them an email about it at least.

There are ways to do it manually, but they look spectacularly tedious. For more on those, start here

If you are shooting in RAW and have access to a Gretag colour target then you can try this.

It works by using the calibration tab in Adobe Camera Raw which you adjust for each lighting condition you are photographing under. Basically speaking, since you are photographing a specific thing under a different set of lighting conditions, you shoot the colour target first, calibrate in ACR for that lighting and then use that calibration to batch alter all teh photos taken at that time. Each time the you shoot under a different light you calibrate again.

Instead of using the Kodak "Color Control Patch" use the Kodak "Grey Scale" instead (i.e. you probably have this because they come together when you buy them).

In Photoshop use the Levels command and click the white eyedropper on the "A" patch, the black eyedropper on the "B" patch and the mid grey eyedropper on the "M" patch.

You only need the black, white and mid-grey patches. Not all the others or any coloured patches.
However the coloured patches give you a nice reference that everything is working correctly.

For this application, it's better to use a chart that has a black velvet patch or a light trap box instead of a printed one.
These are common for motion picture use to get a standard for telecine transfer.

OP, pls check your PM.