White balance tool in Photoshop

Hello all,

here I am with a rather complicated question:

do you know how white balance tool (eyedropper) in Adobe Photoshop works?

Thanks, MM.

Answer 1

[Image Analyst]

I have a crude white balancing program that works simply by linearly scaling each color channel independently. Photoshop probably does something more sophisticated but for what it's worth, I've attached it.

[Image Analyst]

After playing around with Photoshop, it looks like you define a black point and a white point and it will set those to 0 and 255 respectively for each color channel. Then when you set the gray point, it uses a standard gamma curve formula to adjust the gray levels for each color channel such that the pixel you defined as gray will have red = green = blue = gray level on the line between the black point and white point. It should not be too hard to program that up in MATLAB. Give it a shot.

[Image Analyst]

By the way, if anyone wants code to launch Photoshop from MATLAB, see the attached m-file, below in blue.

Answer 2

[Laurent]

Maybe it is better to ask your question in a Photoshop related forum. Anyway I don't think Photoshop will tell you the exact algorithm that they use, but I found some sites that explain what it does, for example this one: http://www.scantips.com/lights/flashbasics1f.html

Answer 3

[Matija]

Hello all,

Laurent, yes, I was interested how Adobe does white balancing and I posted the same question on Photoshop forum...but without any useful reply.

Image analyst, yes, I am already using your version of white balancing algorithm :-)

Thank you!