The method consist in taking a RAW image
during a sunny day
of a white sheet of paper
or a white wall, or everithing else being purely white. You need not to
saturate the image. A standard objective can be used. Focusing is not
Then open this image in Maxim. Please note that for a correct result,
you need to dark or bias subtract the image! So take also this
calibration frame and subtract from the opened image, before proceeding.
Then Color Convert with all the scaling
and background values resetted, like in the image below. That is, RGB
scaling all set to 100% and RGB background levels all to zero.
Then open the information window and select the Area mode, and draw a
rectangle in an area known to be white. The whole image do not need to
be completely white like in the present example. Please note the
average values for the R, G and B channels, that are not similar due to
the color unbalance.
Do this simple operations: use the R channel average intensity as a
reference value, here the value is R_average=731.9. The scaling
valur for R will be 100%. Compute the green and blue color balance
factors with this formulas:
G_factor = R_average / G_average = 731.9 / 835.2 = 0.876 ~= 88%
B_factor = R_average / B_average = 731.9 / 670.9 = 1.091 ~= 109%
If you are lazy, you can use this Excel file that will compute the values for you. XLS file.
To verify that the found values are good, re-open the white image and
color convert with the values. If all is ok, the image should be white
and the average values should be similar.