jonathan wrote: > the only 'quick'n'dirty' method that i see in this case would need > a light point and a dark point present in all images. > The light point would be mapped then to 255 of all values > the dark point to 0 of all values, and then the intermediate > values recalculated/spread with that range. > This would only work if you do have a 'black' spot and a 'white' > spot. And if one of these has uneven values (ie black = 00, 1A, 08 > for RGB) then this could create a color cast over the rest of the image. Great minds think alike! On the way to work I was thinking that subtracting the adjacent background was inappropriate. The background color may vary depending on the thickness of the mounting media (specimens are embedded in a _clear_ plastic). However, the specimen displaces the plastic, so the level of color addition attributable to the relatively thin layers of media over- and under-lying the specimen are much less than the thicker adjacent layer, maybe negligible. So, you're right! I should sample the light color from areas that are consistently present with the specimen (glass slide, coverslip, and microscope optics). The blacks have been so close to 0,0,0 black that it is seems neglible in a linear equation. I know it's not linear. Are there books on imaging algorythms? Any titles? NOTE: Now that this introduction to the problem is out of the way, this topic should become much more FB oriented. Thanks for your patience. ------------------ Pierre A. Zippi ------------------ Home email: paz@... Home web: http://web2.airmail.net/paz