Sven Neumann wrote: > Hi, > > On Tue, 2007-11-27 at 22:04 +0100, Stephane Chauveau wrote: > > >> Nice! I never noticed that the grey point picker in the level tool could >> be used to adjust the WB. It is unfortunately limited to the mid-tones. >> > > How is it limited to the mid-tones? > > > Sven > > > The black point picker is of course totally useless for adjusting the white balance. The white point picker can be very useful for white balance but, since it also set the white point, it can only be used you have a true white point in you image. By that, I mean a point that is both neutral-grey and of maximal brightness. This is usually not the case. So was it left is the 'middle-point' picker. This one sets the middle-point of the RED, GREEN & BLUE levels but without affecting the 'right-point' of those levels. In practice that means that the white balance of the current 'white point' is absolutely not affected by that picker. More generally, the more you are the highlights, the less you are affected by the 'middle-picker'. That was I mean by 'limited to the mid-tones' though I should have written 'mid-tones and shadows' since the 'middle-point' picker also affect the shadows (but in practice they are less interesting). If you are not convinced (or just don't understand me) then think about that: you cannot change a true white point (255,255,255) using the middle-point picker. However, after playing a bit with the middle-point picker, I came to the conclusion that the results are usually quite good. This is because, in Gimp, the WB is usually applied on an image that was already adjusted (AWB and exposure in the camera, ...) so the WB coefficients tend to be small (-15% to 25% on each channel), most of the image is already in the mid-tones or shadows and the parts that are in the highlight are often already white (typically the clouds). Not having to care about clipping the highlights is also nice. The situation in a tool like UFraw is quite different: The WB is usually the first transformation applied to the raw data. The WB coefficients can be huge (-50% to +100% on each channel) and are followed by some complex adjustments (ICC profile, exposure, gamma, highlight clipping and recovery, ...). _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
