From: Frank v. M. <fr...@fr...> - 2009-11-28 16:00:36
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On Sat, Nov 28, 2009 at 04:14:25PM +0100, Jos De Laender wrote: > Frank van Maarseveen schreef: > > On Sat, Nov 28, 2009 at 01:41:04PM +0100, Jos De Laender wrote: [...] > > The human perception comes into play because the algorithm should > > do something which ultimately pleases the eye (or more precise: the > > human brain). For example, the implementation contains a sqrt() which > > I think is an approximation of a gamma compensation > My understanding is that the sqrt is introduced to denoise shadows and > highlights +/- equally. Reading carefully, both explanations could be correct at the same time :-) > The sqrt is for instance not part of the derived gimp plugin. It's not > essential. That's because gamma is usually already applied to the image. [...] > > I've had a look at the hat transform function: two out of three loops are > > there for handling pixels close to the edge of the image. The function > > looks ok to me from a logical/programmer point of view. > No offence, but how can you say without knowing the underlying algorithm ? hat_transform() considers pixels to the "left" and "right". How it handles this close to the edge when either left or right side is not available must at least be symmetrical. It is a corner case which might not even be described in the original math. The middle loop is the real algorithm. The 'st' (step) multiplier is not really part of the algorithm but how to do code it once for >1 dimension. -- Frank |