On Mon, 16 Jul 2001, Karsten Festag wrote: > Hi Oliver, > O.k., I didn't thought enough what happens to the data if one applies a > function to it... I think I understood it now. But: even if I reset the > color corrections directly before the scan, the histogram has its > spikes+holes. But there is no visible difference between an image > scanned by xscanimage and xsane, both with linear transfer function. So > I won't complain. > > Regards > > Karsten > > > Oliver Rauch wrote: > > > > when you set color corrections to default value: > > gamma=1.0, brightness=0, contrast=0 before you do > > the scan/preview scan the histogram should not > > have any spikes/holes. > > > > When you use other color correction values with xsane > > or define a custom gamma table with xscanimage > > you will get the spikes/holes. > > >
I can confirm Karsten's observation: the spikes and holes _do_ exist when scanning with Xsane and do not when using scanimage or xscanimage, when everything is reset at the default values (=no frontend correction of scanned data). And even if visually the images are very similar, I consider this a bug. The eyes are simply not able to discern some missing colour tonalities, but the histogram should be smooth. E.g. for densitometric work, a histogram with holes and spikes is barely useable (yes, a modern scanner, although not as good as a real densitometer, can be used to such purposes). Levente
