On samedi 9 février 2019 08:02:51 CET Luca Benassi wrote: > Hi all! > I've searched the archive but found nothing so ... does anyone knows how to > *stretch* hystograms levels in a way similar to photoshop? > I'm trying to follow this workflow: > http://astronomollylog.blogspot.com/2018/06/image-processing-method-20.html > "post-processing" --> "Stretching" > > In darktable (I'm a newbie) I've tried the "tonal groups"-->"levels" but > I'm not able to achieve something like what's described in the tutorial. > > My goal is to reach a fully open source worflow :) Before we can really answer this, it would be useful to know on what kind of images you are working.
In the link you refer to, the author starts from raw images , pulls them through DeepSkyStacker and then takes the output of DSS to photoshop (as 16 bits/channel). In photoshop (and in darktable) the histogram is based on 8 bits/channel (256 levels). That means that (in the case of 16 bits/channel) for every level in the historgram, there are up to 256 values available. So you can stretch the histogram (e.g. by selecting part of the original range in "levels") without seeing gaps in the histogram. If you start with images with 8 bits/channel, stretching the histogram will cause gaps. Whether internally the program uses float values or not doesn't matter: one integer value maps to one float value for a given image. Remco ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
