On mardi 28 mars 2017 14:49:09 CEST Per Östlund wrote: > Hi, > > I've digitized my father's collection of old slides with the camera + > macro lens + light table method. Most of the images look fine, but some > images with certain blue hues are giving me a headache. I'm guessing the > issue is that the light table I built used LEDs with a poor color > spectrum for the task, causing the blue channel to blow out. > > As soon as I touch e.g. the levels module I get the usual issue that > very saturated blues turn black. Using the gamut clipping option in the > input color profile module fixes that particular issue, but doesn't do > anything for the colors otherwise. > > The best solution I've managed to come up with so far has been to set > the input color profile to "linear Rec709 RGB" which heavily desaturates > the image, and then increasing the saturation a lot with the color > correction module. Hardly an optimal solution, but with some tweaking I > can usually get the colors to look approximately the same except that > the blues don't clip anymore. > > This method can require quite a lot of tweaking to look good though, so > my question is if someone knows of a better way to handle this issue > (besides reshooting with a better light source). Here's an example > RAW-file (don't mind the blur, that's from the original slide): > https://www.dropbox.com/s/6mshjycwm4n10xa/img_014.ARW?dl=0
First the good news: as far as I can see you have no blown channels in the raw file, even the blues stay within range of the sensor. The bad news is that with the default settings, a large part of the image gives 'out-of-gamut' warnings. And to be honest, the image looks over- saturated. So what I tried was: - set base curve to 'leica' (less aggressive than the Sony default, esp. in the highlights). - set gamut clipping to 'adobeRGB' (or sRGB). then I used two copies of 'contrast brightness saturation', - the first for a global saturation correction of -0.2, - the second was at saturation -0.35, with a parametric mask limiting the effect to the blue colors: 'b' channel from -128/-128 (full left) to -29/-3. If all slides are similar, you could set this up for one slide and the create a style to apply those settings as a base to others. But would it be possible that the original slides have faded a bit over time, and especially the red dye? Good luck, Remco ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
