Hi, Just to answer myself my previous post to Pascal Obry, about BW tri-tone Black & White printing from Darktable:
>>> I was hoping to do the same with darktable's print module ... but I have >>> not found the way to apply my custom curve for the blue channel. Tone >>> curves in darktable work in Lab space, and I don't know how to create >>> such a curve in Lab...(end of the off-topic part) >> >> And do you have a way to do that from darkroom? If so just create a >> style with the correction and apply this style from the print module. > > No, I have not found a suitable way :'-( I need to export the image > from Darktable and use GIMP to apply the blue channel curve + ligtnness > correction curve, and send the result to the printer from GIMP. > >> But I'm not sure we can adjust the blue channel from the curve. There >> was a discussion on the mailing-list about adding support for this in >> the tone curve. Not yet there, but there is hope :) > > Ok, I will stay tuned, following the mail list, to see if this happens > some day ;-) > I have found now a way to to this in Darktable, and it's quite easy: using several instances for Lab tone curves with properly adjusted parametric masks. So no need for a RGB curve to achieve this. The recent blog entry "Luminosity Masks in Darktable" has shown me the path. This is how a 21 step grayscale shows after aplying 2 tone curve instances, the first one pulling down the "b" channel, and selecting midtones in the parametric mask, and the second one (shown on the left) pushing up the same "b" channel and selecting higlights in the parametric mask: https://dl.dropboxusercontent.com/u/44995840/DT_BW_curves.png When printing this scale, the black cartridge will be used for deep shadows, the magenta and cyan cartridges (that I fill with medium gray ink) for the midtones, and the yellow cartridge (filled with light gray ink) for the highligts. The final adjustement will be reading the printed strip with Argyll's "spotread" utility and the Colormunky, and use the resulting lightness values to adjust another instance of tone curve to correct the relative density of the steps in the grayscale. Once done, it should be easy to apply as a style in the print module when printing black & white pictures. Josep V. Moragues ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ darktable-devel mailing list darktable-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/darktable-devel
