Hi, m. allan noah writes:
> I believe that most backends are doing no transformation at all. Since > most backends are reverse engineered, I think we consider ourselves > lucky just to get image data out of the scanner. If the blacks look > black, and the whites look white, we ship it :) Some of us also check the RGBs :-) > On Sun, Jul 5, 2020 at 10:38 AM Jürgen Mellinger > <juergen.mellin...@t-online.de> wrote: >> >> Hi, >> >> many SANE backends provide gamma correction options, but I could not >> find any information about the default color space in which scan data >> are being sent to sane_read(). I mean, if there is no custom gamma >> table used, then a backend should be able to use its knowledge about >> a scanner’s CCD’s gamma value to transform it into a pre-defined >> color space, such as sRGB, or linear gamma. If there is no such >> pre-defined color space, then each and every user will have to >> determine the correct gamma for their each and every scanner, and >> perform custom gamma correction just to obtain a reasonable image. >> >> From this I suspect that SANE backends indeed transform scanner data >> into a standard color space. My experience with the genesys backend >> suggests that it’s linear gamma. But I cannot find any documentation >> on this issue. It's backend specific and likely even model specific. I vaguely recall the epson and epson2 backends using a gamma of 2.2 by default. >> Could someone point me to more information on this topic? The best I can think of is the "Image Data Format" section in the SANE Standard at https://sane-project.gitlab.io/standard/environment.html#image-data-format but that doesn't say anything about standard color spaces. Hope this helps, -- Olaf Meeuwissen, LPIC-2 FSF Associate Member since 2004-01-27 GnuPG key: F84A2DD9/B3C0 2F47 EA19 64F4 9F13 F43E B8A4 A88A F84A 2DD9 Support Free Software https://my.fsf.org/donate Join the Free Software Foundation https://my.fsf.org/join