[sane-devel] SANE Color Management

[Olaf Meeuwissen]

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.mellinger at 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
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