Re: [Gimp-print-devel] Question about internal color conversion and gamma flow

[Solomon P. <pi...@sh...>]

On Wed, Sep 11, 2019 at 10:47:19PM -0400, Solomon Peachy wrote:
>  1 foreach ink_channels:
>  2  stp_channel_add(channel)  # CMY in this case
>  3 stp_color_init(256)        # ie 8bpp
>  4 stp_set_float_parameter("AppGammaScale", 1.0)
>
> (4) and (9-10) are interesting, leading to my first questions:
> 
>  * Does these calls have any effect, given that they both occur after 
>    stp_color_init() and/or the stp_color_get_row() calls?

Moving AppGammaScale above stp_color_init() changed the LUT channel 
curves to be completely linear.  This is probably the smoking gun.

Looks like this bass-ackwards order was my doing, in commit bdf7edde3, 
in April of 2018 -- I incorrectly copied the changes made to the color 
laser driver.

I want to correct this, but it's going to affect the output of every 
dyesub model we support.  

If the hanful of test prints I've made so fare are any indication, it's 
definitely for the better (color test charts are visibly improved) but 
it's still a non-trivial change in output.

 - Solomon
-- 
Solomon Peachy			       pizza at shaftnet dot org
High Springs, FL                          ^^ (email/xmpp) ^^
Quidquid latine dictum sit, altum videtur.