[Tuxpaint-devel] Saturation tools

[Bill K. <nb...@so...>]

Other than the "Tint" tool, when used with a saturation-less color
selection (like black or white), there was no way to desaturate parts
of a picture in Tux Paint.  And that was all-or-nothing -- you could
'tint' parts of your picture into greyscale, but not do anything more
subtle.

So I added a pair of new tools, "Desaturate" and "Saturate", to go
along with the "Darken" and "Lighten" which affect the <getting into
dangerous waters, terminology-wise!> value or luminosity of the pixels.

In the end, I simply convert the RGB values into HSV, and then adjust
the S amount.  Right now I'm doing S = S * 3/4 for reduction, and
S = S * 4/3 for increase.  I could probably do better.

Here's an example, using the rocky beach template, and applying
"Desaturate" (via brush) a number of times on the left, and "Saturate"
on the right:

  https://tuxpaint.org/latest/sshots/tuxpaint-0.9.29-sat-desat.png

At one point, I went on a wild goose chase looking into whether using
different color spaces might produce even better results (i.e., converting
the RGB to XYZ then to LUV or L*a*b*) but then I remembered this is a
program meant for young kids, and I don't need to worry _too_ much about
perfection.


Then I decided to add two other saturation-related tools that might be
useful (if people think they are too strange or confusing to use, I
could be convinced to shelve them).  I called them "Keep Color" and
"Remove Color".  They totally desaturate parts of the image (turn it
completely greyscale -- the S in HSV becomes 0.0) based on the currently
selected color.

So for example say you have a colorful drawing with some red balloons.
They idea was to make it easy to turn the entire picture _except the
balloons_ into greyscale.

In this picture, I used "Reflection" to get a mirror-image of the
tree-and-sky photo template (so it's easy to see what's happening),
and the used "Remove Color" to remove the colors from blue sky at
the bottom, and [most of] the green tree leaves at the top.

  https://tuxpaint.org/latest/sshots/tuxpaint-0.9.29-keep-remove-colors.png

Note - All these tools need their own icons and sound effects.


I really need to stop adding new features, so we can get a release
out soon.  Our followers on Twitter are clamouring for some of these
new effects. ;-D

-- 
-bill!
Sent from my computer