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Description:

redmask 1.1.0

redmask
A simple tool to create palette swap mask
How palette swap mask works
A palette swap mask is an image used to map a palette using a gradient scale.
The tool will generate a red gradient image because green and blue values are useless for the mask.
Full explanation about palette mask: https://www.youtube.com/watch?v=u4Iz5AJa31Q

Using the generated mask
The mask can be used in a palette swap shader.
Example shader in Godot Engine 2.1.x:
// fragment
uniform texture palette;
uniform float colors;
uniform float color_step;

if (COLOR.a != 0){
COLOR = tex(palette, vec2((COLOR.r*255.0)/(colors-0.001) / color_step, 0));
}
// '0.001' part is a workaround to fix float precision issues.

Basic usage
# redmask = python redmask.py

redmask <input> <palette>
# generate a mask using default color step (1)

redmask <input> <palette> -s 10
# generate a mask using 10 as color step

redmask <generated-mask> <palette> -a
# apply a palette (paint the mask) using default color step (1)

You can test using images in the tests directory.
Also, you can view usage info using the -h/--help command.

Example art made by Yomieda.