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#!/usr/bin/ruby
# daltonize an image with ruby-vips
# based on
# http://scien.stanford.edu/pages/labsite/2005/psych221/projects/05/ofidaner/colorblindness_project.htm
# see
# http://libvips.blogspot.co.uk/2013/05/daltonize-in-ruby-vips-carrierwave-and.html
# for a discussion of this code
require "vips"
# Vips.set_debug true
# matrices to convert D65 XYZ to and from bradford cone space
xyz_to_brad = [
[0.8951, 0.2664, -0.1614],
[-0.7502, 1.7135, 0.0367],
[0.0389, -0.0685, 1.0296]
]
brad_to_xyz = [
[0.987, -0.147, 0.16],
[0.432, 0.5184, 0.0493],
[-0.0085, 0.04, 0.968]
]
im = Vips::Image.new_from_file ARGV[0]
# remove any alpha channel before processing
alpha = nil
if im.bands == 4
alpha = im[3]
im = im.extract_band 0, n: 3
end
begin
# import to XYZ with lcms
# if there's no profile there, we'll fall back to the thing below
xyz = im.icc_import embedded: true, pcs: :xyz
rescue Vips::Error
# nope .. use the built-in converter instead
xyz = im.colourspace :xyz
end
brad = xyz.recomb xyz_to_brad
# through the Deuteranope matrix
# we need rows to sum to 1 in Bradford space --- the matrix in the original
# Python code sums to 1.742
deut = brad.recomb [
[1, 0, 0],
[0.7, 0, 0.3],
[0, 0, 1]
]
xyz = deut.recomb brad_to_xyz
# .. and back to sRGB
rgb = xyz.colourspace :srgb
# so this is the colour error
err = im - rgb
# add the error back to other channels to make a compensated image
im += err.recomb([[0, 0, 0],
[0.7, 1, 0],
[0.7, 0, 1]])
# reattach any alpha we saved above
if alpha
im = im.bandjoin(alpha)
end
im.write_to_file ARGV[1]
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