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Fix thumbnail color extraction (#14464)
* Fix contrast calculation for thumbnail color extraction Luminance calculation was using 0-255 RGB values instead of 0-1 sRGB values, leading to incorrectly-computed contrast values. Since we use ColorDiff already, just use its XYZ colorspace conversion code to get the value. * Require at least 3:1 contrast for both accent and foreground colors * Lower required contrast for the accent color
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@ -5,6 +5,7 @@ require 'mime/types/columnar'
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module Paperclip
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module Paperclip
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class ColorExtractor < Paperclip::Processor
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class ColorExtractor < Paperclip::Processor
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MIN_CONTRAST = 3.0
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MIN_CONTRAST = 3.0
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ACCENT_MIN_CONTRAST = 2.0
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FREQUENCY_THRESHOLD = 0.01
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FREQUENCY_THRESHOLD = 0.01
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def make
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def make
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@ -26,8 +27,9 @@ module Paperclip
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foreground_palette.each do |color|
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foreground_palette.each do |color|
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distance = ColorDiff.between(background_color, color)
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distance = ColorDiff.between(background_color, color)
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contrast = w3c_contrast(background_color, color)
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if distance > max_distance
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if distance > max_distance && contrast >= ACCENT_MIN_CONTRAST
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max_distance = distance
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max_distance = distance
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max_distance_color = color
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max_distance_color = color
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end
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end
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@ -77,8 +79,8 @@ module Paperclip
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private
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private
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def w3c_contrast(color1, color2)
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def w3c_contrast(color1, color2)
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luminance1 = (0.2126 * color1.r + 0.7152 * color1.g + 0.0722 * color1.b) + 0.05
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luminance1 = color1.to_xyz.y * 0.01 + 0.05
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luminance2 = (0.2126 * color2.r + 0.7152 * color2.g + 0.0722 * color2.b) + 0.05
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luminance2 = color2.to_xyz.y * 0.01 + 0.05
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if luminance1 > luminance2
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if luminance1 > luminance2
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luminance1 / luminance2
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luminance1 / luminance2
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