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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
This commit is contained in:
ThibG 2020-08-02 18:47:44 +02:00 committed by GitHub
parent 635b6a0f1a
commit 0ebc8d8626
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1 changed files with 5 additions and 3 deletions
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8
lib/paperclip/color_extractor.rb
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@ -5,6 +5,7 @@ require 'mime/types/columnar'
module Paperclip module Paperclip
class ColorExtractor < Paperclip::Processor class ColorExtractor < Paperclip::Processor
MIN_CONTRAST = 3.0 MIN_CONTRAST = 3.0
ACCENT_MIN_CONTRAST = 2.0
FREQUENCY_THRESHOLD = 0.01 FREQUENCY_THRESHOLD = 0.01
def make def make
@ -26,8 +27,9 @@ module Paperclip
foreground_palette.each do |color| foreground_palette.each do |color|
distance = ColorDiff.between(background_color, color) distance = ColorDiff.between(background_color, color)
contrast = w3c_contrast(background_color, color)
if distance > max_distance if distance > max_distance && contrast >= ACCENT_MIN_CONTRAST
max_distance = distance max_distance = distance
max_distance_color = color max_distance_color = color
end end
@ -77,8 +79,8 @@ module Paperclip
private private
def w3c_contrast(color1, color2) def w3c_contrast(color1, color2)
luminance1 = (0.2126 * color1.r + 0.7152 * color1.g + 0.0722 * color1.b) + 0.05 luminance1 = color1.to_xyz.y * 0.01 + 0.05
luminance2 = (0.2126 * color2.r + 0.7152 * color2.g + 0.0722 * color2.b) + 0.05 luminance2 = color2.to_xyz.y * 0.01 + 0.05
if luminance1 > luminance2 if luminance1 > luminance2
luminance1 / luminance2 luminance1 / luminance2