From 0ebc8d8626e3982696d1bb3876ec378a3bce81c9 Mon Sep 17 00:00:00 2001
From: ThibG <thib@sitedethib.com>
Date: Sun, 2 Aug 2020 18:47:44 +0200
Subject: [PATCH] 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
---
lib/paperclip/color_extractor.rb | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/lib/paperclip/color_extractor.rb b/lib/paperclip/color_extractor.rb
index 44fe5ff1d..c8bb771a0 100644
--- a/lib/paperclip/color_extractor.rb
+++ b/lib/paperclip/color_extractor.rb
@@ -5,6 +5,7 @@ require 'mime/types/columnar'
module Paperclip
class ColorExtractor < Paperclip::Processor
MIN_CONTRAST = 3.0
+ ACCENT_MIN_CONTRAST = 2.0
FREQUENCY_THRESHOLD = 0.01
def make
@@ -26,8 +27,9 @@ module Paperclip
foreground_palette.each do |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_color = color
end
@@ -77,8 +79,8 @@ module Paperclip
private
def w3c_contrast(color1, color2)
- luminance1 = (0.2126 * color1.r + 0.7152 * color1.g + 0.0722 * color1.b) + 0.05
- luminance2 = (0.2126 * color2.r + 0.7152 * color2.g + 0.0722 * color2.b) + 0.05
+ luminance1 = color1.to_xyz.y * 0.01 + 0.05
+ luminance2 = color2.to_xyz.y * 0.01 + 0.05
if luminance1 > luminance2
luminance1 / luminance2