Add color extraction for audio thumbnails (#14209)

2 files changed, 203 insertions, 0 deletions

diff --git a/lib/paperclip/color_extractor.rb b/lib/paperclip/color_extractor.rb
new file mode 100644
index 000000000..44fe5ff1d
--- /dev/null
+++ b/lib/paperclip/color_extractor.rb
@@ -0,0 +1,189 @@
+# frozen_string_literal: true
+
+require 'mime/types/columnar'
+
+module Paperclip
+  class ColorExtractor < Paperclip::Processor
+    MIN_CONTRAST        = 3.0
+    FREQUENCY_THRESHOLD = 0.01
+
+    def make
+      depth = 8
+
+      # Determine background palette by getting colors close to the image's edge only
+      background_palette = palette_from_histogram(convert(':source -alpha set -gravity Center -region 75%x75% -fill None -colorize 100% -alpha transparent +region -format %c -colors :quantity -depth :depth histogram:info:', source: File.expand_path(@file.path), quantity: 10, depth: depth), 10)
+
+      # Determine foreground palette from the whole image
+      foreground_palette = palette_from_histogram(convert(':source -format %c -colors :quantity -depth :depth histogram:info:', source: File.expand_path(@file.path), quantity: 10, depth: depth), 10)
+
+      background_color   = background_palette.first || foreground_palette.first
+      foreground_colors  = []
+
+      return @file if background_color.nil?
+
+      max_distance       = 0
+      max_distance_color = nil
+
+      foreground_palette.each do |color|
+        distance = ColorDiff.between(background_color, color)
+
+        if distance > max_distance
+          max_distance = distance
+          max_distance_color = color
+        end
+      end
+
+      foreground_colors << max_distance_color unless max_distance_color.nil?
+
+      max_distance       = 0
+      max_distance_color = nil
+
+      foreground_palette.each do |color|
+        distance = ColorDiff.between(background_color, color)
+        contrast = w3c_contrast(background_color, color)
+
+        if distance > max_distance && contrast >= MIN_CONTRAST && !foreground_colors.include?(color)
+          max_distance = distance
+          max_distance_color = color
+        end
+      end
+
+      foreground_colors << max_distance_color unless max_distance_color.nil?
+
+      # If we don't have enough colors for accent and foreground, generate
+      # new ones by manipulating the background color
+      (2 - foreground_colors.size).times do |i|
+        foreground_colors << lighten_or_darken(background_color, 35 + (15 * i))
+      end
+
+      # We want the color with the highest contrast to background to be the foreground one,
+      # and the one with the highest saturation to be the accent one
+      foreground_color = foreground_colors.max_by { |rgb| w3c_contrast(background_color, rgb) }
+      accent_color     = foreground_colors.max_by { |rgb| rgb_to_hsl(rgb.r, rgb.g, rgb.b)[1] }
+
+      meta = {
+        colors: {
+          background: rgb_to_hex(background_color),
+          foreground: rgb_to_hex(foreground_color),
+          accent: rgb_to_hex(accent_color),
+        },
+      }
+
+      attachment.instance.file.instance_write(:meta, (attachment.instance.file.instance_read(:meta) || {}).merge(meta))
+
+      @file
+    end
+
+    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
+
+      if luminance1 > luminance2
+        luminance1 / luminance2
+      else
+        luminance2 / luminance1
+      end
+    end
+
+    # rubocop:disable Style/MethodParameterName
+    def rgb_to_hsl(r, g, b)
+      r /= 255.0
+      g /= 255.0
+      b /= 255.0
+      max = [r, g, b].max
+      min = [r, g, b].min
+      h = (max + min) / 2.0
+      s = (max + min) / 2.0
+      l = (max + min) / 2.0
+
+      if max == min
+        h = 0
+        s = 0 # achromatic
+      else
+        d = max - min
+        s = l >= 0.5 ? d / (2.0 - max - min) : d / (max + min)
+
+        case max
+        when r
+          h = (g - b) / d + (g < b ? 6.0 : 0)
+        when g
+          h = (b - r) / d + 2.0
+        when b
+          h = (r - g) / d + 4.0
+        end
+
+        h /= 6.0
+      end
+
+      [(h * 360).round, (s * 100).round, (l * 100).round]
+    end
+
+    def hue_to_rgb(p, q, t)
+      t += 1 if t.negative?
+      t -= 1 if t > 1
+
+      return (p + (q - p) * 6 * t) if t < 1 / 6.0
+      return q if t < 1 / 2.0
+      return (p + (q - p) * (2 / 3.0 - t) * 6) if t < 2 / 3.0
+
+      p
+    end
+
+    def hsl_to_rgb(h, s, l)
+      h /= 360.0
+      s /= 100.0
+      l /= 100.0
+
+      r = 0.0
+      g = 0.0
+      b = 0.0
+
+      if s == 0.0
+        r = l.to_f
+        g = l.to_f
+        b = l.to_f # achromatic
+      else
+        q = l < 0.5 ? l * (1 + s) : l + s - l * s
+        p = 2 * l - q
+        r = hue_to_rgb(p, q, h + 1 / 3.0)
+        g = hue_to_rgb(p, q, h)
+        b = hue_to_rgb(p, q, h - 1 / 3.0)
+      end
+
+      [(r * 255).round, (g * 255).round, (b * 255).round]
+    end
+    # rubocop:enable Style/MethodParameterName
+
+    def lighten_or_darken(color, by)
+      hue, saturation, light = rgb_to_hsl(color.r, color.g, color.b)
+
+      light = begin
+        if light < 50
+          [100, light + by].min
+        else
+          [0, light - by].max
+        end
+      end
+
+      ColorDiff::Color::RGB.new(*hsl_to_rgb(hue, saturation, light))
+    end
+
+    def palette_from_histogram(result, quantity)
+      frequencies       = result.scan(/([0-9]+)\:/).flatten.map(&:to_f)
+      hex_values        = result.scan(/\#([0-9A-Fa-f]{6,8})/).flatten
+      total_frequencies = frequencies.reduce(&:+).to_f
+
+      frequencies.map.with_index { |f, i| [f / total_frequencies, hex_values[i]] }
+                 .sort_by { |r| -r[0] }
+                 .reject { |r| r[1].size == 8 && r[1].end_with?('00') }
+                 .map { |r| ColorDiff::Color::RGB.new(*r[1][0..5].scan(/../).map { |c| c.to_i(16) }) }
+                 .slice(0, quantity)
+    end
+
+    def rgb_to_hex(rgb)
+      '#%02x%02x%02x' % [rgb.r, rgb.g, rgb.b]
+    end
+  end
+end
diff --git a/lib/paperclip/transcoder_extensions.rb b/lib/paperclip/transcoder_extensions.rb
new file mode 100644
index 000000000..c0b2447f3
--- /dev/null
+++ b/lib/paperclip/transcoder_extensions.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+module Paperclip
+  module TranscoderExtensions
+    # Prevent the transcoder from modifying our meta hash
+    def initialize(file, options = {}, attachment = nil)
+      meta_value = attachment&.instance_read(:meta)
+      super
+      attachment&.instance_write(:meta, meta_value)
+    end
+  end
+end
+
+Paperclip::Transcoder.prepend(Paperclip::TranscoderExtensions)