Distinguish between color extraction strategies

By default, use fast color sampling. Run heavy edge weighted extraction
only on demand.

lib/music_library/colors/color_frequency_extractor.ex

@@ -0,0 +1,132 @@
+defmodule MusicLibrary.Colors.ColorFrequencyExtractor do
+  @moduledoc """
+  Extracts dominant colors from images using Vix.
+
+  Uses a fast but naive approach based on color sampling and histogram
+  analysis.
+
+  Initially by Claude, using Sonnet 4.
+  """
+
+  alias Vix.Vips.{Image, Operation}
+
+  @doc """
+  Extracts the n most dominant colors from image data (defaults to 5)
+  and returns them in hex format, e.g. ["#FF5733", "#33C3FF", "#75FF33"].
+  """
+  @spec extract_dominant_colors(binary(), pos_integer()) :: {:ok, [String.t()]} | {:error, term()}
+  def extract_dominant_colors(image_data, num_colors \\ 5) do
+    with {:ok, image} <- Image.new_from_buffer(image_data),
+         {:ok, processed_image} <- prepare_image_for_analysis(image),
+         {:ok, colors} <- extract_colors_via_sampling(processed_image, num_colors) do
+      hex_colors = Enum.map(colors, &rgb_to_hex/1)
+      {:ok, hex_colors}
+    end
+  end
+
+  @doc """
+  Same as `extract-dominant_colors/2`, but raises an error if extraction fails.
+  """
+  @spec extract_dominant_colors!(binary(), pos_integer()) :: [String.t()] | no_return
+  def extract_dominant_colors!(image_data, num_colors \\ 5) do
+    case extract_dominant_colors(image_data, num_colors) do
+      {:ok, colors} -> colors
+      {:error, reason} -> raise "Failed to extract dominant colors: #{inspect(reason)}"
+    end
+  end
+
+  defp prepare_image_for_analysis(image) do
+    with {:ok, resized} <- Operation.thumbnail_image(image, 150) do
+      ensure_rgb_channels(resized)
+    end
+  end
+
+  defp ensure_rgb_channels(image) do
+    bands = Image.bands(image)
+
+    cond do
+      bands >= 3 ->
+        # Image already has 3+ channels (RGB or RGBA), use as-is
+        {:ok, image}
+
+      bands == 1 ->
+        # Grayscale image, convert to 3-channel by copying the single channel
+        Operation.bandjoin([image, image, image])
+
+      true ->
+        {:error, "Unsupported image format with #{bands} bands"}
+    end
+  end
+
+  defp extract_colors_via_sampling(image, num_colors) do
+    width = Image.width(image)
+    height = Image.height(image)
+
+    # Sample every nth pixel to get a good distribution
+    sample_step = max(1, div(min(width, height), 10))
+
+    pixels =
+      for y <- 0..(height - 1)//sample_step,
+          x <- 0..(width - 1)//sample_step do
+        case Operation.getpoint(image, x, y) do
+          {:ok, [r, g, b | _]} ->
+            {trunc(r), trunc(g), trunc(b)}
+
+          {:ok, [gray]} ->
+            gray_val = trunc(gray)
+            {gray_val, gray_val, gray_val}
+
+          {:ok, [r, g]} ->
+            # Handle 2-channel images
+            {trunc(r), trunc(g), 0}
+
+          _ ->
+            nil
+        end
+      end
+      |> Enum.reject(fn
+        {r, g, b} ->
+          # Filter out very dark or very light colors
+          brightness = (r + g + b) / 3
+          brightness < 20 || brightness > 235
+
+        nil ->
+          true
+      end)
+
+    if length(pixels) > 0 do
+      colors = analyze_color_histogram(pixels, num_colors)
+      {:ok, colors}
+    else
+      {:error, "No valid pixels found for color extraction"}
+    end
+  end
+
+  defp analyze_color_histogram(pixels, num_colors) do
+    # Simple frequency-based approach with color grouping
+    pixels
+    |> group_similar_colors()
+    |> Enum.frequencies()
+    |> Enum.sort_by(fn {_color, count} -> count end, :desc)
+    |> Enum.take(num_colors)
+    |> Enum.map(fn {{r, g, b}, _count} -> {r, g, b} end)
+  end
+
+  defp group_similar_colors(pixels) do
+    Enum.map(pixels, fn {r, g, b} ->
+      # Group colors into buckets to reduce similar colors
+      bucket_size = 64
+      grouped_r = div(r, bucket_size) * bucket_size
+      grouped_g = div(g, bucket_size) * bucket_size
+      grouped_b = div(b, bucket_size) * bucket_size
+      {grouped_r, grouped_g, grouped_b}
+    end)
+  end
+
+  defp rgb_to_hex({r, g, b}) do
+    "#" <>
+      (Integer.to_string(r, 16) |> String.pad_leading(2, "0") |> String.upcase()) <>
+      (Integer.to_string(g, 16) |> String.pad_leading(2, "0") |> String.upcase()) <>
+      (Integer.to_string(b, 16) |> String.pad_leading(2, "0") |> String.upcase())
+  end
+end

lib/music_library/colors/edge_weighted_extractor.ex

@@ -1,4 +1,4 @@
-defmodule MusicLibrary.Records.DominantColors do
+defmodule MusicLibrary.Colors.EdgeWeightedExtractor do
   @moduledoc """
   Simple edge-weighted color extraction using Vix.
 
@@ -6,6 +6,8 @@ defmodule MusicLibrary.Records.DominantColors do
   giving more importance to colors from visually significant regions
   without requiring complex algorithms.
 
+  Extraction is slow, so it should always be done asynchronously.
+
   Generated by Claude, using Sonnet 4.
   """
 

lib/music_library/records.ex

@@ -6,7 +6,8 @@ defmodule MusicLibrary.Records do
   import Ecto.Query, warn: false
 
   alias MusicLibrary.Artists
-  alias MusicLibrary.Records.{ArtistRecord, Cover, DominantColors, Record, SearchParser}
+  alias MusicLibrary.Colors.EdgeWeightedExtractor
+  alias MusicLibrary.Records.{ArtistRecord, Cover, Record, SearchParser}
   alias MusicLibrary.{BackgroundRepo, Repo, Worker}
 
   def essential_fields do
@@ -255,7 +256,7 @@ defmodule MusicLibrary.Records do
   end
 
   def generate_dominant_colors(record) do
-    with {:ok, colors} <- DominantColors.extract_dominant_colors(record.cover_data) do
+    with {:ok, colors} <- EdgeWeightedExtractor.extract_dominant_colors(record.cover_data) do
       update_record(record, %{"dominant_colors" => colors})
     end
   end

lib/music_library/records/record.ex

@@ -5,7 +5,8 @@ defmodule MusicLibrary.Records.Record do
 
   alias MusicBrainz.{Release, ReleaseGroup}
   alias MusicLibrary.Artists.Artist
-  alias MusicLibrary.Records.{Cover, DominantColors}
+  alias MusicLibrary.Colors.ColorFrequencyExtractor
+  alias MusicLibrary.Records.Cover
 
   @formats [:cd, :backup, :vinyl, :blu_ray, :dvd, :multi]
   @types [:album, :ep, :live, :compilation, :single, :other]
@@ -170,7 +171,7 @@ defmodule MusicLibrary.Records.Record do
   end
 
   def generate_dominant_colors(%__MODULE__{cover_data: cover_data} = record) do
-    change(record, dominant_colors: DominantColors.extract_dominant_colors!(cover_data))
+    change(record, dominant_colors: ColorFrequencyExtractor.extract_dominant_colors!(cover_data))
   end
 
   def generate_dominant_colors(changeset) do
@@ -182,7 +183,7 @@ defmodule MusicLibrary.Records.Record do
         put_change(
           changeset,
           :dominant_colors,
-          DominantColors.extract_dominant_colors!(cover_data)
+          ColorFrequencyExtractor.extract_dominant_colors!(cover_data)
         )
     end
   end