ui/gfx/color_analysis.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_GFX_COLOR_ANALYSIS_H_
   6 #define UI_GFX_COLOR_ANALYSIS_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/compiler_specific.h"
  10 #include "base/memory/ref_counted.h"
  11 #include "base/memory/ref_counted_memory.h"
  12 #include "third_party/skia/include/core/SkColor.h"
  13 #include "ui/base/ui_export.h"
  14 #include "ui/gfx/matrix3_f.h"
  15
  16 class SkBitmap;
  17
  18 namespace color_utils {
  19
  20 // This class exposes the sampling method to the caller, which allows
  21 // stubbing out for things like unit tests. Might be useful to pass more
  22 // arguments into the GetSample method in the future (such as which
  23 // cluster is being worked on, etc.).
  24 //
  25 // Note: Samplers should be deterministic, as the same image may be analyzed
  26 // twice with two sampler instances and the results displayed side-by-side
  27 // to the user.
  28 class UI_EXPORT KMeanImageSampler {
  29  public:
  30   virtual int GetSample(int width, int height) = 0;
  31
  32  protected:
  33   KMeanImageSampler();
  34   virtual ~KMeanImageSampler();
  35 };
  36
  37 // This sampler will pick pixels from an evenly spaced grid.
  38 class UI_EXPORT GridSampler : public KMeanImageSampler {
  39   public:
  40    GridSampler();
  41    virtual ~GridSampler();
  42
  43    virtual int GetSample(int width, int height) OVERRIDE;
  44
  45   private:
  46    // The number of times GetSample has been called.
  47    int calls_;
  48 };
  49
  50 // Returns the color in an ARGB |image| that is closest in RGB-space to the
  51 // provided |color|. Exported for testing.
  52 UI_EXPORT SkColor FindClosestColor(const uint8_t* image, int width, int height,
  53                                    SkColor color);
  54
  55 // Returns an SkColor that represents the calculated dominant color in the png.
  56 // This uses a KMean clustering algorithm to find clusters of pixel colors in
  57 // RGB space.
  58 // |png| represents the data of a png encoded image.
  59 // |darkness_limit| represents the minimum sum of the RGB components that is
  60 // acceptable as a color choice. This can be from 0 to 765.
  61 // |brightness_limit| represents the maximum sum of the RGB components that is
  62 // acceptable as a color choice. This can be from 0 to 765.
  63 //
  64 // RGB KMean Algorithm (N clusters, M iterations):
  65 // 1.Pick N starting colors by randomly sampling the pixels. If you see a
  66 //   color you already saw keep sampling. After a certain number of tries
  67 //   just remove the cluster and continue with N = N-1 clusters (for an image
  68 //   with just one color this should devolve to N=1). These colors are the
  69 //   centers of your N clusters.
  70 // 2.For each pixel in the image find the cluster that it is closest to in RGB
  71 //   space. Add that pixel's color to that cluster (we keep a sum and a count
  72 //   of all of the pixels added to the space, so just add it to the sum and
  73 //   increment count).
  74 // 3.Calculate the new cluster centroids by getting the average color of all of
  75 //   the pixels in each cluster (dividing the sum by the count).
  76 // 4.See if the new centroids are the same as the old centroids.
  77 //     a) If this is the case for all N clusters than we have converged and
  78 //        can move on.
  79 //     b) If any centroid moved, repeat step 2 with the new centroids for up
  80 //        to M iterations.
  81 // 5.Once the clusters have converged or M iterations have been tried, sort
  82 //   the clusters by weight (where weight is the number of pixels that make up
  83 //   this cluster).
  84 // 6.Going through the sorted list of clusters, pick the first cluster with the
  85 //   largest weight that's centroid fulfills the equation
  86 //   |darkness_limit| < SUM(R, G, B) < |brightness_limit|. Return that color.
  87 //   If no color fulfills that requirement return the color with the largest
  88 //   weight regardless of whether or not it fulfills the equation above.
  89 //
  90 // Note: Switching to HSV space did not improve the results of this algorithm
  91 // for typical favicon images.
  92 UI_EXPORT SkColor CalculateKMeanColorOfPNG(
  93     scoped_refptr<base::RefCountedMemory> png,
  94     uint32_t darkness_limit,
  95     uint32_t brightness_limit,
  96     KMeanImageSampler* sampler);
  97
  98 // Computes a dominant color for an SkBitmap using the above algorithm and
  99 // reasonable defaults for |darkness_limit|, |brightness_limit| and |sampler|.
 100 UI_EXPORT SkColor CalculateKMeanColorOfBitmap(const SkBitmap& bitmap);
 101
 102 // Compute color covariance matrix for the input bitmap.
 103 UI_EXPORT gfx::Matrix3F ComputeColorCovariance(const SkBitmap& bitmap);
 104
 105 // Apply a color reduction transform defined by |color_transform| vector to
 106 // |source_bitmap|. The result is put into |target_bitmap|, which is expected
 107 // to be initialized to the required size and type (SkBitmap::kA8_Config).
 108 // If |fit_to_range|, result is transfored linearly to fit 0-0xFF range.
 109 // Otherwise, data is clipped.
 110 // Returns true if the target has been computed.
 111 UI_EXPORT bool ApplyColorReduction(const SkBitmap& source_bitmap,
 112                                    const gfx::Vector3dF& color_transform,
 113                                    bool fit_to_range,
 114                                    SkBitmap* target_bitmap);
 115
 116 // Compute a monochrome image representing the principal color component of
 117 // the |source_bitmap|. The result is stored in |target_bitmap|, which must be
 118 // initialized to the required size and type (SkBitmap::kA8_Config).
 119 // Returns true if the conversion succeeded. Note that there might be legitimate
 120 // reasons for the process to fail even if all input was correct. This is a
 121 // condition the caller must be able to handle.
 122 UI_EXPORT bool ComputePrincipalComponentImage(const SkBitmap& source_bitmap,
 123                                               SkBitmap* target_bitmap);
 124
 125 }  // namespace color_utils
 126
 127 #endif  // UI_GFX_COLOR_ANALYSIS_H_