Add ability to constrain dominant color selection to a HSL range.

ui/gfx/color_analysis.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_COLOR_ANALYSIS_H_
 #define UI_GFX_COLOR_ANALYSIS_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/ref_counted_memory.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/gfx_export.h"
 #include "ui/gfx/matrix3_f.h"
 
 class SkBitmap;
 
 namespace color_utils {
 
+struct HSL;
+
 // This class exposes the sampling method to the caller, which allows
 // stubbing out for things like unit tests. Might be useful to pass more
 // arguments into the GetSample method in the future (such as which
 // cluster is being worked on, etc.).
 //
 // Note: Samplers should be deterministic, as the same image may be analyzed
 // twice with two sampler instances and the results displayed side-by-side
 // to the user.
 class GFX_EXPORT KMeanImageSampler {
  public:
@@ skipping 20 matching lines @@
 // Returns the color in an ARGB |image| that is closest in RGB-space to the
 // provided |color|. Exported for testing.
 GFX_EXPORT SkColor FindClosestColor(const uint8_t* image, int width, int height,
                                     SkColor color);
 
 // Returns an SkColor that represents the calculated dominant color in the
 // image.
 // This uses a KMean clustering algorithm to find clusters of pixel colors in
 // RGB space.
 // |png/bitmap| represents the data of a png/bitmap encoded image.
-// |darkness_limit| represents the minimum sum of the RGB components that is
-// acceptable as a color choice. This can be from 0 to 765.
-// |brightness_limit| represents the maximum sum of the RGB components that is
-// acceptable as a color choice. This can be from 0 to 765.
+// |lower_bound| represents the minimum bound of HSL values to allow.
+// |upper_bound| represents the maximum bound of HSL values to allow.
+// See color_utils::IsWithinHSLRange() for description of these bounds.
 //
 // RGB KMean Algorithm (N clusters, M iterations):
 // 1.Pick N starting colors by randomly sampling the pixels. If you see a
 //   color you already saw keep sampling. After a certain number of tries
 //   just remove the cluster and continue with N = N-1 clusters (for an image
 //   with just one color this should devolve to N=1). These colors are the
 //   centers of your N clusters.
 // 2.For each pixel in the image find the cluster that it is closest to in RGB
 //   space. Add that pixel's color to that cluster (we keep a sum and a count
 //   of all of the pixels added to the space, so just add it to the sum and
 //   increment count).
 // 3.Calculate the new cluster centroids by getting the average color of all of
 //   the pixels in each cluster (dividing the sum by the count).
 // 4.See if the new centroids are the same as the old centroids.
 //     a) If this is the case for all N clusters than we have converged and
 //        can move on.
 //     b) If any centroid moved, repeat step 2 with the new centroids for up
 //        to M iterations.
 // 5.Once the clusters have converged or M iterations have been tried, sort
 //   the clusters by weight (where weight is the number of pixels that make up
 //   this cluster).
 // 6.Going through the sorted list of clusters, pick the first cluster with the
-//   largest weight that's centroid fulfills the equation
-//   |darkness_limit| < SUM(R, G, B) < |brightness_limit|. Return that color.
+//   largest weight that's centroid falls between |lower_bound| and
+//   |upper_bound|. Return that color.
 //   If no color fulfills that requirement return the color with the largest
 //   weight regardless of whether or not it fulfills the equation above.
-//
-// Note: Switching to HSV space did not improve the results of this algorithm
-// for typical favicon images.
-GFX_EXPORT SkColor CalculateKMeanColorOfPNG(
-    scoped_refptr<base::RefCountedMemory> png,
-    uint32_t darkness_limit,
-    uint32_t brightness_limit,
-    KMeanImageSampler* sampler);
+GFX_EXPORT SkColor
+    CalculateKMeanColorOfPNG(scoped_refptr<base::RefCountedMemory> png,
+                             const HSL& lower_bound,
+                             const HSL& upper_bound,
+                             KMeanImageSampler* sampler);
 GFX_EXPORT SkColor CalculateKMeanColorOfBitmap(const SkBitmap& bitmap,
-                                               uint32_t darkness_limit,
-                                               uint32_t brightness_limit,
+                                               const HSL& lower_bound,
+                                               const HSL& upper_bound,
                                                KMeanImageSampler* sampler);
 
-// Computes a dominant color using the above algorithm and reasonable defaults
-// for |darkness_limit|, |brightness_limit| and |sampler|.
+// Computes a dominant color for using the above algorithm and reasonable
+// defaults for |lower_bound|, |upper_bound| and |sampler|.
 GFX_EXPORT SkColor
     CalculateKMeanColorOfPNG(scoped_refptr<base::RefCountedMemory> png);
 GFX_EXPORT SkColor CalculateKMeanColorOfBitmap(const SkBitmap& bitmap);
 
 // Compute color covariance matrix for the input bitmap.
 GFX_EXPORT gfx::Matrix3F ComputeColorCovariance(const SkBitmap& bitmap);
 
 // Apply a color reduction transform defined by |color_transform| vector to
 // |source_bitmap|. The result is put into |target_bitmap|, which is expected
 // to be initialized to the required size and type (SkBitmap::kA8_Config).
@@ skipping 10 matching lines @@
 // initialized to the required size and type (SkBitmap::kA8_Config).
 // Returns true if the conversion succeeded. Note that there might be legitimate
 // reasons for the process to fail even if all input was correct. This is a
 // condition the caller must be able to handle.
 GFX_EXPORT bool ComputePrincipalComponentImage(const SkBitmap& source_bitmap,
                                               SkBitmap* target_bitmap);
 
 }  // namespace color_utils
 
 #endif  // UI_GFX_COLOR_ANALYSIS_H_