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

ui/gfx/color_analysis.h

Index: ui/gfx/color_analysis.h
diff --git a/ui/gfx/color_analysis.h b/ui/gfx/color_analysis.h
index dcbfabc9d7757d20ee6e0cf8f26c986fe5fd843f..2f0d940916953751c11cc31239944e5d5f7500a9 100644
--- a/ui/gfx/color_analysis.h
+++ b/ui/gfx/color_analysis.h
@@ -17,6 +17,8 @@ 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
@@ -56,10 +58,9 @@ GFX_EXPORT SkColor FindClosestColor(const uint8_t* image, int width, int height,
 // This uses a KMean clustering algorithm to find clusters of pixel colors in
 // RGB space.
 // |png| represents the data of a png 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 bounding range of HSL values to allow.

[Matt Giuca, 2014/05/22 05:03:52]

"minimum bound of ..." (what is a "minimum bounding range"? The range is both
the min and max).

[calamity, 2014/05/22 07:36:36]

Done.

+// |upper_bound| represents the maximum bounding range 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
@@ -82,21 +83,23 @@ GFX_EXPORT SkColor FindClosestColor(const uint8_t* image, int width, int height,
 //   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 that falls between the given |lower_bound|

[Matt Giuca, 2014/05/22 05:03:52]

Remove "that" and "the given".

[calamity, 2014/05/22 07:36:36]

Done.

+//   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);
+
+// Computes a dominant color for a PNG using the above algorithm and
+// reasonable defaults for |lower_bound|, |upper_bound| and |sampler|.
+GFX_EXPORT SkColor
+    CalculateKMeanColorOfPNG(scoped_refptr<base::RefCountedMemory> png);
 
 // Computes a dominant color for an SkBitmap using the above algorithm and
-// reasonable defaults for |darkness_limit|, |brightness_limit| and |sampler|.
+// reasonable defaults for |lower_bound|, |upper_bound| and |sampler|.
 GFX_EXPORT SkColor CalculateKMeanColorOfBitmap(const SkBitmap& bitmap);

[Matt Giuca, 2014/05/22 05:03:52]

Can you also add an overload to CalculateKMeanColorOfBitmap that takes explicit
values. It doesn't make sense that you have to convert to a PNG to do this (and
you do).

You could do this change, and the addition of the new CalculateKMeanColorOfPNG
overload, in a precursor CL which would be a good way to split it.

[calamity, 2014/05/22 07:36:36]

Done.

 
 // Compute color covariance matrix for the input bitmap.