Complete (but inefficient) implementation of the image retargetting method.

chrome/browser/thumbnails/content_analysis.h

+// Copyright (c) 2013 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 CHROME_BROWSER_THUMBNAILS_CONTENT_ANALYSIS_H_
+#define CHROME_BROWSER_THUMBNAILS_CONTENT_ANALYSIS_H_
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "ui/base/ui_export.h"
+#include "ui/gfx/rect.h"
+#include "ui/gfx/size.h"
+
+class SkBitmap;
+
+namespace thumbnailing_utils {
+
+// Compute in-place gaussian gradient magnitude of |input_bitmap| with sigma
+// |kernel_sigma|. |input_bitmap| is requried to be of SkBitmap::kA8_Config
+// type. The routine computes first-order gaussian derivative on a
+// gaussian-smoothed image. Beware, this is fairly slow since kernel size is
+// 4 * kernel_sigma + 1.
+void ApplyGaussianGradientMagnitudeFilter(SkBitmap* input_bitmap,
+                                          float kernel_sigma);
+
+// Accumulates vertical and horizontal sum of pixel values from a subsection of
+// |input_bitmap| defined by |image_area|. The image is required to be of
+// SkBitmap::kA8_Config type.
+// If non-empty |target_size| is given, the routine will use it to process the
+// profiles with closing operator sized to eliminate gaps which would be smaller
+// than 1 pixel after rescaling to |target_size|.
+// If |apply_log| is true, logarithm of counts are used for morhology (and
+// returned).
+void ExtractImageProfileInformation(const SkBitmap& input_bitmap,
+                                    const gfx::Rect& image_area,
+                                    const gfx::Size& target_size,
+                                    bool apply_log,
+                                    std::vector<float>* rows,
+                                    std::vector<float>* columns);
+
+// Compute a threshold value separating background (low) from signal (high)
+// areas in the |input| profile.
+float AutoSegmentPeaks(const std::vector<float>& input);
+
+// Shrinks the source |bitmap| by removing rows and columns where |rows| and
+// |columns| are false, respectively. The function returns a new bitmap if the
+// shrinking can be performed and an empty instance otherwise.
+SkBitmap ComputeDecimatedImage(const SkBitmap& bitmap,
+                               const std::vector<bool>& rows,
+                               const std::vector<bool>& columns);
+
+// Creates a new bitmap which contains only 'interesting' areas of
+// |source_bitmap|. The |target_size| is used to estimate some computation
+// parameters, but the resulting bitmap will not necessarily be of that size.
+// |kernel_sigma| defines the degree of image smoothing in gradient computation.
+// For a natural-sized (not shrunk) screenshot at 96 DPI and regular font size
+// 5.0 was determined to be a good value.
+SkBitmap CreateRetargettedThumbnailImage(const SkBitmap& source_bitmap,
+                                         const gfx::Size& target_size,
+                                         float kernel_sigma);
+
+}  // namespace thumbnailing_utils
+
+#endif  // CHROME_BROWSER_THUMBNAILS_CONTENT_ANALYSIS_H_