otsuthr.h

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// File:        otsuthr.h
// Description: Simple Otsu thresholding for binarizing images.
// Author:      Ray Smith
//
// (C) Copyright 2008, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
 
#ifndef TESSERACT_CCMAIN_OTSUTHR_H_
#define TESSERACT_CCMAIN_OTSUTHR_H_
 
#include "image.h"
 
#include <vector> // for std::vector
 
struct Pix;
 
namespace tesseract {
 
const int kHistogramSize = 256; // The size of a histogram of pixel values.
 
// Computes the Otsu threshold(s) for the given image rectangle, making one
// for each channel. Each channel is always one byte per pixel.
// Returns an array of threshold values and an array of hi_values, such
// that a pixel value >threshold[channel] is considered foreground if
// hi_values[channel] is 0 or background if 1. A hi_value of -1 indicates
// that there is no apparent foreground. At least one hi_value will not be -1.
// The return value is the number of channels in the input image, being
// the size of the output thresholds and hi_values arrays.
int OtsuThreshold(Image src_pix, int left, int top, int width, int height,
                  std::vector<int> &thresholds,
                  std::vector<int> &hi_values);
 
// Computes the histogram for the given image rectangle, and the given
// single channel. Each channel is always one byte per pixel.
// Histogram is always a kHistogramSize(256) element array to count
// occurrences of each pixel value.
void HistogramRect(Image src_pix, int channel, int left, int top, int width, int height,
                   int *histogram);
 
// Computes the Otsu threshold(s) for the given histogram.
// Also returns H = total count in histogram, and
// omega0 = count of histogram below threshold.
int OtsuStats(const int *histogram, int *H_out, int *omega0_out);
 
} // namespace tesseract.
 
#endif // TESSERACT_CCMAIN_OTSUTHR_H_