thresholder.h

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// File:        thresholder.h
// Description: Base API for thresolding images in tesseract.
// Author:      Ray Smith
// Created:     Mon May 12 11:00:15 PDT 2008
//
// (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_THRESHOLDER_H_
#define TESSERACT_CCMAIN_THRESHOLDER_H_

#include "platform.h"
#include "publictypes.h"

struct Pix;

namespace tesseract {

class TESS_API ImageThresholder {
 public:
  ImageThresholder();
  virtual ~ImageThresholder();

  virtual void Clear();

  bool IsEmpty() const;

  void SetImage(const unsigned char* imagedata, int width, int height,
                int bytes_per_pixel, int bytes_per_line);

  void SetRectangle(int left, int top, int width, int height);

  virtual void GetImageSizes(int* left, int* top, int* width, int* height,
                             int* imagewidth, int* imageheight);

  bool IsColor() const {
    return pix_channels_ >= 3;
  }

  bool IsBinary() const {
    return pix_channels_ == 0;
  }

  int GetScaleFactor() const {
    return scale_;
  }

  // Set the resolution of the source image in pixels per inch.
  // This should be called right after SetImage(), and will let us return
  // appropriate font sizes for the text.
  void SetSourceYResolution(int ppi) {
    yres_ = ppi;
    estimated_res_ = ppi;
  }
  int GetSourceYResolution() const {
    return yres_;
  }
  int GetScaledYResolution() const {
    return scale_ * yres_;
  }
  // Set the resolution of the source image in pixels per inch, as estimated
  // by the thresholder from the text size found during thresholding.
  // This value will be used to set internal size thresholds during recognition
  // and will not influence the output "point size." The default value is
  // the same as the source resolution. (yres_)
  void SetEstimatedResolution(int ppi) {
    estimated_res_ = ppi;
  }
  // Returns the estimated resolution, including any active scaling.
  // This value will be used to set internal size thresholds during recognition.
  int GetScaledEstimatedResolution() const {
    return scale_ * estimated_res_;
  }

  void SetImage(const Pix* pix);

  virtual bool ThresholdToPix(PageSegMode pageseg_mode, Pix** pix);

  // Gets a pix that contains an 8 bit threshold value at each pixel. The
  // returned pix may be an integer reduction of the binary image such that
  // the scale factor may be inferred from the ratio of the sizes, even down
  // to the extreme of a 1x1 pixel thresholds image.
  // Ideally the 8 bit threshold should be the exact threshold used to generate
  // the binary image in ThresholdToPix, but this is not a hard constraint.
  // Returns nullptr if the input is binary. PixDestroy after use.
  virtual Pix* GetPixRectThresholds();

  Pix* GetPixRect();

  // Get a clone/copy of the source image rectangle, reduced to greyscale,
  // and at the same resolution as the output binary.
  // The returned Pix must be pixDestroyed.
  // Provided to the classifier to extract features from the greyscale image.
  virtual Pix* GetPixRectGrey();

 protected:
  // ----------------------------------------------------------------------
  // Utility functions that may be useful components for other thresholders.

  virtual void Init();

  bool IsFullImage() const {
    return rect_left_ == 0 && rect_top_ == 0 &&
           rect_width_ == image_width_ && rect_height_ == image_height_;
  }

  // Otsu thresholds the rectangle, taking the rectangle from *this.
  void OtsuThresholdRectToPix(Pix* src_pix, Pix** out_pix) const;

  // arrays and also the bytes per pixel in src_pix.
  void ThresholdRectToPix(Pix* src_pix, int num_channels,
                          const int* thresholds, const int* hi_values,
                          Pix** pix) const;

 protected:
  Pix*                 pix_;

  int                  image_width_;    //< Width of source pix_.
  int                  image_height_;   //< Height of source pix_.
  int                  pix_channels_;   //< Number of 8-bit channels in pix_.
  int                  pix_wpl_;        //< Words per line of pix_.
  // Limits of image rectangle to be processed.
  int                  scale_;          //< Scale factor from original image.
  int                  yres_;           //< y pixels/inch in source image.
  int                  estimated_res_;  //< Resolution estimate from text size.
  int                  rect_left_;
  int                  rect_top_;
  int                  rect_width_;
  int                  rect_height_;
};

}  // namespace tesseract.

#endif  // TESSERACT_CCMAIN_THRESHOLDER_H_