tesseract/src/ccmain/thresholder.h
Stefan Weil 8a34da027f Fix typo in description
Signed-off-by: Stefan Weil <sw@weilnetz.de>
2019-04-22 21:50:37 +02:00

190 lines
7.7 KiB
C++

///////////////////////////////////////////////////////////////////////
// File: thresholder.h
// Description: Base API for thresholding images in tesseract.
// 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_THRESHOLDER_H_
#define TESSERACT_CCMAIN_THRESHOLDER_H_
#include "platform.h"
#include "publictypes.h"
struct Pix;
namespace tesseract {
/// Base class for all tesseract image thresholding classes.
/// Specific classes can add new thresholding methods by
/// overriding ThresholdToPix.
/// Each instance deals with a single image, but the design is intended to
/// be useful for multiple calls to SetRectangle and ThresholdTo* if
/// desired.
class TESS_API ImageThresholder {
public:
ImageThresholder();
virtual ~ImageThresholder();
/// Destroy the Pix if there is one, freeing memory.
virtual void Clear();
/// Return true if no image has been set.
bool IsEmpty() const;
/// SetImage makes a copy of all the image data, so it may be deleted
/// immediately after this call.
/// Greyscale of 8 and color of 24 or 32 bits per pixel may be given.
/// Palette color images will not work properly and must be converted to
/// 24 bit.
/// Binary images of 1 bit per pixel may also be given but they must be
/// byte packed with the MSB of the first byte being the first pixel, and a
/// one pixel is WHITE. For binary images set bytes_per_pixel=0.
void SetImage(const unsigned char* imagedata, int width, int height,
int bytes_per_pixel, int bytes_per_line);
/// Store the coordinates of the rectangle to process for later use.
/// Doesn't actually do any thresholding.
void SetRectangle(int left, int top, int width, int height);
/// Get enough parameters to be able to rebuild bounding boxes in the
/// original image (not just within the rectangle).
/// Left and top are enough with top-down coordinates, but
/// the height of the rectangle and the image are needed for bottom-up.
virtual void GetImageSizes(int* left, int* top, int* width, int* height,
int* imagewidth, int* imageheight);
/// Return true if the source image is color.
bool IsColor() const {
return pix_channels_ >= 3;
}
/// Returns true if the source image is binary.
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_;
}
/// Pix vs raw, which to use? Pix is the preferred input for efficiency,
/// since raw buffers are copied.
/// SetImage for Pix clones its input, so the source pix may be pixDestroyed
/// immediately after, but may not go away until after the Thresholder has
/// finished with it.
void SetImage(const Pix* pix);
/// Threshold the source image as efficiently as possible to the output Pix.
/// Creates a Pix and sets pix to point to the resulting pointer.
/// Caller must use pixDestroy to free the created Pix.
/// Returns false on error.
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();
/// Get a clone/copy of the source image rectangle.
/// The returned Pix must be pixDestroyed.
/// This function will be used in the future by the page layout analysis, and
/// the layout analysis that uses it will only be available with Leptonica,
/// so there is no raw equivalent.
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.
/// Common initialization shared between SetImage methods.
virtual void Init();
/// Return true if we are processing the full image.
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;
/// Threshold the rectangle, taking everything except the src_pix
/// from the class, using thresholds/hi_values to the output pix.
/// NOTE that num_channels is the size of the thresholds and hi_values
// 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:
/// Clone or other copy of the source Pix.
/// The pix will always be PixDestroy()ed on destruction of the class.
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_