imagefind.h

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// File:        imagefind.h
// Description: Class to find image and drawing regions in an image
//              and create a corresponding list of empty blobs.
// Author:      Ray Smith
// Created:     Fri Aug 01 10:50:01 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_TEXTORD_IMAGEFIND_H__
#define TESSERACT_TEXTORD_IMAGEFIND_H__

#include "host.h"

struct Boxa;
struct Pix;
struct Pixa;
class TBOX;
class FCOORD;
class TO_BLOCK;
class BLOBNBOX_LIST;

namespace tesseract {

class ColPartitionGrid;
class ColPartition_LIST;
class TabFind;

// The ImageFind class is a simple static function wrapper class that
// exposes the FindImages function and some useful helper functions.
class ImageFind {
 public:
  // Finds image regions within the BINARY source pix (page image) and returns
  // the image regions as a mask image.
  // The returned pix may be NULL, meaning no images found.
  // If not NULL, it must be PixDestroyed by the caller.
  static Pix* FindImages(Pix* pix);

  // Generates a Boxa, Pixa pair from the input binary (image mask) pix,
  // analgous to pixConnComp, except that connected components which are nearly
  // rectangular are replaced with solid rectangles.
  // The returned boxa, pixa may be NULL, meaning no images found.
  // If not NULL, they must be destroyed by the caller.
  // Resolution of pix should match the source image (Tesseract::pix_binary_)
  // so the output coordinate systems match.
  static void ConnCompAndRectangularize(Pix* pix, Boxa** boxa, Pixa** pixa);

  // Returns true if there is a rectangle in the source pix, such that all
  // pixel rows and column slices outside of it have less than
  // min_fraction of the pixels black, and within max_skew_gradient fraction
  // of the pixels on the inside, there are at least max_fraction of the
  // pixels black. In other words, the inside of the rectangle looks roughly
  // rectangular, and the outside of it looks like extra bits.
  // On return, the rectangle is defined by x_start, y_start, x_end and y_end.
  // Note: the algorithm is iterative, allowing it to slice off pixels from
  // one edge, allowing it to then slice off more pixels from another edge.
  static bool pixNearlyRectangular(Pix* pix,
                                   double min_fraction, double max_fraction,
                                   double max_skew_gradient,
                                   int* x_start, int* y_start,
                                   int* x_end, int* y_end);

  // Given an input pix, and a bounding rectangle, the sides of the rectangle
  // are shrunk inwards until they bound any black pixels found within the
  // original rectangle. Returns false if the rectangle contains no black
  // pixels at all.
  static bool BoundsWithinRect(Pix* pix, int* x_start, int* y_start,
                               int* x_end, int* y_end);

  // Given a point in 3-D (RGB) space, returns the squared Euclidean distance
  // of the point from the given line, defined by a pair of points in the 3-D
  // (RGB) space, line1 and line2.
  static double ColorDistanceFromLine(const uinT8* line1, const uinT8* line2,
                                      const uinT8* point);

  // Returns the leptonica combined code for the given RGB triplet.
  static uinT32 ComposeRGB(uinT32 r, uinT32 g, uinT32 b);

  // Returns the input value clipped to a uinT8.
  static uinT8 ClipToByte(double pixel);

  // Computes the light and dark extremes of color in the given rectangle of
  // the given pix, which is factor smaller than the coordinate system in rect.
  // The light and dark points are taken to be the upper and lower 8th-ile of
  // the most deviant of R, G and B. The value of the other 2 channels are
  // computed by linear fit against the most deviant.
  // The colors of the two point are returned in color1 and color2, with the
  // alpha channel set to a scaled mean rms of the fits.
  // If color_map1 is not null then it and color_map2 get rect pasted in them
  // with the two calculated colors, and rms map gets a pasted rect of the rms.
  // color_map1, color_map2 and rms_map are assumed to be the same scale as pix.
  static void ComputeRectangleColors(const TBOX& rect, Pix* pix, int factor,
                                     Pix* color_map1, Pix* color_map2,
                                     Pix* rms_map,
                                     uinT8* color1, uinT8* color2);

  // Returns true if there are no black pixels in between the boxes.
  // The im_box must represent the bounding box of the pix in tesseract
  // coordinates, which may be negative, due to rotations to make the textlines
  // horizontal. The boxes are rotated by rotation, which should undo such
  // rotations, before mapping them onto the pix.
  static bool BlankImageInBetween(const TBOX& box1, const TBOX& box2,
                                  const TBOX& im_box, const FCOORD& rotation,
                                  Pix* pix);

  // Returns the number of pixels in box in the pix.
  // The im_box must represent the bounding box of the pix in tesseract
  // coordinates, which may be negative, due to rotations to make the textlines
  // horizontal. The boxes are rotated by rotation, which should undo such
  // rotations, before mapping them onto the pix.
  static int CountPixelsInRotatedBox(TBOX box, const TBOX& im_box,
                                     const FCOORD& rotation, Pix* pix);


  // Locates all the image partitions in the part_grid, that were found by a
  // previous call to FindImagePartitions, marks them in the image_mask,
  // removes them from the grid, and deletes them. This makes it possble to
  // call FindImagePartitions again to produce less broken-up and less
  // overlapping image partitions.
  // rerotation specifies how to rotate the partition coords to match
  // the image_mask, since this function is used after orientation correction.
  static void TransferImagePartsToImageMask(const FCOORD& rerotation,
                                            ColPartitionGrid* part_grid,
                                            Pix* image_mask);

  // Runs a CC analysis on the image_pix mask image, and creates
  // image partitions from them, cutting out strong text, and merging with
  // nearby image regions such that they don't interfere with text.
  // Rotation and rerotation specify how to rotate image coords to match
  // the blob and partition coords and back again.
  // The input/output part_grid owns all the created partitions, and
  // the partitions own all the fake blobs that belong in the partitions.
  // Since the other blobs in the other partitions will be owned by the block,
  // ColPartitionGrid::ReTypeBlobs must be called afterwards to fix this
  // situation and collect the image blobs.
  static void FindImagePartitions(Pix* image_pix,
                                  const FCOORD& rotation,
                                  const FCOORD& rerotation,
                                  TO_BLOCK* block,
                                  TabFind* tab_grid,
                                  ColPartitionGrid* part_grid,
                                  ColPartition_LIST* big_parts);
};

}  // namespace tesseract.

#endif  // TESSERACT_TEXTORD_LINEFIND_H__