///////////////////////////////////////////////////////////////////////

// File:        ccnontextdetect.cpp

// Description: Connected-Component-based photo (non-text) detection.

// Author:      rays@google.com (Ray Smith)

//

// Copyright 2011 Google Inc. All Rights Reserved.

// 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.

//

///////////////////////////////////////////////////////////////////////

#ifdef HAVE_CONFIG_H

#  include "config_auto.h"

#endif

#include "ccnontextdetect.h"

#include "helpers.h"         // for IntCastRounded

#include "imagefind.h"

#include "strokewidth.h"

namespace tesseract {

// Max number of neighbour small objects per squared gridsize before a grid

// cell becomes image.

const double kMaxSmallNeighboursPerPix = 1.0 / 32;

// Max number of small blobs a large blob may overlap before it is rejected

// and determined to be image.

const int kMaxLargeOverlapsWithSmall = 3;

// Max number of small blobs a medium blob may overlap before it is rejected

// and determined to be image. Larger than for large blobs as medium blobs

// may be complex Chinese characters. Very large Chinese characters are going

// to overlap more medium blobs than small.

const int kMaxMediumOverlapsWithSmall = 12;

// Max number of normal blobs a large blob may overlap before it is rejected

// and determined to be image. This is set higher to allow for drop caps, which

// may overlap a lot of good text blobs.

const int kMaxLargeOverlapsWithMedium = 12;

// Multiplier of original noise_count used to test for the case of spreading

// noise beyond where it should really be.

const int kOriginalNoiseMultiple = 8;

// Pixel padding for noise blobs when rendering on the image

// mask to encourage them to join together. Make it too big and images

// will fatten out too much and have to be clipped to text.

const int kNoisePadding = 4;

// Fraction of max_noise_count_ to be added to the noise count if there is

// photo mask in the background.

const double kPhotoOffsetFraction = 0.375;

// Min ratio of perimeter^2/16area for a "good" blob in estimating noise

// density. Good blobs are supposed to be highly likely real text.

// We consider a square to have unit ratio, where A=(p/4)^2, hence the factor

// of 16. Digital circles are weird and have a minimum ratio of pi/64, not

// the 1/(4pi) that you would expect.

const double kMinGoodTextPARatio = 1.5;

CCNonTextDetect::CCNonTextDetect(int gridsize, const ICOORD &bleft, const ICOORD &tright)

    : BlobGrid(gridsize, bleft, tright)

    , max_noise_count_(static_cast<int>(kMaxSmallNeighboursPerPix * gridsize * gridsize))

    , noise_density_(nullptr) {

  // TODO(rays) break max_noise_count_ out into an area-proportional

  // value, as now plus an additive constant for the number of text blobs

  // in the 3x3 neighbourhood - maybe 9.

}

CCNonTextDetect::~CCNonTextDetect() {

  delete noise_density_;

}

// Creates and returns a Pix with the same resolution as the original

// in which 1 (black) pixels represent likely non text (photo, line drawing)

// areas of the page, deleting from the blob_block the blobs that were

// determined to be non-text.

// The photo_map is used to bias the decision towards non-text, rather than

// supplying definite decision.

// The blob_block is the usual result of connected component analysis,

// holding the detected blobs.

// The returned Pix should be PixDestroyed after use.

Image CCNonTextDetect::ComputeNonTextMask(bool debug, Image photo_map, TO_BLOCK *blob_block) {

  // Insert the smallest blobs into the grid.

  InsertBlobList(&blob_block->small_blobs);

  InsertBlobList(&blob_block->noise_blobs);

  // Add the medium blobs that don't have a good strokewidth neighbour.

  // Those that do go into good_grid as an antidote to spreading beyond the

  // real reaches of a noise region.

  BlobGrid good_grid(gridsize(), bleft(), tright());

  BLOBNBOX_IT blob_it(&blob_block->blobs);

  for (blob_it.mark_cycle_pt(); !blob_it.cycled_list(); blob_it.forward()) {

    BLOBNBOX *blob = blob_it.data();

    double perimeter_area_ratio = blob->cblob()->perimeter() / 4.0;

    perimeter_area_ratio *= perimeter_area_ratio / blob->enclosed_area();

    if (blob->GoodTextBlob() == 0 || perimeter_area_ratio < kMinGoodTextPARatio) {

      InsertBBox(true, true, blob);

    } else {

      good_grid.InsertBBox(true, true, blob);

    }

  }

  noise_density_ = ComputeNoiseDensity(debug, photo_map, &good_grid);

  good_grid.Clear(); // Not needed any more.

  Image pix = noise_density_->ThresholdToPix(max_noise_count_);

  if (debug) {

    pixWrite("junknoisemask.png", pix, IFF_PNG);

  }

  ScrollView *win = nullptr;

#ifndef GRAPHICS_DISABLED

  if (debug) {

    win = MakeWindow(0, 400, "Photo Mask Blobs");

  }

#endif // !GRAPHICS_DISABLED

  // Large and medium blobs are not text if they overlap with "a lot" of small

  // blobs.

  MarkAndDeleteNonTextBlobs(&blob_block->large_blobs, kMaxLargeOverlapsWithSmall, win,

                            ScrollView::DARK_GREEN, pix);

  MarkAndDeleteNonTextBlobs(&blob_block->blobs, kMaxMediumOverlapsWithSmall, win, ScrollView::WHITE,

                            pix);

  // Clear the grid of small blobs and insert the medium blobs.

  Clear();

  InsertBlobList(&blob_block->blobs);

  MarkAndDeleteNonTextBlobs(&blob_block->large_blobs, kMaxLargeOverlapsWithMedium, win,

                            ScrollView::DARK_GREEN, pix);

  // Clear again before we start deleting the blobs in the grid.

  Clear();

  MarkAndDeleteNonTextBlobs(&blob_block->noise_blobs, -1, win, ScrollView::CORAL, pix);

  MarkAndDeleteNonTextBlobs(&blob_block->small_blobs, -1, win, ScrollView::GOLDENROD, pix);

  MarkAndDeleteNonTextBlobs(&blob_block->blobs, -1, win, ScrollView::WHITE, pix);

  if (debug) {

#ifndef GRAPHICS_DISABLED

    win->Update();

#endif // !GRAPHICS_DISABLED

    pixWrite("junkccphotomask.png", pix, IFF_PNG);

#ifndef GRAPHICS_DISABLED

    win->AwaitEvent(SVET_DESTROY);

    delete win;

#endif // !GRAPHICS_DISABLED

  }

  return pix;

}

// Computes and returns the noise_density IntGrid, at the same gridsize as

// this by summing the number of small elements in a 3x3 neighbourhood of

// each grid cell. good_grid is filled with blobs that are considered most

// likely good text, and this is filled with small and medium blobs that are

// more likely non-text.

// The photo_map is used to bias the decision towards non-text, rather than

// supplying definite decision.

IntGrid *CCNonTextDetect::ComputeNoiseDensity(bool debug, Image photo_map, BlobGrid *good_grid) {

  IntGrid *noise_counts = CountCellElements();

  IntGrid *noise_density = noise_counts->NeighbourhoodSum();

  IntGrid *good_counts = good_grid->CountCellElements();

  // Now increase noise density in photo areas, to bias the decision and

  // minimize hallucinated text on image, but trim the noise_density where

  // there are good blobs and the original count is low in non-photo areas,

  // indicating that most of the result came from neighbouring cells.

  int height = pixGetHeight(photo_map);

  int photo_offset = IntCastRounded(max_noise_count_ * kPhotoOffsetFraction);

  for (int y = 0; y < gridheight(); ++y) {

    for (int x = 0; x < gridwidth(); ++x) {

      int noise = noise_density->GridCellValue(x, y);

      if (max_noise_count_ < noise + photo_offset && noise <= max_noise_count_) {

        // Test for photo.

        int left = x * gridsize();

        int right = left + gridsize();

        int bottom = height - y * gridsize();

        int top = bottom - gridsize();

        if (ImageFind::BoundsWithinRect(photo_map, &left, &top, &right, &bottom)) {

          noise_density->SetGridCell(x, y, noise + photo_offset);

        }

      }

      if (debug && noise > max_noise_count_ && good_counts->GridCellValue(x, y) > 0) {

        tprintf("At %d, %d, noise = %d, good=%d, orig=%d, thr=%d\n", x * gridsize(), y * gridsize(),

                noise_density->GridCellValue(x, y), good_counts->GridCellValue(x, y),

                noise_counts->GridCellValue(x, y), max_noise_count_);

      }

      if (noise > max_noise_count_ && good_counts->GridCellValue(x, y) > 0 &&

          noise_counts->GridCellValue(x, y) * kOriginalNoiseMultiple <= max_noise_count_) {

        noise_density->SetGridCell(x, y, 0);

      }

    }

  }

  delete noise_counts;

  delete good_counts;

  return noise_density;

}

// Helper to expand a box in one of the 4 directions by the given pad,

// provided it does not expand into any cell with a zero noise density.

// If that is not possible, try expanding all round by a small constant.

static TBOX AttemptBoxExpansion(const TBOX &box, const IntGrid &noise_density, int pad) {

  TBOX expanded_box(box);

  expanded_box.set_right(box.right() + pad);

  if (!noise_density.AnyZeroInRect(expanded_box)) {

    return expanded_box;

  }

  expanded_box = box;

  expanded_box.set_left(box.left() - pad);

  if (!noise_density.AnyZeroInRect(expanded_box)) {

    return expanded_box;

  }

  expanded_box = box;

  expanded_box.set_top(box.top() + pad);

  if (!noise_density.AnyZeroInRect(expanded_box)) {

    return expanded_box;

  }

  expanded_box = box;

  expanded_box.set_bottom(box.bottom() + pad);

  if (!noise_density.AnyZeroInRect(expanded_box)) {

    return expanded_box;

  }

  expanded_box = box;

  expanded_box.pad(kNoisePadding, kNoisePadding);

  if (!noise_density.AnyZeroInRect(expanded_box)) {

    return expanded_box;

  }

  return box;

}

// Tests each blob in the list to see if it is certain non-text using 2

// conditions:

// 1. blob overlaps a cell with high value in noise_density_ (previously set

// by ComputeNoiseDensity).

// OR 2. The blob overlaps more than max_blob_overlaps in *this grid. This

// condition is disabled with max_blob_overlaps == -1.

// If it does, the blob is declared non-text, and is used to mark up the

// nontext_mask. Such blobs are fully deleted, and non-noise blobs have their

// neighbours reset, as they may now point to deleted data.

// WARNING: The blobs list blobs may be in the *this grid, but they are

// not removed. If any deleted blobs might be in *this, then this must be

// Clear()ed immediately after MarkAndDeleteNonTextBlobs is called.

// If the win is not nullptr, deleted blobs are drawn on it in red, and kept

// blobs are drawn on it in ok_color.

void CCNonTextDetect::MarkAndDeleteNonTextBlobs(BLOBNBOX_LIST *blobs, int max_blob_overlaps,

                                                ScrollView *win, ScrollView::Color ok_color,

                                                Image nontext_mask) {

  int imageheight = tright().y() - bleft().x();

  BLOBNBOX_IT blob_it(blobs);

  BLOBNBOX_LIST dead_blobs;

  BLOBNBOX_IT dead_it(&dead_blobs);

  for (blob_it.mark_cycle_pt(); !blob_it.cycled_list(); blob_it.forward()) {

    BLOBNBOX *blob = blob_it.data();

    TBOX box = blob->bounding_box();

    if (!noise_density_->RectMostlyOverThreshold(box, max_noise_count_) &&

        (max_blob_overlaps < 0 || !BlobOverlapsTooMuch(blob, max_blob_overlaps))) {

      blob->ClearNeighbours();

#ifndef GRAPHICS_DISABLED

      if (win != nullptr) {

        blob->plot(win, ok_color, ok_color);

      }

#endif // !GRAPHICS_DISABLED

    } else {

      if (noise_density_->AnyZeroInRect(box)) {

        // There is a danger that the bounding box may overlap real text, so

        // we need to render the outline.

        Image blob_pix = blob->cblob()->render_outline();

        pixRasterop(nontext_mask, box.left(), imageheight - box.top(), box.width(), box.height(),

                    PIX_SRC | PIX_DST, blob_pix, 0, 0);

        blob_pix.destroy();

      } else {

        if (box.area() < gridsize() * gridsize()) {

          // It is a really bad idea to make lots of small components in the

          // photo mask, so try to join it to a bigger area by expanding the

          // box in a way that does not touch any zero noise density cell.

          box = AttemptBoxExpansion(box, *noise_density_, gridsize());

        }

        // All overlapped cells are non-zero, so just mark the rectangle.

        pixRasterop(nontext_mask, box.left(), imageheight - box.top(), box.width(), box.height(),

                    PIX_SET, nullptr, 0, 0);

      }

#ifndef GRAPHICS_DISABLED

      if (win != nullptr) {

        blob->plot(win, ScrollView::RED, ScrollView::RED);

      }

#endif // !GRAPHICS_DISABLED

      // It is safe to delete the cblob now, as it isn't used by the grid

      // or BlobOverlapsTooMuch, and the BLOBNBOXes will go away with the

      // dead_blobs list.

      // TODO: remove next line, currently still needed for resultiterator_test.

      delete blob->remove_cblob();

      dead_it.add_to_end(blob_it.extract());

    }

  }

}

// Returns true if the given blob overlaps more than max_overlaps blobs

// in the current grid.

bool CCNonTextDetect::BlobOverlapsTooMuch(BLOBNBOX *blob, int max_overlaps) {

  // Search the grid to see what intersects it.

  // Setup a Rectangle search for overlapping this blob.

  BlobGridSearch rsearch(this);

  const TBOX &box = blob->bounding_box();

  rsearch.StartRectSearch(box);

  rsearch.SetUniqueMode(true);

  BLOBNBOX *neighbour;

  int overlap_count = 0;

  while (overlap_count <= max_overlaps && (neighbour = rsearch.NextRectSearch()) != nullptr) {

    if (box.major_overlap(neighbour->bounding_box())) {

      ++overlap_count;

      if (overlap_count > max_overlaps) {

        return true;

      }

    }

  }

  return false;

}

} // namespace tesseract.