tess4.0中主要的数据结构

1. Page analysis result: PAGE_RES (ccstruct/pageres.h).
2. Page analysis result contains a list of block analysis result field: BLOCK_RES_LIST.
3. Block analysis result: BLOCK_RES (ccstruct/pageres.h).
4. Block analysis result contains a list of row analysis result field: ROW_RES_LIST.
5. Row analysis result: ROW_RES (ccstruct/pageres.h).
6. Row analysis result contains a list of word analysis result field: WERD_RES_LIST.
7. WERD_RES(ccstruct/pageres.h) is a collection of publicly accessible members that gathers information about a word result.

源码分析

Tesseract主要文字识别主要流程：二值化，切分处理，识别，纠错等步骤。本文主要总结二值化和预处理两部分步骤的处理过程。

Page Layout 分析步骤

二值化

• 算法: OTSU
• 调用栈
  1. main[api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages[api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage[api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize[api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines[api/baseapi.cpp] ->
  6. TessBaseAPI::Threshold[api/baseapi.cpp] ->
  7. ImageThresholder::ThresholdToPix[ccmain/thresholder.cpp] ->
  8. ImageThresholder::OtsuThresholdRectToPix [ccmain/thresholder.cpp]

OTSU 是一个全局二值化算法. 如果图片中包含阴影而且阴影不平均，二值化算法效果就会比较差。OCRus利用一个局部的二值化算法，olf Jolion， 对包含有阴影的图片也有比较好的二值化结果。

切分处理

Remove vertical lines

This step removes vertical and horizontal lines in the image.

• 调用栈
  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. Tesseract::SetupPageSegAndDetectOrientation [ccmain/ pagesegmain.cpp]
  9. LineFinder::FindAndRemoveLines [textord/linefind.cpp]

Remove images

This step remove images from the picture.

• 调用栈

  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. Tesseract::SetupPageSegAndDetectOrientation [ccmain/ pagesegmain.cpp]
  9. ImageFind::FindImages [textord/linefind.cpp]

  I never try this function successfully. May be the image needs to satisfy some conditions.

Filter connected component

This step generate all the connected components and filter the noise blobs.

• 调用栈

  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. Tesseract::SetupPageSegAndDetectOrientation [ccmain/ pagesegmain.cpp] ->
  9. (i) Textord::find_components [textord/tordmain.cpp] ->

  {
      extract_edges[textord/edgblob.cpp] //extract outlines and assign outlines to blobs
      assign_blobs_to_blocks2[textord/edgblob.cpp] //assign normal, noise, rejected blobs to TO_BLOCK_LIST for further filter blobs operations
      Textord::filter_blobs[textord/tordmain.cpp] ->
      Textord::filter_noise_blobs[textord/tordmain.cpp] //Move small blobs to a separate list
  }
  

  (ii) ColumnFinder::SetupAndFilterNoise [textord/colfind.cpp]

  This step will generate the intermediate result, refer to http://blog.csdn.net/kaelsass/article/details/46874627

Finding candidate tab-stop components

• 调用栈

  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. ColumnFinder::FindBlocks [textord/ colfind.cpp] ->
  9. TabFind::FindInitialTabVectors[textord/tabfind.cpp] ->
  10. TabFind::FindTabBoxes [textord/tabfind.cpp]

  This step finds the initial candidate tab-stop CCs by a radial search starting at every filtered CC from preprocessing. Results can refer to http://blog.csdn.net/kaelsass/article/details/46874627

Finding the column layout

• 调用栈

  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. ColumnFinder::FindBlocks [textord/ colfind.cpp] ->
  9. ColumnFinder::FindBlocks (begin at line 369) [textord/ colfind.cpp]

  This step finds the column layout of the page

Finding the regions

• 调用栈

  1. main [api/tesseractmain.cpp] ->
  2. TessBaseAPI::ProcessPages [api/baseapi.cpp] ->
  3. TessBaseAPI::ProcessPage [api/baseapi.cpp] ->
  4. TessBaseAPI::Recognize [api/baseapi.cpp] ->
  5. TessBaseAPI::FindLines [api/baseapi.cpp] ->
  6. Tesseract::SegmentPage [ccmain/pagesegmain.cpp] ->
  7. Tesseract::AutoPageSeg [ccmain/ pagesegmain.cpp] ->
  8. ColumnFinder::FindBlocks [textord/ colfind.cpp]

  This step recognizes the different type of blocks