9.1

Edit

Improve OCR results

What are quality requirements of an input document?

Scanned images can require pre-processing prior to recognition, for example, if scanned documents contain background noise, skewed text, inverted colors, black margins, wrong orientation or resolution. The recommended resolution for a source image: 300 dpi for typical texts (10pt or larger) and 400-600 dpi for texts in smaller fonts (9pt or smaller).

For brightness recommendations, see the table below.

Your image looks like thisRecommendations
The image is suitable for recognition.
Lower the brightness to make the image darker.
Increase the brightness to make the image brighter.

Why PDF searchable document is preferable for recognition than high dpi image created from it?

OCR analyzes internal information within the source PDF files such as annotations, metadata, text objects, font dictionaries, content stream. OCR enhances PDF conversion performance and speed by efficient and accurate text selection. If text is embedded into the PDF file, the OCR engine examines the integrity of the text layer and makes a decision as to whether or not to extract the text or apply OCR on a block by block bases.

Why we should cache OCR results?

ABBYY OCR is part of WorkFusion Product. The way WF partners with ABBYY requires licensing for every commercial user whom we re-sell OCR capability. License cost is based on pages/images processed. This is why it is important to avoid re-processing of exactly the same files.

WorkFusion core feature is exposure business Processes as use Cases allows us to create and distribute OCR sub-process, which contains a solution for caching.

The caching approach is as follows.

  1. For the file you need to OCR, calculate unique hash based on the binary of this file.
  2. The Query Data Store should have this hash.
    • If NO, execute OCR. Write a new hash with OCR results to Data Store.
    • If YES, get OCR results from Data Store.

How to improve OCR results?

  1. For preprocessing, use ImageMagick or GhostScript: convert -colorspace rgb -density 300 input.pdf -monochrome output.tif.
  2. Use PDF searchable document instead of high dpi image created from it.
  3. Use a custom dictionary.
  4. Use the removeGarbageSize parameter for scanned images to remove garbage (excess dots that are smaller than a certain size) from the image
  5. Use the allowedRegionTypes parameter to exclude incorrect region types.
  6. Use xml:writeRecognitionVariants to understand the recognition problems

Example #1

Step #1 (default properties)

file

exportFormat = html, xml

Output results:

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head><meta http-equiv="content-type" content="text/html; charset=UTF-8"/><meta name="generator" content="ABBYY FineReader 11"/><link rel="stylesheet" href="result-html-065017dc-46f5-4c8f-a0bc-4b8996f6d9fb.css" type="text/css"/>
    </head>
    <body style="background-color:#FFFFFF;"><img src="result-html-065017dc-46f5-4c8f-a0bc-4b8996f6d9fb-1.png" style="width:497pt;height:54pt;"/>
    </body>
</html>

XML

<document xmlns="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" languages="" producer="Workfusion" version="1.0" xsi:schemaLocation="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml">
   <page height="80" originalCoords="1" resolution="96" width="682">
      <block b="75" blockName="" blockType="Picture" l="13" r="676" t="3">
         <region>
            <rect b="75" l="13" r="676" t="3" />
         </region>
      </block>
      <block b="19" blockName="" blockType="Separator" l="312" r="389" t="14">
         <region>
            <rect b="16" l="323" r="389" t="14" />
            <rect b="17" l="319" r="389" t="16" />
            <rect b="18" l="312" r="389" t="17" />
            <rect b="19" l="312" r="319" t="18" />
         </region>
         <separator thickness="1" type="Black">
            <start x="312" y="16" />
            <end x="389" y="16" />
         </separator>
      </block>
      <block b="21" blockName="" blockType="Separator" l="46" r="81" t="19">
         <region>
            <rect b="21" l="46" r="81" t="19" />
         </region>
         <separator thickness="1" type="Black">
            <start x="46" y="20" />
            <end x="81" y="20" />
         </separator>
      </block>
      <block b="26" blockName="" blockType="Separator" l="408" r="496" t="20">
         <region>
            <rect b="21" l="408" r="429" t="20" />
            <rect b="22" l="408" r="454" t="21" />
            <rect b="23" l="429" r="492" t="22" />
            <rect b="24" l="454" r="492" t="23" />
            <rect b="25" l="435" r="492" t="24" />
            <rect b="26" l="435" r="496" t="25" />
         </region>
         <separator thickness="2" type="Black">
            <start x="408" y="23" />
            <end x="496" y="23" />
         </separator>
      </block>
      <block b="31" blockName="" blockType="Separator" l="549" r="588" t="30">
         <region>
            <rect b="31" l="549" r="588" t="30" />
         </region>
         <separator thickness="1" type="Black">
            <start x="549" y="30" />
            <end x="588" y="30" />
         </separator>
      </block>
      <block b="61" blockName="" blockType="Separator" l="111" r="169" t="58">
         <region>
            <rect b="59" l="111" r="169" t="58" />
            <rect b="60" l="111" r="164" t="59" />
            <rect b="61" l="128" r="164" t="60" />
         </region>
         <separator thickness="1" type="Black">
            <start x="111" y="59" />
            <end x="169" y="59" />
         </separator>
      </block>
   </page>
</document>

You can see that by default OCR recognize this text with garbage like an image (see the html output img tag). The XML format more is informative for you to see recognized block types: Picture and Separator.

Step #2.A (default + removeGarbageSize properties)

Try to remove garbage and see if the result changes.

removeGarbageSize=1

Output results:

Federal Credit Union, July 25, 2005

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head><meta http-equiv="content-type" content="text/html; charset=UTF-8"/><meta name="generator" content="ABBYY FineReader 11"/><link rel="stylesheet" href="result-html-171a0901-d71c-4f21-a96a-db1dfc18adda.css" type="text/css"/>
    </head>
    <body style="background-color:#FFFFFF;">
        <p><span class="font0">Federal Credit Union, July 25, 2005</span></p>
    </body>
</html>

XML

<document xmlns="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" languages="" producer="Workfusion" version="1.0" xsi:schemaLocation="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml">
   <page height="80" originalCoords="1" resolution="96" width="682">
      <block b="69" blockName="" blockType="Text" l="13" r="678" t="10">
         <region>
            <rect b="69" l="13" r="678" t="10" />
         </region>
         <text>
            <par lineSpacing="2330">
               <line b="62" baseline="54" l="15" r="676" t="23">
                  <formatting lang="EnglishUnitedStates">Federal Credit Union, July 25, 2005</formatting>
               </line>
            </par>
         </text>
      </block>
      <block b="19" blockName="" blockType="Separator" l="312" r="389" t="14">
         <region>
            <rect b="16" l="323" r="389" t="14" />
            <rect b="17" l="319" r="389" t="16" />
            <rect b="18" l="312" r="389" t="17" />
            <rect b="19" l="312" r="319" t="18" />
         </region>
         <separator thickness="1" type="Black">
            <start x="312" y="16" />
            <end x="389" y="16" />
         </separator>
      </block>
      <block b="21" blockName="" blockType="Separator" l="46" r="81" t="19">
         <region>
            <rect b="21" l="46" r="81" t="19" />
         </region>
         <separator thickness="1" type="Black">
            <start x="46" y="20" />
            <end x="81" y="20" />
         </separator>
      </block>
      <block b="26" blockName="" blockType="Separator" l="408" r="496" t="20">
         <region>
            <rect b="21" l="408" r="429" t="20" />
            <rect b="22" l="408" r="454" t="21" />
            <rect b="23" l="429" r="492" t="22" />
            <rect b="24" l="454" r="492" t="23" />
            <rect b="25" l="435" r="492" t="24" />
            <rect b="26" l="435" r="496" t="25" />
         </region>
         <separator thickness="2" type="Black">
            <start x="408" y="23" />
            <end x="496" y="23" />
         </separator>
      </block>
      <block b="31" blockName="" blockType="Separator" l="549" r="588" t="30">
         <region>
            <rect b="31" l="549" r="588" t="30" />
         </region>
         <separator thickness="1" type="Black">
            <start x="549" y="30" />
            <end x="588" y="30" />
         </separator>
      </block>
      <block b="61" blockName="" blockType="Separator" l="111" r="169" t="58">
         <region>
            <rect b="59" l="111" r="169" t="58" />
            <rect b="60" l="111" r="164" t="59" />
            <rect b="61" l="128" r="164" t="60" />
         </region>
         <separator thickness="1" type="Black">
            <start x="111" y="59" />
            <end x="169" y="59" />
         </separator>
      </block>
   </page>
</document>

You can see the block type was changed from Picture to Text, and the image has been recognized successfully.

Step #2.B (default + allowedRegionTypes properties)

Usage of allowedRegionTypes.

note

Be careful using the allowedRegionTypes properties as it may break the original document layout.

You can choose the second way to fix the previous problem. Exclude the Picture block type from allowed regions.

allowedRegionTypes=BT_Table,BT_Text,BT_Barcode,BT_Separator,BT_SeparatorGroup,BT_Checkmark,BT_CheckmarkGroup

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head><meta http-equiv="content-type" content="text/html; charset=UTF-8"/><meta name="generator" content="ABBYY FineReader 11"/><link rel="stylesheet" href="result-html-2ec5f1e3-143e-46f9-a533-1dafc7b7519c.css" type="text/css"/>
    </head>
    <body style="background-color:#FFFFFF;">
        <table border="1">
            <tr>
                <td style="vertical-align:bottom;"><p><span class="font0">Federal CreditUnion, July 25, 2005</span></p></td>
            </tr>
        </table>
    </body>
</html>

XML

<document xmlns="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" languages="" producer="Workfusion" version="1.0" xsi:schemaLocation="http://ocr.crowdcomputingsystems.com/xml/schema-v1.xml">
   <page height="80" originalCoords="1" resolution="96" width="682">
      <block b="19" blockName="" blockType="Separator" l="312" r="389" t="14">
         <region>
            <rect b="16" l="323" r="389" t="14" />
            <rect b="17" l="319" r="389" t="16" />
            <rect b="18" l="312" r="389" t="17" />
            <rect b="19" l="312" r="319" t="18" />
         </region>
         <separator thickness="1" type="Black">
            <start x="312" y="16" />
            <end x="389" y="16" />
         </separator>
      </block>
      <block b="21" blockName="" blockType="Separator" l="46" r="81" t="19">
         <region>
            <rect b="21" l="46" r="81" t="19" />
         </region>
         <separator thickness="1" type="Black">
            <start x="46" y="20" />
            <end x="81" y="20" />
         </separator>
      </block>
      <block b="26" blockName="" blockType="Separator" l="408" r="496" t="20">
         <region>
            <rect b="21" l="408" r="429" t="20" />
            <rect b="22" l="408" r="454" t="21" />
            <rect b="23" l="429" r="492" t="22" />
            <rect b="24" l="454" r="492" t="23" />
            <rect b="25" l="435" r="492" t="24" />
            <rect b="26" l="435" r="496" t="25" />
         </region>
         <separator thickness="2" type="Black">
            <start x="408" y="23" />
            <end x="496" y="23" />
         </separator>
      </block>
      <block b="31" blockName="" blockType="Separator" l="549" r="588" t="30">
         <region>
            <rect b="31" l="549" r="588" t="30" />
         </region>
         <separator thickness="1" type="Black">
            <start x="549" y="30" />
            <end x="588" y="30" />
         </separator>
      </block>
      <block b="61" blockName="" blockType="Separator" l="111" r="169" t="58">
         <region>
            <rect b="59" l="111" r="169" t="58" />
            <rect b="60" l="111" r="164" t="59" />
            <rect b="61" l="128" r="164" t="60" />
         </region>
         <separator thickness="1" type="Black">
            <start x="111" y="59" />
            <end x="169" y="59" />
         </separator>
      </block>
      <block b="75" blockName="" blockType="Table" l="13" r="676" t="3">
         <region>
            <rect b="75" l="13" r="676" t="3" />
         </region>
         <row>
            <cell bottomBorder="White" height="72" leftBorder="White" rightBorder="White" topBorder="White" width="663">
               <text>
                  <par lineSpacing="2330">
                     <line b="62" baseline="54" l="15" r="676" t="23">
                        <formatting lang="EnglishUnitedStates">Federal CreditUnion, July 25, 2005</formatting>
                     </line>
                  </par>
               </text>
            </cell>
         </row>
      </block>
   </page>
</document>

Example #2

Step #1 (default properties)

file =

Output results:

Facility Namer Nortfawoods Home Health and Hospice
Cit> : Lancaster
State r NH

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head><meta http-equiv="content-type" content="text/html; charset=UTF-8"/><meta name="generator" content="ABBYY FineReader 11"/><link rel="stylesheet" href="result-html-efc7eed8-a91c-42ab-9f13-7bf0ba9419f0.css" type="text/css"/>
    </head>
    <body style="background-color:#FFFFFF;">
        <p><span class="font0">Facility Namer Nortfawoods Home Health and Hospice Cit&gt; : Lancaster&nbsp;State r NH</span></p>
    </body>
</html>

Step #2 (default properties + image preprocessing)

Improve vertical and horizontal density of the image (dpi) using the ImageMagick conversion tool command.

convert -colorspace rgb -density 250 example2.png example2-250.tif

file = example2-250.tif

Output results:

Facility Name: Northwoods Home Health and Hospice
City: Lancaster
State :NH

Example #3

Step #1 (default properties)

file =

Output results:

Step #2 (default properties + customRegions)

Single table was split into two tables. To fix the issue, try to use:

customRegions =  [ { "type": "BT_Table " ,  "left":0, "top":0, "right":10000, "bottom":10000} ]  //select full page like a table

tip

For more details, see also OCR FAQ.

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