Add ability to analyse layout without running recognition (#770)

src/index.d.ts

@@ -70,6 +70,7 @@ declare namespace Tesseract {
   interface OutputFormats {
     text: boolean;
     blocks: boolean;
+    layoutBlocks: boolean;
     hocr: boolean;
     tsv: boolean;
     box: boolean;

src/worker-script/constants/defaultOutput.js

@@ -5,6 +5,7 @@
 module.exports = {
   text: true,
   blocks: true,
+  layoutBlocks: false,
   hocr: true,
   tsv: true,
   box: false,
@@ -14,4 +15,5 @@ module.exports = {
   imageColor: false,
   imageGrey: false,
   imageBinary: false,
+  debug: false,
 };

src/worker-script/index.js

@@ -255,7 +255,7 @@ const processOutput = (output) => {
   if (params.tessjs_create_tsv === '1') workingOutput.tsv = true;
   if (params.tessjs_create_unlv === '1') workingOutput.unlv = true;
 
-  const nonRecOutputs = ['imageColor', 'imageGrey', 'imageBinary'];
+  const nonRecOutputs = ['imageColor', 'imageGrey', 'imageBinary', 'layoutBlocks'];
   let recOutputCount = 0;
   for (const prop of Object.keys(output)) {
     workingOutput[prop] = output[prop];
@@ -267,7 +267,8 @@ const processOutput = (output) => {
       }
     }
   }
-  return { workingOutput, recOutputCount };
+  const skipRecognition = recOutputCount === 0;
+  return { workingOutput, skipRecognition };
 };
 
 // List of options for Tesseract.js (rather than passed through to Tesseract),
@@ -302,7 +303,7 @@ const recognize = async ({
       }
     }
 
-    const { workingOutput, recOutputCount } = processOutput(output);
+    const { workingOutput, skipRecognition } = processOutput(output);
 
     // When the auto-rotate option is True, setImage is called with no angle,
     // then the angle is calculated by Tesseract and then setImage is re-called.
@@ -352,14 +353,17 @@ const recognize = async ({
       api.SetRectangle(rec.left, rec.top, rec.width, rec.height);
     }
 
-    if (recOutputCount > 0) {
+    if (!skipRecognition) {
       api.Recognize(null);
     } else {
+      if (output.layoutBlocks) {
+        api.AnalyseLayout();
+      }
       log('Skipping recognition: all output options requiring recognition are disabled.');
     }
     const { pdfTitle } = options;
     const { pdfTextOnly } = options;
-    const result = dump(TessModule, api, workingOutput, { pdfTitle, pdfTextOnly });
+    const result = dump(TessModule, api, workingOutput, { pdfTitle, pdfTextOnly, skipRecognition });
     result.rotateRadians = rotateRadiansFinal;
 
     if (output.debug) TessModule.FS.unlink('/debugInternal.txt');

src/worker-script/utils/dump.js

@@ -79,7 +79,10 @@ module.exports = (TessModule, api, output, options) => {
     return TessModule.FS.readFile('/tesseract-ocr.pdf');
   };
 
-  if (output.blocks) {
+  // If output.layoutBlocks is true and options.skipRecognition is true,
+  // the user wants layout data but text recognition has not been run.
+  // In this case, fields that require text recognition are skipped.
+  if (output.blocks || output.layoutBlocks) {
     ri.Begin();
     do {
       if (ri.IsAtBeginningOf(RIL_BLOCK)) {
@@ -102,8 +105,8 @@ module.exports = (TessModule, api, output, options) => {
 
         block = {
           paragraphs: [],
-          text: ri.GetUTF8Text(RIL_BLOCK),
-          confidence: ri.Confidence(RIL_BLOCK),
+          text: !options.skipRecognition ? ri.GetUTF8Text(RIL_BLOCK) : null,
+          confidence: !options.skipRecognition ? ri.Confidence(RIL_BLOCK) : null,
           baseline: ri.getBaseline(RIL_BLOCK),
           bbox: ri.getBoundingBox(RIL_BLOCK),
           blocktype: enumToString(ri.BlockType(), 'PT'),
@@ -114,8 +117,8 @@ module.exports = (TessModule, api, output, options) => {
       if (ri.IsAtBeginningOf(RIL_PARA)) {
         para = {
           lines: [],
-          text: ri.GetUTF8Text(RIL_PARA),
-          confidence: ri.Confidence(RIL_PARA),
+          text: !options.skipRecognition ? ri.GetUTF8Text(RIL_PARA) : null,
+          confidence: !options.skipRecognition ? ri.Confidence(RIL_PARA) : null,
           baseline: ri.getBaseline(RIL_PARA),
           bbox: ri.getBoundingBox(RIL_PARA),
           is_ltr: !!ri.ParagraphIsLtr(),
@@ -125,8 +128,8 @@ module.exports = (TessModule, api, output, options) => {
       if (ri.IsAtBeginningOf(RIL_TEXTLINE)) {
         textline = {
           words: [],
-          text: ri.GetUTF8Text(RIL_TEXTLINE),
-          confidence: ri.Confidence(RIL_TEXTLINE),
+          text: !options.skipRecognition ? ri.GetUTF8Text(RIL_TEXTLINE) : null,
+          confidence: !options.skipRecognition ? ri.Confidence(RIL_TEXTLINE) : null,
           baseline: ri.getBaseline(RIL_TEXTLINE),
           bbox: ri.getBoundingBox(RIL_TEXTLINE),
         };
@@ -139,8 +142,8 @@ module.exports = (TessModule, api, output, options) => {
           symbols: [],
           choices: [],
 
-          text: ri.GetUTF8Text(RIL_WORD),
-          confidence: ri.Confidence(RIL_WORD),
+          text: !options.skipRecognition ? ri.GetUTF8Text(RIL_WORD) : null,
+          confidence: !options.skipRecognition ? ri.Confidence(RIL_WORD) : null,
           baseline: ri.getBaseline(RIL_WORD),
           bbox: ri.getBoundingBox(RIL_WORD),
 
@@ -162,8 +165,8 @@ module.exports = (TessModule, api, output, options) => {
         const wc = new TessModule.WordChoiceIterator(ri);
         do {
           word.choices.push({
-            text: wc.GetUTF8Text(),
-            confidence: wc.Confidence(),
+            text: !options.skipRecognition ? wc.GetUTF8Text() : null,
+            confidence: !options.skipRecognition ? wc.Confidence() : null,
           });
         } while (wc.Next());
         TessModule.destroy(wc);
@@ -179,8 +182,8 @@ module.exports = (TessModule, api, output, options) => {
         symbol = {
           choices: [],
           image: null,
-          text: ri.GetUTF8Text(RIL_SYMBOL),
-          confidence: ri.Confidence(RIL_SYMBOL),
+          text: !options.skipRecognition ? ri.GetUTF8Text(RIL_SYMBOL) : null,
+          confidence: !options.skipRecognition ? ri.Confidence(RIL_SYMBOL) : null,
           baseline: ri.getBaseline(RIL_SYMBOL),
           bbox: ri.getBoundingBox(RIL_SYMBOL),
           is_superscript: !!ri.SymbolIsSuperscript(),
@@ -191,8 +194,8 @@ module.exports = (TessModule, api, output, options) => {
         const ci = new TessModule.ChoiceIterator(ri);
         do {
           symbol.choices.push({
-            text: ci.GetUTF8Text(),
-            confidence: ci.Confidence(),
+            text: !options.skipRecognition ? ci.GetUTF8Text() : null,
+            confidence: !options.skipRecognition ? ci.Confidence() : null,
           });
         } while (ci.Next());
         // TessModule.destroy(i);
@@ -212,8 +215,9 @@ module.exports = (TessModule, api, output, options) => {
     imageColor: output.imageColor ? getImage(imageType.COLOR) : null,
     imageGrey: output.imageGrey ? getImage(imageType.GREY) : null,
     imageBinary: output.imageBinary ? getImage(imageType.BINARY) : null,
-    confidence: api.MeanTextConf(),
-    blocks: output.blocks ? blocks : null,
+    confidence: !options.skipRecognition ? api.MeanTextConf() : null,
+    blocks: output.blocks && !options.skipRecognition ? blocks : null,
+    layoutBlocks: output.layoutBlocks && options.skipRecognition ? blocks : null,
     psm: enumToString(api.GetPageSegMode(), 'PSM'),
     oem: enumToString(api.oem(), 'OEM'),
     version: api.Version(),