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Improve content rect detection
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@mrtcode
mrtcode committed Jun 25, 2024
1 parent aff2eb5 commit 51b1ed6
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Showing 2 changed files with 136 additions and 72 deletions.
191 changes: 128 additions & 63 deletions src/core/module/content-rect.js
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Original file line number Diff line number Diff line change
@@ -1,10 +1,9 @@
import { distance } from './lib/levenstein.js';
import { getPageLabel } from './page-label.js';
import { getCenterRect, getClusters, getRectCenter } from './util.js';
import { getCenterRect, getClusters, intersectRects } from './util.js';

// TODO: Take into account horizontal pages

function getLinesFromChars(chars) {
function getLinesFromChars(chars, view) {
let lines = [];
let line = null;
for (let char of chars) {
Expand All @@ -27,87 +26,153 @@ function getLinesFromChars(chars) {
}

for (let line of lines) {
let [x, y] = getCenterRect(line.rect);
line.pageIndex = line.chars[0].pageIndex;
line.text = line.chars.map(x => x.c).join('');
line.centerY = getCenterRect(line.rect)[1];
// line.centerX = x - view[0];
line.centerY = y - view[1];
}
return lines;
}

export async function getContentRect(pdfDocument, structuredCharsProvider) {
let numPages = pdfDocument.catalog.numPages;
let pageIndex = Math.floor(numPages / 2);
let startPage = Math.max(pageIndex - 2, 0);
let endPage = Math.min(pageIndex + 2, numPages - 1);
function getPageSizeIntervals(pages) {
let intervals = [];
let currentInterval = [];

let combinedLines = [];
for (let i = startPage; i <= endPage; i++) {
for (let i = 0; i < pages.length; i++) {
let { view } = pages[i];
let width = view[2] - view[0];
let height = view[3] - view[1];

if (currentInterval.length === 0) {
currentInterval.push(i);
} else {
let lastPageIndex = currentInterval[currentInterval.length - 1];
let { view: lastView } = pages[lastPageIndex];
let lastWidth = lastView[2] - lastView[0];
let lastHeight = lastView[3] - lastView[1];

if (width === lastWidth && height === lastHeight) {
currentInterval.push(i);
} else {
intervals.push(currentInterval);
currentInterval = [i];
}
}
}

if (currentInterval.length > 0) {
intervals.push(currentInterval);
}

return intervals;
}

export async function getContentRects(pdfDocument, structuredCharsProvider, pageLabels) {
let contentRects = [];
let { numPages } = pdfDocument.catalog;

let pages = [];
for (let i = 0; i < numPages; i++) {
let page = await pdfDocument.getPage(i);
pages.push(page);
}

for (let i = 0; i < numPages; i++) {
let { view } = pages[i];
contentRects.push(view.slice());
}

if (numPages > 100) {
return contentRects;
}

let intervals = getPageSizeIntervals(pages);

let maxInterval = intervals.reduce((a, b) => a.length > b.length ? a : b);

if (intervals.length > 3) {
return contentRects;
}

let pageLines = [];

for (let i = 0; i < numPages; i++) {
let { view } = pages[i];
let chars = await structuredCharsProvider(i);
let lines = getLinesFromChars(chars);
combinedLines.push(...lines);
let lines = getLinesFromChars(chars, view);
pageLines.push(lines);
}

let clusters = getClusters(combinedLines, 'centerY', 0.2);
for (let i = 0; i < numPages; i++) {
let pageIndex = i;
let startPage = Math.max(pageIndex - 2, 0);
let endPage = Math.min(pageIndex + 2, numPages - 1);

combinedLines = [];
let combinedLines = [];
for (let i = startPage; i <= endPage; i++) {
let lines = pageLines[i];
combinedLines.push(...lines);
}

for (let cluster of clusters) {
let clusters = getClusters(combinedLines, 'centerY', 0.2);
let removeLines = new Set();
for (let i = 0; i < cluster.length; i++) {
let currentLine = cluster[i];
for (let j = 0; j < cluster.length; j++) {
if (i === j || removeLines.has(i) && removeLines.has(j)) {

for (let cluster of clusters) {
if (cluster.length < 2 || cluster.length > 10) {
continue;
}
for (let i = 0; i < cluster.length; i++) {
let currentLine = cluster[i];
if (currentLine.pageIndex !== pageIndex) {
continue;
}
let otherLine = cluster[j];
let dist = distance(currentLine.text, otherLine.text);
let stringsEqual = dist / currentLine.text.length <= 0.2;
if (stringsEqual) {
removeLines.add(i);
removeLines.add(j);
for (let j = 0; j < cluster.length; j++) {
let otherLine = cluster[j];
if (otherLine.pageIndex === pageIndex) {
continue;
}
let min = Math.min(currentLine.text.length, otherLine.text.length);
let max = Math.max(currentLine.text.length, otherLine.text.length);
if (i === j || removeLines.has(currentLine) || (max - min) / max > 0.2) {
continue;
}
let dist = distance(currentLine.text, otherLine.text);
let stringsEqual = dist / currentLine.text.length <= 0.2;
if (stringsEqual) {
removeLines.add(currentLine);
}
}
}
}
for (let i = 0; i < cluster.length; i++) {
let line = cluster[i];
if (!removeLines.has(i)) {
combinedLines.push(line);
}
}
}

let max = combinedLines.reduce((acc, cur) => cur.rect[0] < acc.rect[0] ? cur : acc, combinedLines[0])
let currentPageLines = [];
for (let line of combinedLines) {
let pageLabel = pageLabels[pageIndex];

let eps = 0.1;
let rect = [
Math.min(...combinedLines.map(x => x.rect[0])) + eps,
Math.min(...combinedLines.map(x => x.rect[1])) + eps,
Math.max(...combinedLines.map(x => x.rect[2])) - eps,
Math.max(...combinedLines.map(x => x.rect[3])) - eps,
];

for (let i = startPage; i <= endPage; i++) {
let pageLabel = await getPageLabel(pdfDocument, structuredCharsProvider, i);
if (!pageLabel) {
continue;
if (
!removeLines.has(line) &&
line.pageIndex === pageIndex &&
// Exclude lines that contain current page label. This can definitely lead to many
// false positives, but most of them are compensated by the final bounding rect calculation,
// which means if false positive is anywhere between other lines, the false positives won't have
// any effect
!(line.text === pageLabel || pageLabel.length >= 2 && line.text.includes(pageLabel)) &&
// Exclude lines that are outside PDF page view box
intersectRects(line.rect, contentRects[pageIndex])
) {
currentPageLines.push(line);
}
}
let { rotate, view } = await pdfDocument.getPage(i);
let width = view[2] - view[0];
let height = view[3] - view[1];

let centerRect = getRectCenter(pageLabel.rect);
if (centerRect[1] < height / 8) {
rect[1] = Math.max(rect[1], pageLabel.rect[3] + eps);
}
else if (centerRect[1] > (height / 8) * 7) {
rect[3] = Math.min(rect[3], pageLabel.rect[1] - eps);
}
let eps = 0.1;
contentRects[i] = [
Math.min(...currentPageLines.map(x => x.rect[0])) + eps,
Math.min(...currentPageLines.map(x => x.rect[1])) + eps,
Math.max(...currentPageLines.map(x => x.rect[2])) - eps,
Math.max(...currentPageLines.map(x => x.rect[3])) - eps,
];
}

let { view } = await pdfDocument.getPage(numPages === 2 ? 1 : 0);
let width = view[2] - view[0];
rect[0] = 0;
// Note: Even if page width/height is the same, some pages, in the same PDF,
// can have bigger mediaBox with a smaller cropBox applied on it
rect[2] = Infinity;
return rect;
return contentRects;
}
17 changes: 8 additions & 9 deletions src/core/module/module.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ import { getLinkOverlays, getRegularLinkOverlays } from './link/link.js';
import { getPageLabels } from './page-label.js';
import { getExistingOutline } from './outline-reader.js';
import { extractOutline } from './outline-extractor.js';
import { getContentRect } from './content-rect.js';
import { getContentRects } from './content-rect.js';
import { intersectRects, overlaysIntersect } from './util.js';
import { getCitationAndReferenceOverlays } from './reference/reference.js';

Expand All @@ -26,14 +26,14 @@ export class Module {

cached = this._temporaryStructuredCharsCache.get(pageIndex);
if (cached) {
if (this._contentRect) {
if (this._contentRects) {
let chars = cached;
for (let char of chars) {
if (!intersectRects(this._contentRect, char.rect)) {
if (!intersectRects(this._contentRects[pageIndex], char.rect)) {
char.isolated = true;
}
}
this._structuredCharsCache.set(pageIndex, chars)
this._structuredCharsCache.set(pageIndex, chars);
this._temporaryStructuredCharsCache.delete(pageIndex);
}
return cached;
Expand Down Expand Up @@ -78,9 +78,9 @@ export class Module {
char.pageIndex = pageIndex;
}

if (this._contentRect) {
if (this._contentRects) {
for (let char of chars) {
if (!intersectRects(this._contentRect, char.rect)) {
if (!intersectRects(this._contentRects[pageIndex], char.rect)) {
char.isolated = true;
}
}
Expand Down Expand Up @@ -108,7 +108,8 @@ export class Module {
async getProcessedData({ metadataPagesField } = {}) {
const MAX_PAGES = 100;
await this._pdfDocument.pdfManager.ensureDoc("numPages");
this._contentRect = await getContentRect(this._pdfDocument, this._structuredCharsProvider);
let pageLabels = await getPageLabels(this._pdfDocument, this._structuredCharsProvider);
this._contentRects = await getContentRects(this._pdfDocument, this._structuredCharsProvider, pageLabels);
let citationAndReferenceOverlays = await getCitationAndReferenceOverlays(this._pdfDocument, this._structuredCharsProvider, 100);

let pages = new Map();
Expand Down Expand Up @@ -153,8 +154,6 @@ export class Module {
page.chars = await this._structuredCharsProvider(pageIndex);
}

let pageLabels = await getPageLabels(this._pdfDocument, this._structuredCharsProvider);

pages = Object.fromEntries(pages);

return { pageLabels, pages };
Expand Down

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