Stirling-PDF/shared-operations/functions/detectEmptyPages.ts
2023-11-08 03:33:22 +03:00

50 lines
1.6 KiB
TypeScript

import { DocumentInitParameters, PDFPageProxy } from "pdfjs-dist/types/src/display/api.js";
import PDFJS from 'pdfjs-dist';
import { Image } from 'image-js';
import { getImagesOnPage } from "./getImagesOnPage.js";
export async function detectEmptyPages(snapshot: string | URL | ArrayBuffer | DocumentInitParameters, whiteThreashold: number) {
const pdfDoc = await PDFJS.getDocument(snapshot).promise;
const emptyPages: number[] = [];
for (let i = 1; i <= pdfDoc.numPages; i++) {
const page = await pdfDoc.getPage(i);
console.log("Checking page " + i);
if(!await hasText(page)) {
console.log(`Found text on Page ${i}, page is not empty`);
continue;
}
if(!await areImagesBlank(page, whiteThreashold)) {
console.log(`Found non white image on Page ${i}, page is not empty`);
continue;
}
console.log(`Page ${i} is empty.`);
emptyPages.push(i - 1);
}
return emptyPages;
}
async function hasText(page: PDFPageProxy): Promise<boolean> {
const textContent = await page.getTextContent();
return textContent.items.length === 0;
}
async function areImagesBlank(page: PDFPageProxy, threshold: number): Promise<boolean> {
const images = await getImagesOnPage(page);
for (const image of images) {
if(!await isImageBlank(image, threshold))
return false;
}
return true;
}
async function isImageBlank(image: string | Uint8Array | ArrayBuffer, threshold: number): Promise<boolean> {
var img = await Image.load(image);
var grey = img.grey();
var mean = grey.getMean();
return mean[0] <= threshold;
}