Feat/pdf dpi option

src/app.ts

@@ -120,7 +120,7 @@ function setUp(op: ToolOp) {
   // Every tool that runs outside the qpdf worker. Engines load on first use.
   const LOCAL: Partial<Record<ToolOp, LocalJob>> = {
     'jpg-to-pdf': async (f) => (await import('./engine/local')).imagesToPdf(f),
-    'pdf-to-jpg': async (f, o) => (await import('./engine/local')).pdfToImages(f[0], o.format === 'png' ? 'png' : 'jpg'),
+        'pdf-to-jpg': async (f, o) => (await import('./engine/local')).pdfToImages(f[0], o.format === 'png' ? 'png' : 'jpg', Number(o.dpi) || 150),
     'page-numbers': async (f, o) =>
       (await import('./engine/stamp')).addPageNumbers(f[0], {
         position: o.position as 'bottom-center' | 'bottom-right' | 'top-right',

src/engine/local.ts

@@ -118,8 +118,8 @@ export async function imagesToPdf(files: File[]): Promise<Output> {
   };
 }
 
-/** Renders every page to a JPEG (or PNG) at 150 DPI with pdf.js; several pages come back as a ZIP. */
-export async function pdfToImages(file: File, format: 'jpg' | 'png' = 'jpg'): Promise<Output> {
+/** Renders every page to a JPEG (or PNG) at `dpi` (150 by default) with pdf.js; several pages come back as a ZIP. */
+export async function pdfToImages(file: File, format: 'jpg' | 'png' = 'jpg', dpi = 150): Promise<Output> {
   const pdfjs = await import('pdfjs-dist/legacy/build/pdf.mjs'); // legacy = polyfilled for browsers from 2023 on
   pdfjs.GlobalWorkerOptions.workerSrc = (await import('pdfjs-dist/legacy/build/pdf.worker.min.mjs?url')).default;
   let doc;
@@ -135,7 +135,7 @@ export async function pdfToImages(file: File, format: 'jpg' | 'png' = 'jpg'): Pr
   let last: Blob | undefined;
   for (let number = 1; number <= doc.numPages; number++) {
     const page = await doc.getPage(number);
-    const viewport = page.getViewport({ scale: 150 / 72 });
+    const viewport = page.getViewport({ scale: dpi / 72 }); // PDF units are 1/72 inch
     const canvas = new OffscreenCanvas(Math.ceil(viewport.width), Math.ceil(viewport.height));
     const context = canvas.getContext('2d')!;
     context.fillStyle = '#fff'; // JPEG has no transparency; PDFs assume white paper.

src/i18n.ts

@@ -165,6 +165,7 @@ export const UI = {
   'ws.startAt': 'Start at',
   'ws.targetKb': 'Max file size (KB)',
   'ws.targetAny': 'No limit',
+  'ws.dpiLow': 'Low (smallest file, for the web)',
   'ws.dpiStandard': 'Standard (smaller file)',
   'ws.dpiHigh': 'High (sharper small print)',
   'ws.look': 'Look',

src/seo.ts

@@ -256,6 +256,8 @@ function optionsHtml(c: Copy, tool: Tool) {
     <label>${esc(c.t('ws.saveAs'))}<select name="format">${option('txt', c.t('ws.fmtTxt'))}${option('srt', c.t('ws.fmtSrt'), tool.preset?.format === 'srt')}${option('vtt', c.t('ws.fmtVtt'))}</select></label>
     <p class="note">${esc(c.t('ws.speechEnglish'))}</p>
     <p class="note">${esc(c.t('ws.speechModel', { mb: SPEECH_MODEL_MB }))}</p>`;
+  if (tool.op === 'pdf-to-jpg')
+    return `<label>${esc(c.t('ws.quality'))}<select name="dpi">${option('72', c.t('ws.dpiLow'))}${option('150', c.t('ws.dpiStandard'), true)}${option('300', c.t('ws.dpiHigh'))}</select></label>`; 
   if (tool.op === 'excel-to-json') return `<label class="check"><input name="header" type="checkbox" checked> ${esc(c.t('ws.header'))}</label>`;
   if (tool.op === 'compress-pdf' || tool.op === 'office-compress')
     return `<label>${esc(c.t('ws.compression'))}<select name="level">${option('light', c.t('ws.balanced'))}${option('strong', c.t('ws.strong'))}</select></label>`;

tests/app.e2e.ts

@@ -830,6 +830,19 @@ test('numbers and watermarks PDF pages, and converts between image formats', asy
   await page.getByRole('button', { name: 'Convert to PNG' }).click();
   await expect(page.locator('#status')).toContainText('Done');
   expect((await downloadBytes(page)).name).toMatch(/\.(png|zip)$/);
+
+  // The resolution select sets the image size: a 400 pt wide page is 400 px at 72 DPI, 834 at 150 and 1667 at 300.
+  for (const [dpi, width] of [['72', 400], ['150', 834], ['300', 1667]] as const) {
+    await page.goto('/pdf-to-png/');
+    await expect(page.locator('select[name="dpi"]')).toHaveValue('150');
+    await page.locator('#file-input').setInputFiles(fixture('blank'));
+    await page.locator('select[name="dpi"]').selectOption(dpi);
+    await page.getByRole('button', { name: 'Convert to PNG' }).click();
+    await expect(page.locator('#status')).toContainText('Done — 1 image');
+    const png = await downloadBytes(page);
+    expect(png.name).toBe('blank.png');
+    expect(png.bytes.readUInt32BE(16)).toBe(width);
+  }
 
   await page.goto('/png-to-jpg/');
   await expect(page.locator('select[name="format"]')).toHaveCount(0);