Squished images have a simple cause: width and height were changed by different proportions somewhere between the source image, the html2canvas bitmap, and jsPDF placement. Check each stage, then derive one output dimension from the other. If the source is sourceWidth × sourceHeight and the PDF width is pdfWidth, use pdfHeight = pdfWidth * sourceHeight / sourceWidth.
Find the stage that changes the aspect ratio
There are two separate failure branches. The image may already be distorted in the canvas produced by html2canvas, or the canvas may be correct while jsPDF stretches it when placing it in the PDF. A third class of problem—blank, missing, or clipped images—is usually caused by cross-origin restrictions or canvas limits, not by aspect ratio.
- Inspect the source image’s intrinsic dimensions. For an
<img>, logimg.naturalWidthandimg.naturalHeight. - Inspect the captured canvas with
canvas.widthandcanvas.height. View the canvas itself before converting it to a PDF. - If the canvas is distorted, investigate the DOM dimensions, CSS, viewport settings, and html2canvas options.
- If the canvas looks correct, inspect the dimensions passed to
doc.addImage()or the scaling options used bydoc.html().
Measure the ratios
Calculate naturalWidth / naturalHeight, canvas.width / canvas.height, and the final PDF placement ratio. The first ratio that differs materially from the intended ratio identifies where to fix the code.
const img = document.querySelector('#photo');
console.log({
source: [img.naturalWidth, img.naturalHeight],
sourceRatio: img.naturalWidth / img.naturalHeight
});
const canvas = await html2canvas(document.querySelector('#capture'));
console.log({
bitmap: [canvas.width, canvas.height],
bitmapRatio: canvas.width / canvas.height
});Fix distortion when placing a canvas with addImage()
addImage() accepts an independent width and height. If those values imply a different ratio from the source, jsPDF will stretch the bitmap. A reported issue involving fixed dimensions of 65 × 60 mm illustrates the symptom; it does not mean every call with those values is wrong.
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Derive the PDF height from the source ratio
Choose one dimension and calculate the other. The units must match the jsPDF document’s units (for example, millimetres or points).
const canvas = await html2canvas(document.querySelector('#capture'), {
useCORS: true
});
const sourceWidth = canvas.width;
const sourceHeight = canvas.height;
const pdfWidth = 180; // millimetres in this example
const pdfHeight = pdfWidth * sourceHeight / sourceWidth;
const doc = new jspdf.jsPDF({ unit: 'mm', format: 'a4' });
doc.addImage(canvas.toDataURL('image PNG'), 'PNG', 15, 15, pdfWidth, pdfHeight);
doc.save('export.pdf');If you prefer to fix the height, use pdfWidth = pdfHeight * sourceWidth / sourceHeight. Do not independently tune both numbers until the ratio matches.
Use the displayed element ratio when that is intentional
If the design intentionally crops an image with CSS, decide whether the PDF should preserve the uncropped source or reproduce the displayed crop. For a faithful crop, capture the element as rendered and place the resulting canvas at its canvas ratio. For the complete original image, capture the image itself and calculate placement from its intrinsic dimensions.
Fix distortion during html2canvas capture
html2canvas has separate controls for bitmap resolution, canvas dimensions, viewport dimensions, and cropping. Changing one does not automatically preserve another.
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scale changes resolution, not PDF geometry
scale controls the rendering scale and defaults to window.devicePixelRatio. A higher value can improve sharpness, but it is not an aspect-ratio formula. Keep the same proportional width and height when setting explicit dimensions.
width, height, x, and y
width and height set canvas dimensions; x and y are crop offsets. Setting only one dimension or combining values copied from a different layout can make the captured result appear squeezed. Start without these overrides, then add only the control you need.
windowWidth and windowHeight
These define the window used while rendering and can change responsive layout and media-query results. If a tall or wide element is empty or cut off, try its scroll dimensions:
const element = document.querySelector('#capture');
const canvas = await html2canvas(element, {
windowWidth: element.scrollWidth,
windowHeight: element.scrollHeight,
scale: window.devicePixelRatio
});Do not confuse windowWidth with CSS media-query behavior in the jsPDF HTML plugin; that plugin uses it for the actual container size, while its documentation says it does not alter CSS media queries.
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Using doc.html() without a stretched result
The jsPDF HTML plugin’s width option is the target width in jsPDF units. The rendered element is scaled to fit that width, but the option has no effect when html2canvas.scale is specified or when windowWidth is not specified, according to the current plugin documentation. Check those conditions when changing width appears to do nothing.
const doc = new jspdf.jsPDF({ unit: 'mm', format: 'a4' });
doc.html(document.querySelector('#capture'), {
x: 15,
y: 15,
width: 180,
windowWidth: document.querySelector('#capture').scrollWidth,
callback: (pdf) => pdf.save('export.pdf')
});When you need exact image placement, capturing with html2canvas and using addImage() gives you explicit control over both dimensions. When you need the HTML plugin’s pagination and layout, verify its width, window, and html2canvas settings together rather than changing scale alone.
Blank, missing, or clipped images are different problems
Cross-origin images
html2canvas cannot safely read cross-origin images unless the image server permits it. useCORS: true works only when the server sends an appropriate Access-Control-Allow-Origin header. Otherwise, host the asset on the same origin or use a same-origin proxy.
const canvas = await html2canvas(element, {
useCORS: true,
backgroundColor: '#ffffff'
});A CORS failure commonly produces a blank image or a security exception, not a stretched one. Fix the origin and response headers before adjusting dimensions.
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Canvas size limits
Browser limits vary and change with browser versions and device memory. The html2canvas FAQ gives rough context: Chrome/Chromium and desktop Safari are around 32,767 pixels per dimension; Chrome/Chromium is about 268 megapixels of area and Firefox about 472 megapixels. iOS Safari can be lower depending on RAM. Treat these as approximate limits, not guarantees. Reduce scale, split long content into pages, or capture smaller regions when a canvas is blank or truncated.
Unsupported CSS
html2canvas implements CSS properties manually and does not support every property equally. Reduce the page to a small reproducible case and check whether the layout itself is rendered differently before changing PDF dimensions.
A repeatable export recipe
- Wait for images and fonts to finish loading before capture.
- Record intrinsic image dimensions and the element’s rendered dimensions.
- Capture with html2canvas using proportional dimensions; use
scaleonly for resolution. - Inspect the canvas visually and log its dimensions.
- Choose a PDF width or height and derive the other from the canvas ratio.
- Place the image, then verify it at 100% zoom in the generated PDF.
- For multi-page documents, calculate available page height and start a new page instead of squeezing the image to fit.
Performance, reliability, and cost considerations
- Higher
scalemultiplies pixel count and memory use. Use the smallest scale that meets print or display requirements. - Very tall pages are more likely to hit browser canvas limits; split them logically rather than creating one enormous bitmap.
- Cache or reuse a captured canvas when generating several PDF formats, but keep an eye on memory for large bitmaps.
- Client-side html2canvas depends on
window,document, and computed styles. It is not a server-side screenshot engine; server workflows generally require a real browser such as Puppeteer or Playwright. - Confirm the installed jsPDF and html2canvas versions because their living documentation and defaults can change.
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r.raise_for_status()
open("shot.webp", "wb").write(r.content)Node.js
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Troubleshooting checklist
| Symptom | Likely cause | Fix |
|---|---|---|
| Canvas already looks squeezed | DOM or capture dimensions differ | Inspect CSS, remove arbitrary width/height overrides, and check viewport settings. |
| Canvas is correct, PDF is squeezed | Independent addImage() dimensions |
Derive height or width from the canvas ratio. |
doc.html() width seems ignored |
Conflicting html2canvas.scale or missing windowWidth |
Review the plugin’s documented conditions and set a consistent container width. |
| Image is blank | Cross-origin restriction or failed load | Wait for the image, enable useCORS with valid response headers, or proxy it. |
| Bottom or sides are cut off | Viewport mismatch or canvas limit | Match window dimensions to scroll dimensions, lower scale, or paginate. |
| Layout differs from the browser | Unsupported CSS or responsive breakpoint | Use a reproducible test case and adjust supported CSS or viewport dimensions. |
Frequently Asked Questions
Does increasing html2canvas scale fix a squished image?
No. Scale changes bitmap resolution. It can improve sharpness but does not correct independently chosen PDF width and height.
Which dimensions should I log first?
Log the image’s naturalWidth and naturalHeight, then canvas.width and canvas.height, followed by the dimensions passed to jsPDF.
Can html2canvas generate PDFs on a server without a browser?
No. It depends on browser APIs such as window and document. A server workflow needs a real browser automation tool or a screenshot service.
Quick Recap
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