To capture an element that is taller than 30,000 CSS pixels, render it with a viewport sized to its scroll dimensions, then verify the resulting bitmap against the target browser’s canvas limits. The essential configuration is:
const canvas = await html2canvas(element, {
windowWidth: element.scrollWidth,
windowHeight: element.scrollHeight
});This changes the cloned rendering window; it does not increase the maximum width, height, or total pixel area that the browser permits for a canvas. If the requested bitmap exceeds those limits, lower the effective scale or capture bounded sections and assemble them outside one giant canvas.
Why a very tall html2canvas render becomes blank or truncated
html2canvas does not ask the browser for a native, full-document screenshot. It reconstructs an image by reading the DOM, styles, and resources that it can access. That makes output dependent on supported CSS, same-origin rules, image CORS headers, iframe security, layout, and the destination canvas limits. See the project’s documentation for the rendering model.
The html2canvas FAQ identifies canvas size limits as a common reason a produced canvas is empty or cuts off part way through. A browser may fail during canvas creation without throwing a useful exception. A page can therefore look correct in the DOM while the returned canvas is blank, partially painted, or impossible to export.
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The FAQ gives approximate, undated reference values of about 32,767 pixels for the maximum canvas dimension in Chrome/Chromium, Firefox, and desktop Safari. It also lists rough maximum areas of about 268 million pixels for Chrome/Chromium and 472 million pixels for Firefox. These are guidance values, not guarantees across browser versions, operating systems, devices, or hardware. MDN notes that some iOS environments may limit a canvas to 4096 × 4096 pixels. Check the current target environments rather than treating any figure as a contract.
Area can fail before height does. For example, a 20,000 × 20,000 bitmap is 400 million pixels even though neither dimension reaches 32,767. Conversely, a narrow 32,000-pixel-tall image may fit where a wider one does not. The effective bitmap dimensions also include html2canvas’s scale option, whose default is window.devicePixelRatio.
Measure the document and configure the render window
- Identify the element. Use the element that actually owns the document content, not an outer page shell with unrelated fixed navigation.
- Read its scroll dimensions.
scrollWidthandscrollHeightdescribe the full scrollable content in CSS pixels. - Set the cloned window. Pass those values as
windowWidthandwindowHeightwhen you want the complete element rendered. - Calculate the output size. Multiply the intended CSS width and height by the effective scale, then check both dimensions and total pixels against every target browser.
const element = document.querySelector('#document');
if (!element) throw new Error('Document element was not found');
const cssWidth = element.scrollWidth;
const cssHeight = element.scrollHeight;
const scale = 1; // choose deliberately; the default is devicePixelRatio
const outputWidth = Math.ceil(cssWidth * scale);
const outputHeight = Math.ceil(cssHeight * scale);
const outputPixels = outputWidth * outputHeight;
console.log({ cssWidth, cssHeight, scale, outputWidth, outputHeight, outputPixels });
const canvas = await html2canvas(element, {
windowWidth: cssWidth,
windowHeight: cssHeight,
scale
});
document.body.appendChild(canvas);Use explicit width and height only when you intentionally want a crop or a controlled output size. The windowWidth and windowHeight settings control the cloned/rendered window; they are not a canvas-limit bypass. The official option definitions are in the configuration reference.
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Watch responsive layout changes
Changing the cloned window can activate different media queries, reflow text, reveal or hide navigation, and alter sticky or fixed elements. Compare the clone’s layout with the on-screen document. If the full scroll width causes an unintended desktop breakpoint, deliberately set a width that matches the layout you need and capture the resulting height, rather than assuming the largest possible window is visually correct.
Control scale before the bitmap gets too large
By default, html2canvas uses window.devicePixelRatio. A device-pixel ratio of 2 doubles both dimensions and quadruples pixel area relative to CSS dimensions. A document measuring 16,000 × 20,000 CSS pixels therefore becomes roughly 32,000 × 40,000 pixels at scale 2 and is likely to hit a height or area limit.
Set a lower scale when a single output must fit:
const canvas = await html2canvas(element, {
windowWidth: element.scrollWidth,
windowHeight: element.scrollHeight,
scale: 1
});- Lowering scale reduces memory use and output resolution.
- It cannot rescue a render that already exceeds a hard dimension limit during canvas creation.
- Validate text readability, image sharpness, and export size at the chosen scale.
- Do not infer a safe value from one machine; test each browser/device combination you support.
When one canvas is beyond practical limits: capture sections
If the measured dimensions or area are too large, render separate vertical sections with controlled offsets and dimensions. Keep each canvas comfortably below the smallest limit among your supported environments. Then export the pieces individually or assemble them in a downstream image/PDF pipeline that can handle the desired document format.
Section-capture pattern
async function captureSections(element, sectionCssHeight = 8000) {
const width = element.scrollWidth;
const height = element.scrollHeight;
const sections = [];
for (let y = 0; y < height; y += sectionCssHeight) {
const currentHeight = Math.min(sectionCssHeight, height - y);
const canvas = await html2canvas(element, {
x: 0,
y,
width,
height: currentHeight,
windowWidth: width,
windowHeight: height,
scrollX: 0,
scrollY: y,
scale: 1
});
sections.push({ y, canvas });
}
return sections;
}The exact chunk height is an engineering choice. Leave margin below the suspected browser limit, account for scale, and test with your longest real document. When joining sections, inspect seams at every boundary. A fixed header, sticky toolbar, lazy image, animation, or font that loads between captures can produce repeated or shifted content.
Make chunking deterministic
- Wait for web fonts and images before starting.
- Disable transitions and animations in the clone with custom CSS where necessary.
- Keep the same viewport width for every section so line wrapping does not change.
- Decide whether fixed or sticky elements belong on every section or only the first.
- Record each section’s offset and height so a downstream assembler can place it exactly.
- Test page breaks, tables, positioned elements, and lazy-loaded content at boundaries.
Resources, CORS, and iframe limitations
For images hosted on another origin, useCORS: true only succeeds when that server sends appropriate CORS headers. It does not grant permission by itself. If headers are unavailable, use a same-origin proxy that you control and that is appropriate for the content’s security and licensing.
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const canvas = await html2canvas(element, {
windowWidth: element.scrollWidth,
windowHeight: element.scrollHeight,
useCORS: true,
scale: 1
});A cross-origin iframe cannot be rendered by reading its document because browser security prevents access. Capture content you control inside the frame, obtain a server-side representation, or treat the iframe as an external object rather than expecting html2canvas to reproduce it. The allowTaint option does not make a tainted canvas safely readable; it is not a substitute for CORS.
Extension screenshots versus html2canvas
If you are building a browser extension, the html2canvas FAQ points to native extension screenshot APIs as more reliable and not subject to canvas size limits. Chrome exposes chrome.tabs.captureVisibleTab(); Firefox-compatible extensions use browser.tabs.captureVisibleTab(). These APIs capture the visible tab according to extension permissions and API semantics. They are not a one-call full-document export. You still need scrolling, stitching, or another document strategy for content taller than one viewport.
Performance and reliability checklist
- Memory: canvas memory grows with total pixels and can spike during rendering and encoding. Release section canvases after they are uploaded or merged.
- Encoding:
toDataURL()creates a large string; prefertoBlob()for uploads when supported. - Timing: wait for fonts, images, and application data. A successful promise does not prove that every resource was ready.
- Layout: freeze animations and verify responsive breakpoints at the configured window size.
- Testing: run representative long documents on every browser, operating system, and device class you support.
- Validation: check canvas width/height, file byte size, visible seams, missing images, and text fidelity before declaring success.
Troubleshooting common failures
| Symptom | Likely cause | Fix |
|---|---|---|
| Canvas is completely blank | Dimension or area limit; resource or DOM failure | Log requested dimensions and scale, lower scale, capture sections, then inspect browser console and resource access. |
| Output stops halfway down | Height or total-area limit | Reduce scale if resolution permits; otherwise split by vertical offsets and validate seams. |
| Width is unexpectedly narrow or text wraps differently | Cloned window width triggered a responsive breakpoint | Set an intentional windowWidth, compare layout, and use matching section widths. |
| Images are missing or export throws a security error | Cross-origin image without permitted CORS | Serve the image with CORS headers or use a suitable same-origin proxy; allowTaint is not a fix. |
| An embedded application is absent | Cross-origin iframe security restriction | Capture the iframe separately with authorization or obtain a server-rendered representation. |
| Repeated headers or visible jumps between chunks | Fixed/sticky positioning, animation, or changing content | Freeze the page, define header policy, and inspect every boundary at the final assembly stage. |
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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpimport requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
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| Requirement | Best fit |
|---|---|
| You control a moderate-size DOM and need a client-side image | html2canvas with scroll dimensions and an explicitly tested scale |
| The document exceeds one canvas’s safe area | Section capture with deterministic offsets and downstream assembly |
| You need a visible-tab image in an extension | Native extension screenshot APIs, with scrolling or stitching for full documents |
| You need server-side full-page images or PDFs without browser setup | ScreenshotNeo, especially when consent UI, failed loads, and automated capture billing matter |
There is no universal safe “30,000-pixel” switch. Measure the intended output, include scale in the calculation, test the actual browser/device matrix, and change the capture strategy when one canvas is no longer reliable.
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Frequently Asked Questions
Does setting windowHeight to 100000 make html2canvas support a 100,000-pixel canvas?
No. It enlarges the cloned rendering window only. The browser still enforces its own maximum dimension and total-area limits, so a sectioned capture or another capture method is required when those limits are exceeded.
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Should I always set scale to 1?
No. Scale 1 reduces bitmap size, memory use, and limit pressure, but it also reduces output resolution on high-density displays. Choose it from your required readability and tested browser limits.
Can html2canvas capture a cross-origin iframe if allowTaint is enabled?
No. Browser same-origin security prevents html2canvas from reading a cross-origin iframe document. allowTaint does not bypass that restriction.
Are the FAQ’s 32,767-pixel figures guaranteed for every current browser?
No. They are approximate, undated guidance. Limits vary with browser version, operating system, device, hardware, scale, and available memory; test the environments you support.
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