Use LambdaTest SmartUI to capture a baseline and a new screenshot under matching test conditions, then review the dashboard’s diff. Compare the same page and state at the same viewport in each browser you intend to support; a difference between browsers is not automatically a defect, but an unexpected change within a browser-and-viewport combination may be.
How SmartUI screenshot comparison works
SmartUI compares a newly captured screenshot with a saved baseline and highlights visual differences in the dashboard. The current product documentation is branded across LambdaTest and TestMu AI properties; exact navigation labels can change, so follow the current SmartUI project and build interface rather than relying on an outdated click path. The TestMu AI (formerly LambdaTest) Guided Walkthrough of SmartUI, last updated September 11, 2026, describes the baseline and captured views, diff layers, annotations, Strict mode, and Smart Ignore.
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The comparison is a triage aid, not a verdict. A diff may reveal a real layout or styling regression, or reflect a page that was captured at a different state, dynamic data, loading, animation, or rendering variation. Review the changed area in context before accepting or rejecting it.
Set up a repeatable comparison
1. Create a project and establish a baseline
Create a SmartUI project for the application, then capture the page or component state you want to use as the reference. Give each screenshot a stable, meaningful name, such as checkout-payment-form. The Selenium integration guide recommends matching the screenshot name used for a new capture to the baseline name so SmartUI can pair them.
#1 Best Overall
2. Choose browser and viewport variants
Select browsers and viewport sizes based on your product’s audience and support policy. LambdaTest’s Selenium example lists Chrome, Firefox, Safari, and Edge; its walkthrough also illustrates Chrome, Firefox, Edge, and Playwright WebKit variants. These are examples in the documentation, not a guarantee of the complete current support matrix. Record the actual browser and version for each run, and keep viewport dimensions or device profiles consistent when comparing a new capture with its baseline.
Use the same browser and viewport to assess whether a build changed. Cross-browser testing is still valuable, but Chrome and Firefox, for example, are not expected to render every detail identically. Compare each browser’s result against its own appropriate baseline instead of treating one browser’s screenshot as a universal pixel-perfect reference.
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3. Capture a stable page state
Call the SmartUI snapshot at the point in the Selenium test when the page is ready for visual review. Prefer an explicit ready condition—such as the relevant component appearing and data finishing its update—over an arbitrary long sleep. The integration documentation describes wait settings for slower pages and asynchronous or lazy-loaded content; use a fixed delay only when a dependable ready condition is unavailable or insufficient. Keep URL, login state, test data, and interaction flow the same between runs.
4. Run the test and review the build
Run the test using the documented SmartUI CLI integration, then open the build results. The dashboard presents the baseline and captured screenshots and highlights mismatches. Inspect the changed regions, use the available diff views or annotations to understand them, and decide whether each change is an intended update or a regression. Promote or accept a baseline change only after review; a newly captured build is not automatically the correct reference.
The SmartUI walkthrough describes Strict mode for emphasizing exact pixel mismatches and Smart Ignore for hiding displacement differences. Choose the comparison behavior that fits the review: strict pixel detail is useful when precision matters, while displacement handling can help focus attention on content changes. Neither mode replaces review of what changed.
Control noisy or dynamic regions
When a region changes legitimately between runs—for example, a timestamp or rotating content—stabilize the test data first if practical. If that is not possible, the Selenium SDK documentation describes selecting or excluding DOM elements using IDs, classes, CSS selectors, or XPath. Apply these controls narrowly and document why an area is excluded: a broad ignore can hide a real regression in the same region.
Animations, delayed resources, and font or rendering variation can also produce diffs that are not user-facing defects. Wait for the intended state, avoid capturing mid-animation, and verify the relevant page conditions before changing the comparison settings. If an apparent change is limited to a different browser or viewport, confirm the baseline was created for that same variant.
What to keep consistent between captures
| Comparison factor | What to match or record | Why it matters |
|---|---|---|
| Screenshot identity | Use the same stable screenshot name for the same page or component. | SmartUI’s documented workflow uses matching names to pair captures with baselines. |
| Browser and version | Compare a run with a baseline from the same browser; record the actual version. | Browsers and rendering engines can differ. A cross-browser variation is not by itself a regression. |
| Viewport or device | Keep dimensions or device profile aligned with the baseline. | A changed capture size can cause layout differences unrelated to a code change. |
| Page state | Keep URL, data, login state, and interaction step consistent. | A screenshot of a different state is not an apples-to-apples visual comparison. |
| Comparison mode | Use Strict mode for exact pixel mismatches or Smart Ignore when displacement handling is appropriate. | The mode affects how differences are presented; it does not determine whether they are defects. |
| Baseline updates | Review changes before accepting a new reference. | Automatic acceptance can turn an unintended change into the new expected appearance. |
Common problems and fixes
- No baseline match: Check that the new capture uses the same stable name and belongs to the intended project and browser/viewport variant.
- Many unrelated differences: Verify viewport, page state, data, and capture timing first. Stabilize dynamic content or use a narrow ignore control only for legitimate variation.
- Lazy-loaded content is missing or shifted: Wait for the relevant elements or asynchronous content to finish loading before the snapshot. The SDK guide describes wait settings for slow pages and lazy-loaded components.
- Differences appear only in one browser: Review that browser’s own baseline and inspect the actual browser/version. Do not assume another browser’s rendering should be pixel-identical.
- A diff hides a potentially important change: Revisit ignore selectors and Smart Ignore usage; remove overly broad exclusions and inspect the region in the captured image.
- Unclear current UI labels or browser availability: Consult the current SmartUI documentation for the project, configuration, and supported environment details; product branding and supported options may change.
Or skip the browser setup
If you need a screenshot image or PDF without configuring a cloud browser test, ScreenshotNeo provides a website screenshot API and MCP server. Its API takes one GET request with a URL; cookie/consent banners, newsletter popups, and chat widgets are removed before capture, and each of those steps can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed; response headers report the page verdict and billing status. AI agents can use its MCP server with the take_screenshot, get_page_info, and capture_pdf tools. The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000 shots.
For example, save a WebP screenshot of Stripe with cURL (replace the key with your API key):
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. The API supports PNG, JPEG, WebP, and PDF output, plus options such as viewport and device presets, full-page capture, element selection, waits, custom CSS and JavaScript, request blocking, caching, and bulk capture. It captures a page; it does not replace SmartUI’s named baselines and visual-diff review workflow for cross-browser regression testing.
Sign up for ScreenshotNeo’s free plan to get 1,000 screenshots a month with no card.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Frequently Asked Questions
Can one browser’s screenshot serve as the baseline for every other browser?
No. Keep a suitable baseline for each browser and viewport variant you intend to compare; browser rendering is not expected to be pixel-identical across engines.
Does Smart Ignore prove that a visual difference is harmless?
No. It changes how displacement differences are handled. Review the affected content and confirm the change is acceptable.
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