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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteUse ImageMagick’s compare command to generate a visual difference image, report a numeric metric, or do both. First make sure the two screenshots show the same page state at the same size; then choose a metric that matches what you want to measure.
Compare two screenshots and save a difference image
ImageMagick compares the images pixel by pixel, starting from their page offsets (typically the top-left). In this command, reference.png is the baseline and current.png is the newer capture:
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magick compare reference.png current.png difference.pngOpen difference.png to inspect the changed regions. The compare command creates a visual annotation of the differences. See the official compare documentation.
Save the image and report a metric
Choose a metric with -metric to print a numeric result as well as save the annotated image:
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magick compare -metric AE reference.png current.png difference.pngThe metric is written to the command’s output. Its meaning depends on the metric you select; it is not a universal pass/fail score.
Report only a metric
Use null: as the output when you do not need a saved difference image:
magick compare -metric RMSE reference.png current.png null:ImageMagick documents the command-line tools and the compare command.
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Make the screenshots comparable before running the command
ImageMagick compares the files it receives; it does not make their browser captures equivalent. Capture both pages with the same viewport width and height, browser zoom, device scale, scroll position, and page state. Allow fonts, images, animations, and asynchronously loaded content to settle before capturing.
- Confirm both screenshots show the intended URL, content, and state.
- Check that neither capture has a different scroll position or browser zoom.
- Wait for delayed assets and dynamic content to finish loading, or capture again if they have not.
- Compare image dimensions before interpreting a large difference count.
When dimensions differ, ImageMagick aligns the smaller image with the larger; unmatched areas can be treated as virtual pixels and affect the result. For visual regression checks, matching dimensions is usually easier to interpret. The defines reference documents compare:virtual-pixels, which can limit comparison to authentic pixels:
magick compare -define compare:virtual-pixels=false reference.png current.png difference.pngChoose a metric that answers your question
ImageMagick offers metrics that measure different properties. Pick one based on whether you care about the number of pixels crossing a tolerance, the magnitude of color errors, or structural similarity. The options and metrics reference and compare documentation describe the available metrics.
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| Metric | What it tells you | Useful when |
|---|---|---|
AE (Absolute Error) |
Count of differing pixels; affected by -fuzz. |
You want to count pixels that differ under the selected tolerance. |
PDC |
Count of pixels that differ; affected by -fuzz. |
You need a differing-pixel count and have chosen a suitable tolerance. |
MAE |
Average absolute channel error, normalized. | You want an average error measure across the image. |
RMSE |
Root mean squared difference, normalized. | You want an overall error measure that gives larger errors more influence. |
SSIM / DSSIM |
Structural similarity / structural dissimilarity measures. | You want a structural or perceptual summary rather than an exact count of unequal pixels. |
NCC |
Normalized cross-correlation; ImageMagick describes similarity as corresponding to 1. | You use cross-correlation and account for its different direction: higher similarity, rather than zero difference, is the relevant interpretation. |
An average error can understate a severe but small localized change. A structural metric does not answer exactly the same question as a pixel count. State the metric and its meaning when reporting a result, and do not treat any one threshold as universally meaningful.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteIgnore small color differences with fuzz
The -fuzz option makes colors within a specified distance count as equal for relevant comparisons. For example, this counts differing pixels while allowing a 5% fuzz tolerance:
magick compare -metric AE -fuzz 5% reference.png current.png difference.pngImageMagick’s comparison examples use fuzz to discount minor changes, such as artifacts from lossy JPEG encoding. A fuzz percentage is not a universal tolerance for browser-rendering variation. Tune it for your inputs and inspect the output: a tolerance that hides harmless noise can also conceal a meaningful small change. See the ImageMagick comparison usage guide and options reference.
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Make changed regions easier to inspect
The annotated output is useful for locating changes, but small differences may be visually subtle. Set the colors used for highlighted differences and unchanged regions with -highlight-color and -lowlight-color:
magick compare -highlight-color red -lowlight-color white reference.png current.png difference.pngFor a different view, the ImageMagick Difference composition subtracts the darker input color from the lighter, producing black where colors match. The usage guide demonstrates normalizing a difference image to make low-level changes easier to see. A blend can make small changes more visible, but does not replace a metric or explain whether the difference matters.
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magick composite -compose difference reference.png current.png difference-blend.pngSee the composition-method reference and comparison usage guide.
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Interpret and report the result
- Verify that both files represent the intended page state and viewport.
- Check image dimensions and page alignment before treating the metric as evidence of a layout change.
- Inspect the visual difference to distinguish a broad shift from small pixel noise.
- Report the metric by name and explain what it measures.
- If you used
-fuzz, record the value and check whether it hides changes you consider important. - Repeat the captures if fonts, animations, dynamic content, or delayed assets made the inputs inconsistent.
Troubleshooting common comparison problems
The difference image shows changes everywhere
First check dimensions, alignment, scroll position, zoom, and page state. Different font loading, animation frames, or dynamic content can also make captures diverge. Correct the capture conditions and rerun the comparison before raising fuzz.
The metric is high even though the page looks similar
A pixel-level count can react to many small color changes. Inspect the annotated image, then decide whether a measured tolerance is appropriate. Record the metric and fuzz setting rather than presenting the number without context.
A small but important change is hard to see
Use a more visible highlight color or create a Difference composition, then normalize the difference image as shown in ImageMagick’s comparison guide. Do not assume a low average error rules out a localized defect.
The files have different dimensions
Prefer recapturing them at matching dimensions. If you need to compare only authentic pixels, try -define compare:virtual-pixels=false; unmatched regions otherwise can affect the comparison.
Or skip the browser setup
If you need consistent screenshot files to compare, ScreenshotNeo returns a screenshot or PDF from one GET request. After capturing the two page states, you can use the ImageMagick commands above to inspect their differences.
Quick Recap
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. Cookie banners are accepted and 60+ known consent platforms, newsletter popups, and chat widgets are removed before the shot; each step can be turned off. Bot checks/CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report page verdict and billing status. AI agents can use its MCP server, with tools including take_screenshot, get_page_info, and capture_pdf. The Free plan includes 1,000 shots a month with no card; paid plans start at $5 for 3,000 shots. Sign up for free.
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