Before / after slider
Before / after slider puts two images in one frame with a draggable divider. Retouching checks, compression A/B, “is this crop better.” The images should be the same size or you will be comparing layout as much as content.
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Compare & Measure
Compare two images with a slider or a pixel-difference map, or turn pixel dimensions into print size at a DPI, locally, no upload.
Runs in your browser · Nothing uploaded
- Before / after sliderCompare two images with a draggable divider.Runs in your browser · Nothing uploaded
- Pixel differenceHeatmap of differences between two images.Runs in your browser · Nothing uploaded
- DPI / print sizePixels ↔ inches/cm at a given DPI.Runs in your browser · Nothing uploaded
About Compare & Measure
Compare is for answering “did this export change anything” and “will this print at 8 inches.” The slider is for a human look. The difference map is for when you want the pixels that changed to light up. DPI is arithmetic on the dimensions you already have.
None of these send the pair to a “visual QA” service. If the screenshots are from an unreleased app, that's the point.
The slider and the diff need two files. DPI needs one image plus a number you type.
Tools in this category
Pixel difference
Pixel difference builds a heatmap of where two images disagree. Useful after a re-encode or a supposedly lossless round-trip. It isn't a legal exhibit and it will scream about a one-pixel shift if the canvases aren't aligned.
DPI / print size
DPI / print size converts pixels to inches or centimetres at a DPI you type. It doesn't resample the image. 300 DPI on a 600-pixel-wide file is a 2-inch print, not a sudden 3000-pixel file.
Common questions
When should I use the slider instead of the difference map?
Slider when you care how it looks. Difference map when you care whether any pixel changed, compression tests, “did this tool actually do something.” If the map is noise, the images aren't aligned or the encode is lossy. That's information.
Does the DPI tool change my image?
No. It tells you how large those pixels print at a given DPI. To actually have more pixels, use Resize, and understand that upscaling is invention, not capture.
Are the two images uploaded to compute a diff?
No. Both stay in the tab. The heatmap is computed from decoded pixels in memory. You can turn the network off after the page loads and it still works.
Why these tools don't upload your files
There is no server to upload to. Each page is a static file, and the work happens in your browser. Your file is read from disk into memory, processed, and handed back as a download. Once the page has loaded you can disconnect from the network and it keeps working. The longer explanation