What a before and after slider shows
A comparison slider places two versions of an image in the same frame and lets you drag a divider across it. On one side of the line you see the first image, on the other side you see the second. Moving the line reveals how the two differ at exactly the same position, which is far easier than flipping between two separate files.
This is a visual check, not a measurement. It will not give you a numerical score for how different the images are. What it does well is make differences you can see, such as softness, color shifts, banding, noise or missing detail, easy to notice by comparing the same area side by side.
For the comparison to be meaningful, both images should show the same scene. If they are framed differently, the divider will cut across mismatched content.
When comparing two images helps
The most common use is judging an edit. After applying a filter, retouching a photo or correcting color, you can drag across the original and the result to see what actually changed.
It is also helpful for checking compression and resizing. If you shrink a file with the Image Compressor, you can load the original as "before" and the compressed file as "after" to see whether the savings cost you visible quality. The same idea works for a resized version from the Image Resizer, or for any pair of drafts, renders or screenshots.
How to compare two images with this tool
- Under Before image, drag in or choose your first image.
- Under After image, drag in or choose the second one.
- Once both are loaded, they appear together in one frame. The before image shows on the left of the divider and the after image on the right. The divider starts in the middle.
- On a computer, press and hold the mouse button inside the frame and move sideways to drag the divider. On a touch screen, drag your finger across the frame.
- Release to leave the divider where it is.
Both images are shown only in your browser and are not uploaded by this tool.
Limits to keep in mind
The frame has a fixed widescreen (16:9) shape, and both images are scaled to fill it. Any part that does not fit the frame is cropped, so a tall portrait photo will lose its top and bottom edges in the view. That means you are comparing what is visible in the frame, not the full pictures, and fine details at the edges may be hidden.
Because each image is stretched to fill the same frame, two pictures with different pixel dimensions are scaled differently before you see them. Pixel-level differences caused by size changes will therefore be hard to judge here. For an honest comparison, use two versions with the same dimensions and aspect ratio.
The slider has no download or export button, no zoom, and no way to swap the two images once loaded. To start over with different files, reload the page.