Image Comparison Slider

Compare two images side by side with an interactive before/after slider.

Tested tool guide Tested browser tools Checked August 16, 2026

What Image Comparison Slider does and how it behaves

Image Comparison Slider places a before image and an after image in one interactive comparison view. Moving the divider changes how much of each version is visible, making differences near the boundary easy to inspect. The images remain separate; the slider does not blend them into a new image. The most common surprise is that useful comparison depends on alignment. Images taken from different positions, cropped differently, or shown at different proportions can appear to change even when the underlying subject has not.

How the result is produced

Setting the pair

Choose the two images that represent the states being compared. Their selection order establishes the before and after roles in the comparison. Because the files are handled within the browser, they are not uploaded for processing. For a meaningful reveal, prepare both images with the same crop, orientation, and subject position before loading them.

Reading the reveal

Drag the comparison control to move the boundary across the shared view. Moving it in one direction exposes more of one image and correspondingly less of the other. The boundary position controls visibility only. It is not a similarity score, a measurement of how much changed, or an indication that one version is better.

Good uses

Compare an original portrait with a retouched version while checking localized edits around facial features, hair, or clothing.
Review renovation photographs taken from the same fixed viewpoint to inspect changes to walls, fixtures, finishes, or landscaping.
Place two matching interface screenshots together to examine the visible effect of a layout, color, typography, or spacing revision.

Limits and checks

Confirm that both images depict the same framing. A shifted camera, different crop, or changed aspect ratio can prevent corresponding details from meeting at the slider boundary.
Do not interpret the divider's midpoint as a 50 percent image change. It means only that the viewing area is divided between the two source images.
Treat apparent differences cautiously when exposure, lighting, compression, or capture conditions changed. The slider reveals visible variation but cannot identify what caused that variation.

Common questions

Do the two images need to have identical dimensions?

For the clearest comparison, use identical pixel dimensions and matching aspect ratios. More importantly, the same subject should occupy the same coordinates in both files. If one image is resized or cropped differently, the divider may join unrelated details. Matching dimensions alone will not correct a camera movement, perspective change, or differently positioned subject.

Can the slider tell me how many pixels changed?

No. Its result is an interactive visual reveal, not a numerical image-difference analysis. It can help a person notice where two aligned versions differ, but it does not provide a changed-pixel count, similarity percentage, tolerance threshold, or statistical judgment. Use a dedicated pixel-diff or image-analysis tool when a quantified result is required.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.