Compare images

Drop two versions of a picture and see exactly what changed — drag the slider, flick between them, zoom in to the pixel and read how close they are as PSNR and SSIM.

About this tool

See Every Difference Between Two Pictures

Built for checking exports, compression settings, edits and upscales — both images stay on your device.

Four Ways to Look

A before/after slider (vertical or horizontal), side by side, a toggle that can flicker between the two, and a difference view that shows only what changed, amplified up to 64×.

Zoom to the Pixel

Scroll, pinch or use the buttons to zoom to 100 % or 200 %; every view zooms and pans together, so you always look at the same spot in both pictures. Keyboard: + and − zoom, 0 fits, arrow keys pan.

Numbers You Can Quote

PSNR in dB and SSIM (Wang et al. 2004, 11 × 11 Gaussian window), plus the largest difference and the share of changed pixels, computed in a background worker. Pictures of different sizes are stretched or fitted to the first one.

How to use it

  1. Drop two images, or one now and the second after it. The first is the reference (A).
  2. If the sizes differ, choose whether B is stretched to A or fitted inside it.
  3. Switch between Slider, Side by side, Toggle and Difference, and zoom in where it matters.
  4. Read PSNR, SSIM and the share of changed pixels in the panel.

Frequently asked questions

Are my images uploaded to a server?

No. Every image is decoded, processed and encoded inside your browser tab with Canvas, Web Workers and WebAssembly. Nothing is uploaded, stored or logged.

What do PSNR and SSIM mean?

PSNR (peak signal-to-noise ratio) measures the average pixel error in decibels: higher is closer, and above about 40 dB differences are hard to see. SSIM (structural similarity) compares local brightness, contrast and structure from −1 to 1, where 1 is identical and values above 0.95 usually look the same.

Can I compare images of different sizes?

Yes. B is either stretched to A's size or fitted inside it, keeping its shape; the numbers are measured on the area both pictures cover. Very large pictures are measured at up to 16 megapixels.

How does the difference view work?

It subtracts the two pictures pixel by pixel, so identical areas turn black and changes light up. Raise the amplification to make faint compression artefacts or a slight colour shift visible.

Which formats can I compare?

PNG, JPG, WebP, AVIF and GIF, plus HEIC, TIFF and camera RAW files, which are converted in your browser first. Transparent areas are compared as if both pictures sat on white.

Is it free, and is there a watermark?

Yes, it is free to use without an account, and Toolula never adds a watermark. The free plan has fair-use limits; Toolula Pro, an optional plan, raises them.