Image Quality Checker
Compare two images and get objective PSNR & SSIM scores — useful for checking how much a compressor, resize or format conversion actually changed the picture.
Original image
Drop image here
The reference / source file
Comparison image
Drop image here
The compressed, resized or converted version
What PSNR and SSIM tell you
PSNR (Peak Signal-to-Noise Ratio) measures raw pixel-level difference in decibels — good for catching compression noise and color banding.
SSIM (Structural Similarity Index) instead models how humans perceive structure, contrast and luminance — it correlates better with what you'd actually notice by eye.
Typical PSNR reference points
- > 40 dBVisually lossless
- 30 – 40 dBGood, minor artifacts
- 20 – 30 dBNoticeable loss
- < 20 dBHeavy degradation
Frequently Asked Questions
Do the two images need to be the same size?
No — the comparison image is automatically resampled onto the original's grid before scoring, so you can compare a resized or re-compressed version directly.
Which score should I trust more?
SSIM generally tracks perceived quality more closely than PSNR. Use PSNR as a secondary sanity check, especially for flat/low-detail images where SSIM can be less sensitive.
Are my images uploaded anywhere?
No. Both images are decoded and compared entirely inside your browser using the Canvas API — nothing is sent to a server.
Why did my score change slightly on a re-run?
It shouldn't — the comparison is deterministic. If you see a difference, you likely swapped which file is "original" vs "comparison", which changes the reference grid.