PSNR
PSNR (peak signal-to-noise ratio) is a video and image quality metric that measures how much a compressed frame differs from its original, pixel by pixel, expressed in decibels (dB). Higher PSNR means less difference from the source. PSNR is fast and simple to calculate, but it does not always match what human eyes notice.
Why it matters
PSNR is the cheapest way to check encoding quality at scale. It runs fast enough to test every file in a large library and flag broken or badly compressed outputs. Because it does not track human perception well, relying on it alone can lead to the wrong bitrate decisions.
How it works
- Each pixel in the compressed frame is compared with the same pixel in the original frame.
- The average squared difference across the frame, called mean squared error, is calculated.
- That error is compared with the maximum possible pixel value and converted to decibels.
- Frame scores are averaged across the video, and higher values mean less distortion.
What is a good PSNR value for video?
Typical PSNR values for lossy 8-bit video compression fall between about 30 and 50 dB, and higher is better. Values around 40 dB and above usually mean differences are hard to see, while values in the low 30s or below often show visible artifacts. Treat these as rough guides, because the same PSNR can look different from one type of content to another.
Why is PSNR not a good measure of perceived quality?
PSNR treats every pixel difference the same, but human eyes do not. A slight brightness shift across a whole frame can lower PSNR a lot while looking fine, while blur or blocking on a face can matter more than the score suggests. That is why teams pair PSNR with perceptual metrics such as SSIM or VMAF.
Where it's used
OTT services and video platforms run PSNR as a fast automatic check across thousands of files, catching encodes that came out much worse than the source before viewers see them.
By the numbers
- Typical PSNR values in lossy image and video compression are between 30 and 50 dB for 8-bit content, where higher is better. (Wikipedia: Peak signal-to-noise ratio)
