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PSNR (Peak Signal-to-Noise Ratio)


PSNR (Peak Signal-to-Noise Ratio)

PSNR stands for Peak Signal-to-Noise Ratio. It measures how close a processed image or video is to the original, indicating the level of distortion introduced by compression or processing.

What it means

  • Signal: the original (reference) image or video
  • Noise: distortion or errors from compression, transmission, or processing
  • PSNR compares the peak signal value to the distortion

PSNR is expressed in decibels (dB).

Why it matters

  • Higher PSNR → less distortion → better visual quality
  • Lower PSNR → more visible artifacts and degradation

PSNR is widely used in:

  • Image compression (JPEG, PNG, WebP)
  • Video compression (H.264, H.265, AV1)
  • Image and video quality evaluation

Typical PSNR values

  • > 40 dB: Excellent quality, differences nearly invisible
  • 30–40 dB: Good quality, minor differences
  • 20–30 dB: Noticeable degradation
  • < 20 dB: Poor quality, heavy distortion

How it’s calculated 

        
PSNR = 10 · log₁₀( MAX² / MSE )

Where:

  • MAX is the maximum possible pixel value (255 for 8-bit images)
  • MSE is the Mean Squared Error between the original and processed image

Important notes

  • PSNR is simple and fast to compute
  • It does not always align with human visual perception
  • Often used alongside perceptual metrics like SSIM or VMAF

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