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Peak Signal-to-Noise Ratio (PSNR) is a common metric used to evaluate the quality of compressed images. It measures the difference between the original and the compressed image, providing an indication of how much quality has been lost during compression.
What is PSNR?
PSNR is expressed in decibels (dB) and compares the maximum possible pixel value of an image to the error introduced by compression. Higher PSNR values generally indicate better image quality, with less distortion.
Calculating PSNR
The calculation of PSNR involves two main steps: computing the Mean Squared Error (MSE) and then converting it to PSNR. The formula for MSE is:
MSE = (1 / (m × n)) × Σ Σ [I(x, y) – K(x, y)]²
where I(x, y) is the original image pixel value, K(x, y) is the compressed image pixel value, and m and n are the dimensions of the images.
Once MSE is calculated, PSNR is determined using the formula:
PSNR = 10 × log₁₀ (MAX² / MSE)
Interpreting PSNR Values
PSNR values typically range from 20 dB to 50 dB. Values above 30 dB are generally considered acceptable for most applications, with higher values indicating better quality. However, perceptual quality may vary depending on the image content and viewer sensitivity.
Applications of PSNR
PSNR is widely used in image compression, video encoding, and transmission systems to evaluate and compare the effectiveness of different algorithms. It provides a quick and objective measure of image fidelity after processing.