AJ schrieb:
> Hi All,
>
> I was hoping someone would be able to explain why something I have
> noticed during some image processing analysis occurs.
>
> When I am working with extremely degraded images, and am trying
> different techniques to improve them, I often measure the PSNR (Peak
> Signal-to-Noise Ratio) of the degraded image against the original,
> undamaged image. Often, I find that the techniques that give the best
> (highest) PSNR dB value are NOT the ones that give the best subjective
> quality i.e. I chose restoration techniques that give a lower PSNR
> because they LOOK better.
>
> Can anyone explain why this happens?
PSNR relates bad to human vision. You should try different metrics
with a better correlation to subjective quality.
Recommendations: MS-SSIM (Sheik & Bovik) works quite ok (though not
great),
VDP (Daly's Visual Difference Predictor) works much better, though it is
grey-scale only and it is extremely slow.
> Maybe it is something to do with
> the fact that the image quality of the degraded image is so poor to
> start with, that using PSNR is not that helpful?
If you want to measure subjective quality, PSNR is not very helpful to
begin with...
So long,
Thomas
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