[MPlayer-users] PSNR Questions
Martin Pavon
martin_199ar at yahoo.com.ar
Sat Feb 15 18:53:57 CET 2003
On Sat, Feb 15, 2003 at 05:32:04PM +0000, Ian wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
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> D Richard Felker III wrote:
>
> > Huh?? This is nonsense. You can't compare PSNR relative to two
> > different reference 'signals'. When encoding, the source is considered
> > the signal, and the difference between the encoded picture and the
> > source is the noise, so the source has infinite PSNR automatically.
>
> OK, this is the first time I've seen it stated, a formula would be nice
> too, but in any case see below . . .
>
> > Yes, theoretically. Computational issues might make it come out
> > different tho.
>
> Regardless, since in my experience better quality material (ie. the
> originals!) has a lower PSNR than the copies, I can't take it seriously.
> Obviously your experience is different.
>
> > Huh?? Do you even know what PSNR means??
>
> Can't find the reference (it seems to be unavailable ATM), but I thought
> it was peak signal to noise ratio. I can't be that much of a dimwit if
> I'm using the encoder successfully, now can I? ;)
>
Hi!!!!
Sometimes ago, I found a formula for PSNR in the following link:
http://appliedit.arc.nasa.gov/videotech/psnr.html
A short cut & paste give us:
MSE = 1 / n * ( Sum(i)(j) |P(i)(j) - Q(i)(j)|^2 )
Where P and Q are two images. i and j are the horizontal and vertical
locations of a pixel. P(i)(j) is the value of the pixel at location
(i)(j). n is the total number of pixels in the image.
and
PSNR = 10 log_10 (b^2 / MSE)
Where b is the peak value for a pixel, typically 255 for 8 bit pixels.
PSNR is usually quoted in decibels (dB), a logarithmic scale.
I hope someone can find this usefull
Regards,
Martín
--
Martín Pavón
martin_199ar at yahoo.com.ar
http://mate.dm.uba.ar/~mpavon/
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