> On 02/20/2010 10:17 AM, Phil Ehrens wrote: > >Andrew Church wrote: > > > >>Just as an addendum (though I think it's been mentioned on this list > >>before), PSNR isn't always a good measurement of visual quality, so take > >>these results with a grain of salt. Lower PSNR generally means lower > >>visual quality, but depending on the actual image data, deliberate > >>"errors" such as averaging pixels can help the brain fill in the missing > >>detail on its own, causing the image to look better to a human viewer. > >> > >This is a very important point! Depending upon the source, > >a significantly lower PSNR can look dramatically better - > >When transcoding from VHS source, for example. PSNR is > >mostly useful for things like determining whether 2-pass > >encoding in x264 works or not ;^) > > > I put the Who? in Mishehu wrote: > Note: I have confirmed with Dark_Shikari on #x264 that 2-pass is fully > functional at this time. The goals between CRF and 2-pass are > different. CRF allows you to specify an average quality setting for > your file regardless of the resulting size. 2-pass is more so used when > you want to keep the resulting file at a designated approximate size.
There is a potential for misunderstanding when the difference is stated that way... The file size required to get the same "quality" with CRF could be three times the size of the 2-pass file. And by "quality" I mean subjective viewing quality, not PSNR, so I am not talking about what they talk about in #x264. CRF is very interesting, and it certainly has the potential to be a wonderful thing, but I think it's being oversold right now. I will not discuss this further. This subject can only go in the direction of a holy war, and I'm not a Christian or a Moslem.
