View Full Version : fft3dfilter and black borders

27th September 2008, 04:49
Hey all,

Is there a consensus as to whether or not the remarkable fft3dfilter plugin can be used on letterboxed sources, or is it better to crop, apply fft3dfilter, then add borders? I did a quick search on this forum but couldn't find any discussion on this issue. Thanks in advance :thanks:

27th September 2008, 11:38
I guess smaller resolutions will be faster. If there are no other constraints (mod16, ect.) I think it is save to crop before filtering.

27th September 2008, 23:28
I agree. A lot of times there are scaling artifacts around the border between the image and the matte, so I like to overcrop those out (preferably as mod8 so fft3dfilter can operate on the original MPEG-2 blocks :)


27th September 2008, 23:38
preferably as mod8 so fft3dfilter can operate on the original MPEG-2 blocks

What would be the benefit of running FFT3D on not-shifted mpeg blocks? :) :)

27th September 2008, 23:58
I was under the impression that if you cropped away 8x8 blocks only, it would make fft3dfilter work a bit better - especially its deblocking side effects.

But - clearly you know better than I - so I retract this portion of my post ;)


28th September 2008, 00:15
No, I don't "know better". While it was obvious you were pointing towards the deblocking effect of FFT3D, I was just wondering whether it makes a big difference.

First it's needed that bw/bh and ow/oh of FF3dFilter have values that are aligned to 8/16-blocks at all. E.g. with bw/bh=12, ow/oh=6, it's irrelevant whether the source blocks are mod8 aligned or not, because then the grid of the filtering window does not "fit" to start with.

Then, IF the sample windows do fit (and with most "usual" settings they will indeed), then from a theoretical point of view it's not clear if the deblocking efficiency changes. One could argue in one direction or the other, but it's unclear which arguments were better.

So I thought I could just ask out loud. :)

28th September 2008, 01:00

I might do some testing with a blocky source and see if mod8 cropping makes a difference.

To be honest, I usually just set plane and sigma values. :)