Convolution filter is rotated compared to AVS

[QOAL]

Convolution filter is rotated compared to AVS

[azeem]

Nice find! AVS Convolution isnt working on my machine for some reason. Are you sure it comes up upside down in AVS? Like a happy face or a sad face? Technically, it should come right side up, like a happy face right?

I'm using the following kernel.

    0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,
    1,0,0,0,0,0,1,
    0,1,0,0,0,1,0,
    0,0,1,1,1,0,0,
    0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,

and this is the bug fixed output

please confirm if this is correct.

[QOAL]

The convolution filter doesn't work on more recent operating systems, it works fine on XP though.
I have XP VMs for testing stuff in old IE versions, heh. (My VM currently has WA 5.56 and AVS 2.82)
I highly recommend setting one up to test AVS presets, everything should render correctly with it.
(You may want to see this WA forums thread, if you haven't already: http://forums.winamp.com/showthread.php?t=329743)

[grandchild]

Sorry for bringing this issue up again, but could it be that this is a bug in the ConvoFilter from AVS? Or is this upside-down (and right-side-left!) behavior how a convolution filter should work?
I'd think it more intuitive if I placed a pixel to the bottom left of the center in the kernel, that the pixel should move there as well...

/edit: If this should be turned around again, I'd just update the kernel parser in the converter accordingly.

[azeem]

@grandchild yeah. to me it seems like some kind of mistake in AVS ConvoFilter. When i wrote Webvs convo filter i intuitively followed the right side up formula. I have changed this for compatibility sake.

Most of the convo filter kernels that i came across were symmetric, so i guess the orientation of the kernel doesnt change appearance of most effects. Whether we should implement this correctly in Webvs and turn it around during conversions is debatable. Or maybe we could even have a compat switch similar to the one in DynamicMovement.

[grandchild]

I'd argue for eventually doing it "correctly" since I/we can take care of the AVS peculiarities in the converter.

/edit: what I am trying to say really, is that presets are converted from .avs to json files anyway and thus we don't need to worry too much about representation compatibility in files or the editor, only on-screen.

[azeem]

I have the same opinion. Reopening this bug now. More votes on whether the smiley face up way is the correct way?

[grandchild]

Okay I did a little research and this article shows (a few pages down) that AVS did in fact do this right, convolution filters are mirrored along both axes.
This goes together with the mathematical definition of Convolution where the function (in this case a discrete distribution - the kernel) is inverted before being multiplied with the signal.

[grandchild]

You could turn them "intuitively right" but then you would have to call them "Correlation Filters" :P

[azeem]

Brilliant!

The difference between Convolution and Correlation is that for Convolution you have to mirror the
filter matrix, but usually it's symmetrical anyway so there's no difference.

So I guess, that settles it. We will do it the AVS way. Good work!