WinTV: artifatcs at lower res captures

[snowmoon]

For those that think capturing at 352x240 or 352x480 is good enough!

I have noticed some artifacts on my WinTV card that only appear on lower resolution captures. I believe this has to do the bt878 chip's internal resizing function kicking in and as I'll show it alters the image in a bad way.

The alterations add "ghost" lines above and or below high contrast areas, probably from the fact that internally it is performing some sort of multi-line aware interlaced resize.

All images were resized to 720x480 using VirtualDub's interal neirest neighbor to improve visibility of the artifacts.

Here is a clip from a 720x480 cap, as you can see nice and crisp



Here is a clip from a 352x480 cap, you can see the lines under the letters



But this problem is not restricted to 480 scanline captures here is a set of 240 scanline caps. 720 on top and 352 on the bottom.





I don't know where the cut-off is, as 480x480 appears unaffected by this bug. It appears only to happen resolutions less than half of the TV resolution.

And just for giggles here is the 720 resized doen ( bicubic ) to see what effect it has.

[snowmoon]

Documentation on the bt878/9 chip appears that the added blurring is done to help improve compressability and watchability of such a small image.