Subsampled Chroma decoding(display) question

[Movie-Maker]

Hi,
when chroma is subsampled, depending on the chroma subsampling scheme(4:1:1, 4:2:2, 4:2:0) some pixels get sampled only for the luma(Y), or some pixels get sampled for the luma and only one chroma component i.e. either Cb or Cr only.
In such cases, when the data being converted back to the video display during playback, do those pixels with no chroma or only one chroma get diplayed with no chroma or one chroma only(ofcourse alongwith luma) or do the missing chroma components get calculated real time(from neighbouring chroma samples ?) and all three components Y,Cb, Cr are displayed for that pixel always ?

[jagabo]

The chroma samples are either replicated for each luma or interpolated somehow, depending on the software/hardware. Every displayed pixel must have all three components.

[Movie-Maker]

interpolated - that's the word I was looking for.

so in general, i.e. typical dvd players and software players, do they interpolate the missing information or just slap on the neighbouring values and be done with it ?

[Movie-Maker]

Where can I find more information about implementation level details about chroma upsampling ?
How exactly is it done ?
I know quite familiar with resampling of audio signals but want to understand video chroma upsampling better.

[jagabo]

Many editors replicate because the operation is symetrical. Ie, if you repeatedly convert 4:4:4 to 4:1:1 and back you want to avoid having the chroma get farther and farther from the original values.

Software can use any of the usual digital image scaling algorithms for smoother results. Simple interpolation, bilinear, bicubic, lanczos, etc.

Most media players will use the graphics card's video overlay feature which usually accepts YUY2 video. So the conversion from YUY2 to RGB is dependent on the graphics card.