SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Figure 10-47 shows how 4:2:0 video is split into top and bottom fields in interlaced format. Chroma is attached to alternating Luma lines in the top and bottom fields such that color is equally spread out between the top field and the bottom field. This 4:2:0 interlaced chroma representation is shown in the following figure.
In each interlaced field, the chroma anchor points are separated by 4 pixel lines, or 8 half pels. The 4:2:2 chroma interpolated color space representation of interlaced pictures is shown in Figure 10-48.
Following interpolation, the chroma samples lie on a 4:2:2 grid.
Anchor pixels for the top field have been sited up by half a pel (x = -1/8). The new interpolated pixel is sited 3 half pels (x=3/8) down. Samples from the top field are distinct from samples in the bottom field.
For the bottom field, anchor pixels are sited 3 haf pels up (x = -3/8). The new interpolated pixel is sited 1 half pel down (x=1/8).
The chroma upsampling filter accepts different coefficients for the top field and the bottom field. In the case of progressive input, the coefficients for the top field and bottom field must be the same.
It should be noted that a different implementation could have been chosen to use the same coefficients for the top and bottom fields. Instead of pushing pixels from the top to bottom of a picture, it can be shown that pushing the bottom field through the upsampling filter from the bottom to the top of the picture permits using the same values for x as in the top field case.