[opendtv] Re: PicWidth, PicHeight in Mbs, Table 6.3 of ATSC a72
- From: Ron Economos <w6rz@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 14 Dec 2010 02:53:09 -0800
It's the image size in 16x16 macroblocks. For 1920x1080,
the PicWidth is 120 and the PicHeight is 68.
120 * 16 = 1920 and 68 * 16 = 1088. For this
resolution (and also 176x120), the coded size is
larger than the source image. To take care of that,
you need to set the cropping fields correctly.
That's what this paragraph on the specification is
talking about:
For vertical sizes of 1080 and 120, note that 1088
and 128 lines (respectively) are actually coded in
order to satisfy the AVC requirement that the coded
vertical size be a multiple of 16 (progressive scan)
or 32 (interlaced scan). The bottom 8 lines should
be black and “frame cropping” shall be used. The
value of frame_crop_top_offset shall be 0 and
frame_crop_bottom_offset shall be
2*(1 + frame_mbs_only_flag).
Although H.264 can have smaller block sizes
like 4x4, the basic processing unit of H.264 is
a 16x16 block of luma samples and two
corresponding blocks of chroma samples
(just like MPEG-2).
Ron
On 12/13/2010 9:21 PM, dan.grimes@xxxxxxxx wrote:
Sorry if this is a simple question (I'm not an ATSC expert), but what
is the PicWidth and PicHeight in Mbs as seen on Table 6.3 in the a72
document?
Dan
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