CX25870/871
Appendix E HDTV Output Mode
Flicker-Free Video Encoder with Ultrascale Technology E.10 Color Space Conversion Functionality to Support Analog RGB
E.10 Color Space Conversion Functionality to
Support Analog RGB or YPBPR Component Video
Outputs
The CX25870/871 has the ability to receive a digital RGB stream prevalent in
graphics controllers or chipsets with integrated graphics with a width of 15/16/or
24-bits per pixel and transform it to a set of HDTV-compatible analog YPBPR
component video outputs.
The option of not converting the digital RGB stream to analog YPBPR is
available as well. In this case, the CX25870/871 would output a set of
HDTV-compatible analog RGB component video outputs based on the same
15/16/or 24-bits per pixel RGB digital input.
The CX25870/871 can support the conversion from the HDTV
color-difference digital YPBPR color space directly to analog YPBPR component
video outputs seamlessly. No color space conversion nor register reprogramming
is necessary for this case.
However, the HDTV color-difference digital YPBPR color space is slightly
different from the standard digital 4:2:2 YCrCb (i.e., CCIR601) stream found
within consumer applications such as set-top boxes. As a result, the
CX25870/871 must be reprogrammed to new register values not found in
Table E-1 to accommodate for the differences in the two formats. For this
complete register set, contact your local Conexant Field Applications Engineer.
Once obtained, program up the CX25870 as specified and it will provide analog
YPBPR video outputs based on standard 4:2:2 YCrCb MPEG2 input data. The
resulting outputs will be of high quality and viewable on SMPTE274M and
SMPTE 296M standard HDTVs.
For design simplicity, Conexant recommends the data master just send digital
YPRPB for consumer applications instead of YCrCb. For reference these matrix
equations for conversion into digital Pb and digital Pr are listed below:
Pb = {0.5 / (1 – 0.0722)} (B’ – Y’)
Where (B’ – Y’) = Cb
Pr = {0.5 / (1 – 0.2126)} (R’ – Y’)
Where (R’ – Y’) = Cr
NOTE(S):
1. The CX25870/871’s MCOMPU register must contain a value of 45 hex prior to performing a color space conversion from digital
RGB to analog YPBPR. The CX25870/871’s MCOMPV register must contain a value of 51 hex prior to performing a color space
conversion from digital RGB to analog YPBPR.
2. Digital Pb and Digital Pr are expressed as P’B and P’R in the SMPTE specifications.
Finally, the CX25870/871 cannot provide analog RGB video outputs from
either color-difference digital YPrPb or 4:2:2 YCrCb MPEG2 input data. The
encoder will not perform this color space conversion whatsoever. For analog RGB
component HD out, a digital RGB input stream must be sent by the data master.
100381B
Conexant
E-17
CONEXANT [ CONEXANT SYSTEMS, INC ]
