
Philips Semiconductors
Video Out
File: evo.fm5, modified 7/24/99
PRELIMINARY INFORMATION
7-9
will be 1/4 the size of the Y table. The U and V tables
have the half the number of lines and half the number of
pixels per line as the Y table.
7.10.3
Graphics Overlay Image Format
Graphics overlay image data is stored in a pixel packed
format in SDRAM. Graphics images are stored in YUV
4:2:2+alpha formats.
Figure 7-19 shows this format. The
YUV overlay is always in the image output resolution.
The VO does not upscale the graphics overlay image. If
the VO is upscaling the video image by 2
×, the graphics
overlay must be provided in upscaled format.
7.10.4
Alpha Blending
The VO provides alpha blending of the background video
image with the foreground graphics overlay image. No
chroma keying is supported.
Alpha blending combines the graphics overlay image
with the video image according to an alpha value provid-
ed with each overlay pixel. In the YUV 4:2:2+
α format,
each pixel has a single
α-bit supplied as the least signif-
icant bit of the U and V pixels. The U byte lsb corre-
sponds to the alpha for pixel Y0, the V byte lsb for pixel
Y1, respectively. When the
α-bit is zero, the ALPHA
ZERO register supplies the actual 8 bit
α value. When
the
α-bit is one, the ALPHA ONE register supplies the 8
bit
α value. Alpha blending combines video and overlay
according to
Table 7-4. Although 7 bits of blending reso-
lution are provided for in the architecture, the actual num-
ber of bits implemented depends on the TM1000 version.
TM1000 and TM1000 compatibility mode of TM1100
only implements 25% step resolution. TM1100 EVO
mode and successor chips provide all 129 blending lev-
els.
In the YUV 4:2:2 format, only one set of U and V values
is supplied for the two Y pixels, Y0 and Y1. The alpha bit
in U0 determines the alpha value for U, Y0 and V. The
alpha blend bit in V0 only sets the alpha value for Y1 and
does not affect the U or V values.
7.11
VIDEO IMAGE CONVERSION
ALGORITHMS
The memory video image data formats are converted to
the output YUV 4:2:2 co-sited format and optionally up-
scaled 2x horizontally. The conversion algorithms are
detailed below.
7.11.1
YUV 4:2:2 Interspersed to YUV 4:2:2
Co-sited Conversion
The VO can accept data from SDRAM in either YUV
4:2:2 co-sited, YUV 4:2:2 interspersed or YUV 4:2:0 in-
terspersed formats. If the input data is in YUV 4:2:2 or
YUV 4:2:0 interspersed format, interspersed-to-co-sited
conversion is performed to generate co-sited output. The
VO uses a four-tap, (–1, 5, 13, –1)/16 filter to perform this
conversion on the U and V chroma data. An example of
interspersed
to
co-sited
conversion
is
shown
in
7.11.2
YUV 4:2:0 to YUV 4:2:2 Co-sited
Conversion
YUV 4:2:0 to YUV 4:2:2 conversion is a variation of YUV
4:2:2 interspersed-to-co-sited conversion. The YUV
4:2:0 format has the U and V pixels positioned between
lines as well as between pixels within each line. It also
WIDTH pixels
HEIGHT
lines
pix0
pix1
pix2
pix
W–1
Y_BASE_ADR
WIDTH/2 pixels
HEIGHT
lines
pix0
pix2
U_BASE_ADR
(Repeated for
V_BASE_ADDR,
V_OFFSET)
Y_OFFSET
U_OFFSET
Figure 7-18. Image storage in planar memory format
for YUV 4:2:2.
Y1
V0
Y0
U0
30
YUV 4:2:2+
α
2
1
α
8
Figure 7-19. YUV 4:2:2+alpha overlay format.
Chrominance (U,V)
samples
Luminance
samples
Input Pixels: YUV
Output Pixels: YU’V’
Co-sited Chrominance Output:
U’,V’ = (–1,5,13,–1)/16
×U,V
Figure 7-20. YUV interspersed to co-sited conversion.