Philips Semiconductors
Image Co-Processor
File: icp.fm5, modified 7/26/99
PRELIMINARY INFORMATION
13-5
13.4.2
Image Overlay Formats
The ICP accepts image overlay data in three formats,
RGB-24+
α, RGB-15+α and YUV-4:2:2+α as shown in
Table 13-1. The overlay image format must be the same
type as the output image format generated by the ICP for
the main image. If the output image is one of the RGB
formats, the overlay must be one of the two RGB overlay
formats, RGB-24-
α and RGB-15+α. If the output image
format is YUV, the overlay format must be in YUV-
4:2:2+
α format. The formats must be of the same type
because the ICP does no conversion on the overlay da-
ta.
In RGB-24+
α,a full byte of alpha information is included
with each pixel. In RGB-15+
α,one bit of alpha is included
for each pixel. The pixels are packed as 2 pixels per
word, and the alpha bit is the most significant bit of each
pixel. In the same manner, the YUV-4:2:2+
α format
packs two pixels into one word, and it has one bit of alpha
for each pixel. The least significant bit (LSB) of the U and
V components supplies the alpha bit for the Y0 and Y1
pixels, respectively. The alpha bit in these formats se-
lects between two alpha values stored in the ICP, alpha
1 and alpha 0. The alpha 1 and alpha 0 values are loaded
from the parameter block when the ICP is started.
13.4.3
Alpha Blending Codes
Image overlay uses alpha blending, which combines the
overlay image with the main image according to the al-
pha value. The alpha value is supplied by the alpha byte
in RGB 24+
α format and by the alpha registers, Alpha 0
and Alpha 1 in the other formats. The alpha code format
13.4.4
Output Formats
The output formats are the RGB image formats sent to
the PCI interface or SDRAM. These formats are shown
Table 13-1. Image Overlay Formats
Format
Bits 31-24
Bits 23-16
Bits 15-8
Bits 7-0
RGB 24+
α
a7 - a0
r7 - r0
g7 - g0
b7 - b0
YUV-4:2:2+
α
Y1
(v7-v1) +
α
Y0
(u7-u1) +
α
Pixel 1
Pixel 0
RGB 15+
αα r4 r3 r2 r1 r0 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
α r4 r3 r2 r1 r0 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
Table 13-2. Alpha Blending Codes
Alpha Code
Alpha Value
Image
Overlay
00h
0
100%
0%
20h
32
75%
25%
40h
64
50%
60h
96
25%
75%
80h - FFh
128-255
0%
100%
Table 13-3. Output Data Formats
Format
Word
Bits 31-24
Bits 23-16
Bits 15-8
Bits 7-0
Pixel 3
Pixel 2
Pixel 1
Pixel 0
RGB 8A: 233
1
r1 r0 g2 g1 g0 b2 b1 b0
RGB 8R: 332
1
r2 r1 r0 g2 g1 g0 b1 b0
Pixel 1
Pixel 0
RGB 15+
α
1
α r4 r3 r2 r1 r0 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
α r4 r3 r2 r1 r0 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
RGB-16
1
r4 r3 r2 r1 r0 g5 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
r4 r3 r2 r1 r0 g5 g4 g3
g2 g1 g0 b4 b3 b2 b1 b0
1 Pixel/Word
RGB 24+
α
1
a7 - a0
r7 - r0
g7 - g0
b7 - b0
Packed 4 Pixels/3 Words
RGB-24-packed
1
B1
R0
G0
B0
2G2
B2
R1
G1
3R3
G3
B3
R2
Packed 2 Pixels/Word
YUV- 4:2:2
1
Y1
V0
Y0
U0