Philips Semiconductors
Image Coprocessor
PRELIMINARY SPECIFICATION
14-5
14.4.2
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 14-1
. The overlay image format must be the same
type as the output image format generated by the ICP for
the main image. For example, 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
data.
In RGB 24+
α,
pixels are packed 1 pixel/word
,
a full byte
of alpha information (stored in the most significant byte)
is included with each pixel. In RGB 15+
α,
one bit of alpha
is included for each pixel. The pixels in the overlay image
are packed as 2 pixels per 32-bit word, and the alpha bit
is the most significant bit of each half word. In the same
manner, the YUV-4:2:2+
α
format packs two pixels into
one 32-bit word, and has one bit of alpha for each pixel.
The least significant bit of the U and V components sup-
plies the alpha bit for the Y0 and Y1 pixels, respectively.
The alpha bit in these formats selects 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.
14.4.3
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
is shown in
Table 14-2
.
14.4.4
Output Formats
The output formats are the RGB image formats sent to
the PCI interface or SDRAM. These formats are shown
in
Table 14-3
. Note: B1 = Byte 1 of blue = [b7...b0]
1
.
Table 14-1. Image Overlay Formats
Format
Bits 31-24
Bits 23-16
Bits 15-8
Bits 7-0
RGB 24+
α
YUV-4:2:2+
α
a7 - a0
Y1
r7 - r0
(v7-v1) +
α
g7 - g0
Y0
b7 - b0
(u7-u1) +
α
Pixel 1
Pixel 0
RGB 15+
α
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
Table 14-2. Alpha Blending Codes
Alpha Code
Alpha Value
Image
Overlay
00h
20h
40h
60h
0
32
64
96
100%
75%
50%
25%
0%
0%
25%
50%
75%
100%
80h - FFh
128-255
Table 14-3. 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
RGB 8R: 332
1
1
r1 r0 g2 g1 g0 b2 b1 b0
r2 r1 r0 g2 g1 g0 b1 b0
r1 r0 g2 g1 g0 b2 b1 b0
r2 r1 r0 g2 g1 g0 b1 b0
Pixel 1
g2 g1 g0 b4 b3 b2 b1 b0
g2 g1 g0 b4 b3 b2 b1 b0
r1 r0 g2 g1 g0 b2 b1 b0
r2 r1 r0 g2 g1 g0 b1 b0
r1 r0 g2 g1 g0 b2 b1 b0
r2 r1 r0 g2 g1 g0 b1 b0
Pixel 0
g2 g1 g0 b4 b3 b2 b1 b0
g2 g1 g0 b4 b3 b2 b1 b0
RGB 15+
α
RGB-16
1
1
α
r4 r3 r2 r1 r0 g4 g3
r4 r3 r2 r1 r0 g5 g4 g3
α
r4 r3 r2 r1 r0 g4 g3
r4 r3 r2 r1 r0 g5 g4 g3
1 Pixel/Word
RGB 24+
α
1
a7 - a0
r7 - r0
g7 - g0
b7 - b0
Packed 4 Pixels/3 Words
R0
B2
G3
Packed 2 Pixels/Word
V0
RGB 24-packed
1
2
3
B1
G2
R3
G0
R1
B3
B0
G1
R2
YUV- 4:2:2
1
Y1
Y0
U0