PNX1302EH NXP Semiconductors, PNX1302EH Datasheet - Page 219

• Manufacturer Part Number: PNX1302EH
• Manufacturer: NXP Semiconductors

Specifications of PNX1302EH

• Lead Free Status / RoHS Status: Not Compliant

Philips Semiconductors
pixels adjacent to the output pixel. The shift bypass
mode also forces the coefficient RAM inputs to ‘0’, since
interpolation between adjacent input pixels is no longer
being performed.
Using scaling to convert from YUV 4:2:0 to YUV 4:2:2
YUV information in the 4:2:0 format has the UV pixels off-
set from the input grid in both X and Y. Also, the U and V
pixels are at 1/2 of the horizontal and 1/2 of the vertical
frequencies of the Y pixels. This means the UV pixels
must be filtered and additionally scaled in both X and Y
in order to line up with the output Y pixels even if no initial
scaling is done. To generate 4:2:2 interspersed data,
vertically up-scale U and V by a factor of 2 with a start off-
set of -1/4 pixel. Upscaling by 2 generates the additional
lines required, and starting with a -1/4 pixel offset (rela-
tive to U, V space) moves the output up to the same line
as the Y pixels. To generate 4:2:2 co-sited, then filter hor-
izontally with no scaling factor but with a start offset of -
1/4 pixel, moving the output left 1/4 pixel.
14.5.4
In the ICP, YUV to RGB conversion is done by sequen-
tially processing triplets of Y, U, and V pixel data to con-
vert the pixels to an internal YUV 4:4:4 format and apply-
ing the YUV to RGB conversion algorithm on the YUV
4:4:4 pixels. The results of this conversion normally go to
the PCI bus but can also go back to SDRAM.
YUV to RGB conversion has two steps. First the Y, U and
a V pixel data are used to generate an RGB pixel at the
output location. When the Y,U, and V pixels are ready,
YUV to RGB conversion is performed using the following
algorithms:
In CCIR601, the U and V values are offset by +128 by in-
verting the most significant bit of the 8-bit byte. This is the
way the U and V values are stored in SDRAM. The above
algorithms assume that the U and V values are convert-
ed back to normal signed two’s complement values by in-
verting the MSB before being used.
14.5.5
The ICP can add an overlay image to the main image
when in the horizontal filter to RGB/YUV mode with PCI
output. The overlay image is a user-defined rectangle
within the main image. When the overlay is active, each
overlay pixel is combined with each main image pixel to
generate the resulting pixel to be displayed. Each pixel
combination is controlled by an alpha value which deter-
mines the proportions of overlay and main image that
contribute to the output pixel. The relation is given by:
R
G
B
Pout = (alpha) * Poverlay + (1-alpha) * Pmain =
(alpha) * (Poverlay-Pmain) + Pmain
YUV to RGB Conversion
= Y + 1.375(V)= Y + (1 + 3/8)(V)
= Y - 0.34375(U) - 0.703125(V)
= Y - (11/32)(U) - (45/64)(V)
= Y + 1.734375(U)
= Y + (1 + 47/64)(U)
Overlay and Alpha Blending
where: alpha ranges from 0 to 1
In the ICP, the alpha value range is limited by the hard-
ware to five values: {0.0, 0.25, 0.50, 0.75, 1.0}.
An alpha value is supplied for each overlay pixel. In the
RGB 24+α overlay data format: an 8-bit alpha value is
contained within the overlay data.
In all other overlay data formats (RGB 15+α, etc.), an al-
pha bit in the overlay data determines the alpha value.
The alpha bit selects between two 8-bit values, alpha 1
and alpha 0, supplied by a pair of internal ICP registers.
These registers are loaded from the parameter block
when the ICP is started. When the alpha bit is ‘1’, alpha
1 value is used as the alpha value; when the alpha bit is
‘0’, alpha 0 is used as the alpha value. The two alpha reg-
isters allow translucent images and backgrounds while
being restricted to one bit per pixel for alpha selection.
Alpha blending has several uses.
1. Alpha can be used to disable portions of the overlay,
2. Alpha blending allows translucent (smoky) back-
3. Using alpha at the edges of small images such as font
Chroma keying
The ICP also optionally provides a restricted form of
chroma keying sometimes called color keying. When the
overlay Y value is ‘0’ (an illegal value in the YUV 4:2:2+α
format) or the RGB values are all ‘0’ (RGB15+α format),
the alpha value is forced to ‘0’ and no overlay or blending
occurs. This provides three levels of overlay: none, alpha
zero, and alpha one. This combination can be used to
generate an irregularly shaped menu (an oval shape, for
example) which is translucent (e.g. an alpha value of
50%) that contains opaque (alpha = 100%) letters. In a
game, this could be a message written on a foggy back-
ground in an oval window. The chroma keying provides
the definition of the oval shape, the alpha zero value de-
fines the translucent foggy background and the alpha
one value defines the opaque characters on the foggy
background.
Chroma keying in the ICP is intended for computer gen-
erated or modified overlays. Chroma keying turns off the
overlay process for selected pixels by forcing an alpha
value of ‘0’ for those pixels. Chroma keyed pixels use
special codes to identify them. These codes must be
computer generated in most cases. For example, the
DSPCPU or other CPU would process an overlay image
and convert the overlay pixels to be turned off into chro-
ma keyed pixels by changing the data for those pixels to
the chroma key code.
The ICP does not have full chroma keying. Full chroma
keying has adjustable threshold values for the pixel com-
ponents. Adjustable thresholds allow the user to auto-
matically select an overlay sub-image from a larger over-
lay background, such as selecting an image of an actor
PRELIMINARY SPECIFICATION
called keying. When the alpha for a pixel is ‘0’, there
is no overlay. When the alpha is ‘1’, the overlay is
100%, replacing the image. This allows the user to put
an irregular shaped object in an image without show-
ing the bounding rectangle of the overlay.
grounds and/or translucent (ghostly) overlay images
characters increases their effective visual resolution.
Image Coprocessor
14-9