RIVA128ZX Datasheet, PDF (43/85 Pages) STMicroelectronics – 128-BIT 3D MULTIMEDIA ACCELERATOR

128-BIT 3D MULTIMEDIA ACCELERATOR
RIVA128ZX
7.1 VIDEO SCALER PIPELINE
The RIVA128ZX video scaler pipeline performs
stretching of video images in any arbitrary factor in
both horizontal and vertical directions. The video
scaler pipeline consists of the following stages:
1 Vertical stretching
2 Filtering
3 Color space conversion
4 Horizontal stretching
Vertical stretching
Vertical stretching is performed on pixels prior to
color conversion. The video scaler linearly interpo-
lates the pixels in the vertical direction using an in-
ternal buffer which stores the previous line of pixel
information.
Filtering
After vertical interpolation, the pixels are horizon-
tally filtered using an edge-enhancement or a
smoothing filter. The edge-enhancement filter en-
hances picture transition information to prevent
loss of image clarity following the smoothing filter-
ing stage. The smoothing filter is a low-pass filter
that reduces the noise in the source image.
Color space conversion
The video overlay pipeline logic converts images
from YUV 4:2:2 format to 24-bit RGB true-color.
The default color conversion coefficients convert
from YCrCb to gamma corrected RGB.
Saturation controls make sure that the conversion
does not exceed the output range. Four control
flags in the color converter provides 16 sets of col-
or conversion coefficients to allow adjustment of
the hue and saturation. The brightness of each
R G B component can also be individually adjust-
ed, similar to the brightness controls of the moni-
tor.
Horizontal stretching
Horizontal stretching is done in 24-bit RGB space
after color conversion. Each component is linearly
interpolated using a triangle 2-tap filter.
Windowing and panning
Video images are clipped to a rectangular window
by a pair of registers specifying the position and
width.
By programming the video start address and the
video pitch, the video overlay logic also supports a
panning window that can zoom into a portion of the
source image.
Video composition
With the color keying feature enabled, a program-
mable key in the graphics pixel stream allows se-
lection of either the video or the graphics output on
a pixel by pixel basis. Color keying allows any ar-
bitrary portions of the video to overlay the graph-
ics.
With color keying disabled and video overlay
turned on, the video output overlays the graphics
in the video window.
Interlaced video
The video overlay can display both non-interlaced
and interlaced video.
Traditional video overlay hardware typically drops
every other field of an interlaced video stream,
resulting in a low frame rate. Some solutions have
attempted to overcome the this problem by de-
interlacing the fields into a single frame. This
however introduces motion artifacts. Fast moving
objects appearing in different positions in different
fields, when deinterlaced, introduces visible
artifacts which look like hair-like lines projecting
out of the object.
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