FOCUS Enhancements FS453 - Manual (Page 9)

FS453/4 AND FS455/6 DATA SHEET: HARDWARE REFERENCE
3. Technical Highlights
Creating clear, broadcast quality television video from high resolution computer graphics is a complex
process. PC-to-TV Video Scan Converters have to surmount many technical obstacles. The most
challenging of these are scaling, flicker reduction, and encoding.
3.1 Scaling
Converting high-resolution computer images into relatively low-resolution TV images (such as converting
VGA or XGA images into NTSC standard definition television) is an inherently lossy process that requires
a video scaler. For example, converting an image with 1000 pixels in a line into an image with only 500
pixels in a line, means that there must be 50% less data in each line of output. The video scaler has to
perform its tasks effectively without further degrading the image.
3.1.1 Video Scaler Challenges
Therefore, in addition to reducing pixel count and interpolating pixel values, the scaler must not alter the
digital video data by adding artifacts. Examples of artifacts are the introduction of repeated pixels; the
complete loss of pixel data; and the creation of new pixel colors that are not interpolations of original pixel
colors.
In effect, the video scaler should behave like a high quality filter. It should have a gradual frequency roll
off with a good step response and little overshoot or ringing (less than 5%). This is ideal for maintaining
video quality with detailed images (such as text). Detailed images produce rapid output step transitions
that need to be executed cleanly.
3.1.2 FS453 Solution
The following diagram (Figure 2) illustrates the response of the FS453's video scaler. It is a normalized
plot of the Luma frequency response of the FS453's video scaler. As we can see, the FS453's patented
video scaler behaves like a high quality filter with only a gradual frequency roll off.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
25
20
15
10
5
0
5
Scale 7/8
Scale 3/4
Scale 5/8
Scale 1/2
Normalized Frequency
Gain in Decibels
Figure 2: FS453 Scaler Luma Frequency Response
JANUARY, 2005, VERSION 3.0 9 COPYRIGHT ©2003-4 FOCUS ENHANCEMENTS, INC.
FOCUS Enhancements Semiconductor