Digital Signal Processing Reference
In-Depth Information
5
VIDEO SCALING
CHAPTER OUTLINE
5.1 Understanding Video Scaling 30
5.2 Implementing Video Scaling 33
5.3 Video Scaling for Different Aspect Ratios
36
5.4 Conclusion
38
as anyone who has watched
standard definition DVDs on their high resolution HDTVs has no
doubt experienced. Each video frame, which consists of lines of
pixels, has a different size as shown in
Figure 5.1
.
Video has to be resized to view it on different sized displays
Video comes in different sizes
e
e
this means that the native resolution of the video frame is
adjusted to fit the display available. Video resizing or scaling is an
increasingly common function used to convert images of one
resolution and aspect ratio to another “target” resolution and/or
aspect ratio. The most familiar example of video scaling is scaling
a VGA signal (640
480) output from a standard laptop to an
SXGA signal (1280
1024) for display on LCD monitors.
For high-volume systems dealing with standardized image
sizes such as HD television, video scaling is most efficiently done
using application specific standard products (ASSPs). However,
many video applications such as video surveillance, broadcast
display and monitoring, video conferencing and specialty
displays, need solutions that can handle custom image sizes and
differing levels of quality. This often requires custom scaling
algorithms. FPGAs with an array of high-performance DSP
structures are ideally suited for such algorithms, and FPGA
vendors are beginning to offer user-customizable video-scaling IP
blocks that can be quickly configured for any application.
Scaling is often combined with other algorithms such as
deinterlacing and aspect ratio conversion. In this chapter we will
focus on the digital video processing involved in resizing or
scaling a video frame.
Towards the end of this chapter we will briefly describe the
different aspect ratios since scaling is done many times to stretch
a 4:3 image to display on today's 16:9 HDTV displays.
