Altera Video and Image Processing Suite User Manual
Page 166
Types
Description
Double-buffering
• When you select double-buffering, external RAM uses two frame buffers.
Input pixels flow through the input port and into one buffer while pixels are
read from the other buffer, processed and output.
• When both the input and output sides have finished processing a frame, the
buffers swap roles so that the frame that the output can use the frame that
you have just input. You can overwrite the frame that the function uses to
create the output with a fresh input.
• The motion-adaptive algorithm uses four fields to build a progressive output
frame and the output side has to read pixels from two frame buffers rather
than one. Consequently, the motion-adaptive algorithm actually uses three
frame buffers in external RAM when you select double-buffering.
• When the input and output sides finish processing a frame, the output side
exchanges its buffer containing the oldest frame, frame n-2, with the frame it
receives at the input side, frame n. It keeps frame n-1 for one extra iteration
because it uses it with frame n to produce the next output.
Triple-buffering
• When you use triple-buffering, external RAM usually uses three frame
buffers. The function uses four frame buffers when you select the motion-
adaptive algorithm. At any time, one buffer is in use by the input and one
(two for the motion adaptive case) is (are) in use by the output in the same
way as the double-buffering case. The last frame buffer is spare.
• This configuration allows the input and output sides to swap asynchronously.
When the input finishes, it swaps with the spare frame if the spare frame
contains data that the output frame uses. Otherwise the function drops the
frame which you have just wrote and the function writes a fresh frame over
the dropped frame.
• When the output finishes, it also swaps with the spare frame and continues if
the spare frame contains fresh data from the input side. Otherwise it does not
swap and just repeats the last frame.
• Triple-buffering allows simple frame rate conversion. For example, suppose
you connect the Deinterlacing IP core’s input to a HDTV video stream in
1080i60 format and connect its output i to a 1080p50 monitor. The input has
60 interlaced fields per second, but the output tries to pull 50 progressive
frames per second.
If you configure the Deinterlacing IP cores to output one frame for each input field, it produces 60 frames
of output per second. If you enable triple-buffering, on average the function drops one frame in six so that
it produces 50 frames per second. If you select one frame output for every pair of fields input, the Deinter‐
lacing IP cores produce 30 frames per second output and triple-buffering leads to the function repeating
two out of every three frames on average.
When you select double or triple-buffering, the Deinterlacing IP cores have two or more Avalon-MM
master ports. These must be connected to an external memory with enough space for all of the frame
buffers required. The amount of space varies depending on the type of buffering and algorithm selected.
An estimate of the required memory is shown in the Deinterlacing IP cores parameter editor.
UG-VIPSUITE
2015.05.04
Frame Buffering
12-7
Deinterlacing IP Cores
Altera Corporation