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1/2x
Decimator
1/2x
Decimator
Polyphase
Scaler
YCbCr
422
YCbCr
422
HS Coef Mem
32 phase x 7tap
Internal Modules
197
SPRUHI7A – December 2012 – Revised June 2016
Copyright © 2012–2016, Texas Instruments Incorporated
High-Definition Video Processing Subsystem (HDVPSS)
1.2.11.2.4 Horizontal Scaler
The horizontal scaler is implemented using a 32-phase × 7-tap polyphase filter preceded by two sets of
x1/2 decimators. The general configuration of the Horizontal scaler is performed as follows:
•
For up scaling, the input video is interpolated using the polyphase scaler.
•
For downscaling, it is recommended that input video is decimated by 2 until the modified scale factor
falls between 1/2 and 1. Then, a polyphase filter is configured with coefficients selected based on the
mod_scale_factor calculated as shown below from one of nine different sets of coefficients:
(8,9,10,11,12,13,14,15,16)/16.
if (scale_factor>=1/2) {
dcm_2x=0;
dcm_4x=0;
mod_scale_factor=scale factor;
} else if (scale_factor>=1/4) {
dcm_2x=1;
dcm_4x=0;
mod_scale_factor=2*scale_factor;
} else {
dcm_2x=0;
dcm_4x=1;
mod_scale_factor=4*scale_factor;
}
In auto mode (auto_hs == 1), scaler will operate as per above recommendation. In addition to this, for
(auto_hs==1), polyphase filtering will be bypassed when (scale_factor == 1) or (scale_factor == ½) or
(scale_factor == ¼). If (auto_hs==0) is used, user must provide proper values for dcm_2x, dcm_4x, proper
values for all inputs to polyphase filter in the registers as well as appropriate coefficient sets. There is no
constraint on polyphase filtering in terms of scaling ratio. However, there are constraints on input and
output image width for scaler. Frame dimensions are limited from 64x64 to 2047x2047.
Figure 1-147. Horizontal Scaler Block Diagram