1.0 Functional Description
CX25870/871
1.3 Device Description
Flicker-Free Video Encoder with Ultrascale Technology
The vertical interpolation filtering and vertical anti-alias filtering
requirements are driven by the amount of vertical down scaling required, and do
not vary substantially with image content. The flicker filtering requirement,
however, is dependent upon the image content.
Regions of the image with vertical high frequency content will flicker in
proportion to the amplitude of that high frequency content. Regions with high
amplitude vertical high frequency content require substantial flicker filtering, but
regions with low amplitude or no vertical high frequency content require little or
no flicker filtering.
For this reason, the CX25870/871 provides adaptive flicker filtering. It
analyzes the image content to detect areas that require strong flicker filtering, and
adjusts its vertical filtering to apply stronger flicker filtering to those regions.
This analysis and adjustment occurs on a pixel by pixel basis, so each pixel in the
output line has the optimal amount of flicker filtering applied to it.
The Adaptive_FF1 and Adaptive_FF2 registers (0x34 and 0x36) configure the
adaptive algorithm. The Y_ALTFF[1:0] and C_ALTFF[1:0] fields allow the
selection of the alternative (i.e., stronger) flicker filter to combine with the
standard flicker filter selected by fields F_SELY[1:0] and F_SELC[1:0] (register
0xC8). This creates an array of flicker filters for the Y channel and C channel
respectively. The actual flicker filter applied for a given pixel output depends on
the detection and location of any high amplitude vertical high frequency content
within the input samples that creates that output pixel.
The amplitude of the high frequency content that triggers an adaptation of the
flicker filter can be adjusted via the Y_THRESH[2:0] and C_THRESH[2:0] bit
fields. The FFRTN bit offers two ways to combine the standard and alternate
flicker filters to generate an array of flicker filters. The YSELECT bit allows the
Chroma channel flicker filter to be adapted based on the Chroma channel or the Y
(i.e., Luminance) channel content.
NOTE: Neither standard nor adaptive flicker filtering is supported by the
CX25870/871 in noninterlaced video output formats (VGA style RGB,
HDTV 480p, 720p).
Table 1-16 summarizes recommended configurations of the adaptive flicker
filter for various types of image content and resolutions.
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Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
