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CPP100
SECTION 9
CPP1OPS
25/10/06
www.snellwilcox.com
Version 1 Issue 6
9.19
Enhancer cont.
Mode - De-Enhancement
As well as enhancing picture sharpness the enhancer also incorporates de-enhancement settings for
luminance and chrominance which reduce the sharpness of an image by softening picture detail that MPEG
might otherwise have difficulty in encoding, notably high frequency moving diagonals.
The de-enhancement feature is able to reduce moving diagonals in luminance and chrominance whilst
maintaining full resolution for horizontal frequencies.
The de-enhancement filter has three de-enhancement settings: minimum, medium and maximum
The maximum setting provides greatest attenuation of diagonal frequencies.
Luminance De-enhancement
A diagram of the luminance de-enhancer is shown below.
The first stage of the luminance de-enhancer is a seven point vertical temporal filter. The vertical temporal
filter is followed by a horizontal bandpass filter. The effect of these two cascaded filters is to select the
diagonals that are then reduced or eliminated by de-enhancement gains from the LUT.
The seven-point filter has the added benefit of reducing noise by averaging.
Attenuating luminance high frequency moving diagonals is particularly useful when trying to reduce the bit rate
for MPEG encoding.
The de-enhance levels use different filters to optimise the type and level of de-enhancement. The adaptive
filter allows more de-enhancement of all textures
The table below shows the filter settings for the various levels of luminance de-enhancement.
De-enhance Level
Filter Type
minimum
broad bandpass filter 1
medium
broad bandpass filter 2
maximum
adaptive bandpass between
filters 1 & 2
LUT
delay
Vertical
temporal
filter
Horizontal
bandpass
filter
page select
centre tap
taps