CPP100
SECTION 9
CPP1OPS
25/10/06
www.snellwilcox.com
Version 1 Issue 6
9.17
Enhancer
Introduction
The enhancer has four distinct modes of operation that can be used individually to improve picture quality in
four unique ways. These are: Enhance, MPEG De-enhance, Decoder Matching & Video mode.
Mode - Enhancement
During the process of video recording or transmission, pictures can lose sharpness as high frequency
components of the picture are lost or reduced, resulting in soft or blurred edges.
The aim of the enhancer is to restore the perceived sharpness of an image by adding a correction signal
derived from information from the incoming signal to sharpen edges and boost peaks but in a way that does
not produce unnaturally sharp pictures or excessive unwanted artefacts.
The enhancer correction signal uses a combination of linear and non-linear methods. The linear and non-linear
enhancement signals are calculated separately and combined to provide the final correction signal which is
then summed with the incoming signal.
Non-linear enhancement is able to enhance images without the large increase in overshoots and ringing that
are associated with linear enhancement methods.
The non-linear correction signal consists of a peak enhancement signal and an edge enhancement signal. The
type of non-linear enhancement is determined by analysis of the incoming signal and has a pixel by pixel
response to provide the optimum blend of peaking and edge correction.
Although the benefits of linear enhancement methods are limited, linear enhancement is more successful at
dealing with low amplitude detail and texture in pictures.
The enhancer uses a combination of both methods to provide an optimum correction signal that produces
minimal ringing and overshoots.
The control of enhancement levels together with the adjustable coring make the enhancer a very powerful tool
for improving picture quality.
As mentioned previously the aim of the enhancer is to sharpen edges and boost peaks with minimal ringing
and overshoots. An example of this is shown below. This shows the output of a conventional enhancer
showing large undershoots and overshoots. The dotted line represents the enhanced signal and the solid line
shows the input signal.
Conventional enhancement
