[Gllug] Faster maths?

[Chris Bell]

On Thu 08 Mar, Adrian McMenamin wrote:

> 
> But I turn on dithering it takes half an hour!!
> 

   Standard techniques used in broadcast television involve twice moving the
complete image sideways and vertically by a small amount, taking the once
moved image as the main image and just doing simple arithmetic with the
adjacent values.
   The original use for this was a correction for loss of detail due to the
relatively large size of scanning beams in analogue tubed cameras, so the
undelayed and twice delayed images were compared with the once-delayed image
to create a correction image which could be used to sharpen the picture.
   Similar methods were used to improve the visual quality after the change
to solid state imaging systems with discrete pixels.
   Unfortunately, this kind of comb filtering produces some nasty effects if
the image contains detail related to the pixel spacing, so the correction
signals are also filtered to remove any problem frequencies.
   Digital systems often use matrix look-up tables rather than multiple
calculations to produce standard corrections and effects. Just read out the
answers from ROMs.

-- 
Chris Bell

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