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Old 13 December 2017, 10:45   #1
Moon 1969 = amiga 1985

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sham instead of ham ?

Hi guys, is there some test to make little movies in the so called : sham or shm mode?
instead of ham ?
Like sham has no blur effect but can display 4096 colours it could be cool to use it to make some intros or little clips.

What's the problem with sham (shm) ??
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Old 13 December 2017, 13:45   #2
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There where two different techniques referred to by SHAM. The first was using HAM with a new 15* colour palette every raster line and the second was not using HAM at all, but rather use Hires mode with 15* new colours per raster line and add strategic dithering as required.

The reason these are not used more often in moving graphics (as plenty of stills using these modes where in fact used in demos and the like) are dependent on the mode.

For HAM-with-new-palette you still have fringing. For both HAM-with-new-palette and Hires-with-new-palette you also have the problem that the large amount of DMA bandwidth you use for the display, plus the large amount of Copper use means you only have a very limited amount of raster time left to actually do things in with either CPU or blitter.

Add to that that for the Hires-with-new-palette option you also need to draw more pixels to get the same screen coverage and it should be apparent why not many animating/moving graphics where produced using these modes.

*) It might have been 16, I am not entirely sure. But it doesn't really matter for the result.
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