What is Sliced Ham?

[Retro1234]

What is Sliced Ham and how does it work? and any examples?

[Tigerskunk]

You take some ham and a knife, and then you slice it...

[Retro1234]

I knew this would heppen

[Rotareneg]

Instead of using a single 16 color palette for the whole screen, it loads a new palette for each scanline, which can help reduce HAM artifacts, depending on the image.

There is also the similar dynamic high-res which also loads a new palette per scan line, but in high-res mode instead of HAM.

Digiview 4.0 supported them, not sure what else.

[Retro1234]

Originally Posted by Rotareneg

Instead of using a single 16 color palette for the whole screen, it loads a new palette for each scanline, which can help reduce HAM artifacts quite a bit, depending on the image.

There is also the similar dynamic high-res which loads a new palette per scan line too, but in high-res mode instead of HAM.

Digiview 4.0 supported them, not sure what else.

Thanks for your reply

was it slow? and was it CPU intensive?

[Rotareneg]

I think they typically used the Copper to load the new palette, so it wasn't specifically CPU intensive, but unless you have some fast RAM the CPU isn't going to be doing much as there's little DMA time left.

Apparently the original version of SHAM only changed the palette every other line, leaving more time for the CPU.

[Retro1234]

Thanks for your explaination

[PeterK]

If you would like to play with S-HAM, dynamic Hires or PCHG there is HamLabPlus 2.10 at the FTP site of the user LoadWB (amiga.org):

https://forum.amiga.org/index.php?PH...7399#msg267399

ftp://nexus.polaris.net/pub/forager/Amiga

[Retro1234]

Originally Posted by PeterK

If you would like to play with S-HAM, dynamic Hires or PCHG there is HamLabPlus 2.10 at the FTP site of the user LoadWB (amiga.org):

https://forum.amiga.org/index.php?PH...7399#msg267399

ftp://nexus.polaris.net/pub/forager/Amiga

Thanks I was more wondering about it's use in games?

[jotd]

I suppose that palette had to be computed specifically for each line, so it was good for static images, but not for games (HAM itself had the same issue).

Unless you want to paste a background image and use only sprites for all characters.

Games already use various copper effects to change the palette (copper rainbows, palette change between playfield and status bar...)

[Retro1234]

Thanks for your reply.

maybe the repeating background of a Dual Playfield might work?

[Viceroy]

Originally Posted by Retro1234

I knew this would heppen

Haha!

[Rotareneg]

Dual playfield and HAM are mutually exclusive.

[coder76]

It's of course also possible to use normal bitplane mode or extra halfbright (EHB), and then change palette on every scanline, but leave a set of colors unchanged; that way you can also move around blitter objects without distorting their colors when moving object horizontally or vertically.

The sliced EHB mode certainly works better for games than sliced HAM.

Sliced EHB technique was used by the game Universe. It changes only first 16 colors on a scanline basis and leaves the other 16 colors untouched for objects, and these colors are also used by sprites. It seems that not that many colors are changed per scaline (probably 2-8), as the game is said to have only 256 colors in all, so the copper doesn't also slow down CPU access to chip ram completely. But this mode is probably not suitable for fast action games on OCS.

[Retro1234]

Originally Posted by Rotareneg

Dual playfield and HAM are mutually exclusive.

I was thinking of some kind of Copper Rainbow that could be more than one colour per scanline, sorry.

the guy Kev G did more than one Rainbow Side by Side and I think it worked with Dual
Playfield.
https://www.ultimateamiga.co.uk/index.php?topic=9300.0

[Retro1234]

Originally Posted by coder76

It's of course also possible to use normal bitplane mode or extra halfbright (EHB), and then change palette on every scanline, but leave a set of colors unchanged; that way you can also move around blitter objects without distorting their colors when moving object horizontally or vertically.

The sliced EHB mode certainly works better for games than sliced HAM.

Sliced EHB technique was used by the game Universe. It changes only first 16 colors on a scanline basis and leaves the other 16 colors untouched for objects, and these colors are also used by sprites. It seems that not that many colors are changed per scaline (probably 2-8), as the game is said to have only 256 colors in all, so the copper doesn't also slow down CPU access to chip ram completely. But this mode is probably not suitable for fast action games on OCS.

Intresting to know, people are always asking how it was done.

[bwldrbst]

Originally Posted by Retro1234

Intresting to know, people are always asking how it was done.

Someone should have told the people making Space Quest IV!

[Tigerskunk]

Originally Posted by Retro1234

I was thinking of some kind of Copper Rainbow that could be more than one colour per scanline, sorry.

the guy Kev G did more than one Rainbow Side by Side and I think it worked with Dual
Playfield.
https://www.ultimateamiga.co.uk/index.php?topic=9300.0

Thats actually easy.
Just change the value for that color ($dff180) with the copper inbetween starts of lines.

[Retro1234]

Originally Posted by Steril707

Thats actually easy.
Just change the value for that color ($dff180) with the copper inbetween starts of lines.

How many colours can you have on a line like this?

[jizmo]

It's a technique that was established relatively early on in Amiga history and there's no technical reason why it couldn't have been used in various title screens and background images in Amiga.

Probably the biggest reason for it not being used is similar that of Ham mode: it's really usable to art digitised with quality hardware from quality source or the end result is garbage.

Secondly, it would have given only a debatable step up in the quality compared to HAM as most of the players play their games thru tiny CRT sets anyway.

So, not worth the hassle, extra 3rd party software (for conversion) and the extra code.