AGA color depth - HAM style

[NovaCoder]

Hi,

I just stumbled across the MooVid which appears to be able to display HAM 8 mode in realtime on a AGA chipset? Is this correct? I thought the HAM modes were too slow/difficult to use in realtime?

I've heard of a few AGA demos that use use animated HAM modes and this awesome [ Show youtube player ] seems to show more than 8bit colors in realtime animation.

Does anyone know of any other AGA games/apps that display and animate more than 256 colors at once?

[Leffmann]

Dithering arbitrary truecolor images to good HAM8 representations can be costly, but a typical left to right scanline rasterizer can do HAM8 in realtime, and has been done in several Amiga demos. One that comes to mind is Dolphin's Dream by Push Entertainment. Because of how the HAM mode works you would typically resort to only having 1/3 horizonal resolution, which would speed rendering up as well.

[NovaCoder]

Originally Posted by Leffmann

Dithering arbitrary truecolor images to good HAM8 representations can be costly, but a typical left to right scanline rasterizer can do HAM8 in realtime, and has been done in several Amiga demos. One that comes to mind is Dolphin's Dream by Push Entertainment. Because of how the HAM mode works you would typically resort to only having 1/3 horizonal resolution, which would speed rendering up as well.

Hiya,

Well I knew that you could do a static HAM backround with an animated 8bit object overlay but I didn't know you could animate HAM in realtime. Did any games every use this technique?

I finally got the MooVid player working last night and although it won't render HAM to a window, it will full-screen and it's very impressive

[Leffmann]

What the HAM mode does is give each pixel the ability to either take its color value from one of the color registers, or to take the color value of the pixel to its left and replace one of the R, G or B components, so you can't set any pixel to any color value you want, and arbitrary drawing operations on single pixels can become very costly. I don't know of any game that uses HAM for moving graphics. Since AmigaOS doesn't offer the HAM mode for the Workbench there's no way of getting software to display HAM other than in fullscreen.

How's the player working? Do you get a good picture with a decent frame rate?

[NovaCoder]

Originally Posted by Leffmann

What the HAM mode does is give each pixel the ability to either take its color value from one of the color registers, or to take the color value of the pixel to its left and replace one of the R, G or B components, so you can't set any pixel to any color value you want, and arbitrary drawing operations on single pixels can become very costly. I don't know of any game that uses HAM for moving graphics. Since AmigaOS doesn't offer the HAM mode for the Workbench there's no way of getting software to display HAM other than in fullscreen.

How's the player working? Do you get a good picture with a decent frame rate?

Yep it only displays 'high color' in fullscreen. The frame-rate is not great (about 8fps) but it is not only doing the HAM render, it's also decoding the AVI and mixing the sound.

[thomas]

I already told you on Utilitybase that RGB-to-HAM conversion is faster than RGB-to-greyscale conversion if you use lowest quality, i.e. stupidly use one pixel to change red, one to change green and one to change blue. HAM is similar to JPEG: it is great for smooth color changes but fails completely on sharp contrasts. So for a movie player using HAM8 gives better results than greyscale if the movie shows a landscape and not a computer screen.

Some examples:

[NovaCoder]

Hiya Thomas,

Nice pics

I'm just amazed to find that you can get generate HAM images so quickly, I always thought HAM was only used for static images....very cool stuff for my old machine