.. and mine is HAM
HAM is a screen mode on the AMIGA series of computers. It allowed images to be displayed in all their full palette glory of 4096 colours. Doesnt sound much but this is 1989 and I remember it blowing my mind when i first saw it
The Amiga could display colour indexed images up to 32 colours. Each index pointing to a colour within its 4096 colour palette. (16*16*16). It then had 2 special modes; EHB and HAM
EHB
EHB (Extra Half Bright) allowed the a 32 colour index and an extra 32 colour of half bright colours using the last bit of the 6 bit pixel. Each pixel was spread across 6 bitplanes, Drawing in the last bitplane would draw the darker colour. Great for drawing quick shadows.
HAM
HAM (Hold And Modify) mode would have 16 base colours. The 16 colour index is referenced in the first 4 bits of the 6 bit per pixel value
6 5 4 3 2 1
+-+-+-+-+-+-+
| | |X|X|X|X|
+-+-+-+-+-+-+
The last 2 bits are reserved for HAM.
00 then the index is colour is used.
01 then the blue value is changed to the first 4 bits (0-15) but the other red and green values are held.
Ive added HAM mode to my PXL64 application, so now you can convert your favourite images to near photo-realistic from the early 90s
HAM is a screen mode on the AMIGA series of computers. It allowed images to be displayed in all their full palette glory of 4096 colours. Doesnt sound much but this is 1989 and I remember it blowing my mind when i first saw it
The Amiga could display colour indexed images up to 32 colours. Each index pointing to a colour within its 4096 colour palette. (16*16*16). It then had 2 special modes; EHB and HAM
EHB
EHB (Extra Half Bright) allowed the a 32 colour index and an extra 32 colour of half bright colours using the last bit of the 6 bit pixel. Each pixel was spread across 6 bitplanes, Drawing in the last bitplane would draw the darker colour. Great for drawing quick shadows.
HAM
HAM (Hold And Modify) mode would have 16 base colours. The 16 colour index is referenced in the first 4 bits of the 6 bit per pixel value
6 5 4 3 2 1
+-+-+-+-+-+-+
| | |X|X|X|X|
+-+-+-+-+-+-+
00 then the index is colour is used.
01 then the blue value is changed to the first 4 bits (0-15) but the other red and green values are held.
10 then the red value is changed to the first 4 bits (0-15) but the other green and blue values are held.
11 then the green value is changed to the first 4 bits (0-15) but the other red and blue values are held.
This meant that any colour from the 4096 palette could be acheived within 3 pixels.
As most photos feature gradients, like skin tone, the colour could be reached within 1 or 2 pixels.
11 then the green value is changed to the first 4 bits (0-15) but the other red and blue values are held.
As most photos feature gradients, like skin tone, the colour could be reached within 1 or 2 pixels.
So in no more graphical memory than EHB mode, the Amiga could achieve photo like images. This made it stand out from other home computers at the time.
Sadly HAM mode couldnt be used for games as due to the HAM indexing, strange ghosting would happen as the 16 base colours shift across the screen on sprites.
Ive added HAM mode to my PXL64 application, so now you can convert your favourite images to near photo-realistic from the early 90s
Comments
Post a Comment