Amiga color palette ibrowse5/30/2023 You won't get completely rid of the artifacts, but they might now be unnoticeable unless you take a closer look.Identifying an ILBM file as HAM-E is difficult it can apparently only be done by looking for a special signature near the beginning of the pixel data. To counteract the bleeding, you would have to design a routine that figures out which pixels to the right of a blit to adjust and which pixel values are the optimal ones that let the apparent pixel colors match the original ones as closely as possible. Note that I scaled the image by a factor of 2 to make the artifacts easier to see Only in column 103 will you have modified all three color components and the apparent pixel color will be the same $0676 as the original one before blitting.ĭepending on how many and which color components you consecutively modify, the color bleeding can affect more or less pixels and depending on how different the colors are to the originally intended colors, the artifacts can be more or less visible. What this means is that the white will bleed into the next 2 pixels:ĭue to modifying just the red component, the visible color in column 101 will be $06FF, a bright cyan.ĭue to modifying just the green component, the visible color in column 102 will be $067F, a bright blue. Say the rightmost pixel of that character ends up in column 100 and it is a bright white, palette value $0FFF. So far so good, but say you now want to blit an animated character onto the bitmap. Note that each differently colored square represents 1 pixel The resulting pixel in column 103 will now have a color equivalent to $0676, which is a dark gray with a very slight shimmer of green. The resulting pixel in column 102 will now have a color equivalent to $0673, which is a brown-greenish color.įinally, lacking a matching color in the palette once more, you modify the blue component in column 103 to $6 (using a pixel value of $16 = 22). Next, again lacking a matching color in the palette, you modify the green component in column 102 to $7 (using a pixel value of $37 = 55). The resulting pixel in column 101 will now have a color equivalent to $0633, which is a dark unsaturated red. Then, lacking a matching color in the palette, you modify the red component in column 101 to $6 (using a pixel value of $26 = 38). So the pixel in column 100 will appear gray. Say also that this palette entry is $0333, i. Say you set the color to palette entry 8 in column 100. The other two color components remain unchanged from the previous pixel. However, value sets 16 to 31 (modify blue component), 32 to 47 (modify red component) and 48 to 63 (modify green component), respectively, each just change one of the color components relative to the color of the previous pixel. Values 0 to 15 select a full RGB color from the 16 color palette, the same way other normal screen modes would. In HAM mode you usually use 6 bitplanes (you can also use it with 5 bitplanes, but there's not much point to that). The reason why it is unfeasible to use HAM for animated action is that you will either have to tolerate so-called color bleeding to the right of pixels or you will need to employ sophisticated algorithms to counteract the color bleeding, which timing constraints may forbid or which are just not worth it to come up with. See robc's answer.)įury of the Furries uses HAM for its still images, for example the title image and the images that are displayed before entering a new world (each consisting of a set of levels). ( Update: There were at least 2 games using HAM for their animated action. I used to be unaware of any game that uses it for gameplay. The way HAM (Hold And Modify) mode works makes it unsuitable for ingame animation in most cases. However, it requires a machine more powerful than a stock Amiga 500. It can then render its ingame 3D graphics to an EHB mode display. I'm not sure if it uses it ingame, but I consider it unlikely.Ī newer game, Nemac IV, presents you with a screen mode selection at the beginning, offering EHB mode as an option. it waits for raster line $42 (66) and uses BPLCON0 to set the number of bitplanes to 6 without the HAM bit set, which means EHB mode.Ĭannon Fodder uses EHB for some of its still pictures. In my example run of the Beat Box table I can find the following in the copper list: $00D6EA WAIT $4211FFFE For example, a game that uses EHB (Extra HalfBrite) mode during the game action (i.
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