Convert 16 colour pic 2 OCS/ECS

[Retro1234]

I cannot covert the following picture to OCS its only -16 colours
the results are the second picture
In 16 colour AGA the picture is fine but in OCS the results are not good.

[Retro1234]

Anyone got any ideas on this why 16 colour AGA is ok but 16 Colour OCS is not?
I assume because there is nothing similar in the OCS palette?

[hooverphonique]

OCS colors use 12bit palette entries, aga uses 24 bit, so when colors are similar/close, you get banding like that.. It's practically the same phenomenon you see in a jpeg picture, if you compress it too hard..

[Retro1234]

is there anything I can do to get better results.

[idrougge]

Use a good program.

[Master484]

is there anything I can do to get better results.

Try converting the colors of the picture to OCS color values before loading and displaying it.

When I make OCS graphics on the PC and convert them to OCS IFFs, I always have to convert the colors to OCS colors first, or else the colors will be wrong.

I don't know if it helps, but to convert a Windows RGB color ( value range 0-255 ) to an OCS color ( value range 0-15 ), you should divide the RGB value with the number 17, and then round up the result to the closest OCS value (0-15).

So for example 255 / 17 would be 15.
But 240 / 17 would be 14.117 so it has to rounded up to 14.

The easier way would be to draw OCS images by using the directly corresponding RGB values, so that no conversion is required after the image is ready.

Here is a chart for the OCS values and their corresponding RGB value:
OCS Value --- RGB Value
0 --- 0
1 --- 17
2 --- 34
3 --- 51
4 --- 68
5 --- 85
6 --- 102
7 --- 119
8 --- 136
9 --- 153
10 --- 170
11 --- 187
12 --- 204
13 --- 221
14 --- 238
15 --- 255

This works for me, but I create all my gfx on PC, so I don't know how things work if you're doing an AGA --> OCS conversion in Amiga DPaint for example.

[Retro1234]

Thanks ill try that.

[Retro1234]

dividing these values by 17 doesnt seem to work am I doing something wrong.

[Retro1234]

dividing by 17 does work but I just dont think these colours exist within the OCS palette.
So the picture cant be converted but a similar picture only.

[Master484]

dividing by 17 does work but I just dont think these colours exist within the OCS palette.
So the picture cant be converted but a similar picture only.

That's right, the exact same colors are often not possible with the OCS palette. OCS only has 16 different values for each color component (Red, Green and Blue), and each component has a range between 0 to 15. AGA and RGB color components have 256 different values, ranging between 0 to 255.

So you just have to choose the closest color, and if it doesn't look good, then re-design the image palette for OCS.

[Retro1234]

Its the Rainbow from Super Mario 1 SNES so im surprised I cant match it but I dont seem to be able to.

[idrougge]

I just did a quick conversion in PPaint and the results are similar to yours. The range of the OCS palette just isn't big enough for those gradients. You could get better results by using dithering.

[Retro1234]

dithering is no good I load it in to copper raindow.
I guess the Snes had a wider palette.

[idrougge]

I suspected as much. If you make your own rainbow by eye, you'll get better results than a dumb colour mapping algorithm will turn out.

The SNES has a much wider palette; 32 768 colours as opposed to the Amiga's 4 096.

[pandy71]

With few tricks probably you can improve picture - temporal dithering and spatial dither (loading BPLxDAT with pattern like 1010...) should work.