Commander X16

hstubbs3 wrote: ↑Mon Mar 18, 2024 8:16 pm 16 is not allowed.

https://www.youtube.com/watch?v=xOrgLj9lOwk&t=89s


what you're describing, as it being desirable to have 239 round up to 240 to then be considered 15 whence one does proceed with the division, would require some min or rescaling somewhere ...

R4 = int(min(R8,247)/16 + 0.5)

or indeed, as it may not actually be the case that the output DAC on the VERA board is linearly aligned with what one may be expecting of the 8bit per color source, it may actually be needed to employ some sort of table or other device to properly map R8G8B8 to R4G4B4 ... As I recall this is true of the Sega Genesis's output circuitry, but I have not yet put my X16 hardware together, for lack of desk space at the moment, and so have only seen it via the emulator...

hstubbs3 wrote: ↑Mon Mar 18, 2024 8:16 pm or indeed, as it may not actually be the case that the output DAC on the VERA board is linearly aligned with what one may be expecting of the 8bit per color source, it may actually be needed to employ some sort of table or other device to properly map R8G8B8 to R4G4B4 ... As I recall this is true of the Sega Genesis's output circuitry, but I have not yet put my X16 hardware together, for lack of desk space at the moment, and so have only seen it via the emulator...

hstubbs3 wrote: ↑Tue Mar 19, 2024 8:12 pm Funkheld,

"In order to have an almost real color tone for the x16 (emu) out of 256 color" -
for what image??? if you have some full-color image you want to display, you would have to get best 256 colors -for that image- something like telling GIMP to use an "indexed" color mode and set it to "optimized palette"

(On the above I concur)

......................................

but mapping 8bit range to the 4bit could be as simple or complex as one desires to make it - maintaining hue and such is complicated.. Color spaces can be tricky..

hstubbs3 wrote: ↑Tue Mar 19, 2024 8:12 pm Funkheld,

"In order to have an almost real color tone for the x16 (emu) out of 256 color" -
for what image??? if you have some full-color image you want to display, you would have to get best 256 colors -for that image- something like telling GIMP to use an "indexed" color mode and set it to "optimized palette"

if instead you want to take some random image and use the default palette, that could be done in GIMP say, using the 'indexed' image mode but telling GIMP to use a particular palette... And then you would have to supply the palette that the X16 is using (or your palette if you are loading a custom one )

The default 256 palette that is in the x16 at startup is depicted in a png in the vera doc -
If you just want to know where a shade of Red or orange is by default, this is arranged 16 to a row, so 8th color in the 2nd row is a middle gray and would be color $18 using the 8bit color mode..

https://github.com/X16Community/x16-doc ... alette.png



at some point I wrote a python script or something to pull the 8bit per color RGB values from these in order here -
https://github.com/hstubbs3/CommanderX1 ... x16pal.txt
Where line number is palette # +1 ... so the first line is color 0...

I could see maybe later / tomorrow or so making a file one could import into GIMP to have the default 256 palette there.. Then making image from true color to indexed, specify use that palette... and then saving the PNG would automagickally have that PNG use the same palette color numbers as the x16...

I would assume _someone_ has already made some sort of color quantization tool to map to the default X16 palette though???

writing something in Python wouldn't take too much effort to have a command line utility that accepted true color png and spat out 8bit x16 color data, question would be what format(s) should it generate???


possibly worth noting ....

Is that these RRGGBB values all have same high/low nibbles... IE -> this palette suggests that if you take some 8bit R,G,B value ... You would divide by 17 and do no rounding.. the scale appears to be -
decimal | 8bit | 4bit 0 | $00 | 0 17 | $11 | 1 34 | $22 | 2 51 | $33 | 3 68 | $44 | 4 85 | $55 | 5 102 | $66 | 6 119 | $77 | 7 136 | $88 | 8 153 | $99 | 9 170 | $AA | A 187 | $BB | B 204 | $CC | C 221 | $DD | D 238 | $EE | E 255 | $FF | F 163 | $99 | 9 163 | $99 | 9 163 | $99 | 9

but mapping 8bit range to the 4bit could be as simple or complex as one desires to make it - maintaining hue and such is complicated.. Color spaces can be tricky..