Hello,
i am wondering if i upgrade my NMS8280 to MSX2+, will it be possible to digitize to 19000 colours (SCREEN 12) ?

The original BIOS will not do this, for sure, but maybe some software will do. I read in some dutch docs that it is possible.

Is the hardware fixed to MSX2 RGB (RRRGGGBB) or is it possible modify it to make 19000 colours captures?

is no possible because electronics converters are for 256 colors
if you upgrade don't miss modify the synchro signal
see on hansoranje.demon.nl
hbi-v1 is required for 19000 colors

Tho in all honesty: wouldn't it make more sense to digitize with a PC, and use a tool like BMP2MSX to convert the result to s12? I dunno exactly how that HBI-V1 is dealing with color-depth, but typically one wants more colordepth than the end-result will have, so there's extra color-information to use for dithering.

I have an HBI-V1 digitizer and the quality is far from as good as if you digitize on a PC and convert the image to screen 12. Its a quite fun toy though but not good enough to use in productions.

It would require a lot of added hardware to let a NMS8280 with a V9938 digitize in screen 12. So no, it is not easy and I have never seen it done. There was a lot of talk in the old days about it being possible, but how?

About the HB-V1 as digitizer: when it appeared in the Netherlands, adapted to PAL, it was like a miracle. Nothing comparable (at least one could afford) was available for the PC at that time. Resulting pictures are not bad at alll, screen 12 of course has color spill and that limits the possibilities. And video itself has lousy quality itself.
Nowadays PC's have the power and hardware is affordable, video standards have evolved (DVD is low quality, HD is here, component or RGB is normal), so the HB-V1 and screen 12 and composite signals look oldfashioned. limited and underpowered. But in its time, wow!

Don't get me wrong when I said the HBI-V1 is not particularly good I was of course comparing to a modern PC and modern capture devices. When it came out it was of course rocking big time

An MSX digitizer could be quite handy do do old school overlays on videos and stuff so its not all useless. For digitizing images I'd prefer a PC though.

About the dithering thing I mentioned. Does that HBI-V1 dither from analogue to s12 specs? I dunno who remembers those kids' faces in the Philips 8280 ads on the backside of MCM in the ol' days, but those were ugly. While sc8 can actually show decent photos when they've been dithered from a true-color image.

The HBI-V1 does digitize from composite (analog) video signal to its own memory. And it does that in real Screen 12 format. No v9938/9958 vdp involved, it is complete standalone.
The PAL adaptation I wrote about is in the analog part, where the composite video signal is converted to RGB (or YUV for MSX2+ color spec). The original HBI-V1 does this for NTSC encoed signals, the adaptation switches that to PAL and 50 Hz. Not a big adaptation,it is something a television repair guy can do with the right equipment and knowledge.
The digital part is not changed, as you can see: only the top 525 lines are digitized (since NTSC only has 525 lines), PAL has 625 lines.