Creating pixel art

Yes, AGE5 is the tool for screen 5. I've heard that AGE7 for screen 7 also exists, but I've not seen it. For screen 8 I like Philips Video Graphics. Graph Saurus was used by many, but I didn't like it because it felt a bit slow... Same problem even more with Paint IV... Many functions, but some bugs and horribly slow to use. Screen 12? Don't even bother to try.

I think SC12 was specifically designed for that, image scanning. You could always use any PC program without limitations (Blender, hand drawing + scanner...), and then convert. I think the SC12 is for that as said.

Note that Graph Saurus II supports 4 graphic modes (sc5, 7, 8, 12).

I would take approach something like this:
- Make a tile with your favourite graphics tools.
- Resize or resample it to 16x16 ...or what ever you use. Naturally X must by multiple of 4. (Using bigger source picture and resampling it down may give a nice, but a bit soft look)
- Convert it to SC11 with BMP2MSX (Use no scaling)
- Experiment with conversion parameters
- If still not good, experiment with Gamma & contrast and repeat previous step.
- When the tile looks good, use BASIC COPY-command to add it to your custom tileset.
- Draw software sprites with AGE5

But that’s why it actually seems very suitable for pixeling, screen 11 especially, very similar to the colour spill in screen 2 or 4… You can manually take care of the pixel alignment so that similar colours are in 4-pixel groups, e.g. a 4-pixel wooden edge around 8 pixels of stone. And when there is an area where you need different colours, try to find good J / K compromise values for it and tweak the surrounding pixels to match, or use one of screen 11’s palette colours to patch it up.

Just, if I could think of a good way to actually do that… Preferably in my usual editor.

After thinking about this a bit… I think this might be a good approach, slightly different from yours:

1. Draw a couple of tiles with your favourite graphics tools (256x256 24 bpp). Make them with the 4-pixel attribute clash in mind, using gradients of similar colours where possible. But also have a few places where you break the restriction to challenge the conversion and touchup later.
2. Convert to screen 11 or 12 with a script or BMP2MSX or similar and see how it turns out.
3. Touch it up it in an editor which allows you to tweak the Y, J and K values, like GraphSaurus or FUC’s editor msd mentioned, or a PC tool if anyone ever makes one. In this step you learn which colour ramps work for your graphics. Also you can define some palette colours.
4. Convert it back to 24 bpp PNG, now with 16-colour palette included in the PNG.
5. Draw more tiles, with the help of the colour picker and new knowledge of the ramps that you use. If you want to add tiles which don’t use the ramps you used before, just draw them in full-colour and repeat from step 2 for the new tiles.
6. Use a scratch area to put the colour ramps that you use, for easy use with a colour picker.

I think in this way you may be able to pixel pretty freely, and gradually learn what the best colour ramps are for your image or in general, and how to patch them up by either compromising a bit or using cleverly picked palette colours. Getting better over time with practice.