CPC mode 2 is quite challenging! (double height pixels, 640x200 resolution, only 2 colors)
I haven't even conformed to all the restrictions here, these are only mode2-ish. some areas use more than 2 colors and you would have to resort to stacking CPC+ sprites to display them properly.
If you're curious, you can do doubleheight-pixel pixeling by exactly the same method as doublewidth, just swapping the axes.
In GIMP I set the horizontal dpi to match the reported monitor DPI, set the vertical DPI to half that, and toggle 'view->dot per dot' OFF.
doublewidth and doubleheight pixels are both quite challenging, I'm just more used to doublewidth. The combination of 2 colors and doubleheight really pushes me esp. WRT dithering and shape definition.
