I've always wondered if you could just stick a colourimeter on a GBA SP and generate an ICC profile for it, then use that profile to adapt the colours to your display. It probably wouldn't be that easy, but there are colour management tools and libraries available that are designed for adapting colours between devices, so if you could somehow obtain a device profile for the GBA LCD, it might be possible to use it to produce very accurate colour emulation.
As I understand it, colorimeter expect the display to output a particular colour or shade and measure it precisely. You probably couldn't run colorimeter software on a GBA, but you could write homebrew that let the user manually cycle to the correct patterns at the right times.
Some issues would be:
- There's at least three models of GBA display: the original front-lit display, the GBA SP back/front-lit display, and the later GBA SP backlit-only display, and they probably all have different profiles
- It's probably not possible to use a colorimeter on the original front-lit GBA display, because with a colorimeter clamped on top of it, it would always look black
- Colour-correction software that works with ICC profiles is typically built for print/still image work, so it expects a single high-resolution image with high-precision output, not a 60fps stream of very-low-resolution images. Maybe it's fast enough to run in real-time, who knows?
I think relaying the image with a lens onto the colorimeter should work assuming you modify the game so the hardware displays a full screen equivalent of all possible variations of a single pixel. it might be necessary to switch to a color cube with 3 photodiodes, and perhaps read in with 3 DC-coupled audio channels, or alternatively use an arduino's ADC (I know ...) but with a proper antialiasing filter capacitor for the sample rate used.
Yeah, writing homebrew to get the GBA screen to display whatever a screen displays under a colourimeter, and getting that to work with the actual colourimeter might not be so easy. I think getting a device profile for the frontlit SP would be the most interesting, since I've heard it produces colours more like the original GBA than the backlit one, but maybe a colourimeter designed for backlit PC monitors would have trouble with it. I don't think performance would be an issue though. mpv can do colour management in real time by generating a LUT from the ICC profile and applying it to each frame with GPU shaders.
Most colorimeters also have a projector mode for measuring beamer screens. You can just point the colorimeter to the gba screen bar an angle and shine a high quality light source at it
That's cool. I didn't know that (I've never used one before.) Maybe it would make more sense to do the original GBA then. The SP frontlight has a bit of a blueish tinge to it.
