Support polycolour QRs

[Noitarud]

This is a novel idea, so this will only work in QRs created by the app.

Why not have multicolour QRs, it will increase data capacity and appear simpler. Here I used paint.net to add colours together, cyan background plus red background equals white. Three will be R+G+B (but R+Y+Cyan+B won't work since Y+Cn make white).

My attached GIF image should be scannable with anaglyphic 3D (red/cyan) glasses to separate the layers.

As for more, you could have levels, one at 1/3 and another at 2/3 brightness for each colour (sums to 3/3 where both converge). The problem with colours is they: fade unevenly, are not evenly visible under all lighting and blue is the dimmest colour (easier to miss or fewer levels for it. Brightness fractions in white light is 56% Green, 11 Blue, 33 red).

I have decided greyscale will be best in the long run (but will still be difficult if unevenly faded, discover the average by area and boost the black). The greyscale levels will have to be in powers of two for proper overlaying, blackness=(½+¼+⅛)/⅞ for three layers (0-bits would remove the respective ⅟ from the internal sum).