divide pixel values by 256

[kazzmir]

fixes #92

[andydotxyz]

Thanks for this.

Upon looking I see that there is another issue, in that the RGBA in Go is pre-multipled alpha, but the values we need are not - could you perhaps swap in their maths for getting the right values instead?

https://cs.opensource.google/go/go/+/refs/tags/go1.24.2:src/image/color/color.go;l=60

Your solution will work when the Alpha value is strictly higher than all other colour channels, but for a semi-transparent white (for example) it would create an invalid colour.

[andydotxyz]

Thanks for the update, but can you address this point regarding the (non-)pre-multiplied alpha?
The Go image package is a way to see how it is handled by others:

Your solution will work when the Alpha value is strictly higher than all other colour channels, but for a semi-transparent white (for example) it would create an invalid colour.