I can already convert 32bit integers into their rgba values like this:
pixelData[i] = {
red: pixelValue >> 24 & 0xFF,
green: pixelValue
To reverse it, you just have to combine the bytes into an integer. Simply use left-shift and add them, and it will work.
var rgb = (red << 24) + (green << 16) + (blue << 8) + (alpha);
Alternatively, to make it safer, you could first AND each of them with 0xFF:
var r = red & 0xFF;
var g = green & 0xFF;
var b = blue & 0xFF;
var a = alpha & 0xFF;
var rgb = (r << 24) + (g << 16) + (b << 8) + (a);
(You may use bitwise OR |
instead of +
here, the outcome will be the same).