The first 8 least-significant bits represent the red component, the next 8 least-significant bits represent the green component, and the next 8 bit represent the blue component. The last 8 most-significant bits are not used
# The image data, each cell contains a pixel.
# The first 8 least-significant bits represent the red component,
# the next 8 least-significant bits represent the green component,
# and the next 8 bit represent the blue component.
# The last 8 most-significant bits are not used
private var data = new Array[Array[Int]]
lib/bitmap/bitmap.nit:85,2--90,41