How to reverse in modular arithmetic

Question

Given an RGB color {127, 255, 212} where scale is 0-255, VBA's RGB function find a long integer x such that

IntegerPart@{Mod[x,256],Mod[x/256,256],Mod[x/256^2,256]}

is equal to {127,255,212}. In this particular case the

x=13959039

How do i replicate this function in Mathematica?

Answer 1

You could use NumberCompose:

NumberCompose[{212,255,127},{256^2,256,1}]

13959039

Answer 2

fromRGB[{r_, g_, b_}] := r + 256*g + 65536*b
fromRGB[{127, 255, 212}]
(* 13959039 *)

or

fromRGB[rgb_List] := {1, 256, 65536}.rgb

(same result)

Answer 3

Reverse@IntegerDigits[13959039, 256]
FromDigits[Reverse@{127, 255, 212}, 256]

{127, 255, 212}

13959039