Converting hex to RGB and vice-versa

Question

What is the most efficient way to do this?

Answer 1

A hex value is just RGB numbers represented in hexadecimal. So you just have to take each pair of hex digits and convert them to decimal.

Example:

#FF6400 = RGB(0xFF, 0x64, 0x00) = RGB(255, 100, 0)

Answer 2

just real quick:

int r = ( hexcolor >> 16 ) & 0xFF;

int g = ( hexcolor >> 8 ) & 0xFF;

int b = hexcolor & 0xFF;

int hexcolor = (r << 16) + (g << 8) + b;

Answer 3

Real answer: Depends on what kind of hexadecimal color value you are looking for (e.g. 565, 555, 888, 8888, etc), the amount of alpha bits, the actual color distribution (rgb vs bgr...) and a ton of other variables.

Here's a generic algorithm for most RGB values using C++ templates (straight from ScummVM).

template<class T>
uint32 RGBToColor(uint8 r, uint8 g, uint8 b) {
return T::kAlphaMask |
       (((r << T::kRedShift) >> (8 - T::kRedBits)) & T::kRedMask) |
       (((g << T::kGreenShift) >> (8 - T::kGreenBits)) & T::kGreenMask) |
       (((b << T::kBlueShift) >> (8 - T::kBlueBits)) & T::kBlueMask);
}

Here's a sample color struct for 565 (the standard format for 16 bit colors):

template<>
struct ColorMasks<565> {
enum {
 highBits    = 0xF7DEF7DE,
 lowBits     = 0x08210821,
 qhighBits   = 0xE79CE79C,
 qlowBits    = 0x18631863,


 kBytesPerPixel = 2,

 kAlphaBits  = 0,
 kRedBits    = 5,
 kGreenBits  = 6,
 kBlueBits   = 5,

 kAlphaShift = kRedBits+kGreenBits+kBlueBits,
 kRedShift   = kGreenBits+kBlueBits,
 kGreenShift = kBlueBits,
 kBlueShift  = 0,

 kAlphaMask = ((1 << kAlphaBits) - 1) << kAlphaShift,
 kRedMask   = ((1 << kRedBits) - 1) << kRedShift,
 kGreenMask = ((1 << kGreenBits) - 1) << kGreenShift,
 kBlueMask  = ((1 << kBlueBits) - 1) << kBlueShift,

 kRedBlueMask = kRedMask | kBlueMask

};
};

Answer 4

In python:

def hex_to_rgb(value):
    value = value.lstrip('#')
    lv = len(value)
    return tuple(int(value[i:i+lv/3], 16) for i in range(0, lv, lv/3))

def rgb_to_hex(rgb):
    return '#%02x%02x%02x' % rgb

hex_to_rgb("#ffffff")             #==> (255, 255, 255)
hex_to_rgb("#ffffffffffff")       #==> (65535, 65535, 65535)
rgb_to_hex((255, 255, 255))       #==> '#ffffff'
rgb_to_hex((65535, 65535, 65535)) #==> '#ffffffffffff'