RGB888 to RGB565 / Bit Shifting

问题

I want to combine three characters into a short using bit shifting. This is for implementing the RGB565 color palette (where there are 5 bits for red, 6 for green, 5 for blue).

Here is my example program, i'm just missing a step in the middle i think where i need to do some anding.

#include <stdio.h>

int main( ){
        unsigned char r, g, b;
        unsigned short rgb;

        r = 255;        // 0xFF 1111 1111
        g = 100;        // 0x64 0110 0100
        b = 50;         // 0x32 0011 0010

        r = r >> 3;     // 0x31 0001 1111
        g = g >> 2;     // 0x19 0001 1001
        b = b >> 3;     // 0x06 0000 0110

        //r = r & something; //
        //g = g & something; //
        //b = b & something; //

        // Desired result:
        //          R      G     B
        // 0xFB26 11111 011001 00110
        rgb = r | g | b;

        printf( "r 0x%x g 0x%x b 0x%x, rgb 0x%08x\n", r, g, b, rgb );
}

You can see my desired result at the end. Thanks for the help!

回答1:

rgb = ((r & 0b11111000) << 8) | ((g & 0b11111100) << 3) | (b >> 3);

We shift r left by 11 bits, g left by 5 bits and bitwise OR these with b shifted right by 3 bits. (NB: this assumes the values have already been correctly masked, if needed, to remove any unwanted bits.)

回答2:

Thanks for A2A. I had also faced the same issue. The below code would help you.

unsigned int r,g,b; // Pixel data in the RGB
unsigned char x1,x2; // The container for resulting 2 bytes

x1 = (r & 0xF8) | (g >> 5); // Take 5 bits of Red component and 3 bits of G component

x2 = ((g & 0x1C) << 3) | (b  >> 3); // Take remaining 3 Bits of G component and 5 bits of Blue component

You can find the python program in the GIThub. https://github.com/ajay126z/RGB888ToRGB565-Converter

来源：https://stackoverflow.com/questions/11471122/rgb888-to-rgb565-bit-shifting

标签

bit-manipulation

rgb