To convert RGB 12 bit data to RGB 12 bit packed data

Question

Hello,

I have some RGB(image) data which is 12 bit. Each R,G,B has 12 bits, total 36 bits. Now i need to club this 12 bit RGB data into a packed data format. I have tried to mention the packing as below:-

At present I have input data as - B0 - 12 bits G0 - 12 bits R0 - 12 bits B1 - 12 bits G1 - 12 bits R1 - 12 bits .. so on. I need to convert it to packed format as:-

Byte1 - B8 (8 bits of B0 data)

Byte2 - G4B4 (remaining 4 bits of B0 data+ first 4 bits of G0)

Byte3 - G8 (remaining 8 bits of G0)

Byte4 - R8 (first 8 bits of R0)

Byte5 - B4R4 (first 4 bits of B1 + last 4 bits of R0)

I have to write these individual bytes to a file in text format. one byte below another.

Similar thing i have to do for a 10 bit RGB input data.

1.) Is there any tool/software to get the conversion of data i am looking to get done.

2.) I am trying to do it in a C program - I am forming a 64 bit from the individual 12 bits of R,G,B (total 36 bits). But after that i am not able to come up with a logic to pick the necessary bits from a R,G,B data to form a byte stream, and to dump them to a text file.

Any pointers will be helpful.

Thank you.

-AD

Answer 1

Use bitwise & (and), | (or), and shift <<, >> operators.

Answer 2

This is pretty much untested, super messy code I whipped together to give you a start. It's probably not packing the bytes exactly as you want, but you should get the general idea.

Apologies for the quick and nasty code, only had a couple of minutes, hope it's of some help anyway.

#include <stdio.h>

typedef struct
{
    unsigned short B;
    unsigned short G;
    unsigned short R;

} UnpackedRGB;

UnpackedRGB test[] = 
{
    {0x0FFF, 0x000, 0x0EEE},
    {0x000, 0x0FEF, 0xDEF},
    {0xFED, 0xDED, 0xFED},
    {0x111, 0x222, 0x333},
    {0xA10, 0xB10, 0xC10}
};

UnpackedRGB buffer = {0, 0, 0};

int main(int argc, char** argv)
{   
    int numSourcePixels = sizeof(test)/sizeof(UnpackedRGB);

    /* round up to the last byte */
    int destbytes = ((numSourcePixels * 45)+5)/10; 

    unsigned char* dest = (unsigned char*)malloc(destbytes); 
    unsigned char* currentDestByte = dest;

    UnpackedRGB *pixel1;
    UnpackedRGB *pixel2;
    int ixSource;
    for (ixSource = 0; ixSource < numSourcePixels; ixSource += 2)
    {      
        pixel1 = &test[ixSource];
        pixel2 = ((ixSource + 1) < numSourcePixels ? &test[ixSource] : &buffer);

        *currentDestByte++ = (0x0FF) & pixel1->B;
        *currentDestByte++ = ((0xF00 & pixel1->B) >> 8) | (0x0F & pixel1->G);
        *currentDestByte++ = ((0xFF0 & pixel1->G) >> 4);
        *currentDestByte++ = (0x0FF & pixel1->R);
        *currentDestByte++ = ((0xF00 & pixel1->R) >> 8) | (0x0F & pixel2->B);

        if ((ixSource + 1) >= numSourcePixels)
        {
            break;
        }

        *currentDestByte++ = ((0xFF0 & pixel2->B) >> 4);
        *currentDestByte++ = (0x0FF & pixel2->G);
        *currentDestByte++ = ((0xF00 & pixel2->G) >> 8) | (0x0F & pixel2->R);
        *currentDestByte++ = (0xFF0 & pixel2->R);
    }

    FILE* outfile = fopen("output.bin", "w");
    fwrite(dest, 1, destbytes,outfile);
    fclose(outfile);
}