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

Question

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

Answer 1

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);
}

Answer 2

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