CODEWITHSUNDEEP
cgccrgbdata-conversionrgba
SoleCore
SoleCore

Reputation: 37

C - RGBA Conversion Not Returning The Desired RGB Result

Okay, I have a method that I am having a difficult time with returning the desired results. So I made a test result, and it is returning a result that I was not expecting.

Here is an example -->

int color = 0x00FFFF00;

return 0xFF & (color >> 24) | 0xFF & (color >> 16) | 0xFF & (color >> 8);

From what I know, this should return:

0x00FFFF

However, it actually returns:

0x0000FF

Can someone please explain what is happening? I would also like to know how I could properly convert the 32-bit RGBA integer to the 24-bit RGB integer, thank you.

Upvotes: 0

Views: 183

Answers (2)

SoleCore
SoleCore

Reputation: 37

I also caught what I did wrong. I was not shifting the red and green elements of the integer cast to match the RGB integer --->

int color = 0x00FFFF00;

// Returns 0x0000FF
return 0xFF & (color >> 24) | 0xFF & (color >> 16) | 0xFF & (color >> 8);

Here is the fixed code --->

unsigned int color = 0x00FFFF00; // Unsigned Integer to avoid shifting the Two's Complement flag into the RGB value as clearlight pointed out.

// Returns 0x00FFFF
return (0xFF & (color >> 24)) << 16 | (0xFF & (color >> 16)) << 8 | 0xFF & (color >> 8);

Upvotes: 1

clearlight
clearlight

Reputation: 12625

Try this:

#include <stdio.h>
int main() {

        unsigned int x = 0x00FFFF00;
        printf("0%8.8x", (x >> 8) & 0x00FFFFFF);
}

$ cc -o shft shft.c
$ ./shft
0x0000ffff

It's better if you make color an unsigned int, otherwise you can get the sign bit shifted in from the left, but in this case we're masking off the shifted in bytes, but be careful of that.

Upvotes: 0

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