What is the meaning of & 0xff when separating RGB channels from an RGB image?
I have the following piece of code
for(int row=0; row<r; row++)
{
for(int col=0; col<c; col++)
{
alphaPixels[row][col] = ((RGBarray[ii]>>24)&0xff);
redPixels[row][col] = ((RGBarray[ii]>>16)&0xff);
greenPixels[row][col] = ((RGBarray[ii]>>8)&0xff);
bluePixels[row][col] = (RGBarray[ii]&0xff);
ii++;
}
}
Why should we use the bitwise AND & 0xff
operation after the switch operation?
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Why should we use bitwise AND and 0xff operations after switching operation?
Oxff
is a hexadecimal number equal to decimal 255.
In your case, & 0xff
make sure that the entire range of pixel values is between 0 and 255 (i.e. positive 8 bits). For example, if any value is greater than 255, then it truncates it within the range 0-255
int value=257;
int result = value & 0xff; // result will be 1
Thus, it works like a %
positive remainder operator . But the bitwise operator &
is faster than the remainder operator %
.
int result = value % 256; //You will get same result for positive value
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0xff
has an integer value of 255.
>> n
on the right shifts the number of bits n
, the operator &
performs a bitwise AND operation.
So it & 0xff
masks the variable. It only leaves the last 8 bits and ignores all other bits.
This is a common trick when you are trying to convert color values from a custom format to standard RGB values (since it is 8 bits).
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