Crash on unsigned char of an image due to bad access

Question

Im trying to get RGB values of an image at particular point. Sometimes it get crashed by bad access.

+ (void)pixelValueForData:(unsigned char*)data
               atOffset:(int)offset {
        int red = data[offset+1];
        int green = data[offset+2];
        int blue = data[offset+3];
        NSLog(@"offset: %i colors: RGB A %i %i %i ",offset,red,green,blue);
}

offset calculated as

                int offset = 4*((width*y)+x);

What should i do to avoid that crash ?

Answer 1

Yes it was problem with calculating offset. It should obey conditions x >= 0, x <= width , y >=0 and y <= height. offset satisfying above conditions only should pass to pixelValueForData: method. Else it get crashed.