Here's a simple way to allow the CPU to get pixel values from a UIImage. The steps are
- allocate a buffer for the pixels
- create a bitmap memory context using the buffer as the backing store
- draw the image into the context (writes the pixels into the buffer)
- examine the pixels in the buffer
- free the buffer and associated resources
- (void)processImage:(UIImage *)input
{
int width = input.size.width;
int height = input.size.height;
// allocate the pixel buffer
uint32_t *pixelBuffer = calloc( width * height, sizeof(uint32_t) );
// create a context with RGBA pixels
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate( pixelBuffer, width, height, 8, width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast );
// invert the y-axis, so that increasing y is down
CGContextScaleCTM( context, 1.0, -1.0 );
CGContextTranslateCTM( context, 0, -height );
// draw the image into the pixel buffer
UIGraphicsPushContext( context );
[input drawAtPoint:CGPointZero];
UIGraphicsPopContext();
// scan the image
int x, y;
uint8_t r, g, b, a;
uint8_t *pixel = (uint8_t *)pixelBuffer;
for ( y = 0; y < height; y++ )
for ( x = 0; x < height; x++ )
{
r = pixel[0];
g = pixel[1];
b = pixel[2];
a = pixel[3];
// do something with the pixel value here
pixel += 4;
}
// release the resources
CGContextRelease( context );
CGColorSpaceRelease( colorSpace );
free( pixelBuffer );
}