Gaussian Noise using Core Graphics only? - cocoa

Question

How would I ever use Core graphics only to generate a noise texture background? I'm stuck on the noise part because there is no way to add a noise filter in core graphics...

Answer 1

About a year later, I've found the answer:
CGImageRef CGGenerateNoiseImage(CGSize size, CGFloat factor) CF_RETURNS_RETAINED {
NSUInteger bits = fabs(size.width) * fabs(size.height);
char *rgba = (char *)malloc(bits);
srand(124);
for(int i = 0; i < bits; ++i)
rgba[i] = (rand() % 256) * factor;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef bitmapContext = CGBitmapContextCreate(rgba, fabs(size.width), fabs(size.height),
8, fabs(size.width), colorSpace, kCGImageAlphaNone);
CGImageRef image = CGBitmapContextCreateImage(bitmapContext);
CFRelease(bitmapContext);
CGColorSpaceRelease(colorSpace);
free(rgba);
return image;
}
This effectively generates a noise image that's guaranteed to be random, and can be drawn, using the code from Jason Harwig's answer.

Answer 2

Create a noise png, then draw it using an overlay blend.
// draw background
CGContextFillRect(context, ...)
// blend noise on top
CGContextSetBlendMode(context, kCGBlendModeOverlay);
CGImageRef cgImage = [UIImage imageNamed:#"noise"].CGImage;
CGContextDrawImage(context, rect, cgImage);
CGContextSetBlendMode(context, kCGBlendModeNormal);

Answer 3

There is a CIRandomGenerator in CoreImageFilters as of iOS 6.
But bear in mind that this one is not gaussian noise (as it is not in the previous answer).
- (UIImage*)linearRandomImage:(CGRect)rect
{
CIContext *randomContext = [CIContext contextWithOptions:nil];
CIFilter *randomGenerator = [CIFilter filterWithName: #"CIColorMonochrome"];
[randomGenerator setValue:[[CIFilter filterWithName:#"CIRandomGenerator"] valueForKey:#"outputImage"] forKey:#"inputImage"];
[randomGenerator setDefaults];
CIImage *resultImage = [randomGenerator outputImage];
CGImageRef ref = [randomContext createCGImage:resultImage fromRect:rect];
UIImage *endImage=[UIImage imageWithCGImage:ref];
return endImage;
}