设置CIAdditionCompositing过滤器时，为什么会看到NSUnknownKeyException？

Question

I'm trying to set up a CIAdditionCompositing filter using the following code:

CIImage *imageOne = [CIImage imageWithCGImage:[UIImage imageNamed:@"picOne"].CGImage];
CIImage *imageTwo = [CIImage imageWithCGImage:[UIImage imageNamed:@"picTwo"].CGImage];

filter = [CIFilter filterWithName:@"CIAdditionCompositing"];
[filter setDefaults];
[filter setValue:imageOne forKey:kCIInputImageKey];
[filter setValue:imageTwo forKey:kCIInputBackgroundImageKey];

CIImage *imageResult  = [filter outputImage];
CGImageRef imageRef = [context createCGImage:imageResult fromRect:imageResult.extent];
_imageView.image = [UIImage imageWithCGImage:imageRef];

and am seeing the following error:

Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSCFConstantString 0x2e2d60> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key inputImage.'

on the line

[filter setValue:imageOne forKey:kCIInputImageKey];

What am I doing wrong in the setup of this Core Image filter?

Answer 1

Vary strange, this method works...

filter = [CIFilter filterWithName:@"CIAdditionCompositing" keysAndValues:kCIInputImageKey, imageOne, kCIInputBackgroundImageKey, imageTwo, nil];

can anyone explain the difference?