Make all black pixels transparent using CIImage

I'm trying to get something akin to a color mask using exclusively CIImage filters.

Basically, I'm looking to make all black pixels transparent. I don't mind what color all the non-black pixels end up having, so long as they have maximum alpha.

The code I'm familiar with in Core Graphics to achieve this would look like:

// Convert black sections to transparent using a color mask
const CGFloat maskingColors[6] = { 0, 0, 0, 0, 0, 0 };
CGImageRef result = CGImageCreateWithMaskingColors(image, maskingColors);

I've given it a shot in Core Image using a color matrix filter but it just sets result to nil since the CIVector values are greater than 1.0f.

// Create color matrix filter
CIFilter *matrix = [CIFilter filterWithName:@"CIColorMatrix"];

// Set filter properties
[matrix setValue:image forKey:kCIInputImageKey];
[matrix setValue:[CIVector vectorWithX:1.0f Y:0.0f Z:0.0f W:0.0f] forKey:@"inputRVector"];
[matrix setValue:[CIVector vectorWithX:0.0f Y:1.0f Z:0.0f W:0.0f] forKey:@"inputGVector"];
[matrix setValue:[CIVector vectorWithX:0.0f Y:0.0f Z:1.0f W:0.0f] forKey:@"inputBVector"];
[matrix setValue:[CIVector vectorWithX:255.0f Y:255.0f Z:255.0f W:0.0f] forKey:@"inputAVector"];

// Get the mapped image
CIImage *result = [matrix valueForKey:kCIOutputImageKey];

Note: For what it's worth, this is an OSX app.