How can I create a finite CIImage?

Question

The CIColorMap CIFilter takes a CIImage as an input. It makes sense to generate that input image dynamically using another CIFilter (such as CILinearGradient) but providing the result of a filter to the color map filter will result in the following error like the following:

[CIColorMap outputImage] requires the inputGradientImage to be finite

Even though the start/end points of the gradient are specified as inputs to the CILinearGradient filter the image itself is not finite. How can I generate a finite CIImage to pass to my filter?

Answer 1

Here's an example of how to create a fixed size CIImage to use as an input to another CIFilter:

CGFloat gradientSize = 100.f;         
CIFilter *gradientFilter = [CIFilter filterWithName:@"CISmoothLinearGradient"];
[gradientFilter setValue:[CIVector vectorWithX:0 Y:0] forKey:@"inputPoint0"];
[gradientFilter setValue:[CIVector vectorWithX:gradientSize Y:0] forKey:@"inputPoint1"];
[gradientFilter setValue:[CIColor colorWithCGColor:[[UIColor cyanColor] CGColor]] forKey:@"inputColor0"];
[gradientFilter setValue:[CIColor colorWithCGColor:[[UIColor magentaColor] CGColor]] forKey:@"inputColor1"];
CIImage *gradientImage = [[gradientFilter outputImage] imageByCroppingToRect:CGRectMake(0, 0, gradientSize, 1)];

// Other filter to receive cropped gradientImage
CIFilter *gradientMapFilter = [CIFilter filterWithName:@"CIColorMap"];
[gradientMapFilter setValue:gradientImage forKey:@"inputGradientImage"];