如何创建有限的CIImage？

Question

CIColorMap CIFilter将CIImage作为输入。使用另一个CIFilter（例如CILinearGradient）动态生成输入图像是有意义的，但是向颜色映射过滤器提供过滤器的结果将导致以下错误，如下所示：

  

[CIColorMap outputImage]要求inputGradientImage是有限的

即使将渐变的起点/终点指定为CILinearGradient滤镜的输入，图像本身也不是有限的。如何生成有限的CIImage以传递给我的过滤器？

Answer 1

以下是如何创建固定尺寸CIImage以用作另一个CIFilter的输入的示例：

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"];