I'm converting ciimage to monochrome, clipping with CICrop and running sobel to detect edges, #if section at the bottom is used to display result
CIImage *ci = [[CIImage alloc] initWithCGImage:uiImage.CGImage];
CIImage *gray = [CIFilter filterWithName:@"CIColorMonochrome" keysAndValues:
@"inputImage", ci, @"inputColor", [[CIColor alloc] initWithColor:[UIColor whiteColor]],
nil].outputImage;
CGRect rect = [ci extent];
rect.origin = CGPointZero;
CGRect cropRectLeft = CGRectMake(0, 0, rect.size.width * 0.2, rect.size.height);
CIVector *cropRect = [CIVector vectorWithX:rect.origin.x Y:rect.origin.y Z:rect.size.width* 0.2 W:rect.size.height];
CIImage *left = [gray imageByCroppingToRect:cropRectLeft];
CIFilter *cropFilter = [CIFilter filterWithName:@"CICrop"];
[cropFilter setValue:left forKey:@"inputImage"];
[cropFilter setValue:cropRect forKey:@"inputRectangle"];
// The sobel convoloution will produce an image that is 0.5,0.5,0.5,0.5 whereever the image is flat
// On edges the image will contain values that deviate from that based on the strength and
// direction of the edge
const double g = 1.;
const CGFloat weights[] = { 1*g, 0, -1*g,
2*g, 0, -2*g,
1*g, 0, -1*g};
left = [CIFilter filterWithName:@"CIConvolution3X3" keysAndValues:
@"inputImage", cropFilter.outputImage,
@"inputWeights", [CIVector vectorWithValues:weights count:9],
@"inputBias", @0.5,
nil].outputImage;
#define VISUALHELP 1
#if VISUALHELP
CGImageRef imageRefLeft = [gcicontext createCGImage:left fromRect:cropRectLeft];
CGContextDrawImage(context, cropRectLeft, imageRefLeft);
CGImageRelease(imageRefLeft);
#endif
Now whenever 3x3 convolution is not part of the ciimage pipeline the portion of the image I run edge detection on shows up gray, but whenever CIConvolution3X3 postfix is part of the processing pipeline the colors magically appear back. This happens no matter if I use CIColorMonochrome or CIPhotoEffectMono prefix to remove color. Any ideas how to keep the color out all the way to the bottom of the pipeline? tnx
UPD: not surprisingly running a crude custom monochrome kernel such as this one
kernel vec4 gray(sampler image)
{
vec4 s = sample(image, samplerCoord(image));
float r = (s.r * .299 + s.g * .587 + s.b * 0.114) * s.a;
s = vec4(r, r, r, 1);
return s;
}
instead of using standard mono filters from apple results in the exact same issue with the color coming back when 3x3 convolution is part of my ci pipeline