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Xcode: alpha composition using kernel image

I would like to create a chain of CoreImage filters and be able to control the "intensity" of each filter in the chain, adding its individual effect with the alpha or opacity settings, but I don’t see a way to composite with alpha or opacity in documents.

I could jump out of the Core filter chain and compositions with the main graphics context, I think.

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It ended like that. Code from this answer: fooobar.com/questions/167068 / ...

UIImage *bottomImage = inputImage;
UIImage *image = filterOutput;
CGSize newSize = CGSizeMake(inputImage.size.width, inputImage.size.height);
UIGraphicsBeginImageContext( newSize );
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:_opacity];
UIImage *blendedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
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CIColorMatrix - CIImage, :

CIImage *overlayImage = … // from file, CGImage etc
CIImage *backgroundImage = … // likewise

CGFloat alpha = 0.5;
CGFloat rgba[4] = {0.0, 0.0, 0.0, alpha};
CIFilter *colorMatrix = [CIFilter filterWithName:@"CIColorMatrix"];
[colorMatrix setDefaults];
[colorMatrix setValue:overlayImage forKey: kCIInputImageKey];
[colorMatrix setValue:[CIVector vectorWithValues:rgba count:4] forKey:@"inputAVector"];

CIFilter *composite = [CIFilter filterWithName:@"CISourceOverCompositing"];
[composite setDefaults];
[composite setValue:colorMatrix.outputImage forKey: kCIInputImageKey];
[composite setValue:backgroundImage forKey: kCIInputBackgroundImageKey];

UIImage *blendedImage = [UIImage imageWithCIImage:composite.outputImage];
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