CODEWITHSUNDEEP
ioscifilter
Sjakelien
Sjakelien

Reputation: 2317

Applying the CIScreenBlendMode filter

I want to blend an image with a blue color, using the CIScreenBlendMode filter.

For that, I use the following code:

-(CIImage*)makeitBlue:(CIImage*)greyImage{
    
    CIImage* outputImage = nil;
    
    //create some blue
    CIFilter* blueGenerator = [CIFilter filterWithName:@"CIConstantColorGenerator"];
    CIColor* blue = [CIColor colorWithString:@"0.1 0.5 0.8 1.0"];
    [blueGenerator setValue:blue forKey:@"inputColor"];
    CIImage* blueImage = [blueGenerator valueForKey:@"outputImage"];
    
    //apply a screen filter
    CIFilter* filter = [CIFilter filterWithName:@"CIScreenBlendMode"];
    [filter setValue:blueImage forKey:@"inputImage"];
    [filter setValue:greyImage forKey:@"inputBackgroundImage"];
    outputImage = [filter valueForKey:@"outputImage"];
    
    return outputImage;
    
}

This method makes my app crash and I don't know why.

In its documentation Apple states the following parameters for CIScreenBlendMode:

inputImage | A CIImage object whose display name is Image.

inputBackgroundImage | A CIImage object whose display name is Background Image.

I think that is just what I'm providing.

When I replace CIScreenBlendMode with CIMultiplyCompositing, this code is running fine.

Maybe some of you can spot the mistake I make?

Upvotes: 0

Views: 542

Answers (1)

Sjakelien
Sjakelien

Reputation: 2317

I found the answer here: Using a CIImage from CIColor in a CIFilter: getting empty image.

As user578205 states:

You should crop the generated image to beginImage size because generated image's size is infinite. I don't know why, but CIOverlayBlendMode isn't tolerant to infinite size

And in a way it makes sense: how could you align two images of which one is of infinite size?

Upvotes: 0

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