CIColorInvert and CIColorMatrix does not invert image properly

Question

I got stuck on inverting CIImage colors. I am creating CIImage from CGImage and then appling CIColorInvert filter or CIColorMatrix filter but none of them is working properly. When rendering CIImage as CGImage, I obtain results, which seems to be saturated (see attached example).

exmples of color invert using different approaches

I guess that the problem is colorspace but I have no idea how to fix it. I was following Core Image Programming Guide (chapter: Subclassing CIFilter: Recipes for Custom Effects, section: Subclassing CIFilter to Create the CIColorInvert Filter) but without any success.

I would be very thankful for any hints...

Answer 1

The problem was in working color space. I found answer to my question here. The CIContext which I creates looks now as follwing:

var ciContext = CIContext(options: [
    kCIImageColorSpace: NSNull(), 
    kCIImageProperties: NSNull(), 
    kCIContextWorkingColorSpace: NSNull()
])

To be honest, I do not know exactly the background, so I am not sure, why it is not working without setting WorkingColorSpace to NSNull. If someone knows, I would be really thankful for explanation.