How do I save a CIImage to Photos with its P3 color space intact?

Question

I'm building a camera app that captures a photo in the BGRA format, and applies a Core Image filter on it before saving it to the Photos app. On the iPhone 7 Plus, the input photo is in the Display P3 color space, but the output is in the sRGB color space:

How do I prevent this from happening?

Here's my code:

let sampleBuffer: CMSampleBuffer = ...
let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
let metadata = CMCopyDictionaryOfAttachments(nil, self, kCMAttachmentMode_ShouldPropagate)!
let ciImage = CIImage(cvImageBuffer: pixelBuffer,
                      options:[kCIImageProperties: metadata])
NSLog("\(ciImage.colorSpace)")

let context = CIContext()
let data = context.jpegRepresentation(of: ciImage,
                                      colorSpace: ciImage.colorSpace!,
                                      options: [:])!
// Save this using PHPhotoLibrary.

This prints:

Optional(<CGColorSpace 0x1c40a8a60> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; Display P3))

(In my actual code, I apply a filter to the CIImage, which creates another CIImage, which I save. But I can reproduce this problem even with the original CIImage, so I've eliminated the filter.)

How do I apply a Core Image filter to a P3 image and save it as a P3 image, not sRGB?

---

Notes:

(1) This is on iPhone 7 Plus running iOS 11.

(2) I'm using the wide camera, not tele, dual or front.

(3) If I ask AVFoundation to give me a JPEG-encoded image rather than BGRA, and save it without involving Core Image, this problem doesn't occur — the color space isn't reduced to sRGB.

(4) I tried using kCIImageColorSpace, but it made no difference:

let p3 = CGColorSpace(name: CGColorSpace.displayP3)!
let ciImage = CIImage(
    cvImageBuffer: pixelBuffer,
    options:[kCIImageProperties: metadata,
             kCIImageColorSpace: p3])

(5) I tried using kCIContextOutputColorSpace in addition to the above, as an argument when creating the CIContext, but it again made no difference.

(6) The code that takes a Data and saves it to PHPhotoLibrary is not the problem, since it works in case (2) above.

let context = CIContext(options: [kCIContextOutputColorSpace: CGColorSpace.p3])

How do I apply a Core Image filter to a P3 image and save it as a P3 image, not sRGB?

Answer 1

I've had the same issue and I think this may be a bug with context.jpegRepresentation(..).

I've had more success using ImageIO to create the JPEG data, as shown in the createJPEGData function below. For example:

let eaglContext = EAGLContext(api: .openGLES2)
let options = [kCIContextWorkingColorSpace: CGColorSpace(name: CGColorSpace.extendedSRGB)!, 
               kCIContextOutputPremultiplied: true, 
               kCIContextUseSoftwareRenderer: false] as [String : Any]

let ciContext = CIContext(eaglContext: eaglContext, options: options)

let colorSpace = CGColorSpace(name: CGColorSpace.displayP3)!
guard let imageData = createJPEGData(from: image, 
                                     jpegQuality: 0.9,                           
                                     outputColorSpace: colorSpace,
                                     context: ciContext) else {
      return
}

PHPhotoLibrary.shared().performChanges({ () -> Void in
    let creationRequest = PHAssetCreationRequest.forAsset()
    creationRequest.addResource(with: .photo,
                                data: imageData,
                                options: nil)
}, completionHandler: { (success: Bool, error : Error?) -> Void in
    // handle errors, etc
})


func createJPEGData(from image: CIImage,
                    jpegQuality: Float,
                    outputColorSpace: CGColorSpace,
                    context: CIContext) -> Data? {

    let jpegData: CFMutableData =  CFDataCreateMutable(nil, 0)

    if let destination = CGImageDestinationCreateWithData(jpegData, kUTTypeJPEG, 1, nil) {
        if let cgImage = context.createCGImage(image,
                                               from: image.extent,
                                               format: kCIFormatRGBA8,
                                               colorSpace: outputColorSpace) {
            CGImageDestinationAddImage(destination, cgImage, image.properties as CFDictionary?)
            if CGImageDestinationFinalize(destination) {
                return jpegData as Data
            }
        }
    }
}