Changing the Color Space of NSImage

Question

Is there a way I can change the color space of an NSimage or NSBitmapImageRep/CGimage or the like. I am open to any way. Preferably the way photoshop does it.

Answer 1

CGImageRef CGImageCreateCopyWithColorSpace (
   CGImageRef image,
   CGColorSpaceRef colorspace
);

To get a CGColorSpaceRef, you can do things like

CGColorSpaceRef CGColorSpaceCreateDeviceRGB();

OR see this page for how to create other color spaces.

Answer 2

The problem with the code you see below

CGImageRef CGImageCreateCopyWithColorSpace (
CGImageRef image,
CGColorSpaceRef colorspace
);

is not working because Quartz2D does not support alpha for CMYK images or gray images, it is supported only by RGB images. What you should do is creating 2 images then combine then in case of a CMYK color space and image with alpha. I have searched a lot about this topic and finally found. May be author of this question doesn't need it anymore but someone else may need it.

1. Create new NSBitmapImageRep

   let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil,
                                         pixelsWide: Int(round(imageSize.width)),
                                         pixelsHigh: Int(round(imageSize.height)),
                                      bitsPerSample: 8,
                                    samplesPerPixel: 4,
                                           hasAlpha: false,
                                           isPlanar: false,
                                     colorSpaceName: NSDeviceCMYKColorSpace,
                                       bitmapFormat: NSBitmapFormat(rawValue: 0),
                                        bytesPerRow: Int(round(imageSize.width) * CGFloat(4)),
                                       bitsPerPixel: 0)
   

2. You need to draw your image into the new bitmap lets say you have colorSpace: NSColorSpace

   let context = NSGraphicsContext(bitmapImageRep: imageRep)
   NSGraphicsContext.saveGraphicsState()
   NSGraphicsContext.setCurrentContext(context)
   imageRep.setProperty(NSImageColorSyncProfileData, withValue: colorSpace.ICCProfileData)
   // Do your drawing here
   NSGraphicsContext.restoreGraphicsState()
   

3. After this you will have an imageRep that is the image with correct color space but no alpha (transparency).

4. You need a mask bitmap. Obtaining mask is tricky.

   let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil,
                                         pixelsWide: Int(round(imageSize.width)),
                                         pixelsHigh: Int(round(imageSize.height)),
                                      bitsPerSample: 8,
                                    samplesPerPixel: 1,
                                           hasAlpha: false,
                                           isPlanar: false,
                                     colorSpaceName: NSDeviceWhiteColorSpace,
                                       bitmapFormat: NSBitmapFormat(rawValue: 0),
                                        bytesPerRow: Int(round(imageSize.width)),
                                       bitsPerPixel: 0)
   

5. Clip white image to your image with transparency

   if let graphicsPort = NSGraphicsContext.currentContext()?.graphicsPort {
       let context = unsafeBitCast(graphicsPort, CGContextRef.self)
       let imgRect = NSRect(origin: NSPoint.zero, size: image.extent.size)
       let ciContext = CIContext()
       let cgImage = ciContext.createCGImage(image, fromRect: image.extent)
       CGContextClipToMask(context, imgRect, cgImage)
   }
   

6. Colorize all pixel in white color, this will be clipped to image.

   let context = NSGraphicsContext(bitmapImageRep: imageRep)
   NSGraphicsContext.saveGraphicsState()
   NSGraphicsContext.setCurrentContext(context)
   imageRep.setProperty(NSImageColorSyncProfileData, withValue: colorSpace.ICCProfileData)
   NSColor.whiteColor().setFill()
   NSBezierPath.fillRect(NSRect(origin: NSPoint.zero, size: imageSize))
   NSGraphicsContext.restoreGraphicsState()
   

7. At this step you have a image and a mask. Next we need to combine them. I am using this little algorithm (you need to verify that mask and source image have same sizes and same colorSpaceModel):

   func createCMYKAImageRepByApplingAlphaMask(srcImageRep: NSBitmapImageRep, alphaMaskImageRep alphaMask: NSBitmapImageRep) -> NSBitmapImageRep? {
       if canApplyMaskRepOnImageRep(srcImageRep, maskRep: alphaMask) == false {
           return nil
       }
       let alphaData = alphaMask.bitmapData
       let srcData = srcImageRep.bitmapData
       if let imageWithAlphaMaskRep = createEmptyCMYKABitmapImageRep(alphaMask.size) {
           if let colorSpaceData = imageColorSpace?.ICCProfileData {
                imageWithAlphaMaskRep.setProperty(NSImageColorSyncProfileData, withValue: colorSpaceData)
           }
           fillPixelsWithComponentsData(imageWithAlphaMaskRep, components: { (pixelIdx: Int) -> (UInt8, UInt8, UInt8, UInt8, UInt8) in
               let cyan = srcData[pixelIdx * 4 + 0]
               let magenta = srcData[pixelIdx * 4 + 1]
               let yellow = srcData[pixelIdx * 4 + 2]
               let black = srcData[pixelIdx * 4 + 3]
               let alpha = alphaData[pixelIdx]
               return (cyan, magenta, yellow, black, alpha)
           })
           return imageWithAlphaMaskRep
       }
       return nil
   }
   
   func createEmptyBitmapImageRep() -> NSBitmapImageRep? {
       let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil,
                                             pixelsWide: Int(round(imageSize.width)),
                                             pixelsHigh: Int(round(imageSize.height)),
                                          bitsPerSample: 8,
                                        samplesPerPixel: 5,
                                               hasAlpha: true,
                                               isPlanar: false,
                                         colorSpaceName: NSDeviceCMYKColorSpace,
                                           bitmapFormat: NSBitmapFormat(rawValue: 0),
                                            bytesPerRow: Int(round(imageSize.width) * CGFloat(5)),
                                           bitsPerPixel: 0)
       return imageRep
   }
   
   private func fillPixelsWithComponentsData(imgRep: NSBitmapImageRep,
   components: (Int) -> (cyan:UInt8, magenta:UInt8, yellow:UInt8, black:UInt8, alpha:UInt8)) {
       let imageRawData = imgRep.bitmapData
       let imageWidth = Int(imgRep.size.width)
       let imageHeight = Int(imgRep.size.height)
       for pixelIdx in 0 ..< (imageWidth * imageHeight) {
           let (cyan, magenta, yellow, black, alpha) = components(pixelIdx)
           let fAlpha = Float(alpha) / 255
           imageRawData[pixelIdx * 5 + 0] = UInt8(Float(cyan) * fAlpha)
           imageRawData[pixelIdx * 5 + 1] = UInt8(Float(magenta) * fAlpha)
           imageRawData[pixelIdx * 5 + 2] = UInt8(Float(yellow) * fAlpha)
           imageRawData[pixelIdx * 5 + 3] = UInt8(Float(black) * fAlpha)
           imageRawData[pixelIdx * 5 + 4] = alpha
       }
   }