Changing the Color Space of NSImage - objective-c

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

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

Answer 2

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.