改变 NSImage 的色彩空间

Question

有没有办法可以更改 NSimage 或 NSBitmapImageRep/CGimage 等的颜色空间。我对任何方式都持开放态度。最好是Photoshop的方式。

Answer 1

您在下面看到的代码的问题

CGImageRef CGImageCreateCopyWithColorSpace (
CGImageRef image,
CGColorSpaceRef colorspace
);

不工作，因为 Quartz2D 不支持 CMYK 图像或灰度图像的 alpha，它仅受 RGB 图像支持。您应该做的是创建 2 个图像，然后在 CMYK 颜色空间和带有 alpha 的图像的情况下进行组合。我已经搜索了很多关于这个主题，终于找到了。可能是这个问题的作者不再需要它，但其他人可能需要它。

1. 创建新的 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. 您需要将图像绘制到新的位图中，假设您有 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. 在此之后，您将拥有一个 imageRep，它是具有正确色彩空间但没有 alpha（透明度）的图像。

4. 您需要一个遮罩位图。获得面具是一件棘手的事情。

   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. 将白色图像剪辑到具有透明度的图像

   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. 将所有像素着色为白色，这将被剪辑到图像中。

   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. 在这一步你有一个图像和一个蒙版。接下来我们需要将它们组合起来。我正在使用这个小算法（您需要验证蒙版和源图像具有相同的大小和相同的颜色空间模型）：

   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
       }
   }