1 Image img = Bitmap.FromFile("图片路径", true);
2 
3 PixelFormat pf = (PixelFormat)img.PixelFormat;
4 if (pf.ToString() == "8207")
5 {
6     MessageBox.Show("图片是CMYK模式！");
7 }

c'=255-r;
m'=255-g;
y'=255-b;
k=min(c',m',y');
c=c'-k;
m=m'-k;
y=y'-k;

R‘ =R/255
G‘ =G/255
B‘ = B/255
K= 1-max(R‘,G‘,B‘)
C= (1-R‘-K) / (1-K)
M= (1-G‘-K) / (1-K)
Y= (1-B‘-K) / (1-K)

 MagickImage magickImage = new MagickImage("图片路径");
 //MessageBox.Show(magickImage.ColorSpace.ToString());
 //magickImage.TransformColorSpace(ColorProfile.AdobeRGB1998);
 //magickImage.Settings.ColorSpace = ImageMagick.ColorSpace.CMYK;
 magickImage.ColorSpace = ColorSpace.CMYK;
 string path = @"D:\cmyk" + ((TimeSpan)(DateTime.Now.ToUniversalTime() - new DateTime(1970, 1, 1))).TotalMilliseconds + ".jpg";

 magickImage.Write(path);
 magickImage.Dispose();
 MessageBox.Show("图片已转换CMYK模式！\n 路径:" + path);