C# convert RGB value to CMYK using an ICC profile?

Question

this question seems posted at many places over the interwebs and SO, but I could not find a satisfactory answer :(

How can I convert a RGB value to a CMYK value using an ICC profile?

The closest answer I have is there, where it explains how to convert from CMYK to RGB but not the other way around, which is what I need. (http://stackoverflow.com/questions/4920482/cmyk-to-rgb-formula-of-photoshop/5076731#5076731)

float[] colorValues = new float[4];
colorValues[0] = c / 255f;
colorValues[1] = m / 255f;
colorValues[2] = y / 255f;
colorValues[3] = k / 255f;

System.Windows.Media.Color color = Color.FromValues(colorValues,
new Uri(@"C:\Users\me\Documents\ISOcoated_v2_300_eci.icc"));
System.Drawing.Color rgbColor = System.Drawing.Color.FromArgb(color.R, color.G, color.B);

I guess I should be using some classes/structures/methods from the System.Windows.Media namespace.

The System.Windows.Media.Color structure contains a method FromRgb, but I can't get CMYK values after, out of that System.Windows.Media.Color!

Many thanks

Answer 1

I don't know of any C# API or library that can achieve this. However, if you have enough C/C++ knowledge to build a wrapper for C#, I see two options:

• Windows Color System (WCS) (part of Windows)
• LittleCMS

The System.Windows.Media namespace is very limited. There's probably a powerful engine (WCS?) behind it, but just a small part is made available.

Update:

Here's some C# code to do the conversion using WCS. It certainly could use a wrapper that would make it easier to use:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace ICM
{
    public class WindowsColorSystem
    {
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        public class ProfileFilename
        {
            public uint type;
            [MarshalAs(UnmanagedType.LPTStr)]
            public string profileData;
            public uint dataSize;

            public ProfileFilename(string filename)
            {
                type = ProfileFilenameType;
                profileData = filename;
                dataSize = (uint)filename.Length * 2 + 2;
            }
        };

        public const uint ProfileFilenameType = 1;
        public const uint ProfileMembufferType = 2;

        public const uint ProfileRead = 1;
        public const uint ProfileReadWrite = 2;


        public enum FileShare : uint
        {
            Read = 1,
            Write = 2,
            Delete = 4
        };

        public enum CreateDisposition : uint
        {
            CreateNew = 1,
            CreateAlways = 2,
            OpenExisting = 3,
            OpenAlways = 4,
            TruncateExisting = 5
        };

        public enum LogicalColorSpace : uint
        {
            CalibratedRGB = 0x00000000,
            sRGB = 0x73524742,
            WindowsColorSpace = 0x57696E20
        };

        public enum ColorTransformMode : uint
        {
            ProofMode = 0x00000001,
            NormalMode = 0x00000002,
            BestMode = 0x00000003,
            EnableGamutChecking = 0x00010000,
            UseRelativeColorimetric = 0x00020000,
            FastTranslate = 0x00040000,
            PreserveBlack = 0x00100000,
            WCSAlways = 0x00200000
        };


        enum ColorType : int
        {
            Gray = 1,
            RGB = 2,
            XYZ = 3,
            Yxy = 4,
            Lab = 5,
            _3_Channel = 6,
            CMYK = 7,
            _5_Channel = 8,
            _6_Channel = 9,
            _7_Channel = 10,
            _8_Channel = 11,
            Named = 12
        };


        public const uint IntentPerceptual = 0;
        public const uint IntentRelativeColorimetric = 1;
        public const uint IntentSaturation = 2;
        public const uint IntentAbsoluteColorimetric = 3;

        public const uint IndexDontCare = 0;


        [StructLayout(LayoutKind.Sequential)]
        public struct RGBColor
        {
            public ushort red;
            public ushort green;
            public ushort blue;
            public ushort pad;
        };

        [StructLayout(LayoutKind.Sequential)]
        public struct CMYKColor
        {
            public ushort cyan;
            public ushort magenta;
            public ushort yellow;
            public ushort black;
        };

        [DllImport("mscms.dll", SetLastError = true, EntryPoint = "OpenColorProfileW", CallingConvention = CallingConvention.Winapi)]
        static extern IntPtr OpenColorProfile(
            [MarshalAs(UnmanagedType.LPStruct)] ProfileFilename profile,
            uint desiredAccess,
            FileShare shareMode,
            CreateDisposition creationMode);

        [DllImport("mscms.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
        static extern bool CloseColorProfile(IntPtr hProfile);

        [DllImport("mscms.dll", SetLastError = true, EntryPoint = "GetStandardColorSpaceProfileW", CallingConvention = CallingConvention.Winapi)]
        static extern bool GetStandardColorSpaceProfile(
            uint machineName,
            LogicalColorSpace profileID,
            [MarshalAs(UnmanagedType.LPTStr), In, Out] StringBuilder profileName,
            ref uint size);

        [DllImport("mscms.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
        static extern IntPtr CreateMultiProfileTransform(
            [In] IntPtr[] profiles,
            uint nProfiles,
            [In] uint[] intents,
            uint nIntents,
            ColorTransformMode flags,
            uint indexPreferredCMM);

        [DllImport("mscms.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
        static extern bool DeleteColorTransform(IntPtr hTransform);

        [DllImport("mscms.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
        static extern bool TranslateColors(
            IntPtr hColorTransform,
            [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2), In] RGBColor[] inputColors,
            uint nColors,
            ColorType ctInput,
            [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2), Out] CMYKColor[] outputColors,
            ColorType ctOutput);



        public static void Test()
        {
            bool success;

            StringBuilder profileName = new StringBuilder(256);
            uint size = (uint)profileName.Capacity * 2;
            success = GetStandardColorSpaceProfile(0, LogicalColorSpace.sRGB, profileName, ref size);

            ProfileFilename sRGBFilename = new ProfileFilename(profileName.ToString());
            IntPtr hSRGBProfile = OpenColorProfile(sRGBFilename, ProfileRead, FileShare.Read, CreateDisposition.OpenExisting);

            ProfileFilename isoCoatedFilename = new ProfileFilename(@"C:\Users\me\Documents\ISOcoated_v2_300_eci.icc");
            IntPtr hIsoCoatedProfile = OpenColorProfile(isoCoatedFilename, ProfileRead, FileShare.Read, CreateDisposition.OpenExisting);

            IntPtr[] profiles = new IntPtr[] { hSRGBProfile, hIsoCoatedProfile };
            uint[] intents = new uint[] { IntentPerceptual };
            IntPtr transform = CreateMultiProfileTransform(profiles, 2, intents, 1, ColorTransformMode.BestMode, IndexDontCare);

            RGBColor[] rgbColors = new RGBColor[1];
            rgbColors[0] = new RGBColor();
            CMYKColor[] cmykColors = new CMYKColor[1];
            cmykColors[0] = new CMYKColor();

            rgbColors[0].red = 30204;
            rgbColors[0].green = 4420;
            rgbColors[0].blue = 60300;

            success = TranslateColors(transform, rgbColors, 1, ColorType.RGB, cmykColors, ColorType.CMYK);

            success = DeleteColorTransform(transform);

            success = CloseColorProfile(hSRGBProfile);
            success = CloseColorProfile(hIsoCoatedProfile);
        }
    }
}