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POcolor conversion CMYK - RGB - Lab with WCS by using a ICC Profile
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copied!<p>Since last week I try to use the Windows Color System for my color conversion. By the conversion from CMYK to RGB i get the correct values:</p> <pre><code> // Example CMYK - VALUES with 0 float[] cmykValues = new float[4]; cmykValues[0] = 0f / 255f; cmykValues[1] = 0f / 255f; cmykValues[2] = 0f / 255f; cmykValues[3] = 0f / 255f; System.Windows.Media.Color color = Color.FromValues(cmykValues, new Uri(@"ISOcoated_v2_300_eci.icc")); System.Drawing.Color rgbColor = System.Drawing.Color.FromArgb(color.R, color.G, color.B); </code></pre> <p>When I try to convert the RGB Values to Lab Values, then I get a incorrect Lab - Result:</p> <pre><code>[StructLayout(LayoutKind.Sequential)] public struct RGBColor { public ushort red; public ushort green; public ushort blue; public ushort pad; }; [StructLayout(LayoutKind.Sequential)] public struct LABColor { public ushort L; public ushort a; public ushort b; public ushort pad; }; 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(@"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(); LABColor[] labColors = new LABColor[1]; labColors[0] = new LABColor(); rgbColors[0].red = Convert.ToUInt16(rgbColor.R * 257); rgbColors[0].green = Convert.ToUInt16(rgbColor.G * 257); rgbColors[0].blue = Convert.ToUInt16(rgbColor.B * 257); success = TranslateColors(transform, rgbColors, 1, ColorType.RGB, labColors, ColorType.Lab); double colorL = Convert.ToDouble(labColors[0].L) / 65535; double colorA = Convert.ToDouble(labColors[0].a) / 65535; double colorB = Convert.ToDouble(labColors[0].b) / 65535; </code></pre> <p>When I convert the CMYK Value (0;0;0;0) to RGB (= 254:254;254) and the RGB Value to Lab I get the following values:</p> <pre><code>L = 0.0039978637360036373 a = 0.002777141984552145 b = 0.0030670634005218744 </code></pre> <p>But the L-Value should be about 100%</p>

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