Built-in Conversion (Visual Basic)

The Color Conversion C API provides built-in conversion. To do a built-in conversion, follow the steps below:

  1. Define the following global variables:

    Dim RGBData(100) As Byte   
     Dim LABData(100) As Byte   
     Dim nWidth As Integer   
     Dim nHeight As Integer   
     Dim nInAlign As Integer   
     Dim nOutAlign As Integer   
     Dim ClrHandle As Long 'color handle   
     Dim cnvParam As CONVERSION_PARAMS 'conversion params   
     Dim wtPoint As WHITEPOINT 'white point definition 

  2. Set the conversion options by filling a CONVERSION_PARAMS structure:

    'set the whitepoint   
     wtPoint.nWhitePoint = CIELAB\_D50   
     wtPoint.xWhite = 0   
     wtPoint.yWhite = 0   
        
     'initialize the conversion structure   
     cnvParam.uStructSize = Len(cnvParam)   
     cnvParam.nQuantization = 8   
     cnvParam.nMethod = USE_BUILTIN   
     cnvParam.nActiveMethod = USE_BUILTIN   
     cnvParam.pCmykParams = 0   
     cnvParam.pLabParams = 0   
     cnvParam.pYuvParams = 0   
     cnvParam.sDstInputTable(0) = 0   
     cnvParam.sInputProfile(0) = 0   
     cnvParam.sOutputProfile(0) = 0   
     cnvParam.pWpoint = VarPtr(wtPoint) 

  3. Initialize the color conversion handle with L_ClrInit:

    L_ClrInit ClrHandle, CCS\_RGB, CCS\_LAB, cnvParam

  4. Convert from RGB to CIELab:

    L_ClrConvert ClrHandle, RGBData(0), LABData(0), nWidth, nHeight, nInAlign, nOutAlign

  5. At the end, free the color conversion handle:

    L_ClrFree ClrHandle

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