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