Emulation Tables (Visual Basic)

The LEAD Color Conversion toolkit provides emulation tables as one of its conversion methods. This method however is provided only for the following conversions:

$image\sqrblit.gif$ CMYK to RGB.

$image\sqrblit.gif$ CIELab to RGB

$image\sqrblit.gif$ and RGB to CIELab

The Emulation tables' method supports both built-in and custom options. For built-in emulation tables, use the USE_ET option. The custom emulation tables' option, USE_CUSTOM_ET, provides custom conversion using user-supplied images, converted from the source images distributed with the library by any tool, as follows:

Conversion	Source	Convert to
CMYK to RGB	src_cmyk_image.tif	RGB image (i.e. dst_cmyk2rgb_image.tif)
RGB to Lab	src_rgb_image.tif	Lab image ( i.e. dst_rgb2lab_image.tif)
Lab to RGB	src_lab_image.tif	RGB image (i.e. dst_lab2rgb_image.tif)

A set of images, already converted and ready for use (dst_cmyk2rgb_image.tif, dst_rgb2lab_image.tif, and dst_lab2rgb_image.tif), is provided. However, using the provided set of converted images will produce the same results as the built-in emulation tables.

The code below shows how a conversion can be done using the built-in tables:

Function Tables_Convert_CMYKToRGB(RGBData() As Byte, LABData() As Byte, nWidth As Integer, nHeight As Integer, nInAlign As Integer, nOutAlign As Integer) As Integer
   'This function converts an RGB24 image to LAB using built-in emulation tables.
   '-RGBData: pointer to the input RGB data.
   '-LABData: pointer to the output LAB beffer
   '-nWidth: width of the passed image.
   '-nHeight: height of the passed image.
   '-nInAlign: input buffer alignment.
   '-nOutAlign: output buffer alignment.

   Dim ClrHandle As Long 'color handle
   Dim cnvParam As CONVERSION_PARAMS 'conversion params
   Dim ret As Integer 'return value

   'initialize the conversion structure
   cnvParam.uStructSize = Len(cnvParam)
   cnvParam.nQuantization = 8
   cnvParam.nMethod = USE_ET
   cnvParam.nActiveMethod = USE_ET
   cnvParam.pCmykParams = 0
   cnvParam.pLabParams = 0
   cnvParam.pYuvParams = 0
   cnvParam.sDstInputTable(0) = 0
   cnvParam.sInputProfile(0) = 0
   cnvParam.sOutputProfile(0) = 0

   'initialize the conversion engine
   ret = L_ClrInit (ClrHandle, CCS_RGB, CCS_LAB, cnvParam)

   'do we have a valid handle
   If (ret = SUCCESS) Then
      'do the conversion from RGB to CIELab
      ret = L_ClrConvert (ClrHandle, RGBData(0), LABData(0), nWidth, nHeight, nInAlign, nOutAlign)
      If (ret <> SUCCESS) Then
         MsgBox "Failed to convert from RGB to LAB"
         Tables_Convert_CMYKToRGB = ret
      End If

      'do not forget to free every thing
      L_ClrFree (ClrHandle)
   Else
      MsgBox "Failed to initialize LTCLR"
      Tables_Convert_CMYKToRGB = ret
   End If

End Function

The code below shows how a conversion can be done using user-defined tables:

Function Tables_Convert_CMYKToRGB(RGBData() As Byte, LABData() As Byte, nWidth As Integer, nHeight As Integer, nInAlign As Integer, nOutAlign As Integer, strDst As String) As Integer
   'This function converts an RGB24 image to LAB using built-in emulation tables.
   '-RGBData: pointer to the input RGB data.
   '-LABData: pointer to the output LAB beffer
   '-nWidth: width of the passed image.
   '-nHeight: height of the passed image.
   '-nInAlign: input buffer alignment.
   '-nOutAlign: output buffer alignment.
   '-strDst: destination custom table.

   Dim ClrHandle As Long 'color handle
   Dim cnvParam As CONVERSION_PARAMS 'conversion params
   Dim ret As Integer 'return value
   Dim i As Integer

   'initialize the conversion structure
   cnvParam.uStructSize = Len(cnvParam)
   cnvParam.nQuantization = 8
   cnvParam.nMethod = USE_CUSTOM_ET
   cnvParam.nActiveMethod = USE_CUSTOM_ET
   cnvParam.pCmykParams = 0
   cnvParam.pLabParams = 0
   cnvParam.pYuvParams = 0
   cnvParam.sDstInputTable(0) = 0
   cnvParam.sInputProfile(0) = 0
   cnvParam.sOutputProfile(0) = 0

   For i = 0 To Len(strDst) – 1
      cnvParam.sDstInputTable(i) = Asc(Right(strDst, Len(strDst) - i))
   Next i

   'initialize the conversion engine
   ret = L_ClrInit (ClrHandle, CCS_RGB, CCS_LAB, cnvParam)

   'do we have a valid handle
   If (ret = SUCCESS) Then
      'do the conversion from RGB to CIELab
      ret = L_ClrConvert (ClrHandle, RGBData(0), LABData(0), nWidth, nHeight, nInAlign, nOutAlign)
      If (ret <> SUCCESS) Then
         MsgBox "Failed to convert from RGB to LAB"
         Tables_Convert_CMYKToRGB = ret
      End If

      'do not forget to free every thing
      L_ClrFree (ClrHandle)
   Else
      MsgBox "Failed to initialize LTCLR"
      Tables_Convert_CMYKToRGB = ret
   End If

End Function