Emulation Tables (Visual Basic)

Show in webframe

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

CMYK to RGB.
CIELab to RGB
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