void image_plot_set_colormap()
{
	// Point to active graph layer
	GraphLayer gly = Project.ActiveLayer();
	if( !gly ) return;
	
	// Check to ensure first plot in layer is a matrix image plot
	StyleHolder sh = gly.StyleHolders(0);
	if( sh.GetPlotId() != IDM_PLOT_MATRIX_IMAGE )
		return;
	DataPlot dp = gly.DataPlots(0);
	if( !dp ) return;
	
	// Get colormap 
	Tree tr; 
	dp.GetColormap(tr); 

	// The colormap for matrix image plot has 256 fixed levels
	
	// Declare R, G, B vectors to hold color info
	vector<uint> vecR(256), vecG(256), vecB(256);
	
	// You can fill these vectors with any color scheme that you desire
	// by directly assigning values to vector such as
	// for(int i = 0; i < nLevels; i++)
	//{
	//	vecR[i] = 256* i / nLevels;  // linear in R
	//	vecG[i] = 256 * i^2 / nLevels^2; // power of 2 in G
	//	vecB[i] = 128 + 128 * sin(2 * Pi * i / nLevels) ; // sinusoidal in B
	//}
	
	// For this example, let us read the colors from a palette file instead
	// In this example, let us read in a binary palette file that has 256 colors
	// Origin ships with three palette files, one of which is rainbow
	string strPaletteFile = GetAppPath(TRUE) + "Palettes\\Rainbow.PAL";
	// Call function to read binary palette file
	int iRet = read_palette(strPaletteFile, vecR, vecG, vecB);
	if( iRet < 0 )
	{
		out_str("Error reading palette file!");
		return;
	}
	if( iRet != 256 )
		out_str("Palette file contained less than 256 colors!");

	// Now that R, G, B vectors are ready, need to combine them into one vector to set
	// colors for the colormap
	vector<uint> vecColors(256);
	for(int i = 0; i < 256; i++)
		vecColors[i] = vecR[i] + 256 * vecG[i] + 65536 * vecB[i] + OCOLOR_RGB_FLAG_BIT;
	// The constant OCOLOR_RGB_FLAG_BIT tells Origin to treat the color map in 
	// accordance with what is needed for the image plot coloring
	

	// Now set the colormpa to the tree
	tr.Details.Colors.nVals = vecColors;
	
	// Set the dataplot using modified tree
	dp.SetColormap(tr);
	
	// Refresh graph page (may not be required)
	gly.GetPage().Refresh();
}



/////////////////////////////////////////////////////////////////////////////////////
// This function reads the color map from a binary palette file - the format for the
// binary file is same as the Microsoft Palette file
//
static int read_palette(string strFileName, vector<uint>& vecR, vector<uint>& vecG, vector<uint>& vecB)
{
	bool bRet;
	int ierr;

	file ff;
	bRet = ff.Open(strFileName, file::modeRead);
	if(!bRet) return -1;
	
	// first read header information that includes some text 
	// plus information on file size etc.

	int ijunk;
	ierr = ff.Read(&ijunk,4);	// read and discard "RIFF"
	int isize;
	ierr = ff.Read(&isize,4);	// read file size
	ierr = ff.Read(&ijunk,4);	// read and discard "PAL "
	ierr = ff.Read(&ijunk,4);	// read and discard "data"

	ierr = ff.Read(&isize,4);	// read size
	short nShort;
	ierr = ff.Read(&nShort,2);	// read short
	short nCols;
	ierr = ff.Read(&nCols,2);	// read num colors
	
	if (nCols < 2 | nCols > 256)
	{
		bRet = ff.Close();
		return -1;
	}	
	// now read icol entries of the color map
	for (int ii=0; ii < nCols; ii++)
	{	
		uint ivalue;
		ierr = ff.Read(&ivalue,4);	
		vecB[ii] = (int) (ivalue / (256 * 256));
		ivalue = ivalue - vecB[ii] * 256 * 256;
		vecG[ii] = (int) (ivalue / 256);
		vecR[ii] = ivalue - vecG[ii] * 256;		

	}

	// close file
	bRet = ff.Close();
	if(!bRet) return -1;
	
	return nCols;
}