How to apply a raster function to an image service

public static string ApplyHillshadeFunction(IImageServer imageServer)
{
    //Define a hillshade function.
    IRasterFunction hillshadeFunction = new HillshadeFunctionClass();
    IRasterFunctionArguments functionArgument = new HillshadeFunctionArgumentsClass()
        ;
    functionArgument.PutValue("Altitude", 45);
    functionArgument.PutValue("Azimuth", 315);
    functionArgument.PutValue("ZFactor", 1.0);

    //Attach the function to a rendering rule.
    IRenderingRule renderRule = new RenderingRuleClass();
    renderRule.Function = hillshadeFunction;
    renderRule.Arguments = functionArgument;
    renderRule.VariableName = "DEM";

    //Define the image description.
    IGeoImageDescription geoImageDesc = new GeoImageDescriptionClass();
    geoImageDesc.Compression = "LZ77";
    geoImageDesc.Extent = imageServer.ServiceInfo.Extent;
    geoImageDesc.Width = 800;
    geoImageDesc.Height = 600;
    geoImageDesc.Interpolation = rstResamplingTypes.RSP_BilinearInterpolation;
    IGeoImageDescription2 geoImageDesc2 = (IGeoImageDescription2)geoImageDesc;
    geoImageDesc2.RenderingRule = renderRule;

    //Define the return image type.
    IImageType imgType = new ImageTypeClass();
    imgType.Format = esriImageFormat.esriImagePNG;
    imgType.ReturnType = esriImageReturnType.esriImageReturnURL;

    //Export the image.
    IImageResult imgResult = imageServer.ExportImage(geoImageDesc2, imgType);
    return imgResult.URL;
}

Public Shared Function ApplyHillshadeFunction(ByVal imageServer As IImageServer) As String
'Define a hillshade function.
Dim hillshadeFunction As IRasterFunction = New HillshadeFunctionClass()
Dim functionArgument As IRasterFunctionArguments = New HillshadeFunctionArgumentsClass()
functionArgument.PutValue("Altitude", 45)
functionArgument.PutValue("Azimuth", 315)
functionArgument.PutValue("ZFactor", 1)

'Attach the function to a rendering rule.
Dim renderRule As IRenderingRule = New RenderingRuleClass()
renderRule.[Function] = hillshadeFunction
renderRule.Arguments = functionArgument
renderRule.VariableName = "DEM"

'Define the image description.
Dim geoImageDesc As IGeoImageDescription = New GeoImageDescriptionClass()
geoImageDesc.Compression = "LZ77"
geoImageDesc.Extent = imageServer.ServiceInfo.Extent
geoImageDesc.Width = 800
geoImageDesc.Height = 600
geoImageDesc.Interpolation = rstResamplingTypes.RSP_BilinearInterpolation
Dim geoImageDesc2 As IGeoImageDescription2 = DirectCast(geoImageDesc, IGeoImageDescription2)
geoImageDesc2.RenderingRule = renderRule

'Define the return image type.
Dim imgType As IImageType = New ImageTypeClass()
imgType.Format = esriImageFormat.esriImagePNG
imgType.ReturnType = esriImageReturnType.esriImageReturnURL

'Export the image.
Dim imgResult As IImageResult = imageServer.ExportImage(geoImageDesc2, imgType)
Return imgResult.URL
End Function