Mask or alpha blending

<!-- METADATA TYPE="typelib" UUID="{3CE48541-DE7A-4909-9314-9D0ED0D1CA5A}"--> 
<%

'Declarations
Dim objBackground	' The background image. It will contain the result of merge.
Dim objBitmap		' The image you put on the background.
Dim objMask		' This bitmap will contain alpha channel

Dim x, y			' Offset coordinates of the objBitmap on objBackground

Dim strBackgroundFilename
Dim strBitmapFilename
Dim strMergedFilename
Dim strMaskFilename

' Specify file names here
strBitmapFilename = Server.MapPath("FrontImage.jpg")
strBackgroundFilename = Server.MapPath("BackgroundImage.jpg")
strMergedFilename = Server.MapPath("Result.jpg")
strMaskFilename = Server.MapPath("Mask.tif")

' Create bitmaps
Set objBitmap = Server.CreateObject("GraphicsMill.Bitmap")
Set objBackground = Server.CreateObject("GraphicsMill.Bitmap")
Set objMask = Server.CreateObject("GraphicsMill.Bitmap")

' Load bitmaps
objBackground.LoadFromFile strBackgroundFilename
objBitmap.LoadFromFile strBitmapFilename
objMask.LoadFromFile strMaskFilename

' Check if alpha channel exists in the image. If not, 
' we must add it.
If Not objBitmap.Data.HasAlphaChannel Then
	objBitmap.Channels.AddAlpha
End If

' In this sample we will put the image into the center. 
' To centrize the coordinates, make these calculations:
x = (objBackground.Data.Width - objBitmap.Data.Width) / 2
y = (objBackground.Data.Height - objBitmap.Data.Height) / 2

' Alpha channel is always 8-bit grayscale image. That's why we need 
' to convert our 1-bit mask to grayscale.
objMask.Data.ConvertTo8bppGrayscale

' If your mask contains black as opaque area, and white as transparent,
' you must invert it. By the way, if you always use 1-bit images, the 
' optimal way to invert the image is to swap palette entries before converting
' to grayscale instead of using Invert method.
objMask.Effects.Invert

' To be able to retrieve objMask to alpha channel of the image, we 
' need make sure that it has the same dimensions as target image. 
' You can also use Resize instead of Crop if necessary.
objMask.Transforms.Crop 0, 0, objBitmap.Data.Width, objBitmap.Data.Height

' This method replaces channel with given number (zero-based) to the given
' grayscale image. Number 3 means alpha in ARGB pixel format. 
objBitmap.Channels.Replace objMask, 3

' Apply alpha blending
objBitmap.DrawOnBitmap objBackground, x, y, , , , , , , CombineModeAlpha

' Save the result
objBackground.SaveToFile strMergedFilename
objBackground.SaveToStream Response

' Cleanup
Set objMask = Nothing
Set objBitmap = Nothing
Set objBackground = Nothing
%>

<%@ Page Language="C#" %>
<%@ import Namespace="GraphicsMill" %>
<%

// Declarations
GraphicsMill.Bitmap bitmap = new GraphicsMill.Bitmap();
GraphicsMill.Bitmap background = new GraphicsMill.Bitmap();
GraphicsMill.Bitmap mask = new GraphicsMill.Bitmap();

// Offset coordinates of the bitmap on background
int x, y; 

// Filenames
string bitmapFilename = Server.MapPath("FrontImage.jpg");
string backgroundFilename = Server.MapPath("BackgroundImage.jpg");
string mergedFilename = Server.MapPath("Result.jpg");
string maskFilename = Server.MapPath("Mask.tif");

// Load bitmaps
background.LoadFromFile(backgroundFilename);
bitmap.LoadFromFile(bitmapFilename);
mask.LoadFromFile(maskFilename);


// Check if alpha channel exists in the image. If not, 
// we must add it

if (!bitmap.Data.HasAlphaChannel)
{
	bitmap.Channels.AddAlpha();
}

// In this sample we will put the image into the center. 
// To centrize the coordinates, make these calculations:
x = (background.Data.Width - bitmap.Data.Width) / 2;
y = (background.Data.Height - bitmap.Data.Height) / 2;

// Alpha channel is always 8-bit grayscale image. That's why we need 
// to convert our 1-bit mask to grayscale.
mask.Data.ConvertTo8bppGrayscale(false, GraphicsMillConstants.ColorWhite);

// If your mask contains black as opaque area, and white as transparent,
// you must invert it. By the way, if you always use 1-bit images, the 
// optimal way to invert the image is to swap palette entries before converting
// to grayscale instead of using Invert method.
mask.ColorAdjustment.Invert();

// To be able to retrieve mask to alpha channel of the image, we 
// need make sure that it has the same dimensions as target image. 
// You can also use Resize instead of Crop if necessary.
mask.Transforms.Crop (0, 0, bitmap.Data.Width, bitmap.Data.Height, GraphicsMillConstants.ColorWhite);

// This method replaces channel with given number (zero-based) to the given
// grayscale image. Number 3 means alpha in ARGB pixel format. 
bitmap.Channels.Replace(mask, 3);

// Apply alpha blending
bitmap.DrawOnBitmap(background, x, y, -1, -1, 0, 0, -1, -1, CombineMode.CombineModeAlpha, 255, InterpolationMode.InterpolationModeMediumQuality, true, true, true);

// Save the result
background.SaveToFile(mergedFilename);
Response.ContentType = "image/jpeg";
Response.BinaryWrite((byte[])background.SaveToMemory());
%>