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Watermarking and general image manipulation within the .NET Framework has become quite an easy thing to carry out thanks to the features provided by the System.Drawing namespace. The System.Drawing namespace contains types to help you with…well…drawing and rendering images. I will not be covering the basic use of the System.Drawing class. But feel free to carry out a Google.

My example consists of using a .NET (aspx) page and a Generic Handler (ashx). The .NET page will allow me to select an image, add a logo to the top left and some text. The Generic Handler will contain all the magic needed to manipulate the image based on selections made within the .NET page. The screenshot (below) shows my basic program in action.

Firstly, let me start off by showing you the code for the Generic Handler.

ImageRenderJpeg.ashx

using System;
using System.Web;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;

public class ImageRenderJpeg : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "image/jpeg";

        //Retrieve image details
        string imageUrl = context.Request.QueryString["ImageUrl"].ToString();
        string imageComment = context.Request.QueryString["ImageComment"].ToString();
        string imageIconUrl = context.Request.QueryString["Icon"].ToString();

        if (!String.IsNullOrEmpty(imageUrl))
        {
            //Get the location of the image
            Image imagePhoto = Image.FromFile(imageUrl);

            // Get dimensions of image
            int imageHeight = imagePhoto.Height;
            int imageWidth = imagePhoto.Width;

            //Create a new Bitmap
            Bitmap oBitmap = new Bitmap(imageWidth, imageHeight, PixelFormat.Format24bppRgb);

            //Load Background Graphic from Image
            Graphics oGraphics = Graphics.FromImage(oBitmap);
            oGraphics.SmoothingMode = SmoothingMode.HighQuality;
            oGraphics.DrawImage(imagePhoto, new Rectangle(0, 0, imageWidth, imageHeight), 0, 0, imageWidth, imageHeight, GraphicsUnit.Pixel);

            //Layer 1: Add an Image Logo to the top left
            if (!String.IsNullOrEmpty(imageIconUrl))
            {
                Image imageIcon = Image.FromFile(imageIconUrl);
                oGraphics.DrawImage(imageIcon, new Rectangle(5, 5, 124, 48), 0, 0, imageIcon.Width, imageIcon.Height, GraphicsUnit.Pixel);

                imageIcon.Dispose();
            }
            
            //Layer 2: Add Comment
            if (!String.IsNullOrEmpty(imageComment))
            {
                Font commentFont = new Font("Arial", 14, FontStyle.Regular); //Font Style
                StringFormat commentFormat = new StringFormat();
                commentFormat.Alignment = StringAlignment.Near; //Align text in left of layer

                SolidBrush commentBrush = new SolidBrush(Color.Black); //Font Colour

                oGraphics.FillRectangle(Brushes.Beige, 5, imageHeight - 55, imageWidth - 15, 50); //Create a rectangle with white background
                oGraphics.DrawString(imageComment, commentFont, commentBrush, new Rectangle(5, imageHeight - 55, imageWidth - 15, 50), commentFormat); //Add comment text inside rectangle
            }
            
            //Layer 3: Add Copyright watermark
            Font watermarkFont = new Font("Arial", 40, FontStyle.Bold); //Font Style
            SolidBrush semiTransBrush = new SolidBrush(Color.LightGray); //Font Colour
            StringFormat watermarkFormat = new StringFormat();
            watermarkFormat.Alignment = StringAlignment.Center; //Align text in center of image

            oGraphics.DrawString("Copyright",
                watermarkFont,
                semiTransBrush,
                new PointF(imageWidth / 2, imageHeight / 2), watermarkFormat);

            //Dispose of graphic objects
            imagePhoto.Dispose();
            oGraphics.Dispose();

            //Output image
            oBitmap.Save(context.Response.OutputStream, ImageFormat.Jpeg);
        }
        else
        {
        }

    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

You can see that I am manipulating my image based on the query string parameters I pass from my .NET page into my Generic Handler. Hopefully, my code is commented well enough to explain the general overview on what is going on.

The following code displays how my aspx page parses all the parameters needed to generate an image on the page:

Default.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Image Generator</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        Select an Image:
        <asp:DropDownList ID="ddlImage" runat="server">
            <asp:ListItem Text="*" Value="*">Select Image</asp:ListItem>
            <asp:ListItem Text="The Tumbler" Value="C:\Users\Surinder\Documents\Visual Studio 2010\WebSites\ImageCreator\Images\batmobile_Tumbler.jpg"></asp:ListItem>
            <asp:ListItem Text="Audi TT" Value="C:\Users\Surinder\Documents\Visual Studio 2010\WebSites\ImageCreator\Images\new-audi-tt-coupe.jpg"></asp:ListItem>
            <asp:ListItem Text="Volvo Concept" Value="C:\Users\Surinder\Documents\Visual Studio 2010\WebSites\ImageCreator\Images\volvo-s60-concept-interior1.jpg"></asp:ListItem>
        </asp:DropDownList>
        <br />
        <br />
        Add Logo: <asp:TextBox ID="txtImage" runat="server"></asp:TextBox>
        <br />
        <br />
        Add a comment:
        <asp:TextBox ID="txtComment" runat="server" TextMode="MultiLine" Width="500" Height="50"></asp:TextBox>
        <br />
        <br />
        <asp:Button ID="btnCreateImage" Text="Create Image" runat="server" onclick="btnCreateImage_Click" />
        <br />
        <br />
        <img id="imgRender" alt="Image Render" title="Image Render" runat="server" />        
    </div>
    </form>
</body>
</html>

Default.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (ddlImage.SelectedValue == "*")
        {
            imgRender.Visible = false;
        }
        else
        {
            imgRender.Visible = true;
        }
    }

    protected void btnCreateImage_Click(object sender, EventArgs e)
    {
        if (ddlImage.SelectedValue != "*")
        {
            //The Image source will be pointed to our Generic Handler to display the image.
            imgRender.Src = String.Format("ImageRenderJpeg.ashx?ImageUrl={0}&ImageComment={1}&Icon={2}", ddlImage.SelectedValue, txtComment.Text, txtImage.Text);
        }
    }
}