Build a Simple Watermarking Utility in C#

Introduction

This article shall describe an approach to building a simple watermarking utility that may be used to add watermarks to any supported image file format. The resulting application shall permit the user to open any supported image file format into a scrollable picture box, to define the text to be applied as a watermark (with a default version supplied), to set the font and color of the watermark, to define the opacity of the watermark, to determine whether or not the watermark appears at the top or bottom of the image, and to preview the watermark prior to saving it to the image.

Figure 1: the Utility Application showing a Watermarked Image.

If you are at all curious about the image, it is of an American Goldfinch, this time of year, I have a about 50 or so such birds hanging around my bird feeders. I took the picture with my Fuji S700 digital camera through the kitchen window.

Getting Started

The solution contains a single Windows Forms project called "Watermarking" written in C#; the application contains only a single form (frmWatermark.cs) and all of the code necessary to drive the application is contained in that single form class.

Figure 2: Solution Explorer with the Project Visible.

Code: Watermarking Main Form (frmWatermark.cs)

All of the code necessary for this project is contained in this single form; that form shall be described entirely in this section.

The code for this form class begins with the following: (Note the highlighted text showing additional libraries added to the project; these additions to the default configuration were added to support the manipulation of the image files and the rendering of the watermark onto an image).

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Drawing.Imaging;

using System.Text;

using System.Windows.Forms;

namespace Watermarking

{

/// <summary>

/// An Image Watermarking Utility

/// </summary>

public partial class frmWatermark : Form

{

Following the declaration of the namespace and the form class, the next order of business in the application is to declare a collection of member variables requiring form wide scope; these variables are contained in a defined region entitled, "Member Variables". The declaration of the variables follows; as can been determined, the variables are used to keep track of the current file location and image, codec and encoder information used to translate the image from one format to another, and the color and font used to display the image watermark.

#region Member Variables

string CurrentFile;

Image img;

ImageCodecInfo myImageCodecInfo;

System.Drawing.Imaging.Encoder myEncoder;

EncoderParameter myEncoderParameter;

EncoderParameters myEncoderParameters;

System.Drawing.Color myWatermarkColor;

System.Drawing.Font myFont;

#endregion

The next block of code in the form class is the constructor; in this instance, the constructor is used to establish a default configuration including the definition of the watermark color, the opacity level of the watermark, the positioning option (top or bottom), the text contained in the watermark, and the font used to display the watermark.

#region Constructor

/// <summary>

/// constructor with default configuration settings

/// </summary>

public frmWatermark()

{

InitializeComponent();

// setup default settings

myWatermarkColor = Color.SteelBlue;

cboOpacity.SelectedIndex = 2;

optTop.Checked = true;

txtWaterMark.Text = "Your Name " +

char.ConvertFromUtf32(169).ToString() + " " +

DateTime.Now.Year.ToString() + ", All Rights Reserved";

myFont = txtWaterMark.Font;

}

#endregion

Following the constructor, there is a region defined to handle file input/output operations. This region contains two event handlers, one for the selection of the Open File menu strip option, and one for the save buttons's click event. The open file menu option is used to allow the user to navigate to and select an image file for load; the selected image file is placed into a scrollable picturebox.

The save button click event handler is used to save the image file with the watermark; the original file may be renamed or overwritten.

#region File IO

/// <summary>

/// Open an image file into the picture box control

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void openToolStripMenuItem_Click(object sender, EventArgs e)

{

// configure the open file dialog to point to some

// common (usable) image file formats

openFileDialog1.Title = "Open Image File";

openFileDialog1.Filter = "Bitmap Files|*.bmp" +

"|Enhanced Windows MetaFile|*.emf" +

"|Exchangeable Image File|*.exif" +

"|Gif Files|*.gif|JPEG Files|*.jpg" +

"|PNG Files|*.png|TIFF Files|*.tif|Windows MetaFile|*.wmf";

openFileDialog1.DefaultExt = "bmp";

openFileDialog1.FilterIndex = 1;

openFileDialog1.FileName = "";

openFileDialog1.ShowDialog();

// if the user did not select a file, return

if (openFileDialog1.FileName == "")

return;

// update the current file and form caption text

CurrentFile = openFileDialog1.FileName.ToString();

this.Text = "Watermark Utility: " + CurrentFile.ToString();

try

{

// open the image into the picture box

img = Image.FromFile(openFileDialog1.FileName, true);

picContainer.Image = img;

// resize the picture box to support scrolling

// large images

picContainer.Size = img.Size;

}

catch (Exception ex)

{

MessageBox.Show(ex.Message, "File Open Error");

}

}

/// <summary>

/// Save the Current Image with the Watermark

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void btnSave_Click(object sender, EventArgs e)

{

try

{

// get the extension to figure out how to limit the save

// option to the current image file type

string strExt;

strExt = System.IO.Path.GetExtension(CurrentFile);

strExt = strExt.ToUpper();

strExt = strExt.Remove(0, 1);

// if the current image is, for example, a gif, only

// allow the user to save the file with the watermark

// as a gif

SaveFileDialog1.Title = "Save File";

SaveFileDialog1.DefaultExt = strExt;

SaveFileDialog1.Filter = strExt + " Image Files|*." + strExt;

SaveFileDialog1.FilterIndex = 1;

if (SaveFileDialog1.ShowDialog() == DialogResult.OK)

{

if (SaveFileDialog1.FileName == "")

{

return;

}

else

{

// save the file with the name supplied by the user

picContainer.Image.Save(SaveFileDialog1.FileName);

}

// update the current image file to point to the newly saved image

CurrentFile = SaveFileDialog1.FileName;

this.Text = "Watermark Utility: " + CurrentFile;

MessageBox.Show(CurrentFile.ToString() + " saved.", "FileSave");

}

else

{

MessageBox.Show("The save file request was cancelled by

user.", "Save Cancelled");

}

}

catch (Exception ex)

{

MessageBox.Show(ex.Message.ToString(), "Image Save Error");

}

}

#endregion

After handling the file IO operations, the next region of code is the Image Format Conversion section. In this region, the methods provided are used to convert the open image into an alternative format (e.g., bitmap to JPEG, or JPEC to GIF, etc.). Each section of code is annotated and may be reviewed in the following:

#region Image Format Conversion

/// <summary>

/// Return the available image encoders

/// </summary>

/// <param name="mimeType"></param>

/// <returns></returns>

private static ImageCodecInfo GetEncoderInfo(String mimeType)

{

int j;

ImageCodecInfo[] encoders;

encoders = ImageCodecInfo.GetImageEncoders();

for (j = 0; j < encoders.Length; ++j)

{

if (encoders[j].MimeType == mimeType)

return encoders[j];

}

return null;

}

/// <summary>

/// Convert the current file to a bitmap

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void bitmapToolStripMenuItem_Click(object sender,

EventArgs e)

{

// create a new name with the bitmap extension

string newName = System.IO.Path.GetFileNameWithoutExtension(CurrentFile);

newName = newName + ".bmp";

try

{

// save the file as a bitmap

img.Save(newName, ImageFormat.Bmp);

CurrentFile = newName;

picContainer.Image = Image.FromFile(CurrentFile);

this.Text = "Watermark Utility: " + CurrentFile.ToString();

}

catch

{

MessageBox.Show("Failed to save image to bitmap.", "Error",

MessageBoxButtons.OK, MessageBoxIcon.Error);

return;

}

MessageBox.Show("Image file saved to " + newName.ToString(),

"Image Saved", MessageBoxButtons.OK,MessageBoxIcon.Information);

}

/// <summary>

/// Convert the current image file to an EMF file

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void emfToolStripMenuItem_Click(object sender, EventArgs e)

{

string newName = System.IO.Path.GetFileNameWithoutExtension(CurrentFile);

newName = newName + ".emf";

try

{

img.Save(newName, ImageFormat.Emf);

CurrentFile = newName;

picContainer.Image = Image.FromFile(CurrentFile);

this.Text = "Watermark Utility: " + CurrentFile.ToString();

}

catch