C# How to: Generating Icons from Images

Article Purpose

This illustrates the process of generating files (*.ico) from user specified input . The accompanying Sample Source Code implements a , allowing for easily testing the generation process.

Sample source code

This is accompanied by a sample source code Visual Studio project which is available for download .

Using the sample Application

The Sample Application can be used to test/implement the concepts described in this . The user interface enables the user to browse and select an file from the file system, which loads as a scaled preview. In addition, the user can select an size from a list of standard dimensions: 16×16, 24×24, 32×32, 48×48, 64×64, 96×96 and 128×128 pixels. When a user clicks on the “Save Icon” button the sample application generates an in memory based on the specified size converting and scaling the provided input . If an was successfully generated, the in-memory representation will be saved to the file system, based on the filename and file path specified by the user.

The image below is screenshot of the Image to Icon Generator application in action:

Image To Icon Generator

The source features Bellis perennis also known as the common European Daisy (see Wikipedia). The file is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license. The original can be downloaded from .

The resulting file generated by the sample application:

Generating Icons from Images

Scaling and Aspect Ratio

conform to a set of standard dimensions, all of which equate to a square due to the width and height values being equal. A potential issue exists in that the specified source might not have exact square dimensions. In other words, the width and height values of specified source might differ. The solution lies in creating a square based on the specified source . Consider the concept of a square canvas onto which is drawn the source whilst maintaining its aspect ratio, implementing center alignment from the horizontal and vertical aspect. Listed below is the implementation of an defined as CopyToSquareCanvas, targeting the class.

public static Bitmap CopyToSquareCanvas(this Bitmap sourceBitmap, Color canvasBackground)
    int maxSide = sourceBitmap.Width > sourceBitmap.Height ? sourceBitmap.Width : sourceBitmap.Height;

Bitmap bitmapResult = new Bitmap(maxSide, maxSide, PixelFormat.Format32bppArgb);
using (Graphics graphicsResult = Graphics.FromImage(bitmapResult)) { graphicsResult.Clear(canvasBackground);
int xOffset = (sourceBitmap.Width - maxSide) / 2; int yOffset = (sourceBitmap.Height - maxSide) / 2;
graphicsResult.DrawImage(sourceBitmap, new Point(xOffset, xOffset)); }
return bitmapResult; }

The size of the resulting is determined by the source ’s longest side, either width or height. To ensure middle alignment both vertically and horizontally the source is drawn at an offset, determined by the additional buffer area added by the canvas.

Generating the Icon

Once we have created an conforming to exact square dimensions the next step would be to scale said to the desired size. A convenient method of quickly scaling source to icon dimensions comes in the form of creating .

The sample source code defines the enumeration IconSizeDimensions, which serves to provide a developer friendly reference coupled with actual dimension values by means of specifying explicit enumeration values. Consider the following code snippet:

public enum IconSizeDimensions
    IconSize16x16Pixels = 16,
    IconSize24x24Pixels = 24,
    IconSize32x32Pixels = 32,
    IconSize48x48Pixels = 48,
    IconSize64x64Pixels = 64,
    IconSize96x96Pixels = 96,
    IconSize128x128Pixels = 128

The crux of this and sample source code can considered to be the definition of the CreateIcon , which targets the class. The definition is as follows:

public static Icon CreateIcon(this Bitmap sourceBitmap, IconSizeDimensions iconSize)
    Bitmap squareCanvas = sourceBitmap.CopyToSquareCanvas(Color.Transparent);
    squareCanvas = (Bitmap)squareCanvas.GetThumbnailImage((int)iconSize, (int)iconSize, null, new IntPtr());

Icon iconResult = Icon.FromHandle(squareCanvas.GetHicon());
return iconResult; }

As discussed the first step is to ensure that the source conforms to square dimensions, implemented here by invoking the CopyToSquareCanvas . Next the source code implements scaling by creating a of which the size is based on the specified IconSizeDimensions value. The method returns a handle to an in the form of an , which serves as a parameter to the static method, which returns an instance of the class.

The Implementation

When the user clicks the “Save” button the Sample Application will present the user with a file save dialog. After the user specifies a file name and file path the Sample Application creates a reference of the source by casting the picturebox’s property to type .

private void btnSaveIcon_Click(object sender, EventArgs e)
    if (picSource.Image != null)
        SaveFileDialog sfd = new SaveFileDialog();
        sfd.Title = "Specify a file name and file path";
        sfd.Filter = "Icon Files(*.ico)|*.ico"; 
if (sfd.ShowDialog() == System.Windows.Forms.DialogResult.OK) { System.Drawing.Icon tempIcon = ((Bitmap)picSource.Image).CreateIcon( (IconSizeDimensions)cmbIconSize.SelectedItem);
using (StreamWriter streamWriter = new StreamWriter(sfd.FileName, false)) { tempIcon.Save(streamWriter.BaseStream);
streamWriter.Flush(); streamWriter.Close(); } } } }

When the CreateIcon is invoked, the dimensions selected through the user interface will be passed as a parameter. The last step performed involves persisting the in-memory data to the file system.

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about.me :: Dewald Esterhuizen

Dewald Esterhuizen

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