How to zoom an image in C#

By FoxLearn 11/28/2024 2:12:30 PM   14.44K
To zoom an image in a PictureBox in C#, you can manipulate the Image property of the PictureBox by adjusting the SizeMode and scaling the image.

With C#, you can easily implement image zoom functionality using a PictureBox control and a few simple methods. This article demonstrates how to zoom an image dynamically based on user input, such as adjusting a TrackBar for scaling the image.

How to Zoom an Image Using PictureBox in C#?

Open Visual Studio, then click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "ImageZoom" and then click OK

Design your form as shown below.

zoom image in c#

The user can load an image by clicking the btnOpen button. This opens a file dialog, allowing them to select a JPEG image, which is then displayed in the PictureBox.

private void btnOpen_Click(object sender, EventArgs e)
{
    //Open image
    using (OpenFileDialog ofd = new OpenFileDialog() { Multiselect = false, ValidateNames = true, Filter = "JPEG|*.jpg" })
    {
        if (ofd.ShowDialog() == DialogResult.OK)
        {
            pictureBox1.Image = Image.FromFile(ofd.FileName);
            imgOriginal = pictureBox1.Image;
        }
    }
}

The zoom functionality is controlled by a TrackBar. As the user moves the slider, the trackBar1_Scroll event is triggered, and the image is resized according to the current value of the slider.

private void trackBar1_Scroll(object sender, EventArgs e)
{
    if (trackBar1.Value > 0)
    {
        pictureBox1.Image = Zoom(imgOriginal, new Size(trackBar1.Value, trackBar1.Value));
    }
}

The Zoom method takes the original image and a Size object, which is based on the TrackBar value. The new size is calculated by adding a percentage of the image's width and height. The zoom is applied using the Graphics class to ensure the image scaling looks smooth and maintains its visual quality.

//Zoom image file
Image Zoom(Image img, Size size)
{
    Bitmap bmp = new Bitmap(img, img.Width + (img.Width * size.Width / 100), img.Height + (img.Height * size.Height / 100));
    Graphics g = Graphics.FromImage(bmp);
    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
    return bmp;
}

The use of HighQualityBicubic interpolation mode ensures that the zoomed image maintains high visual quality, reducing the distortion often seen with simple scaling.

The Form1_FormClosing event ensures that the image resource is properly disposed of when the form is closed, preventing memory leaks.

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
    if (pictureBox1.Image != null)
        pictureBox1.Dispose();
}

Add code to button click event handler as below

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ImageZoom
{
    public partial class Form1 : Form
    {
        Image imgOriginal;

        public Form1()
        {
            InitializeComponent();
        }
    }
}

This simple yet powerful C# application demonstrates how to create a dynamic image zoom feature using a PictureBox and a TrackBar.

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