C#实现图片缩略图功能的示例详解

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    public Image ResourceImage;
    private int ImageWidth;
    private int ImageHeight;
    public string ErrMessage;

    public bool ThumbnailCallback()
    {
        return false;
    }

    public bool GetReducedImage(double Percent, string targetFilePath)
    {
        try
        {
            Bitmap bt = new Bitmap(120, 120);
            Graphics g = Graphics.FromImage(bt);
            g.Clear(Color.White);
            Image ReducedImage;
            Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
            ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);
            ImageHeight = Convert.ToInt32(ResourceImage.Height * Percent);
            ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);
            if (ImageWidth > ImageHeight)
            {
                g.DrawImage(ReducedImage, 0, (int) (120 - ImageHeight) / 2, ImageWidth, ImageHeight);
            }
            else
            {
                g.DrawImage(ReducedImage, (int) (120 - ImageWidth) / 2, 0, ImageWidth, ImageHeight);
            }

            g.DrawRectangle(new Pen(Color.Gainsboro), 0, 0, 119, 119);
            bt.Save(@targetFilePath, ImageFormat.Jpeg);
            bt.Dispose();
            ReducedImage.Dispose();
            return true;
        }
        catch (Exception e)
        {
            ErrMessage = e.Message;
            return false;
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (openFileDialog1.ShowDialog() == DialogResult.OK)
        {
            pictureBox1.Image = Image.FromFile(openFileDialog1.FileName);
        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        double percent;
        string imgpath = openFileDialog1.FileName;
        string imgName = imgpath.ToString().Substring(imgpath.ToString().LastIndexOf("\\") + 1,
            imgpath.ToString().Length - 1 - imgpath.ToString().LastIndexOf("\\"));
        imgName = imgName.Remove(imgName.LastIndexOf("."));
        if (openFileDialog1.FileName.Length != 0)
        {
            ResourceImage = Image.FromFile(openFileDialog1.FileName);
            if (ResourceImage.Width < ResourceImage.Height)
            {
                percent = (double) 120 / ResourceImage.Height;
            }
            else
            {
                percent = (double) 120 / ResourceImage.Width;
            }

            GetReducedImage(percent, "c:\\_" + imgName + ".JPG");
            pictureBox2.Image = Image.FromFile("c:\\_" + imgName + ".JPG");
        }
    }
}

partial class Form1
{
    /// <summary>
    /// 必需的设计器变量。
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary>
    /// 清理所有正在使用的资源。
    /// </summary>
    /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Windows 窗体设计器生成的代码

    /// <summary>
    /// 设计器支持所需的方法 - 不要
    /// 使用代码编辑器修改此方法的内容。
    /// </summary>
    private void InitializeComponent()
    {
        this.pictureBox1 = new System.Windows.Forms.PictureBox();
        this.pictureBox2 = new System.Windows.Forms.PictureBox();
        this.button1 = new System.Windows.Forms.Button();
        this.button2 = new System.Windows.Forms.Button();
        this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).BeginInit();
        this.SuspendLayout();
        // 
        // pictureBox1
        // 
        this.pictureBox1.Location = new System.Drawing.Point(11, 42);
        this.pictureBox1.Name = "pictureBox1";
        this.pictureBox1.Size = new System.Drawing.Size(262, 232);
        this.pictureBox1.SizeMode = System.Windows.Forms.PictureBoxSizeMode.Zoom;
        this.pictureBox1.TabIndex = 0;
        this.pictureBox1.TabStop = false;
        // 
        // pictureBox2
        // 
        this.pictureBox2.Location = new System.Drawing.Point(305, 80);
        this.pictureBox2.Name = "pictureBox2";
        this.pictureBox2.Size = new System.Drawing.Size(155, 132);
        this.pictureBox2.SizeMode = System.Windows.Forms.PictureBoxSizeMode.Zoom;
        this.pictureBox2.TabIndex = 1;
        this.pictureBox2.TabStop = false;
        // 
        // button1
        // 
        this.button1.Location = new System.Drawing.Point(11, 13);
        this.button1.Name = "button1";
        this.button1.Size = new System.Drawing.Size(75, 23);
        this.button1.TabIndex = 2;
        this.button1.Text = "选择图片";
        this.button1.UseVisualStyleBackColor = true;
        this.button1.Click += new System.EventHandler(this.button1_Click);
        // 
        // button2
        // 
        this.button2.Location = new System.Drawing.Point(93, 12);
        this.button2.Name = "button2";
        this.button2.Size = new System.Drawing.Size(75, 23);
        this.button2.TabIndex = 3;
        this.button2.Text = "显示缩略图";
        this.button2.UseVisualStyleBackColor = true;
        this.button2.Click += new System.EventHandler(this.button2_Click);
        // 
        // openFileDialog1
        // 
        this.openFileDialog1.Filter = "图片文件|*.jpg;*.jpeg;*.bmp;*.png";
        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(487, 296);
        this.Controls.Add(this.button2);
        this.Controls.Add(this.button1);
        this.Controls.Add(this.pictureBox2);
        this.Controls.Add(this.pictureBox1);
        this.Name = "Form1";
        this.Text = "Form1";
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).EndInit();
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.PictureBox pictureBox1;
    private System.Windows.Forms.PictureBox pictureBox2;
    private System.Windows.Forms.Button button1;
    private System.Windows.Forms.Button button2;
    private System.Windows.Forms.OpenFileDialog openFileDialog1;
}