C# 以任意比例转换图像大小(可做缩略图)

【核心代码】

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace Image
{
	/// <summary>
	/// Form1 的摘要说明。
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		private System.Windows.Forms.Button button1;
		private System.Windows.Forms.OpenFileDialog openFileDialog1;
		/// <summary>
		/// 必需的设计器变量。
		/// </summary>
		private System.ComponentModel.Container components = null;
		private System.Windows.Forms.Label label1;
		private System.Windows.Forms.Label label2;
		private System.String StrFileName="";
		private System.Windows.Forms.Button button2;
		private System.Windows.Forms.PictureBox pictureBox1;
		private System.Drawing.Bitmap NewBitmap;
		private System.Windows.Forms.NumericUpDown numericUpDown1;
		private System.Windows.Forms.SaveFileDialog saveFileDialog1;
		private System.Windows.Forms.NumericUpDown numericUpDown2;
		public Form1()
		{
			//
			// Windows 窗体设计器支持所必需的
			//
			InitializeComponent();

			//
			// TODO: 在 InitializeComponent 调用后添加任何构造函数代码
			//
		}

		/// <summary>
		/// 清理所有正在使用的资源。
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (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()
		{
			System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(Form1));
			this.button1 = new System.Windows.Forms.Button();
			this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
			this.label1 = new System.Windows.Forms.Label();
			this.label2 = new System.Windows.Forms.Label();
			this.button2 = new System.Windows.Forms.Button();
			this.pictureBox1 = new System.Windows.Forms.PictureBox();
			this.saveFileDialog1 = new System.Windows.Forms.SaveFileDialog();
			this.SuspendLayout();
			// 
			// button1
			// 
			this.button1.Location = new System.Drawing.Point(8, 184);
			this.button1.Name = "button1";
			this.button1.Size = new System.Drawing.Size(80, 23);
			this.button1.TabIndex = 0;
			this.button1.Text = "浏览图像";
			this.button1.Click  = new System.EventHandler(this.button1_Click);
			// 
			// openFileDialog1
			// 
			this.openFileDialog1.Filter = "Image files (JPeg, Gif, Bmp, etc.)|*.jpg;*.jpeg;*.gif;*.bmp;*.tif; *.tiff; *.png|"  
				" JPeg files (*.jpg;*.jpeg)|*.jpg;*.jpeg |GIF files (*.gif)|*.gif |BMP files (*.b"  
				"mp)|*.bmp|Tiff files (*.tif;*.tiff)|*.tif;*.tiff|Png files (*.png)| *.png |All f"  
				"iles (*.*)|*.*";
			// 
			// label1
			// 
			this.label1.Location = new System.Drawing.Point(104, 192);
			this.label1.Name = "label1";
			this.label1.Size = new System.Drawing.Size(104, 16);
			this.label1.TabIndex = 3;
			this.label1.Text = "图像长度(像素)：";
			// 
			// label2
			// 
			this.label2.Location = new System.Drawing.Point(104, 216);
			this.label2.Name = "label2";
			this.label2.Size = new System.Drawing.Size(104, 16);
			this.label2.TabIndex = 5;
			this.label2.Text = "图像宽度(像素)：";
			// 
			// button2
			// 
			this.button2.Location = new System.Drawing.Point(8, 208);
			this.button2.Name = "button2";
			this.button2.Size = new System.Drawing.Size(80, 23);
			this.button2.TabIndex = 7;
			this.button2.Text = "保存图像";
			this.button2.Click  = new System.EventHandler(this.button2_Click);
			// 
			// pictureBox1
			// 
			this.pictureBox1.Image = ((System.Drawing.Image)(resources.GetObject("pictureBox1.Image")));
			this.pictureBox1.Location = new System.Drawing.Point(8, 8);
			this.pictureBox1.Name = "pictureBox1";
			this.pictureBox1.Size = new System.Drawing.Size(304, 168);
			this.pictureBox1.TabIndex = 8;
			this.pictureBox1.TabStop = false;
			// 
			// Form1
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
			this.ClientSize = new System.Drawing.Size(320, 238);
			this.Controls.Add(this.pictureBox1);
			this.Controls.Add(this.button2);
			this.Controls.Add(this.label2);
			this.Controls.Add(this.label1);
			this.Controls.Add(this.button1);
			this.MaximizeBox = false;
			this.Name = "Form1";
			this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
			this.Text = "演示以任意比例转换图像大小";
			this.ResumeLayout(false);

		}
		#endregion

		/// <summary>
		/// 应用程序的主入口点。
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}

	
		private void button1_Click(object sender, System.EventArgs e)
		{//浏览图像
		   Controls.Remove(numericUpDown1);
     	   Controls.Remove(numericUpDown2);
           this.openFileDialog1.ShowDialog();
		   this.StrFileName=this.openFileDialog1.FileName;		
 		   if(this.StrFileName.Trim()=="")
				return;				   		   
		   System.Drawing.Bitmap MyBitmap=new Bitmap(this.StrFileName);
		   this.pictureBox1.Image=MyBitmap;		 
		   //添加第一个微调控件
		   this.numericUpDown1 = new NumericUpDown();
		   this.numericUpDown1.Location = new System.Drawing.Point(208, 184);
		   this.numericUpDown1.Name = "numericUpDown1";
		   this.numericUpDown1.Size = new System.Drawing.Size(104, 21);
		   this.numericUpDown1.Maximum = 2500;
		   this.numericUpDown1.Minimum = 0;
		   this.numericUpDown1.Value =MyBitmap.Width;		   
   		   Controls.Add(this.numericUpDown1);	
		   //托管第一个微调控件值改变事件
		   this.numericUpDown1.ValueChanged  = new System.EventHandler(this.numericUpDown1_ValueChanged);		
			//添加第二个微调控件
			this.numericUpDown2 = new NumericUpDown();
			this.numericUpDown2.Location = new System.Drawing.Point(208, 209);
			this.numericUpDown2.Name = "numericUpDown1";
			this.numericUpDown2.Size = new System.Drawing.Size(104, 21);
			this.numericUpDown2.Maximum = 2500;
			this.numericUpDown2.Minimum = 0;
			this.numericUpDown2.Value =MyBitmap.Height;		   
			Controls.Add(numericUpDown2);	
			//托管第二个微调控件值改变事件
			this.numericUpDown2.ValueChanged  = new System.EventHandler(this.numericUpDown2_ValueChanged);	

		}

		private void numericUpDown1_ValueChanged(object sender, System.EventArgs e)
		{//改变图像长度
		  System.Drawing.Bitmap MyBitmap=new Bitmap(this.StrFileName);		
		  NewBitmap=new  Bitmap(MyBitmap,(int)this.numericUpDown1.Value,(int)this.numericUpDown2.Value);
		  this.pictureBox1.Image=NewBitmap;
		}
		private void numericUpDown2_ValueChanged(object sender, System.EventArgs e)
		{//改变图像宽度
			System.Drawing.Bitmap MyBitmap=new Bitmap(this.StrFileName);		
			NewBitmap=new  Bitmap(MyBitmap,(int)this.numericUpDown1.Value,(int)this.numericUpDown2.Value);
			this.pictureBox1.Image=NewBitmap;
		}

		private void button2_Click(object sender, System.EventArgs e)
		{//保存转换后的图像								
			string StrFileExt=this.StrFileName.Substring(this.StrFileName.Length-3,3);
			string StrName=this.StrFileName.Substring(0,this.StrFileName.Length-3);
			if(this.saveFileDialog1.ShowDialog()==DialogResult.Cancel)
                return;
			string StrFileName=this.saveFileDialog1.FileName;
			try
			{			
				if(StrFileExt=="BMP")
				{					
					this.pictureBox1.Image.Save(StrFileName ".bmp",System.Drawing.Imaging.ImageFormat.Bmp);
				}
				if(StrFileExt=="GIF")
				{
					this.pictureBox1.Image.Save(StrFileName ".gif",System.Drawing.Imaging.ImageFormat.Gif);
				}
				if(StrFileExt=="JPG")
				{
					this.pictureBox1.Image.Save(StrFileName ".jpg",
						System.Drawing.Imaging.ImageFormat.Jpeg);
				}
				if(StrFileExt=="PNG")
				{
					this.pictureBox1.Image.Save(StrFileName ".png",
						System.Drawing.Imaging.ImageFormat.Png);	
				}
				if(StrFileExt=="TIF")
				{
					this.pictureBox1.Image.Save(StrFileName ".tif",
						System.Drawing.Imaging.ImageFormat.Tiff);	
				}
				if(StrFileExt=="WMF")
				{
					this.pictureBox1.Image.Save(StrFileName ".wmf",
						System.Drawing.Imaging.ImageFormat.Wmf);
				}		
			}
			catch(Exception Error)
			{
				MessageBox.Show(this,"转换图像文件时发生错误！请检查是否有同名文件存在！","信息提示",
					MessageBoxButtons.OK,MessageBoxIcon.Information);
			}
            

		}		
	}
}