C#图片按比例缩放

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ZoomImage.Utils
{
    /// <summary>
    /// 图片缩放
    /// </summary>
    public class ZoomImageUtil
    {
        /// <summary>
        /// 图片缩放
        /// </summary>
        /// <param name="bmp">图片</param>
        /// <param name="width">目标宽度，若为0，表示宽度按比例缩放</param>
        /// <param name="height">目标长度，若为0，表示长度按比例缩放</param>
        public static Bitmap GetThumbnail(Bitmap bmp, int width, int height)
        {
            if (width == 0)
            {
                width = height * bmp.Width / bmp.Height;
            }
            if (height == 0)
            {
                height = width * bmp.Height / bmp.Width;
            }

            Image imgSource = bmp;
            Bitmap outBmp = new Bitmap(width, height);
            Graphics g = Graphics.FromImage(outBmp);
            g.Clear(Color.Transparent);
            // 设置画布的描绘质量         
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(imgSource, new Rectangle(0, 0, width, height + 1), 0, 0, imgSource.Width, imgSource.Height, GraphicsUnit.Pixel);
            g.Dispose();
            imgSource.Dispose();
            bmp.Dispose();
            return outBmp;
        }
    }
}

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

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

        private void Form1_Load(object sender, EventArgs e)
        {
            openFileDialog1.Multiselect = true;
        }

        private void txtWidth_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar != 8 && !Char.IsDigit(e.KeyChar))
            {
                e.Handled = true;
            }
        }

        private void txtHeight_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar != 8 && !Char.IsDigit(e.KeyChar))
            {
                e.Handled = true;
            }
        }

        private void btnSelectImage_Click(object sender, EventArgs e)
        {
            try
            {
                if (txtWidth.Text == "" && txtHeight.Text == "")
                {
                    return;
                }

                if (openFileDialog1.ShowDialog() == DialogResult.OK)
                {
                    string path = Path.GetDirectoryName(openFileDialog1.FileNames[0]) + "\\NewImage\\";

                    foreach (string fileName in openFileDialog1.FileNames)
                    {
                        Bitmap bmp = ZoomImageUtil.GetThumbnail(new Bitmap(fileName), Convert.ToInt32(txtWidth.Text == "" ? "0" : txtWidth.Text), Convert.ToInt32(txtHeight.Text == "" ? "0" : txtHeight.Text));
                        if (!Directory.Exists(path))
                        {
                            Directory.CreateDirectory(path);
                        }
                        File.Delete(path + Path.GetFileName(fileName));
                        bmp.Save(path + Path.GetFileName(fileName));
                    }

                    MessageBox.Show("成功！");
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

    }
}