ASP.NET 不经保存，直接生成上传图片的等比例的高质量缩略图

本文介绍了一种在不保存原始图片的情况下，直接生成等比例高质量缩略图的方法。通过ASP.NET实现图片上传，并使用C#处理图片，确保缩略图既保持原图的宽高比又具备良好的视觉效果。

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<title>不经保存，直接生成上传图片的等比例的高质量缩略图</title>
</head>
<body>

<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="上传并生成缩略图" />

</body>
</html>

后台代码

protected void Button1_Click(object sender, EventArgs e)
        {
            String fileExt = System.IO.Path.GetExtension(FileUpload1.FileName);
            System.Drawing.Image image = System.Drawing.Image.FromStream(new System.IO.MemoryStream(FileUpload1.FileBytes));
            int newWidth = 122, newHeight = 122;
            if ((decimal)image.Width / image.Height > (decimal)newWidth / newHeight)
            {
                newHeight = Convert.ToInt32((decimal)image.Height * newWidth / image.Width);
            }
            else if ((decimal)image.Width / image.Height < (decimal)newWidth / newHeight)
            {
                newWidth = Convert.ToInt32((decimal)image.Width * newHeight / image.Height);
            }
            System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(newWidth, newHeight);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            System.Drawing.Rectangle rectDestination = new System.Drawing.Rectangle(0, 0, newWidth, newHeight);
            g.DrawImage(image, rectDestination, 0, 0, image.Width, image.Height, System.Drawing.GraphicsUnit.Pixel);
            bmp.Save(Server.MapPath("~/") + DateTime.Now.ToString("yyyyMMddHHmmss") + fileExt);
            bmp.Dispose();
            image.Dispose();
        }