从寸照获取圆形头像

[Mr Dang]

从2寸照的相片（626px*413px）获取圆形图像（压缩成直径24px），不使用第三方工具

[Mr Dang]

圆形图像就是 CSDN 这种头像，只是不要这么大。

[王志威丶]

.contentDiv{display:inline-block;margin:5px auto;width:100px;height:100px;border-radius:100px;-webkit-border-radius:100px;-moz-border-radius:100px;border:2px solid #fff;box-shadow:0 0 4px #ccc;overflow:hidden;}

圆形头像样式，大小可以自己进行调整

[全栈极简]

https://blog.csdn.net/chinacsharper/article/details/50854852

[Mr Dang]

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 WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Image image = this.pictureBox1.Image;
            int left = image.Width / 4;
            int right = image.Width / 4;
            int width = image.Width / 2;
            int height = image.Height / 2;
            Image newImage = CutEllipse(image, new Rectangle(left, right, width, height), new Size(width, height));
            this.pictureBox2.Image = ZoomPicture(newImage, 28, 28);
        }

        // 按比例缩放图片
        public Image ZoomPicture(Image SourceImage, int TargetWidth, int TargetHeight)
        {
            int IntWidth; //新的图片宽
            int IntHeight; //新的图片高
            try
            {
                System.Drawing.Imaging.ImageFormat format = SourceImage.RawFormat;
                System.Drawing.Bitmap SaveImage = new System.Drawing.Bitmap(TargetWidth, TargetHeight);
                Graphics g = Graphics.FromImage(SaveImage);
                //g.Clear(Color.White);

                //计算缩放图片的大小 http://www.cnblogs.com/roucheng/

                if (SourceImage.Width > TargetWidth && SourceImage.Height <= TargetHeight)//宽度比目的图片宽度大，长度比目的图片长度小
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height > TargetHeight)//宽度比目的图片宽度小，长度比目的图片长度大
                {
                    IntHeight = TargetHeight;
                    IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height <= TargetHeight) //长宽比目的图片长宽都小
                {
                    IntHeight = SourceImage.Width;
                    IntWidth = SourceImage.Height;
                }
                else//长宽比目的图片的长宽都大
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                    if (IntHeight > TargetHeight)//重新计算
                    {
                        IntHeight = TargetHeight;
                        IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                    }
                }

                g.DrawImage(SourceImage, (TargetWidth - IntWidth) / 2, (TargetHeight - IntHeight) / 2, IntWidth, IntHeight);
                SourceImage.Dispose();

                return SaveImage;
            }
            catch
            {

            }

            return null;
        }


        private Image CutEllipse(Image img, Rectangle rec, Size size)
        {
            Bitmap bitmap = new Bitmap(size.Width, size.Height);
            using (Graphics g = Graphics.FromImage(bitmap))
            {
                using (TextureBrush br = new TextureBrush(img, System.Drawing.Drawing2D.WrapMode.Clamp, rec))
                {
                    br.ScaleTransform(bitmap.Width / (float)rec.Width, bitmap.Height / (float)rec.Height);
                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
                    g.FillEllipse(br, new Rectangle(Point.Empty, size));
                }
            }
            return bitmap;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            OpenFileDialog dialog = new OpenFileDialog();
            if (dialog.ShowDialog() != DialogResult.OK) return;
            pictureBox1.Image = Image.FromFile(dialog.FileName);
        }
    }
}

结贴，贴上最后的解决代码