我的更改图片的大小

注意先建立目录

#region 自己写的不改变形状
/// <summary>创建规定大小的图像
/// 源图像只能是JPG格式
/// </summary>
/// <param name="oPath">源图像绝对路径</param>
/// <param name="tPath">生成图像绝对路径</param>
/// <param name="width">生成图像的宽度</param>
/// <param name="height">生成图像的高度</param>
public void CreateImage(string oPath, string tPath, int width, int height)
{
Bitmap originalBmp = new Bitmap(oPath);
// 源图像在新图像中的位置
int left, top;

if (originalBmp.Width <= width && originalBmp.Height <= height)
{
// 原图像的宽度和高度都小于生成的图片大小
left = (int)Math.Round((decimal)(width - originalBmp.Width) / 2);
top = (int)Math.Round((decimal)(height - originalBmp.Height) / 2);

// 最终生成的图像
Bitmap bmpOut = new Bitmap(width, height);
using (Graphics graphics = Graphics.FromImage(bmpOut))
{
// 设置高质量插值法
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
// 清空画布并以白色背景色填充
graphics.Clear(Color.White);
// 把源图画到新的画布上
graphics.DrawImage(originalBmp, left, top);
}
bmpOut.Save(tPath);
bmpOut.Dispose();

return;
}

// 新图片的宽度和高度，如400*200的图像，想要生成160*120的图且不变形，
// 那么生成的图像应该是160*80，然后再把160*80的图像画到160*120的画布上
int newWidth, newHeight;
if (width * originalBmp.Height < height * originalBmp.Width)
{
newWidth = width;
newHeight = (int)Math.Round((decimal)originalBmp.Height * width / originalBmp.Width);
// 缩放成宽度跟预定义的宽度相同的，即left=0，计算top
left = 0;
top = (int)Math.Round((decimal)(height - newHeight) / 2);
}
else
{
newWidth = (int)Math.Round((decimal)originalBmp.Width * height / originalBmp.Height);
newHeight = height;
// 缩放成高度跟预定义的高度相同的，即top=0，计算left
left = (int)Math.Round((decimal)(width - newWidth) / 2);
top = 0;
}

// 生成按比例缩放的图，如：160*80的图
Bitmap bmpOut2 = new Bitmap(newWidth, newHeight);
using (Graphics graphics = Graphics.FromImage(bmpOut2))
{
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);
graphics.DrawImage(originalBmp, 0, 0, newWidth, newHeight);
}
// 再把该图画到预先定义的宽高的画布上，如160*120
Bitmap lastbmp = new Bitmap(width, height);
using (Graphics graphics = Graphics.FromImage(lastbmp))
{
// 设置高质量插值法
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
// 清空画布并以白色背景色填充
graphics.Clear(Color.White);
// 把源图画到新的画布上
graphics.DrawImage(bmpOut2, left, top);
}
lastbmp.Save(tPath);
lastbmp.Dispose();
}
#endregion

public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

int towidth = width;
int toheight = height;

int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;

switch (mode)
{
case "HW"://指定高宽缩放（可能变形）
break;
case "W"://指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
break;
case "H"://指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
break;
case "Cut"://指定高宽裁减（不变形）
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
oh = originalImage.Height;
ow = originalImage.Height * towidth / toheight;
y = 0;
x = (originalImage.Width - ow) / 2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width * height / towidth;
x = 0;
y = (originalImage.Height - oh) / 2;
}
break;
default:
break;
}

//新建一个bmp图片
System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

//新建一个画板
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);

//设置高质量插值法
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

//设置高质量,低速度呈现平滑程度
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

//清空画布并以透明背景色填充
g.Clear(System.Drawing.Color.Transparent);

//在指定位置并且按指定大小绘制原图片的指定部分
g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
new System.Drawing.Rectangle(x, y, ow, oh),
System.Drawing.GraphicsUnit.Pixel);

//以jpg格式保存缩略图
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

originalImage.Dispose();
bitmap.Dispose();
g.Dispose();

}