///
/// 等比例缩放生成缩略图
///
/// 源图路径（物理路径）
/// 缩略图宽度
/// 缩略图高度（依缩略图宽度等比例计算所得）
public void MakeThumbnail(String originalImagePath, Int32 width, Int32 height)
{
//获取原始图片
using (System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath))
{
double orwidth = (double)originalImage.Width;
if (orwidth < 320)
{
width = Convert.ToInt32(orwidth);
}
height = Convert.ToInt32(((double)originalImage.Height) / (orwidth / (double)width));
//缩略图画布宽高
Int32 towidth = width;
Int32 toheight = height;
//原始图片写入画布坐标和宽高(用来设置裁减溢出部分)
Int32 x = 0;
Int32 y = 0;
Int32 ow = originalImage.Width;
Int32 oh = originalImage.Height;
//原始图片画布,设置写入缩略图画布坐标和宽高(用来原始图片整体宽高缩放)
Int32 bg_x = 0;
Int32 bg_y = 0;
Int32 bg_w = towidth;
Int32 bg_h = toheight;
//倍数变量
double multiple = 0;
//获取宽长的或是高长与缩略图的倍数
if (originalImage.Width >= originalImage.Height)
{
multiple = (double)originalImage.Width / (double)width;
}
else
{
multiple = (double)originalImage.Height / (double)height;
}
//上传的图片的宽和高小等于缩略图
if (ow <= width && oh <= height)
{
//缩略图按原始宽高
bg_w = originalImage.Width;
bg_h = originalImage.Height;
//空白部分用背景色填充
bg_x = Convert.ToInt32(((double)towidth - (double)ow) / 2);
bg_y = Convert.ToInt32(((double)toheight - (double)oh) / 2);
}
//上传的图片的宽和高大于缩略图
else
{
//宽高按比例缩放
bg_w = Convert.ToInt32((double)originalImage.Width / multiple);
bg_h = Convert.ToInt32((double)originalImage.Height / multiple);
//空白部分用背景色填充
bg_y = Convert.ToInt32(((double)height - (double)bg_h) / 2);
bg_x = Convert.ToInt32(((double)width - (double)bg_w) / 2);
}
//新建一个bmp图片,并设置缩略图大小.
using (System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(towidth, toheight))
{
//新建一个画板
using (System.Drawing.Graphics gr = System.Drawing.Graphics.FromImage(bitmap))
{
gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;//设置高质量插值法
gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//设置高质量,低速度呈现平滑程度
gr.Clear(System.Drawing.ColorTranslator.FromHtml("#F2F2F2")); //清空画布并设置背景色
//在指定位置并且按指定大小绘制原图片的指定部分
//第一个System.Drawing.Rectangle是原图片的画布坐标和宽高,第二个是原图片写在画布上的坐标和宽高,最后一个参数是指定数值单位为像素
gr.DrawImage(originalImage, new System.Drawing.Rectangle(bg_x, bg_y, bg_w, bg_h), new System.Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel);
Int32 index = originalImagePath.LastIndexOf(‘\\‘) + 1;
String path = String.Concat(originalImagePath.Substring(0, index), "App_", originalImagePath.Substring(index));
try
{
//获取图片类型
string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower();
//按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题.
switch (fileExtension)
{
case ".gif": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Gif); break;
case ".jpg": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg); break;
case ".bmp": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Bmp); break;
case ".png": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Png); break;
}
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
gr.Dispose();
}
}
}
}
}
原文地址：https://www.cnblogs.com/lvjy-net/p/8297501.html