/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalImage">原图</param>
/// <param name="thumbnailPath">缩略图路径（物理路径）</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="mode">生成缩略图的方式</param>
public static void MakeThumbnail(this Image originalImage, string thumbnailPath, int width, int height, ThumbnailCutMode mode)
{
int towidth = width;
int toheight = height;
int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;
switch (mode)
{
case ThumbnailCutMode.Fixed: //指定高宽缩放（可能变形）
break;
case ThumbnailCutMode.LockWidth: //指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
break;
case ThumbnailCutMode.LockHeight: //指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
break;
case ThumbnailCutMode.Cut: //指定高宽裁减（不变形）
if (originalImage.Width / (double)originalImage.Height > 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;
}
//新建一个bmp图片
Image bitmap = new Bitmap(towidth, toheight);
//新建一个画板
Graphics g = Graphics.FromImage(bitmap);
//设置高质量插值法
g.InterpolationMode = InterpolationMode.High;
//设置高质量,低速度呈现平滑程度
g.SmoothingMode = SmoothingMode.HighQuality;
//清空画布并以透明背景色填充
g.Clear(Color.Transparent);
//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：对哪张图片进行操作。
//二：画多么大。
//三：画那块区域。
g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel);
try
{
//以jpg格式保存缩略图
bitmap.Save(thumbnailPath, ImageFormat.Jpeg);
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalImage">原图</param>
/// <param name="thumbnailPath">缩略图路径（物理路径）</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="mode">生成缩略图的方式</param>
public static void MakeThumbnail(this Image originalImage, string thumbnailPath, int width, int height, ThumbnailCutMode mode)
{
using var bitmap = MakeThumbnail(originalImage, width, height, mode);
bitmap.Save(thumbnailPath, originalImage.RawFormat);
}
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalImage">原图</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="mode">生成缩略图的方式</param>
public static Image ThumbnailImage(this Image originalImage, int width, int height, ThumbnailCutMode mode = ThumbnailCutMode.Cut)
{
int towidth = width;
int toheight = height;
int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;
switch (mode)
{
case ThumbnailCutMode.Fixed: //指定高宽缩放（可能变形）
break;
case ThumbnailCutMode.LockWidth: //指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
break;
case ThumbnailCutMode.LockHeight: //指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
break;
case ThumbnailCutMode.Cut: //指定高宽裁减（不变形）
if (originalImage.Width / (double)originalImage.Height > 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;
}
//新建一个bmp图片
Image bitmap = new Bitmap(towidth, toheight);
//新建一个画板
Graphics g = Graphics.FromImage(bitmap);
//设置高质量插值法
g.InterpolationMode = InterpolationMode.High;
//设置高质量,低速度呈现平滑程度
g.SmoothingMode = SmoothingMode.HighQuality;
//清空画布并以透明背景色填充
g.Clear(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 Rectangle(0, 0, towidth, toheight), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel);
try
{
return(bitmap);
}
catch (Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
g.Dispose();
}
}
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalFileName">原图文件</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="thumbnailFileName">缩略图文件（物理路径）</param>
/// <param name="mode">生成缩略图的方式</param>
public static void MakeThumbnail(string originalFileName, int width, int height, string thumbnailFileName = "", ThumbnailCutMode mode = ThumbnailCutMode.Cut)
{
Image originalImage = Image.FromFile(originalFileName);
string ext = Path.GetExtension(originalFileName);
if (thumbnailFileName == "")
{
thumbnailFileName = originalFileName.Replace(ext, "_thumb" + ext); //没有指定缩略图文件名，原文件名后面跟上_thumb
}
originalImage.ThumbnailImage(width, height, mode).Save(thumbnailFileName);
}
