/// <summary>
/// 生成缩略图(选择Cute可保证图片不变形)
/// </summary>
/// <param name="fileStream">源图流</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="bgColor">缩略图背景填充色</param>
/// <param name="mode">根据枚举类型确定压缩策略</param>
public static Stream MakeThumbnail(Stream fileStream, int width, int height, Color bgColor, ImageThumbStrategy mode)
{
if (null == fileStream)
{
return(null);
}
Stream ms = null;
Image originalImage = Image.FromStream(fileStream);
int towidth = width; //指定的缩略图的宽度
int toheight = height; //指定缩略图的高度
int drawX = 0; //指定在新的画布上开始画图的左顶点左边X
int drawY = 0; //指定在新的画布上开始画图的左顶点左边Y
int drawW = width; //指定在画布中需要画的宽度
int drawH = height; //指定在画布中需要画的高度
int cuteX = 0; //在源图上进行截图的坐标X
int cuteY = 0; //在源图上进行截图的坐标Y
int cuteW = originalImage.Width; //在源图上进行截图的宽度
int cuteH = originalImage.Height; //在源图上进行截图的高度
Image ThumbImage = null;
switch (mode)
{
case ImageThumbStrategy.Cut:
#region 指定高宽裁减（不变形）
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
cuteH = originalImage.Height;
cuteW = originalImage.Height * towidth / toheight;
cuteY = 0;
cuteX = (originalImage.Width - cuteW) / 2;
}
else
{
cuteW = originalImage.Width;
cuteH = originalImage.Width * toheight / towidth;
cuteX = 0;
cuteY = (originalImage.Height - cuteH) / 2;
}
break;
#endregion
case ImageThumbStrategy.SmartCut: //智能裁剪,小图周围填充色
#region 智能裁剪,取短板压缩到指定,长版从中间截取,都小则使用填充色
/*
* 缩略图的宽与高都比源图大,执行将源图放在新的图片的正中间策略
*/
if (originalImage.Width <= width && originalImage.Height <= height)
{
//图中图的左顶点坐标
drawX = (width - originalImage.Width) / 2;
drawY = (height - originalImage.Height) / 2;
drawW = originalImage.Width;
drawH = originalImage.Height;
}
else
{
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
cuteH = originalImage.Height;
cuteW = originalImage.Height * towidth / toheight;
cuteY = 0;
cuteX = (originalImage.Width - cuteW) / 2;
}
else
{
cuteW = originalImage.Width;
cuteH = originalImage.Width * toheight / towidth;
cuteX = 0;
cuteY = (originalImage.Height - cuteH) / 2;
}
}
break;
#endregion
case ImageThumbStrategy.SmartFill: //智能填充,小图周围填充色
#region 智能裁剪,取长板压缩到指定,短版居中绘制,都小则使用填充色(只是复制了 尚未开发 研究中)
/*
* 缩略图的宽与高都比源图大,执行将源图放在新的图片的正中间策略
*/
if (originalImage.Width <= width && originalImage.Height <= height)
{
#region 宽高均小，居中 四周填充
//如果源图宽和高都小于指定压缩的图片的宽高，将源图置于画布中间，四周填充色
drawX = (width - originalImage.Width) / 2;
drawY = (height - originalImage.Height) / 2;
drawW = originalImage.Width;
drawH = originalImage.Height;
//指定源图截取部分为全图
cuteW = originalImage.Width;
cuteH = originalImage.Height;
cuteX = 0;
cuteY = 0;
#endregion
}
else
{
double origRate_wh = (double)originalImage.Width / (double)originalImage.Height;
double toRate_Wh = (double)towidth / (double)toheight;
if (origRate_wh > toRate_Wh)
{
#region 宽度进行等比缩放到指定压缩宽度
int thumb_w = towidth;
int thumb_h = (int)((double)originalImage.Height * (double)towidth / (double)originalImage.Width);
ThumbImage = originalImage.GetThumbnailImage(thumb_w, thumb_h, ThumbnailCallback, IntPtr.Zero);
//指定源图在画布中所要展示的左定点位置与大小（计算居中坐标）
drawW = ThumbImage.Width;
drawH = ThumbImage.Height;
drawX = 0;
drawY = Math.Abs(toheight - ThumbImage.Height) / 2;
//指定源图截取部分为全图
cuteW = ThumbImage.Width;
cuteH = ThumbImage.Height;
cuteX = 0;
cuteY = 0;
#endregion
}
else
{
#region 高度进行等比缩放到指定压缩高度
int thumb_w = (int)((double)originalImage.Width * (double)toheight / (double)originalImage.Height);
int thumb_h = toheight;
ThumbImage = originalImage.GetThumbnailImage(thumb_w, thumb_h, ThumbnailCallback, IntPtr.Zero);
//指定源图在画布中所要展示的左定点位置与大小（计算居中坐标）
drawW = ThumbImage.Width;
drawH = ThumbImage.Height;
drawX = Math.Abs(towidth - ThumbImage.Width) / 2;
drawY = 0;
//指定源图截取部分为全图
cuteW = ThumbImage.Width;
cuteH = ThumbImage.Height;
cuteX = 0;
cuteY = 0;
#endregion
}
}
break;
#endregion
case ImageThumbStrategy.Width: //指定宽，高按比例
#region 指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
drawH = toheight;
break;
#endregion
case ImageThumbStrategy.Height: //指定高，宽按比例
#region 指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
drawW = towidth;
break;
#endregion
default:
break;
}
//新建一个bmp图片
Bitmap b = new Bitmap(towidth, toheight);
try
{
//新建一个画板
Graphics g = Graphics.FromImage(b);
//设置高质量插值法
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
//设置高质量,低速度呈现平滑程度
g.SmoothingMode = SmoothingMode.AntiAlias;
g.PixelOffsetMode = PixelOffsetMode.HighQuality;
//清空画布并以透明背景色填充
g.Clear(bgColor);
if (null != ThumbImage)
{
//在指定位置并且按指定大小绘制原图片的指定部分
g.DrawImage(
ThumbImage, //要绘制的源图
new Rectangle(drawX, drawY, drawW, drawH), //指定源图所在画布的位置与大小
new Rectangle(cuteX, cuteY, cuteW, cuteH), //指定需要绘制源图中的部分
GraphicsUnit.Pixel
);
ImageFormat actFormat = GetFormat(originalImage.RawFormat.Guid);
if (null == actFormat)
{
throw new Exception("图片格式异常");
}
ImageCodecInfo ici = GetCodecInfo("image/" + actFormat.ToString().ToLower());
ms = SaveImage(b, ici);
ms.Position = 0;
}
else
{
//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, //要绘制的源图
new Rectangle(drawX, drawY, drawW, drawH), //指定源图所在画布的位置与大小
new Rectangle(cuteX, cuteY, cuteW, cuteH), //指定需要绘制源图中的部分
GraphicsUnit.Pixel
);
ImageFormat actFormat = GetFormat(originalImage.RawFormat.Guid);
if (null == actFormat)
{
throw new Exception("图片格式异常");
}
ImageCodecInfo ici = GetCodecInfo("image/" + actFormat.ToString().ToLower());
ms = SaveImage(b, ici);
ms.Position = 0;
}
}
catch (System.Exception e)
{
throw e;
}
finally
{
if (null != ThumbImage)
{
ThumbImage.Dispose();
}
originalImage.Dispose();
b.Dispose();
fileStream.Seek(0, SeekOrigin.Begin);
}
return(ms);
}
/// <summary>
/// 生成缩略图(选择Cute可保证图片不变形)
/// </summary>
/// <param name="fileStream">源图流</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="mode">根据枚举类型确定压缩策略</param>
public static Stream MakeThumbnail(Stream fileStream, int width, int height, ImageThumbStrategy mode)
{
return(MakeThumbnail(fileStream, width, height, Color.Transparent, mode));
}