生成缩略图是一个十分常用功能，找到了一个方法，重写部分代码，实用又好用，.net又一个生成缩略图的方法，不变形
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/// <summary>
/// 为图片生成缩略图
/// </summary>
/// <param name="phyPath">原图片的路径</param>
/// <param name="width">缩略图宽</param>
/// <param name="height">缩略图高</param>
/// <returns></returns>
public System.Drawing.Image GetHvtThumbnail(System.Drawing.Image image, int width, int height)
{
Bitmap m_hovertreeBmp = new Bitmap(width, height);
//从Bitmap创建一个System.Drawing.Graphics
Graphics m_HvtGr = Graphics.FromImage(m_hovertreeBmp);
//设置
m_HvtGr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
//下面这个也设成高质量
m_HvtGr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
//下面这个设成High
m_HvtGr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
//把原始图像绘制成上面所设置宽高的缩小图
Rectangle rectDestination = new Rectangle(0, 0, width, height);
int m_width, m_height;
if (image.Width * height > image.Height * width)
{
m_height = image.Height;
m_width = (image.Height * width) / height;
}
else
{
m_width = image.Width;
m_height = (image.Width * height) / width;
}
m_HvtGr.DrawImage(image, rectDestination, 0, 0, m_width, m_height, GraphicsUnit.Pixel);
return m_hovertreeBmp;
}
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C#缩略图生成类，采用高质量插值法实现缩略图生成，高质量,低速度呈现平滑程度，可以保持缩略图纵横比，在获取缩略图的时候一开始就根据百分比获取图片的尺寸、根据设定的大小返回图片的大小，并高质量保存缩略图图片，为原图片设置EncoderParameters 对象。
以下为类文件，建议保存文件名为：ImageHelper.cs
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using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
namespace HtmlSnap
{
public static class ImageHelper
{
/// 获取缩略图
public static Image GetThumbnailImage(Image image, int width, int height)
{
if (image == null || width < 1 || height < 1)
return null;
// 新建一个bmp图片
Image bitmap = new System.Drawing.Bitmap(width, height);
// 新建一个画板
using (Graphics g = System.Drawing.Graphics.FromImage(bitmap))
{
// 设置高质量插值法
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
// 设置高质量,低速度呈现平滑程度
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
// 高质量、低速度复合
g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.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(image, new Rectangle(0, 0, width, height),
new Rectangle(0, 0, image.Width, image.Height),
GraphicsUnit.Pixel);
return bitmap;
}
}
/// <summary>
/// 生成缩略图，并保持纵横比
/// </summary>
/// <returns>生成缩略图后对象</returns>
public static Image GetThumbnailImageKeepRatio(Image image, int width, int height)
{
Size imageSize = GetImageSize(image, width, height);
return GetThumbnailImage(image, imageSize.Width, imageSize.Height);
}
/// <summary>
/// 根据百分比获取图片的尺寸
/// </summary>
public static Size GetImageSize(Image picture, int percent)
{
if (picture == null || percent < 1)
return Size.Empty;
int width = picture.Width * percent / 100;
int height = picture.Height * percent / 100;
return GetImageSize(picture, width, height);
}
/// <summary>
/// 根据设定的大小返回图片的大小，考虑图片长宽的比例问题
/// </summary>
public static Size GetImageSize(Image picture, int width, int height)
{
if (picture == null || width < 1 || height < 1)
return Size.Empty;
Size imageSize;
imageSize = new Size(width, height);
double heightRatio = (double)picture.Height / picture.Width;
double widthRatio = (double)picture.Width / picture.Height;
int desiredHeight = imageSize.Height;
int desiredWidth = imageSize.Width;
imageSize.Height = desiredHeight;
if (widthRatio > 0)
imageSize.Width = Convert.ToInt32(imageSize.Height * widthRatio);
if (imageSize.Width > desiredWidth)
{
imageSize.Width = desiredWidth;
imageSize.Height = Convert.ToInt32(imageSize.Width * heightRatio);
}
return imageSize;
}
/// <summary>
/// 获取图像编码解码器的所有相关信息
/// </summary>
/// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
/// <returns>返回图像编码解码器的所有相关信息</returns>
public static ImageCodecInfo GetCodecInfo(string mimeType)
{
ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
foreach (ImageCodecInfo ici in CodecInfo)
{
if (ici.MimeType == mimeType) return ici;
}
return null;
}
public static ImageCodecInfo GetImageCodecInfo(ImageFormat format)
{
ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();
foreach (ImageCodecInfo icf in encoders)
{
if (icf.FormatID == format.Guid)
{
return icf;
}
}
return null;
}
public static void SaveImage(Image image, string savePath, ImageFormat format)
{
SaveImage(image, savePath, GetImageCodecInfo(format));
}
/// <summary>
/// 高质量保存图片
/// </summary>
private static void SaveImage(Image image, string savePath, ImageCodecInfo ici)
{
// 设置 原图片 对象的 EncoderParameters 对象
EncoderParameters parms = new EncoderParameters(1);
EncoderParameter parm = new EncoderParameter(Encoder.Quality, ((long)95));
parms.Param[0] = parm;
image.Save(savePath, ici, parms);
parms.Dispose();
}
}
}
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