C#图片裁剪与缩放
C#图片裁剪与缩放【参考】http://www.cnblogs.com/wu-jian/archive/2011/02/21/1959382.html
最近由于需要C#图片处理的相关应用，遂在网上参考一下，写出如下代码作为总结。
通常需要将图片缩放到指定宽度与高度的缩略图，若只对原图片进行缩放，当图片前后高宽比例不同时，缩放后的图片就会拉伸变形。可以采取的办法是先按照目标图片的高宽比进行裁剪，然后缩放到目标图片的高宽就ok了。
原理很简单：
1）首先根据目标图片的高宽比计算原图片的裁剪矩形区域
2）然后将该矩形区域内的图像拷贝到目标高宽的矩形区域中，下面上代码：
/// <summary> /// 图片转换（裁剪并缩放） /// </summary> /// <param name="ASrcFileName">源文件名称</param> /// <param name="ADestFileName">目标文件名称</param> /// <param name="AWidth">转换后的宽度（像素）</param> /// <param name="AHeight">转换后的高度（像素）</param> /// <param name="AQuality">保存质量（取值在1-100之间）</param> public static void DoConvert(string ASrcFileName, string ADestFileName, int AWidth, int AHeight, int AQuality) { Image ASrcImg = Image.FromFile(ASrcFileName); if (ASrcImg.Width <= AWidth && ASrcImg.Height <= AHeight) {//图片的高宽均小于目标高宽，直接保存 ASrcImg.Save(ADestFileName); return; } double ADestRate = AWidth * 1.0 / AHeight; double ASrcRate = ASrcImg.Width * 1.0 / ASrcImg.Height; //裁剪后的宽度 double ACutWidth = ASrcRate > ADestRate ? (ASrcImg.Height * ADestRate) : ASrcImg.Width; //裁剪后的高度 double ACutHeight = ASrcRate > ADestRate ? ASrcImg.Height : (ASrcImg.Width / ADestRate); //待裁剪的矩形区域，根据原图片的中心进行裁剪 Rectangle AFromRect = new Rectangle(Convert.ToInt32((ASrcImg.Width - ACutWidth) / 2), Convert.ToInt32((ASrcImg.Height - ACutHeight) / 2), (int)ACutWidth, (int)ACutHeight); //目标矩形区域 Rectangle AToRect = new Rectangle(0, 0, AWidth, AHeight); Image ADestImg = new Bitmap(AWidth, AHeight); Graphics ADestGraph = Graphics.FromImage(ADestImg); ADestGraph.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; ADestGraph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; ADestGraph.DrawImage(ASrcImg, AToRect, AFromRect, GraphicsUnit.Pixel); //获取系统image/jpeg编码信息 ImageCodecInfo[] AInfos = ImageCodecInfo.GetImageEncoders(); ImageCodecInfo AInfo = null; foreach (ImageCodecInfo i in AInfos) { if (i.MimeType == "image/jpeg") { AInfo = i; break; } } //设置转换后图片质量参数 EncoderParameters AParams = new EncoderParameters(1); AParams.Param = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)AQuality); //保存 ADestImg.Save(ADestFileName, AInfo, AParams); }
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