如何在保持原有宽高比的条件下更改图片尺寸

如何在保持原有宽高比的条件下更改图片尺寸

解决方案源码

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在改变图片尺寸的时候，如何保持原有图片的宽高比并将多余部分填充颜色？

解决方案

先创建一个目标尺寸的Graphics绘图图层，然后将原始图片进行等比缩放，再将缩放后的图片放置到绘图图层中间，并另存为新图片即可。

首先加载原始图片，并获取原始宽高值：

// tempFullFileName为原始图片路径 var image = Image.FromFile(tempFullFileName); var originalWidth = image.Width; var originalHeight = image.Height;

新建一个矢量图类，将其加载到Graphics绘图图层类中,并设置初始化参数：

// 比如目标尺寸是1080*1080 var thumbnail = new Bitmap(1080, 1080); var graphic = Graphics.FromImage(thumbnail); graphic.InterpolationMode = InterpolationMode.HighQualityBicubic; graphic.PixelOffsetMode = PixelOffsetMode.HighQuality; graphic.CompositingQuality = CompositingQuality.HighQuality;

计算出原始图片转换到目标尺寸图片的缩放比例：

var ratioX = (double)1080 / (double)originalWidth; var ratioY = (double)1080 / (double)originalHeight; // 上述两个值中最小值则是缩放比例 var ratio = ratioX < ratioY ? ratioX : ratioY;

计算出原始图片缩放后的宽度和高度：

var newHeight = Convert.ToInt32(originalHeight * ratio); var newWidth = Convert.ToInt32(originalWidth * ratio);

计算出缩放后的图片相对Graphics左上角的坐标， 横坐标和纵坐标必然有一个值是为0的：

var posX = Convert.ToInt32((1080 - (originalWidth * ratio)) / 2); var posY = Convert.ToInt32((1080 - (originalHeight * ratio)) / 2);

将Graphics绘图图层用白色填充，然后将缩放后的图片，根据计算出来的宽高、位置绘制到Graphics绘图图层中：

graphic.Clear(Color.White); // 填充为白色 graphic.DrawImage(image, posX, posY, newWidth, newHeight);

最后将通过Graphics绘制之后的矢量图保存下来即可：

thumbnail.Save(fullFileName);

源码

private static void ResizeImage(string tempFullFileName, string fullFileName) { using (var image = Image.FromFile(tempFullFileName)) { var originalWidth = image.Width; var originalHeight = image.Height; var thumbnail = new Bitmap(1080, 1080); var graphic = Graphics.FromImage(thumbnail); graphic.InterpolationMode = InterpolationMode.HighQualityBicubic; graphic.SmoothingMode = SmoothingMode.HighQuality; graphic.PixelOffsetMode = PixelOffsetMode.HighQuality; graphic.CompositingQuality = CompositingQuality.HighQuality; var ratioX = (double)1080 / (double)originalWidth; var ratioY = (double)1080 / (double)originalHeight; var ratio = ratioX < ratioY ? ratioX : ratioY; var newHeight = Convert.ToInt32(originalHeight * ratio); var newWidth = Convert.ToInt32(originalWidth * ratio); var posX = Convert.ToInt32((1080 - (originalWidth * ratio)) / 2); var posY = Convert.ToInt32((1080 - (originalHeight * ratio)) / 2); graphic.Clear(Color.White); // white padding graphic.DrawImage(image, posX, posY, newWidth, newHeight); thumbnail.Save(fullFileName); } }

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c# Image resizing to different size while preserving aspect ratio