将JPEG图像调整为固定宽度，同时保持纵横比不变

如何在保持纵横比的同时将JPEG图像调整为固定宽度？ 以简单的方式，同时保持质量。

这将仅在垂直轴上缩放： 

public static Image ResizeImageFixedWidth(Image imgToResize, int width) { int sourceWidth = imgToResize.Width; int sourceHeight = imgToResize.Height; float nPercent = ((float)width / (float)sourceWidth); int destWidth = (int)(sourceWidth * nPercent); int destHeight = (int)(sourceHeight * nPercent); Bitmap b = new Bitmap(destWidth, destHeight); Graphics g = Graphics.FromImage((Image)b); g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.DrawImage(imgToResize, 0, 0, destWidth, destHeight); g.Dispose(); return (Image)b; }

如果要将宽度减小25％到固定值，则必须将高度降低25％。

如果要将宽度增加25％到固定值，则必须将高度增加25％。

这真的很直接。

假设有一个（ double width ）变量： 

 Image imgOriginal = Bitmap.FromFile(path); double height = (imgOriginal.Height * width) / imgOriginal.Width; Image imgnew = new Bitmap((int)width, (int)height, PixelFormat.Format32bppArgb); Graphics g = Graphics.FromImage(imgnew); g.DrawImage(imgOriginal, new Point[]{new Point(0,0), new Point(width, 0), new Point(0, height)}, new Rectangle(0,0,imgOriginal.Width, imgOriginal.Height), GraphicsUnit.Pixel);

最后你会有一个widthxheight的新图像，然后，你需要刷新图形e保存imgnew。

如果你搜索它们，我认为有很多样本。 这是我经常使用的那个…… 

  public static Stream ResizeGdi(Stream stream, System.Drawing.Size size) { Image image = Image.FromStream(stream); int width = image.Width; int height = image.Height; int sourceX = 0, sourceY = 0, destX = 0, destY = 0; float percent = 0, percentWidth = 0, percentHeight = 0; percentWidth = ((float)size.Width / (float)width); percentHeight = ((float)size.Height / (float)height); int destW = 0; int destH = 0; if (percentHeight < percentWidth) { percent = percentHeight; } else { percent = percentWidth; } destW = (int)(width * percent); destH = (int)(height * percent); MemoryStream mStream = new MemoryStream(); if (destW == 0 && destH == 0) { image.Save(mStream, System.Drawing.Imaging.ImageFormat.Jpeg); return mStream; } using (Bitmap bitmap = new Bitmap(destW, destH, System.Drawing.Imaging.PixelFormat.Format48bppRgb)) { using (System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(bitmap)) { //graphics.Clear(Color.Red); graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; graphics.DrawImage(image, new Rectangle(destX, destY, destW, destH), new Rectangle(sourceX, sourceY, width, height), GraphicsUnit.Pixel); } bitmap.Save(mStream, System.Drawing.Imaging.ImageFormat.Jpeg); } mStream.Position = 0; return mStream as Stream; }

调用代码示例... 

 Stream stream = File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.None); resizedStream = ImageUtility.ResizeGdi(stream, new System.Drawing.Size(resizeWidth, resizeHeight));

快速搜索代码项目已找到以下文章。 它允许调整接受布尔值的图像的大小以限制新图像以保持原始高宽比。 由于没有提供截图，我不确定质量是什么样的。 请参阅此处的文章

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