将 JPEG 图像大小调整为固定宽度，同时保持纵横比不变

Question

如何将 JPEG 图像的大小调整为固定宽度，同时保持纵横比？以简单的方式，同时保持质量。

Answer 1

这只会在垂直轴上缩放：

    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;
    }

Answer 2

如果要将宽度减少 25% 至固定值，则必须将高度减少 25%。

如果要将宽度增加 25% 达到固定值，则必须将高度增加 25%。

这真的很简单。

Answer 3

假设有一个（双宽度）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);

最后您将得到一个宽度x高度的新图像，然后，您需要刷新图形并保存新的图像。

Answer 4

我想如果你搜索一下的话，会有很多这样的例子。这是我常用的...

    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));

Answer 5

快速搜索代码项目发现了以下文章。它允许调整图像大小，该图像接受布尔值来限制新图像以保持原始宽高比。我不确定质量如何，因为没有提供屏幕截图。请参阅文章此处< /a>