调整jpeg图像的大小会影响它们的压缩吗？

Question

我正在使用Graphics.DrawImage方法调整jpeg的大小(参见下面的代码片段).任何人都可以确认这不会影响新图像的压缩吗？我见过这个帖子,但我特别谈到jpegs的压缩.

    private byte[] getResizedImage(String url, int newWidth)
    {
        Bitmap bmpOut = null;
        System.IO.MemoryStream outStream = new System.IO.MemoryStream();

        //input image is disposable
        using (Bitmap inputImage = LoadImageFromURL(url))
        {
            ImageFormat format = inputImage.RawFormat;
            decimal ratio;  //ratio old width:new width
            int newHeight = 0;

            //*** If the image is smaller than a thumbnail just return it
            if (inputImage.Width < newWidth)
                return null;

            ratio = (decimal)newWidth / inputImage.Width;
            decimal h = inputImage.Height * ratio;
            newHeight = (int)h;

            bmpOut = new Bitmap(newWidth, newHeight);
            Graphics g = Graphics.FromImage(bmpOut);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            // try testing with following options:
            //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
            //g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

            g.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);
            g.DrawImage(inputImage, 0, 0, newWidth, newHeight);
            bmpOut.Save(outStream, getImageFormat(url));
        }

        return outStream.ToArray();

    }

Answer 1

JPEG没有保存在其中的"压缩"值.当您调整大小并保存它们时,它们会使用您告诉保存函数使用的任何值进行压缩.由于您没有传递值,它只会使用库的默认值.