嘗試調整大小和壓縮高度，僅保持高品質的寬高比

Question

在這里，我正在處理從文件加載的圖像，並覆蓋將小寫名稱轉換為大寫形式的目標圖像，但是這里使用固定大小調整其大小，我需要使用260像素的高度進行調整，並保持其寬高比不設置圖像寬度

//--------------------------------------------------------------------------------//

    private void ProcessImage()
    {
        if (File.Exists(pictureBox1.ImageLocation))
        {
            string SourceImagePath = pictureBox1.ImageLocation;
            string ImageName = Path.GetFileName(SourceImagePath).ToUpper();
            string TargetImagePath = Properties.Settings.Default.ImageTargetDirectory + "\\" + ImageName;
           //Set the image to uppercase and save as uppercase
            if (SourceImagePath.ToUpper() != TargetImagePath.ToUpper())
            {

                using (Image Temp = Image.FromFile(SourceImagePath))
                {
                  // my problem is here, i need to resize only by height
                  // and maintain aspect ratio
                    Bitmap ResizedBitmap = resizeImage(Temp, new Size(175, 260));

                    //ResizedBitmap.Save(@TargetImagePath);
                    ResizedBitmap.Save(@TargetImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);

                }
                pictureBox1.ImageLocation = @TargetImagePath;
                File.Delete(SourceImagePath);
            }
        }
    }
    //--------------------------------------------------------------------------------//
    private static Bitmap resizeImage(Image imgToResize, Size size)
    {
        int sourceWidth = imgToResize.Width;
        int sourceHeight = imgToResize.Height;

        float nPercent = 0;
        float nPercentW = 0;
        float nPercentH = 0;

        nPercentW = ((float)size.Width / (float)sourceWidth);
        nPercentH = ((float)size.Height / (float)sourceHeight);

        if (nPercentH < nPercentW)
            nPercent = nPercentH;
        else
            nPercent = nPercentW;

        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 b;
    }
    //--------------------------------------------------------------------------------//

Answer 1

您的意思是只想將圖像調整為指定的高度，並保持寬度成比例？

    /// <summary>
    /// Resize the image to have the selected height, keeping the width proportionate.
    /// </summary>
    /// <param name="imgToResize"></param>
    /// <param name="newHeight"></param>
    /// <returns></returns>
    private static Bitmap resizeImage(Image imgToResize, int newHeight)
    {
        int sourceWidth = imgToResize.Width;
        int sourceHeight = imgToResize.Height; 

        float nPercentH = ((float)newHeight / (float)sourceHeight);

        int destWidth = Math.Max((int)Math.Round(sourceWidth * nPercentH), 1); // Just in case;
        int destHeight = newHeight;

        Bitmap b = new Bitmap(destWidth, destHeight);
        using (Graphics g = Graphics.FromImage((Image)b))
        {
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;
            g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
        }

        return b;
    }

注意-而不是顯式地處理Graphics g ，請使用using語句，因為這樣可以保證在發生異常時進行處理。

更新我建議將ResizedBitmap包裝在調用方法中的using語句中。

更新2我無法找到一種方法來保存具有指定最大尺寸的JPG。 您可以做的就是以指定的質量保存它，如果文件太大，請以較低的質量重試：

    public static void SaveJpegWithSpecifiedQuality(this Image image, string filename, int quality)
    {
        // http://msdn.microsoft.com/en-us/library/ms533844%28v=vs.85%29.aspx
        // A quality level of 0 corresponds to the greatest compression, and a quality level of 100 corresponds to the least compression.
        if (quality < 0 || quality > 100)
        {
            throw new ArgumentOutOfRangeException("quality");
        }

        System.Drawing.Imaging.Encoder qualityEncoder = System.Drawing.Imaging.Encoder.Quality;
        EncoderParameters encoderParams = new EncoderParameters(1);
        EncoderParameter encoderParam = new EncoderParameter(qualityEncoder, (long)quality);
        encoderParams.Param[0] = encoderParam;

        image.Save(filename, GetEncoder(ImageFormat.Jpeg), encoderParams);
    }

    private static ImageCodecInfo GetEncoder(ImageFormat format)
    {
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();
        foreach (ImageCodecInfo codec in codecs)
        {
            if (codec.FormatID == format.Guid)
            {
                return codec;
            }
        }
        return null;
    }

請注意， 調整大小算法的質量與保存時文件壓縮的質量不同 。 兩種操作都是有損的 。 我建議您使用最佳質量算法調整大小（更新如上所示），然后嘗試保存質量，直到找到可行的算法。