上傳圖檔時，使用GDI+中重繪方式将CMYK圖檔轉為RGB圖檔

原文:

上傳圖檔時，使用GDI+中重繪方式将CMYK圖檔轉為RGB圖檔

我們知道，如果網站上傳圖檔時，如果使用者上傳的是CMYK圖檔，那麼在網站上将是無法顯示的，通常的現象是出現一個紅叉。

下面使用将Image重新繪制為Format24bppRgb的方式來解決此問題：

public static void SavePostedImage(HttpPostedFile postedFile, string destFileName, int maxHeight, int maxWidth)

{

     System.Drawing.Imaging.ImageFormat imgFormat;

     if (destFileName.ToLower().EndWith("jpg"))

     {

          imgFormat = ImageFormat.Jpeg;

     }

     else //這裡可以加更多選項，比如png,gif,tif....

          imgFormat = ImageFormat.Gif;

     Bitmap bmp = new Bitmap(postedFile.InputStream);

     if (IsCMYK(bmp))

          bmp = ConvertCMYK(bmp);

     }

     if ((bmp.HorizontalResolution > 72) || (bmp.VerticalResolution > 72))

          bmp.SetResolution(72, 72);

     Bitmap saveBmp;

     if ((bmp.Height > maxHeight) || (bmp.Width > maxWidth))

          Double heightRatio = Convert.ToDouble(maxHeight) / Convert.ToDouble(bmp.Height);

          Double widthRatio = Convert.ToDouble(maxWidth) / Convert.ToDouble(bmp.Width);

          Double scaleRatio;

          if (heightRatio > widthRatio)

          {

               scaleRatio = widthRatio;

          }

          else

               scaleRatio = heightRatio;

          int height = Convert.ToInt32(bmp.Height * scaleRatio);

          int width = Convert.ToInt32(bmp.Width * scaleRatio);

          saveBmp = new Bitmap(bmp, width, height);

     else

          saveBmp = new Bitmap(bmp);

     bmp.Dispose();

     saveBmp.Save(destFileName, imgFormat);

     saveBmp.Dispose();

     postedFile.InputStream.Close();

}

public static string GetImageFlags(System.Drawing.Image img)

     ImageFlags FlagVals = (ImageFlags)Enum.Parse(typeof(ImageFlags), img.Flags.ToString());

     return FlagVals.ToString();

public static bool IsCMYK(System.Drawing.Image img)

     bool isCmyk;

     if ((GetImageFlags(img).IndexOf("Ycck") > -1) || (GetImageFlags(img).IndexOf("Cmyk") > -1))

     { isCmyk = true; }

     { isCmyk = false; }

     return isCmyk;

public static Bitmap ConvertCMYK(Bitmap bmp)

     Bitmap tmpBmp = new Bitmap(bmp.Width, bmp.Height, PixelFormat.Format24bppRgb);

     Graphics g = Graphics.FromImage(tmpBmp);

     g.CompositingQuality = CompositingQuality.HighQuality;

     g.SmoothingMode = SmoothingMode.HighQuality;

     g.InterpolationMode = InterpolationMode.HighQualityBicubic;

     Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);

     // 将CMYK圖檔重繪一遍,此時GDI+自動将CMYK格式轉換為RGB了

     g.DrawImage(bmp, rect);

     Bitmap returnBmp = new Bitmap(tmpBmp);

     g.Dispose();

     tmpBmp.Dispose();

     return returnBmp;

} 

更多讨論:

(1)如何将RGB圖檔轉換為CMYK圖檔?

(2)如何将RGB圖檔轉換為索引圖檔?

(3)如何将RGB圖檔轉換為灰階/黑白線條圖檔?

(4)上述轉換如果是在WPF中,又如何進行呢?

留給讀者去思考吧.