C# Image Save as CMYK

Question

Please see my code below. I'm saving an image. My input image color mode is CMYK, but once I saved, it become RGB and rest. I just want to do following things:

1. I just want to keep it to CMYK color mode.
2. I just want to keep same input quality.

3. I just want to keep same width and height as input.

       Bitmap bmp = new Bitmap(Image.FromFile(@"D:\input.jpg"));            
       Graphics gr = Graphics.FromImage(bmp);
   
       using (Font myFont = new Font("Arial", 42))
       {
           gr.DrawString("Hello!", myFont, Brushes.Green, new Point(2, 2));
           gr.DrawString(textBox1.Text, myFont, Brushes.Green, new Point(700, 750));
       }
       ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);
       System.Drawing.Imaging.Encoder myEncoder = System.Drawing.Imaging.Encoder.Quality;
       EncoderParameters myEncoderParameters = new EncoderParameters(1);
   
       EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 100L);
       myEncoderParameters.Param[0] = myEncoderParameter;
       bmp.Save(@"D:\test.jpg", jgpEncoder, myEncoderParameters);
   

Answer 1

The act of converting the image to a bitmap so that you can manipulate it

Bitmap bmp = new Bitmap(Image.FromFile(@"D:\input.jpg"));

Does the conversion internally (the color pallette in a Bitmap is RGB). You will have to use a conversion algorithm (one of the ones in the link suggested by ArgentFire, or something else) before the save back to your file.

In response to your comment:

1. Not going to happen. To perform the manipulation of the image you need, you will have to use a Bitmap, which does the conversion internally. (in .Net the Bitmap is the standard in-memory representation of an image)

2. The image quality is going to be determined by the jpg encoder when you re-encode the Bitmap for saving. Jpeg uses a lossy compression so keeping the original image quality is doubtful.

3. I don't see where you are doing anything that should alter the aspect ratio of the image.

You would probably be better off using a lossless image format like tiff. Start from a tiff, convert to Bitmap to manipulate, encode back to tiff to save. All lossless with respect to the image quality.