Saving JPG file from stream increases size in C#

Question

A little bit of background:

I'm writing a bar code image scanner desktop app using WPF, that can take input from either a file location (previously scanned image) or have it come directly from a scanner (using NTWAIN). In both cases I create or get a stream.

Now when I create a new Bitmap from the stream and save it as a JPEG file using an Encoder

  using (var bmp = Image.FromStream(rawStream))
        {
            EncoderParameter ratio = new EncoderParameter(Encoder.Quality, 100L);
            EncoderParameter depth = new EncoderParameter(Encoder.ColorDepth, 8L);
            EncoderParameters codecParams = new EncoderParameters(2);

            codecParams.Param[0] = ratio;
            codecParams.Param[1] = depth;
            ImageCodecInfo jpegCodecInfo = ImageCodecInfo.GetImageEncoders().FirstOrDefault(x => x.FormatID == ImageFormat.Jpeg.Guid);

            bmp.Save(file.FileFullPath, jpegCodecInfo, codecParams); // Save to JPG
        }

or the built in

bmp.Save(file.FileFullPath, ImageFormat.Jpeg);

I tend to end up with much larger file sizes. Of course, this isn't always the case, but definately true when I'm loading a small black and white tiff file into memory and encoding as jpg.

My knowledge on image handling is rudimentary, but I think it is because the jpg files are saved with a color depth of 24 bits and the tiff images are originally stored as 1 bit. (Black and white)

No matter what I do, I can't get the jpg files to match the original file's bit depth.

The only work around I found is simply renaming the file to "filename.jpg" and saving like so

   using (Bitmap bmp = new Bitmap(rawStream))
   {
      Save(file.FileFullPath);
   }

But this feels like a solution that won't work indefinitely (as a side question, can one simply rename any *.bmp or *tiff file to *.jpg and it will still work?)

Based on my initial research it seems like

bmp.Save()

doesn't honor the encoding parameter for bit depth in jpeg images. Understandably my clients won't be happy having files grow from 16kb to 200kb for "no reason".

Is there a known work around for this problem or am I missing something obvious when it comes to working with streams and images?

you're re-encoding the jpgs. and whatever quality setting you're using on this new jpg is different than whatever was used to produce the original. — Marc B
Have you tried changing the line of your code that sets the color depth to 8L to something else? — itsme86

Peter B Peter B · Accepted Answer · 2016-10-24T15:21:01

JPEG works best for photographs with a multitude of colors, shades and gradients. Typical bit-depths: 8 (for greyscale) or 24 (for full color).

If you want monochrome (1-bit), I'd recommend agains using JPEG, not least because JPEG will introduce encoding artifacts that may not matter for photographs, but which will look like "added pepper and salt" if your original source is 1-bit. And the more you compress them, the more it will be there.

You should try using PNG instead, it has no such artifacts, and is better suited for digital sources with sharp edges.

You could also try making the TIFF smaller by 50% or 75% using a smart resize algorithm (using e.g. 8-bit output) that will convert micro-dots in the original into small gradients in the output. I did so long ago with 1-bit fax/scanner images, with actually quite good results. But too long to still have those sources.

Saving JPG file from stream increases size in C#

1 Answers