Re: Jpeg Compression Ratio

Hi Simon,

> If I have a System.Drawing.Bitmap instance and want to save it as a jpg file, does anyone happen to know if there's a way to control the compression ratio it gets saved as? 

First of all you need to retrieve the encoder for the Jpeg image format:

---------------
ImageCodecInfo jpegCodec = null;

// Retrieve the codec for the jpeg format

foreach (ImageCodecInfo codec in ImageCodecInfo.GetImageEncoders())
{
    if (codec.FormatID == ImageFormat.Jpeg.Guid)
    {
        jpegCodec = codec;
        break;
    }
}

if (jpegCodec == null)
    throw new NotSupportedException("...");
---------------

Then you should configure the encoder with the settings you need.
Should you need a 50% quality (compression) factor output, for example, 
you can use the following code:

---------------
// Defines the parameters the encoder will use (quality factor

EncoderParameters encoderParameters = new EncoderParameters(1);
encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 50);
---------------

After that, the codec and its parameters can be used to (re)save the 
original bitmap:

---------------
Bitmap bmp = ...;
bmp.Save("...", jpegCodec, encoderParameters);
---------------

HTH

--
Efran Cobisi
http://www.cobisi.com

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