Bitmapを品質指定で保存する

MyClass mc0 = new MyClass();
mc0.SaveEx( bmp, "test.jpg", 80 );

MyClas mc1 = new MyClass();
string msg = "";
mc1.SaveEx( bmp, "test.jpg", 80, out msg );

using System;
using System.Drawing;
using System.Drawing.Imaging;

public class MyClass
{
	public bool SaveEx( Bitmap bmp, string filepath, int quality_0_to_100 )
	{
		string excp_message = "";

		return SaveEx(
			bmp,
			filepath,
			quality_0_to_100,
			ref excp_message
			);
	}

	public bool SaveEx( Bitmap bmp, string filepath, int quality_0_to_100, ref string excp_message )
	{
		int quality = quality_0_to_100;

		excp_message = "";

		if ( bmp == null )
		{
			excp_message = "Bitmap is null.";
			return false;
		}

		if ( filepath == null )
		{
			excp_message = "File path is null.";
			return false;
		}

		if ( filepath == "" )
		{
			excp_message = "File path is empty.";
			return false;
		}

		if ( quality < 0 )
		{
			excp_message = "Quality must be 0 to 100.";
			return false;
		}

		if ( quality > 100 )
		{
			excp_message = "Quality must be 0 to 100.";
			return false;
		}

		ImageCodecInfo jpeg_codec = null;
		ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

		for ( int n = 0; n < codecs.Length; n++ )
		{
			if ( codecs[ n ].FormatID == ImageFormat.Jpeg.Guid )
			{
				jpeg_codec = codecs[ n ];
			}
		}

		if ( jpeg_codec == null )
		{
			excp_message = "JPEG encoder was not found.";
			return false;
		}

		try
		{
			using ( EncoderParameters enc_params = new EncoderParameters( 1 ) )
			{
				Encoder quality_encoder = Encoder.Quality;
				long quality_value = (long)quality;

				using ( EncoderParameter quality_param = new EncoderParameter( quality_encoder, quality_value ) )
				{
					enc_params.Param[ 0 ] = quality_param;
					bmp.Save( filepath, jpeg_codec, enc_params );
				}
			}
		}
		catch ( Exception excp )
		{
			excp_message = excp.Message;
			return false;
		}

		return true;
	}
}