使用保存位图时，“参数无效。”

Question

Im trying to save a bitmap jpg format with a specified encoding quality. However im getting an exception ("Parameter is not valid.") when calling the save method.

If i leave out the two last parameters in the bmp.save it works fine.

        EncoderParameters eps = new EncoderParameters(1);
        eps.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 16);
        ImageCodecInfo ici = GetEncoderInfo("image/jpeg");
        string outfile = outputpath + "\\" + fileaddition + sourcefile.Name;
        bmp.Save(outfile,ici,eps );

        bmp.Dispose();
        image.Dispose();
        return true;
    }
    ImageCodecInfo GetEncoderInfo(string mimeType)
    {
        int j;
        ImageCodecInfo[] encoders;
        encoders = ImageCodecInfo.GetImageEncoders();
        for (j = 0; j < encoders.Length; ++j)
        {
            if (encoders[j].MimeType == mimeType)
                return encoders[j];
        }
        return null;
    }
}

Thank you

Answer 1

GDI+ is pretty flaky. You'll need to use 16L for the value or cast to (long).

Answer 2

您应该将质量值转换为long，如下所示：

eps.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)16);