How to convert BMP to GIF in C#

I'd recommend a minor tweak to your code to remove the 'magic' string of the mimeType from the code, using the following:

static void Main(string[] args)
{
    Bitmap bitMap = new Bitmap(@"test.bmp");
 
    var codecInfo = GetEncoderInfo(ImageFormat.Gif);
 
    var paramsEncoder = new EncoderParameters(2);
    paramsEncoder.Param[0] = new EncoderParameter(Encoder.Compression, (long)EncoderValue.CompressionLZW);
    paramsEncoder.Param[1] = new EncoderParameter(Encoder.Quality, 0L);
 
    bitMap.Save("Output.gif", codecInfo, paramsEncoder);
}
 
private static ImageCodecInfo GetEncoderInfo(ImageFormat format)
{
    return ImageCodecInfo.GetImageEncoders().FirstOrDefault(x => x.FormatID == format.Guid);
}