AForge.Imaging.Formats.PNMCodec.ReadHeader C# (CSharp) Method

        private PNMImageInfo ReadHeader( Stream stream )
        {
            // read magic word
            byte magic1 = (byte) stream.ReadByte( );
            byte magic2 = (byte) stream.ReadByte( );

            // check if it is valid PNM image
            if ( ( magic1 != 'P' ) || ( magic2 < '1' ) || ( magic2 > '6' ) )
            {
                throw new FormatException( "The stream does not contain PNM image." );
            }

            // check if it is P5 or P6 format
            if ( ( magic2 != '5' ) && ( magic2 != '6' ) )
            {
                throw new NotSupportedException( "Format is not supported yet. Only P5 and P6 are supported for now." );
            }

            int width = 0, height = 0, maxValue = 0;

            try
            {
                // read image's width and height
                width = ReadIntegerValue( stream );
                height = ReadIntegerValue( stream );
                // read pixel's highiest value
                maxValue = ReadIntegerValue( stream );
            }
            catch
            {
                throw new ArgumentException( "The stream does not contain valid PNM image." );
            }

            // check if all attributes are valid
            if ( ( width <= 0 ) || ( height <= 0 ) || ( maxValue <= 0 ) )
            {
                throw new ArgumentException( "The stream does not contain valid PNM image." );
            }

            // check maximum pixel's value
            if ( maxValue > 255 )
            {
                throw new NotSupportedException( "255 is the maximum pixel's value, which is supported for now." );
            }

            // prepare image information
            PNMImageInfo imageInfo = new PNMImageInfo( width, height, ( magic2 == '5' ) ? 8 : 24, 0, 1 );
            imageInfo.Version = (int) ( magic2 - '0' );
            imageInfo.MaxDataValue = maxValue;

            return imageInfo;
        }