Class HDecompressor


  • public class HDecompressor
    extends Object
    HDecompressor. Uncompress astronomical images compressed using the H-compression algorithm. Examples :
              DataInputStream dis = new DataInputStream( new FileInputStream(arg[0]));
              byte [] pixels=Hdecomp.decomp( (InputStream)dis );
     
    where the user needs to translate the byte stream back into a series of shorts.
              DataInputStream dis = new DataInputStream( new FileInputStream(arg[0]));
              Hdecomp         hd  = new Hdecomp(dis);
              hd.decomp();
              int[] pixels        =  hd.getImage();
              int   nx            =  hd.getNx();
              int   ny            =  hd.getNy();
     
    • Constructor Detail

      • HDecompressor

        public HDecompressor()
        Create a bare decompressor object.
      • HDecompressor

        public HDecompressor​(InputStream dis)
        Create a decompressor associating it with a given input stream.
        Parameters:
        dis - The input stream from which the compressed data is derived.
    • Method Detail

      • setInputStream

        public void setInputStream​(InputStream dis)
        Set the input stream for an Hdecomp object.
        Parameters:
        dis - The input stream from which the compressed data is derived.
      • decompress

        public static int[] decompress​(InputStream fdis)
                                throws Exception
        Hdecompress static method.
        Parameters:
        fdis - The input stream from which compressed data is to be extracted. It should begin with the magic characters [0xDD, 0x99]. If the compressed data is preceded by a FITS header it is the responsibility of the program to skip past the header before calling this routine.
        Returns:
        byte[] The uncompressed Fits image. Note that this image is actually an array of shorts and the calling program should combine pairs of bytes to get the value for each pixel.
        Throws:
        Exception
      • decompress

        public void decompress()
                        throws Exception
        Decompress the input stream. The result is left in the a[] array and can be accessed using the various get methods.
        Throws:
        Exception
      • getNx

        public int getNx()
        Get the X-dimension of the decompressed image.
        Returns:
        The number of columns in the image.
      • getNy

        public int getNy()
        Get the Y-dimension of the decompressed image.
        Returns:
        The number of rows in the image.
      • getImage

        public int[] getImage()
        Get decompressed image as a one-d array of ints. Note that this returns a pointer to the internal array. If another image is compressed it may overwrite the current image in place. The caller should copy the array if multiple files are being decompressed using the same Hdecomp object.
        Returns:
        The decompressed image as a 1-D int array.