Package nom.tam.fits.header

Enum Compression

java.lang.Object
java.lang.Enum<Compression>
nom.tam.fits.header.Compression
All Implemented Interfaces:
Serializable, Comparable<Compression>, java.lang.constant.Constable, IFitsHeader
public enum Compression extends Enum<Compression> implements IFitsHeader
The following keywords are defined by the compression convention for use in the header of the FITS binary table extension to describe the structure of the compressed image.

  • Nested Class Summary

    Nested classes/interfaces inherited from class java.lang.Enum

    Enum.EnumDesc<E extends Enum<E>>

    Nested classes/interfaces inherited from interface nom.tam.fits.header.IFitsHeader

    IFitsHeader.HDU, IFitsHeader.SOURCE, IFitsHeader.VALUE

  • Enum Constant Summary

    Enum Constants
    Enum Constant
    Description
    ZBITPIX
    (required keyword) The value field of this keyword shall contain an integer that gives the value of the BITPIX keyword in the uncompressed FITS image.
    ZBLANK
    When using the quantization method to compress floating-point images, this header is used to store the integer value that represents undefined pixels (if any) in the scaled integer pixel values.
    ZBLOCKED
    Deprecated.
    ZCMPTYPE
    (required keyword) The value field of this keyword shall contain a character string giving the name of the algorithm that must be used to decompress the image.
    ZCTYPn
    The value field of these keywords shall contain a charac- ter string giving the mnemonic name of the algorithm that was used to compress column n of the table.
    ZDATASUM
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZDITHER0
    (optional keyword) The value field of this keyword shall contain an integer that gives the seed value for the random dithering pattern that was used when quantizing the floating-point pixel values.
    ZEXTEND
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZFORMn
    The value field of these keywords shall contain the character string values of the corresponding TFORMn keywords that defines the data type of column n in the original uncompressed FITS table.
    ZGCOUNT
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZHECKSUM
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZIMAGE
    (required keyword) This keyword must have the logical value T.
    ZMASKCMP
    (optional keyword) Used to record the name of the image compression algorithm that was used to compress the optional null pixel data mask.
    ZNAMEn
    (optional keywords) These pairs of optional array keywords (where n is an integer index number starting with 1) supply the name and value, respectively, of any algorithm-specific parameters that are needed to compress o r uncompress the image.
    ZNAXIS
    (required keyword) The value field of this keyword shall contain an integer that gives the value of the NAXIS keyword in the uncompressed FITS image.
    ZNAXISn
    (required keywords) The value field of these keywords shall contain a positive integer that gives the value of the NAXISn keywords in the uncompressed FITS image.
    ZPCOUNT
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZQUANTIZ
    (optional keyword) This keyword records the name of the algorithm that was used to quantize floating-point image pixels into integer values which are then passed to the compression algorithm.
    ZSIMPLE
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZTABLE
    (required keyword) This keyword must have the logical value T.
    ZTENSION
    The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image.
    ZTHEAP
    Stores the original heap offset of the uncompressed heap.
    ZTILELEN
    The value field of this keyword shall contain an integer representing the number of rows of data from the original binary table that are contained in each tile of the compressed table.
    ZTILEn
    (optional keywords) The value of these indexed keywords (where n ranges from 1 to ZNAXIS ) shall contain a positive integer representing the number of pixels along axis n of the compression tiles.
    ZVALn
    (optional keywords) These pairs of optional array keywords (where n is an integer index number starting with 1) supply the name and value, respectively, of any algorithm-specific parameters that are needed to compress o r uncompress the image.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final String
    BLOCKSIZE
    The blocksize parameter for the rise algorithm.
    static final String
    BYTEPIX
    The number of 8-bit bytes in each original integer pixel value.
    static final String
    COMPRESSED_DATA_COLUMN
    Each row of this variable-length column contains the byte st ream that is generated as a result of compressing the corresponding image tile.
    static final String
    GZIP_COMPRESSED_DATA_COLUMN
    When using the quantization method to compress floating-poi nt images that is described in Section 4, it sometimes may not be possible to quantize some o f the tiles (e.g., if the range of pixels values is too large or if most of the pixels have the sam e value and hence the calculated RMS noise level in the tile is close to zero).
    static final String
    NULL_PIXEL_MASK_COLUMN
    The null pixels in integer images are flagged by a reserved BLANK value and will be preserved if a lossless compression algorithm is used.
    static final String
    SCALE
    The integer scale parameter determines the amount of compression.
    static final String
    SMOOTH
    At high compressions factors the decompressed image begins to appear blocky because of the way information is discarded.
    static final String
    UNCOMPRESSED_DATA_COLUMN
    Use of this column is no longer recommended, but it may exist i n older compressed image files that were created before support for the GZIP COMPRESSED DATA column (describe above) was added to this convention in May 2011.
    static final String
    ZBLANK_COLUMN
    When using the quantization method to compress floating-point images that is described in Section 4, this column is used to store the integer value that represents undefined pixels (if any) in the scaled integer pixel values.
    static final String
    ZCMPTYPE_GZIP_1
    Gzip is the compression algorithm used in the free GN U software utility of the same name.
    static final String
    ZCMPTYPE_GZIP_2
    If ZCMPTYPE = ’GZIP 2’ then the bytes in the array of image pixel values are shuffled in to decreasing order of significance before being compressed with the gzip algorithm.
    static final String
    ZCMPTYPE_HCOMPRESS_1
    Hcompress is an the image compression package written by Richard L.
    static final String
    ZCMPTYPE_NOCOMPRESS
    compression algorithm that specifies that the data is uncompressed.
    static final String
    ZCMPTYPE_PLIO_1
    If ZCMPTYPE = ’PLIO 1’ then the IRAF PLIO (Pixel List) algorithm is used to compress and uncompress the image pixels.
    static final String
    ZCMPTYPE_RICE_1
    If ZCMPTYPE = ’RICE 1’ then the Rice algorithm is used to compress and uncompress the image pixels.
    static final String
    ZCMPTYPE_RICE_ONE
    alternative name for 'RICE 1'
    static final String
    ZQUANTIZ_NO_DITHER
    This is the simplest option in which no dithering is performed.
    static final String
    ZQUANTIZ_SUBTRACTIVE_DITHER_1
    It should be noted that an image that is quantized using this technique can stil l be unquantized using the simple linear scaling function given by Eq. 1.
    static final String
    ZQUANTIZ_SUBTRACTIVE_DITHER_2
    This dithering algorithm is identical to the SUBTRACTIVE DITHER 1 algorithm described above, ex- cept that any pixels in the floating-point image that are equa l to 0.0 are represented by the reserved value -2147483647 in the quantized integer array.
    static final String
    ZSCALE_COLUMN
    name of the column containing the quant scale value.
    static final String
    ZZERO_COLUMN
    name of the column containing the quant zero value.

    Fields inherited from interface nom.tam.fits.header.IFitsHeader

    MAX_INDEX

  • Method Summary

    Modifier and Type
    Method
    Description
    IFitsHeader
    getUncompressedKey()
    Returns the equivalent of this comression keyword in the uncompressed HDU.
    final FitsKey
    impl()
    (primarily for internal use) Returns the concrete implementation of this header entry, which provides implementation of access methods.
    static Compression
    valueOf(String name)
    Returns the enum constant of this type with the specified name.
    static Compression[]
    values()
    Returns an array containing the constants of this enum type, in the order they are declared.

    Methods inherited from class java.lang.Enum

    compareTo, describeConstable, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

    Methods inherited from class java.lang.Object

    getClass, notify, notifyAll, wait, wait, wait

    Methods inherited from interface nom.tam.fits.header.IFitsHeader

    comment, extractIndices, hdu, key, n, status, valueType

  • Enum Constant Details

    • ZTABLE

      public static final Compression ZTABLE
      (required keyword) This keyword must have the logical value T. The value field of this keyword shall be ’T’ to indicate that the FITS binary table extension contains a compressed BINTABLE, and that logically this extension should be interpreted as a tile-compressed binary table.

    • ZIMAGE

      public static final Compression ZIMAGE
      (required keyword) This keyword must have the logical value T. It indicates that the FITS binary table extension contains a compressed image and that logically this extension should be interpreted as an image and not as a table.

    • ZCMPTYPE

      public static final Compression ZCMPTYPE
      (required keyword) The value field of this keyword shall contain a character string giving the name of the algorithm that must be used to decompress the image. Currently, values of GZIP 1 , GZIP 2 , RICE 1 , PLIO 1 , and HCOMPRESS 1 are reserved, and the corresponding algorithms are described in a later section of this document . The value RICE ONE is also reserved as an alias for RICE 1 .

    • ZBITPIX

      public static final Compression ZBITPIX
      (required keyword) The value field of this keyword shall contain an integer that gives the value of the BITPIX keyword in the uncompressed FITS image.

    • ZNAXIS

      public static final Compression ZNAXIS
      (required keyword) The value field of this keyword shall contain an integer that gives the value of the NAXIS keyword in the uncompressed FITS image.

    • ZNAXISn

      public static final Compression ZNAXISn
      (required keywords) The value field of these keywords shall contain a positive integer that gives the value of the NAXISn keywords in the uncompressed FITS image.

    • ZTILEn

      public static final Compression ZTILEn
      (optional keywords) The value of these indexed keywords (where n ranges from 1 to ZNAXIS ) shall contain a positive integer representing the number of pixels along axis n of the compression tiles. Each tile of pixels is compressed separately and stored in a row of a variable-length vector column in the binary table. The size of each image dimension (given by ZNAXISn ) is not required to be an integer multiple of ZTILEn, and if it is not, then the last tile along that dimension of the image will contain fewer image pixels than the other tiles. If the ZTILEn keywords are not present then the default ’row by row’ tiling will be assumed such that ZTILE1 = ZNAXIS1 , and the value of all the other ZTILEn keywords equals 1. The compressed image tiles are stored in the binary table in t he same order that the first pixel in each tile appears in the FITS image; the tile containing the first pixel in the image appears in the first row of the table, and the tile containing the last pixel in the image appears in the last row of the binary table.

    • ZNAMEn

      public static final Compression ZNAMEn
      (optional keywords) These pairs of optional array keywords (where n is an integer index number starting with 1) supply the name and value, respectively, of any algorithm-specific parameters that are needed to compress o r uncompress the image. The value of ZVALn may have any valid FITS datatype. The order of the compression parameters may be significant, and may be defined as part of the description of the specific decompression algorithm.

    • ZVALn

      public static final Compression ZVALn
      (optional keywords) These pairs of optional array keywords (where n is an integer index number starting with 1) supply the name and value, respectively, of any algorithm-specific parameters that are needed to compress o r uncompress the image. The value of ZVALn may have any valid FITS datatype. The order of the compression parameters may be significant, and may be defined as part of the description of the specific decompression algorithm.

    • ZMASKCMP

      public static final Compression ZMASKCMP
      (optional keyword) Used to record the name of the image compression algorithm that was used to compress the optional null pixel data mask. See the “Preserving undefined pixels with lossy compression” section for more details.

    • ZSIMPLE

      public static final Compression ZSIMPLE
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy of the original FITS file when the image is uncompressed.preserves the original SIMPLE keyword.may only be used if the original uncompressed image was contained in the primary array of the FITS file.

    • ZTENSION

      public static final Compression ZTENSION
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original XTENSION keyword.may only be used if the original uncompressed image was contained in in IMAGE extension.

    • ZEXTEND

      public static final Compression ZEXTEND
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy of the original FITS file when the image is uncompressed.preserves the original EXTEND keyword.may only be used if the original uncompressed image was contained in the primary array of the FITS file.

    • ZBLOCKED

      @Deprecated public static final Compression ZBLOCKED
      Deprecated.
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original BLOCKED keyword.may only be used if the original uncompressed image was contained in the primary array of the FITS file,

    • ZPCOUNT

      public static final Compression ZPCOUNT
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original PCOUNT keyword.may only be used if the original uncompressed image was contained in in IMAGE extension.

    • ZGCOUNT

      public static final Compression ZGCOUNT
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original GCOUNT keyword.may only be used if the original uncompressed image was contained in in IMAGE extension.

    • ZHECKSUM

      public static final Compression ZHECKSUM
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original CHECKSUM keyword.

    • ZDATASUM

      public static final Compression ZDATASUM
      The following optional keyword is defined to store a verbatim copy of the the value and comment field of the corresponding keyword in the original uncompressed FITS image. These keywords can be used to reconstruct an identical copy o f the original FITS file when the image is uncompressed.preserves the original DATASUM

    • ZQUANTIZ

      public static final Compression ZQUANTIZ
      (optional keyword) This keyword records the name of the algorithm that was used to quantize floating-point image pixels into integer values which are then passed to the compression algorithm.

    • ZDITHER0

      public static final Compression ZDITHER0
      (optional keyword) The value field of this keyword shall contain an integer that gives the seed value for the random dithering pattern that was used when quantizing the floating-point pixel values. The value may range from 1 to 100.00, inclusive.

    • ZBLANK

      public static final Compression ZBLANK
      When using the quantization method to compress floating-point images, this header is used to store the integer value that represents undefined pixels (if any) in the scaled integer pixel values. These pixels have an IEEE NaN value (Not a Number) in the uncompressed floating-point image. The recommended value for ZBLANK is -2147483648 (the largest negative 32-bit integer).

    • ZTHEAP

      public static final Compression ZTHEAP
      Stores the original heap offset of the uncompressed heap.
      Since:
      1.19.1

    • ZTILELEN

      public static final Compression ZTILELEN
      The value field of this keyword shall contain an integer representing the number of rows of data from the original binary table that are contained in each tile of the compressed table. The number of rows in the last tile may be less than in the previous tiles. Note that if the entire table is compressed as a single tile, then the compressed table will only contains a single row, and the ZTILELEN and ZNAXIS2 keywords will have the same value.

    • ZFORMn

      public static final Compression ZFORMn
      The value field of these keywords shall contain the character string values of the corresponding TFORMn keywords that defines the data type of column n in the original uncompressed FITS table.

    • ZCTYPn

      public static final Compression ZCTYPn
      The value field of these keywords shall contain a charac- ter string giving the mnemonic name of the algorithm that was used to compress column n of the table. The current allowed values are GZIP_1, GZIP_2, and RICE_1, and the corresponding algorithms

  • Field Details

    • ZQUANTIZ_NO_DITHER

      public static final String ZQUANTIZ_NO_DITHER
      This is the simplest option in which no dithering is performed. The floating-point pixels are simply quantized using Eq. 1. This option should be assumed if the ZQUANTIZ keyword is not present in the header of the compressed floating-point image.
      See Also:

    • ZQUANTIZ_SUBTRACTIVE_DITHER_1

      public static final String ZQUANTIZ_SUBTRACTIVE_DITHER_1
      It should be noted that an image that is quantized using this technique can stil l be unquantized using the simple linear scaling function given by Eq. 1. The only side effect in this ca se is to introduce slightly more noise in the image than if the full subtractive dithering algorith m were applied.
      See Also:

    • ZQUANTIZ_SUBTRACTIVE_DITHER_2

      public static final String ZQUANTIZ_SUBTRACTIVE_DITHER_2
      This dithering algorithm is identical to the SUBTRACTIVE DITHER 1 algorithm described above, ex- cept that any pixels in the floating-point image that are equa l to 0.0 are represented by the reserved value -2147483647 in the quantized integer array. When the i mage is subsequently uncompressed and unscaled, these pixels are restored to their original va lue of 0.0. This dithering option is useful if the zero-valued pixels have special significance to the da ta analysis software, so that the value of these pixels must not be dithered.
      See Also:

    • ZCMPTYPE_GZIP_1

      public static final String ZCMPTYPE_GZIP_1
      Gzip is the compression algorithm used in the free GN U software utility of the same name. It was created by Jean-loup Gailly and Mark Adler and is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algor ithms which, at the time, limited the usability of compress and other popular archivers. Furt her information about this compression technique is readily available on the Internet. The gzip alg orithm has no associated parameters that need to be specified with the ZNAMEn and ZVALn keywords.
      See Also:

    • ZCMPTYPE_GZIP_2

      public static final String ZCMPTYPE_GZIP_2
      If ZCMPTYPE = ’GZIP 2’ then the bytes in the array of image pixel values are shuffled in to decreasing order of significance before being compressed with the gzip algorithm. In other words, bytes are shuffled so that the most significant byte of every pixel occurs first, in order, followed by the next most significant byte, and so on for every byte. Since the most significan bytes of the pixel values often have very similar values, grouping them together in this way often achieves better net compression of the array. This is usually especially effective when compressing floating-point arrays.
      See Also:

    • ZCMPTYPE_RICE_1

      public static final String ZCMPTYPE_RICE_1
      If ZCMPTYPE = ’RICE 1’ then the Rice algorithm is used to compress and uncompress the image pixels. The Rice algorithm (Rice, R. F., Yeh, P.-S., and Miller, W. H. 1993, in Proc. of the 9th AIAA Computing in Aerospace Conf., AIAA-93-4541-CP, American Institute of Aeronautics and Astronautics) is simple and very fast, compressing or decompressing 10 7 pixels/sec on modern workstations. It requires only enough memory to hold a single block of 16 or 32 pixels at a time. It codes the pixels in small blocks and so is able to adapt very quickly to changes in the input image statistics (e.g., Rice has no problem handling cosmic rays, bright stars, saturated pixels, etc.).
      See Also:

    • ZCMPTYPE_PLIO_1

      public static final String ZCMPTYPE_PLIO_1
      If ZCMPTYPE = ’PLIO 1’ then the IRAF PLIO (Pixel List) algorithm is used to compress and uncompress the image pixels. The PLIO algorithm was developed to store integer-valued image masks in a compressed form. Typical uses of image masks are to segment images into regions, or to mark bad pixels. Such masks often have large regions of constant value hence are highly compressible. The compression algorithm used is based on run-length encoding, with the ability to dynamically follow level changes in the image, allowing a 16-bit encoding to be used regardless of the image depth. The worst case performance occurs when successive pixels have different values. Even in this case the encoding will only require one word (16 bits) per mask pixel, provided either the delta intensity change between pixels is usually less than 12 bits, or the mask represents a zero floored step function of constant height. The worst case cannot exceed npix*2 words provided the mask depth is 24 bits or less.
      See Also:

    • ZCMPTYPE_HCOMPRESS_1

      public static final String ZCMPTYPE_HCOMPRESS_1
      Hcompress is an the image compression package written by Richard L. White for use at the Space Telescope Science Institute. Hcompress was used to compress the STScI Digitized Sky Survey and has also been used to compress the preview images in the Hubble Data Archive. Briefly, the method used is:
      1. a wavelet transform called the H-transform (a Haar transform generalized to two dimensions), followed by
      2. quantization that discards noise in the image while retaining the signal on all scales, followed by 10
      3. quadtree coding of the quantized coefficients.
      The technique gives very good compression for astronomical images and is relatively fast. The calculations are carried out using integer arithmetic and a re entirely reversible. Consequently, the program can be used for either lossy or lossless compression , with no special approach needed for the lossless case (e.g. there is no need for a file of residuals .)
      See Also:

    • ZCMPTYPE_RICE_ONE

      public static final String ZCMPTYPE_RICE_ONE
      alternative name for 'RICE 1'
      See Also:

    • ZCMPTYPE_NOCOMPRESS

      public static final String ZCMPTYPE_NOCOMPRESS
      compression algorithm that specifies that the data is uncompressed.
      See Also:

    • COMPRESSED_DATA_COLUMN

      public static final String COMPRESSED_DATA_COLUMN
      Each row of this variable-length column contains the byte st ream that is generated as a result of compressing the corresponding image tile. The datatype o f the column (as given by the TFORMn keyword) will generally be either ’1PB’, ’1PI’ , or ’1PJ’ (or the equivalent ’1Q’ format), depending on whether the compression algorithm ge nerates an output stream of 8-bit bytes, 16-bit integers, or 32-bit integers, respectively.
      See Also:

    • GZIP_COMPRESSED_DATA_COLUMN

      public static final String GZIP_COMPRESSED_DATA_COLUMN
      When using the quantization method to compress floating-poi nt images that is described in Section 4, it sometimes may not be possible to quantize some o f the tiles (e.g., if the range of pixels values is too large or if most of the pixels have the sam e value and hence the calculated RMS noise level in the tile is close to zero). There also may be other rare cases where the nominal compression algorithm can not be applied to certain tiles. In these cases, one may use an alternate technique in which the raw pixel values are loss lessly compressed with the GZIP algorithm and the resulting byte stream is stored in the GZIP COMPRESSED DATA column (with a ’1PB’ or ’1QB’ variable-length array column format). The corresponding COMPRESSED DATA column for these tiles must contain a null pointer.
      See Also:

    • UNCOMPRESSED_DATA_COLUMN

      public static final String UNCOMPRESSED_DATA_COLUMN
      Use of this column is no longer recommended, but it may exist i n older compressed image files that were created before support for the GZIP COMPRESSED DATA column (describe above) was added to this convention in May 2011. This variable length co lumn contains the uncompressed pixels for any tiles that cannot be compressed with the norma l method.
      See Also:

    • ZBLANK_COLUMN

      public static final String ZBLANK_COLUMN
      When using the quantization method to compress floating-point images that is described in Section 4, this column is used to store the integer value that represents undefined pixels (if any) in the scaled integer pixel values. These pixels have an IEEE NaN value (Not a Number) in the uncompressed floating-point image. The recommended value for ZBLANK is -2147483648 (the largest negative 32-bit integer).
      See Also:

    • ZZERO_COLUMN

      public static final String ZZERO_COLUMN
      name of the column containing the quant zero value.
      See Also:

    • ZSCALE_COLUMN

      public static final String ZSCALE_COLUMN
      name of the column containing the quant scale value.
      See Also:

    • NULL_PIXEL_MASK_COLUMN

      public static final String NULL_PIXEL_MASK_COLUMN

      The null pixels in integer images are flagged by a reserved BLANK value and will be preserved if a lossless compression algorithm is used. If the image is compressed with a lossy algorithm, however (e.g., H-Compress with a scale factor greater than 1), then some other technique must be used to identify the null pixels in the image.

      The recommended method of recording the null pixels when a lossy compression algorithm is used is to create an integer data mask with the same dimensions as the image tile. Set the null pixels to 1 and all the other pixels to 0, then compress the mask array using a lossless algorithm such as PLIO or GZIP. Store the compressed byte stream in a variable-length array column called ’NULL PIXEL MASK’ in the row corresponding to that image tile. The ZMASKCMP keyword should be used to record the name of the algorithm used to compress the data mask (e.g., RICE 1). The data mask array pixels will be assumed to have the shortest integer datatype that is supported by the compression algorithm (i.e., usually 8-bit bytes).

      When uncompressing the image tile, the software must check if the corresponding compressed data mask exists with a length greater than 0, and if so, then uncompress the mask and set the corresponding undefined pixels in the image array to the appropriate value (as given by the BLANK keyword).

      See Also:

    • BYTEPIX

      public static final String BYTEPIX
      The number of 8-bit bytes in each original integer pixel value.
      See Also:

    • BLOCKSIZE

      public static final String BLOCKSIZE
      The blocksize parameter for the rise algorithm.
      See Also:

    • SCALE

      public static final String SCALE
      The integer scale parameter determines the amount of compression. Scale = 0 or 1 leads to lossless compression, i.e. the decompressed image has exactly the same pixel values as the original image. If the scale factor is greater than 1 then the compression is lossy: the decompressed image will not be exactly the same as the original.
      See Also:

    • SMOOTH

      public static final String SMOOTH
      At high compressions factors the decompressed image begins to appear blocky because of the way information is discarded. This blockiness is greatly reduced, producing more pleasing images, if the image is smoothed slightly during decompression. When done properly, the smoothing will not affect any quantitative photometric or astrometric measurements derived from the compressed image. Of course, the smoothing should never be applied when the image has been losslessly compressed with a scale factor (defined above) of 0 or 1.
      See Also:

  • Method Details

    • values

      public static Compression[] values()
      Returns an array containing the constants of this enum type, in the order they are declared.
      Returns:
      an array containing the constants of this enum type, in the order they are declared

    • valueOf

      public static Compression valueOf(String name)
      Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
      Parameters:
      name - the name of the enum constant to be returned.
      Returns:
      the enum constant with the specified name
      Throws:
      IllegalArgumentException - if this enum type has no constant with the specified name
      NullPointerException - if the argument is null

    • impl

      public final FitsKey impl()
      Description copied from interface: IFitsHeader
      (primarily for internal use) Returns the concrete implementation of this header entry, which provides implementation of access methods.
      Specified by:
      impl in interface IFitsHeader
      Returns:
      the implementation of this keyword, which provides the actual access methods. Implementations of this interface should simply return themselves.

    • getUncompressedKey

      public IFitsHeader getUncompressedKey()
      Returns the equivalent of this comression keyword in the uncompressed HDU. For example, the compression keyword ZBITPIX that stores the data type of the compressed image will return BITPIX.
      Returns:
      the equivalent keyword in the uncompressed HDU