matlab.io.fits.setHCompScale

Set scale parameter for images compressed with HCOMPRESS algorithm

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Syntax

matlab.io.fits.setHCompScale(fptr,scale)

Description

matlab.io.fits.setHCompScale(fptr,scale) sets the scale parameter for the specified FITS file to use with the HCOMPRESS compression algorithm. If you set the scale parameter, then the algorithm operates in lossy mode.

Examples

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Open Live Script

Create a new FITS file and add an image to the file.

import matlab.io.*
data = 50*ones(256,512) + 10*rand([256 512]);
fptr = fits.createFile("myfile.fits");
fits.createImg(fptr,"double_img",[256 512])
fits.writeImg(fptr,data)

Set the HCOMPRESS compression algorithm with a scale parameter of 2.5, add another copy of the same image to the file, and then close the file.

fits.setCompressionType(fptr,"HCOMPRESS")
fits.setHCompScale(fptr,2.5)
fits.createImg(fptr,"double_img",[256 512])
fits.writeImg(fptr,data)
fits.closeFile(fptr)

Examine the file metadata and then delete the file.

fitsdisp("myfile.fits",Mode="full")
HDU:  1 (Primary HDU)
	SIMPLE  =                    T / file does conform to FITS standard
	BITPIX  =                  -64 / number of bits per data pixel
	NAXIS   =                    2 / number of data axes
	NAXIS1  =                  512 / length of data axis 1
	NAXIS2  =                  256 / length of data axis 2
	EXTEND  =                    T / FITS dataset may contain extensions
	COMMENT   FITS (Flexible Image Transport System) format is defined in 'Astronomy
	COMMENT   and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H

HDU:  2 
	XTENSION= 'BINTABLE'           / binary table extension
	BITPIX  =                    8 / 8-bit bytes
	NAXIS   =                    2 / 2-dimensional binary table
	NAXIS1  =                   24 / width of table in bytes
	NAXIS2  =                   16 / number of rows in table
	PCOUNT  =                33212 / size of special data area
	GCOUNT  =                    1 / one data group (required keyword)
	TFIELDS =                    3 / number of fields in each row
	TTYPE1  = 'COMPRESSED_DATA'    / label for field   1
	TFORM1  = '1PB(2103)'          / data format of field: variable length array
	TTYPE2  = 'ZSCALE  '           / label for field   2
	TFORM2  = '1D      '           / data format of field: 8-byte DOUBLE
	TTYPE3  = 'ZZERO   '           / label for field   3
	TFORM3  = '1D      '           / data format of field: 8-byte DOUBLE
	ZIMAGE  =                    T / extension contains compressed image
	ZBITPIX =                  -64 / data type of original image
	ZNAXIS  =                    2 / dimension of original image
	ZNAXIS1 =                  512 / length of original image axis
	ZNAXIS2 =                  256 / length of original image axis
	ZTILE1  =                  512 / size of tiles to be compressed
	ZTILE2  =                   16 / size of tiles to be compressed
	ZQUANTIZ= 'SUBTRACTIVE_DITHER_1' / Pixel Quantization Algorithm
	ZDITHER0=                 2503 / dithering offset when quantizing floats
	ZCMPTYPE= 'HCOMPRESS_1'        / compression algorithm
	ZNAME1  = 'SCALE   '           / HCOMPRESS scale factor
	ZVAL1   =        2.5000000E+00 / HCOMPRESS scale factor
	ZNAME2  = 'SMOOTH  '           / HCOMPRESS smooth option
	ZVAL2   =                    0 / HCOMPRESS smooth option

delete myfile.fits

Tips

  • This function corresponds to the fits_set_hcomp_scale function in the CFITSIO library C API.

  • To use this function, you must be familiar with the CFITSIO C interface. You can access the CFITSIO documentation at the CFITSIO website.

Extended Capabilities

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Version History

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See Also

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