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FITSPNG(1) User Commands FITSPNG(1)


fitspng - FITS to PNG converter.


fitspng [options] file(s)


Fitspng is an utility intended to convert of images in astronomical FITS format to computer graphics PNG format.

The primary goal of fitspng is to transform of the high dynamic images to a limited numerical range of PNG format. The transformation uses global tone mapping by a set of tone functions with machine estimated or user provided scaling parameters.

The detailed description can be found at homepage:


Scale output intensities by specified profile: linearly, asinh, log, gamma (as in sRGB), normal (Gauss cumulative distribution function [5]), square root, square, logistic (emulating classical photography sensitivity [6]), atan and ratio (x/1+x).
Specifies scale of output profile: f*Func(i).
Specifies zero (black level) of output profile: Func(i) + z.
Output intensities, in case of colour depth 8 bites, are scaled according this formula: (output intensities) = Func((input intensities - (med - u*mad))/(mad/v)) where med is median of every 10 pixel in the image, mad is mean of positive deviations from the median of every 10 pixel (same frequency). If the pixel is out of level range from 0 to 255, than value is replaced by 0 and 255 respectively. The default is u = 3, v = 1/3.
Output intensities, in case of colour depth 8 bites, are scaled according this formula: (output intensities) = Func((input intensities - t)/s). The setup completely disable internal parameter estimation.
The colour saturation is multiplied by the given ratio (for colour FITS only).
Set coordinates of white point.
When used, switch-on mode which emulates humans night vision. It is useful only for colour FITS.
Select the colour-space of output image.
Shrink image: scale down the size of image by the specified factor s as a (non-zero) positive integer number. If the s factor is greater of one, any output pixel is constructed as arithmetic mean of s*s input pixels.
Specify an output file name, valid only if a single file is passed.

If this switch is omitted, the output filename is determined by modification of input filenames: suffixes, like *.fits, are replaced by *.png, and the directory path is removed. The approach leaves original data untouched, results are stored in current working directory.

8 bites per pixel of colour (gray) depth of output. This is default. 16 bites per pixel of colour (gray) depth of output. There is frequently problem with additional rendering. Most of utilities doesn't work with this colour depth correctly. On the other side, 16 bit per pixel images has saved photometric content more precisely.
Print additional info during processing.
Show summary of options.
Display software version.


Convert an image from FITS to PNG:
$ fitspng -o gray.png gray.fits

Emulate human's night vision:
$ fitspng -fn 100,10 -o scotopic.png colour.fits

Emulate classical photography sensitivity function (density curve):
$ fitspng -f logistic -o photo.png colour.fits

Create semi-gray image:
$ fitspng -fs 0.2 -o reduced.png colour.fits

Select the specified band from colour FITS (with help of FITS file name extension):
$ fitspng -o green.png "colour.fits[1]"

Create thumbnails:
$ fitspng -s 10 *.fits


Filip Hroch <>






January 2019 Fitspng