Colour FITS
X component
Rawtran is a wrapper around dcraw developed to produce images in the standard astronomical FITS format by processing of raw (CR2, CRW, MRW, etc.) photos.
Selected digital cameras offers possibility to save raw photos, eg. only slightly pre-processed photos intended for further image processing. Rawtran is developed as a wrapper around dcraw due D.Coffin to produce FITS files from the raw photos. FITS files are widely used by astronomers and can be processed by many standard astronomical software by analogical way as ones acquired by an ordinary scientific CCD camera. FITS files produced by Rawtran are suitable for all photometry, spectroscopy or astrometry measurements.
Proper conversion of data acquired by common digital cameras has two key features:
Metadata or a description of physical parameters of frame like date and time, used optics etc. as the integral part of frames. It is absolutely necessary for any regular scientific processing. Therefore Rawtran carefully implements conversion of EXIF data enclosed to every raw photo and interprets its in scope of usual astronomical conventions.
Colours and its proper handling is important for both photometry or spectroscopy interpretations. Therefore Rawtran implements conversion from CIE 1931 XYZ colour space to common astronomical photometry bands (conversion from instrumental to XYZ is provided by dcraw). Saving frames in Colour FITS format is just side effect of the conversions.
Rawtran also implements a few convenience functions common in astronomical photometry for using of dark frames.
The output image is Colour FITS image. Because, there is no widely accepted convention or definition of the colour representation in FITS world, Rawtran uses Munipack's specification of Colour FITS:
The purpose of the conversion type is a simple manipulation (and representation) of colour images in FITS format. Colour FITS can be displayed by xmunipack (GUI for Munipack) or converted to PNG by fitspng (used to generate all images on this page).
The output image contains one 3D primary array without any photometric transformations. Four original bands are stored in the array with the structure: width ⨉ height ⨉ 4. The bands are storing Bayer's colours in the order: B (blue), G1 (green1), G2 (green2), R (red). According to astronomical terminology, the single bands are in an instrumental photometric system.
The conversion type provides absolutely raw access to data in FITS format. One offers a direct conversion between file formats (it rearranges bytes only) and does NOT modify data itself. To be useful, transform the data to any known colour space by using of a transformation matrix (included in the source code of dcraw.c) or derive the transformation matrix yourself.
The conversion is intended for representation of the intensity in the selected colour band. The output image is a grey-scale and data are stored as two dimensional FITS primary array.
Note, that all data are slightly modified as result of a colour interpolation on Bayer's mask. Use -X "-h" to switch-off the interpolation.
All data must be supposed as RELATIVE quantities only.
A required photometry band can be selected with -c switch.
Selected colours band is simply copied out from the the Bayer's mask. Gi is derived as the arithmetical mean Gi = (Gi1 + Gi2)/2. These instrumental filters are specific for an unique camera model.
Instrumental bands are difficult to reconstruct a standard colours or photometric information. Therefore there is possibility to get a standard band. Colours are converted to primary col or space XYZ.
Y component represents luminance. Its spectral profile is similar to humans eye spectral sensitivity under well-light conditions (photopic vision).
With exact definition of XYZ spectral profiles, we can derive of colour transformation matrix to another colour-space. Rawtran has built-in a transformation matrix from XYZ to Johnson UBVRI system (wide-band astronomical photometry system).
It is also possible to specify of a wide-spectral band (like the human eye or an unfiltered CCD image) or to simulate scotopic vision (like human eye under low-light conditions). The visual difference between colour images (or Y component) and the scotopic one illustrates Purkyňův effect.
rawtran.fits. Use dash '-' for redirection
to the standard output. Precede the filename with exclamation point
(!) to overwrite an existing file. Usually, to prevent shell expansion,
it will be require to escape it: \!rawtran.fits.
dcraw -D -4 -j -t 0 file.RAW
and pass it to dcraw -K file.pgm.
Note that sometimes can be necessary to switch-off automatic frame
rotation using -A "-t 0" option.
See Dark Frame section for more info.
dcraw -D -4 -j -t 0 dark.RAW.
See Dark Frame section for more info.
Splitting of conversion parameters for dcraw on three groups of options -C,-X,-A is conventional. Main purpose is separating important options -C,-X and optional -A to prevent potential mistakes. Changing of the important parameters is recommended only for experienced users.
The zero indicates successful conversion. A non-zero value is returned when an error is occurred during conversion. If the utility is launched without options or with -h switch, zero means that Rawtran's internal checker can run dcraw binary and non-zero value otherwise.
It converts a raw photo to colour FITS. The results is displayed by xmunipack:
$ rawtran -o IMG_0666.fits IMG_0666.CR2 $ xmunipack IMG_0666.fits
It converts an image to grey-scale meaning to be an equivalent seen by human eye at good light conditions:
$ rawtran -c Y -o IMG_0666.fits IMG_0666.CR2
It converts an image to be equivalent of Johnson's B filter:
$ rawtran -c B -o IMG_0666.fits IMG_0666.CR2
It extracts the (mean) green component (camera specific) of the raw photo:
$ rawtran -c Gi -o IMG_0666.fits IMG_0666.CR2
The output file can be overwritten:
$ rawtran -o '!IMG_0666.fits' IMG_0666.CR2
A large set of raw photos can be converted with help of shell functionality:
$ for A in *.CR2; do rawtran -o ${A%CR2}fits ${A}; done
All this gallery examples has been generated by processing of the reference raw photo IMG_5952.CR2:
$ rawtran IMG_5952.CR2 -o IMG_5952.fits $ rawtran IMG_5952.CR2 -o IMG_5952_X.fits -c X $ rawtran IMG_5952.CR2 -o IMG_5952_Y.fits -c Y $ rawtran IMG_5952.CR2 -o IMG_5952_Z.fits -c Z $ rawtran IMG_5952.CR2 -o IMG_5952_B.fits -c B $ rawtran IMG_5952.CR2 -o IMG_5952_V.fits -c V $ rawtran IMG_5952.CR2 -o IMG_5952_R.fits -c R $ rawtran IMG_5952.CR2 -o IMG_5952_Bi.fits -c Bi $ rawtran IMG_5952.CR2 -o IMG_5952_Gi.fits -c Vi $ rawtran IMG_5952.CR2 -o IMG_5952_Ri.fits -c Ri $ rawtran IMG_5952.CR2 -o IMG_5952_s.fits -c s $ rawtran IMG_5952.CR2 -o IMG_5952_u.fits -c u $ fitspng IMG_5952.fits -fl 0,20000 -s 10 -o IMG_5952.png $ fitspng IMG_5952_X.fits -fl 0,20000 -s 10 -o IMG_5952_X.png $ fitspng IMG_5952_Y.fits -fl 0,20000 -s 10 -o IMG_5952_Y.png $ fitspng IMG_5952_Z.fits -fl 0,20000 -s 10 -o IMG_5952_Z.png $ fitspng IMG_5952_R.fits -fl 0,20000 -s 10 -o IMG_5952_R.png $ fitspng IMG_5952_V.fits -fl 0,20000 -s 10 -o IMG_5952_V.png $ fitspng IMG_5952_B.fits -fl 0,20000 -s 10 -o IMG_5952_B.png $ fitspng IMG_5952_s.fits -fl 0,20000 -s 10 -o IMG_5952_s.png $ fitspng IMG_5952_u.fits -fl 0,40000 -s 10 -o IMG_5952_u.png $ fitspng IMG_5952_Ri.fits -fl 128,1000 -s 10 -o IMG_5952_Ri.png $ fitspng IMG_5952_Gi.fits -fl 128,1000 -s 10 -o IMG_5952_Gi.png $ fitspng IMG_5952_Bi.fits -fl 128,1000 -s 10 -o IMG_5952_Bi.png
Colour FITS
X component
Y component
Z component
R filter
V filter
B filter
R Bayer instrumental
G Bayer instrumental
B Bayer instrumental
Unfiltered
Night vision
Rawtran provides convenience functions for handling of dark frames.
The basic way is use of -D option which launch dcraw to create PGM file representing of the dark. While dcraw sometimes saves results to PPM file, a transparent conversion to PGM can be required. Therefore the time duration of the procedure will depend on the conversion and generally one will be twice slower than passing a PGM file directly by -A "-K file.pgm". An user is responsible to provide correct dark frame.
A little bit advanced way is to use a FITS file as dark frame which is on the fly converted to PGN. Purpose of the option is to offer possibility for averaging of darks. A hypothetical session can be:
$ rawtran -c P -A "-j -t 0" -o dark1.fits dark1.CR2 $ rawtran -c P -A "-j -t 0" -o dark2.fits dark2.CR2 $ munipack dark -o dark.fits dark?.fits # or equivalent $ rawtran -E dark.fits -o light.fits light.CR2
First two lines (or possible more) converts dark frames to FITS format using of -c P option. Than the created FITSes are averaged (munipack utility is only an example, any another software can be used). The averaged file is used as the dark frame.
The tar-ball or the development repository with a source code is freely available under GPL2 license. cfitsio library with files required for development (headers, static libraries) is necessary for building. Building itself does not depends on dcraw.
A recommended way of local installation from the tar-ball is:
$ tar zxf rawtran-X.Y.Z.tar.gz $ cd rawtran-X.Y.Z/ $ autoreconf -i # for Mercurial $ ./configure CFLAGS="-O4 -DNDEBUG" $ make # make install
The last step must be executed under root account.
Both binary and
man page are installed under /usr/local tree. It would be
nice to keep the source directory for a case of later uninstalling.
Building under RPM-bases distributions (RHELL, Fedora) requires place of Rawtran tarball to a directory where RPM places sources (rpmbuild), unpack the spec file and we can use the following commands to build:
$ rpmbuild -bb rawtran.spec
where the package must by placed in your RPM building directory.
Rawtran runs under any Unix-like operating system (all flavors of GNU/Linux and BSD, Solaris, Mac OS X, etc). Usage under Windows or DOS has not been reported yet. Rawtran packages can be found in Debian and Ubuntu.
By design, Rawtran is a wrapper around dcraw. One internally launches dcraw as a sub-process and grabs its output. The info about image (EXIF information) is obtained as:
dcraw -i -v -c
The image data oneself are imported by one from these alternatives:
dcraw -4 -c -o 5 (standard bands) dcraw -4 -c -D (instrumental bands)
Passed parameters can be changed with -C option (except -c).
Rawtran internally represents all image data as 4-byte real (with precision of 7 decimals and the maximum value 1033) during all numerical operations. Values stored in FITS files are rounded to a nearest integer (if necessary).
Fitspng is a converter from FITS to PNG. Munipack is a general utility to work with FITS images.
Development notes can be found in Hroch's diary.
Rawtran is free software licensed under the GNU General Public License. This gives you the freedom to use and modify Rawtran to suit your needs.
Copyright © 2007 — 2018, F. Hroch, Institute of Theoretical Physics and Astrophysics, Masaryk University, Brno, Czech Republic.