7.11 File Formats
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of image details. Vector file formats store the image as a series of vectors. Increasing
the size of an image does not therefore necessarily increase the size of the image file,
and two different images of the same size may, in this case, result in different file
sizes. Both Portable Document Format (PDF) and Encapsulated PostScript (EPS)
are forms of vector file formats. Vector formatted images are commonly used in
publishing, and you may be asked to supply images in this format for a journal.
However, they are not suitable for astronomical imaging.
If the detector you are using doesn’t allow files to be saved as FITS, then it is
likely that it will be saved either as a proprietary format, one of several hundred in
use, or as one of the standard formats.
FITS is always the preferred format, being the standard format for astronomy: lossless, uncompressed, and containing a header with information regarding the image.
RAW is a similar format to FITS and is used with DSLR cameras. RAW is uncompressed and like FITS has a header. Most DSLRs use a proprietary form of RAW,
for example, NEF or CRW, but effectively there is very little difference between the
formats, most being based on the TIFF image format with the addition of a header
and other additional data structures.
Tagged Image File Format (TIFF) is an uncompressed image format developed
in the mid-1980s for use with imaging systems such as scanners. Although not so
widely used as in the past, TIFF is still found as a common output option for many
imaging software packages.
Like TIFF, BMP (BMP is not an acronym) is an uncompressed image format
developed by Microsoft. BMP is a common output file format and is a suitable
alternative if TIFF, FITS, or RAW is unavailable. The most common image format
in use universally is the Joint Photographic Experts Group (JPEG) format. JPEG
is a lossy compressed image format, although some applications do allow for zero
compression, which would make a JPEG file lossless. However, as JPEG does not
support a significant header, there is no way to determine the degree of loss. JPEG is
an extremely common file format, and most image applications can read and write
in JPEG. However, it should be considered only if all of the other file formats are
unavailable, which in a good astronomical imaging setup should never be the case.
101
of image details. Vector file formats store the image as a series of vectors. Increasing
the size of an image does not therefore necessarily increase the size of the image file,
and two different images of the same size may, in this case, result in different file
sizes. Both Portable Document Format (PDF) and Encapsulated PostScript (EPS)
are forms of vector file formats. Vector formatted images are commonly used in
publishing, and you may be asked to supply images in this format for a journal.
However, they are not suitable for astronomical imaging.
If the detector you are using doesn’t allow files to be saved as FITS, then it is
likely that it will be saved either as a proprietary format, one of several hundred in
use, or as one of the standard formats.
FITS is always the preferred format, being the standard format for astronomy: lossless, uncompressed, and containing a header with information regarding the image.
RAW is a similar format to FITS and is used with DSLR cameras. RAW is uncompressed and like FITS has a header. Most DSLRs use a proprietary form of RAW,
for example, NEF or CRW, but effectively there is very little difference between the
formats, most being based on the TIFF image format with the addition of a header
and other additional data structures.
Tagged Image File Format (TIFF) is an uncompressed image format developed
in the mid-1980s for use with imaging systems such as scanners. Although not so
widely used as in the past, TIFF is still found as a common output option for many
imaging software packages.
Like TIFF, BMP (BMP is not an acronym) is an uncompressed image format
developed by Microsoft. BMP is a common output file format and is a suitable
alternative if TIFF, FITS, or RAW is unavailable. The most common image format
in use universally is the Joint Photographic Experts Group (JPEG) format. JPEG
is a lossy compressed image format, although some applications do allow for zero
compression, which would make a JPEG file lossless. However, as JPEG does not
support a significant header, there is no way to determine the degree of loss. JPEG is
an extremely common file format, and most image applications can read and write
in JPEG. However, it should be considered only if all of the other file formats are
unavailable, which in a good astronomical imaging setup should never be the case.