[fitsbits] FITS vs. TIFF (or other image formats)

[Rick Armstrong]

> FITS is designed to record the value of image pixels with high precision
and
> is probably not suitable for your application, especially if you are
dealing
> with true color images.

I'm storing 8-bit unsigned chars, so the precision of FITS is probably
super-overkill for my needs (w.r.t. precision).

> To answer your second question, however, CFITSIO
> does support a type of image compression that is well suited
> for very large images.
> ...CFITSIO will transparently uncompress the appropriate
> subimages and return the original image pixel values to the
> application.

Now _that's_ _exactly_ what I need! CFITSIO might give me a big leg-up.
Looks like it's time to dig in and start reading and experimenting.

Thanks very much for your help,
Rick Armstrong





"William Pence" <pence at tetra.gsfc.nasa.gov> wrote in message
news:3BF9526E.BF22A2F5 at tetra.gsfc.nasa.gov...
> Rick Armstrong wrote:
> >
> > I'm writing an C++ application that gathers images acquired from a
> > microsocope with a motorized x-y stage. The app stitches the acquired
images
> > into extended-field-of-view mosaics. To create mosaics of objects of
> > significant size, I need to create enormous image files (at 40X
> > magnification, with a 1300x1030 image size, a 1.5 x 1.5mm area gets a
file
> > that's on the order of tens of GB). In the process of thinking about how
to
> > read/write/browse files of this size, I realized that astronomers and
> > geo-mapper type people must run into this all the time!
> >
> > While surfing about, I stumbled on FITS and I have two question for the
> > group:
> >
> > 1) Why do astronomers use FITS, instead of just writing huge TIFFs or
files
> > of some other format?
> >
> > 2) Can I use CFITSIO to write a "compressed stream", i.e., can I write
and
> > compress in the same operation using CFITSIO? Is it necessary to create
a
> > complete, uncompressed file, _then_ compress it? Is this a naive
question?
>
> FITS is designed to record the value of image pixels with high precision
and
> is probably not suitable for your application, especially if you are
dealing
> with true color images.  To answer your second question, however, CFITSIO
> does support a type of image compression that is well suited for very
large
> images.  The image is first divided into a grid of rectangular subimages
(in
> many cases it is convenient to treat each row of the original image as a
> subimage), then each subimage is compressed and stored as a variable
length
> array in a row of a FITS binary table.  When application programs read
this
> 'image', CFITSIO will transparently uncompress the appropriate subimages
and
> return the original image pixel values to the application.  This technique
> is especially useful in cases where the application program  usually only
> wants to read a small section of the whole image.  CFITSIO then only has
to
> uncompress the subimages that make up that piece of the image, rather than
> having to uncompress the entire huge image.  Several different compression
> algorithms are supported, and it can be used for both integer and
> floating-point data format images.
>
> For more information see the CFITSIO Reference Guide at:
>
> http://heasarc.gsfc.nasa.gov/docs/software/fitsio/c/c_user/node109.html
>
> or the original paper by White, Greenfield, Pence, and Tody that defines
> this format:
>
>
http://heasarc.gsfc.nasa.gov/docs/software/fitsio/compression/compress_image
.html
>
> -Bill Pence
> --
> ____________________________________________________________________
> Dr. William Pence                          pence at tetra.gsfc.nasa.gov
> NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)
> Greenbelt MD 20771                         +1-301-286-1684 (fax)
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