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Rendering FITS Data



 
 
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  #1  
Old October 14th 03, 03:59 AM
Grinder
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Default Rendering FITS Data

This is more of a general question about rendering data to an
image, than about FITS data per se.

For astronomers, what are some of the more useful data-to-color
transformations? I'm having difficulty resolving
domain-specific vocabulary, so I hope I'm not being
confusing -- it has certainly stymied my attempts to google
this information.

For instance:

If you have a 2d array of 16-bit signed integer values, you can
make a simple linear transformation to and 8-bit grayscale
palette. I imagine log and poly transforms are of use as well.

Basically, I'm looking for a discussion of useful techniques,
either here, or some existing web resources. Thanks for your
time and consideration.


  #2  
Old October 15th 03, 10:52 PM
Steve Allen
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Default [fitsbits] Rendering FITS Data

On Mon 2003-10-13T21:59:24 -0500, Grinder hath writ:
If you have a 2d array of 16-bit signed integer values, you can
make a simple linear transformation to and 8-bit grayscale
palette. I imagine log and poly transforms are of use as well.


In the absence of the experts (see below) I suppose that the best
(only?) way to determine this is to survey the existing FITS display
programs. I have encountered programs that map the image to display
using sqrt, square, log, linear, and various histogram equalization
and/or cutoff methods.

Basically, I'm looking for a discussion of useful techniques,
either here, or some existing web resources. Thanks for your
time and consideration.


This parallels a question that has been bouncing around the FITS
community -- should there be various levels of FITS conformance? In
this case perhaps what would help most is a class of FITS documents
which could have a status akin to the Internet (IETF) RFCs that are
known as Best Current Practice (BCP). The problem with this notion is
that writing and approving any such documents are mostly thankless
tasks which subtract from the valuable time of the few who are
interested in implementing them.

If these sorts of techniques are published it is likely that many of
their authors are currently at the ADASS conference, so this
discussion is likely to take many days to finish.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93

  #3  
Old October 17th 03, 08:47 PM
Grinder
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Posts: n/a
Default [fitsbits] Rendering FITS Data

"Steve Allen" wrote in message
rao.edu...

Thanks for your response. I can't say I'm a dedicated fan, but
enjoyed your appearance on "Homicide: Life on the Streets" a
few years ago.

On Mon 2003-10-13T21:59:24 -0500, Grinder hath writ:
If you have a 2d array of 16-bit signed integer values, you

can
make a simple linear transformation to and 8-bit grayscale
palette. I imagine log and poly transforms are of use as

well.

In the absence of the experts (see below) I suppose that the

best
(only?) way to determine this is to survey the existing FITS

display
programs. I have encountered programs that map the image to

display
using sqrt, square, log, linear, and various histogram

equalization
and/or cutoff methods.


I've taken a look at ds9 and FITSView. My rendering methods
match the output from ds9, but FITSView must mean something
different by "linear" than ds9, as it's output is radically
different. For example:

Given a 16-bit integer data set, ds9 apparently maps the MSB of
each pixel to a linear 8-bit grayscale. So values like, 0x0000
to 0x0400 appear essentially the same -- black. FITSView,
though, has much better contrast for these low values even when
set to linear. Examining a screenshot of the rendering shows
that it is not strictly using grayscale colors. Small
variations in the RGB components are present, providing a
larger palette, but still appearing as a grayscale.

Any idea what they're doing?

Basically, I'm looking for a discussion of useful

techniques,
either here, or some existing web resources. Thanks for

your
time and consideration.


This parallels a question that has been bouncing around the

FITS
community -- should there be various levels of FITS

conformance? In
this case perhaps what would help most is a class of FITS

documents
which could have a status akin to the Internet (IETF) RFCs

that are
known as Best Current Practice (BCP). The problem with this

notion is
that writing and approving any such documents are mostly

thankless
tasks which subtract from the valuable time of the few who

are
interested in implementing them.

If these sorts of techniques are published it is likely that

many of
their authors are currently at the ADASS conference, so this
discussion is likely to take many days to finish.


That's good background. Does the FITS community have any
collecting points on the web?


  #4  
Old October 18th 03, 07:34 AM
Grinder
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Posts: n/a
Default [fitsbits] Rendering FITS Data

Sorry to so egregiously pump you for links/ideas, but do you
have any suggestions as to where I can find a wide variety of
test images. Google searches have turned up some goods, but
nothing as rigorous as:
http://www.schaik.com/pngsuite/pngsuite.html

Thanks again for your consideration already rendered.


  #5  
Old October 20th 03, 01:49 PM
Patrick P Murphy
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Posts: n/a
Default [fitsbits] Rendering FITS Data

On Sat, 18 Oct 2003 01:34:21 -0500, "Grinder" said:

Sorry to so egregiously pump you for links/ideas, but do you
have any suggestions as to where I can find a wide variety of
test images.


I'd try http://www.cv.nrao.edu/fits/ for starters, and look at Don
Wells' collection of FITS data: http://www.cv.nrao.edu/fits/data/.

- Pat
--
Patrick P. Murphy, Ph.D. Division Head, CV Computing, NRAO
Home: http://goof.com/~pmurphy/ Work: http://www.nrao.edu/~pmurphy/
"Laws of nature are...just parochial by-laws in our cosmic patch"
- Martin Rees

  #6  
Old October 20th 03, 05:27 PM
Doug Mink
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Posts: n/a
Default [fitsbits] Rendering FITS Data

Grinder wrote:

For astronomers, what are some of the more useful data-to-color
transformations? I'm having difficulty resolving
domain-specific vocabulary, so I hope I'm not being
confusing -- it has certainly stymied my attempts to google
this information.


As one of those who just got back from ADASS in Strasbourg, I'll
add the ways which the venerable SAOimage program (which I maintain
at http://tdc-www.harvard.edu/software/saoimage/ ) converts from
FITS input data to 8-bit display pixels. It supports linear
(a linear scale from the minimum value at 0 and the maximum at 256),
square root, log, wrap (which produces a sort of contour image),
and histogram. The histogram can be clipped at the ends to emphasize
the middle values. All of the code is in C in the sclmap.c file
of the source code which is available through the page cited above.

-Doug Mink
Telescope Data Center
Smithsonian Astrophysical Observatory
Cambridge, Massachusetts USA

  #7  
Old October 20th 03, 08:29 PM
Grinder
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Posts: n/a
Default [fitsbits] Rendering FITS Data


"Doug Mink" wrote in message
rao.edu...
Grinder wrote:

For astronomers, what are some of the more useful

data-to-color
transformations? I'm having difficulty resolving
domain-specific vocabulary, so I hope I'm not being
confusing -- it has certainly stymied my attempts to google
this information.


As one of those who just got back from ADASS in Strasbourg,

I'll
add the ways which the venerable SAOimage program (which I

maintain
at http://tdc-www.harvard.edu/software/saoimage/ ) converts

from
FITS input data to 8-bit display pixels. It supports linear
(a linear scale from the minimum value at 0 and the maximum

at 256),
square root, log, wrap (which produces a sort of contour

image),
and histogram. The histogram can be clipped at the ends to

emphasize
the middle values. All of the code is in C in the sclmap.c

file
of the source code which is available through the page cited

above.

Thank you Steve, Doug and Patrick.


 




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