ASTRO: Command line SNR tool

I made a simple tool to create snr images. The tool is based on compiled
versions of two of the FITSTOOLS components free on the NASA website. I am
not a programmer though, so the interface is clunky but the tool works.

here's a link to a page on my website where you can download it (6.5MB
including two test image files)

http://www.narrowbandimaging.com/snr...ol_xp_page.htm

read the README!!!!

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The tool is invoked from a DOS window on a command line

stest_q input.fit gain background_adu read_noise snr.fit

input.fit is the input file (calibrated!)
gain is the camera gain: electrons/adu
background_adu is the average value of a star free and nebulosity free part
of the background of the image you wish to measure (measure this ahead of
time!)
read_noise is the read noise of the camera in electrons

snr.fit is the output file you wish to create

start with the input file in 32bit floating point to avoid numeric
truncation

I also included two sample files for testing purposes, one is called
file1.fit and the other is file2.fit

the read noise for this camera was 11.3electrons (measured) and the gain was
1.5 electrons/adu (measured)

the fit file that is created as the output directly reads as signal to noise
ratio. So if the numerical value of a pixel is 8, then the SNR is 8 at that
pixel.

the tool calculates the signal as the delta between the image and the
background on a pixel by pixel basis (using a global vaolue for the
background). that's the numerator.
the denominator, which is the noise, is this quantity sqrt(image +
background^2 + read_noise^2)

Since the noise of the image is the square root when the term is added in
quadrature with the other noise terms, the square root squared winds up as
the image data itself under the radical just in case there was any
confusion.

here's the source for the bat file

del %5
fitscopy.exe "%1[pix X/%2 - %3/%2]" num.fit
fitscopy.exe "%1[pix SQRT((X/%2)+(%3/%2)^2 +%4^2)]" denom.fit
imarith.exe num.fit denom.fit d %5
del num.fit
del denom.fit

---it is a useful way to assess the impact of changing something in the
system, from cleaning optics to operating temperature of the camera to
exposure time experiments to the number of darks/flats etc.