Sigma image

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SDSS sigma image

http://data.sdss3.org/datamodel/files/BOSS_PHOTOOBJ/frames/RERUN/RUN/CAMCOL/frame.html

There is gain + rdnoise depending on camcol (for each filter) in the table (same link)!

    1. To get sigma image go from Nmgy to DN: sky-subtracted image as well as calibrated in nanomaggies/pixel

img= mrdfits(framename,0,hdr) nrowc= (size(img,/dim))[1] sky= mrdfits(framename,2)

    1. Sky image must be of the same size as the frame image, in units of counts

simg= interpolate(sky.allsky, sky.xinterp, sky.yinterp, /grid)

  1. a calibration image the same size as the frame image, in units of nanomaggies per count

calib= mrdfits(framename,1) cimg= calib#replicate(1.,nrowc)

  1. Original image in DN

dn= img/cimg+simg

  1. Corresponding sigma image

dn_err= sqrt(dn/gain+darkVariance) ; in counts

  1. To get those errors into nanomaggies, you simply apply back the calibration:

img_err= dn_err*cimg

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