Sigma image
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There is gain + rdnoise depending on camcol (for each filter) in the table (same link)! | There is gain + rdnoise depending on camcol (for each filter) in the table (same link)! | ||
| - | + | To get sigma image go from Nmgy to DN: sky-subtracted image as well as calibrated in nanomaggies/pixel | |
| - | img= mrdfits(framename,0,hdr) | + | img= mrdfits(framename,0,hdr) |
| - | nrowc= (size(img,/dim))[1] | + | nrowc= (size(img,/dim))[1] |
| - | sky= mrdfits(framename,2) | + | sky= mrdfits(framename,2) |
| - | + | 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) | + | simg= interpolate(sky.allsky, sky.xinterp, sky.yinterp, /grid) |
| - | + | a calibration image the same size as the frame image, in units of nanomaggies per count | |
| - | calib= mrdfits(framename,1) | + | calib= mrdfits(framename,1) |
| - | cimg= calib#replicate(1.,nrowc) | + | cimg= calib#replicate(1.,nrowc) |
| - | + | Original image in DN | |
| - | dn= img/cimg+simg | + | dn= img/cimg+simg |
| - | + | Corresponding sigma image | |
| - | dn_err= sqrt(dn/gain+darkVariance) ; in counts | + | dn_err= sqrt(dn/gain+darkVariance) ; in counts |
To get those errors into nanomaggies, you simply apply back the calibration: | To get those errors into nanomaggies, you simply apply back the calibration: | ||
img_err= dn_err*cimg | img_err= dn_err*cimg | ||
Revision as of 10:27, 11 June 2018
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)!
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)
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)
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)
Original image in DN
dn= img/cimg+simg
Corresponding sigma image
dn_err= sqrt(dn/gain+darkVariance) ; in counts
To get those errors into nanomaggies, you simply apply back the calibration:
img_err= dn_err*cimg
