Sigma image
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m (→SDSS sigma image) |
m (→SDSS sigma image) |
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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: | |
img_err= dn_err*cimg | img_err= dn_err*cimg | ||
Revision as of 10:26, 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
