Sigma image
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(Difference between revisions)
m (→SDSS sigma image) |
m (→SDSS sigma image) |
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To get sigma image go from Nmgy to DN: sky-subtracted image as well as calibrated in nanomaggies/pixel | 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 | Sky image must be of the same size as the frame image, in units of counts | ||
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a calibration image the same size as the frame image, in units of nanomaggies per count | 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 | Original image in DN | ||
| - | dn= img/cimg+simg | + | dn = img/cimg + simg |
Corresponding sigma image | Corresponding sigma image | ||
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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 10:28, 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
