Background

Pippo wrote on Jan 23, 2009

Hi, I would want to know how I can eliminate the sky from a scientific image for photometrical analysis.

Thanks

Pippo

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James Turner wrote on Jan 23, 2009

I'm no expert, but photometric analysis routines typically calculate the background around the extraction aperture for you and subtract it off. They may even require that your image contain the sky level for proper signal-to-noise optimization or whatever. Otherwise, if you have several images taken at slightly different pointings/offsets and your source is not too extended, you could combine the exposures with statistical rejection of the brightest pixels (eg. using imcombine) to remove the stars and just get sky, then subtract that from each image with imarith or imexpr.

James.

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Last post on Jan 23, 2009