[AstroPy] reproject and flux conservation

[Thomas Robitaille]

Hi Yannick,

By default, reproject preserves surface brightness rather than flux - so
for now if you want to preserve flux, you'll need to multiply the final
image by the ratio of the pixel area after reprojection to the pixel area
before reprojection.

See also https://github.com/astropy/reproject/issues/68 for a related issue.

Cheers,
Tom

On Thu, 27 Jun 2019 at 17:13, Yannick Roehlly <yannick.roehlly at gmail.com>
wrote:

> Hi all,
>
> I'm working with a student who needs to have a visible image rebinned to
> the
> pixel size of an infra-red one with one to one pixel overlap. I suggested
> it
> would be simpler to use `reproject` to re-project the visible map onto the
> infrared one.
>
> What we don't understand, is that whereas reproject_exact is supposed to
> conserve the flux, the sum of the reprojected array is much higher that
> the
> sum of the initial one (I would have expected it to be lower because of
> parts
> of the visible map not being on the IR coverage).
>
> Where are we wrong?
>
> Regards,
>
> Yannick
>
> --
> Every man who is high up likes to think that he has done it all himself,
> and the wife smiles and lets it go at that.
>                 -- Barrie
>
>
>
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