Add convert method of XRImage

[katherinekolman]

• Tests added (for all bug fixes or enhancements)
• Tests passed (for all non-documentation changes)
• Passes git diff origin/master **/*py | flake8 --diff (remove if you did not edit any Python files)

[coveralls]

Coverage increased (+0.3%) to 86.88% when pulling 45a955a on katherinekolman:master into c8ff27e on pytroll:master.

[mraspaud]

Looks good.

[mraspaud]

While the Image object implements the convert method as in-place conversion (mainly due to memory constraints), I would like to take the opportunity to change that to convert returning the converted image instead, since with dask, we won't have the same limitation anymore. What do you think ?

[pnuu]

While the Image object implements the convert method as in-place conversion (mainly due to memory constraints), I would like to take the opportunity to change that to convert returning the converted image instead, since with dask, we won't have the same limitation anymore. What do you think ?

I'd also like the convertion to return a new image. In this way it would be possible to easily use the same object to get several different colorspaces for what ever use. E.g. to get (in future) YCbCr version and still use the original RGB(A) for something.

[katherinekolman]

Close #21

[pnuu]

I tested the updated .colorize() via SatPy (colorized_ir_clouds composite), end the performance boost is quite significant compared to the non-dask version.

[djhoese]

Awesome job. There are a couple things I'd like changed.

[mraspaud]

Starts to shape up nicely!