"Make RGB" docs are incomplete and over-specific

[keflavich]

I had a student come to me asking how to make RGB figures with astropy, and she found this page:
http://docs.astropy.org/en/stable/visualization/lupton_rgb.html

which is fine, but (a) didn't work out of the box (something wrong with image dimensions...) and (b) is doing more than she wanted.

We should have a document showing how to make an RGB image with scalings selected from astropy's visualization tools, for example like this script:
https://github.com/keflavich/SgrB2_ALMA_2015.1.00550.S/blob/master/analysis/threecolorfigure.py
but without all the reprojection and other stuff. Some indication that an RGB image is just a 3D image where the 3rd dimension consists of 3 planes would also be helpful.

We could probably also use some tutorials showing the mix of reprojection and RGB image making.

[bsipocz]

This is still an issue, and came up again. Digging into the source code we quite a lot of classes in that module that are still not exposed to the API docs, and it's not trivial to see how to make RGB images with the other scaling (e.g. log) already available in astropy.

[biprateep]

Hi @bsipocz I am willing to take up this issue. Is there anything specific you would like to add/modify?
An immediate thing that I see is that there is no way to use the AsinhZScaleMapping even though the class is defined.

and coming back to providing alternate scalings like log, we can have a general plot_rgb function which does a log and other scalings. We can have a particular mode for plot_rgb function that will boil down to the traditional Lupton RGB plotting algorithm.

Also it will be nice to add some of the improvements and flexibility that Phil Marshal has incorporated in his plotting routine available here: https://github.com/drphilmarshall/HumVI

let me know of your views.