Make a colorbar for datashaded images?

I know there might be another issue about this around somewhere, but I couldn’t find it, so I thought I’d write a new one. I understand that a colorbar for a datashaded image can’t be handled the same way as other colorbars, since there’s no way to get the data back from the image once it’s created. I was thinking that one possible solution might be to generate an inset image of a colorbar at the same time each datashaded view is generated, and superimpose it onto the image in some specified location. Or even something as simple as optional (and discreet) labeling of the max/min of the scale being used at any time would be useful. And it would be nice to have an option for this sort of thing within the datashade operation, rather than having to hack it up using dynamic=False and passing streams manually, etc.

[rabernat]

I just hit this issue. As much as I love datashader, the lack of an easy way to get a colorbar is a major downside.

What workarounds do people use for this?

[jbednar]

From within holoviews, usually we just use rasterize() rather than datashade(), which lets Bokeh do the colormapping, so that there will be a colorbar. The main downside is that Bokeh doesn’t support histogram equalization; it otherwise has all the benefits of datashading.