PR in response to ppinard/matplotlib-scalebar#21

@timhoffm I was able to reduce the size by ~5. I decreased the resolution by 2 and using Gimp I converted the image to greyscale and applied the highest compression.

The original image is from Wikipedia Commons and it is in in the Public Domain: https://commons.wikimedia.org/wiki/File:Gold_on_Carbon.jpg

Thanks @ppinard !

@tacaswell I'm afraid the merge was a bit too fast.

• The image is not optimal:

  • JPG would be more suited for such an image.
  • The image has not gone through a compressor. (There are optimizations to reduce image size apart from the compression level).

  A visually equivalent (compressor post-processed) JPG would be 13kb instead of 33kb.

• The ReST code forces an image height of 200px while the actual image is just 150px. This upscaling degrades quality visibly. We should show the image in it's original size. So either use a larger image or make it smaller in the docs.

Given that this is already merged, how do we proceed from here? Is there any way of replacing that image without carrying the unused version in the repo for eternity and without breaking existing clones?

Edit: On a side-note, the above issues are present for a number of images on https://matplotlib.org/devdocs/thirdpartypackages/index.html. Changing them would be a separate matter of discussion.

Push a new PR to fix those things and once that is merged add it to the backport PR.

I will make a new PR today.