Allow turning certain colours transparent when inserting image

[Glodenox]

It should be possible to allow users to remove certain colours so those areas become transparent. By using a canvas element instead of a regular img tag, this might indeed be possible. See https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Pixel_manipulation_with_canvas

Things to consider: this can currently already be done with external image editing software. Implementing this is not trivial, especially from a UX standpoint. This would also certainly require a way to undo changes while editing and the odds are high that once this gets added, other features will be requested that are already available within image editing software.

[Glodenox]

Ideas for reasonable filters that could be toggled for the images individually:

• make white pixels transparent (or maybe do some subsampling to identify the background colour?)
• make black pixels white
• make all colours brighter (as the satellite imagery is generally quite dark)