Fill tool should have a threshold

[fsih]

Expected Behavior

Fill tool should be able to fill similar colors to the one clicked on. This would help with e.g. removing background color from photos, as you can fill with transparent.

Actual Behavior

Fill tool only fills that 1 color. It can be hard to fill in backgrounds on jpegs.

Steps to Reproduce

Use bitmap fill tool

Operating System and Browser

Windows Firefox

[fsih]

Design question: should the threshold be preset, like in scratch 2, or should you be able to adjust it?

[chexbox]

You be able to adjust it, but it needs a default value similar to the preset in 2.0.

[fsih]

Once saw a fill tool where you click and drag to see a live preview of changing the threshold. It was pretty neat, but probably processing intensive. (Maybe procreate? https://www.youtube.com/watch?v=zod-z7GTWek)

Lisa and Carmelo also demoed https://clippingmagic.com/ where you erase a background using an edge aware algorithm. You could use similar tech to do a smart fill. It's probably too intensive for us to want to use, but here's an implementation: http://groups.csail.mit.edu/graphics/bilagrid/