Why this would be helpful

I suggest an addon that gives users the ability to upscale and/or downscale bitmap costumes in the costume editor.

Scratch 3 has a feature where small bitmaps are "scaled up" when imported. The thing is, the bitmap costume editor actually works in half-size pixels; a pixel in the costume editor is technically one quarter of a pixel in a traditional image editor.

This is so you can import images bigger than 480 by 360, but it also creates a disconnect between how big a costume is in Scratch's native bitmap editor, and how big the image actually is.
Since many Scratchers paint their graphics in Scratch's half-sized pixels, this makes importing new graphics made in an external image editor a chore, since it imports twice as big as the project's other costumes look.
My suggested addon would help alleviate this quirk.

How this addon works

This addon would add two buttons in the upper toolbar of the paint editor, one for scaling up the image, and the other for downscaling it.
The Scratch 3 file format already has a property for costumes called bitmapResolution, which is set to 2 by default for images that can fit on-stage without resorting to half-pixels. This property could easily be increased or decreased by the addon to scale the image.

Possible alternatives

Another option could be to add a button to import a bitmap automatically scaled down to half-pixel size, like how HD import works. It may also be merged with HD import in some way instead.

Additional context

Example of a small bitmap; notice the resolution reads "7 x 7" despite appearing to be 14 pixels wide.

Example of a bitmap imported from an external editor without modifications; the image appears twice as big as the other costumes.