White BG in PNG Scanned Line Art needs to become transparent!

Here's how to do "white to transparency" in Photoshop. I've tested it and it works perfectly. Nevermind the subsequent posts, just use the recipe in the OP, and record it as an action for future use:

https://forums.adobe.com/thread/1395311

Although not Photoshop, these pages will help you understand how to process your scanned line art. To achieve a flawless transparent bg & lineart, Krita's Color to Alpha command is quite helpful. Photoshop doesn't have a command like that, and the quick round-trip in Krita makes life as a comic artist easier.

From blue sketch to digital in Krita - David Revoy

Krita also has an extremely helpful feature to assist in colouring your comic art:

Auto-Flatting Comic with Krita (+Gmic plugin) - David Revoy

You scanner scans what on its bed.  If the object on its bed is not a rectangle the scan will scan its white or any other color bed it has.  Even if the scanner software save png file there will be no transparency in the image the scanner give you. The software does not know the shape of the object you scanned.  You must select the white background and delete those white pixels you do not want.  You need to extract your line art.  There are programs the will try to trace your art.  Adobe AI has such a feature.  Photoshop tools can also be used to select your line art create a new layer and fill the selection with a color like black which may have some less then opaque area because of feathering partly selected areas in the selection.

Photoshop Script Black and White Raster to Vector