How to convert a sketch into a specific mode?
Hey there! This is my first time here so I apologize if this isn't the right place to ask this.
There's this one artist that posted their drawing process for a piece and I wanted to know how to do a certain thing they did using photoshop.

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So they started with a sketch, then made a line art, and then the next step just completely lost me and I haven't been able to find the right tool to replicate it (the second picture). Converting to bitmap didn't work, doing that in 50% threshold didn't work, fiddling with curves and levels didn't work either. However, it's also possible that I just didn't do it right. They somehow started with a line art and used a certain tool or filter or transformation to transform the line art into pure black-and-white areas which show where shadows should be in the line art. So the picture became one with just black and white areas which enhance the locations of highlights and shadows. Is there any way to know what tool transforms the first picture into the second one?

