Drawing for normal maps
Most of what makes a sprite hard to light is decided before this program sees it. If you know a normal map is coming, a few habits while drawing will save more time than any amount of work here afterwards.
None of this is required. Everything below has a fix inside the application, and the rest of these pages is about those fixes. But a problem avoided at drawing time costs nothing, and the same problem solved afterwards costs a hint layer and your attention, so it is worth knowing which is which.
Export at the size you drew
The single most damaging thing that happens to pixel art on its way here is being enlarged. A 44×73 sprite exported at 8× arrives as a 336×558 image, and every setting in this program is measured in drawn pixels: stroke width, blur radius, relief radius, the smallest feature the form pass keeps.
Solve the original. Scale the finished normal map up afterwards with nearest-neighbour — a normal map of pixel art enlarges perfectly, because each drawn pixel is one flat facing and a nearest-neighbour copy of it is still that facing. Enlarge first and the tool measures everything against a ruler eight times too long.
The application detects this and names the size it thinks you drew at, and can recover that grid from the file. It cannot recover detail an enlargement has already smoothed away.
Keep the shadow out of the sprite
A contact shadow baked into the artwork is opaque, and opaque means "part of the object" to anything that reads a silhouette. It will be inflated into a lump lying on the floor.
Keep it on its own layer, and either leave it out of the export or name that layer contact shadow, which the importer
will offer to exclude for you. If it is already flattened in, fill it with Not the object X.
The same goes for glows, bloom around a lamp, and any backdrop matte.
Separate the parts that overlap
Where an arm crosses a chest, the shared edge looks exactly like a fold in one continuous surface, and nothing in the picture distinguishes them.
If the arm is already a separate layer you have answered the question for free: import the layered file and map that layer onto In front, or onto Artwork (new layer) if it should be its own object in the scene. Drawing with overlapping parts separated costs nothing at the time and removes a whole category of correction later.
That is for parts of one object. Two objects that happen to share a picture — a crate in front of a character — are better imported as scene layers. Solving them as one silhouette is what invents a relationship the artwork never had.
Close your outlines
Several things here read the drawing as a set of enclosed areas — most obviously Flat face, which splits one fill into separate walls and a roof along the lines between them. A single-pixel gap joins two areas into one, and the symptom is not subtle: two walls come out as one averaged plane.
Worth a glance before exporting, since a gap you cannot see at 100% is a gap a fill will walk straight through.
Do not shade what you want lit
The awkward one, because it runs against how a good deal of 2D art is made.
Painted shading describes a light that has already been chosen. A normal map is for lighting that has not been chosen yet, and the two fight: your painted highlight stays where it is while the real one moves across it. For anything that will be dynamically lit, flatter artwork carrying its form in the line work rather than in the rendering gives a better result and is less drawing.
Where shading genuinely describes form rather than a light source it is useful, and the detail methods can read it — see Solver settings. But it is a choice worth making deliberately.
Give thin features somewhere to be
A surface reconstructed from an outline needs an interior. A feature two pixels across is all edge, with nothing between its two rims for a shape to occupy, so it comes out flat or pinched however it is hinted.
If a detail matters and it is one or two pixels wide, either draw it wider or accept that it will read as line work rather than as form. That is a limit of the method, not a setting waiting to be found.
Where this advice comes from
Some of it is this project's own experience. The rest is from artists interviewed for Amine El Bouhattaoui's 2024 thesis on 2D normal map generators, whose experts made the same point independently: when you know maps are coming, you can head most of the trouble off in the drawing, by working a little larger and by keeping important edges on separate layers.