render_stl

Drop in any STL, get a finished product photograph.

One Blender script that imports a mesh, scales it, rests it on paper, lights it like a studio shoot and frames it — no scene setup, no tweaking. Default settings reproduce the same look every time, whatever the model's original size or units.

_{DIN‑5 connector · Stargate ring · Stanford bunny · Duke Nukem — 1000 px previews. The two figures are shot at --el 34 so the pose reads instead of being flattened from above.}

./render.sh --stl part.stl

part-render.png   2400 × 2400
part-render.jpg   same frame, quality 95

Sample input and output live in examples/ — the 13 × 14 mm DIN‑5 socket above, rendered at 2400 px.

More than one knob

./render.sh --stl part.stl --rot 90 0 0                    # lay it on its side
./render.sh --stl part.stl --color "#1E4D4B" --paper "#C9BFA8"
./render.sh --stl part.stl --fill 0.72 --res 3200 --samples 512

flag	default
--stl	required	input model
--rot RX RY RZ	0 0 -10	rotation in degrees, before framing
--color	#731811	body colour
--paper	#A8A196	paper / backdrop colour
--out	<stl>-render.png	output path
--fill	0.60	subject size as a fraction of the frame
--az --el	240 63	camera azimuth / elevation
--lens	200	focal length, mm
--res --samples	2400 360	square size, Cycles samples
--exposure	-6.1	film exposure
--no-post --no-jpg	off	skip grading / skip the JPEG

What it does

1. Imports & cleans — welds duplicate vertices, drops strays, unifies normals.
2. Normalises — rotates, centres, rests on the paper (min z = 0), scales the largest dimension to 14 mm. The light rig is identical for every model, at any unit or size.
3. Softens — 0.035 mm angle-limited bevel plus smooth-by-angle, so print tessellation reads as a moulded surface rather than a mesh.
4. Frames itself — projects every vertex onto the camera axes and solves the distance so the silhouette fills --fill, centred to within a percent.
5. Lights it — a large warm key, cool fill, narrow rim, over a procedural paper sweep with fibre bump and a gentle undulation.
6. Finishes — denoised 16-bit render, then highlight-safe exposure, gentle contrast, vignette, fine grain and unsharp mask, written as PNG + JPEG.

Tested on 21 real files

Every STL found in one machine's ~/Documents and ~/Downloads: 96 → 500 118 triangles, 0.01 → 25 MB, binary and ASCII — 19 rendered, 2 rejected as corrupt, 36 seconds for the whole batch at preview quality. (contact sheet)

Notes

• Corrupt files fail loudly. NaN or empty geometry exits with a clear message and a non-zero status instead of writing a broken image.
• Orientation is the one manual knob. If a model arrives lying down, --rot 90 0 0 (or -90, or a Z twist) is usually the only adjustment it needs.
• Camera angle is the second knob. The 63° default looks into open parts (a socket, a cup); standing figures read better lower, --el 34; flat or sheet-like parts want face-on, --el 85.

Requirements

Blender 4.1+ (developed on 5.2). Uses Cycles with Metal on macOS and falls back to CPU. BLENDER=/path/to/blender overrides the wrapper's default location.