Free online image to STL converter

Your image already tells you which mode will print well. A photo — a face, a pet, a landscape — carries shadows, skin texture, and background clutter that are not real shapes, so it belongs in relief mode, where brightness honestly becomes height. A clean logo, black-and-white drawing, QR-like mark, badge outline, or stencil artwork belongs in stencil mode, where the threshold strips the background and keeps the shape you actually care about. Black line art on a white background usually needs invert turned on, or the background becomes the solid part. A transparent PNG works in your favor: transparent areas count as empty in stencil selection. A JPG deserves a quick cleanup first, because compression blocks can turn into tiny islands or bumps in your print.

Your details only print if they are wider than your nozzle, so pick physical size and resolution together. Say you export a 100 mm wide STL sampled at 250 columns: each column of your image prints at about 0.4 mm — exactly the width of a typical FDM printer's 0.4 mm nozzle, so a one-pixel feature is already at the edge of what can print. Give raised details, narrow bridges, and stencil ribs two or three pixels of width and they will come out clean. Shrink the same export to 50 mm at the same 250 columns and each sampled pixel becomes about 0.2 mm — too fine for the nozzle even though the STL looks sharp on screen. On a resin printer you can hold smaller features, but thin stencil connections still need enough width to survive washing, curing, and handling.

You are really setting three things: how tall your detail stands, how sturdy your part is, and what counts as shape. Relief height first — a shallow 1-2 mm relief reads as a subtle plaque or label, while a taller relief makes icons, map ridges, and decorative textures easier to see. Base thickness (or stencil thickness) is what keeps your print from being a fragile paper sheet: it closes the STL into a solid volume you can actually handle. The stencil threshold decides what stays: lower values keep more of your image as solid material with fewer holes; higher values keep only the bright regions, which cleans up a messy background but can break thin strokes. Flip invert when your dark artwork should be the raised or retained part. After each change, glance at the live preview for disconnected pieces, hair-thin bridges, or speckled noise before you download.