How HoopFile auto-digitizes an image
Digitizing means turning a picture into a path the needle follows. Here is exactly what happens to your image, so you know what to expect.
1. Reduce colors
The image is resampled to a 0.25 mm grid at your chosen size, then reduced to the number of thread colors you pick. Near-identical shades and antialiasing fringes are merged, so a black logo stays one thread instead of five. The background color (the one covering most of the border) is dropped unless you turn that off.
2. Clean up regions
Specks smaller than about 3 mm² are merged into their neighbours: the machine cannot sew them, and they would add trims. Each remaining color area is split into connected shapes.
3. Underlay
Shapes bigger than 25 mm² get an underlay layer first: sparse rows at 90° to the top stitches, inset 0.4 mm. It holds the fabric down so the fill lies flat and covers.
4. Tatami fill
The top layer is a tatami fill: rows 0.4 mm apart (0.5 light, 0.33 dense), stitches up to 3.5 mm long, with a brick offset so needle holes do not line up into a visible groove. Rows are extended 0.2 mm on each side for pull compensation, because thread tension pulls a fill narrower than drawn.
5. Path planning
Rows are joined into back-and-forth runs and ordered nearest-first. Moves between runs stay inside the shape as hidden travel stitches where possible; otherwise the machine trims and jumps. A typical 3-color logo ends with under 10 jumps. Stitches under 0.3 mm are removed (they cause thread breaks).
6. Writing the machine file
The stitch list is written with the open-source pyembroidery library into PES (version 6, with thumbnail and Brother thread colors), DST, JEF, EXP, VP3 and XXX. We validated every format by reading the files back with two independent readers and comparing stitch counts and sizes.
What it does not do (yet)
- Satin columns: narrow parts are filled, not satin-stitched, so lines under about 1 mm wide and text under about 6 mm tall do not stitch cleanly.
- Photo-realistic shading: photos come out as posterized color blocks.
Always check the sew-out preview, and do a test stitch on scrap fabric with stabilizer before your final piece.