How embroidery digitizing works: stitch types, underlay and sewing order

Embroidery digitizing turns artwork into instructions for a needle. Every shape becomes a stitch object with a stitch type (running, satin or fill), a direction, a density, underlay and pull compensation, and all objects are put in a sewing order. The machine file you download is the result: a list of needle positions, jumps, trims and colour changes.

What does digitizing decide for each shape?

Six things, for every object in the design. A machine can't read a JPG or an SVG. It needs coordinates: move here, needle down, jump there, stop for the next colour. Whoever digitizes a design, a person in editing software or an automated pipeline like ours, decides six things per object:

1. Stitch type: running, satin or fill.
2. Angle: which way the stitches lie. Thread reflects light differently at each angle, so neighbouring fills get clearly different directions.
3. Density: how close the rows or zig-zags sit.
4. Underlay: a lighter foundation sewn first.
5. Pull compensation: extra width so the shape still matches the art after the thread pulls the fabric in.
6. Sewing order: which object comes first, where the needle travels and where it has to trim.

The numbers in this guide are the defaults of the digitizer that produces every design in our library, set beside what the major embroidery software documents.

The three stitch types

Running stitch

A single line of stitches. It draws fine lines, forms most underlay, and is how the needle travels between objects. In our files a running stitch is 1.8 to 2.0 mm long, which matches Wilcom's advice to shorten stitches to about 1.8 mm on sharp curves. The best travel runs are the ones you never see, because they lie where a later satin will cover them.

Satin stitch

A tight zig-zag between two edges. Wilcom's documentation explains its look: "Because there are generally no needle penetrations breaking up the fill, satin stitch gives a glossy, high-quality appearance." That makes satin the stitch for outlines, borders, small details and most lettering.

Satin only works within a width range. Wilcom warns that if a satin is too wide, "stitches may be loose or fail to cover the fabric properly," and in narrow columns density can become so high that needle penetrations damage the fabric. Machines also have a hard limit on stitch length, 12.1 mm on Tajima-type machines and 12.7 mm on Barudan-type, and Ink/Stitch notes that satins of 1 mm or less "often produce poor results." Our digitizer keeps satins between about 0.8 and 5 mm and turns any detail wider than 5 mm into a small fill.

Fill (tatami) stitch

Rows of running stitches laid back and forth to cover an area. Wilcom describes how the rows are offset: "Stitch offsets in each row are used to eliminate horizontal split lines." Our default is 0.40 mm between rows and 3 mm stitches, with the offset repeating every three rows.

Underlay: the layer you never see

Underlay is sewn before the visible stitches, and Wilcom's documentation lists what it does: it "helps to stabilize fabrics and reduce puckering and pulling," provides "loft" that keeps cover stitches from sinking into soft fabrics, and can flatten a napped fabric. Wilcom adds that it is "much more effective" than simply raising the density.

The standard types each have a job. Wilcom describes a center run for narrow columns of about 2 to 3 mm, an edge run around larger shapes, zigzag or double zigzag under wide satins, and an open tatami underlay, angled against the top stitching, under large fills. Knits and large areas need more underlay than small objects on firm fabric.

Our files use the same toolkit:

• Fills get an open underlay laid across the direction of the top rows, about 1.8 mm apart.
• Outline satins are sewn "walk out, satin back": a running stitch along the centre-line is the underlay, and the satin covers it on the way back.
• Lettering columns wider than 1.6 mm get a zig-zag underlay; narrower strokes get a centre run.
• Tiny fills under 20 mm² get none, because underlay there only adds bulk.

Fluffy fabrics need support beyond underlay: towels and fleece also need a water-soluble topping, as the stabilizer guide explains.

Pull compensation: why shapes shrink

Every stitch pulls the fabric together along its own direction. In Wilcom's words, "the needle tends to pull fabric inwards," which causes puckering, small gaps between shapes and distorted outlines. Pull compensation makes stitches extend slightly beyond the drawn outline to make up for it. The opposite effect, push, makes satin columns grow at their ends, so long satins sew out longer than drawn.

The right amount depends on the fabric. Wilcom's guideline table gives 0.20 mm for drill and cotton, 0.35 mm for T-shirts, 0.40 mm for fleece and 0.2 to 0.3 mm for lettering. Our defaults sit at the woven end: 0.2 mm at the ends of fill rows and 0.12 mm per side on outline satins, rising to 0.3 mm on fills when we digitize for knits.

These values are absolute millimetres. They don't grow or shrink with the design, which is one reason a finished stitch file can't be scaled freely: resizing embroidery designs explains what goes wrong.

Sewing order, travel and trims

Sewing order affects three things you can see: trims, registration and how cleanly objects meet. Wilcom's documentation advises planning the stitching sequence in advance and states that "details should always be stitched last." Trims cost time as well as thread ends; Wilcom's blog puts each trim at about 3 to 4 seconds on a typical machine.

Our digitizer orders a design like this:

1. Colour blocks back to front. Shapes behind sew first, for example ears and arms, then the body, then the head.
2. Inside each colour: fills, then outlines, then details. Eyes, mouths and stripes sew last. A satin on top of a fill pulls on it, so details go where they can't shift anything sewn after them.
3. Hidden travel before trims. Travel runs aren't trimmed, so Wilcom warns they may stay visible. Ours run only where a later satin will cover them, up to 60 mm, and the needle trims only where no hidden route exists.
4. Lock stitches at every trim. Three short stitches tie in after a jump and two tie off before a trim, so nothing unravels.

One format detail matters here. Tajima DST has no trim command, so a trim is written as a short burst of jump stitches that the machine reads as a cut. Some home machines ignore that burst; then you snip the jump threads by hand. The file formats guide covers what each format stores.

Clean crossings: our tiered outline method

Outlined cartoon art has many places where two outlines meet: an ear line runs into the head, an arm line into the body. Sewn in an arbitrary order with rounded ends, these joins pile up five to seven layers of thread and look lumpy.

We solve it with tiers. Every outline gets the tier of the shape it outlines, ordered by what is in front in the picture:

• Lower tiers sew first. An ear line ends about 0.5 mm under the head line instead of running to its far edge.
• Higher tiers sew last, as one continuous satin that runs unbroken over every join.
• A shared edge takes the higher tier. Where an arm lies against the body, that stretch belongs to the body line, so it stays one stroke.
• Rings sew in one piece. A head circle starts and ends away from any join, and the zig-zag carries over its first stitches so the seam interlocks.

At every crossing exactly one line is visibly on top, and thread build-up stays around 3.5 to 4.5 layers instead of piling up. The order only matters for lines that touch, so the digitizer interleaves tiers to keep one continuous run. On the bird design we used to develop the method, sewing the black outline strictly tier by tier meant about ten trims; the tier rule allows interleaving, which brings it down to the drawing's minimum of two.

Test sew-outs shaped these rules. On that bird, fills that stopped short of the outline left a strip only the satin covered, so now neighbouring fills run almost to the outline's centre-line, 0.15 mm apart, and the satin sews over both edges. The monogram and lettering maker applies the same tier rule to pen strokes: a thin hairline is sewn first and tucks under the thick stroke it joins.

How do we check every file?

A preview can look perfect and still hide problems. Each file in our library gets an automatic quality report before it is published:

• Coverage: finds spots where fabric would show through a fill or an outline.
• Thread build-up: measures layers of thread per square millimetre and flags anything above five. A normal satin reads about 1.5, a clean crossing 3 to 4.
• Hidden travel: confirms that every travel stitch is covered by something sewn later.
• DST round trip: reads the written file back and compares every needle position with what was planned.

Digitizing your own designs

You can learn all of this hands-on. Ink/Stitch is a free, open-source digitizing extension for the Inkscape drawing program, with good documentation on each setting above. Commercial programs such as Wilcom EmbroideryStudio, Hatch, BERNINA Embroidery Software and Brother PE-DESIGN automate more of the work.

If you would rather start from finished artwork, our SVG to embroidery tool applies the rules in this guide to your own vector art, and the AI design generator draws new art in our style before digitizing it. Before you stitch any file, the free embroidery file viewer shows its stitch count, colours and size.