Which images auto-digitise well for embroidery, and which do not

Automatic digitising does one thing: it looks at shapes and colours and decides where a needle should go. It cannot ask what you meant. So the quality of the file it writes is set, before anything else, by how clearly the picture says what is a shape, what is a colour and what is background. This guide lists what helps and what hurts, with the physical limits behind each point, so you can tell in advance whether the image to embroidery tool will give you a file worth stitching.

The limits are physical, not software

Forty-weight embroidery thread is about 0.4 mm wide once it is sewn. A needle makes a hole about 0.8 mm across. Fabric stretches and pulls in as it is stitched. Everything below follows from those three facts.

• A satin column needs about 1 mm of width. Narrower than that, the two sides of the zigzag land almost on top of each other, the thread piles up, and the needle starts cutting the stitches it has already made. Shapes between roughly 0.4 and 0.9 mm can only be a running stitch.
• A satin column should not exceed about 7 mm on a garment. Longer stitches snag and lift. In the digitiser here, turning satin is used up to 3.4 mm and wider shapes are filled with staggered 3.6 mm stitches, which is the conservative choice for a file nobody will hand-tune.
• Details under about 0.4 mm do not exist in thread. A speck that small is smaller than one stitch. It is absorbed into whatever surrounds it.
• Adjacent colours need to overlap. Fabric pulls in along the stitch direction by 0.15 to 0.4 mm depending on the material, so two areas that meet exactly in the artwork would show a gap in the embroidery unless the first runs under the second.

None of this is a setting you can turn off. A picture that respects these limits digitises well; one that ignores them gets simplified, and the audit tells you what was lost.

File type, from best to worst

SVG. A vector has mathematically exact edges and exact colours, and it can be rendered at the working resolution for any size you ask for. A 60 mm cap logo and a 250 mm jacket back start from equally clean shapes. Strokes are read at their real width, so you control the stitch type directly: a 1.2 mm stroke becomes satin, a 0.5 mm stroke a running stitch. If the customer has a vector, ask for it.

PNG with transparency. Lossless, and the background is unambiguous: transparent means unstitched. The only noise is the one-pixel anti-aliased rim around every edge, which is well under 0.3 mm at stitch size and is folded into the neighbouring shapes.

PNG or JPG on a plain background. The background has to be found by colour: whatever dominates the frame is flooded in from the edges and removed. That works for a logo on a white or single-colour page. Enclosed areas of the same colour, the holes in an A or an O, are treated as holes. If they are actually part of the design, white eyes on a mascot for example, the tool has a setting to stitch them.

Compressed JPG. JPEG compression surrounds every edge with a halo of slightly wrong colours. A naive converter turns the halo into an extra thread colour and a fringe of tiny stitches around everything. The digitiser here detects colours that exist almost only as thin rims beside a near twin and merges them back, but a very small or very compressed file still has soft edges, and soft edges make for uncertain widths and ragged satin.

A photo of a printed logo. Workable if it is shot square on in even light. Shadows and paper texture become colours.

Resolution: ten pixels per millimetre is enough

The artwork is scaled so that one pixel equals 0.1 mm of finished embroidery, up to 1,400 pixels on the long side. That is finer than the 0.1 mm grid stitch formats store positions on, so more pixels add nothing. Fewer do cost you: a 300 px logo stretched to 90 mm has one source pixel per 0.3 mm, which means every edge is a blur three stitches wide. If the only copy you have is small, reduce the finished size or redraw it.

Colour: flat, few and distinct

Colours are grouped in CIELAB, a colour space arranged so that equal distances look equally different to the eye, and any two groups closer than about 11 ΔE are merged into one thread. Below that difference no thread chart offers two distinct spools anyway.

What this means for your artwork:

• Flat fills digitise cleanly. Gradients, glows, drop shadows and 3D bevels become bands of intermediate colours. Flatten them before you start, or lower the colour limit until the bands merge.
• Two near-identical shades become one. If the difference matters, make it bigger in the artwork.
• Fewer colours sew faster. Each one is a stop. On a single-needle home machine that is a rethread; on a multi-needle it is a few seconds and a trim.

Line width and text size

These are the two places where artwork most often asks for something thread cannot do.

| In the finished embroidery | What happens | |---|---| | Line under 0.4 mm | Left out, and listed in the audit | | Line 0.4 to 0.9 mm | Triple running stitch along its centre | | Shape 0.9 to 3.4 mm wide, elongated | Satin column that follows the shape | | Wider, or small and compact | Tatami fill; rows under 6.5 mm sewn as single stitches |

For text, the rule of thumb is a 5 mm cap height minimum in a plain bold sans-serif, which gives strokes of about 1 mm. Light weights, serifs and scripts need 8 mm or more. Below that, consider dropping the tagline from the embroidered version, which is what most brand guidelines do anyway. Embroidery font sizes that stitch has a table by font style.

Size is your main lever. The same logo that loses three details at 60 mm keeps all of them at 100 mm, because every feature is two-thirds larger. Change the size in the tool and watch the "details too small to stitch" row of the audit.

A checklist before you upload

1. Use the vector if one exists; otherwise the largest lossless copy.
2. Crop to the design so the frame colour really is the background.
3. Remove shadows, glows and gradients.
4. Decide the finished size first, then check text height and thinnest line against the table above.
5. Count the colours you expect, and set the colour limit to that.
6. After digitising, read the audit and drag the compare slider over the small details. They are where automatic digitising and a human digitiser differ most.

What the audit will tell you afterwards

The production audit measures the finished stitches rather than guessing from the picture: how much of the artwork is covered, how many stitches are shorter than 0.3 mm or longer than 12.1 mm, how much of the area is stitched too densely, how many trims there are per thousand stitches, and how many details were dropped for being too small. If a row is not green, its note names the cause in the artwork. The same file can be opened in the pre-flight check for a density heat map, and in the viewer to step through the sew-out.