Threadsmith Stitch File Writer

How it works

Encodes stitches as a Tajima DST (512-byte header, balanced-ternary 3-byte records, jumps split to ≤ 12.1 mm, colour changes, trims as zero-sum jumps, END) or Melco EXP file. The file is decoded again to verify every stitch position before you download it.

• Coordinates are rounded to 0.1 mm on absolute positions, so rounding never accumulates; each move becomes the difference to the previous rounded position.
• DST: each axis is written in balanced ternary with digits for 1, 3, 9, 27 and 81 (±121 max). Byte 3 = 0x03 | flags: 0x80 jump, 0xC0 colour change; END = 00 00 F3. Longer moves are split into equal records. Y is inverted (DST is y-up).
• Trims are written as three jumps (+2,+2) (−4,−4) (+2,+2) that cancel out — the convention machines use to trigger a trim after a run of jumps.
• Header: LA label, ST record count, CO colour changes, ±X/±Y extents in 0.1 mm, AX/AY end offset, MX/MY 0, PD ******, 0x1A, padded with spaces to 512 bytes.
• EXP: 2 signed bytes per stitch (±127), 0x80 0x04 dx dy jump, 0x80 0x01 colour change; trims as three zero-sum jumps.

DST and EXP carry no thread colours: set the needle/colour order on the machine using the colour list from Threadsmith. Test on scrap fabric first.

Sources

• Embroidery format DST (header fields, ternary stitch encoding, control codes, trim convention) (EduTech Wiki, University of Geneva)
• Embroidery format EXP (2-byte two’s-complement stitches, 0x80 control codes) (EduTech Wiki, University of Geneva)
• pyembroidery – reference readers/writers for DST and EXP (EmbroidePy)
• Ink/Stitch manual – stitch types, underlay, pull compensation (Ink/Stitch project)
• Felzenszwalb & Huttenlocher, Distance Transforms of Sampled Functions, Theory of Computing 8 (2012)