Every DTF operator has seen the symptom — a thin white halo peeking out from under colour edges on a dark shirt. Someone calls it registration drift. Someone else calls it under-base overshoot. The engineers who write DTF RIPs call it exactly what it is: the white layer is printed bigger than the colour layer. The fix is the choke.
The physics, in one paragraph
DTF is a three-step film stack: colour, white, powder adhesive. Colour prints first, white prints over it as an opaque under-base, powder bonds on top. When the transfer hits the shirt, the white layer is what blocks the fabric from showing through. That means the white has to cover at least every pixel that carries colour. So most RIPs default to generating the white layer by reading the colour alpha channel and expanding it by 0.5–1.0 mm — a process called spread or trap. Spread first, so the two layers can drift a bit during pressing and still line up.
The problem: when they don’t drift, you get a visible white border. The halo.
Where the choke lives in common RIPs
If you are running MainTOP, the choke is under White Ink Setting → White Choke and takes a value in pixels at your working DPI. Cadlink Digital Factory calls it Choke under the white channel; value is in millimetres directly. AcroRIP exposes it as Spread/Choke with a positive value being spread and a negative value being choke. VersaWorks and VerteLith both handle it through the white-ink mask settings at the driver level. The numbers move the same way everywhere — more choke, smaller white — but the sign convention and units differ, so check the documentation for your specific RIP before copying a value from someone else’s workflow.
The choke
The choke is the opposite of spread. Instead of expanding the white layer, you shrink it — usually by a fraction of a millimetre — so the white stops just inside the colour edge. A well-chosen choke value is small enough that normal registration drift still covers the colour, but large enough that if the layers hit dead-on, the white is hidden behind the colour instead of peeking past it.
A sensible default value for most DTF workflows is in the 0.2–0.4 mm range. Why that band:
- 0.0 mm (no choke) — every minor drift leaves a halo. Operators hate this default.
- Below 0.2 mm — still leaves a visible white border on high-contrast designs (fine text on black, especially).
- 0.2–0.4 mm — covers typical press variability on a well-calibrated machine. White stays hidden under colour edges on anything thicker than about 1 pt stroke.
- Above 0.5 mm — starts eating into thin strokes and small type. Fine text looks chopped.
When to change the default
A single fixed value works for maybe 80 % of jobs. The other 20 % fall into three buckets where a stock choke is wrong:
Very thin line art (pen-weight illustrations, signatures, tiny text). If the stroke is thinner than twice the choke, the white under-base is narrower than the ink line — or disappears entirely on the thinnest pixels. Either turn the choke down for this job, or thicken the stroke by the same amount in vector.
Loose-weave fabric (heather, tri-blend, French terry). Fabric stretches during press. You get more registration drift than on a tight-weave tee. Go to the high end of the band (0.3–0.4 mm) or slightly beyond.
High-contrast designs on white/light shirts. Irony alert: on light fabric, the white under-base is not for opacity but for ink hold. You can run much lower choke, sometimes zero, because a halo against white is invisible. Separating this case out of your default workflow is the single biggest quality improvement most shops leave on the table.
Knowing you got it right
Press a test sheet with the candidate choke value. Look at the transfer on the release paper before pressing, under angled light. Every colour edge should show a hair-line of white showing through — that hair-line is the registration margin you have on this job. Zero hair-line means press registration has to be perfect. A visible band means you over-shot.
On XP600 and i3200 printhead configurations the visible registration tolerance is typically tighter than on older DX5/DX7 setups, so you can usually run a slightly smaller choke on a modern head without losing coverage.
Press the transfer onto dark fabric. Pull it off, inspect under the same angled light. If the halo is gone and the edges look crisp, you are done. If there is still a halo, the choke was not enough. If the colour looks like it was bitten (particularly on thin strokes), the choke was too much.
The takeaway
The choke is one of those pre-press settings where “a sensible default” handles most of the work, but the last 20 % of jobs ruin averages if you don’t tune. A gang-sheet tool that lets you set per-job choke — and writes the TIFF straight into MainTOP, Cadlink, AcroRIP, VersaWorks, VerteLith or Wasatch without a second pass through another app — pays for itself within a week of shirt returns avoided.
