---

title: "White / underbase producer" description: "White-ink / underbase / varnish / foil plate generation — adds a named DeviceN separation derived from the input's ink coverage." group: "Reference" order: 15

White / underbase producer

The white-underbase producer generates a white-ink (or underbase / varnish / foil) plate for an input PDF and registers it as a named separation, for label / garment / foil work on dark or specialty substrates.

Ships as the compile-pdf-white-underbase satellite package. Mounted under /v1/white-underbase when COMPILE_PRODUCER is white_underbase or all. Schema version: WHITE_UNDERBASE_SCHEMA_VERSION = "1.0.0" (owned by the satellite's version.py, re-exported into /v1/contract).

Endpoint

POST /v1/white-underbase/apply

Request — input PDF inline as base64 plus a generation policy (every knob optional; the common real-world request is just {"separation_name": "White"}):

{
  "input_pdf_b64": "…",
  "policy": {
    "separation_name": "White",
    "plate_use": "white",
    "strategy": "auto",
    "knockout_threshold_pct": 5.0,
    "choke_pt": 0.0,
    "page_indices": null
  }
}

• strategy — auto (white wherever coverage exceeds the threshold), union (white wherever any ink prints), knockout (white where artwork is absent), or manual (register the separation, trace nothing).
• plate_use — white | underbase | varnish | foil; recorded as DeviceN colorant metadata so downstream RIPs treat the plate correctly.
• choke_pt — shrink (negative) / grow (positive) the plate relative to source geometry, ±2pt.
• page_indices — restrict to these 0-indexed pages; null means every page.

Response:

{
  "output_pdf_b64": "…",
  "pdf_sha256": "…",
  "input_sha256": "…",
  "policy_sha256": "…",
  "cache_key": "…",
  "cache_hit": false,
  "summary": {
    "pages_processed": 4,
    "separation_name": "White",
    "plate_use": "white",
    "strategy_applied": "auto"
  },
  "schema_version": "1.0.0",
  "compile_version": "0.7.0"
}

Errors: 400 (malformed / empty base64), 422 (engine rejected the policy), 500 (post-condition verify failed, with the failure list).

CLI

compile-pdf white-underbase --policy policy.json input.pdf output.pdf

--policy is optional (defaults apply); --no-verify skips post-condition checks.

Status

Shipped (passthrough engine). The response shape is final; once the real coverage tracer lands, the only caller-visible change is that output_pdf_b64 differs from the input when the policy selects any pages.