Imposition
How to read imposition plans, imposed PDF output, evidence, and production limitations.
Imposition
Architecture note
Imposition math lives in ntp-pdf-imposition. Studio displays plans, collects settings, and
explains evidence status; it is not the source of placement math.
Internal alpha status
The current imposition surface is operator-only internal alpha. A plan can be correct and still not be downloadable, production-ready output until the output receipt, post-imposition preflight, and proof status are present.
Imposition places PDF pages onto press sheets for cutting, folding, binding, and production handoff. A good plan improves sheet usage, preserves page order for finishing, and gives the supplier a shared technical reference.
The critical distinction
An imposition preview plan is not an imposed PDF output.
A plan shows where pages land on each sheet side, which page boxes are used, and what transforms apply. An imposed PDF output is a separate export artifact and must be validated with an output receipt.
- A preview plan is for on-screen review.
- Imposed PDF output requires real PDF bytes, SHA-256, a safe file name, page count, and engine identity.
- Measured render proof is never claimed without native PDFium render evidence.
- Browser fallback and preview pixels do not satisfy measured proof.
Selected sheet, effective sheet, and minimum sheet
The selected sheet is the sheet size chosen by the user. The effective sheet is the sheet size used by the current plan/preview. The minimum sheet is the smallest custom sheet NowToPrint can calculate for the current layout without silently scaling or overflowing pages.
If the selected sheet is too small, Studio may calculate a larger minimum sheet for preview. That is an adjusted plan, not an accepted output state. Export availability stays locked until the user accepts the minimum sheet or chooses a larger sheet, and the output path still needs the normal receipt/proof chain.
If the output writer is unavailable in the current runtime, Studio keeps the download action disabled and shows the reason. A disabled export button should not call the endpoint. If the server returns a controlled unavailable/failure response, the UI should show the specific next action instead of raw 500/503 text.
Why page boxes matter
Imposition uses MediaBox, CropBox, TrimBox, and BleedBox from the ntp-pdf-core PageGeometryTruth model.
- TrimBox defines the finished product boundary.
- BleedBox describes the safe bleed extent after trimming.
- CropBox constrains the visible working area.
- Non-zero origin and rotation are handled explicitly so overlays do not drift.
Bleed content is not synthesized
If bleed is missing, NowToPrint does not paint, mirror, rasterize, or invent new artwork at the page edge. Missing bleed remains a finding, limitation, or customer action. If the artwork must change, upload a corrected PDF.
Foundation modes
| Mode | Use case | Evidence language |
|---|---|---|
| N-up | Place multiple pages on one sheet | Placement, trim/bleed rectangles, utilization |
| Step-and-repeat | Repeat one source page across a grid | Repeat count, order, waste |
| Booklet | Saddle-stitch brochures and booklets | Page pairing, blank padding, creep status |
| Cut-and-stack | Cut and stack production flows | Stack order, cut direction, limitation |
Perfect-bound sections, large-format tiling, packaging ganging, and true-shape nesting are not production-ready public claims in Foundation v1. Unsupported parts stay visible as limitations.
Marks and guides
Crop marks, fold marks, registration marks, color bars, gray bars, bleed guides, safe-area guides, spine guides, job labels, and QR/barcode identity marks can be carried as plan evidence.
Generated barcode or QR marks are not scanner-certified. Scanner verification needs separate evidence.
What creep means
Creep is the page shift that appears in thicker saddle-stitch work. Foundation v1 has a basic linear creep model that is disabled by default. If enabled, the plan reports it explicitly; advanced creep profiles remain limitations.
Checks before production
Even when an imposed PDF is downloadable, the production claim is not automatic. The sequence is:
- Source PDF preflight completes.
ntp-pdf-impositionproduces the plan.- The export sidecar creates imposed PDF bytes.
- The output validation receipt verifies PDF header, SHA-256, file name, and page count.
- Post-imposition preflight is pending or completed.
- Render-verified status requires native measured render proof.
The output receipt proves that the derived PDF bytes were produced and validated. It does not prove
that the imposed PDF is production-safe. proof_pending remains the honest state until measured
imposed-output render evidence exists; only then can Studio show production_proof_ready.
NowToPrint does not convert RGB to CMYK, convert spot colors to process, flatten transparency, generate trapping, mutate overprint, or outline/substitute fonts. Design intent, color behavior, and late-binding integrity are preserved.
Supplier handoff
Send the supplier the plan summary, selected profile, source preflight report id, plan hash, output receipt status, limitations, and post-imposition preflight/render proof state. Raw storage refs, local paths, and debug JSON stay out of customer and public views.
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