lineart-rich-black

Convert black-and-white line-art PNGs into print-ready CMYK TIFFs, building the plates directly from a rich-black formula. PNG decoding via the battle-tested pngjs (palette, 16-bit, and interlaced PNGs all work); the CMYK TIFF encoder is purpose-built because no Node library offers byte-order, InkSet, and ICC-assign control.

Generic ICC conversion lets the profile's black-generation curve decide your plates. For line art you usually want the opposite: exact, chosen ink values. This tool computes them per pixel:

tint = 1 − luma/255                    (0 = paper, 1 = solid black)
C = tint·c   M = tint·m   Y = tint·y   K = tint·k    ← your formula

Solid blacks print as your rich black, anti-aliased edges become proportional tints (smooth edges on press), and paper stays a true 0/0/0/0.

Install

npm install -g lineart-rich-black     # or: npx lineart-rich-black art.png

Node 20+. One small pure-JS dependency (pngjs) — no native modules, no ImageMagick, no Photoshop.

Quick start

# one file -> art.tif alongside it (20/30/20/100 rich black, 600dpi, GRACoL tagged)
lineart-rich-black art.png

# a folder of pngs -> print-tifs/, with your own formula
lineart-rich-black --formula 20,30,20,100 --out print-tifs/ pngs/

Options

| flag | default | meaning | |---|---|---| | --formula C,M,Y,K | 20,30,20,100 | plate percentages for solid black (TAC 170) | | --k-only | off | grays/edges ride the K plate alone (scaled by the formula's K); solids keep the full formula — avoids registration fringe on fine hatching | | --gates [B,W] | off (80,10 when given) | snap tints ≥B% to solid and ≤W% to paper before building plates — cleans vectorizer/upscaler output that has near-blacks and near-whites instead of pure ones | | --drop-paper [T,S] | off (25,25 when given) | force light, low-saturation pixels (tint ≤T%, saturation ≤S%) to paper — removes tan/cream "old photo" backgrounds | | --dpi N | 600 | resolution tag (600dpi ⇒ a 4096px image places at ~6.8") | | --profile <path\|name> | auto | ICC profile to assign (embed, not convert). Auto searches Adobe/ColorSync folders for GRACoL → SWOP → Generic CMYK | | --no-profile | — | write an untagged TIFF (your numbers hit the RIP verbatim) | | --byte-order ii\|mm | ii | TIFF byte order: ii little-endian ("IBM PC"), mm big-endian ("Mac") | | --compression deflate\|none | deflate | Deflate is ZIP (TIFF tag 8) — not LZW — smaller than LZW for line art and read by every modern app and RIP | | --out <dir> | alongside input | output directory | | --force | off | overwrite existing .tif (default: skip — idempotent batch re-runs) |

Why --gates matters for AI-vectorizer output

Upscalers and vectorizers emit near-blacks (rgb(13,13,14)) and near-whites instead of pure ones. Without gates those become ghost tints across your paper (a faint warm veil over the whole sheet) and not-quite-solid blacks. On a real test image, gating flipped 45% of pixels from ghost-tint to true paper and 48% from near-black to true solid, leaving genuine mid-grays untouched. If your PNGs came out of an AI pipeline, run with --gates.

Rich black & fine lines

A high-TAC rich black on thin strokes risks registration fringe (C/M/Y peeking out from under fine hatching). Mitigations, in order: use a lower-TAC formula (the default 20/30/20/100 = TAC 170 is chosen for line art), or --k-only so only large solids carry the support colors. Ask your printer about their fine-line guidance if unsure.

ICC tagging

The profile is assigned, not converted — pixel values are your formula's numbers; the tag just tells layout apps how to preview them. Profiles are discovered from /Library/Application Support/Adobe/Color/Profiles and the ColorSync folders (Adobe's profiles can't be bundled with this tool for licensing reasons). --profile <file.icc> works anywhere.

Library use

import { decodePng, toCmyk, encodeTiff, convert, findProfile } from 'lineart-rich-black';
const tiff = convert(pngBuffer, { formula: [20, 30, 20, 100], gates: [80, 10], dpi: 600 });

decodePng normalizes any PNG to 8-bit RGBA (via pngjs); encodeTiff is a dependency-free CMYK TIFF writer — both usable on their own.

Companions

Part of a small suite for AI-assisted line-art production: svg-color-rinse (normalize SVG colors), svg-silver-age-bg (deterministic comic backgrounds), gemini-vectorize (photo → redraw → vector pipeline).

Development

npm test    # node --test: plate math, TIFF container (both byte orders), CLI

License

MIT