Print production and prepress

In short

Print production and prepress is everything that happens between an approved design file and a correctly printed, finished job: converting colours, setting resolution, adding bleed and marks, trapping, imposition, proofing, plate-making and specifying paper, printing process and finishing. A designer who hands over a beautiful file in RGB at 72 ppi with no bleed will have it rejected by the press, so this is the one area of graphic design judged purely on technical correctness. Indian university Visual Communication syllabuses examine it as "Printing Technology / Print Production" with theory on processes, screening, colour separation and paper sizes, plus a practical of preparing a press-ready file. It is the most common technical round in interviews at printing houses, packaging converters, newspapers (The Hindu, Malayala Manorama, Dainik Bhaskar), ad agencies and print-on-demand companies, where the first question is almost always "what will you check before sending this to press?"

Explained

Colour: RGB, CMYK, spot and colour management

• RGB is additive light (screens, cameras); CMYK is subtractive ink (Cyan, Magenta, Yellow, Key/black). Print files are built or converted to CMYK because ink reflects light rather than emitting it.
• RGB gamut is wider than CMYK, so bright screen greens, oranges and blues print duller; this shift is normal, not a printing fault. Check with a soft proof before conversion.
• Why black is "K": three-colour black is muddy, expensive and hard to register; a dedicated black plate gives sharp text and real shadow depth.
• Registration black (100C 100M 100Y 100K) is only for crop/registration marks. Small text uses 100K only; large solid areas use a rich black (common Indian press recipe around 60C 40M 40Y 100K — ask the press for theirs).
• Spot colour: a pre-mixed ink printed from its own plate, specified by the Pantone Matching System (PMS). Used for exact brand colours, metallics, fluorescents and for two-colour economy jobs.
• Process colour = built from CMYK screens; spot = one solid ink. A logo in PMS 185 C prints identically on every job; the same colour "simulated" in CMYK varies with press, ink and stock.
• TAC / TIL (Total Area Coverage / Total Ink Limit) = sum of the four percentages at the heaviest point. Keep within about 300% for coated offset, 240-260% for newsprint, or ink will not dry and will set off onto the next sheet.
• Colour management: ICC profiles describe how a device reproduces colour; a CMM converts between them using a rendering intent (Relative Colorimetric for most print work, Perceptual for photographs with out-of-gamut colour). Common output profiles in India: ISO Coated v2 / FOGRA for coated offset, and a newsprint profile (IFRA/ISOnewspaper) for newspapers.
• Overprint and knockout: by default top ink knocks out the ink below. Overprint lets inks print on top of each other (deliberately for rich blacks and trapping; accidentally it makes white objects vanish on press).
• Trapping = a tiny deliberate overlap between adjacent colours so slight misregistration does not show a white gap. Mostly handled by the RIP now, but the designer must avoid hairline multi-colour rules and small reversed-out text in four colours.

Resolution, screening and halftones

• ppi (pixels per inch) describes a raster image; dpi (dots per inch) describes an output device; lpi (lines per inch) is the halftone screen ruling. Students must not treat them as synonyms.
• Press needs roughly 2 × lpi in ppi at final printed size — the "quality factor" of 1.5-2. A 150 lpi magazine job therefore wants about 300 ppi images.
• Typical screen rulings: newspaper 85-100 lpi, sheet-fed coated offset 150-175 lpi, fine art books 200+ lpi, screen printing on fabric 55-80 lpi, flexo on corrugated board 45-85 lpi.
• Line art / bitmap (logos, line drawings scanned as 1-bit) needs 1,200 ppi because there is no grey to hide the jaggies.
• AM screening (amplitude modulated): equal-spaced dots of varying size — the classic rosette. FM / stochastic screening: equal-size dots of varying spacing — sharper detail, no moiré, but harder to control on press.
• Screen angles avoid moiré: typically K 45°, M 75°, C 105° (or 15°), Y 90°. Yellow sits at 90° because it is least visible. Rescanning an already-printed halftone creates moiré — rescreen or descreen it.
• Dot gain (TVI, tone value increase): dots spread as ink soaks into paper, so a 50% file dot may print as 65% on newsprint, 53-58% on coated stock. Compensation is built into the ICC profile or press curve; this is why uncorrected images print darker and muddier than the screen.
• Vector art (AI, EPS, PDF paths) is resolution-independent and scales freely; raster art does not. Logos, type and die lines stay vector.

The prepress workflow, step by step

1. Job specification / docket: size (flat and finished), number of pages, colours (4/4, 4/1, 2/0), paper and GSM, print process, quantity, finishing, delivery date.
2. File build: correct document size, CMYK, spot swatches named exactly, fonts licensed, all links present, bleed 3 mm (5 mm for packaging and large formats), safety/margin 3-5 mm inside trim.
3. Preflight: software check (InDesign Preflight, Acrobat Pro, PitStop, Enfocus Switch) for low-resolution images, RGB or Lab objects, missing fonts and links, spot colours, hairlines under 0.25 pt, TAC, overprint, transparency.
4. Export as PDF/X (ISO 15930) — the exchange standard. PDF/X-1a flattens transparency and demands CMYK + spot only; PDF/X-4 keeps live transparency and allows ICC-tagged colour. Most Indian presses still ask for X-1a; packaging and digital increasingly accept X-4.
5. Proofing: soft proof on a calibrated monitor; digital contract proof on a calibrated inkjet with the output profile; plotter/blueprint for position and imposition; wet proof on the actual press and stock when colour is critical (packaging, brand work).
6. Imposition: arranging pages on the press sheet in the right order and orientation for folding, with gutters, creep compensation, colour bars and marks. Done in Preps, Dynastrip or the RIP.
7. RIP and trapping: the Raster Image Processor interprets PDF, applies profiles, dot-gain curves, screening and trapping, and produces 1-bit separations.
8. Plate-making: CTP (computer-to-plate) exposes aluminium plates directly from the RIP — the current norm; the older film-and-contact route (imagesetter, film, manual stripping) is largely obsolete but still examined.
9. Printing and make-ready: register, ink density (measured with a densitometer/spectrophotometer, checked against the colour bar), fountain solution, press OK sheet signed by the client or QC.
10. Post-press / finishing and dispatch.
11. Marks on the sheet: trim/crop marks, bleed marks, registration marks, colour control bar, fold marks, slug with file name, date and job number.

Printing processes compared

• Offset lithography (indirect planographic): image and non-image areas on one plane; the plate carries ink only on the oleophilic image area, transfers it to a rubber blanket, then to paper. Sheet-fed for brochures, books, cartons; web offset (reel-fed, heat-set or cold-set) for newspapers and magazines. Best quality-to-cost for medium and long runs; high make-ready cost means short runs are uneconomic.
• Digital printing: electrophotography/toner (HP Indigo uses liquid ElectroInk; Xerox, Konica dry toner) or production inkjet. No plates, so variable data and one-off runs are possible; cost per sheet is nearly flat, so it wins below the crossover with offset (typically a few hundred to a couple of thousand sheets, depending on size and press).
• Flexography: relief printing from a flexible photopolymer plate, fast-drying solvent/water/UV inks; the standard for flexible packaging, labels, corrugated cartons and polythene.
• Gravure (rotogravure): intaglio — image is engraved as cells into a copper cylinder, doctor blade wipes the surplus, ink transfers under pressure. Very long runs, excellent on film substrates; cylinder cost is high. Used for cigarette and snack packaging, laminates, gift wrap.
• Screen printing (serigraphy): ink forced through a stencilled mesh; thick ink film, almost any substrate (textile, glass, metal, PVC, boards), ideal for T-shirts, banners, dials, signage; coarse detail, slow.
• Letterpress: original relief process from type and blocks; now a premium craft finish for debossed wedding cards and business cards.
• Pad (tampo) printing: silicone pad lifts ink from an etched plate onto irregular 3-D objects — pens, toys, appliance parts.
• Large-format inkjet: solvent/eco-solvent/UV on vinyl, flex, canvas and boards for hoardings and standees; resolution needed at the file is low (20-60 ppi at size for a hoarding viewed from far).

Paper, substrates and sizes

• GSM (g/m²) is grammage — mass per unit area, not thickness. Thickness (caliper) is measured in microns; bulk = caliper/grammage. Board over roughly 200 gsm is called board/card.
• Common Indian usages: newsprint 42-52 gsm, letterhead/copier 70-100 gsm, brochure art paper 115-170 gsm, visiting card 300-350 gsm, folding carton 250-400 gsm board.
• Coated (art/matt/gloss, chromo one-side) gives sharper dots, less dot gain and higher lpi; uncoated (maplitho, cartridge, bond) absorbs ink, gains more dot, reads better in long text.
• Grain direction — fibres align along the machine direction; fold and bind parallel to the grain, or the fold cracks and the book will not open flat. Long grain / short grain is quoted on the reel or sheet.
• ISO A series (IS 1064 covers paper sizes in India, following ISO 216): A0 = 1 m², each step halves the area, ratio 1:√2. A4 = 210 × 297 mm, A3 = 297 × 420 mm, A5 = 148 × 210 mm. B and C series (C for envelopes: a C4 envelope takes an A4 sheet).
• Indian trade still quotes demy, crown, double crown, 1/8 crown and sheet sizes like 18×23, 20×30, 23×36 inches; press sheet choice decides how many pages impose economically.
• Other substrates: BOPP, PET and metallised films, aluminium foil laminates, PVC/vinyl, corrugated board (flute types E/B/C), synthetic paper, textiles.
• Eco points: FSC certification is voluntary; recycled and agro-residue papers are available. Printing on plastic packaging must carry the markings required under the Plastic Waste Management Rules (resin code, manufacturer/brand owner details), and food packaging ink migration is regulated via FSSAI packaging regulations — confirm current requirements for any live job, as these rules are amended often.

Post-press, finishing and binding

• Cutting and trimming on a guillotine; die cutting for shaped jobs from a steel-rule die — supply a vector die line on a separate spot layer, with crease/perforation lines distinguished.
• Folding: letter/roll, Z/accordion, gate, French; allow for creep (shingling) in saddle-stitched books — the inner pages push out at the fore-edge, so imposition shifts their content towards the spine (giving slightly narrower gutters on inner pages); extra gutter allowance is a perfect-binding issue, where the glued spine swallows part of the inner margin.
• Binding: saddle stitching (wire, pages in multiples of 4, up to ~64-80 pages), perfect binding (glued spine, needs a spine width = pages/2 × caliper + cover, and 3 mm hinge allowance), section/thread sewn for durability, wiro/spiral, case binding for hardbacks.
• Surface finishes: gloss/matt lamination (BOPP or thermal), UV coating (flood or spot UV for selective gloss), aqueous varnish, soft-touch/velvet lamination.
• Embellishments: foil stamping (hot foil from a brass/copper block), embossing/debossing, blind embossing, thermography, flocking.
• Other: numbering, perforation, creasing (always crease board above ~170 gsm rather than folding it), round cornering, index tabs, window patching, rigid box pasting.
• Specialist: Braille embossing on pharma cartons, scratch-off panels, variable barcodes and QR codes — always check the barcode's magnification, bar width reduction (BWR) and quiet zone with the converter.

Quality control, costing and common standards

• Densitometer reads ink density on the colour bar; spectrophotometer reads L*a*b* and gives ΔE (colour difference). ΔE around 1 is barely visible; brand work often specifies ΔE ≤ 2-3 on solids.
• ISO 12647 series defines process control for offset (12647-2), newspapers (-3), gravure (-4) and screen (-5): tone value, solid density, grey balance. ISO 15930 = PDF/X. ISO 9001:2026 is the current quality-management edition and is voluntary.
• G7 / Fogra PSO are voluntary certification schemes for grey balance and process control used by larger Indian printers.
• Costing drivers: plates (number of colours × number of forms), make-ready wastage, paper (the biggest single cost in most jobs), impressions, finishing, and die/block cost. GST on printing services and on printed material depends on classification — printing with the printer's own paper is generally treated differently from job-work on customer-supplied paper, and the slab structure since 22 September 2025 is 5%/18%/40%; confirm the applicable rate and HSN/SAC for the specific job rather than assuming.

Key points

• Prepress - all file preparation, proofing, imposition and plate-making between approved design and press.
• CMYK vs RGB - subtractive ink versus additive light; CMYK has the narrower gamut, so convert and soft-proof before delivery.
• Spot colour - one pre-mixed ink on its own plate (PMS), used for exact brand colour; process colour is built from CMYK screens.
• Bleed - 3 mm artwork extension beyond trim (5 mm for packaging/large format) so trimming never leaves a white edge.
• Safety margin - keep live text and logos 3-5 mm inside trim against cutting tolerance.
• Resolution rule - image ppi at final size ≈ 2 × lpi; 300 ppi for 150 lpi, 1,200 ppi for 1-bit line art.
• ppi / dpi / lpi - image pixels, device dots, halftone screen ruling: three different things.
• Dot gain (TVI) - printed dot larger than file dot; worst on uncoated and newsprint, compensated in the profile or press curve.
• Screen angles - K 45°, M 75°, C 15/105°, Y 90°, chosen to produce a rosette instead of moiré.
• TAC limit - about 300% coated offset, 240-260% newsprint; exceeding it causes set-off and slow drying.
• Rich black vs 100K - rich black for large solids, 100K only for small text; registration black only for marks.
• Trapping and overprint - small overlaps hide misregistration; stray overprint on white objects makes them disappear.
• PDF/X - ISO 15930 press-ready exchange format; X-1a flattens transparency (CMYK+spot), X-4 keeps it live with ICC colour.
• Imposition - laying pages on the press form for folding, with creep compensation, gutters, marks and colour bar.
• CTP - computer-to-plate, direct plate imaging from the RIP; has replaced film and manual stripping.
• GSM - grammage in g/m², a mass measure, not thickness; caliper in microns is thickness.
• Grain direction - fold and bind parallel to grain, else folds crack and books do not lie flat.
• Process choice - offset for medium/long runs, digital for short runs and variable data, flexo for flexible packaging and labels, gravure for very long packaging runs, screen for thick ink on any substrate.

Formulas and examples

Example 1 — resolution and scaling. A client supplies a photograph 1,200 × 1,800 pixels at 300 ppi (so 4 × 6 inches) and wants it to fill an A4 page (210 × 297 mm ≈ 8.27 × 11.69 in) in a 150 lpi brochure.

• Required ppi = 2 × 150 = 300 ppi.
• Scaling needed on the long side = 11.69 / 6 ≈ 1.948, i.e. 195%.
• Effective ppi = 300 × (100/195) ≈ 154 ppi — about half of what is needed.
• Maximum usable size at 300 ppi = 1,200/300 × 1,800/300 = 4 × 6 in (102 × 152 mm). Verdict: unusable full-page; request a larger original or use it at quarter-page size.

Example 2 — paper quantity and cost. A 16-page A4 saddle-stitched booklet, 5,000 copies, printed 8 A4 pages per side of an A1-ish press sheet laid out as 16 pages per sheet (8 up, work-and-turn/sheetwise both sides), on 130 gsm art paper, sheet size 630 × 900 mm.

• Pages per press sheet (both sides) = 16, so sheets per copy = 16/16 = 1.
• Net sheets = 5,000 × 1 = 5,000; add 6% make-ready and finishing wastage → 5,000 × 1.06 = 5,300 sheets.
• Mass of one sheet = 130 × 0.630 × 0.900 = 73.71 g.
• Total paper = 5,300 × 73.71 g = 390,663 g ≈ 390.7 kg.
• At ₹95/kg, paper cost = 390.7 × 95 ≈ ₹37,117; per copy ≈ ₹7.42.
• Plates for 4/4 on one form = 8 plates; at ₹450 each = ₹3,600.

Example 3 — TAC check and rich black. A background is specified 80C 70M 70Y 100K and the press (coated offset) limits TAC to 300%.

• TAC = 80 + 70 + 70 + 100 = 320% — 20 points over the limit.
• Corrected rich black 60C 40M 40Y 100K → TAC = 60 + 40 + 40 + 100 = 240%, within limit and still visually dense.
• A 100K-only black on the same stock looks washed out in a large area, which is why the three-colour under-support is kept.

Example 4 — spine width and cover layout. A 248-page perfect-bound annual report on 90 gsm maplitho (caliper 0.11 mm per sheet) with a 300 gsm cover (caliper 0.35 mm).

• Leaves = 248/2 = 124 sheets → text block = 124 × 0.11 = 13.64 mm.
• Covers add 2 × 0.35 = 0.70 mm → spine ≈ 14.34 mm, round to 14.5 mm.
• Cover flat size for A4 trim = 2 × 210 + 14.5 = 434.5 mm wide × 297 mm high, plus 3 mm bleed all round → artboard 440.5 × 303 mm, with a 3 mm hinge allowance marked each side of the spine.

Example 5 — digital or offset? A 4-colour A4 flyer: offset = ₹3,600 plates + ₹2,500 make-ready (fixed ₹6,100) + ₹1.10 per copy; digital = ₹0 fixed + ₹4.50 per copy.

• Crossover Q = (6,100 − 0) / (4.50 − 1.10) = 6,100 / 3.40 ≈ 1,794 copies.
• At 1,000 copies: offset = 6,100 + 1,100 = ₹7,200; digital = ₹4,500 → digital wins.
• At 5,000 copies: offset = 6,100 + 5,500 = ₹11,600; digital = ₹22,500 → offset wins.

Where it is used

• Commercial printing and repro houses — prepress operator, CTP operator, DTP/preflight executive; Manipal Technologies, Thomson Press, Repro India, Pragati Offset, Parksons.
• Packaging converters — dieline and artwork adaptation, colour management, barcode verification for FMCG cartons, pharma packs and flexible pouches (Huhtamaki, ITC PSPD, TCPL, Uflex).
• Newspapers and publishing — cold-set web offset with newsprint-specific TAC and dot gain; page imposition and ad booking at The Hindu, Manorama, Bhaskar, Jagran; textbook printing for NCERT and state boards.
• Advertising and branding studios — artwork/production artist roles: releasing press-ready PDF/X files, picking paper and finishes, attending press OK.
• Signage and large-format — hoardings, standees, vehicle wraps, exhibition graphics in vinyl, flex and UV-printed boards.
• On-demand and personalised print — Vistaprint/Printvenue-style web-to-print, wedding stationery, photo books, variable-data mailers; merchandise via screen and DTG printing.

Interview questions

• Q: Why must a print file be in CMYK and not RGB? A: Printing lays down subtractive inks, so the RIP needs separations; RGB has a wider gamut, and uncontrolled conversion on the press shifts bright colours unpredictably.
• Q: What is bleed and how much do you give? A: Artwork extended beyond the trim line so cutting tolerance never leaves a white sliver — normally 3 mm, 5 mm for packaging and large format, with live content kept 3-5 mm inside trim.
• Q: Difference between dpi, ppi and lpi? A: ppi is pixels per inch in the image, dpi is the output device's addressable dots, lpi is the halftone screen ruling; images should be about twice the lpi in ppi at final printed size.
• Q: When do you use a spot colour instead of CMYK? A: For an exact brand colour, a metallic or fluorescent that CMYK cannot reach, or a one- or two-colour job where fewer plates are cheaper than four.
• Q: What is dot gain and how do you deal with it? A: The printed dot grows as ink spreads into paper, darkening midtones; it is compensated by the output ICC profile or press curve, and is far larger on newsprint than on coated stock.
• Q: Why are screen angles different for each colour? A: Offsetting the angles makes the four screens form a rosette; identical or close angles produce moiré patterns.
• Q: What is trapping and who does it? A: A small overlap between touching colours to hide misregistration; the RIP or prepress software normally applies it, but the designer must avoid fine multi-colour hairlines and tiny four-colour reversed type.
• Q: PDF/X-1a or PDF/X-4 — which do you send? A: X-1a if the press wants flattened CMYK-and-spot-only files (still common in India); X-4 when the workflow supports live transparency and ICC-tagged colour, which keeps gradients and shadows cleaner.
• Q: What is GSM and does 300 gsm always mean thicker than 250 gsm? A: GSM is mass per square metre, not thickness; a bulky 250 gsm uncoated board can be thicker than a dense 300 gsm coated one, so caliper must be checked for spine and die work.
• Q: Why does grain direction matter? A: Paper fibres align in the machine direction; folding or binding against the grain cracks the fold and stops the book lying flat.
• Q: A client wants 200 copies of a 4-colour brochure tomorrow. Which process? A: Digital — there are no plate or make-ready costs, turnaround is hours, and offset only becomes cheaper above roughly a couple of thousand copies.
• Q: What is the difference between a die line and a trim line? A: The trim line is a straight guillotine cut; a die line is the vector outline of a shaped cut, supplied on its own layer as a spot colour with creases and perforations distinguished from cut lines.
• Q: A white logo disappeared on the printed sheet though it looked fine on screen. Why? A: It was almost certainly set to overprint, so it printed transparently over the background instead of knocking out; preflight with overprint preview catches it.

Common mistakes

• Exporting RGB images or Lab/untagged objects inside a "CMYK" PDF, and not checking with output preview or separations preview.
• Scaling a 300 ppi image up on the page and assuming it is still 300 ppi — effective resolution, not file resolution, is what prints.
• Omitting bleed, or adding bleed but leaving page numbers and logos within 1 mm of trim.
• Using registration black (400%) or four-colour black for body text, giving fuzzy, misregistered, slow-drying type.
• Quoting GSM as thickness, and so getting the spine width or die creasing wrong.
• Confusing dpi with lpi and supplying 1,200 ppi photographs (huge files, no gain) or 1-bit logos at 300 ppi (jagged edges).
• Forgetting imposition realities — page counts not in multiples of 4 for saddle stitch, no creep allowance, folding across the grain.
• Treating a desktop inkjet print or an uncalibrated monitor as a contract proof and then blaming the press for the colour.

Related topics

Publication design and layout · Packaging design · Design software: Adobe tools · Colour theory and colour management · Typography fundamentals · Branding and communication design