PDF/X — Print-Ready PDF ISO 15930: 1a, 3, 4 — Why RGB is Forbidden

PDF/X is a subset of PDF specifically designed for prepress document preparation and exchange between designer and printer. The abbreviation expands to "PDF for Exchange". Standardized as ISO 15930 in several parts released from 2003: PDF/X-1a (color-only, no transparency), PDF/X-3 (color-managed RGB allowed), PDF/X-4 (transparency supported). The goal — eliminate all ambiguities that lead to preflight surprises at the print shop: color space strictly CMYK or Spot (RGB forbidden), fonts fully embedded, transparency allowed only in PDF/X-4, OutputIntent (target ICC profile) always specified. A city map in PDF/X format is a file that can be sent to an offset print shop without explanation, and the printer will produce a result precisely matching the specified color coordinates. For atlases, city booklets, magazine inserts, cartographic posters — PDF/X is the de facto exchange standard.

History: the prepress problem

In the mid-1990s, with the spread of PDF as a universal format, a new pain emerged. A designer made a map in Adobe Illustrator in RGB colors (because it's convenient on screen), sent PDF to the printer. The printer opened the file, saw RGB colors, converted them to CMYK using their own profile — and got a result not matching the designer's expectations. Especially painful for bright blues and greens — fine on screen, dull beyond recognition in offset. Endless correspondence ensued with color proofs, test prints, extra fees for corrections.

In 2001 the international working group ISO/TC 130 (Graphic technology) was created, including representatives from Adobe, Heidelberg, Agfa, printing associations (BPIF in UK, NPES in US, drupa). The goal — create a formal PDF subset where all sources of ambiguity are eliminated. The result — the ISO 15930 series "Graphic technology — Prepress digital data exchange — Use of PDF".

Timeline. ISO 15930-1:2001 — PDF/X-1a, first part, based on PDF 1.3. Strict rules: only CMYK or Spot colors, no transparency, no JavaScript, no embedded RGB images. ISO 15930-3:2002 — PDF/X-3, added color-managed RGB via ICC profiles (RGB can be stored if an exact target-color-space description is included). ISO 15930-7:2008 — PDF/X-4, allowed transparency from PDF 1.6+ (critical for modern graphics). ISO 15930-8:2010 — PDF/X-5, experimental, allows references to external files.

Today the main workflow in print shops is PDF/X-1a (for legacy CMYK pipelines) and PDF/X-4 (for modern RIP servers with transparency support). PDF/X-3 is practically supplanted by PDF/X-4 as a more flexible option.

PDF/X levels: 1a, 3, 4 — comparison

Which to choose. PDF/X-1a is required by some newspaper print shops, Russian offset print shops with old RIP servers (pre-2010), magazines with a consistent CMYK pipeline. PDF/X-3 — a compromise between flexibility and compatibility; rarely used in new projects. PDF/X-4 — the recommendation for modern print shops: book, cartographic, magazine. It is the de facto standard now.

ICC profiles and OutputIntent

The main PDF/X idea — bind each color in the file to a specific printing process. This is done via OutputIntent — a PDF trailer structure containing the target system's ICC profile. Without OutputIntent, no PDF can be PDF/X — a format axiom.

FOGRA39 (ISO Coated v2 300%) — main ICC profile for European offset printing on coated paper. Used in most European print shops including Russian ones with European equipment. Sum value 300% (total CMYK ink in the darkest point) — typical for coated paper.

FOGRA51 (PSO Coated v3) — updated European profile from 2015, replaces FOGRA39 in new workflows. Sum value 300%, uses ISO 12647-2:2013.

FOGRA52 (PSO Uncoated v3) — for offset printing on uncoated paper (newspapers, cheap booklets). Sum value 260%.

GRACoL 2013 CRPC6 (US standard) — main American profile for commercial printing on coated paper.

JapanColor 2011 Coated — Japanese standard, sum value 350%.

Profile choice depends on the print shop: they usually publish "PDF/X requirements" on their site with the specific ICC. If unclear — ask the prepress department. There is no universal "always FOGRA39" answer.

PDF/X file structure

Key requirements:

All fonts embedded. No system fonts, no references to font directories. If the map uses Arial for labels — Arial must be embedded inside the PDF. Subsetting (only used glyphs) is allowed.

Color space CMYK or Spot. In PDF/X-1a all colors must be CMYK (with C, M, Y, K in 0-100%) or Spot (PANTONE, HKS, RAL). In PDF/X-3/4 RGB is allowed, but only with an explicit ICC profile describing what RGB it is.

TrimBox / BleedBox / CropBox. A PDF page contains several rectangles. TrimBox — the actual final trimmed page size. BleedBox — larger than TrimBox by 3-5 mm each side (bleed zone for trim). CropBox — what's visible in Acrobat. For PDF/X the TrimBox is required.

No JavaScript. As in PDF/A, any executable code is forbidden.

No external references. In PDF/X-1a/3/4 all resources must be inside the file. In PDF/X-5g/n external references are allowed but must be precisely described.

Who needs PDF/X: five scenarios

Atlas publisher. A city or tourist atlas in offset. Hundreds of district maps, unified style, fixed color palette. PDF/X-4 of each map guarantees that the green "park" on the cover at the start of the atlas and the same park 200 pages later will print in identical shade.

Municipal print department. A city booklet for tourists with a center map. Run of 5-50 thousand copies, fixed budget. Color reproduction errors mean reprinting the run, losing money. PDF/X-1a (for old pipeline) or PDF/X-4 (for new) — guarantee of one pass through the printer.

Magazine cartographic department. National Geographic, Geo, Smithsonian, Vokrug Sveta — magazines with regular cartographic inserts. PDF/X is required by publisher requirements; press service issues specs (FOGRA51 for Europe, GRACoL for US) and the author must comply.

Souvenir merchandise producer. Posters with city maps, postcards, art-gallery placards. For offset printing on various substrates (coated paper, board, canvas) different ICC profiles are needed; PDF/X with the right OutputIntent is the quality/cost compromise.

Architect / urbanist. Presentation materials for a competition or approval: A1 poster with district plan, project render, situational map. PDF/X-4 with CMYK FOGRA39 — standard for sending to repro-print.

Software for creating PDF/X: five programs

Adobe InDesign. Paid, $20/month. Main tool for prepress. File → Export → choose Adobe PDF (Print) → Adobe PDF Preset → "[PDF/X-4:2008]" or "[PDF/X-1a:2003]". InDesign guarantees the result complies with ISO 15930. adobe.com/indesign

Adobe Illustrator. Paid, $20/month. For map-posters and single-page designs. File → Save As → Adobe PDF → preset "PDF/X-4". Illustrator checks compatibility and warns of violations. adobe.com/illustrator

Acrobat Pro DC. Paid, $20/month. Has a built-in Preflight engine for checking PDF/X compliance. File → Print Production → Preflight → choose profile "Convert to PDF/X-4". Acrobat fixes detected issues automatically (where it can). adobe.com/acrobat

Scribus. Free, GPL. Main open-source InDesign analog. Supports PDF/X-1a and PDF/X-3 export (PDF/X-4 currently limited). For Russian government structures requiring open-source — this is the way. scribus.net

callas pdfToolbox. Paid, $1000+. Professional preflight tool. Accepts any PDF, converts to PDF/X with automatic fixes. Used by large print shops for input file QC from clients. callassoftware.com

Pitfalls and tips

RGB → CMYK conversion. When you export RGB-source colors to CMYK for PDF/X-1a, conversion through ICC profiles occurs. Hue preservation is guaranteed only for colors inside the CMYK gamut. Bright blues, saturated greens, pure reds — outside the CMYK gamut, lose saturation. Solution: design the map originally in CMYK, accounting for limitations.

Transparency in PDF/X-1a. Forbidden. Semi-transparent layers must be flattened in Illustrator/InDesign (Object → Flatten Transparency) before export. This turns them into opaque objects with matched colors — visually similar but not identical.

TrimBox vs BleedBox. Designers often forget the BleedBox — the 3-5 mm overflow beyond final size. Without BleedBox the printer gets white edges after trim. In Illustrator: File → Document Setup → Bleed → set 3 mm. In InDesign: File → Document Setup → Bleed and Slug → 3 mm.

Sum value 300%. The CMYK sum in the darkest point must not exceed 300% (for coated paper) or 280% (for newsprint). Black composed of 100% C + 100% M + 100% Y + 100% K = 400% will over-saturate paper and cause smearing. Solution: use "registered black" (40, 30, 30, 100) or "rich black" (60, 40, 40, 100).

Font embedding. Acrobat and InDesign by default subset fonts. This is correct for PDF/X, but if the font collection in the file is large, document size may grow. For final production this is the norm.

OutputIntent vs Working Color Space. In InDesign File → Document Setup → Working Color Space sets the color space during editing. OutputIntent on export — what the printer is bound to. They may differ. The main thing — OutputIntent is correct.

FOGRA39 vs FOGRA51. Old Russian offset print shops may still work with FOGRA39 as the familiar. New print shops (with 2018+ equipment) may prefer FOGRA51. Clarify with the specific manufacturer.

How to create a PDF/X map via osm2cdr.ru

osm2cdr.ru supports direct PDF/X export with level selection. Step 1: on osm2cdr.ru choose PDF/X format. Step 2: in suboptions specify level (PDF/X-4 recommended by default) and ICC profile (FOGRA39 for Europe, GRACoL for US). Step 3: specify BleedBox 3-5 mm if needed. Step 4: draw the map area — for A4/A3 poster a district fits; for A2 atlas a larger fragment. Step 5: run export.

The service automatically performs color conversion to CMYK via the chosen profile, embeds fonts, adds OutputIntent, sets up TrimBox/BleedBox.

Step 6: verify with Acrobat Preflight (Adobe Acrobat Pro):

1. File → Print Production → Preflight
2. Choose profile "PDF/X-4 compliance"
3. Run. In 10-30 seconds you get a report.

If ✓ Pass — the map is ready to send to the printer. If ✗ — usually it's about colors outside the CMYK gamut. Acrobat offers automatic fixes.

Related formats and resources

• PDF/A — archival PDF for long-term preservation
• PDF — regular universal PDF
• EPS — PostScript for print
• TIFF — raster format for prepress
• PDF/X landing page
• PDF landing page

Sources

• ISO 15930-1:2001, PDF/X-1a — iso.org/standard/29061.html
• ISO 15930-3:2002, PDF/X-3 — iso.org/standard/29062.html
• ISO 15930-7:2008, PDF/X-4 — iso.org/standard/45953.html
• ISO 15930-8:2010, PDF/X-5 — iso.org/standard/45954.html
• callas software, PDF/X preflight whitepapers — callassoftware.com/en/products/pdftoolbox
• FOGRA, ICC reference profiles — fogra.org
• Adobe, PDF/X documentation — helpx.adobe.com/acrobat/using/pdf-a-pdf-x-pdf-e-pdf-vt.html