There are some common issues in the printing industry that often cause confusion. Understanding them clearly – from basic knowledge to practical operations – can help us avoid many detours.
Basic Printing Knowledge
1. Basic Principle of Printing: What is CMYK Four-Colour Printing?
CMYK is a colour model based on subtractive colour mixing and is the foundation of most printing.
Brief explanation: White light shines on an object; the object absorbs (subtracts) part of the coloured light and reflects the remaining light into our eyes, thereby creating colour. The CMYK model simulates this process. In printing, we use dot screens of four ink colours – Cyan (C), Magenta (M), Yellow (Y) and Black (K) – at different sizes and densities to "absorb" light, producing thousands of colours in our vision. Black (K) is introduced because the black produced by overprinting C, M and Y is not pure enough and tends to cause excessive local ink thickness.
2. Why is a Printed Image Composed of Tiny Dots?
What we commonly call "print resolution" refers to the fineness of these dots.
Why dots are needed: Printing cannot display continuous tone gradations by varying the brightness of each pixel like a computer screen. Therefore, printing technology uses halftone dots to simulate them. By controlling dot size (e.g., a 50% dot means half the area is covered with ink) and dot spacing, and exploiting the human eye's optical illusion, a smooth transition from light to dark and rich colour variations are achieved macroscopically. The fineness of the dots is determined by the screen ruling (lines per inch, lpi). The higher the lpi, the finer the dots and the more detailed the image.
Pre-press File Preparation
3. Why Must Files Be in CMYK Mode Instead of RGB?
RGB (Red, Green, Blue) is based on additive colour mixing and is mainly used for electronic displays; CMYK is based on subtractive colour mixing and is used for printing. Submitting an RGB file directly for printing leads to colour mapping errors, causing the final printed colours to deviate significantly from expectations. Therefore, before sending a design file for printing, its colour mode must be converted to CMYK. For designs with specific colour requirements, spot colours (e.g., Pantone) can be used. They have their own standard colour numbers and are more accurate.
4. What is "Bleed"? Why Do Files Need Bleed?
This is a very vivid term. "Bleed" has nothing to do with wounds; it concerns cutting accuracy.
Concept of bleed: Bleed refers to the 3 mm extra area added to each side of the design beyond the final finished size. Its function is to act as a safety margin, compensating for minor variations that may occur during trimming.
Consequences of no bleed: If a design file has no bleed, cutting inaccuracies may result in white edges (unprinted paper) on the finished product, or important text may be cut off. Standard practice is to extend all elements intended to run to the edge of the page (background colours, images, etc.) into this 3 mm bleed area.
Printing Colour & Variation
5. Why Does the Printed Colour Look Different from What I See on My Screen?
This is one of the most common questions in the printing industry and is almost impossible to avoid completely.
Main causes: Three main factors. First, different display media – a screen emits light actively, while a printed piece reflects light passively. Second, colour space differences – the RGB colour gamut of a screen is larger than the CMYK gamut of printing; some bright colours on screen cannot be reproduced at all. Third, objective physical limitations – the absorbency and gloss of inks and paper, plus the dynamic balance of ink coverage during printing, all cause final colours to deviate from the original design.
Solutions: The most critical step is physical proofing (also called press proofing), i.e., producing a standard sample using the actual paper and inks before full production. On the design side, it is recommended to use a colour-calibrated monitor and ask the printer for their ICC colour profiles.
6. What is Spot Colour Printing? How Does It Differ from Four-Colour Printing?
Simply put, four-colour process uses four basic inks overprinted as halftone dots to simulate thousands of colours, while spot colour printing uses a single, pre-mixed special ink applied directly.
Comparison and selection:
Four-colour process: suitable for colour-rich photographs and illustrations, cost-effective.
Spot colour: suitable for brand logo colours (e.g., Coca-Cola red) and large solid areas, ensuring accurate and consistent colour; it can also achieve special effects such as metallic foil, fluorescent colours, etc., but is more expensive. The industry uses Pantone colour swatches as an international standard.
7. What is Proofing? Why is it So Important?
Proofing can be understood as the "model room" before mass production.
Definition and purpose: It is the final verification step before printing, producing a small number of samples that closely match the final printed product to simulate the end result.
Function: The core purpose of proofing is to identify problems early and avoid risks in large-scale printing. It not only verifies the accuracy of text, images, layout and other file contents, but also guides the press operator to match colours more reliably than a screen preview. It can also verify the feasibility of post-press processes such as foil stamping, embossing, and die-cutting. Once the proof is signed off, it becomes the sole quality reference for the subsequent mass production.
Printing Processes & Defects
8. How Do Common Printing Defects Like Filling-In and Ghosting Occur?
Various defects can occur during printing. Two of the most common are described below.
Filling-in (also known as plugging): The printed image/text becomes blurred, ink appears in non-image areas, and fine text becomes solid blobs. Causes include ink-water imbalance, excessively thick ink, excessive printing pressure, inadequate doctor blade cleaning, and too high pressroom temperature.
Ghosting: A defect that appears in flexographic printing – a faint, unwanted image of another part of the print shows up in a large solid area. The main cause is insufficient ink transfer from the anilox roll cells.
Prevention: Regardless of the defect, prevention depends on strict process control, including maintaining good ink-water balance, optimising ink performance and viscosity, keeping the printing equipment in optimal condition, and strictly controlling pressroom temperature and humidity.
Cost & Budgeting
9. Why Do Seemingly Identical Printed Products Vary So Much in Price?
Printing quotations consist of many items. Price differences mainly arise from the following "invisible" aspects:
Design fee: Original design vs. template-based design have completely different rates.
Pre-press costs: Including plate-making (film or CTP), proofing, etc.
Material costs: Brand, basis weight, and texture of paper; whether inks are eco-friendly – prices vary significantly.
Press costs: Age and brand of equipment (e.g., Heidelberg vs. domestic) affect printing efficiency and quality.
Post-press processes: Whether special processes such as lamination, foil stamping, die-cutting, or UV coating are required.
Print quantity: This is the core variable affecting unit cost. There is a cost break-even point. For small quantities (e.g., under 1,000 copies), digital printing is more advantageous. As quantity increases, the unit cost of conventional offset printing becomes much lower than digital printing.
Environmental Protection & Sustainability
10. What Environmental Challenges Does the Printing Industry Currently Face?
Against the backdrop of increasingly stringent global environmental regulations, the printing industry is actively undergoing a green transformation.
Regulatory drivers: Represented by the EU's latest Packaging and Packaging Waste Regulation (PPWR), jurisdictions worldwide are mandating that packaging be fully recyclable. This has spurred the rise of nitro-free inks, because conventional inks contain nitrocellulose (a compound once used as an explosive ingredient) that severely hinders paper recycling.
Industry response: To meet these requirements, major ink manufacturers such as Siegwerk, Flint Group, and hubergroup have introduced polyurethane (PU) ink systems that do not contain nitrocellulose, thereby improving packaging recyclability.
Green caution: When pursuing green printing, one must also beware of greenwashing – claiming to be environmentally friendly without substantive action. Genuine green printing encompasses the entire lifecycle, from material sourcing to production and delivery.
