The document discusses the processes involved in printing, particularly the formation of colors using halftones with cyan, magenta, yellow, and black inks (CMYK). It describes various screening methods, including conventional and stochastic screening, and details the impact of print density and screen angles on print quality. Additionally, it highlights typical screen rulings for different types of paper, emphasizing the need for higher rulings for finer detail rendering.

1. Formation of print

2. Contents
• Formation of print
– Colour formation
– Halftone formation
– Screening and detail rendering

3. Picture consist of millions of different
colours and tones
In photography
colours are created
by continuous tone
In printing colours
are created by
halftones (dots)

4. All colours can be created using three
process colours (in theory)
Cyan Magenta Yellow CMY
=

5. Use of black ink
• Black is added to increase contrast
CMY Black CMYK
+ =

6. Use of black ink
• Example 2
CMY Black CMYK
+ =

7. Print density
• Print density (darkness) is created by
increasing the inked area (halftone
percentage)
Black 20% Black 40% Black 60% Black 80%

8. Print colour
• Print colour (tone) is created by mixing halftone percentages
of process colours
M80%/C20% M60%/C40% M40%/C60% M20%/C80%

9. Conventional and stochastic screening
Conventional screening Stochastic screening
– tone is formed by altering – tone is formed by altering
dot size dot position and spacing,
number of dots
– distance of dots constant
– no screen angles (in
– dot size depends on
theory)
screen ruling

10. Examples of screening methods
Staccato 25µm Conventional 60 l/cm

11. Examples of halftone dots and
text
Offset Flexo Gravure
(20%, 75 l/cm) (20%, 60 l/cm) (~20%, 100 l/cm)
• Dots are uniformly • Ink is pressed to • Broken shape of dots and
covered with ink edges, print density missing dots are typical for
• Edges are ragged inside dot varies light tones
(uncoated papers) • Edges are smooth • Doughnut shaped dots
• Uniform text • Shadow in the edge • Text is screened, serrated
of text edge

12. Examples of halftone dots and text
Inkjet Electrophotography
(20%) (~20%)
• Dots are quite uniformly • Dots are quite uniformly
covered with ink covered with toner
• Dot is formed by using • Edges are ragged
several droplets • Separate toner particles
• Edges are ragged or (dry toner methods)
even depending on paper • Uniform text
• Satellites, escaped
droplets

13. Screen angles
•Screen angle usually
90°
differs from 0° and 90°
75°
– horizontal and vertical
45° lines are most visible to
eye
– yellow is usually at 90°
because it is so weak
colour
15°
•Correct screen angles
minimize moiré-effect

14. Moiré and Rosette patterns
• Moiré and Rosette are both caused by regular halftone
structure

15. Moiré and Rosette patterns
• Moiré and Rosette are both caused by regular halftone
structure
Moiré

16. Moiré and Rosette patterns
• Moiré and Rosette are both caused by regular halftone
structure

17. Moiré and Rosette patterns
• Moiré and Rosette are both caused by regular halftone
structure Moiré is minimized
=> Rosette pattern

18. Screen ruling vs. detail rendering
• Higher ruling is needed for finer details
60 l/cm 70 l/cm 80 l/cm

19. Screen ruling
• Typical screen rulings
– newspaper printing 30-48 l/cm
– SC-paper in heatset 48-54 l/cm
– coated paper in heatset 54-60 l/cm
– fine paper in heatset 60-70 l/cm
– fine paper and board in sheet-fed 60-80 l/cm
– gravure printing 60-100 l/cm
60 l/cm 80 l/cm
40 l/cm

20. Examples
Newsprint,
LWC, 48l/cm
60l/cm
Coated Fine, SC,
70l/cm 54l/cm