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History
The basic idea which opened to the development of lenticular technology was to use screen properties (alternating parallel matt and transparent lines separated by a constant gap) as a means to select images. These properties were first announced by the French Berthier on 20 May 1896 in the Cosmos review.
Cinegraphy was born as a graphic process capable to supply flat prints where different images appear depending on the observer's sight angle.
This type of print enables two main effects:
- Animation , when it reproduces several images of the same subject in different positions, such as a movement in progress
- Flipping when it shows two or more heterogeneous images visible from different sight angles (parallaxes).
Technological innovations in the field of computer-aided digitized images, the possibility to print on plastic materials using sheet-fed offset presses, and above all replacing the screen with the lenticular sheet have enabled mass production and diffusion of lenticular products as we know them today.
Basic Principles
The lenticular image is obtained by integrating two components:
- The pre-press
- The lenticular sheet
The different images to be seen by the observer, should be opportunely "combined" and "edited" into a single compressed image consisting in a series of separate print bands of extremely reduced size (approx. 32 m m.).
If the printed "composed" image is observed on the flat side of the lenticular sheet or printed on paper, it turns out to be totally blurred as the different images look as if they were overlapped.
Geometry of the lenticular sheet lens pattern influences the optical
characteristics of the image reproduced.
This document only deals with the reproduction of lenticular images directly on lenticular sheets by means of offset printing systems.
The lenticular pre-press
Image cutting
The different images to be printed should be opportunely 'cut' or 'sliced', approached to one another, and "edited" as a single print image on the four-colour films.
Images should be overlapped and shifted parallel to the lens pattern axis so that as many print bands as the moving images or deepness levels can be arranged under each lens.
The figure shows a reproduction consisting of 7 different images.
The lens size has been divided into 7 bands, each with width equal to 1/7 of the lens.
The band associated to an image (ex. image 1) should always be positioned in the same reference position relative to the lens shape, so that the observer can see the whole of the 'slices' making up the same image correctly.
This operation is known as "image cutting". Provided that powerful processing hardware is used (600Mhz Pentium III and 512Mbyte RAM's minimum), image cutting can be made using standard graphic software such as Photoshop adapted to meet specific lenticular technology requirements.
Editing
After cutting, the image is edited using a computer (computer to film process) on a standard four-colour offset film minimum ruling of 120 lines per cm.
Film Printing
To make films from CD, we suggest to use computer-to-film systems with a 4000 DPI photoplotter resolution or higher.
The lenticular sheet
Material
The lenticular print medium consists in a PETG-Starlight plastic sheet with a smooth surface on one side and an embossed surface on the other, where the lens pattern is located.
The sheet is transparent because it should be printed on the smooth side opposite the observation side with the lens pattern.
The sheet is obtained by extruding the granulated raw material. The film is embossed in line using a calendering lenticular roll, cut parallel to the lens pattern direction, and trimmed.
LPI
The lenticular sheet is generally identified not only by its size, but also by the pitch of its ruling, that is measured in lpi (lines per inch).
Theoretically, the lenticular sheet thickness can range from a few microns (about 300 for 150 lines-per-inch pitches) to a few millimetres (pitches of about 4-8 lpi).
Thickness is strictly connected to the lens geometric characteristics (shape and focus) that determine the possibility to show different effects visible from different observation distances.
Thickness
Most sheet-fed offset presses accept sheets with maximum thickness 0.8 to 0.9 mm; in some cases, even 1.2 mm can be used.
This means that you can offset-print lenticular sheets with pitches ranging from 150 to 60 lpi (used for small printed products, such as cards, and up to A4 and A3 formats, to be observed from distances between 30 cm and 3 metres).
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