The printing raster – we optimise each picture down to the smallest detail
When an order is placed, we decide with the customer which printing process is to be used: the printing process is determined, together with the number of copies and the printing substrate (paper, cardboard, plastic or other materials depending upon the purpose of the print product). Printing inks, further processing and the packaging and dispatch also form part of the order.
On the basis of the order information the prepress is produced: this is the summary of all information prior to printing, data preparation, scanning, image processing and layout, carried out by experienced graphics experts. Using texts, images and graphics from different sources, printable data on the computer is then produced for the printing process. At LONGO we optimise each picture down to the smallest detail, with the printing raster used playing an important role.
Rastering - dividing images into pixels
In 1881, Georg Meisenbach in Munich invented the glass engraving raster whereby images were divided into dots: in simple terms, the closer the dots are together, the more intense the colour.
In most printing processes, a colour is either printed or not at a certain point. A mixture – half-tones – is not possible. In order to obtain fine gradations – tone values that accurately correspond to the template – extremely fine printer dots are produced.
In order to be able to reproduce mixtures and half-tones, an ever-finer raster is needed as the quality requirements of the finished print product increase. Extremely fine aligning produces highly varied mid- and half-tones. Simple binary information is used for this printing raster: “1 = print; 0 = do not print”. So far, so simple. But the technical requirements in terms of the quality of the finished print product necessitate specialised raster methods.
The amplitude-modulated (AM) raster
The frequency-modulated (FM) raster
The AM raster is also known as the periodic or autotypical raster. The component parts are evenly formed and the distances are likewise equal. The tone values are produced by the size of the raster dots: the larger the dot, the darker the tone. The surface has a fixed number of raster dots.
The FM raster dot is smaller, with variations in the printing plate production more clearly visible. The FM raster requires very precise process calibration. We rarely use the frequency-modulated raster as its advantages – very soft imagery, no moiré formation and photo-realistic representations without the typical rosettes produced by the AM raster – can also be achieved with the Sublima.
Sublima is a new raster solution that combines two raster technologies: the conventional amplitude-modulated raster (AM) and the frequency-modulated raster (FM). We thus call this combination XM or cross-modulated rastering.
Sublima is so designed that the smallest reproducible dot in the critical tone ranges, i.e. light and shade, will be reproduced in good quality. In other words it will not drop below a certain dot size and thus omits certain other nearby raster dots. In the other tone ranges it behaves like a normal AM raster.
Benefits of the Sublima raster:
- no visible rosettes
- considerably reduced risk of moiré
- sharp details for small coloured fonts
- clean, stepless processes and full-tone surfaces
- photo-realistic reproduction of images
- suitable for wide range of tasks
- no additional print costs
- conventional printing behaviour
- increased print quality
- problem-free printing repeatability
XM Sublima (left), AM (right)
LONGO – perfect collaboration, perfect printing
To ensure perfect results on paper, there must be perfect collaboration in the printworks: image processing, preliminary work, printing plate production, exposure, printing and controlling – all work procedures and processes that are perfectly co-ordinated at LONGO’s printworks in Bozen/Bolzano and Augsburg.
In addition to the latest technology and up-to-date know-how, seamless interlinking of highly different procedures is a major factor in the quality we deliver – this is a vital contribution to the success of our printworks in South Tyrol and our digital printing specialists in Augsburg.