Title: STUDY MATERIALS - Pre-press procedure in practice and equipment setup
Course: Pre-Press Procedure / e-design > Section: Part V - Pre-press procedure in practice and equipment setup

After the online lectures, the study materials along with the map of new concepts will be uploaded to Moodle.

Preparation for post-treatment

PREPARATION FOR POST-TREATMENT

An important part of planning the design of a print is considering the post-treatment requirements during the design, which must result in a mock-up.

By a mock-up, we generally mean a simplified structure of a print in physical form (or also as a digital drawing). It must contain all the components relating to the post-treatment:

- die-cutter drawing,
- folding scheme,
- creasing,
- perforation,
- spot varnish, effects,
- trim marks and
- other information specific to this print.

A mock-up is “life insurance” in order to avoid large expenses later and to simplify the work of the post-processing specialists of the printing house. Here are some requirements on how to consider the post-processing during the design process and what conditions the post-processing drawings must meet.

Die-cutting shape guide

Die-cutting shape guide

Often there is a need to produce prints of different shapes, where the print is not rectangular but follows the outlines of some objects, for example, when it comes to packaging and its development. To cut out the special-shaped print a mechanical die is used, which is essentially a system of knives attached to a wooden board.

By using a mechanical die, a print can be processed in three ways: cutting, creasing or perforating.

When making a die-cutter drawing, a line thickness of c‘ 0.5 pt should be used and possible special ways should be marked with lines of different colours. It is also worth keeping in mind that since we are dealing with real metal knives, it is not possible to plan a print with very fine details and sharp corners.

A laser die-cutter has been invented for cutting prints with many details, cutting is performed with a laser and theoretically there are no limitations as to details. The structure of the drawing is similar to the drawing of a mechanical die-cutter. The advantage of a laser die-cutter is its very high accuracy, but the disadvantage is that it takes much longer time and therefore this technology is mostly used for processing small circulations.

Crop marks

Trim marks

Trim marks are marks that indicate the pure size of a print.

Generally, the marks are defined by all the colours used in the print - registration colour. When using trim marks, it should be remembered that some printing houses want the trim marks offset (the distance of the mark from the pure size) as far as the bleed reaches. In Adobe CS design programs, the offset is set to 2.117 mm by default. If the requirement of the printing house differs from this, it must be set manually.

Bleed

Bleed

All print files with a design that reaches to the edge of the print must have a bleed. This is necessary as shifts may occur during the trimming of the print.

The traditional bleed is 3-5mm depending on prints. All prints that go into die-cutting for post-treatment must also have a bleed. Bleed must be already taken into account during the design process, so that all design elements extend beyond the pure size of the print. Due to the shifts in post-treatment, it is not recommended to design/place important details closer to the edge of the pure size than the bleed provided by the printing house, i.e. if the printing house has provided a 5 mm bleed for the print, the safety area extends 5 mm inwards. The accompanying figure shows the pure size, sheet size (slug), safety area and bleed.

Taking binding methods into consideration

Taking binding methods into consideration

When designing a wire-bound brochure, the outward shifting of the inner pages and thus the cutting narrower must be taken into account.

This phenomenon is called creep, and its extent depends on the thickness of the paper and the number of pages. For booklets up to twenty pages, creep does not have a significant effect, but for larger prints, be sure to place important details at a safe distance or use a layout software (Adobe InDesign) add-on that takes into account page shifts when creating a print file. Creep must be especially taken into account when placing page numbers or with lines or similar details very close to the edge.

While wire binding is mostly used for brochures of up to 100 pages, one way to bind larger prints is quite often adhesive binding. In the case of adhesive binding, it is important to observe the so-called dark area, which is towards the edge of the binding. Depending on the technology, it is 6-8mm. It is not possible to use this area effectively in the design, because the bind will hide it. It is quite easy to take this area into account when determining the margins of prints, but if it is necessary to use photographs across two pages, we can often see such a view as a result of the binding.

There should also be the third person in the photo

The text has been partially lost

Pre-press procedure for hardcovers

Prepress procedure for hardcovers

All hardcovers consist of three outer parts: front, spine and back and an inner paper holding the cover together, which is glued to the cardboard between the covers.

The accompanying figure shows the structure of the hardcover.

When starting to design the covers, it is essential to make a layout, because unlike conventional prints, the edges of the designed and printed sheet are used as folded by 18-20 mm inside the covers, where in turn the inner paper is glued. Consequently, it is necessary to add a part to be folded + bleed to the pure size of the covers. When designing, it is also necessary to pay attention to the spine crease, which does not really change the width of the print, but which can visually create a similar impression. The distance from the binding edge, depth and width of the spine crease depend on the technology used.

The width and depth of the spine crease may spoil the visual impression. Book design is off-centre and seems like an unintentional mistake.

Folding and creasing (ruling)

Folding and creasing (ruling)

In the case of simpler prints (leaflets, covers, invitations, etc.), folding or creasing marks are usually not added to the design file and are shown either on the mock-up or in the cover letter of the printing house. However, in the case of more complex prints, folding is traditionally indicated by a dashed line placed at the same distance from the pure size of the print as the trim marks. The accompanying figure shows some folding schemes and the development of the print with the necessary marks. It is obvious that in the case of examples 2, 3 and 4, the print file does not provide enough information about the final structure of the print and definitely requires a physical mock-up. In the case of examples 3 and 4, when creating the design it must be taken into account that the pages to be folded inside must be slightly narrower; otherwise, it will not be possible to fit them there.

Special finishing – spot varnish, foil printing, stamping

Special finishings – spot varnish, foil printing, stamping

In the case of more complex prints, we sometimes have to use special finishes that give visual effects for the end result. From the point of view of prepress, it doesn't really matter what technique we are dealing with; a drawing is enough either in a design file or as a separate file.

We just have to keep in mind a few technical nuances: whether we use spot or process colour to mark a special solution, we must have 100% colour quantity, and we may also use 1-bit pixel graphics for marking. If special solutions are marked inside a design file with an additional colour, an overprint must be set for those colours. The same applies to the display of all other possible guidelines or drawings (e.g. die-cutter drawing).

Spot varnish is mostly applied to the print by means of screen printing (serigraphy). Due to the low resolution and inaccuracy of the technology, the design cannot be very detailed. The minimum line thickness is 0.5 pt. If the spot varnish is placed to cover the printed object, it is recommended to make a small overlap (trap) depending on the detail of the object 0.5-1 pt.

Foil is applied to the print through a metal letter press block, and since the foil itself is essentially a thin layer of metal, there are some technical limitations: lines with a thickness less than 0.5 pt may not be transferred or they fall off relatively quickly from the print. In addition, in the case of foil it is not recommended to use fonts less than 6-7 points.

Inks and other materials are not used for goffering and embossing, and the “resolution” depends foremost on the paper, but this method is primarily designed to highlight large areas and the details are not likely to make an impression. Goffering or embossing is often used to highlight printed objects.

Whatever special finishes need to be marked on the design file, we must first and foremost keep in mind that it must be understood by the repro specialists of the printing house. As already mentioned above, the easiest way to specify them is to use additional colours and to give them the name of the corresponding special solution (spot varnish, die-cutter drawing, etc.) and not to forget setting overprint to these additional colours.

The accompanying figure shows the AI-generated additional colours containing information about their intentions. Transferring the file this way allows the printing house to take off the additional colours for printing the printing plates and send them separately for the production of the silk frame or to make the matrix/die, respectively.

Screens - Offset printing plate

Offset printing plate technology

The printing plate is a so-called litho-aluminum sheet, on which the layers necessary for printing are applied by using an electrochemical method. The special feature of litho-aluminum is that it is made of cast aluminium by means of hot and cold rolling. By using this technology it is possible to produce an aluminium sheet with a very uniform structure and thickness, which is very important in the offset printing process. Cold rolling provides the necessary flexibility to a printing plate. Only one side of the plate is electrochemically treated. The very first process is to clean the plate from the oils added during production, i.e. to degrease it. Next, the plate is roughened by performing an electrolytic process. In an acid environment, by means of electric current a layer of aluminium salts is created on the plate. As required, the plates are roughened at different densities. Smaller plates have denser roughness and larger ones have sparser roughness. The purpose of roughening is to ensure the adhesion of water molecules to roughened areas. Water molecules in the roughened area prevent ink from entering this area. Next, the printing plate is anodised. A layer of alumina is "grown" on the roughened side to ensure greater mechanical and chemical resistance of this plate side. The technology consists in wetting one side of the aluminium plate and creating an additional layer of aluminium oxide on that side of the plate by means of electric current. Next, light-sensitive layers are made on the plate.

There are two types of offset plates: positive and negative plates

In the case of a positive plate, the part that does not need to be printed is illuminated to obtain an image, and in the case of a negative plate, the part that needs to be printed is illuminated. Therefore, the light-sensitive layers of negative and positive plates have different chemical compositions, and the chemical solutions (developer) with which the plate is later treated are also different. The printing plates are further classified according to the imaging technology and the substrate: traditional printing plates CTP (computer to plate) – plates obtained by using a laser plate printer. These in turn are divided into: UV – plate printers with UV lighting, thermal printing plates are not only UV-sensitive but also heat-sensitive so heat is added in the plate printer by lasers. These plates are more durable and have a longer service life; they are chemical and process free. Chemical-free plates are those in which, after illumination, the unnecessary layer is removed with water and only the plate rubber is added. Process-free plates are those in which the layer is removed in a printing machine at the beginning of the printing. The plate is moistened and ink and printing pressure are added. The emulsion goes with an ink into the first printing sheets.

Screens - Polymer plates

Polymer plates

The plates are not made of aluminium, but of a cheaper polymer, which is also covered with a light-sensitive layer. These plates are used in the production of small format and small circulation prints. By using these plates, it is difficult to make accurate registration and they are mostly designed for printing monochrome or two-colour projects. Paper plates are similar to polymer plates, where the base material is paper, respectively.

Traditional printing plate preparing method

Traditional method of preparing a printing plate

To use the traditional method, the following is required:

- For assembly, a light table, assembly membranes, assembly materials (tapes, adhesives, retouching tools) and an assembly strip (a metal strip corresponding to the plate mounting of the printing machine).
- Copy frame to illuminate the plate. A copy frame is a frame with glass and a vacuum pad on which the assembly and the plate connected by means of the mounting strip are placed.
- In addition to the frame, there is a UV lighting device. Lighting can come from the top or from the bottom. Modern frames have digitally programmable illuminating time. Newer frames also have a UV lighting scattering membrane (matte film).
- Developing device. A developing device consists of three parts – a developing bath, washing bath, rubberising and drying.

Assembly can be done manually or by means of a special program. Manual imposition means that the films are attached to the assembly film on the light table, either with assembly tape or adhesive. Using the sheet assembly program, the finished assembly is printed out by a film printer, and if there are punches, it is not necessary to glue the film on the assembly membrane. The film is immediately placed in the copy frame together with the plate. After assembly, copying or transfer of the image to the printing plate takes place. Copying in prepress is a contact copying of an image from a film to a printing plate using UV light. For copying, the assembly membrane or film is punched according to the plate mounting holes of the printing machine. The printing plate is placed on the assembly strip of the copy frame. An assembled membrane is placed on the plate. The assembly strip is necessary to ensure that the film or membrane is fixed in relation to the plate and stays in place. For copying, the frame is closed and a vacuum is created to press the membrane firmly against the plate. On newer frames, the pad is pressed even harder against the glass by using air so that the contact between the plate and the film is tighter. The plate is illuminated with a UV lamp for a certain time. If a scattering membrane used, the overall illumination time is reduced and the UV light is additionally used for illuminating through the matte film. Illuminating from top means that there is a lamp above the frame, which illuminates the plate for a certain period of time. For this period, it is ensured that light from elsewhere does not reach the plate – for example, with the help of dark curtains. All modern frames are built with a light from bottom. Once the plate is placed in the frame and pulled into vacuum, the frame is turned towards the lamp below the device and illuminated with UV light. The whole system is closed and usually operates in a programmed manner and protected from incidental light. After illumination, the plate is developed.

Developing device

A developing device is an automatic developing machine where the plate is developed by means of brushes and rollers. The rollers pass the plate through the developer, washing water and rubberising into the dryer and the plate is ready for printing. The developing devices are also digitally programmable. In the developing device it is possible to set the speed of the plate movement, the temperature of the developer, the refreshing interval of the developer. Development takes place in the development section and depends on the speed of the plate and the temperature of the developer. The development bath is provided with filters to remove solid residues arising from the development process. There is a continuous circulation through the filters. The developer is also refreshed periodically to ensure a stable reaction of the developer.  However, as a result of developing a certain number of plates, the developer must be replaced, and at that occasion the device is also usually very thoroughly cleaned.

Making the plate by means of the CPT method

Making the plate using the CTP method

To make a plate by using the CTP method, you need a plate printer, a sheet assembly program, a plate printer management program, and a program to transfer plate files to CTP, and a developing device.

A CTP device is a laser plate printer where a laser or bundle of lasers draws (burns) an image on a plate based on a file sent to the printer. The plate file is called 1bit Tiff. To calibrate the printer and manage the plate formats, a plate printer management program is used. If plate cassettes are available, the number of plates in cassettes and the plate format in the corresponding cassette are determined. The management program monitors all CTP activities. A program that transfers plate files to the printer allows setting the plate sizes and the order in which the plates are made. It works by using the so-called hotfolders system. The developing device is similar to the device used in the traditional method. However, in the case of CTP, the developing device can be integrated to CTP so that a plate is directed to the developing machine immediately after illumination. This ensures a faster plate making process.

Advantages of CTP over the traditional plate production method:

- No need for membranes
- No dust problems
- No registration problem due to membrane stretching
- The possibility of assembly errors is reduced

Printing plate quality

Printing plate quality

The quality of a printing plate made by the traditional method depends on:

- illumination time,
- lighting frame,
- developing time and
- temperature of the developer,
- freshness and quality of the developer and
- dust.

The printing plate obtained by copying is checked by means of a special strip which is applied to the plate during copying and which remains outside the printing area. After developing the plate, the difference in dot size between the check strip and the corresponding check strip on the plate is measured with a special plate densitometer. The dot on the plate is always bigger than on the check strip, but it must be within an appropriate range. This quantity is called the dot gain and is measured as a percentage. It should normally be 2-4%.

The quality of the printing plate for CTP-printing depends on:

- the intensity of the light beam from laser(s),
- developing time and
- temperature of the developer,
- freshness of the developer.

The check strip of the CTP plate is added to the bottom of the plate in the sheet assembly program, and when measuring on the plate, the dot gain there must be 1-2%. In addition, this strip has so-called visual check fields, which allow an instantaneous assessment of the quality of the development process. In the case of a CTP plate, the raster density, shape and dot stability throughout the plate are also checked with a plate densitometer.

Screens for flexographic printing

Screens for flexographic printing

Flexographic printing uses photopolymer plates or engraved printing cylinders as an image carrier. Photopolymer plates are made similarly to traditional offset image carriers. Contact copying is also used. However, the printing plate becomes significantly more embossed, and according to this printing technology, the plate is a direct ink carrier to the material. Due to flexo technology, prior to CTP technology, such a method could not be used to make image carriers with very dense raster or to obtain high quality printing results. For now, CTP technology has also been developed for photopolymer plates, and the print quality is approaching that of offset printing.

Another form of printing in flexo is gravure printing. Gravure printing is a chrome cylinder of a corresponding diameter on which the images to be printed are engraved. Printing takes place in such a way that the cylinder rotates in the ink bath. After applying the ink to the cylinder, a special rubber knife is pressed against the cylinder, which directs the excess ink back to the ink bath, and the ink remains only in the engraved grooves. The cylinder is then pressed against the printing material to which the ink in the grooves is applied. This printing technology allows printing very large circulations without the slightest wearing of the image carrier. Similar technology has been developed for offset printing technology to print very large circulations, 500,000 and above. In the case of smaller circulations, there is no point to use gravure printing technology, because the production of engraving carriers is time-consuming and very expensive.

Imposition

Imposition

Imposition is the arrangement of an image on a printing plate according to the technical parameters of the printing machine and post-processing needs. Imposition can be done manually or using special programs. Manual editing is done using the copying method from film. For manual imposition, an illuminated assembly table is required. Usually, each printing press is accompanied by a millimetre film corresponding to the plate of the printing press which has all the important notes of the technical dimensions of the printing press. These include plate size, plate edge to start printing and grab. A grab is a technologically “blind” area on the paper. Since the paper is conveyed in the printing machine by the grippers, printing does not take place to the extent that the grippers hold the paper. There is also a contact area between paper and offset rubber. This can extend the grab of the rubber when worn out. The corresponding film of the printing machine is glued permanently on the light table. The so-called terminal strip is also glued to the corresponding place of the film. The terminal strip is intended for fastening assembly films or pre-printed films. It marks the mounting of the printing plate in the printing machine. This ensures that the assembly is positioned accurately in relation to the printing plate. The terminal strip on the assembly table has higher pins than the terminal strip used to make the printing plate. Imposition requires an assembly membrane with the required transparency and strength. For imposition, membranes are perforated usually with the same punch that is used to perforate printing plates. The perforated membrane is placed on the assembly table on the pins of the terminal strip. Today, films are made assembled from a film printer, where it is possible to make punches in a film printer. In this case, it is not necessary to use assembly membranes separately, but the film is placed directly on the plate and copying is done directly from the film coming from the film printer. Manual imposition on a membrane is usually done by assembling one partial colour and then placing the next membrane on the assembly strip where the next partial colour is assembled to ensure the accuracy of the assembly’s registration. A special assembly adhesive or assembly sticker is used for imposition. Under no circumstances must ordinary retail stickers be used as they lack the necessary transparency. In addition, you need pencils for retouching and an assembly knife and scissors. An assembly knife is like a scalpel, so that in addition to cutting, it is possible to remove smaller areas of film emulsion from the film if necessary.

The terminal strip required for the printing plate must be made in such a way that the height of the mounting pins is exactly the thickness of the printing plate + the thickness of the assembly membrane. Once everything you need for imposition is available, you need to know how to perform the layout on the plate. Since the imposition principles are the same both manually and when using a sheet imposition program, we will discuss imposition on the basis of the use of the program.

By using a sheet imposition program

Today, sheet imposition is performed by using special programs. The best known are: Signastation (Heidelberg), Preps (Kodak). In addition, it is possible to make simpler impositions using design programs. In any case, it is more appropriate to use a special sheet imposition program, as it takes better account of the needs of the printing house. The Aheet imposition software is designed so that the parameters of the most commonly used printing machines are already integrated into the program. In their absence, it is quite easy to configure the respective printing machines yourself. In most cases, the most important parameters are the size of a printing plate and some other special parameters of the printing machines. Next is the maximum possible printing surface – the printable area. It is never possible to use the entire surface of the printing plate for printing. The maximum printing surface depends on the diameter and width of the print rubber cylinder. Furthermore, you need to know the distance of the paper from the edge of the plate. It is usually written in the manual of the technical parameters of the printing machine or indicated on the millimetre film mentioned above. Next, you need to consider the grab, i.e. the area where you cannot print yet. Then the minimum and maximum paper that can be used in the given printing machine are important parameters.

Sheet imposition programs consist of interconnected modules. The products of different software manufacturers are built quite similarly because the principles of the sheet imposition are basically the same.

The sheet imposition modules are the following:

Printing plates

In this module, all used printing plates are configured with their own parameters. The printing plate configuration specifies:

    - the printing plate size,
    - grab,
    - the distance of the paper from the edge,
    - the maximum permitted printing surface, and
    - necessary marks. There are two types of marks – the ones related to printing and the ones related to post-treatment.

Marks related to printing are registration marks, colour scales, “cutting marks” (on roller machines), auto registration marks (if the printing machine has a device that sets the registration marks itself), marking marks (indicates possible image fluctuations with respect to paper during printing), plate quality check marks, and marks of the name of the partial colour and the name of the product. They may be different depending on the printing machine. Post-treatment-related marks are trim marks and folding marks. In the case of adhesive binding, spine or collection marks. These marks are usually added during assembly. In the plate configuration, the marks that must be on each print when printing on a given printing machine are added to the plate. Depending on the capabilities of the program, it is possible to associate marks with a plate, image or the paper. This means that the mark moves with or is stationary in relation to the plate, image, or paper. For example, the marking mark is always exactly at the edge of the paper. As the paper changes size, the mark moves so that it always stays at the edge. However, the registration marks are associated with the image in such a way that they are always at the same distance from the image. It is also possible to set the marks to appear on both sides or on one side only for duplex printing. For example, in roller printing, the scales come on both sides of the print, but the cutting mark is only on the front plate.

Schemes

Schemes are the layouts of images on a plate according to post-treatment requirements. All programs come with the so-called standard schemes that can be used for imposition. But it is always possible to make suitable ones yourself. In the configuration of the schemes, you can set the number of pages, the layout, and the orientation. It is also possible to automatically generate a scheme for the second side according to the first, either turned around the horizontal or vertical axis. For roller printing and single-sided printing plates, turning around the vertical axis is selected (the term “vertical flip” is used), and for rotary sheet printing machines, turning around the horizontal axis is selected (the term “horizontal flip” is used). The schemes can be configured according to the folding schemes required for post-treatment.

Output parameters

All printing devices, including various plate file outputs (virtual printers). This module contains all integrated printers and their settings as well as all various output plate files, considering the printing machine and the raster density on the plate. For example, whether a plate file comes with or without a printout. The virtual printer can be either a PDF or a JPEG printer that generates a ripped PDF or JPEG version of the sheet imposition. They can also be configured to come from RIP with plate files or as a standalone printer.

Marks

The most commonly used standard marks are integrated into the marks module. However, the module includes the ability to create marks yourself or to import and export marks. When performing plate configuration or sheet imposition, the marks from the marks module are used. In addition, there are modules for making all or part of the work bases, which are easy to use for print imposition. There are modules for users or a client base. All these modules are integrated into the sheet imposition program, where they are used during imposition. The program itself also consists of different parts. First, information about the job is entered: order number, product name, paper size – that is, everything you need to see in the product name. Next, the page parameters are set such as page size, bleed, or number of pages, for example, from which number the page numbering starts.

Next, alignment is set – whether everything is centred, aligned to the clipboard in the file, or the alignment parameters are set manually. It is also possible to simultaneously use pages of different sizes, if necessary.

Next, the method of binding, either adhesive or wire binding, is determined. However, impositions that are independent of the binding method can also be made. In the case of milled adhesive binding, the width of the mill is selected. With the appropriate binding method, the program makes itself the correct page order. It is also possible to set the parameters of the clipboards. Bleed sizes at the head or front and back edges of the product.

In the case of wire binding, the so-called creeping sizes can also be set. In the case of adhesive binding, the so-called creeping effect occurs related to the number of pages and the thickness of the paper. When binding a magazine, the inner pages shift outward due to the thickness of the paper. Therefore, when you open a ready magazine, you can see that inner pages are always narrower than the outer ones. By fine-tuning the creeping, the program can be used to make the images shift to the centre in a calculated way. In this case, when you open a magazine, page numbers and other images are at the same distance from the outer edge. However, this setting can only be used if there are no overlapping images from one page to another or designs are not very close to the centre.

The next section is the base of the plate selection. Here you select the base of the plate and, if necessary, enter the paper size and whether the other side of the imposition is to be turned around the vertical or horizontal side. There is also the option to print only one side.

Next is the selection of imposition schemes and the adjustment of bleeds and the height of the scheme in relation to the paper. The last part is the selection of the output parameter. Here you select the output where the imposition is directed – it can be plate files, sheet proofs, digital proofs or anything else that is entered in the output parameters.

Modern sheet imposition programs allow you to quickly make impositions on various plates. Impositions made with programs significantly reduce the time and labour required for prepress. They also reduce or eliminate potential problems rising from manual imposition, such as the need to make new plates due to stretching of the membranes and because of dust.

Modern file management software in pre-press

Modern file management software in prepress

Major prepress software producers have developed special programs to manage the entire prepress process in a single program.

These allow the JDF (Job definition file) file format to be used in the process to connect the program also to business software if necessary.  This provides an opportunity to digitally integrate prepress with the rest of the digitised business and production process software. File management software consists of modules that can be used both as standalone single components and as a whole.

The software consists of:

- the preflight module of the files,
- the sheet imposition,
- RIP and
- The client management module.

The control module defines the settings that are checked in the client files. These are adjusted or changed if necessary. If the files match, the files are sent to either an imposition or RIP. Different software manufacturers offer different solutions here. Agfa and Kodak offer a solution where PDFs are ripped before editing and making plate files. In Heidelberg, an imposition must first be made with PDFs and only then can ripping happen.

During ripping, plate files are generated, which are then used to make printing plates. Lately, a very important part has been the client management module. This allows the client to upload files and get instant information about file compatibility. The client can check their files after ripping and, if necessary, replace inappropriate files and electronically confirm the material sent by them. In the program it is possible to make work bases with repetitive parameters.

For example, in the case of a weekly magazine, it is possible to set up the program so that when the files are sent, the pages are placed in the right places in the editing immediately, and after receiving the client's confirmation, the printing plates can be started immediately. In this case, the prepress process is significantly accelerated.

Kodak provides file management software called Prinergy, and the client module is called InSide. Agfa sells the Apogee software, and the client module is called the Apogee Portal. Heidelberg has Printready and Remote Access, respectively. Efi offers similar software.

Calibration and profiling

Calibration and profiling

Calibration is the process of bringing a device into a safe and repeatable state by using the correction functions of the device itself.

Profiling, or ICC profiling, is the measurement of the colour rendering of a device and the adjustment of the signal entering the device to achieve the most accurate colour rendering possible. The profile describes the colour tone values of the device in absolute colour space (CIELAB). Colour conversion always takes place between two profiles, which are the source profile (e.g. monitor) and the end profile (e.g. printer).

Location of the colour profile in the system

Colour profiles are stored in a specific directory in the computer. Depending on the operating system, the profile must be copied or installed (Windows).

Equipment calibration

Calibration of equipment

If we want to compare and evaluate the correctness of colours in different colour rendering devices, we need to make sure that the colours of the device that is the basis for the comparison are correct. To do this, the devices must be calibrated according to the colour space in relation to which we want to evaluate the colours. For correct colour rendering, it must be ensured that the measuring instruments with which we check the result are calibrated and in order. The devices that are calibrated to check and ensure colour accuracy are: monitors, projectors, digital cameras, digital and photo printers, scanners, plate printers, etc.

For accurate calibration the following is required:

- colour management and control software compatible with the device;
- measuring instrument and
- icc profile.

Calibration software can usually be purchased together with the measuring instruments. For example, spectrophotometers come with software for printers, monitors, scanners and digital cameras. Calibration software may also be included with the device or purchased as an accessory.

Displays

Monitors

A monitor that is not properly calibrated and profiled is not suitable for image processing and design work where colour accuracy is judged visually.

From the point of view of the proper functioning of colour management, the colour representation of the monitor is of key importance, because it is the "window" of the designer into the digital world. However, it is never possible to achieve a situation where the monitor image corresponds 100% to the image coming from the print. The reason is the differences between RGB and CMYK, and even from a CMYK image, the monitor always shows us the closest possible version created in the RGB system.

Different technologies are used to manufacture monitors that also affect the colour performance of the monitor. Different manufacturers may also have different preferences for brightness and contrast settings, so it is very unlikely that different monitors will be able to display a colour with a similar numerical value in the same way. However, the monitor user can definitely improve the situation by calibrating and profiling. Monitors are also produced in very different price ranges and qualities. Laptop monitors are not suitable for image processing due to their limited setup options as well as because their colour rendering properties depend very much on the viewing angle. Better LCD monitors allow the light temperature and colour channels to be adjusted. High-end monitors specifically designed for graphics processing usually have a built-in internal calibration system that allows the use of 10-12-bit colour depth per channel.

When calibrating the monitor, it must first be ensured that the lighting conditions are as stable as possible. Direct sunlight and brightly coloured walls are not good conditions for calibration. The most suitable room for image processing is steadily dim (preferably with window coverings), with neutral lighting (D50) and walls of a neutral colour. The light source should come as backlight and not be reflected back from the monitor.

Calibrating the monitor and creating a monitor profile

Although the new operating systems come with monitor calibration software and settings, the use of special software and a spectrophotometer provides more reliable and better results. For example The calibration module included with Windows 8 is based on a visual assessment that depends on the assessor's vision and is not necessarily reliable. Calibration results and reliability depend largely on the monitor used and its quality. Today, LCD or LED monitors are mostly used. The quality of a monitor is determined by its colour resolution and the durability of LCD or LED lamps. The LCD brightness of conventional consumer monitors is maintained for 3-4 years. After that, the radiant power of the lamps decreases and the brightness required for calibration is no longer available. Another problem with LCD monitors is the change of colours as the viewing angle changes. Consumer LCD monitors only deliver the right colour when the viewing angle is exactly 90. High-quality monitors used for image processing and design are of higher quality and have a longer service life, but unfortunately they are also more expensive.

Read more about calibrating LCD monitors.

Summary – the calibration and profiling steps are guided by the software used. Put simply, they are the following:

- The monitor must warm up as recommended in the monitor specifications before calibration is started to achieve the most stable operating conditions possible. Screen saver mode must not be used during warm up, calibration and profiling.
- It must be ensured that the workplace lighting is as stable and neutral as possible during calibration and that the screen of the monitor is not exposed to direct light.
- If the software does not adjust itself automatically, the appropriate light temperature must be set in the calibration software. 5000 K must be selected when designing prints.
- If the software allows specifying the range of the colour spectrum, gamma 2.2 must be used, which allows a sufficiently wide range of colours to be used.
- Adjust the black and white levels, i.e. brightness and contrast, and the different RGB colour channels according to the software instructions.
- Lastly, the measuring instrument measures the ability of the monitor to accurately render colour and create a profile based on it. The software automatically saves the profile as the default profile of the monitor.

Colour management in Photoshop

Image processing software Photoshop

For a workflow where a print-ready CMYK file is sent to the printer, the most important step in colour management is proper image processing.

The image processing software processes the image and converts the colour separation RGB file to a CMYK file, and using the correct profiles ensures the best printing results. If the file contains information about the colour space in which it was created, Photoshop can also translate it correctly for that monitor. If the file does not come with a profile, the device may translate the colour values incorrectly, and we may also see incorrect colours on the monitor.

There are several different terms associated with using profiles in Photoshop:

Tag – means whether or not a colour profile has been added to the file.

Assign – assigning a colour profile to an untagged file. In this case, the numeric values of the colour information of the file do not change. Used to find the correct profile for a file without a profile, and sometimes for image processing.

Convert – converting colour information from one profile to another. The numeric values of the colour information change. Used for image processing and colour separation.

Assume – assuming what happens when a file does not have a profile. The software cannot use the file without a profile. The assumed profile is the default profile set in colour settings.

Embed – saving a colour profile to a file that occurs when you save the file, also used to merge fonts into the output file (indicates whether a font is included).

Setting up Photoshop and colour spaces

The very first step after installing Photoshop is to configure Edit/Colour Settings. Working Spaces are colour spaces in which image processing takes place. The choice of the colour space for processing must take into account where the processed image is to be used.

There are different colour spaces to choose from:

sRGB – the most widely used RGB profile that describes the colour space of the average monitor. Suitable for web images and photos taken to a photo lab, but not suitable for processing print images due to its limited colour gamut.

AdobeRGB – with larger colour space and suitable for CMYK convertible images.

AppleRGB – Mac OS colour space. Suitable for processing files from older versions of image editing programs (such as Photoshop 4.0 and earlier) or files displayed on Mac OS monitors. Not suitable for print or web photos.

ColorMatchRGB – smaller than AdobeRGB, sometimes used for Mac workflows.

ProPhotoRGB and Wide Gamut RGB – very large RGB colour spaces that contain colours that cannot be printed with conventional printers or displayed on most monitors. Used for processing high quality photos, preferably at 16-bit colour depth.

The default settings of the program are sRGB and US Web Coated (SWOP) profiles as colour spaces, which do not comply with European printing industry standards. A scanner profile or a digital camera profile is also not suitable for image processing because they are device-specific and therefore uneven in design. A uniform structure of the colour profile is necessary for the image processing tools to work properly.

To use a scanner or camera, they must be assigned to an image when you open the file (Edit/Assign Profile), which gives Photoshop information on how to interpret numeric values. However, to process an image, the image must be converted to a device-independent colour profile (such as sRGB or AdobeRGB).

CMYK profile depends on the printing paper used, for coated paper ISO Coated v2 300% (ECI) or Coated FOGRA39 is suitable. The Euroscale Uncoated v2 profile is usually suitable for uncoated paper.

Converting to profile

During this process, the colour information is converted from one profile to another. The colour tone is retained, but the numeric values of the colour information change. The most common translation is RGB-CMYK colour resolution.

Edit/ Convert to Profile shows the source profile and allows choosing a destination profile. In addition, other conversion options can be set.

Colour Management Engine, belonging to Adobe or Microsoft, may be used. Typically, Adobe Engine is used.

Rendering Intent determines how the colour management module translates from one profile to another. For example, how to deal with colour tones that do not fit the destination profile.

The choice of the rendering intent depends on the image to be translated. Sometimes different interpretations give a similar result and sometimes not.

1. Perceptual conversion, is suitable if the target profile is smaller than the original profile and there is a lot of slightly different tonal information in the image (e.g. green forest massif, cloudy sky or snowy field). Helps reduce loss of detail by maintaining a chromatic ratio between colours. However, the colours may change more than with colorimetric conversions.

2. Saturation. Uses the full colour space of the target profile and converts tones as vividly and saturated as possible. Usually not suitable for images but can be tried when converting illustrations and infographics (e.g. spreadsheet diagrams).

3. Relative colorimetric compensates for the white point, and if the white point of the source profile does not fit the target profile, all colours are made darker. Colours outside the target profile are replaced by the closest possible one. Initially, different colours may become the same. It is the standard choice in Europe and North America.

4. In the case of absolute colorimetric, the colours that match exactly in both profiles are translated; colours remaining outside are replaced by the closest possible ones. Initially, different colours may become the same. Used in proofing.

Black point compensation helps maintain shadow detail. Typically recommended for printing on quality paper and not used for newspaper printing.

Upon activating use dither in Photoshop mixes the colours in the destination profile, creating visual noise that tries to simulate the missing colour that existed in the source profile. Helps to avoid gradation.

Flatten image merges all layers in a file into one layer to maintain the colour appearance. In most cases, it is a good idea to merge layers before converting. CMYK images are sent for printing in single layers to prevent errors.

Screenshot or Soft Proof

When performing image processing for a printing company, it is possible to use the soft-proof screen mode to check the colour matching. This converts the information of the colour profile of the file to a CMYK target profile and displays it as accurately as possible on the monitor.  The colour information of the file is not changed numerically during this process. The disadvantage of this method is that the monitor is not able to display all CMYK colours, and although we can use different proofing settings, there is always some difference. However, this feature simplifies the work of an image editor, when they learn to interpret these differences correctly. The advantage of soft proof is speed and flexibility.

View / Proof Setup / Custom allows setting device to simulate, the rendering intent and determining whether to simulate the colour of the paper and black colour.  In the case of some interpretations, it is also possible to select black point compensation, which ensures that details are preserved in the dark area.

 Gamut warning

Another useful feature for image processing is Gamut Warning. When View / Gamut Warning is turned on, some areas of the image may turn grey, indicating the colours that are out of the target profile. The image should be processed so that the grey area is as small as possible before conversion. However, certain colour losses are inevitable.