Who is this guide for? This guide is for PTS employees and our trade partners who may only have a limited knowledge of what actually happens in the production process. Whether you’re a new starter or you’ve worked in print for years this booklet is an invaluable guide to pre-press and print information. So, if you’ve always secretly wondered what ‘CMYK’ actually is or perhaps a customer of yours has asked a technical question and you couldn’t answer it (chances are, they may know less than you!), this guide will go some way to explaining some of the steps that are involved before, during and after printing (and possibly give an insight into why the Studio can’t output ‘that‘ file). This is a fun, easy guide to pre-press & print and is by no means an absolute definitive manual but it should go a little way to broach the everyday technical jargon you may have come across, in clear concise terms. Also, it should act as a guide to save time, delays (and money) by asking the right questions to secure good quality artwork, resulting in a fast turnaround of the job.
Ink
Artwork
Plate Cylinder
Plate Water
Blanket Cylinder
Impression Cylinder
Illustration 1
Illustration 3
Untrimmed Sheets
Illustration 2
Trimmed Sheet
How does printing work? The basic principle on which it works is that oil and water don’t mix. A lithographic printing plate has nonimage areas which accept water. During printing, the plate is kept wet so that the ink (which is inherently greasy) is rejected by the wet areas and adheres to the image areas.
trimming, folding and binding.
Artwork is produced digitally and, at PTS, sent directly to an imagesetter to produce plates. When printing with more than one colour, separate plates are produced for each ink colour. In 4 colour process printing, 4 plates are produced (black, yellow, cyan & magenta - more of which later) - see Illustration 1.
So, the basic studio stages in Illustration 3:
The plates, which are flexible (usually 0.15 - 0.3mm aluminium) are then attached to the plate cylinder on the printing press. During every cycle of the press the ink image is first transferred to a rubber surfaced blanket cylinder and from there onto the paper. This indirect method is called ‘offset’ after which the process is named. The blanket’s flexibility both preserves the delicate plate and conforms to the surface of textured papers for good results - see Illustration 2. After printing, the sheets are taken for finishing -
The press can either be fed with paper, one sheet at a time (sheet fed), or from a large roll of paper (web - or continuous).
• Original artwork - images and logos are scanned and digitally converted. • These elements are combined into a document and text is added using page makeup software (InDesign/Quark Xpress etc). • These files, once approved (following proofing) are output to plates using a high resolution imagesetter. • Printing plates are made using the Agfa Acento imagesetter which splits the plates for 4 colour process printing (as shown). • The plates are attached to the printing press and the job is printed - all 4 separate colours combining to make a full colour finished product.
Illustration 1
Illustration 2
Illustration 3
Illustration 4
PANTONE 021 Orange
PANTONE 021 Orange from an inkjet printer
What on earth is image resolution?
Why does my image look good on screen, then?
The resolution is determined by how many pixels per inch an image has. High quality printed images must be at least 300dpi (dots per inch). So, a high quality image will have more ‘dpi’ than a poor quality image, as we can see with Inky’s holiday snap - Illustration 1. Many logos are sent to PTS that have been taken from websites or the internet. Logos for websites are low quality (usually 72dpi) images and cannot be used in printing - Illustration 2.
This is due to monitor resolution. Most monitors view at anything from 72dpi to 96dpi. Hence, an image at 72dpi may look good on the website (on screen) but not when printed (on paper). This is because image pixels are translated directly into monitor pixels. When the image resolution is higher than the monitor resolution the image appears larger on-screen than its print dimensions.
Why doesn’t my final print look like my colour proof? Most desktop printers these days produce excellent quality prints but can differ vastly from the professionally produced, printed article. Even though some printers have a resolution of 600dpi or higher the imagesetter (for producing plates) works at 1200dpi (but can go to 3400dpi!). Inkjet printers produce a spray of ink, not actual dots (as an imagesetter) so can make an image look better
than it is. Imagesetters produce actual dots and are more accurate than inkjet printers, the disadvantage being that poor quality images are intensified. Colours produced with an inkjet printer are just a facsimile compared to the consistency of Pantone matched prints - Illustration 3 & 4.
Illustration 1
detail
Illustration 2
Illustration 3
Illustration 4
Illustration 5
Illustration 6
Isn’t an image just an image? Computer graphics initially fall into 2 main categories:
Bitmap (usually Photoshop) Vector (usually Illustrator)
Vector images are made up of lines & curves defined by mathematical objects called vectors. They can be easily enlarged, edited, colours changed etc. - see Illustration 2.
Bitmap images use a grid of colours (pixels or picture elements) to represent images - see Illustration 1. Must be high resolution for printing (unsuitable for enlarging and changing to spot colours as they’re usually RGB).
Both PTS logos opposite look the same - what’s the difference? Illustration 3 is the Vector logo (Illustrator in this case) and can be edited and enlarged easily without degradation. It also has a transparent background. Illustration 4 is the Bitmap logo (an RGB jpeg - more of this later) and cannot have its colour changed and will not enlarge without degradation or the logo looking ‘blocky’ or ‘pixelated’. Also, will have a white ‘box’ area behind it so it can’t be placed on a screen or other colour (the white area is not transparent) - see
our blue background screen behind the Vector and Bitmap logo - do you see the difference? Illustration 5 & 6 shows what happens when the logos are enlarged. Illustration 5 shows the high quality of the vector logo and can be enlarged to any size. Illustration 6 shows the Bitmap (Photoshop) logo’s quality becomes poor once enlarged.
Illustration 1 Illustration 3
Pantone PMS 021
Illustration 2
CMYK of PMS 021
Red, Green, Blue Additive colour space
Cyan, Magenta, Yellow Subtractive colour space
Spot colours Think of spot colour in relation to the Dulux colour chart when buying paint from B&Q. You select your 1 or more colours and that’s exactly what you get.
Colours are specified, matched and accurately produced using the internationally recognised Pantone Matching System - see Illustration 1.
RGB and CMYK The RGB colour space is primarily used for computer monitors and CMYK is used for printing - i.e. full colour leaflets, brochures etc. The main difference is that whereas monitors emit light, inked paper absorbs or reflects light depending on the colour used. On a monitor, white light is produced by the Red, Green and Blue (additive) colours being emitted at full strength; whereas, in printing CMYK (subtractive), white is produced by simply not printing any colour - i.e. the white of the paper showing through. Graphics for the internet are supplied as RGB (because you will view them on a monitor) but files for print must always be CMYK (Cyan, Magenta, Yellow and blacK - K is used so there’s no confusion with blue) - see Illustration 2. Many files supplied to PTS (logos mainly) are in RGB even if it’s only printed one or two colours. This can
cause us problems because, on the whole, RGB files aren’t editable in the way that vector (Illustrator) files can be. RGB files must be converted to CMYK for printing. If files are supplied separately this can be done easily problems arise when RGB files are embedded within PDF’s - these can be out of gamut (see overleaf). Because of their different colour space, files in RGB that view perfectly well on a monitor may view differently after printing. CMYK colour matching to Pantone Spot colours is anything but perfect - for example, trying to match Orange 021 (or any spot colour) using CMYK 4 colour process will always give a questionable result compared to the actual spot colour, which will usually be much more vivid - see Illustration 3.
Illustration 1
Illustration 2
Illustration 3
Illustration 4
Converting RGB to CMYK - easy? It can sometimes be difficult to visualise the colour differences between CMYK and RGB. The chart shows the colour spectrum as the large ‘coloured’ area and within this a plot of CMYK and RGB colour. You can see that some of the RGB is outside the CMYK space. These areas result in problems - usually with
‘brighter’ colours being unable to be translated into print - see Illustration 1. Basically, there are millions more colours in RGB space than in CMYK colour space and some cannot be converted correctly - these colour are listed as out of gamut.
What are half-tone dots? In offset lithography, the density of CMYK inks can’t be varied in a continuous fashion across an image, so a range is produced by means of halftoning. In halftoning, translucent CMYK ink dots of variable sizes are printed in overlapping grids (or rosettes). These grids are placed at different angles for each of the 4 colours. Smaller dots absorb less light giving more reflected light resulting in the object appearing lighter - see Illustration 2.
So, if you were to look at your favourite magazine under a magnifying glass the result would resemble something like the far right image in Illustration 2 or the images shown in Illustration 3 & 4. Because the dots are so small, your eye is deceived into thinking that the image is made up of millions of colours and not made up of thousands of dots from just 4 colours. Look at the picture enlarged to see how the dots look when magnified - Illustration 4.
WHAT’S AN FAQ?
Top 10 FAQ’s? These are the most common questions we ask and get asked. If we can get the right answers from the beginning then costs can be reduced and schedules will be achieved - result! Even Inky has spotted a spelling mistake!
Is there a high resolution logo available? This will most likely be a ‘.eps’ or ‘.ai’ file.
How many colours in the job?
Please supply the Pantone references for the colours.
Is there any artwork available?
This won’t be a ‘jpeg’ but we may be able to use a PDF proof from a previous supplier.
Is the PDF artwork supplied print ready?
printer parameters: Have you got ‘Print to Fit’ ticked? If your proof is A4 or larger, your PDF won’t fit your A4 printer due to it adding margins all the way around (If need be, we can supply a hard copy for you to check the size correctly - just ask).
You want a booklet printing, you have some booklet software, should you paginate it?
This PDF will have fonts embedded, bleed (if the colour goes to the edge) and non-RGB images at 300dpi.
No thanks, please supply a PDF as one document with single pages from 1-12 if a 12pp brochure, etc. Please do not save as spreads.
Do you need a logo scanning/re-drawing?
Does your job contain folds?
If possible, please supply a printed copy (don’t fold the image or staple through it).
Please supply a copy showing which way the job folds.
Are all instructions clear and concise?
If your PDF looks strange (especially full colour leaflets) and there are white or black areas covering the job where there should be colour, then you may be viewing the PDF in Acrobat with Overprint turned off. Go to Acrobat preference / Page Display / Show Overprint - Always (the wording may be slightly different depending on PC or Mac and which version of Acrobat you’re using).
Have a quick read through it - if it’s not clear to you, it won’t be clear to us.
Is the job full colour, possibly with images?
Please supply a printed sample to help us match your previous job.
The PDF proof doesn’t print correctly?
If your PDF doesn’t print to the correct size check your
Your PDF proof views incorrectly on screen?
The vigilant amongst you will have spotted that there are, in fact 11 FAQ’s!
Inky’s Artwork Checklist: • Is there artwork available? This is a real timesaver - just ask if there’s any available. • Does the supplied PDF have high resolution images, fonts embedded and bleeds? If the customer amends, the job might be delayed - if we amend it, there might be charges. • Are instructions clear and concise? Clear, legible instructions are easy to follow and get the job done quicker. • Is there a previously printed copy? This is essential if the job is in full colour and we have something to match to. Also handy for folded jobs. • Are there spot colours on the job - what are their Pantone colours? Always request Pantone colours from the start. For example, if it says, ‘black and red’, what Pantone is the red? • Is there a high resolution image/logo available? Tip: If the logo looks like an illustration, the file may end in ‘.ai’ (an Adobe Illustrator file). Tip: If it’s an image and it ends in ‘.gif’ or the file size is less than 10kb, then this is an image from a website and won’t be good enough for print.