Whether you're a seasoned professional or just starting out in your marketing career, there are times when it seems like designers and printers are talking in a language all of their own. And, oftentimes, that's because they are! We get caught up in all the technical stuff and don't always know how to translate that into a language that the rest of the world can understand. So here is a brief guide to some of the most commonly used bits of technical jargon and what they mean.
One of the key things to understand about images is resolution. Resolution refers to the amount of detail in a digital image - or raster image - to go by its technical name. A raster image is made up of tiny squares called pixels. Image resolution is measured in pixels per square inch (ppi). The higher the number, the higher the image resolution. The simplified diagram below shows this relationship.
For commercial printing we need to use high resolution images. That means images which have a minimim pixel depth of 300 pixels per square inch (300ppi). In addition, the image must be physically big enough to hold its resolution. So if we want to print an image that fills half of an A4 page, the size of the image should be 148mm x 210mm at 300ppi. But if we used the same image and enlarged it to fill the A4 page, the resolution would drop to 150ppi, since we're using the same amount of pixels but fitting them into twice the area with the result that the print quality would not be as good. This is why raster images are referred to as being "resolution-dependent". Since the number of pixels per square inch is fixed, the resolution will decrease or increase as you scale the image up or down. Let's see what happens when we enlarge an image of Fido. The original small image is about 5cm square at 300ppi. When it's enlarged to twice its size the amount of pixels per square inch stays the same, but the pixels themselves are enlarged. And you can see that Fido's nose is starting to get pixelated. And when we enlarge to four times its original size the image quality is getting pretty bad. Poor Fido. He just doesn't have the resolution to grow into a big dog.
The answer is to look at the file size which you'll find beside the file name of an image. Then to check it against the reference chart below which shows the file size of an image in JPG format for each corresponding paper size.
|Paper Size||Dimensions in mm (h x w)||Pixel Dimensions (h x w)||JPG File Size (RGB)*|
|A7||105 mm x 74.2 5mm||1249 px x 874 px||1.2 Mb|
|A6||148.5 mm x 105 mm||1754 px x 1240 px||2.17 Mb|
|A5||210 mm x 148.5 mm||2480 px x 1754 px||3.5 Mb|
|A4||297 mm x 210 mm||3508 px x 2480 px||5.4 Mb|
|A3||420 mm x 297 mm||4960 px x 3508 px||8.5 Mb|
* JPG images saved in CMYK will be almost twice the size of RGB images.
So, if you have an image file and its size is less than 1 Mb you'll know that it's going to have pretty low resolution and it might only be suitable for print at business card size or less. Files under 500 Kb are not going to be useable for print.
For more about paper sizes Click Here
Websites, on the other hand, use low resolution images to allow web pages to load up quickly. Since computer monitors typically have a resolution of @ 96 pixels per inch, web images don't need to have a resolution any higher than this. So, if you download an image from a website and print it out, you'll notice that it's pretty small. And if you enlarge the image and then print it out, you'll see that it becomes fuzzy or "pixelated". That's because there isn't enough resolution (or detail) in the image to make it print nice and sharp.
The two flowers below are the same size, but have different resolutions. The flower on the right is a high resolution image of 300ppi and you can see that it's nice and sharp. The flower on the left is low resolution at 72ppi and you can see how it's gone fuzzy and blurred at the edges. We mentioned earlier that pixel images are "resolution-dependent" There is a different type of image however which is "resolution independent". In other other words it can be scaled up or down without losing resolution. These are called "vectors". Vectors are graphics that are created using drawing software like Adobe Illustrator. Fonts and type are also vector-based. When designers create a logo, they'll create it as a vector so that it can be easily edited and so that it is scaleable. That means it can be enlarged, or reduced, without losing resolution. From time to time you may need to send a copy of your logo to a printer or designer and chances are they will ask for a vector graphic. So it's a handy thing to know about.
In a nutshell it works like this: an image is transferred from a computer to metal plates. The number of plates depends on the number of ink colours. The plates are put onto a printing press. Ink is applied to the plates, which in turn put the inked image onto a transfer plate which in turn puts the image onto paper, and, hey presto, out pops your image.
Digital printing doesn't require plates or use traditional inks. Digital printers use laser technology to electrostatically apply microfine toner which is fused to the paper by passing it through hot "fuser" rollers. The result is high quality colour printing without all the set-up time and associated cost of conventional lithography. Digital print makes short-run colour printing affordable but, because of the unique way in which digital printing is costed, it's not as economical for large quantity runs as traditional lithographic printing and there are also restrictions on the type of paper, inks and special finishes that can be used.
Colors created for use in lithographic (offset) printing fall into two categories:
Spot colour or Full Colour (also called 4-colour process).
When we see colour images on the TV or on computer screens, the colours are generated using the primary colours Red, Green and Blue (RGB) - because this is the way the human eye perceives light-emitted colours. But RGB doesn't work in printing so the secondary colours Cyan, Magenta, and Yellow are used instead. Black is added to these three to give extra depth and definition. This combination of Cyan, Magenta, Yellow and Black is known as CMYK. So, a nice bright red colour like Pantone 485 expressed in CMYK would be C=0, M=100, Y=100, K=0; meaning zero % cyan, 100% magenta, 100% yellow and zero % black.
Design software separates colour Images into these colours from which four plates can be made. The colours are then printed simultaneously. The inks don't sit on top of each other - otherwise they'd mix together to form a muddy brown colour - but are printed at different angles which form a tiny rosette pattern. You can see this easily if you look at a printed picture through a magnifying glass. It's the human eye that merges the colours in the rosette pattern to create the perception of full colour. Clever, eh?
Since we're talking about rosettes, here's a nice image of some roses that's been scanned from a gardening magazine. When we enlarge a section of the image, you can clearly see the pattern made by the four inks sitting at angles to each other.
Spot Colours are single ink colours made up of specific pigments, mixed to specific formulae according to a defined colour system - just like a paint chart. The most commonly used colour system is the Pantone system, which is why spot colour printing is often referred to as Pantone printing. Pantone printing is most commonly used for corporate stationery where the colours are applied in separate runs on a printing press. Here's a section from Pantone swatch. Again, very similar to something you might pick up in a paint shop.
These two colour systems tick along nicely on their own, but problems arise when you try to match CMYK with Pantone. Pantone inks are specific mixes of certain pigments so it's almost impossible to reproduce this complex system of pigmentation using just the four colours available in CMYK. The diagram below shows how four of the most common Pantone colours break down into their CMYK equivalent and you can see the variations straight away. Some colours provide a better match than others - some yellows, greens and reds from the Pantone system can print quite accurately in CMYK; but blues, oranges and purples can be very problematic. (Nor can you ever match silver and gold with CMYK.) This can be very frustrating when you're trying to match corporate logo colours in a full colour brochure. And whilst it's possible to minimise the difference between Pantone and CMYK, it's rare to get an exact match. It's just something you have to live with.
We mentioned earlier that colours on computer screens are generated from the primary colours, Red, Green and Blue (RGB) and so websites are built with RGB colour. The pixels in each Red, Green and Blue LED on a screen have values from 0 to 256. For example when the red pixel is set to 0, the LED is turned off. When it's set to 256 it's fully on. So a value of RGB (0,0,0) would produce black, since all the LEDs are turned off, whereas RGB (256,0,0) would produce a full red - since the red LED is on full. A value of RGB (256,256,256) would produce white, as all the LED's are turned up to the maximum and, as we all know, when you combine all the colours of the spectrum you get white light.
But more often than not you'll see RGB values expressed in HTML code or HEX code, which uses the hexadecimal numerical system. Hexadecimal code is made up of integers from 1-9 and letters from A to F to describe to a computer browser how much red, green and blue to apply to a colour. We've just seen that each of the primary colours can have a value from 0 to 256. Computers need a way to count up to 256. If a computer reads the number 256, it just sees the indiviudal digits, 2, 5, 6, and that's not we want. Hexadecimal code provides two sets of values which, multiplied together, deliver the correct number. So the number 256 is expressed as 16 x 16. But computers see 16 as 1,6 because they can only count from 0 to 9. And this is where hexadecimal numbers come in handy: numbers 10-16 are replaced by the letters A to F. Let's put this into context. Say we want to write code for pure red. We'll want to set a value of 256 Red and zero for Green and Blue. In hex code it would be written: #FF0000, So that's FF for Red, where FF is equal to 16 x 16, and 0 for each of Green and Blue.
The best way to get a good understanding of Hex Codes is to see them in action. Below is small selection of RGB colours showing their hexadecimal values. For a more detailed look at hex codes have a look at http://www.color-hex.com which is a great resource for finding and generating colours in html. You're probably not going to have to worry too much about how to make colours in hex code. But it's useful to know what they are especially when it comes to matching the Pantone or CMYK colours that we talked about earlier to RGB. The fact is that RGB is an even harder colour system to match to printing colours because you're simply not comparing like with like. RGB is based on light emitted primary colours whereas CMYK is based on light reflecting secondary colours. So you when you're discussing your brand colours with a designer it's useful to be aware of the issues that can arise when trying to maintain colour consistency across your print and digital media.
Most of us are already familiar with common file formats. But here is a brief description of the most widely used file types and quick outline of what they are for.
PDF files are independent of application software, hardware, and operating systems. Each PDF file encapsulates a complete description of a document, including the text, fonts, graphics, and other information needed to display it, which is why PDF is the preferred file type for sharing documents for print. It's important to note, however, that not all PDFs are the same. PDFs generated by industry professionals, such as designers and printers fall into two categories: screen-resoluton and print-resolution. We've already seen how resolutions differ depending on their application. Screen PDFs are optimised for viewing on a computer monitor so they typically have a low resolution of 72ppi and a colour mode which is set to RGB. They're' fine for viewing as proofs, but you won't be able to use them for print. Unless you have professional PDF writing software in your office, these are the type of PDFs that would be generated from a Microsoft environment.
Print-resolution PDFs are high-resolution files with a pixel depth of 300ppi and colour mode which is set to Pantone or CMYK. They will usually have trim marks just outside the outer border (see Crops & Bleeds). The file size of a print PDF will very often be quite (or very!) large, especially when they include images. Sending low-resolution PDFs out for print can be an easy mistake to make if you are dealing with both a designer and a third-party print provider. When you've' signed a proof off for print, make sure that you get a print-resolution PDF from your designer and have your print provider confirm to you that the print-file is o.k to print before you give approval to proceed.
Strictly speaking JPEG - or JPG as it's now shortened to - is not a file format but a method for compressing images as standardised by the "Joint Photographics Expert Group"(hence JPEG). JPG compression is extremely efficient and results in very compact file sizes even when the original image size is very large. As a result the JPEG standard has been widely adopted by the imaging industry and is the default file capture standard for digital cameras and smart phones. JPGs can be saved in a number of different resolutions but the ones you'll most commonly encounter are JPGs used for screen or web: 72-96ppi and those used for print: 300 - 350ppi.
EPS is a file extension for a graphics file that uses PostScript language to draw its image. You must have a specific software application to create an EPS file, such as Adobe Photoshop or Adobe Illustrator so unless you have any of the software above, you won't be able open and view an EPS. EPS files are most commonly used when creating vector graphics - such as a logo. (Remember that we looked at vectors in the section about resolution). Sometimes you may be asked for an EPS of your company logo, in other words a vector file. But be careful here: Files in photoshop can also be saved in EPS and these are not vector files - they are pixel files (or raster images) and they can't be used in the same way as vectors. So when you're dealing with an EPS, make sure it's a vector.
GIF files are a format commonly used for producing very low resolution files for websites. GIFs are based on indexed colors, which is a palette of at most 256 colors. GIF files are great for small icons and animated images, but they lack the color range to be used for high-quality photos. GIF also supports transparency, where the background color can be set to transparent in order to let the color on the underlying Web page to show through. But these days GIFs are less common and are being replaced by the more popular PNG file.
PNG files are image files that have been developed to improve on GIF. The PNG format supports the same colour spectrum as JPEG , so a PNG image may include over 16 million colors. This is a significant difference between GIF and PNG, since GIF images can include a maximum of 256 colors. Whilst JPEG images do not support transparent pixels and GIF images only support completely transparent pixels, PNG can support partial transparency which allows Web developers and icon designers to fade an image to a transparent background, which is a neat trick.
The "A" series for paper sizes was introduced in mainland Europe in the mid twentieth century and is now in common use throughout the world apart from in the US, Canada and parts of Mexico. The A series is based on a very straightforward idea: A0 = 1 square metre. Divide this in half and you get the next size down, A1. Divide in half again and you get A2...and so it goes on all the way down to A10 (less than half the size of a business card). Here's a quick graphic to show how this works.
When specifying formats it's common practice to refer to the number of sides on which a specific A-size will be printed. For example, if you printed on both sides of an A4 landscape and folded it in half , this would be called a "4 page A5 portrait"; since there will be 4 viewable sides of A5 size and the orientation of the page will be upright (or portrait). Similarly a portrait A4 printed and folded in half would be called a "4 page A5 Landscape".
The exception to this is the "DL" size which is excactly one third of an A4 (99mm x 210mm) and is so named because it fits into a DL envelope. One of the most common small brochure formats is the 6 page DL: an A4 page printed and folded into three.
A quick visual guide to the more common print formats is as follows:
Printers don't print onto exact "A" size papers. They generally print onto sizes which are just a bit bigger than the finished "A" size. These sheets are known as SRA sizes. For example an SRA4 will be trimmed to a finished size of A4. SR sizes are used so that printers can add crop marks, registration marks and bleed.
Below is a simple A4 layout for a fictitious furniture retailer based in the North Pole showing print-ready artwork with registration marks, crop marks, bleed and type area.
That's it for the moment folks. But I'll be adding more useful tips as we go along. In the meantime if there's something you'd like to know about, why not drop me a line?