HALFTONES
One of the most common problems encountered in digital prepress is that images are supplied to Tandym at too low a resolution. The final resolution of scanned halftone images should generally be 300 dpi at 100% of the reproduction size. If you are in doubt about the resolution at which to scan your original image, calculate the scanning resolution using the following equation:

2 × line ruling (in lpi) × reproduction factor The line ruling used for covers is 150 lpi and for text pages it is between 120 and 150 lpi.

To find the reproduction factor, divide the final size by the original size. For example, you have a 4" × 5" original which is to be reproduced on a cover as at 10", the reproduction factor (using the width of the original) is:

8" ÷ 4" = 2"

In this example, the image is for the cover, so the line ruling is 150 lpi. Therefore, you would need to scan the original at:

2 × 150 lpi × 2 = 600 dpi

This resolution amount may seem high, but bear in mind your 4" × 5" original is being enlarged by 200%.

If you had an 8" × 10" original that was only going to be reproduced at 2.5", then the reproduction factor would be:

2" ÷ 8" = 0.25"

You would need to scan the original at:

2 × 150 × 0.25 = 75 dpi

This resolution amount may seem low but your 8" × 10" image is being reduced to 25% of its original size.

This is generally a good way to calculate your scanning resolution, except that sometimes you have no way of knowing what the final dimensions of the image will be. If this is the case, scanning at a slightly higher resolution will allow you to enlarge the image slightly without sacrificing quality. Remember though, if you have a 300 dpi image that you enlarge to 200%, it is now only a 150 dpi image!

LINE ART
While the scanning resolution equations mentioned above are helpful for halftone scans (people, landscapes, etc.), line art graphics such as logos, type, CAD drawings, etc., are treated somewhat differently. For line art, a high resolution scan is required. They should also be scanned as Monochrome and not as Grayscale. You may use the following chart as a quick reference for minimum and ideal image resolution.

	Halftone Minimum	Halftone Ideal	Line Art Minimum	Line Art Ideal
Resolution	150 DPI	300DPI	600DPI	1200DPI

INCLUDING FONTS WITH ELECTRONIC JOBS

Fonts are the cause of some of the most persistent problems in imaging electronic files. The fonts used to output your files at Tandym must be of the same version, name and manufacturer as you used to create them. While it is Tandym’s responsibility to maintain licensed versions of the fonts used in our production processes, please remember that your job cannot move through the manufacturing process unless you have included all of the fonts used in the creation of your document.

When you send your book files to Tandym for printing, it’s important to follow these guidelines for including the electronic fonts with your job:

-	In applications, always use the actual stylized typeface. Avoid the use of style attributes such as bold, italic, bold italic, outline and shadow from the measurements palette. Some applications will attempt to simulate the requested style but the results are usually poor. More often than not, if there is no corresponding printer font available for the style you’ve chosen, the computer will ignore the command and use the printer font for the non-stylized version. On the Mac OSX avoid using fonts ending with .dfont as these fonts are system fonts and can cause conflicts when we use them to process your files.
-	Send all the fonts used in the document. If you’re not using specific preflighting software, often your page layout software can give you information about the fonts used. In QuarkXPress, try the Font Usage menu. In PageMaker® 6.5, use the Save for Service Provider plug-in for built-in preflighting. On the Mac, sending fonts usually means that you must include both a copy of the bitmap screen font (the font suitcase) and the printer fonts for each style instance. On the PC, send files ending in .TTF for TrueType fonts, and for PostScript fonts send both .PFM and .PFB files.
-	Use a unique naming structure when creating custom fonts. If you elect to create your own custom design typefaces with a program such as Fontographer®, make sure that you have assigned a unique name both to the screen and the printer version of the font to avoid conflict with industry standard names. Unless your last name is Garamond, using your own name to identify the font is a safe way to avoid conflicts.

FONTS IN PDF FILES
The PDF file format has eliminated many of the problems associated with the transfer of files from customer to supplier but font issues persist. In order for us to process a PDF file successfully all fonts must be embedded before the files are sent to us.

Colour Management
Understanding colour management starts not with technology but with the nature of colour itself, because colour doesn't really exist. Of course that sounds like nonsense because in the real live analogue world glittering and shimmering all around us, colour is everywhere. We can see it, we know it's there. But it isn't really there because colour is what we perceive when we see light bouncing all around us. Colour then, is a property of our environment, so it can't easily be pinned down and fixed.

Colour is an attribute, perceptible when light interacts with the objects and surfaces that make up our world. Everything absorbs and reflects light to some extent. Some things absorb so much light they appear black, some so little they appear white, but most do both. The combination of how the eye captures light and the brain processes the photometric signals, turns bouncing light into colours, even though it's only inside our heads.

Real Colour Capture
Light enters the eye through the iris, which expands and contracts to control how much of it enters, much like the aperture on a camera. Information about the light gets sent to the brain, which differentiates it as colours. They range from no perceivable differentiations, where there is no light reflected, to where all wavelengths are reflected and there can be no differentiation. We perceive the former as black and the latter as white.

In many ways, a digital capture device works rather like the eye, but there is one very important difference. Digital capture with a digital camera or scanner samples a series of points in a scene or image. Software builds a digital equivalent of the image based on the red, green and blue light information captured in each sample, converted from analogue information to digital data. Although such mathematically constructed colour descriptions can never exactly match perception, they can be controlled to come extremely close. Colour management is entirely about control.

Additive & Subtractive Colour
So light is made up of red, green and blue wavelengths and when it hits a surface some wavelengths get absorbed and some don't. Adding together all of the wavelengths of light makes white, and adding selected wavelengths together creates different colours, hence the term additive colour.

If there is no light source such as the sun or a computer screen to emit the red, green and blue light, there is only black. When emitted light hits a surface such as paper or board, the fixed texture of the surface absorbs or reflects it. Printers rely on how a surface absorbs and reflects light to create the illusion of colour, using subtractive rather than additive colour principals. They use cyan, magenta and yellow inks each of which absorb and reflects different parts of the visible spectrum, working rather like a filter. Light passes through the ink filters both as it reaches the page and when it is reflected from the white paper. Ink that absorbs the red component transmits green and blue to appear cyan; ink that absorbs the green component transmits red and blue to appears magenta; ink that absorbs blue transmits red and green and so appears yellow. With this subtractive colour system cyan, magenta and yellow are the primary colours and together all three colours will absorb all of the light, to appear black.

Basic Black
But impurities in inks mess up the physics here, so if one overprints cyan, magenta and yellow the result is a sort of murky brown, not black. Printers add black as the key colour (K) to pull the rest together, enhance contrast and achieve a really deep, dark black. Together cyan, magenta, yellow and black print (CMYK) can mimic many, but not all, of the red, green and blue combinations visible on televisions, computer screens and the real world. A clever printer can even convince us that the cyan, magenta, yellow and black on the page replicates what we see in the natural world.

Black effectively increases the apparent density and richness of the print. It's cheaper and dries faster than coloured inks, so it can save money. Black can be used to enhance contrast and achieve a really deep dark black. It is also better for printing text and black line art, which look blurred if printed CMYK or only CMY.

The Temperature of Light
Wherever it occurs, be that in the natural world on a monitor or in print, colour is about light. If colour management is about control, it's also about understanding how light affects colour perception. One way of classifying a light source is its colour temperature, which is measured in Kelvin units (Lord Kelvin was a British physicist and inventor, who defined the light temperature scale). Candlelight is the gloomiest at around 2000ºK and the brightest sunlight is at the top, at around 10,000ºK. Within these extremes colour appearance will obviously vary, so graphic arts professionals use D50 with a colour temperature of 5000°K, as a standard light source. D65 is defined as an average daylight simulation. D50 or 5000° Kelvin is a compromise between indoor light (3-4000° K) and outdoor light (6500° K) and is often used for viewing on press.

Colour Spaces
The only way to turn the RGB data captured with a digital camera or scanner into something that can be printed with CYMK inks, is to convert the source data into data defined for the target colour space: RGB to CMYK. It's a bit like transposing a piece of music from one instrument to another. The music should sound the same on both instruments, without compromising the characteristics and attractions of each.

Conversions from RGB to CMYK are notoriously badly behaved, but not only because they are based on different principles of rendition. Colour data conversions have to include some means of mathematically defining the characteristics of the digital devices used to create and render it. And the maths has to kick in every time a colour file is opened or printed on a different device. This is what ICC standards are all about.

International Colour Consortium (ICC) & Device Profiles
ICC standards are developed by colour scientists, technology developers and users from all areas of printing and publishing. ICC standards optimise accuracy in data transfers, taking into account the colour spaces and the devices in the workflow. In a controlled workflow, where all devices are calibrated and accurately profiled, colours appear the same wherever they are rendered, on screen or in print.

Any device used for colour production has to be calibrated and profiled. A device profile is a small data file with information about the device's characteristics and how closely it matches the colour values it is supposed to have. The ICC's standard file format for these profiles is one of the great leaps forward for digital colour management

ICC colour management works on the principle that all colour spaces can be defined within the CIEL*a*b* colour space (CIE stands for Commitée Internationale d'Eclairage). CIEL*a*b* is a perceptual colour space that defines colours according to their luminance, from black to white and degrees of red or green-ness, and of yellow-ness or blue-ness. It can define most colours that exist in nature and its vast gamut means that there are no colours in either RGB or CMYK colour spaces that cannot be defined. It's a sort of universal melting pot for colours, turning data defined in the source colour space to CIEL*a*b* values, then converting them into those required for the destination colour space. It sounds simple but the maths involved also has to include the device profile data, so it's far from straightforward. This may be why for many people it's just easier to dismiss ICC colour management and rely instead on a closed system, even though closed systems belong to another age.

Colour use in print is rising and modern workflows are open, not closed. Converting red, green and blue data to cyan, magenta, yellow and black data isn't trivial, but it can be done and done reliably. There is no clear consensus on colour management best practices, so a basic understanding of colour principles can only help matters. Awareness of the nature of the problem, plus control in the workflow and good housekeeping for all devices and software used in production is what colour management is all about.