Better prints at home

A clear and simple guide to getting the most from your desktop inkjet printer

>> The basics is here.

Printing in colour

coloured_dots_image

Inkjet prints are composed of tiny coloured dots. The dots are too small for the naked eye to see; dots of different-coloured inks blend together to create new hues.


Part one: Colour management

Colour management is the art and science of getting colours to come out the same on each of your devices. It's a deep and potentially complex subject, so let's start by getting the big questions out of the way.

Do I need it?

For many people, getting colours to print right can be a bewildering technical challenge. Often, the hardest part is not knowing what to blame when things go wrong. Is it the printer, the camera, the monitor – or all three? Colour management can sort things out by getting all your devices speaking the same colour language. It's like a magic bullet for your printing woes.

Is it expensive?

Of all the links in your printing chain – printer, computer, display – colour management hardware is likely to be the least costly. For most people, a display calibration device will be all they need. These range in price from affordable to surprisingly steep. You may wish to go further and buy a device for profiling your printer, too. In this case, a package such as the SpyderSTUDIO, or an all-in-one device such as the X-Rite Colormunki, can go some way towards easing the pain in your wallet.

Will it take much time?

Done well, colour management can be quite time-consuming. On the other hand, making flubbed prints is time-consuming, too, as well as being a frustrating waste of money and resources. Unlike printing duds, colour management can be rewarding and even rather enjoyable. Be aware, though, that it is not a one-time thing, but rather a process requiring regular maintenance and attention.

This page outlines some of the bare essentials of colour management. For more detailed information, books such as 'Real World Colour Management' (Fraser, Murphy & Bunting; Peachpit Press, 2nd Ed., 2004) and online discussion boards such as The Luminous Landscape's Colour Management forum are invaluable resources.


How do we reproduce colour?

Colour management does not require an in-depth knowlege of colour theory. However, it does help to have a basic grasp of the different ways in which we artificially recreate the natural phenomenon of colour.

In the natural world, the sensation of colour is produced within our eyes and brains by light of different wavelengths. By a quirk of perception, most of those colours can be simulated by mixing light of just three primary colours: red, green and blue. This process, called additive colour or RGB colour, is used by cameras, scanners and computer displays.

In the digital world, each colour is defined using three numbers, representing the amounts of red, green and blue light in that colour (its RGB value, eg R=35, G=160, B=0), whereby 0 equals none and 255 is the maximum possible. In this way, a theoretical maximum of 16.7 million colours can be described.

A related process, called subtractive colour, simulates colours using three hues of ink, dye or some other colorant. Each colorant absorbs (subtracts) some parts of the spectrum and reflects others, appearing either cyan, magenta or yellow (CMY). Mixed in different amounts on a white background, these three hues can reproduce a wealth of colours. This is how printers reproduce colours.

PK vs. MK: what's the difference?

You may have noticed that your printer has two flavours of black: PK (Photo Black) and MK (Matte Black). PK is used on photo (glossy or semi-gloss) papers. On matte papers it prints as a dull dark grey. MK is formulated to provide deep blacks on matte papers. However, it won't adhere properly to photo papers. Some high-end HP printers use both PK and MK inks at once to produce smoother results on matte papers.


Some printers add green, red or blue to their inksets, as well as paler shades of C,M and Y. They are also obliged to have separate black inks, called K, to avoid confusion with blue.

Part of the art of printing lies in reconciling these two fundamentally incompatible colour models.

James_Clerk_Maxwell_additive_colour_image

Left: Red, blue and green light in equal quantities combine to produce cyan, magenta, yellow and white. The additive colour process was the bright idea of Scottish physicist James Clerk Maxwell (1831–1879), who used it to make the first colour photograph in 1861.

Below: Subtractive colour blends cyan, magenta and yellow colorants. In theory, a solid black can be produced using all three, but in practice an extra black, K, is usually required.

subtractive_colour_diagram

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Why is printing in colour so difficult?

Dull, washed out colours; colour casts; prints too dark ...

Like it or not, there's more to digital printing than just hitting 'Print'. The biggest problem is that each of your devices has its own idiosyncracies when it comes to handling colour. To be able to print with confidence, you need to identify and compensate for these differences. This process is called colour management, and, for our purposes, can be divided into three basic components, each of which will be described in more detail below.

  1. Calibrating and profiling your display and printer
  2. Tagging your images with a known colour space
  3. Controlling viewing conditions for your prints

Making and using profiles

Calibration is the act of measuring a device's output against a known (ICC) colour standard, and correcting for any deviation. Calibration measurements are collated into small files called profiles. Your camera, scanner, display and printer can all be profiled.

How do I profile my display?

Installing profiles

Most profiling software will install your new profiles for you automatically. Instructions for manually installing profiles can be found here. (After installation, your display profile may need to be manually set to be the Default.)

Profiles can be removed through your Control Panel or by simply deleting them from the relevant folder.


D50 or D65?

The so-called D illuminants are standard illuminants designed to represent different colours of daylight. The numbers refer to their approximate colour temperature in degrees Kelvin (K) ÷ 100. D65 (bluish white) is considered 'standard' daylight; The warmer, relatively colour-neutral D50 is traditionally used in the pre-press industry. You can calibrate your display to either temperature, or choose another value altogether, as long as what you use matches your print-viewing conditions (see below, Viewing the print).

screen_calibration_image
Screen calibration with a hardware calibration device, or 'puck'

Display calibration should be the first step in your colour management process. Without it, you can't trust what you see on your screen.

A display profile is a description of the colour characteristics of your particular monitor. It contains a simple look-up table (LUT) that tells your video card how to correct for irregularities. Some advanced displays, such as the NEC Spectraview series, make adjustments directly in the monitor hardware, giving a more precise calibration.

Display profiles are generally created with a hardware measuring device (either a colorimeter or spectrophotometer) and profiling software. The device rests on the screen and reads the light from a sequence of colour patches. The data it gathers is then converted into an ICC-compliant profile which is automatically installed on your system.

Is my display good enough?

LCD displays come with different kinds of panel, and some are better for colour-critical work than others; you'll usually need to dig around in a display's specs to discover what kind of panel it has, though.

IPS panels are the choice of many professional photographers for their wide viewing angles and consistent colour. PVA panels offer comparable performance at a much lower price. TN panels are the cheapest kind, and as with most things, you get what you pay for. (Don't expect miracles from a budget laptop computer, no matter how carefully calibrated it is!)

When calibrating, you should set your display to 32-bit colour and its native resolution. Give it at least half an hour to warm up, and do the calibration away from direct light, with a muted on-screen background. Before installing new profiling software, make sure that any existing calibration software is disabled, taking special care to remove any profile loaders in your Startup folder, as these can screw up your calibration.

Tip: Don't rely on display-calibration utilities that allow visual calibration without the aid of hardware; although better than no calibration at all, these solutions are generally too imprecise to be relied upon.

Tip: Displays have a tendency to 'drift' over time. Ideally, they should be recalibrated every two or three months.

How do I profile my printer?

profiling_image
Using the SpyderPRINT to create a profile specifically
for black and white output.

Printer profiling is a lot more involved than display profiling, because a different profile is required for each paper you use. A printer profile describes the colour output of a specific paper/printer/ink combination. An associated media type describes the paper's physical properties: its thickness, surface type and drying time, as well as certain ink handling characteristics.

The importance of decent printing profiles can't be overstated. A good profile not only unlocks the full gamut and tonal range of the paper, providing accurate colours, smooth transitions and neutral black and white. It also saves you ink, paper and time that would otherwise be spent doing the same thing by trial and error.

Most printers are supplied with presets for a limited number of OEM papers. For many people, these will be all they ever need. But adventurous printers looking to experiment with third-party papers will need to download, make or buy custom profiles. Otherwise, your printer won't know what to do with your expensive paper.

Tip: Most third-party paper makers provide decent free profiles online. However, these are usually for professional printers rather than the consumer desktop models used in most homes.

Why not buy?

You don't have to make your own profiles. There are many professionals who will be happy to do it for you, usually for a modest fee. All you need to do is print out and send in your targets. Your profiles will be emailed back to you within days.

Custom profiles are relatively easy and rewarding to make. Once again, you will need specialist equipment: usually a spectrophotometer such as the X-Rite Colormunki.

To build a profile, you select a media type in the printer driver, then print out a set of colour patches (the colour target) and allow them to dry. Next, you scan the patches with the spectro and let the profiling software work its magic.

During the profile building, you may be offered various options, such as choosing either a neutral grey or a paper-coloured grey. When the profile is complete, it will be automatically installed on your system, although it may not become available until you restart your printing software.

Tip: It is crucial that the target is printed out without using profiles, ie with colour management turned off. The easiest way to ensure this is to print it through your profiling software.

Tip: Another way to bypass your computer's colour management is by printing through Adobe Color Print Utility, a free app available from Adobe's website.

targets_image
A full-size colour target is a thing of beauty.

How do I use printer profiles?

Which media type?

Choosing the right media type is critical. Usually the choice is made by trial and error: printing test images using different settings and comparing such things as colour richness, black depth and tonal separation. Paper manufacturers often recommend media types, although fine adjustments to ink limits and printing resolution and direction may still be necessary. Some profiling packages automate parts of the process.

The idea behind printer profiles is simple: just select the correct profile for the paper, and the printer adjusts its ink levels and other settings accordingly. However, using custom profiles is often less straightforward. Some high-end printers can store custom profiles so that you can select them from the driver, just as you do the built-in OEM profiles. You need only supply a tagged image (see below, Tagging images) and let the printer handle the maths. But mostly you'll need to use your custom profile in conjunction with printing software such as Lightroom, Photoshop or Qimage.

In this case (and depending on your software), you choose your custom profile in the software's Print dialogue, then select your media type and settings in the printer driver (sometimes found under the Advanced tab. You must select the media type and settings that were used to print the targets. Make sure your printer driver is set to No Colour Management or its equivalent.

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Tagging images

In a colour-managed set-up, images are tagged with a colour space. An image's colour space is the key that enables any device to correctly decode its colour data.

Why should I care about colour spaces?

The problem with digital images is that their RGB values (see box above, How do we reproduce colour?) are a lot like map coordinates: without the right map, they're not terribly useful. In colour terms, the 'map' is a colour space. Unless an image's RGB values are associated with a particular colour space, your display and printer will be forced to guess which colour each RGB value represents.

What is a colour space?

Space considerations

Not all colour spaces use the RGB colour model; there are CMYK colour spaces, and others that are derived from a theoretical colour space called CIE XYZ. These include the vast Lab colour space, which is used as a universal reference space and contains many imaginary colours.

I see what?

ICC stands for International Color Consortium. The ICC is an industry body formed to oversee colour management standards, particularly with regard to colour profiles.

Gamma gamma hey!

Gamma refers to the Tone Response Curve (TRC) applied to an image's brightness, or luminance, by a computer display. Usually, some correction is required to prevent blocked shadows or blown highlights in the displayed image. Most modern displays – both Windows and Mac – use a gamma (decoding value) of 2.2, and this is usually the best value to choose when profiling your display.

A colour space is a defined set of colours. Each colour in a colour space is described using numbers – in an RGB colour space, the numbers are the three values for Red, Green and Blue. These values only work with one specific colour space: just as using map coordinates with the wrong map is a bad idea, taking RGB values from one colour space and applying them to another just won't work.

We can tell by the numbers that R=200, G=10, B=10 is a strong red. But which exact strong red depends on the specific colour space within which it is defined.

How do I use colour spaces?

To ensure all devices 'see' your images the same way, you need to tag each file with a specific colour space, or profile. This profile is different from a display or printer profile because it is device-independent; that is, it doesn't simply describe the behaviour of one piece of equipment, but rather acts as a theoretical reference (or colour 'dictionary') against which your image's colour data can be checked. Tagging can be done automatically, when the image is created inside your camera or scanner, or manually, in your image-editing application.

Tip: Images created within Photoshop are automatically tagged with the current working space, as specified under Colour Settings.

Tip: An image's colour profile can be changed in two ways: Assigning a new profile simply changes the tag without altering the numbers, usually causing colour shifts when the image is viewed or printed. Converting to a new profile maintains the image's appearance as far as possible by remapping its colour values to the new colour space.

colour_image
Photograph © Peter Rees

What do I do about untagged images?

You can tell if an image is untagged because Photoshop tells you so (assuming you have checked Missing profiles: Ask when opening under Colour Settings; other applications will have different routines). The first thing to do with your untagged image is to assign a profile. To do this, go to Edit/Assign Profile and choose a profile from the drop-down list. You may find your colours need adjusting after you have assigned the new profile.

Which colour space do I choose?

Are more bits better?

You have the choice of saving your TIFF or PSD in 8-bits or 16-bits. 16-bit files take up a lot of space, but their advantages become apparent during post-processing.

8-bit images are limited to 256 tonal values per channel; a simple editing adjustment can spread those values further apart, leading to banding, or posterization. 16-bit images, on the other hand, contain 65,536 values per channel, allowing profound adjustments to be made without visible artifacts.

If you wish, you can convert your 8-bit images to 16-bit for editing and then back again – the majority of printers convert to 8-bits before printing in any case. (Incidentally, 8-bit RGB and 16-bit RGB images are usually described as 24-bit (8-bit × 3) and 48-bit (16-bit × 3) respectively.)

There are hundreds of colour spaces, but only a small handful are in common use by photographers. You should choose the one which most suits your purpose – multiple copies of one image (eg, one for web display and one for printing) can be saved with different profiles.

Tip: Image editing in ProPhoto RGB must be done in 16-bits to avoid colour banding (see sidebar, Are more bits better?).

Tip: Even though your inkjet printer has CMYK inks, it reads RGB files, so stick to RGB colour spaces for your images.

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Viewing the print

Your display and your print-viewing conditions must be set up to match each other before you can judge your prints effectively.

Getting a match between display and viewing conditions is the last, and most underappreciated, aspect of colour management. It doesn't matter what those conditions are, or which of the two elements you adjust to bring them in line. All that matters is that they are in line, and that the colour and intensity of the light falling on your print approximates the colour and intensity of the light coming from your screen.

Tip: Don't worry if the print will eventually be displayed under different lighting conditions; our eyes are designed to adjust for those differences. What's important is that you are able to check your print against your on-screen image with confidence.

How should I set my display?

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Photograph © Peter Rees

When calibrating your display, it pays to choose targets that match your prints. For example, you shouldn't set an absurdly high brightness level (more than 200cd/m2, say) and expect your paper to match it. Similarly, keep your display's contrast under control. Few papers ever exceed a contrast ratio of 350:1, so there's no point setting your monitor to anything higher. Select a colour temperature for your display that's close to the colour of your favourite paper – for a natural white paper, that might be 5000–5800K, for brighter papers it can exceed 6500K (D65).

How do I control my viewing conditions?

Matching your display to your viewing conditions can be a process of trial and error. Some printers find it easier to control their viewing conditions instead. Print-viewing booths, such as those made by GTI and JUST Normlicht, provide consistent, controllable illumination. They come in a range of sizes and are often dimmable to match your display luminance.

Daylight halogen lamps and full-spectrum fluorescent tubes are cheaper alternatives. Mounted in desk lamps or ceiling fixtures, they extend your printing time beyond the hours of daylight.

Tip: Solux halogen lamps produce light that is very close to D50. Full-spectrum fluorescents tend to be cooler and exhibit 'spikes' at certain frequencies. Ideally, daylight fluorescents should have a CRI (Colour Rendering Index) rating of at least 96 and a colour temperature of around 5000–6000K.


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>> or next page: Printing in colour: Part two

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