CAD User Online Article Archive

Feature

Getting into Colour

From CAD User AEC Magazine Vol 22 No 9 - SEPTEMBER/OCTOBER 2009

There are a number of ways that you can get images out of your wide format printer that more closely match the ones you have displayed on the screen - without having to become a graphics colour expert

You may not want or need to produce the natural looking flesh tones of a supermodel as seen in the likes of Vogue, but there's no reason why you shouldn't want to produce the very best in coloured images on your wide format printer. Such delicate tone changes may well be beyond the ability of most printers anyway - but that shouldn't stop you from getting the best possible colour out of your wide format machine. There are two main issues. Actually there are loads, but it is best to bear these two in mind. Wide format printers are geared up for specific markets. The CAD market has different requirements to the graphics markets - the need to handle fine lines, sharper blacks and so on - so the range of inks include special matte blacks to supplement the standard black inks. This is the case with Canon's 6 colour imagePROGRAF 610, 710 and now the 650 and 750 - with CMYK and two Matte Black cartridges (MB).

Graphics printers, though, need a wider colour gamut, and you will now find printers being produced with up to a dozen different inks. Canon's imagePROGRAF 5100,6100, 6200 and 8100 and 9100 series including standard red, green and blues, alongside pale cyan's yellows and magentas. This is achieved using Canon's 12-colour LUCIA II pigment inks. The additional R (Red) G (Green) and B (Blue) inks broaden the colour gamut, and the addition of GY (Grey) and PGY (Photo Grey) enables smooth gradation and less graininess to produce constant monochromes with improved colour shifts and metamerism.

Metamerism is a psychophysical phenomenon commonly defined incorrectly as "two samples which match when illuminated by a particular light source and then do not match when illuminated by a different light source." This enables them to print subtler shades of colour in each area. If you look at the range of colours that are available on any printer, you will see that each of them is slightly different. This is because of the precise formulation of inks developed for each printer, and the media it is going to be used with.

And that brings up a different problem. Printers use a different set of colours to computer screens - CMYK as opposed to RGB. CMYK is also a reflective colour - it's what you get when light is bounced off the page. Graphic artists, though, want to print out what they see on the screen, and that means matching the output on the printer to what's on their monitor! However, the display of each monitor can differ as a result of different MASTERCLASS: LARGE FORMAT technology (CRT versus LCD, for instance) or screen settings, such as the brightness and contrast settings being turned up or down according to personal preferences. The printer driver has the job of converting the RGB signals it gets from the monitor into the CMYK equivalents. It's not just a straightforward conversion, either. Colour printers are designed as part of a system, including both the inks and the media that they will use. If you print out an image on a HP printer, and then on a Canon, you will not get an exact match, as each has its own colour space or gamut.

COLOUR MATCHING

Help is at hand! There are some software and hardware tools to assist you, regardless of whether your images are sourced from scanned analogue photographs or taken with high quality digital cameras. Some of these are mechanical processes - i.e. using the technology to do the match for you - whilst others use internationally recognised standards to match colours. Or, if you have the time, you can play around with the levels of intensity of each colour to create the match that you find most suitable. Colour perception is, after all, a personal thing.

Going slightly off topic, there is another factor that also needs to be considered, namely how durable you want the images to be. Inks are normally either dye or pigment based. With the former, the colour is dissolved completely within the supporting aqueous base, whilst pigment inks remain in solution - and are usually more durable, or light fast. But it's a bit more complicated than just that. Inks must be used in combination with specially coated print media that has a surface receptor coating, which acts to keep the ink on the media, otherwise it would simply pool on the surface. It also controls the dot gain, drying time, durability, water-fastness, surface appearance and colour interaction of the inks, and depending upon where it is being displayed, the images may need protection.

Coatings are relatively fragile and may need to be laminated to protect the surface from abrasion, UV, moisture, airborne contaminates, etc., all of which will further govern the viewer's perception of the image. You could easily write an article just on the interaction of inks and paper media, but a perfect illustration of their symbiosis is the use of Giclee printing - digital reproduction of fine art originals. If you want a picture to last a long time, even when exposed to artificial light that would normally decay the quality of an inkjet image, then you can use acid-free paper, canvas or other media that is designated as archival quality with acid-free coatings and water resistant surfaces.

SOFTWARE COLOUR MATCHING TOOLS

Let's start with the premise that what we see on the screen is accurate. If we are using Adobe's Photoshop to view it (and I am reliably informed that many architects use the software to improve their visuals) then you can match the image to the media loaded on a Canon, or any other printer. Selecting View, Proof Set-up, and then Custom, and then clicking on Profile in the window, presents you with a host of colour modes, ranging from standard international colour consortium (ICC) profiles (Colourmatch RGB, Apple RGB, Euroscale and many others, to a separate profile for each media type. Each profile enables the computer RGB output to be matched directly with the right media to produce the closest approximation possible. You can even take it further still, as Canon does in its latest printers, the imagePROGRAF 650 and 750. If you can match the screen to the media, then theoretically you can modify the output to match anything else - or any other printer. So now you can pop one of these Canon printers in a line-up of HP Designjets, tell it to pretend it's an HP printer - and not be able to differentiate the output! In the Custom box within Photoshop you can also tick the Simulate box, which allows the screen to simulate Paper White. You are, after all, going to print on white paper, and this takes you one step further on the road to visualising, and matching the output you are going to get. You can play around with individual colours under the View tool, or the whole CMYK image. And, using Image/Adjustments under- Selective Colour - you can visually change the constituent amount of each colour within an image, using a slider bar to increase or decrease levels in each of the basic CMYK, RGB and Grey/Black colours.

This works in conjunction with the Colour output profile you have previously set up. Later versions of Photoshop (CS4) allow you to display a range of options in preview format, so that you can see how modifications appear compared to each other before you print.

That brings up an important point. You are never going to get a perfect image the very first time you print it out, but the more you can do beforehand the closer you will get - and the fewer the number of expensive rejects you will end up with in your bin! And the more you use the different tools, the more you will become familiar with the effect that each of your tweaks has on your output.

CANON IMAGEPROGRAF COLOUR SETTINGS

If you are not printing from Photoshop then you may want to modify the output colours directly within the printer driver. This can be achieved within the standard print set-up window. Under the Main tab you have a further two tabs, the first of which handles Colour Adjustment, allowing you to change the saturation of each individual colour for graphics, images and text.

The second tab provides options for four different types of image; standard, portrait, landscape and graphics. Using slider bars, each colour can be manipulated to provide the most natural solution for each type - a very simple, and clever, way of setting suitable colour levels for nonprofessional printers, again relying on the user's visual perception. You can also set brightness, contrast and colour saturation levels in the same way. Using the Matching mode, you can set the colour levels according to the printer driver's settings - either ICC Mode, or the Driver or Host ICM (Windows Integrated Colour Management) mode.

It's pretty important, as well, to tell the printer what type of media you have installed, as Canon have gone to far too much trouble matching software inks and media just for you to tell the printer driver that you are printing to Premium Matte Paper, when you have loaded, and keyed in, Glossy Photo paper on the printer menu!

SCREEN CALIBRATION

Most of the above relies on the visual perceptions of the user, which is normally good enough for most CAD purposes. For absolute perfection, though, some form of mechanical calibration is required, and this can be achieved with some fairly inexpensive tools - basically light metres that can pick up the colour levels emanating from the screen, which can then be entered into the computer.

A variation of this is available with Adobe Photoshop CS4 Extended, which allows users to specify Monitor Matching Mode, picking up the monitor settings automatically from the system and applying them directly to the colour profiles for the paper, modifying it to produce the correct colour matches.

KYUANOS

Canon has developed colour matching a stage further. Besides Canon's proprietary programmes such as Poster Artist, for rapid layout of posters on Canon printers, and a QuickCopy programme, there is Kyuanos, which is available in one of Canon's image management applications, PosterArtist 2007.

Kyuanos uses Ambient Light Adjustment to match colour output to its ultimate setting, and optimises the image output so that it can guarantee consistent colour in the different lighting environments. Light readings are taken of the spot where the artwork is going to be displayed - studio, gallery, exhibition - in order to find the right 'light temperature'. The data is then fed back into the system, and the image colour altered accordingly. You can also use Kyuanos to print several pictures at different light casts if you don't have a light meter and then look at them in the ambient light of the display area, gauge which one looks best and feed that back into the printer manually.

CONCLUSION

There are so many variables that perfection in colour matching may only be achievable after years of experience and trial and error. That, however, may only apply if you are attempting to produce posters for the fashion industry. Thankfully, the tools we currently have available are capable of producing very close matches. It's well worth spending the time to get to know them better. www.canon.co.uk/largeformat

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