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Color management for textile printing

Colors and Control for Designers

Posted on Thursday, 25 January 2018. Posted in Prepress, Pressroom . Written by Paul Lindström

Colors and Control for Designers In order to color manage print you need a spectrophotometer. One of the most affordable is the X-Rite ColorMunki, shown here. The ColorMunki can also be used to calibrate a monitor

One of the most rapidly growing segments of digital printing is printed fabrics. As in every other area of digital printing this means that it won’t only be textile production experts who will provide artwork for and initiate print projects on many types of fabrics.

At the heart of any print project is the desire to achieve the highest possible image quality, and especially getting the colors right. But to get there all the involved parties need to cooperate fully, and each do their part to ensure a successful and pleasing result. As with any printing technology digital print quality, and the colors that can be achieved, depends on three main factors: the print technology used, the inks and, not least, the substrate used. There are some technical factors to consider when it comes to image quality, and for pixel-based images (photos) the two major concerns are resolution and sharpness. The images need to be of a high enough resolution for the images to be scaled up. The rule of thumb says you need twice the resolution in terms of pixels per inch (ppi) relative to the screen ruling you will use in print. In commercial print conventional screens are still common, and a screen ruling of 150 lines per inch (lpi) used to be very common, and while higher screen rulings are more common nowadays, an image resolution of 300 ppi is often stated as the required resolution for images. 

25color 1
Not all spot colors can be reproduced in the color space available when using the CMYK process colors. The colored cubes in the illustration represent single spot colors, while the inner sphere represents the color gamut of offset print on coated stock. About 40% of the spot colors are found to be out of gamut, non-printable, in CMYK

But in digital printing many types of screening technologies are used, and the calculation of necessary image resolution is not always as straight forward as it used to be. And if the printed product will be viewed at a distance, you may get away with a lower end resolution of the image, maybe down to around 100 ppi, after scaling. If in doubt, ask the print service provider what image resolution they recommend for the type of print you are planning. 

Logos and other vector based artwork can be scaled up and down freely, and aren’t restricted to a certain resolution as can be the case with photos. But this means that these types of images and illustrations need to be created using software such as Illustrator or similar, which defines the artwork as spline curves (often called line art or vector graphics). 

25color 2
In applied color management we handle both the Subtractive (left) and Additive (right) color systems, as well as the special colors available when using spot color ink setups.

How many colors do you need?
All printing devices are limited as to how many colors they can reproduce. So, when you plan your print production you will need to ask yourself what colors are most important in your artwork. 

There are two main categories of printing inks used in the industry. For general use the inkset for process colors (Cyan, Magenta, Yellow and Black) is most commonly used to reproduce a reasonably large color gamut of around 400,000 unique colors. But for brand colors, such as a specific logo color, ‘spot colors’ are used. One of the most well-known manufacturers of spot colors is Pantone, which offers over 1000 special hues in the Pantone color system. If you try and reproduce those special spot colors using CMYK you will find that only about 60% of the spot colors can be accurately color matched using the CMYK ink set. So, if one or several spot colors are critical for your print, you will need to pay extra for the printer to use these special inks. The problem is that few digital printing systems, if any, can load all the Pantone spot color inks in the press. 

For this reason more and more printing systems have started to use what is called an extended color gamut, which means that the traditional CMYK base colors are complemented with Orange, Green and Violet. Using an extended color gamut ink in the printing press, around 90% of the Pantone spot colors can be reproduced faithfully, depending on what substrates are used. 

If you have used the Pantone color guides you will have noticed that they come in at least two base versions. One guide is printed on glossy paper, and will show the most saturated and rich colors. Another color sampler is printed on uncoated paper, and the same colors will now look less saturated. This is just how it is, a physical phenomenon, and every type of printing substrate has its limitation in terms of what color gamut it can reproduce, given a specific inkset. 

So, if certain colors in your design are crucial for you, make sure the printer can reproduce them in a color accurate way, and ask for printed, color-accurate proofs beforehand, so you are not disappointed when you receive the final prints. 

Hard or soft proofs?
The beauty of using a digital printer for print production is that you can then normally use that printer as the proofing device. It should be possible to print an example of your artwork in the very same printer that will be used for the final print run. But there is a way to simulate the printed result on other digital devices, including a monitor. This is by using the ICC profile created to calibrate and characterise the digital press. This technology has been around for many years now. The International Color Consortium which introduced the technology was founded in 1993. But for some reason this color management technology is not entirely understood or used in all parts of the graphic arts industry. Correctly implemented it means that every device that is used to create, modify or reproduce colors can be calibrated and characterised using ICC technology. At the core of this is the ICC profile, the data file which describes what color gamut the device is capable of reproducing. 

So, if you save your images (photos) in Adobe RGB, for example, you work in a color gamut of around 1.2 million colors. If you save them as sRGB (very common in consumer cameras and images prepared for web publishing), instead, you work in a smaller color gamut of around 800,000 colors. Every printing press has limitations for how big a color gamut it can reproduce, meaning how many unique colors there are in its color space. 

A common reference color gamut is the offset gamut of colors printed on good quality coated stock, using standard CMYK process inks. This color gamut covers about 400,000 colors. It may sound like this is far from sRGB or Adobe RGB but, since the primary colors for a monitor are RGB, while in print the primary colors are CMYK, the visual result is not so different because those two color systems work in a completely different way from each other. The monitor (and camera) color system use an additive color system, since different wavelengths of light are added to produce the color by emitting light directly into the eyes. When all wavelengths are present at full strength, we perceive this as being white. In print however the CMYK color system is based on a subtractive process, where light is projected to the surface, and then reflected through a thin layer of ink film. When we add colors to the printed surface the reflected light will give the appearance of different colors depending on the mix. If all colors are present we get black (or almost black, because of impurities in the CMY pigments). So, we add a pure black ink and call it K because it is the “Key color”. It is also practical when printing black text. 

There are some colors in the CMYK subtractive system which are not present in either sRGB or Adobe RGB, especially the saturated Yellows and Cyan. Visually however, the Adobe RGB color gamut matches the gamut of high quality offset quite well, and this is in part why the offset gamut is used as a reference color gamut when using many other printing processes. 

When you set up a proofing device, and this could be your own color printer, you need first to calibrate it to a set status, for a certain type of paper. You will need a spectrophotometer to do this, but there are quite affordable solutions on the market, for example the X-Rite ColorMunki. The ColorMunki can by the way also be used to calibrate your monitor, so you’ll get a long way using it. After you have calibrated your device you print (or on a monitor project) several colors and measure them with your spectrophotometer. Those measurements are then used to create the ICC profile for the device. When you apply color management you use the necessary ICC profiles to either convert colors between color spaces, or simulate colors on one device using the ICC profile for another device. Once you have understood how this works you can manage all colors in your printing project, and have serious discussions with your print service provider if you think that they should be able to manage the colors better. 

If you use the Adobe Creative Cloud or similar when creating your artwork, you can set the color settings to use the correct ICC profiles to either make hard-copy proofs on your calibrated printer, or do what is called softproofing on your monitor. From now on there shouldn’t be any nasty surprises when you get the final prints because you have checked that the colors are what they should be early on in the process using hard or soft proofs. 

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