PRINTERS

RGB, CMYK and photo printing

Learn about RGB and CMYK colour systems. Find out how Canon inks and paper are designed to work in harmony with printers, providing colour accuracy.
The sensor in a digital camera contains millions of tiny photosites (light receptors), each one of which is sensitive to light – but not to colour. To capture colour data, each photosite is covered by a red, green or blue light filter. This means that some photosites are now sensitive only to red light, some only to green, and some only to blue. By clever processing of the data from all the photosites, the sensor can work out the exact proportion of red, green and blue light at any given point, which determines the colour of the corresponding picture element (pixel) in the full-colour image created in-camera from that data.

Computer screens also use red, green and blue (RGB) data. In fact, any imaging system using emitted light (such as a digital projector or a television screen) uses the RGB system. With RGB, when no light is emitted, you have black, while mixing all three colours at equal intensity produces white. In between these extremes, combining different intensities of one, two or three of the primary colours produces the entire range of hues you see on-screen.

The problem is that this system does not work when you want to transfer an image to paper. Paper does not emit light, it reflects it. If you lay down red, green and blue inks together on paper, you get a muddy brown colour, not white. And if you put no inks on the paper, white paper remains white, not black. So, for printing onto paper, the CMYK printing process is used.

CMY stands for cyan, magenta, yellow. Mix equal amounts of two of these together and you can make red, green or blue. Mix equal amounts of all three and you get black – almost. Because inks are not perfectly opaque, the black appears as more of a dark brown colour, so a pure black ink is added. Black is not denoted with the letter B because it would be confused with blue, so K is used instead. The result is the CMYK system. All the colours produced by a CMYK printer are created by laying down cyan, magenta, yellow and black ink in different proportions. (Strictly speaking, the different colours of ink are never actually mixed. If you enlarge a printed image, you can see that it consists of tiny dots of distinct colours, and the "mixing" is an optical effect, causing the eye to perceive different colours.)

In the RGB system, when no light is emitted you get black, and increasing the intensity of all the colours gets you closer to white. For this reason, the RGB system is described as additive. In the CMYK system, when no ink is laid down, white paper remains white, and adding more colour gets you closer to black. Accordingly, CMYK is described as subtractive.

Although printers work with CMYK and your images are in RGB, you should not perform a CMYK conversion yourself in your image editing software prior to printing your images except in very specific cases, such as when you are producing a hard proof to send to a client for colour matching. The printer driver software will do the appropriate conversion from RGB to CMYK to ensure the best results.
A diagram showing how red, green and blue mix in the RGB colour system (left) and how cyan, magenta and yellow mix in the CMY system (right).

Left, a representation of the RGB system, which produces different colours by mixing the three primary colours of light – red, green and blue. Mixing equal intensities of all three (by projecting them onto a screen, for example, so they overlap) produces white, while mixing red and green produces yellow, mixing red and blue creates magenta, and mixing green and blue produces cyan. Right, the CMY system, which is used in printing to create different colours by overlaying three colours of ink – cyan, magenta and yellow. Cyan plus magenta produces blue, cyan plus yellow makes green, and magenta plus yellow makes red. In theory, mixing all three produces black, but in practice the result is a dark brown, so in photo printing a black (K) ink is usually added, giving the four-colour CMYK printing process.

A diagram of a Bayer array, with alternating rows of red-and-green and blue-and-green colour filters.

A representation of the most common type of colour filter array in digital sensors, a Bayer array. This is what makes it possible for the sensor to capture colour data, not just light intensity information. As it happens, the human eye is more sensitive to green light than to blue or red, so in a Bayer array there are two photosites for green to every one for blue and one for red. For this reason, the green channel in a digital image invariably has a better signal-to-noise ratio, and hence less image noise, than the other colour channels.

How many inks?

Canon inkjet printers use anything from three to ten different colours of ink. In the same way that black ink is added to the CMY system to improve contrast, so inks such as photo cyan, photo magenta, red and blue are used to compensate for other deficiencies. It is not that the CMY system is at fault – it is just very difficult to make perfect cyan, magenta and yellow inks.

In theory, the more ink colours, the wider the colour gamut the printer is able to reproduce. Nevertheless, printers with only six inks can still produce photo-quality prints. Professional printers use the largest number of inks (up to 12). The extra colours are likely to matter only to professionals who are selling their prints and require absolute colour fidelity. In practice, the differences are subtle – in many cases you will find it difficult to detect the difference between a six-ink print and an eight-ink print.

Inks and papers

Inkjet printers generally use dye-based inks. This is true of Canon's PIXMA range of printers, with the exception of the black inks in some, which are pigment-based. Because of the way dye-based inks react with photo paper, they tend to produce more vibrant colours than pigment inks – the dyes permeate the paper, while the pigment inks sit on top of the paper. For the same reason, dye-based inks tend to produce prints that more accurately reflect the character of the paper – for example, high gloss paper appears as a true high gloss.

Bear in mind that prints are usually touch-dry as they emerge from the printer but may need a few more minutes to fully dry out.
A Canon PIXMA PRO-200 printer on a desk alongside a computer monitor, with various colourful photo prints displayed on the wall behind.

Digital cameras, projectors and computer screens all display colour using the RGB system. Printers produce colour using the CMYK system. To get from one to the other, the driver software built into your printer does some clever conversion – and the more it knows about the ink and paper you're using, the better it can fine-tune the output to match what you expect to see.

A selection of Canon photo papers.

Whether you're printing photos for an album or creating gallery-quality prints for sale or display, Canon offers a range of papers designed for use with PIXMA PRO and imagePROGRAF PRO printers. This is just a selection – they are available in a choice of sizes, weights and finishes to suit the most diverse requirements.

ChromaLife 100+

You will get the best quality prints if you use a Canon printer with Canon paper and inks, because they are engineered to work together in harmony with the printer. With its combination of ink, paper and nozzle technologies, Canon can claim 100 years light-fastness for prints made using products with the ChromaLife 100+ badge.

However, there are certain caveats. Temperature, exposure to direct sunlight, humidity and atmospheric gases all play a part in degrading the quality of a print over a period of time. The ChromaLife standard claims 100 years light-fastness for a print stored in an archival album, 30 years for images displayed in photo frames and experiencing around 10 hours of light per day (though not direct sunlight), and 10 years for images pinned on a board or stuck to a refrigerator.

Like dye-based inks, the special LUCIA PRO pigment inks used by the imagePROGRAF PRO series are light-fast for 100 years and gas-fast for 50 years (meaning the inks do not fade in the presence of ozone and other atmospheric gases) when used with a suitable paper such as Canon Photo Paper Plus Semi-gloss.1

Printing and colour accuracy

No matter how good your printer, you will not be able to produce prints with colours that are fully accurate if your workflow isn't colour-managed. Typically, monitor and laptop screens tend to be too bright and their colours too cool (too blue) compared to normal viewing conditions for prints, so a printed image will look very different from the image on-screen. Ideally you should calibrate your monitor and get your workspace lighting conditions as close as possible to the conditions in which you intend to display your print. When you're printing, Canon recommends using its specialist Professional Print & Layout (PPL) software, which offers powerful soft proofing and hard proofing features to help you match your printed image with what you see on screen.

If you're using Canon inks and papers, then your prints should have a good level of colour accuracy, particularly if you take the professional approach and print using ICC profiles for reliable quality and consistent results. In PPL, the key step is to select the right paper from the Media Type drop-down menu under the General Settings tab. PPL has a library of built-in ICC profiles for Canon papers, which means it can fine-tune the output settings for the precise characteristics of the paper you're using, such as its reflectivity and ink absorption. If you're using third-party papers, you can often find the appropriate ICC profile available for download from the paper manufacturer's website. There are very clear instructions and useful advice about this on the Hahnemühle website, for example.

Sometimes, if you're using a third-party paper, there might not be an ICC profile for that particular paper, so for predictable results without a lot of trial-and-error, you'll need to create a profile for it yourself. Canon's Media Configuration Tool is a free download designed to help with this, which is worth the effort if you plan to use a particular very expensive paper frequently and want to avoid wasting a lot of it on numerous test prints. The Media Configuration Tool may be installed when you initially install your printer driver software. Otherwise, visit Canon's printer support page, select your printer, then click Software. Find Media Configuration Tool in the list, and install following the instructions. Your printer User Guide will contain a section explaining how to use the software.
A user reaches for one of the ink cartridges in a PIXMA PRO-200 printer, shown from above on a desk with various colourful prints.

In theory, full-colour images can be printed using just three inks – cyan, magenta and yellow. In practice, though, inks are not perfectly opaque, so that mixing all three colours does not produce a true black. That's why printers use a black ink as well. For similar reasons, printers often use additional inks such as photo cyan, photo magenta, red and blue. For photo-quality prints, the PIXMA PRO-200 printer uses 8 dye-based inks.

A Canon imagePROGRAF PRO-1000 printer, with its 12 ink tanks visible at the front.

To produce gallery-quality prints at up to A2 size, the Canon imagePROGRAF PRO-1000 uses a pigment-based 12-ink system, including a special ink called the Chroma Optimiser, which results in prints with uniform glossiness, greater colour fidelity and reduced bronzing.

Printer specifications

SELPHY

Canon's SELPHY range of compact photo printers produce images very similar to the standard 6x4-inch prints you would receive from a traditional mini-lab. They use dye-sublimation technology (with the exception of the DS-series, which uses inkjet technology). Some are portable and run on batteries, enabling you to produce photo prints on the go.


PIXMA

The PIXMA printer range is the largest – and most popular – in the Canon line-up. PIXMA printers use inkjet technology to produce near-photo-quality prints. For most photographers, printing up to A4 size is more than adequate, but there is a semi-professional model, the PIXMA PRO-200, which prints up to A3+ size.

Most PIXMA printers use single-colour ink tank technology for more economical printing and less wastage. You need to replace only the individual cartridge that has run out, rather than an entire multi-ink cartridge in which there could still be plenty of some colours.

If you do a lot of printing, Canon's MegaTank printers – a wide choice of PIXMA G-series and MAXIFY models for home or office – feature refillable ink tanks for low-cost, high-yield printing with outstanding ease of use and effortless connectivity.


Pro

Canon's pro photo printers use the same inkjet technology found in the PIXMA range, but with different inks. The PIXMA PRO-200 uses eight dye-based inks, while the imagePROGRAF PRO-300 uses 10 inks, and the imagePROGRAF PRO-1000 uses 12 LUCIA PRO pigment-based inks. The pro printers are A3+/A2 printers – ideal for producing large, "gallery-quality" prints suitable for selling or exhibiting.

As we've noted, the extra inks are designed for greater colour accuracy where it matters. For example, the Matte Black ink delivers greater black intensity and better reproduction of shadow details on absorbent papers than Photo Black, which is formulated for use on glossy papers. In addition, the unique Chroma Optimiser adds a specialised coating for more uniform light reflection off glossy paper, ensuring enhanced dynamic range and eliminating bronzing.

Related articles

Related products

Get the newsletter

Click here to get inspiring stories and exciting news from Canon Europe Pro