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How Colour Works

Life looks better in colour. Vivacious reds, deep sultry blues and bright invigorating yellows all serve to lighten the soul. We perceive these colours from human eyes picking up a huge range of light frequencies, and we are limited by the frequencies we can pick up. This limitation is referred to as our visible spectrum, and ranges from primary red to deep violet and encompassing all the blues, greens and yellows in between. This spread of colour is known as the “colour gamut” of vision.

While nature has given us quite a wide range of colours to see, the devices we use to produce colours and images have an even more restrictive gamut. The two that have the most impact for photographers are printers and monitors. These two groups of devices use very different ways of making colour namely additive and subtractive colour. Understanding these, and the effect they have on your final images, can change the quality of print you end up with significantly.

Additive colour

How Colour Works

This is the system of light, and includes devices that use light to capture or display images such as cameras, scanners, monitors and projectors. As the three primary colours of light, red, green and blue, are mixed they create colours that grow closer and closer to white light. Devices using RGB describe the final colour with three numbers, ranging from 0 to 255, one for each colour; this is known as the RGB value of a colour.

Subtractive colour

Subtractive Colour.jpeg

Printers and paint on the other hand use subtractive colour, based on the science of reflected light it is very distinct from additive colour. As any child with a set of paints can tell you the more colours you mix the closer you get to a revolting dark coloured mess.

Printers use three colours of ink: Cyan, Magenta and yellow (CMY) and mix them to create most of the colours that are needed. Due to the make-up of the inks they don’t all mix to create a black instead the product of mixing all three is a dark brown. To combat this many printers use a true black ink to print text and improve the quality of dark colours. Printers such as this use CMYK taking the K from the last letter of Black to avoid mix-ups with the “B” in “RGB”.
To assist with the correct reproduction of paler shades in skin tones and skies, photo printers add light cyan and light magenta. So to attain higher quality photo printing finding a device with more than the CMYK inks would be a good start.

Turning your photograph into print

The process of turning the RGB values your monitor shows you and the CMYK combination from your printer into a quality hardcopy is no easy task. The colour matching process used to convert between the two systems can be frustrating to understand. So I’m going to discuss colour spaces and why they can affect your photos.
The colour matching process between the two systems can be a very frustrating process, and you firstly need to understand what it is you are trying to accomplish, before you can take your first steps into optimising your photographic printing.

So let’s start with colour spaces, and how they affect your photos.

Sharks fin diagram.jpg

Colour Spaces

The diagram on this page is known as a “sharks fin” diagram because of its shape. It shows the gamuts that a particular device can display. The largest area on the diagram is the gamut of the human eye. Inside this there are three roughly triangular areas which define the range of colours displayed under three different colour standards.

The central blue triangle borders the area covered by the sRGB colour space. This was defined by Microsoft and Hp back in 1996 and was based around the gamut of colours an old fashioned cathode ray tube monitor. This standard is still common for home and office monitor use.

The largest orange shape is the Adobe RGB colour space. Aimed at graphics professionals, like many of Adobe’s products, the broader range of colours allow a higher specification than a device that only meets the sRGB standard.

Lastly the other orange triangle borders the typical colour space of an inkjet printer, while similar to the Adobe specification it covers some tones that Adobe lacks while missing some others. Any colour in the range can be reproduced on paper.

If you were to try and print a colour from the sRGB or Adobe RBG colour space that was outside the colour space of the CMYK your printer uses, your printer’s software will pick the closest colour it can re-create to provide the best approximation for you.

Whilst this may not sound too big of an issue, if you study this colour gamut image and some of the huge overlaps that can be experienced, then compare that to the astounding array of colours you can get from even a standard photographic camera, you’ll quickly see how the impact of your pictures can quickly deteriorate.

Understanding the constraints on your different devices, the colours that your camera sees, the ones it’s LCD can show you, those that your monitor can display and finally those that your printer can make, is the first step on the road to improving your prints.

Michael Derges is a writer for research for printer cartridge retailer Stinkyink.com. A graduate in Maths and computer science, he is an amateur photography enthusiast, and mixes a keen interest in this with Youth and Volunteer Work out of business works.

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