How Colour Works

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

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 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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Some Older Comments

  • Dave August 1, 2011 06:19 am

    0-255 is only 8 bit colour, you increase these steps as you add bits. 2 to the power of 8 is 256 which is your 256 (0-255) range, so 16 bit is 65536.
    Colour with a "u" is English, without can be viewed as a mockery or a lazy take on efficiency. In matters of English I think it's wise to side with the English.

  • tutness July 23, 2011 04:32 am

    Good introduction article :) I think you did a great service for people who want to get more into printing their work.

    I actually work in digital print, and what I can say is that a lot of your choices should also refer to the media you choose to print on. I specialize in canvas prints, which is fairly limited media compared to photo paper. The gamut of good quality paper will easily cover Adobe RGB, whereas the gamut of canvas is just enough to cover sRGB. And if you're printing at a digital printer, forget altogether about converting to CMYK, it's too narrow and will botch up your colors. Completely unnecessary. CMYK is the way to go only if you're doing offset print.

    Anywho, since at the end of the day colors are "just" numeric values ... you can feel free to play around with them, it's much like trying on different "glasses". You can easily assign profiles to check the difference in color range which is a non-destructive practice. And then if you're a cheat like me, you can also make conversions from profile to profile and gain "Adobe RGB" looking colors in an "sRGB" color space ;)

    Really simply put - Adobe RGB gives images a summer like look, sRGB feels more like winter.

    I'm hoping you follow up on this article, I'm interested in your take on things as I think there's a lot that can be said :)

  • Andy Mills July 23, 2011 12:10 am

    While the article is useful and tells you about colour, it doesn't really say what you should/can do with the information, and has probably just confused some people further.

    Basically, Adobe RGB is supposed to allow extra colour information to be stored in the image than the sRGB colour space.

    Nearly everyone (especially non-photographers) will be using sRGB to view images on monitors, so stick to sRGB when sharing digital files as other people may not be set up to view Adobe RGB and may get strange results (as some people have alluded to in comments above).

    This isn't necessary for RAW files. You can save your own working/end files (or set in camera for JPEG) - JPEG, TIFF, PSD, etc., with an Adobe RGB colour space/profile, which when you print yourself should give a slightly better print quality. But you would need to test to see if you do get any advantage with your equipment, and if it's worth the extra hassle.

    But if you outsource your printing, check to see what they want - they usually stipulate an sRGB profile, or they have created their own profile matched to their printers. Again, if you share with someone else, convert to sRGB.

  • DaveA July 22, 2011 11:30 pm

    First, the "shark fin" diagram is actually known as the "chromaticity" diagram, as it shows all the possible colors that can be reproduced by the spectrum (the numbers on the edge referencing the wave lengths in nanometers from Blue (400nm) to Red (700nm). It is the shape it is because of the inability to show magentas and purples, which are combinations of Red and Blue at opposite ends of the spectrum. Moreover, the shape indicates the 1931 chromaticity diagram, with a newer diagram and color theory associated with it released in 1964.

    As for color space, I always recommend the use of Adobe RGB as it allows for greater saturation and color gamut of the image. Once captured, you can always reduce the color gamut for the intended purpose (web, print, etc.) but once confined or compressed, you can never truly bring it back! Remember, sRGB is the lowest common denominator, which means it can be used with the cheapest camera and monitor as well as the best. If you've got a Canon 5D or the like. with all of its capabilities, why would you want to ham-string it (reduce its performance) with sRGB?



  • Lucie July 22, 2011 03:19 pm

    This article is very timely for me, as I have just joined a camera club and am thinking about printing my photos for the first time. I soon came across the dilemma of sRGB vs aRGB, and discovered that almost all commercial printers use sRGB. I also read that sRGB and aRGB both have the same NUMBER of colours but that aRGB has more colours (I'm an Aussie and we use British English too) while sRGB has more shades of fewer colours - something that all the teachers telling me to set my camera to aRGB hadn't mentioned.
    Thank you to 'ua' for confirming what I had begun to suspect, that if I am taking RAW photographs then I can decide in post whether to go for sRGB or aRGB, or I can do a jpeg of each, without degrading the end result.
    At the moment I am doing just that, and getting the results printed so I can compare them. There is a difference.
    Please can we have more on this subject.

  • ShooterMum July 22, 2011 05:21 am

    I've been doing the Photography Institute Course (online) and George Seper always tells us to shoot in Adobe RGB for each module. But, I still find this issue confusing, so a well timed article. Thanks!

    I don't have a printer and had to try a couple of print shops to get the image to look like it did on screen (and of good quality). If you're like me and you haven't invested in your own printer (and live in NZ), I would recommend using Photo International in Christchurch. Their prints are always top quality in colour (and their B&W is great - it doesn't have that awful green cast that some print shops have) and you can do it all online.

  • Matt July 22, 2011 03:01 am

    @Robin--If you don't know why you would use Adobe RGB, just use sRGB. You only want to be providing Adobe RGB to clients if that is what they want to work with--everybody else is going to expect sRGB, whether they realize it or not.

    @The rest--Just use RAW--you can do all the same stuff you would do shooting a jpeg, but then you can do so much more with it when you get it back to your computer, if you want to. And if you only shoot jpegs, most of this color space information isn't going to be very helpful anyway.

  • Thom Holland July 20, 2011 09:38 pm

    As always, very useful post for beginners like myself.

  • ihateliver July 20, 2011 06:44 am

    As a newbie, I also followed the suggestion in "Canon EOS 450D for Dummies" to set the colour ("two countries separated by a common language") space to Adobe RGB. After getting some very strange looking red tulips on my monitor (and some help from a DPS forum), I switched to sRGB - with much better/consistent colours.
    Thanks for the tip about RAW - could be useful for the rare times I think I'll be printing anything.

  • F-64 stopper July 20, 2011 04:07 am

    Finally words on this site that make sense and are factual and not biased opinons. Great write up!

  • Robin Öberg July 20, 2011 03:58 am


    I would say one would want as large a range of colour as possible, whether it be in printing or on screen.


    Problem is, I cannot save jpegs in cmyk?
    So on microstock websites I have to make a choice between srgb and adobe rgb...
    But which one to go with...
    Does it depend on the image?
    More reds equals adobe, whilst more blues equals srgb?
    Or should I go be the spikes in the histogram?
    I am confused :D

  • Doug Sundseth July 19, 2011 11:21 pm

    It's a good thing the British are so good at understated humor and sarcasm. Otherwise they'd probably completely miss it when it passed by in the street waving a flag and leading a 98-piece band.

    You know, if that were to happen.


  • UA July 19, 2011 10:49 pm

    If you are worried about wether to shoot sRGB or Adobe RGB, start shooting only RAW. Since RAW is basically the information that the sensor was able to capture, you move the decision of color space to the post processing. In fact, most sensors can exceed the Adobe RGB gamut and you have more color space on your RAW files.

    This way you can export sRGB for web publications and Adobe RGB for printed publication (if required). I think sRGB is always the safer selection for JPEGs, but you do not get the best possible colors to a print. However, is this difference remarkable in any situation, I do not know, but what I do know is that edit you Adobe RGB jpeg on sRGB color space calibrated monitor and your printed results might look awful.

  • Mandy July 19, 2011 08:43 pm

    A great introductory post about colour, but could we have some more please...

    and yes being British I spell colour with a 'u'!

  • Robert July 19, 2011 07:52 pm

    I'll get flamed for stripping this out to such simplicity I'm sure but....
    Since sRGB is what monitors can display, and falls entirely inside what CYMK printers can draw, does it not follow that an image captured using sRGB can be reproduced identically on both screens and print so it is only when going "off piste" with other colour spaces that we will have any issues anyway?

    Is using 'bigger' colour spaces just another way to make sure you have to spend hours in software 'getting it right', when if you used the standard sRGB, your expensive camera would probably have got it right already?

    As far as I can tell, the only reason to use adobe colour spaces is when doing pro printing work with print shops that use adobe products. Always remember Adobe are a company concerned with the print industry, Digital Photography is one tool they use, not their primary business.

  • Mike July 19, 2011 07:10 pm

    Heh, I'd never even thought about double checking the CMYK thing, turns out wiki tells me I'm wrong. Cheers Matthew for correcting me, guess I learned something today.

  • Yngve Thoresen July 19, 2011 04:54 pm

    Informative article, but I would like to know when to use what colour space, adobe rgb or srgb? I'm currently trying to use adobe RGB when I work with images, but when I save the image to jpeg and convert to srgb for web, I experience a rather big change in colour.

    This is very frustrating and leads me to believe that 1) I'm doing something very wrong. or 2) I should just stick to srgb all the way.

    Any thoughts on this?

    It's only in American English that colour is spelled "Colour", the rest of the world (British English) use "Colour".

  • Johnp July 19, 2011 04:49 pm

    Great article. I made the mistake of setting my camera and printer to Adobe RGB as that covered a greater colour range. I'm no expert but found in practice for normal printing there is no difference in quality to sRGB. Adobe RGB does not work so well on monitors and I would suggest therefore you always stick to sRGB.

  • fotomate July 19, 2011 04:36 pm

    great article! now waiting to include contrast of colors to make outstanding picture :)

  • Marisela July 19, 2011 03:55 pm

    Very informative article for newbies like me. I definitely had an "A-HA" moment, and am curious to learn more. Thank you!

  • Matt July 19, 2011 12:58 pm

    British English is also the English used by Canadians so the "u" in words like harbour, favour, and colour are very common. There's also centre vs center, etc...

    Anyway, great article - will be sharing this with my students!

  • Veronica July 19, 2011 12:20 pm

    @ Major Bokeh and Madison Raine

    Actually, Colour is the British way of spelling the word. Color on the other hand is the American spelling.

  • Diogo July 19, 2011 11:54 am

    Colour With U is British english... :)

  • Madison Raine July 19, 2011 11:30 am

    @ Major Bokeh,
    sometimes people use "U" in color to be artistic. That's just what I heard. I've never spelled it that way.

  • Robert July 19, 2011 11:04 am

    I never really noticed issues with color until I started printing my digital work. Even with a calibrated monitor I've had some minor issues with subtle color casting on some of my larger prints. I seem to recall things being much simpler back in the film days?

  • scottc July 19, 2011 10:07 am

    A challenge of an article to understand, but well worth the read and further study. The quality of color can be easily overlooked when we're used to our own devices.

    I think perhaps you may have overlooked how the available light can affect the color in a photo, it is a key starting point.

  • Dennis July 19, 2011 08:50 am

    The letter K, in CMYK, comes the German word 'Kraft', which means 'power' or 'strength'. And represents the black plate in the print industry. And the (book) printing industry started and was invented in Germany.

  • af July 19, 2011 08:30 am

    I agree with Robin: I would like to see more technical writing at DPS. It would be nice to see a follow-up on how to go about getting the best results in print, once you're satisfied with what you see on-screen. When I'm fussy, I print strips using various printer/paper profiles, then select the best for the final product. I'd be interested in learning how others go about it.

  • Major Bokeh July 19, 2011 07:50 am

    Great article, but you'll never get your "color" right if you keep spelling it with a "U"!! :-D

  • Robin Öberg July 19, 2011 07:16 am

    Hmm, I am not sure I understand this. Which one do I choose if I want to try to sell jpegs on a microstock website? And how do I make that setting in Lightroom?

    It is good to see something that is slightly above the standard level here at DPS. Thanks! :)

  • Matthew Rigdon July 19, 2011 06:54 am

    The K in CMYK comes from the word "key", as the black plate is referred to as the key plate in print work. You can read a discussion about this here.