Date posted 11 March 2015

understanding colour

I think its fair to say that most people do not understand colour, Although we all see it in our every day life the whole concept of colour is actually quite hard to get to grips with. For example try explaining the colour of the sky to a blind person without any references to other colours. Its really difficult to not draw on other things you as a sighted person can compare with. This often is the very problem a commercial printer has when attempting to print a clients provided artwork.

It seem quite reasonable to draw a blue box in some editing software and expect a blue box to be printed. Well you will get a blue box but maybe not the blue or shade you was after. Why is it so complex and hard to pass on your requirements to a commercial printer ? after all you can print it out just fine on your £50 ink jet printer and it looks great.

Not all monitors are the same

crt type of monitor TFT style monitor


First of all lets look just a little deeper into what you as a client might be viewing. In most cases you will be viewing your artwork on a computer screen, the bets are that its a TFT-LCD type of display. If your computer is quite old then it maybe a CRT screen. (these typically are as deep as the screen size) most people tend not to use these now as also the power consumption is a lot higher plus the desk space required is drastically increased.

Whilst the modern day flat screen is considered the norm they do tend to have some major draw backs over the older style CRT screen. Firstly the amount of colour that can be reproduced on a TFT screen is vastly reduced when compared to the CRT monitor. TFT screens are digital and as such each pixel shows a single colour. The amount of colours that can be displayed does vary depending on which monitor you are using but typically 8 bits per channel, All monitors work in RGB (Red, Green Blue) so with a 8 bit system you can have 256 shades of each colour, This may not sound like a lot but it works out 256 * 256 * 256 = 16 million colours. WOW I hear you say thats huge, well no its not, the human eye can detect far more colours than this, in fact the human eye is closer to a 10 bits per channel display and capable of viewing far more than we give ourselves credit for. The human eye though is not digital and is more of an analogue device (like the CRT monitors) so in theory the number of colours is endless. However tests carried out have shown most people with a good colour vision struggle past to see differences over 10 bits per channel. So in some respects its a shame that the old style CRT monitors are now considered outdated by most computer users.

Just by adding these 2 extra bits per channel the number of possible colours rises from 16 million to a whooping 68 billion so the difference between the old style and the new is quite huge.

Now you would think having even the limited number of colours of a 8 bit system would still be good enough to create your artwork and send it off to a printer and get the same back. Well we have to consider what happens to the colours in-between 2 values, the monitor will jump to its closest colour it can produce. It is this jumping which often produces what is known as banding. Groups of colours in bands when you wanted it smooth. If you see this on your screen its because your monitor is just not capable of displaying them.

Printers tend to try and smooth out this problem by dithering the pixels to blur the sharp lines, this has the effect of smoothing out the banding so even if you see it on screen it does not mean all is lost but it does show that there maybe be problems looming.

Now all this is fine but there is one very important step missing here. Your monitor is working in RGB, your computer is working in RGB, when you save your file it is stored in RGB but and this is the big but, printers don't use RGB, inks are CMYK (cyan, magenta yellow and black) so therefore a conversion must take place to try and get what you see and the printed material are the same.

In the example below you will see full Red full Green and full Blue (RGB), each one has been set to its maximum so this is the full colour for each. i.e. red = 255 and so on. On the right is the same image when displayed as a CMYK image. You will see they are very different. There is no tricky going on here this is a straight conversion of the first image to a CMYK version. The red is ok but not as bright, the green has gone quite dull and the blue is just wrong full stop.

understanding colour, RGB v CMYK

Most home users never have to worry about this as their domestic printer will do a conversion and attempt to produce a better job than the example above but it will never be able to match it perfectly. For example it will attempt to mix yellow and magenta to make a red close to the RGB value but will never be quite as bright as when viewed on a monitor,

The issue really starts to get more complex when we take into account paper stock. Printers rarely print white. So white needs to come from the paper stock, so for a pink for example it relies on the white of the paper plus some yellow and magenta to produce a pink. Different paper stocks have different brightness of the white (or pure white) so will vary and effect the resulting colour.

Each printer will use a colour profile for their paper stock so that the resulting colour will match fairly close to what is seen on screen and adjust the amounts of ink laid down for each paper stock so the resulting colours should be fairly accurate but there is still one thing missing here which can drastically effect what the customers see and what is printed.

Above we explained a little about monitors, This is really the killer in matching colours, if a client has unpacked their brand new computer system and fired up their editing software then the chances are what they are seeing on screen will be vastly different. All monitors need calibrating which adjusts the colours that is displayed, it does not effect the artwork it just allows you to see truer colours. The art of calibrating is a complex one as there are many variables to take into account, such as the light in the room, the viewing angle, how long the monitor has been on etc. Ideally you can buy a device which adjusts your screen in real time, these work by attaching themselves to a corner of the screen and measuring the colours being produced and adjust the monitor accordingly, however these are quite expensive and outside the budget of most end users.

If you wish to prove this print out a image then turn down the brightness of your monitor and reprint the same image. The images will be exactly the same however on screen they will look very different, this is exactly the problem a commercial printer faces as he has no idea what you as a end customer is seeing. He will print the artwork provided and it will be fairly close to what it should be however not knowing how your monitor is configured it is a pure guess that it will be what you are expecting to receive.

There is one other point that needs mentioning that may not be apparent to why your prints dont match what you see on screen.

Screens produce light, so what you see is the light produced from the monitor and if you view your monitor in a dark room this will appear much brighter than if viewed in normal daylight.

Prints however rely on reflected light so it takes what ever light source is available and bounces back to your eye, if viewed in daylight the colours appear quite bright but if viewed by a domestic light bulb then the colours will change as the colour of the light source will be different and bounce very differently to normal sunlight. A good example of this is try viewing your print by candle light, whites will have a yellow cast as the light source is yellow.