There are 2 main ways of digitally producing the colour we see:

Additive colour (e.g. Monitors - RGB) Additive colour works by mixing light sources. The primary additive colours used are Red, Green & Blue and are measured on a scale of 0 to 255 (0 being no light and 255 being full intensity). If you combine 255 of all Red, Green & Blue then we see White. If all 3 are at 0 then we see black.

Subtractive Colour (e.g. Print - CMY) Subtractive colour is based on light being absorbed by a surface, and the light that isn’t absorbed is reflected as a colour. The Primary colours we use are Cyan, Yellow & Magenta. If you coat a white surface equally with 100% of Cyan, Yellow & Magenta then we see black and where there is no colour we see white. In printing we also add Black to achieve better grey shading than what can be achieved with CMY alone. Black also allows us to make a darker colour than we can produce with just CMY.

Our eyes are actually RGB devices:

The human eye has red, green, and blue cones in the retina. Unfortunately you can't calibrate and profile your eyes, so you should remember that everyone sees colour from a different perspective and you might not actually be seeing the same thing.

An only colour specialist joke that was bandied around at one stage is:

What is the colour of Cyan?

It's not that funny, but a little ironic I guess. From a technical perspective we all see cyan as a different colour and this will depend on our individual eyes and also what we have learnt as that colour as a child.

A good tip for comparing colour:

Because a colour you are trying to compare in the middle of a print is being visually tainted by what surrounds it, it's a good idea to cut a black card with 2 holes of equal size and shape that are the right size to show only the colour you are comparing. Place the colour in the print that you are trying to match under one hole, and your reference (e.g. pantone swatch) under the other hole. Here is an example of what to create:

This eliminates many of the pitfalls of colour comparison and it's something I highly recommend trying at some stage. If you are unsure why you need this then I suggest you look at the Dale Purves web site in our links page. This site gives clear and obvious examples of what you can experience on a print.

I am looking at producing these if there is enough call for it. Please register your interest with me.

Screen colour versus printed colour:

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Scanners and Monitors use an emitted light, and so images are produced using red, green & blue coloured lights (or “guns”).

When printing we are usually coating a white surface with colour. This means that we use cyan, magenta, yellow & black inks or toners to reflect colour.

To match what you see on your monitor accurately on your printer, both devices need to be carefully calibrated and profiled. If you do this you have the best chance of this situation.

It's important to note, that some people mistakenly adjust their monitor by eye to look more like what their printer produces. The reason they do this is so that they can predict what a print will look like on their printer, but there are some serious flaws in doing this:

You are completely forgetting what colour data in in your file (because now both your monitor and printer are producing incorrect results) and when you send that file outside for someone else to print you are almost 100% guaranteed of a different result from their printer that you aren't expecting or want. This is not because they have done anything wrong, the problem (although it might not at first thought seem to be) is with your setup. Unfortunately I have often herd of some suppliers suggesting this as a way of matching a screen to a printer and it's totally bypassing the true problem.

The accurate way to resolve this situation is to use measurement equipment and software to calibrate and profile BOTH your monitor and your printer media. This allows them both to know how to accurately produce the colour in your file and by default, they will match each other.

 

Some monitors are not capable of being calibrated the same as the high end equipment, and often this can be why there is a noticeable difference in cost between a cheap LCD or CRT to a quality monitor built specifically for the colour critical markets.

This can also have other benefits such as stability meaning that the monitor requires re-calibration less often. Often cheap, or quite old monitors are not capable of producing accurate colour results, even with calibration and profiling and should be replaced with equipment that can. Monitors that are colour critical should be replaced about every 2 years to ensure accuracy and consistency. Higher quality monitors will last much longer but remember: "you get what you pay for".

Compare Colour specialist monitors at cielab colourshop

These two colour process cannot be absolutely 100% matched due to the different systems, although when both are correctly calibrated & profiled, they can become visually very close depending on the quality of your equipment and the software you use.

What Else?

Colour is also affected buy your surroundings (colour of walls / light quality etc.). This can often have a massive impact on the colour people see. The most common example I find regularly is some B/W prints appear to have a colour cast through the printed result - simply take the print into outdoor natural light and this often changes the appearance dramatically.

A great way to see examples onscreen of this is at Dale Purve's web site on colour (in our links page).

The best solution to this in your environment is to get a light viewing booth. These booths are calibrated to have the exact value of light at the viewing surface. This can not be easily done by simply changing your fluorescent light bulbs to daylight bulbs and painting your room a light neutral grey (although these is better than nothing).

Compare light viewing booths at cielab colourshop

Is Offset ink the same as Digital ink

Most offset printers are very accustomed to working with colour values to achieve a result on their press and make the assumption that you can work in the same way with a digital device. I have seen this many times, and have great respect to the printers that understand colour that well, although unfortunately the ink & print technology in ALL digital printers does not react the same as a press with film or plates will.

If you took 3 different digital printers, unfortunately you would have 3 very different coloured Cyan, Magenta, and Yellow ink sets. Not only that but because the media these printers are laying ink onto has a specially formulated coating to receive and hold this ink, each machine will produce a different reaction to the same colours. This means that by not using custom profiles and adjusting the CMYK file values as you could do if you were making film or plates will not work on a digital printer or proofer. If the colour of Magenta is different from one printer to the next, then by simply adjusting the density curves will not achieve the same results between these machines. This also explains why digital proofers mix additional colours into what could  seem incorrect as a primary colour.

A typical example of this is in yellow, where additional colour are sometimes visible on a digital printer making it appear dirty: this comes from the problem that the actual colour of the yellow ink is different to what you have asked it to print, and the profile tries to match the same yellow by mixing in other colours in very small quantities. Sometimes in a profile that has a limited gamut this can give an undesired result by making primary colour appear dirty, but on a quality media & profile combination this will work for you and not against you.

I once worked along side an offset printer that created a manual calibration curve in the rip software and used no colour profile (as you would on a press) and then tried to produce canvas prints with very specific colour requirements. I respect this person's ability very highly, but he was not able to get a satisfactory result in doing this. I then used measurement equipment and software, and calibrated his rip and produced a custom ICC profile for his media/printer combination, and nailed the result that he was unable to get otherwise.

So why was this the case? By adjusting the curves on his digital printer, he was able to maintain very clean primary colours, but by the simple fact that each colour curve, is a curve. When you move the curve in one place, it affects the colours around it. In an ICC profile, each colour is it's own unique calculation and has no relation to a similar colour that it would otherwise. Each colour is uniquely considered in relation to LAB (or how it should look to the average human eye after it's printed) from an ICC profile.

If you have questions on this topic, unfortunately it's too advanced to explain in full detail on this web site, but I welcome you to contact me to discuss it further.

There are a few ways people commonly choose a colour for digital output:

• Pantone

• HSB / HLS

• CIE/LAB

 

Pantone

Most people are familiar with Pantone colours, although don’t usually realise this does not specify what colour is expected from a final printed result.

Pantone only describes the colour of the ink used by offset presses. The final printed offset colour may even vary depending on different stock used. See Pantone's official web site in our links page.

Pantone works for a set of 14 base colours (not including specialties such as fluorescent or metallic inks) and many people can better compare it to mixing paint at the hardware store. A base is used and then tints are added in specific amounts to mix the pantone colours.

Ink digital printing (referred to "Process" in offset terminology) you are only working with 3 colours (cyan, magenta, and yellow) with black for shade. So it's impossible to exactly match every single offset colour in the Pantone Coated/Uncoated guides. Depending on the colour gamut of the ink and media combination in your digital printer, you will produce different amounts of pantone colours, and without careful calibration and profiling of your printer, you will battle to often get PMS colours on your digital printer (however, once again, with careful calibration and profiling of the printer you will have the best automatic match to the pantone sets).

The Pantone Coated guide (as an example - seen right) shows what result could typically be expected from an offset coated stock when approved pantone inks are used to mix each swatch in the book. But remember, even in offset, when you print these inks onto different papers you will get a different finished colour. People comparing pantone colours to a digital printer should use the "Pantone Bridge" guide (seen above), as this gives examples of both the coated and process (CMYK) expected results, and also gives RGB values under the coated swatches.

Other processes that don't use these 14 colours to produce Pantone colour (like ALL digital printers) are just a representation of that offset ink system.

There is an article that I produced for the Visual Impact magazine that talks in more depth on this topic in the Reference tab.

Compare Pantone products online at cielab colourshop

HSB / HLS

You may have seen HSB (Hue, Saturation & Brightness) or HLS (Hue, Lightness & Saturation).

These models were created, and are used by the graphic art industry as they’re more intuitive way to discuss colour.
 

CieLab

A better method for describing colour scientifically is a system called CieLab.

This was created by the “International Colour Consortium” (ICC) and is based on 3 dimensional numerical values representing how the average human eye sees colour. See the ICC web site in our links page. There is a more advanced explanation on our What is Cielab page.

Just because we can describe a colour does not mean that the output device can accurately reproduce it.

These topics and more are addressed in the courses we hold. Our goal is to help educate the industry, so please feel free to contact us if you have any questions. Please contact us for more information.