Mar 182011
 

Calibration (also known as Linearization) will standardise the result of a printer and also make it repeatable. Every printer, ink, and media each need to be independently calibrated to remain accurate.

If you use 3 of exactly the same printer in your office, with exactly the same ink, media & profile – without calibration you are likely to see 3 different results, whereas 3 calibrated printers in this same situation will match each other. This calibration will also allow re-calibration if there are any variances – this is what I mean by a repeatable state.

Climate also affects paper and printers drastically and with the climate changes between winter and summer as an example, the colour being produced will also change. Recalibration will bring the printer back to the state that it was originally calibrated to. Without this, a profile with no calibration or recalibration must be redone from scratch if there is any variance, causing valuable labour and consumables being wasted time and time again.

 

Mar 182011
 

The story doesn’t end with a colour profile, some profiles have a larger colour gamut than other profiles, so what happens to colour that can not be produced? This is where something called a “Rendering Intent” comes into action. It the way that colour is mapped between profiles. You may note that in my example above that i have selected “Relative Colorimetric” intent under conversion options. There are 4 primary rendering intents as follows:

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Mar 182011
 

A printer media profile controls other things like ink limiting, gray balance, linearity of colour and more:

Because the profile was specifically produced for the exact printer/ink/media combination you have loaded, it will use the precise amount required to produce colour (saving on ink consumption) but can also eliminate bleedingcocklingpooling, and flooding.

It also knows how to lay down the exact CMY mix to produce a neutral gray without the use of any black ink at all if you choose. Many people have experienced printed gray results that have a coloured cast throughout. Some printer manufacturers add additional light black or gray inks to their printers to overcome this, although this is completely unnecessary in a calibrated and profile state and often adds to the running costs of the printer.

Another thing that is improved by using the correct profile is better linearity, or colour distribution. When using generic profiles, people often see “Posterisation“. This is a visible line that appears between graduations of colour.

 

Mar 182011
 

Profiles are a part of the method for conversion between varying colour spaces.

For example, while viewing a CMYK file on a monitor (an RGB device), there is no direct link between RGB and CMYK colours. There needs to be a translation in the middle that allows this to happen (cielab) plus a description of how these colours should look. Different RGB devices will produce colour differently to each other, and be different to other RGB devices like scanners or digital cameras. Likewise, CMYK will produce colour differently on different devices and media. Each specific output requires a description of how to accurately produce the colour in a digital file.

There are always 2 profiles in any conversion (with the exception of files created in cielab). There is an “Input or Reference” profile that describes what the file should look like, and an “Output or Media” profile that explains how to achieve that result. In between these two profiles is cielab to allow this conversion to happen.

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Mar 182011
 

Colour management is the calibration and profiling of each device that digitally produces colour in a file workflow so that produced results are consistent from file capture, design, view, and print or output. Without this results can be somewhat random.

Sometimes peoples whole focus when attempting to control colour workflow can be on “Profiles“, they are just a very small part of the equation. Every device and media or ink needs it’s own unique profile to be accurate.

 

Mar 182011
 

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.

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Mar 182011
 

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

 

Mar 182011
 

TO

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.

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Mar 182011
 

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.

 

Mar 182011
 

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.

 

Mar 182011
 
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.

 

Mar 182011
 

cielab is industry terminology for a way to describe colour.

Pronounced: “See-Lab”.

cielab is a 3D XYZ axis that scientifically describes how the average human eye sees colour proposed by the CIE (Commission Internationale de I’Éclairage). L, A & B are the three axis that place the colour in this 3D space. Any colour conversion needs a universal middle way to convert the colour. As an example, if viewing a CMYK file on an RGB monitor you are actually using 2 ICC profiles even if you don’t realise it or aren’t controlling it. But CMYK has absolutely no relationship to RGB, so these 2 ICC profiles (RGB & CMYK) go into cielab as a way to calculate this conversion.

Example of how the conversion works:

CMYK -> lab -> RGB
File Being Edited Output on Monitor