Using colour management system for perfect colour accuracy

For quality conscious printers as well as print buyers, colour management system is no doubt unavoidable tools before one goes for final printing of any given print product scheduled to be printed on a sheetfed or web machine.

01 Jul 2016 | By Som Nath Sapru

A colour management system (CMS) is a collection of software tools designed to reconcile the different colour capabilities of scanners, monitors, printers, imagesetters, and eventually desktop printers, proofing presses and printing presses. CMS maps colours from device with a large colour gamut, such as a monitor, to a consequently, all colours on the monitor represent colours that the output device can reproduce.

Colour Management System is used to ensure that colours remain the same regardless of the device or medium used to display colours. This is extremely difficult because different devices use different technologies and models to produce colours, which would match exactly or near exactly as the original shoot. In addition, colour is highly subjective. The same colours look different to different people and of course, under different light conditions.

Let us say Colour Management System is a set of software tools and concepts that try to preserve as much as possible, the same colours from the shooting stage to the final reproduction of the print product – sometimes as the project demands – enhance or decrease the values of the picture as per print buyer’s requirement. All this to avoid those too often heard things – “Oh the colours of my prints are very different what I see on my laptop or tablet” – or “your colours are not like mine what I see back home,” etc.

Colour management thus serves to align all scanners, monitors and printers on the same colour values, at least close to it. The ultimate goal is to display a picture with same values at all places may it be home, work place or any other public display centre, with the same aspect to achieve all this we have to calibrate.

To measure colour precisely, one requires specialised instruments – for example to measure only transmitted light and it has no light source of its own. These are mostly used to calibrate and profile monitors. One can easily measure printer and monitor both for colour values by this device simultaneously.

Whereas to measure colour on a piece of paper one needs a spectrophotometer – this device has capability of giving accurate and correct calibrated end values besides it can calibrate and measure monitors and even can take readings from printed material with absolute accuracy.

Hypothetically, if we are looking for background colour for a particular given illustration on any publication cover – say Mogul Red – the readings one will get is L=42, a=61, b=57 – by the readings of one’s monitor – the software conveys to computer and PhotoShop, or InDesign – what the monitor looks like and then only the software calculates, how to display the colours properly on one’s screen. When one adjusts colour swatch in InDesign to make the required background “Mogul Red” one will get the colour one has indicated and targeted for.

In normal situations, Spectrophotometers are used for all measurement tasks of a given print project – these are used to calibrate monitors, create proofs and ICC profiles and to quality control proofs – Spectrophotometers are as important as the computer – without a Spectrophotometer no desired quality print project can be accomplished.

For the improvement and enhancement of colour management – it is believed that one should profile one’s monitor right at the beginning. Basically, what one needs is a colourimeter – most popular brands are XRite i1 and Data Colour Spyder – of course one can trace many more on the web. There are several new brands of monitors available like NEC, Eizo etc. I believe Eizo Self calibrating monitors are considered the best in the industry for soft proofing and designing applications, etc. By putting this basic step in order one can easily be very close to colour management for most of one’s print projects.

It has to be kept in mind that Spectrophotometers are used for all measurement tasks, besides for calibration of monitors as well, create proofs and ICC profiles and of course to control quality of proofs. Spectrophotometer is essentially very important to measure everything in pre-press operations for a quality conscious printer and print-buyer as well.

The basis of colour management is constituted by the calibration of different devices that are to be used and in the first place comes the monitor. The digital camera can also be calibrated – then of course printer of the set-up which is to be used for the colour management. If colour settings are set properly right from the beginning and these settings can improve and enhance colour consistency between scanner and monitors, between different monitors, and between monitors and printers – and in case they are set incorrectly, it can cause irreversible damage to one’s given image.

When one runs Photoshop for the first time for any given print project with colour transparencies/illustrations or any colour backgrounds, it will ask one to set colour settings. One has to go to Edit and then colour settings and one may set as per standard practice and as per required need of any image—may it be a transparency, colour drawing or even a colour background or a colour patch. Next step is to calibrate the monitor – without it one may not see the advantages of the sophisticated system created by amazing software meant for the job.

For the correct operation of colour management system it is necessary to consistently calibrate the equipment, normalise the technological process of manufacturing for print products, as well as characterise all the colour reproduction devices, namely, create a profile of each device involved to create or manufacture a printed product. Let me repeat, calibration is the process of setting up colour device for a given state, for example, in case of monitors to a certain white point and gamma correction. Calibration ensures that colour reproduction system from day to day and from machine to machine will produce stable results. Calibration can be in the absence of information about the relationship between hardware signals and colorimetric characterization of the device. Calibration is used to know and then neutralizing the defects of a monitor, for example so that it displays the “right” colours, or in other words, the correct colours and if possible very close to all other calibrated monitors. The uncalibrated monitor can therefore have many display defects that calibration will attempt to correct. Once calibrated, all monitors, all printers must be close enough to each other in terms of colours and most importantly, one must have the satisfaction of saying: “Okay, my print and my picture displayed on the display are identical or, at least which looks essentially the same”.

Therefore, in order to ensure accurate image reproduction process conversion between the colours of the device and the device-independent colour should be done with pinpoint accuracy. Active competition in the development of a various colour management modules indicates that the current model of transformation, as well as a method of converting colour data are far from perfect and requires a detailed analysis of all factors affecting the quality of operations and methodology of colour transformation.

Analytical stage is represented by reading the colour information of each element of the original image and its translation in the form of three colour components corresponding to the transmitted (reflected) light streams in three zones of the visible spectrum red, green, and blue RGB. At the stage of gradation and colour correction the image converts into a suitable form for the next step that is printing process. This stage includes the transformation of colour information from the source to the target colour space (from RGB to CMYK or another model through the device-independent colour space Lab) mapping the original colour space into a target colour space with a colour gradation conversion, providing psychologic colorimetric accuracy.

Within RGB and CMYK spaces, more variations in gamut exist. Monitors, for example, have a much smaller gamut than slide film and high quality digital cameras, which in turn have a much smaller gamut than what the human eye can critically look at. Between monitors, there are also differences in gamut dependent on the phosphors and other hardware components used. Gamuts of printers also vary so that even though they follow the same colour recipe, they often output varying /different results. Due to all this, colour and printing of colour is highly device-dependent.

The total range of colours able to be produced by a device is called its gamut. The explanation above is usually summarised by saying that the RGB gamut is larger than the CMYK gamut. Gamut applies to device capabilities, but can also be applied to other components of the reproduction process. For example, a given printer can reproduce a wider range of colours on coated paper than it can print on newsprint.

Printing industry’s focus has always been on the conversion of colour from RGB to CMYK with much accuracy and consistency as much as close to originals. Photoshop, as a major component of the printing process, has had to address the issue as well. In previous versions of Photoshop, the RGB values were always defined as those displayed by one’s monitor. This was simpler, but the RGB values in an image were “clipped” to the gamut of the monitor, which, as mentioned above, has a much smaller gamut than film. Specifically, the monitors clip some of the cyan values that actually can be printed in CMYK, resulting in a smaller printing gamut than necessary. Also, because monitors vary so widely in their behaviour, images look different on each new machine. Images would print differently on each different printer. It would be very difficult to predict what an image would look like when printed on a particular stock of paper.

There is an unique methodology for the operation of colour management system as explained herewith: using the colour data obtained from the device profiles, the software module converts the colour of input device’s colour space to device-independent colour space and then simulates the same colour in the colour space of the target device with the purpose of the goal of the reproduction. Colour management helps to achieve the same appearance on all devices, which are capable of delivering the required colour intensities.
One should not confuse colour management with colour correction. A colour management system won’t correct an image that was saved with tonal or colour balance problems. It provides an environment where you can evaluate images reliably in the context of your final output.

A colour management system reconciles colour differences among devices so that you can confidently predict the colours your system ultimately produces. The value of colour management increases when you have more variables in your production process. Colour management is recommended if you anticipate reusing colour graphics for print and online media, using various kinds of devices within a single medium (such as different printing presses), or if you manage multiple workstations.

A colour management system reconciles colour differences among devices so that one can confidently predict the colours one’s system ultimately produces. Viewing colour accurately allows you to make sound colour decisions throughout your workflow, from digital capture through final output. Colour management also allows you to create output based on ISO, SWOP, and Japan Colour print production standards.