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Colour Management

 

Colour Management in Photoshop

 

One of the main frustrations encountered in the printing of colour images from digital files is the apparent inability to reproduce on paper the absolute colours and saturation as seen on the monitor. The solution to this problem lies in the use of Colour Management.

 The three elements involved in the capturing, processing and outputting of the image, i.e. the camera, computer system and printer must all speak the same language in terms of colour – in other words they must all use the same Colour Space. An explanation of the intricacies of Colour Space is outside the scope of this article, but well known examples are sRGB and Adobe 1998. Software programs such as Photoshop have the ability to convert from one colour space to another, but the best results are to be expected when there is no translation.

 Most cameras default to the restrictive sRGB Colour Space, but in the mid-range and above DSLR’s and compacts there is an option to set the default Colour Space to Adobe 1998 and this is recommended whenever possible.

 On the computer there are two interwoven elements involved in managing colour – hardware and software, specifically the graphics card and monitor and the imaging software, e.g. Photoshop. The Colour Space in which Photoshop displays images is selected under Edit > Colour Settings – select the same Colour Space as set on the camera, Fig 1. The other settings shown are those recommended for general use in digital imaging.

 

 Fig 1. Colour Settings in Photoshop CS3

The monitor is one the most important elements in terms of reproducing the colours of the original scene onto paper and it is of paramount importance that the colours shown on the screen are true and not shifted or distorted in any way. All monitors have their own characteristics depending on make, model and type – LCD or CRT and most, if not all, are supplied with default settings more suited to the eye candy of Windows XP or Vista and gaming – bright and ‘in your face’. These are not ideal settings for digital imaging! Adjustments to the hue and saturation of the colours displayed on the monitor can only be made accurately with the knowledge that the colour shown on the screen is as true as possible. Thus there is a need to colour calibrate the monitor and the tools and software needed to do this are readily available, e.g Greta Macbeth eye-one display 2, Spyder 3, Pantone Huey, etc and are not necessarily expensive.

Versions of Photoshop prior to CS3 included Adobe Gamma – a very basic monitor calibration tool which is very imprecise in that it depends entirely on visual judgment in adjusting the settings, but better than nothing!

Monitor calibration devices such as those listed above work in the following manner – the brief outline which follows is based on the Greta Macbeth eye-one display 2. The calibration device is placed on the screen and in conjunction with software measures and sets – with user input, the contrast, colour temperature (the mix of RGB required to give the a colour temperature of 6500 oK) and the brightness. Once these are set the software outputs to screen a series of colour patches which are ‘read’ by the sensor in the calibration device and fed back to the software.

The difference between the colour input to the screen and the colour seen on the screen by the sensor are integrated in software and a monitor profile created. This is installed automatically as the default monitor profile – Control Panel > Display > Settings > Advanced > Colour Management, Fig 2. With the eye-one display 2 software a reminder to re-profile the monitor can be setup and every 4 weeks is a good time span – graphics professionals would probably re-profile on a weekly basis if not more frequently. After calibration you can be sure that the colours displayed on the monitor are as accurate as possible for the system and can adjust the colours in images with confidence.

 

Fig 2. Default Monitor Profile

 

The final link in the chain is the printer and this also needs calibrating to ensure that the colour on the print matches the colour on the screen. To understand why this is necessary consider the following – the information sent to the printer contains the colour information for every pixel and the printer driver refers to this information in assessing which colour inks should be used and in what quantity on a pixel by pixel basis – strictly speaking on a dot by dot basis. This is fine up to a point, but no two printers of the same make/model are exactly the same in that both are subject to manufacturing tolerances. In addition, the colours produced by different combinations of ink and paper from different manufacturers can differ significantly. The solution is to use a paper profile – effectively a printer profile for each combination of paper and ink used to print out images. Most major paper suppliers make generic paper profiles for specific paper/ink combinations available on their web sites and these are generally very satisfactory. To achieve the ultimate in colour fidelity a bespoke or custom paper profile specific to your printer is required. Several manufacturer’s offer this service – Permajet for example. The process of generating a custom profile follows the same track as generating a monitor profile. One or two sheets of colour patches, downloaded from the manufacturer’s web site are printed out, without adjustment, under a given set of conditions on the printer in question using the paper/ink combination to be profiled and the prints sent to the manufacturer. The printouts are ‘read’ with a colour spectrometer and the true colour of each patch compared with the actual colour on the printout; the results are integrated in software and a paper profile produced which is emailed to the customer. The profile is specific to the printer on which the patches were printed out and to the paper/ink combination. A separate profile is required for each paper/ink combination used.

To install a printer profile it is only necessary to right click on the file and select Install. The default location for installed printer profiles is ….

C:\WINDOWS\system32\spool\drivers\color\

To print from Photoshop using a paper profile the following procedure must be followed – the description which follows is for CS3 using an R2400 printer, but the same or similar settings apply to other Epson printer dialogues.

In the Print Dialogue box select the Printer (if more than one installed) and then Page Setup, Fig 3.

 

        Fig 3 Printer Properties

On the Main tab under Colour Management select ICM and turn off Colour Management – the reason for this action is that we require Photoshop to manage the colour using a paper profile and not the printer driver. Set up the other parameters for the print and click on OK. Returning to the Print Dialogue box (Fig 4) select ‘Photoshop Manages Colours’ from the Colour Handling Dropdown list and then select the Paper Profile from the Printer Profile dropdown list. Checking the Match Print Colours checkbox soft proofs the image – i.e. the paper profile is applied to the preview.

 

Fig 4. Print Dialogue Box

 

Hit the print button and wait for you masterpiece to be printed out with full colour fidelity!

 

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