Colour Management

At the latest when you start processing images, the time has come to address colour management. Imagine you have been processing your images for hours and have corrected brightness, contrast and colour. Once you’ve printed off copies or projected the image, you suddenly realise that the photos are too bright, too dark or have a colour cast.

At the latest when you start processing images, the time has come to address colour management. Imagine you have been processing your images for hours and have corrected brightness, contrast and colour. Once you’ve printed off copies or projected the image, you suddenly realise that the photos are too bright, too dark or have a colour cast. What happened? The differences in device’s display of colour and brightness are caused by the fact that every device has different properties in terms of displaying colour. Therefore, colour management is required to adapt the colour display of each individual device. Here another problem can arise. The individual devices are limited in colour to varying degrees, meaning that certain colours can be displayed by some devices, but not by others. To solve this problem, colour profiles are used for each individual device. These ICC colour profiles (ICC= International Colour Consortium) are required to adjust the different ways colour, contrast and brightness are displayed as best as possible.
A colour management is required to ensure that the actual image subject and the outputs are as close in colour as possible. This means that devices, e.g., printers and monitors display the colours in the same way they were captured. Due to the fact that almost every device has varying colour displays, these different properties needed to be adapted. This is where the ICC colour profiles come in. These profiles provide the software and hardware with information about the colour properties of the other devices. This allows for an almost unvarying display of colour by every device.

Monitor Calibration
Before processing images on the computer, we should first deal with calibration and colour management, starting off with monitor calibration. This is due to the fact that only a calibrated monitor displays the colours almost identically to those in the file – go to article “Monitor Calibration”…

 

Printer Calibration
High quality printers often already have different profiles to choose from, from the manufacturer. Different printer ink involves a recalibration. For this process you need to print a test file. Then the printing result is evaluated using a spectrophotometer. With the help of the gained knowledge, the ICC profile for the printer, ink and paper combination can be established.


Colour management when capturing images

Colour management should already be taken into consideration. Especially users of JPG formats should starting thinking about the colour space (more information about image formats can be found under Compression and file format) before capturing images. More attention should also be paid to the white balance than in RAW format. In JPEG the colour depth also only reaches 8 bit. This means there 256 shades in each colour channel, which is less than professional digital cameras can capture. This can result in reduced image quality, especially in image processing or when changing colour profile.

Many cameras provide sRGB and Adobe with colour spaces.

  • The sRGB colour space is smaller than the Adobe RGB colour space. For displaying images on the internet, sRGB is a good choice. Even if no image processing should occur, this colour profile is advantageous.
  • For further image processing and/or prepress the larger colour space AdobeRGB should be selected. In larger colour spaces contain shades and structures that are reduced to a homogenous surface in smaller colour spaces. In image processing, slightly reduced image quality can occur in smaller colour spaces.

Both of these colour spaces are important in terms of changes in colour depending on the device. There is usually an overlap between common devices used in photo and graphics workflow. They are often used in image processing even though these profiles can often only display some of the colours a camera can. Both profiles use red, green and blue – i.e. the colour method RGB.
For images in the internet, you should use the sRGB model. Changing larger colour spaces into smaller colour spaces is usually relatively unproblematic. The larger the overlap of the individual colour spaces is, the better this is for an authentic display of colour. However, changing profiles or models can result in a shift in colour.

CMYK colour model
A further well-known colour model, especially in the area of professional printing, is the CMYK model (Cylan, Magenta, Yellow and Key (black). The conversion of this colour model can result in noticeable shifts in colour. Here you should use the softproof option in order to assess the result. Photoshop for instance can simulate, using a softproof, what the image were to look like in print. If you need to pass on images, find out which colour model is desired. Otherwise the image may differ from the desired result, despite comprehensive colour management and calibration.

Further information about colour management can be found here:

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