Colour management systems are integrated solutions, which are intended to ensure the uniform rendering of colours on all input and output devices.To the article
LCD monitors by panel type
The panel type is a key criterion when selecting an LCD monitor for CMS.
The LCD panel is the primary component of every LCD monitor. There are LCD panels with three different construction types:
The key features of the individual panel types are shown in the following table:
|Viewing angle (colour shift)||Excellent (almost no colour shift)||Very good (little colour shift)||Good (visible colour shift)|
|Response time||Good (visible colour shift)||Excellent||Excellent|
|Contrast ratio||approx. 500:1||1000:1 or more||Depends on panel type|
|Gamut||Depends on panel type|
For graphics applications, the viewing angle is very important, in particular if multiple people are expected to look at the monitor from different directions. While the colours largely remain the same on IPS monitors if the monitor is viewed from different directions – from above, from below, from the left, and from the right – colour tone changes are visible in VA and TN monitors.
In the case of widescreen monitors, viewers who are sitting right in front of the monitor can sometimes get different colour impressions between the middle and the edges of the screen, as the viewers are looking at the different areas of the monitor from different viewing angles.
A higher contrast ratio does not necessarily lead to better results. If the contrast ratio is too high, some brightness differences appear too severe, meaning that images appear overstructured and it becomes more difficult to compare the colours on the monitor and in the end product. The options to configure the contrast ratio can also be a criteria when selecting a calibratable monitor.
Taking into account these aspects, IPS and VA monitors are recommended for graphics applications.
Distinction between LCD monitors by gamut
Three gamut groups can be allocated to modern monitors.
- Adobe RGB gamut
- sRGB gamut
- Gamut is at least sRGB but smaller than Adobe RGB
The Adobe RGB gamut is marked with a red triangle; the sRGB gamut is marked with the blue triangle.
A third widespread gamut is defined in the NTSC standard and is used in video and television devices, amongst other things. The green triangle in the diagram marks 92% of the NTSC gamut. The JMPA colours shown in the diagram produce the typical CMYK gamut. When selecting the gamut, the requirements of the intended purpose and environment are key. To display all colours in Adobe RGB data or CMYK print data, a monitor with Adobe RGB gamut is required.
Even a monitor that shows 92% of the NTSC gamut, the lively green tones from the Adobe RGB gamut or the yellow tones from the CMYK gamut are never displayed.
In a separate seminar, we will deal with aspects such as methods for using monitors with a wide gamut.
A CMS requires a calibrated monitor
The calibration of monitors that is indispensable for colour management systems (CMS) can be performed with two different procedures: Software calibration or hardware calibration.
Selecting a suitable monitor for software calibration
1. Select an LCD monitor capable of colour adjustments
LCD monitors generate colours as a combination of red (R), green (G), and blue (B). The colour rendering is adjusted by increasing or lowering the amplification (i.e. the luminosity) of the individual RGB colours. When selecting the colour temperature for white tone – a particularly important step when adjusting monitors – the colour rendering is adjusted by amplifying or reducing these RGB colours.
For example, to generate a cold white, the blue rendering is amplified.
For a warm white, red is amplified. As such changes are not possible with all monitors, this aspect is to be considered when selecting a monitor.
2. Select an LCD monitor, in which the luminance can be set to appropriate values.
Modern LCD monitors have very high luminance and therefore enable very bright rendering. This means that the brightness can be reduced to a limited extent in several monitors. This aspect is vital when selecting a monitor.
Sometimes, normal light sources have such low brightness that it is impossible to match the monitor image to the colour rendering on printed paper. On the right-hand side of the example shown below, the monitor image of the printed photo is shown in the middle with high luminance. When making a decision on an LCD monitor, it is very important to choose a model, in which the luminance can be set to suitable values.
3. Select a monitor with the best brightness gradation possible.
Software calibration is not only used to set a good white tone, but should also ensure optimal brightness gradation. It is therefore important to select a monitor with good gradation properties or tone banding.
In several monitors, the brightness gradation is not optimally configured ex works. This is evident in particular when rendering very fine image structures, for example hairs or folds in fabric.
We therefore recommend selecting a monitor that already has good gradation properties in the default settings.
Selecting a suitable monitor for hardware calibration
One advantage of hardware calibration is simple and precise calibration that is possible using suitable hardware (i.e. a suitable monitor) and specialised software.
In hardware calibration, important CMS properties such as colour temperature (white balance or white point) and luminance are configured automatically. However, if these simple adjustments are not performed to a sufficient degree of accuracy or if the profiles for the colour management system have not been carefully prepared, the effect achieved will be unsatisfactory.
As there are big differences in monitors that are expressly specified for hardware calibration, a monitor with an excellent overall performance should be selected.