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REPORTS
Hardware and software calibration of monitors for beginners
By Simon Blohm
25.07.2008, 09:09
Translation by Siobhán Hayes
The calibration of a monitor plays an important role, and not just for professional users in advertising agencies or in electronic page setting (CEPS), who are dependent on natural, or, to put it better, "neutral" colour reproduction.
Ambitious PC users in the amateur sector also wish to be able to display their images or games as colour accurately as possible. Amateur photographers often purchase high-quality digital mirror reflex cameras and are then disappointed with the pictures they take when they view them on the monitor.
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Not all too seldom, the cause for this is a monitor which has not been sufficiently calibrated enough, then, to work more intensively on the calibration process. The concept "calibration" originated in measuring technology and denotes the measuring of a device with the aid of defined target values.
When it comes to the calibration of a monitor, this definition is extended and means the adjustment of particular characteristics which have an influence on the brightness, contrast and colour reproduction of the monitor.
The direct way: adjustments on the device itself
Fundamentally, we differ between hardware and software calibration. In both cases a measuring device (colorimeter) is used, with which the current colour values of the display to be calibrated can be determined. In software calibration, colour management software such as iColor from Quato is also needed.
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The product Silver Haze Pro from Quato offers the colorimeter X-Rite DTP94 and the iColor Display software. You can buy this product, amongst others, from TFTshop.net for 199.00 Euro. (Photo: Quato)
The manual adjustment of brightness and contrast are simple examples of software-based calibration which is possible on any LCD monitor. An attempt is made to achieve target values provided in the calibration software as closely as possible by changing the contrast, gamma, RGB and brightness values within the monitor’s OSD.
Expensive graphics monitors also allow all additional parameters to be established: here, grey balance, gamma value and black point can be established on the monitor itself – so in the hardware.
Unlike conventional LCD monitors, they also offer more precise setting of the white point via the colour channels. Instead of 50, 100 or 256 adjustable levels per colour channel, graphics monitors offer up to 16,384 levels with 10, 12 or 14-Bit LUTs.
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In the left picture, the Color Graphic series from Eizo and on the right, the SpectraView series from NEC. Both ranges offer hardware calibration, but not with any colorimeter or any software. (Photos: Eizo und NEC)
Thus, a high level of precision is offered to the user because, unlike software calibration, no adjustments need be made via the graphics card and colour management software. With hardware calibration, the colour space of the monitor can be used in its in entirety.
The indirect way – when the software has to intervene
In contrast, software calibration us used where no hardware calibration is possible or where the hardware calibration is limited. This is the case with almost all conventional models, which usually only allow adjustments for brightness, contrast and the colours red, green and blue.
All other settings such as gamma value, grey balance and black value must then be changed via the colour management software. This creates a colour profile which modifies the colour output directly.
Because colour gradients are generally discarded in the process, losses are unavoidable in colour reproduction; especially in gradients, scales and tears then become visible – known as banding.
The closer the settings on the monitor can be calibrated to the target values, the less the software has to intervene in the process and the more evenly fine gradients are displayed.
With pure hardware calibration, on the other hand, the signal of the graphics card remains unaffected; all calibration parameters are controlled and stored directly on the monitor so that undesired banding does not arise and the complete colour spectrum is retained.
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