Monitor Calibration

Monitor Calibration

The starting point for calibrating a system into a colour managed workflow is the monitor. This is where an image is first viewed and changes are made to that image on the basis of how it looks on screen. It is thus somewhat important to know that what appears to be grey, for instance, on the screen is actually grey in the image.

Changing monitor colour and luminosity.

There are three ways to make changes to the monitor's output. These are:

A Typical Monitor Adjustment Window.

A typical Windows Graphics Card
Driver LUT Adjustment Window.

On the Monitor.
Commonly there are controls for contrast, brightness and colour balance and/or white balance. Some monitors may offer restricted controls, this applies particularly to cheaper LCD displays, laptops and older CRTs. The level of control here is generally quite coarse and fine balancing is almost impossible. However, as will be seen, this is where calibration starts.
On the Graphics card.
Most graphics cards have a table of figures which are used to adjust its colour output. This table is called a look up table, or LUT. Typically the LUT is adjusted from software related to the graphics driver but it is also changed by monitor calibration software such as Adobe's Gamma utility. The level of control exerted by the LUT is quite fine but balanced adjustment by hand remains tricky.
In the Colour Management System.
Items one and two work directly on the monitor itself influencing the whole of the monitor's output. Conversely, the colour management system makes no change to the monitor at all. By knowing what the monitor's output is compared to a common standard and being able to compensate for any divergence from that standard it can show colours in an CM-compliant application's image window correctly. This is the most accurate method of controlling colour with fine control over all aspects of colour output.

To calibrate a monitor fully will involve all three of these controls working from the coarse to the finest.

The Monitor Profile.

The basis of all colour management is the profile. This is the table of values which tells the colour management system how a piece of hardware 'sees' colours and compares it with the standard.

Most modern monitors will have a dedicated monitor profile provided by the manufacturer. This profile is is designed to provide consistent colour but, unless the other monitor controls have been set correctly the colours will be consistently wrong.

As the manufacturer's monitor profile is generic, designed to apply to the 'range' of monitors, it takes no account of an individual monitor's variance from the norm - and they do vary.

The two ways to calibrate:

Software

The software approach will normally only involve adjustments to the monitor and the LUT. Only very rarely will any changes be made to the monitor profile. Changes to the LUT need to be set each time the system is started. Normally this will happen automatically when a small programme runs on start-up. Some calibration utilities, such as Adobe Gamma, tag the LUT values onto the end of the monitor profile so all the calibration is kept in one place. No actual change is made to the profile's colour tables.

What follows is a list of the stages in setting the monitor using Adobe's Gamma utility. The vast majority of such utilities (examples can be found on the Internet) work in much the same way.

Using Adobe Gamma

The Adobe Gamma Window.
This example is in great need of adjustment.

Step 1.
a/ Ensure the right monitor profile shows in the 'Description' box.
b/ If you know what your monitor's phosphors are then set them here, if not leave as you find the setting.
c/ Set the Gamma to 2.2.
d/ Set the White point to 6500°K and 'Same as Hardware' in the box underneath.

Step 2.
Set the monitor's Contrast to 100%. A CRT monitor is unable to show pure black or pure white. Setting the contrast to its maximum will ensure that these extremes are as close to black and white as the monitor can produce. LCD monitors are inherently more contrasty so it may be necessary to reduce this after some experimentation

Step 3.
Adjust the Brightness until you can just make out a difference between the dark squares on the dark strip.

Step 4.
Adjust the sliders under the red, green and blue squares until the inner square disappears within the larger.

Step 5.
Save the file using a new filename.

Hardware/Software
One reason that no attempt is made to edit the profile in the above case is that all the adjustments have been made by eye. The eye is just not a critical enough measuring tool to be able to adjust a profile.

The Eye 1 Display 2 in position.

The hardware in this section replaces the eye with a colorimeter, a device which can measure colour and light intensity accurately. Consequently, such a system will be able to make changes to the LUT once the contrast and brightness levels have been determined using the colorimeter and then fine tune the colour output by creating a proper, full, monitor profile.
There are several such systems available, such as Gretag Macbeth's Eye 1 Display 2, which allows measurements of a room's ambient light levels and the Monaco Spyder with which one can profile an LCD projector.

The software which controls the process is usually quite simple to use and should automatically place the new profile correctly within the computer system.

Conclusion.

One way or another that monitor needs calibration. Quite how is the decision.

The hardware solution is considerably more costly than the software alone. Whether the cost is justified is a matter of personal preference. It should be said that confidence in the adjustments can only follow on from the confidence in the measuring apparatus used. So, if you are 100% confident that you can assess colours correctly by eye, then it would be difficult to justify the additional cost of the hardware solution.

To be 100% sure of one's eyes and be correct at the same time...what an achievement!