In the early days of colour management, the promises of better colour and greater colour predicability were not always kept by vendors of calibration devices and software. Everyone had different approaches and “secret sauce” so that they could corner the market. Today, however, this is no longer the case. Colour management helps photographers, ad agencies, printing and sign companies manage colour reproduction from input devices such as cameras and scanners to output devices such as inkjet printers and printing presses.
We are often called by clients to help them create a sensible, colour-manageable workflow to make sure that various input and output devices behave as they should. One of the first thing we suggest is to calibrate (profile or characterize) the colour monitors. Very often they pull out an old monitor calibration device (Spyder, ColorMunki or other cute name) and state that this has not worked for them. The images they view on screen looks nothing like the printed output. It’s then I ask “What did you calibrate this to?” Puzzled looks follow.
Calibrating or profiling your monitor involves setting various parameters such as luminance (brightness) and gamma (tone reproduction curve) as well as options to set something called “white point” with a range from D50 to D75 being common. For most of us in the printing industry, we have set these as follows:
White Point: D50 to D55 (colour temperature measured in degrees Kelvin, i.e. D50 equals 5000 degrees K)
Luminance: 120 cd/m2 (candela’s per metre squared)
Gamma: 2.20 (now the standard for all monitors)
Contrast Ratio: Native (uses the full contrast possible from the monitor)
These settings makes sure the monitor is realistic and not too bright as compared to a print or proof, and that the “weights” of tones are in the right place with both delicate highlight and dark shadow details preserved. Greys should look neutral. But why choose this white point of D50 to D55, especially when most monitors are much bluer (and thus seem whiter much like your grandmother’s Reckett’s Bluing she used in the laundry)?
The answer is quite simple. The sun is the ideal for viewing and is of course available all around the world. The sun’s colour temperature as measured on earth between mid-morning and mid-afternoon is about 5000 degrees Kelvin.
Manufacturers of these calibration devices somehow neglect to mention the very important detail of controlling one’s ambient light to the white point as set above. Our eyes are magnificent at adapting to various lighting conditions, but unfortunately our monitors are not. Thus, if we use halogen lighting, any print or proof is going to look warm, and the monitor to look cool. Use typical industrial cool white fluorescent tubes and the opposite will be true. However, it’s not hard to resolve this and it needn’t be an expensive fix.
One can hang a two lamp 48” / 32 watt fluorescent light fixture about a metre over the monitor and install a couple of lamps that fit the requirements of D50. The best fluorescent lamps are from GTI or Just Normalicht. Many lighting stores will carry less expensive lamps that are very close to the D50 requirements. Look for 5000K and a CRI (Colour Rendering Index) of 90 or better. (more about this in another article). A white or polished metal surface behind the tubes and silver “egg-crate” grill keeps the colour output of the lamps accurate.
A simple (but not entirely accurate) way to test for the correct lighting is by way of RHEM Light Indicator strips. In daylight or under D50 lighting, little to no variation will be visible. Under other forms of lighting, two stripes will appear caused by a phenomenion called metameric failure (again, more on this in a subsequent post).