Monitor Calibration and Viewing Environment for CAPA Judges
Dr. Bob Ito, FCAPA, Hon FCAPA
CAPA Director of Photographic Imaging
Monitor “calibration” is somewhat of a confusing topic and is not well clarified by makers of “calibration” devices. In fact, the advertising hype for these devices is misleading as they imply that a bad quality device can be converted into a high-quality device, but this is impossible.
The default mode of most monitor calibration devices should be actually called “profiling” and attempts to measure the colour and tonal characteristics of a monitor. We can call the result – the “Monitor Colour Space (MCS)” The MCS space may be smaller, equal to or larger than the sRGB colour space.
If an image in the sRGB colour is sent directly to a monitor with a MCS smaller than the sRGB colour space, then the MCS of the monitor becomes the defacto colour space and this is bad for image judging as judges would not see the full range of colours of the sRGB colour space This also applies to user viewing and editing of images. Unfortunately, most PC monitors and laptop computers are in this poor-quality class unless one buys a better, stand alone monitor
If an image in the sRGB colour space is directly sent to a monitor with MCS equal to or larger than the sRGB colour space then sRGB becomes the defacto colour space, overriding the MCS characteristics, and this is why one wants a high quality monitor with a MCS equal to or larger than the sRGB colour space.
Some calibration devices (e, Spyder Elite) have an actual “calibration” feature that attempts to convert the apparent monitor colour space from the native MCS space to the sRGB colour space. This of course only works if the original MCS space is equal to or larger than the sRGB space – it definitely does not work if the MCS space is smaller than the sRGB space.
In “profiling” with or without the “calibration” feature the “white point” is set by setting the colour temperature. The default colour temperature for most “profiling”/”calibration” devices is 6500 K, but some people prefer a slighting warmer colour temperature of 5800K or 5500 K as outdoor daylight is typically closer to 5500K. Leaving the colour temperature at the default value of 6500 K is probably OK for most people using a profiling/calibration device.
In the sRGB specification, the gamma is not a constant value but has the approximate value of 2.2 over most of the usable luminance levels and this is the default value used by most profiling/calibration devices. Some profiling devices, such as the Xrite i1 Display Pro, allow one to specify the variable sRGB gamma curve for the profiling.
In monitor profiling/calibration, the black point is not specified as this varies considerably depending on the monitor and viewing environment. For judging/viewing photographic images the static dynamic range of a monitor, within its viewing environment, is important and ideally shout be 1000:1 (10stops) or better. Many monitors have difficulty in achieving 512:1 (9 stops) in a darkened environment and the apparent static dynamic range drops to 100:1 or less in bright environments. This is why a darkened environment is essential for editing and judging images.
Some profiling/calibration devices in the “dummy” profiling/calibration mode do the profiling/calibration at whatever brightness setting the display is set at. This is bad – one should use the “advanced” or “expert mode” that allows measurement and user adjustment of the monitor brightness. Alternatively, one could pre-adjust the brightness. The target brightness should be approximately 120 nits.
Monitor Colour Space: Equal to or larger in size than sRGB
Gamma: 2.2 or sRGB , if available
White Point/Colour temperature: 6500 K
Screen Brightness ( white screen); 120 nits
Static Dynamic Range: 1000:1 or greater