1. Environmental Lighting
Wrong or unsufficient environmental lighting is one of the most problematic issues upon comparing soft proofs, contract proofs and prints. The tonal response of a print always depends on the light that is used to illuminate the viewing area.
The perception of a color highly depends on the surrounding colors and the lighting conditions. Colored backgrounds and the contrast between two areas influence our idea of the color. Due to that, a standard mid gray background for the computer´s desktop is more suited for color editing than a fruity flavoured scene.
Apart from this, the light that iluminates the colors that are observed has an even larger influence on the perception of the color. As the color appearance changes with different illuminants, the ISO3664 (Viewing Conditions) and ISO12647-x (Graphic Technology) define a standardized lighting for judging proofs: the D50 standard.
The orange is always the same, but due to the surrounding colors, it looks different. The same applies to the gray patch. It seems to be darker or lighter, depending on how much black is dominant.
The Pantone orange gets a severe color shift if it is viewied under suboptimal lighting conditions.
2. Calibration recommendations
There are some fundamental issues that have to be taken into account for a calibrated screen:
- Whitepoint (or color temperature)
- Chromatic adaption
- Luminance (brightness)
- Gamma (gradation)
Since the 1930s, D50 is defined to be the standard lighting for judging color, but it is obviously unsuitable for calibrating a display. A D50 calibrated display seems to be much to warm compared with a D50 viewing booth or the human eye´s expectation of what D50 should look like on a screen. During extensive research, a whitepoint (or color temperature) for the monitor between 5.600 k and 6.000 k - or an average of 5.800 K - was found to be much more suitable for the comparison betweeen proof and screen.
90 % of the test persons define the matching whitepoint of a display and a viewing booth to an area between 5.600 K and 6.000 K.
But if the whitepoint is defined to be different than D50, a chromatic adaption function must be applied. D50 is the color communication standard with ICC colormanagement. Every device or color that uses a different whitepoint must be retransformed back to D50. This retransformation is called chromatic adaption. Common chromatic adaptions are Bradford or vonKries.
Warm colored image parts appear to be colder than they are. Thus, the softproof does not match the printed results, If this retransformation is done without an adaption.
With chromatic adaption (left), the image appears as printed. Without chromatic adaption (right), the image appears much to cold.
Additionally, the display is - compared to a viewing booth - much to dark. The ISO 3664 defines 1800 Lux for the light intensity. The displays brightness is specified in Candela per squaremeter (or nits) and booth terms do not match. To get the equivalent of 1800 Lux in Candela, we have to devide Lux by Pi (3). 1800 Lux result in something like 600 Candela. None of today´s displays will survive for a long time with such an intensity.
That´s why most of the professional viewing booths have an electronic dimmer to reduce the intensity to a value that matches a display´s luminance much better. Most of the viewing booths can reduce their light intensity to an equivalent of 400 Lux. To match this value, the display should have a luminance of at least 120 Candela (cd/m2).
Aside from the whitepoint and the luminance, the gradation has to be specified. In the past, a gamma of 1.8 was referred to be the standard Macintosh gamma, while 2.2 was the PC´s gamma. With ICCColormanagement this is no longer suitable for the workflow.
Gamma 1.8L (*r Girgadhatti)o na nd LG*a m(cmean 2t.2er) ofGfaemrm ab 1e.8tter details in the darks and the lights than Gamma 2.2 (left).
Back in the 80´s, a gamma of 1.8 was defined to match the dot gain of a standard offset press better than gamma 2.2. This is still valid and can be used for both systems, Macintosh and PC. The two polular D50 RGB working spaces, ECI-RGB and ColorMatch-RGB, are based on Gamma 1.8 an recommended for the use in an icc-workflow.
The also D50 based L* is an alternative to Gamma 1.8 that is more adapted to the human eye´s tonal rsponse curve. But one has to use a L* based RGB working space like L*-RGB to avoid large deviations.
Gamma 2.2 is not suited for soft proofing, because a lot of the image details in the darks and lights will be lost. The gamma 2.2 and D65 (6.500 K) based Adobe RGB is not well suited for D50 workflows.
Thinking workflow, means in this case that the display should be calibrated with the end of the workflow in mind. Most likely this will be a print.
Finally, a guideline for calibrating a screen can be like the following:
- Whitepoint: 5.000 K - 6.000 K
- Luminance at least 120 cd/m2
- Gradation: Gamma 1.8 or L*
A chromatic adaption like Bradford is recommended and most of the calibration software offer this adaption by default.
The profile type should be a Matrix/TRCtype as display LUT-profiles are not well supported by popular applications.
This basic setup will help make the match between display and viewing booth much closer.
