In color management and print quality verification processes, visual assessment of colors is a key. In order to acquire color accuracy, a proper lighting condition becomes a must. The ISO3664:2009 standard specifies a set of five conditions which all must be present in order to assure the benefits of this standard in critical color viewings. The five conditions include Color Quality, Light Intensity, Evenness, Surround and Geometry.

It is a fundamental principal that human could see and perceive colors only under lighting. There are no colors without lights. Due to the specific structure of the human eye, our sensitivity to lighting varies at different wavelengths. Because of this, we can perceive various colors. And this ability to perceive colors depends on both the quality and quantity of lighting.

Consistent light intensity is fundamental to consistent color reproduction. The ISO3664:2009 standard proposes a standard intensity to allow full tonal visibility of shadow details in an image without washing out highlights.

In particular, ISO3664:2009 applies to:

1. Critical comparison between transparencies, reflection photographic or photomechanical prints;

2.  Appraisal of the tone reproduction and colorfulness of prints and transparencies at illumination level similar to those for particular use;

3.  Critical appraisal of transparencies that are viewed by projection, for comparison with prints, objects or other reproductions;

4.  Appraisal of images on color monitors that are not viewed in comparison to any form of hardcopy.

Based on above, ISO3664:2009 covers five major types of viewing conditions:

1.     Conditions for critical comparison for viewing a print. (P1)

2.     Condition for viewing a transparency directly on an illuminator that has a diffusing screen (as opposed to viewing by projection). (T1)

3.     Conditions for practical appraisal of prints, including routine inspection. (P2)

4.     Conditions for viewing small transparencies by projection. (T2)

5.     Conditions for appraisal of images displayed on color monitors.

The perceived tonal scale and colors of a print or transparency can be significantly influenced by the chromaticity and luminance of other objects and surfaces in the field of view. For this reason, ambient conditions, which will possibly affect the state of visual adaptation, need to be designed to avoid any significant effects on the perception of color and tone, and immediate surround conditions also need to be specified.

Experience in the industries covered by this international standard has revealed the need for two levels of illumination:

1. a high level for critical evaluation and comparison;

2. a lower level for appraising the tone scale of an individual image under illumination levels similar to those under which it will be finally viewed.

The following specifications of light intensity in critical color viewing are provided in ISO3664:2009.

  Figure 1. Light intensity specified by ISO3664:2009 standard.