Draft Joint Statement by ISA & SEGD

Transcription

1 Draft Joint Statement by ISA & SEGD Summary Neither SEGD nor ISA oppose any aspect of the Americans with Disability Act that enables persons with disabilities to successfully access public buildings. In fact, both organizations are active members of the ANSI A117 committee for ADA regulations and each is proud of efforts to educate our respective memberships in all aspects of ADA regulations as they relate to signage and wayfinding systems design. Essentially, we believe that the proponent of a 70% contrast mandate for ADA signage has presented an inadequate methodology based on the rationale that any standard is better than no standard. Instead of providing scientific fact or reputable research to demonstrate the validity of this proposal, the proponent offers only anecdotal evidence and references to unrelated or incomplete studies of detectable warnings or electrical wires. Furthermore, the proposed amendment depicts opponents of this measure as those few who don t care whether architecture is accessible or not. But ISA and SEGD do not oppose any measure that may be demonstrated to provide significant improvements in accessibility for individuals affected by low vision. What we do oppose are the drafting of new rules, with far reaching consequences, that are based on inadequate evidence and research. Because the proponent is requesting a significant change in long standing contrast guidelines for ADA signage, we believe that they, not ISA or SEGD, should bear the burden of proof. The intent of this rebuttal, therefore, is not to recommend an ideal threshold of visual contrast for interior ADA signage. This can only be achieved after first establishing a measurement process that allows non-restrictive analysis to be conducted. Such a process should be firmly grounded in principles of CIE color science and should offer psychometric values that correlate with visual perception, as well as considering the needs of individuals with visual impairments and Color Deficiency. The process also needs to include standardized Illumination Conditions and must account for the effects of a phenomenon know as Metamerism. To have any viable utility, therefore, recommendations describing a specific measurement process must be well documented, accurate and repeatable.

2 For your reference, an example of definitions and the CIE metrics appropriate for a standardized color analysis are listed in the appendix. Discussion Color Science is complex and requires not only an understanding of the precise definitions used, but also of the most appropriate method to obtain metrics that are meaningful for the task at hand. For example, there is not always a direct correlation between physical measurements and the visual sensations perceived by observers having normal or reduced/impaired vision. This is the reason for the existence of two very different metric analysis systems; Photo metrics and Color metrics. The proposed amendment is incomplete because it fails to define any reputable, scientific analysis based on either of these standardized approaches to color science. Essentially, Photometry is the science relating to the physical measurement of the attributes of light. Colorimetry is the science relating to how we measure color difference or color appearance based upon psychometric or physiological models that correlate with our visual perception and the sensation of color. These two methods are not the same, even though they have some inter dependencies. We should not, however, use Photometric terms to describe our visual perceptions as observers, any more than we should use Colorimetric terms to describe the power distribution of a particular light source. The worldwide professional body for these sciences and the corresponding, precise measurement methodologies is the International Commission on Lighting (CIE), Here you will find everything you ever wanted to know about the science of color measurement and color appearance. In fact, CIE metrics are used in just about all of our ANSI National standards as well as in ISO standards on worldwide basis. To illustrate why Light Reflectance Values (LRVs) are technically inappropriate for measuring perceptual color values of anything other than an achromatic colors or grayscales, the following explanation defines LRVs and how they are obtained: Developed as a means for assessing grayscales, LRVs are based upon the CIE Luminosity function. LRVs represent values approximating the relative brightness (Diagram 1.) of a color, but devoid of the influence of hue and chroma. Misunderstandings often exist with respect to color because of the assumption that this word refers only to those colors that exhibit a hue. In fact,

3 however, achromatic colors such as black, white gray and silver also are colors, but colors devoid of hue. In Diagram 1. We can see the spectral sensitivity of photopic vision as a function of wavelength (nanometers), covering a range of approximately 380 to about 740nm. Diagram 1. CIE Luminosity Function Please note the area under the curve and the limited dynamic range covered compared to Diagram 2. This is intentional, as this model was designed to assess the relative brightness of achromatic colors and not intended for use with chromatic colors. Studies have shown, however, that persons with color deficiencies perceive a combination of yellow text on a black background, just as well as black text on a white background. In fact, this is currently used by the Royal National Institute for the Blind in the UK, thus making such a model quite limited in scope. On the other hand, colorimetry requires the calculation of what are known as the CIE tristimulus values (XYZ) which represent the redness, greenness and

4 blueness of a given color. Tristimulus values are the bases for all color transformations in any of the defined CIE linear and non linear color spaces, such as CIELUV and CIELAB. CIE tristimulus values can be obtained using either a spectrophotometer that measures reflectance factor, or a three filter colorimeter. In the case of the latter, the red, green and blue filters and photo detectors are designed to approximate one of the CIE Standard Observer functions, either 2 or 10 (see diagram 2). Diagram 2. CIE Colorimetric 2 Standard Observer It is important to note the differences between Diagrams 1 & 2. Diagram 1 uses only the green sensitivity curve to assess achromatic applications. Whereas in Diagram 2, we can clearly see, as observers, that we have a blue and red sensitivity that must be included in any chromatic color assessment. For most color science applications, a spectrophotometer is used to measure the reflectance factor of a color across the visible spectrum and this is the method of choice for a majority of the world s color scientists. The reason is that, once you have the actual reflectance data, you can perform any color transformation to obtain CIE tristimulus values XYZ, relative to the desired illuminant conditions under which the color is being viewed.

5 The CIE process starts by first measuring the reflectance factor of a color across the visible spectrum from roughly nanometers (at 10mn intervals). Next, a mathematical representation of the power distribution for a given illuminant condition is multiplied, wavelength by wavelength, by that of the reflectance data. The product is then multiplied by the weighted values of redness, greenness and blueness using a CIE Standard Observer function (either 2 or 10 ) show in Diagram 2. The normalized areas under the three resulting curves are the CIE tristimulus values XYZ; representing redness, greenness and blueness as a function of the given illuminant used for the color(s) being assessed. LRVs cannot achieve this, nor were they ever intended to do so. LRVs are based upon the power distribution of CIE Source, A or a representation of tungsten light (the power distribution of this source is displayed in Diagram 3). By design, therefore, LRVs ignore both the redness and blueness components of most colors. Many industries have standardized the illuminant used for color assessment. The printing and publishing industry, for example, uses (CIE illuminant D50) the third illuminant displayed in Diagram 3. But the point is that LRVs are based upon a type of illumination that is inappropriate for any visual chromatic color assessment. Diagram 3. The Power Distribution of 4 typical CIE Illuminants One of the key benefits of using colorimetry is, if you have the reflectance values of the measured color, under any defined illumination condition, we can transform these data using any other illumination conditions ( e.g. D50, D65, C, CWF or either of the CIE Standard Observer functions). Each of these conditions

6 corresponds to defined, mathematical values as a function of each specific wavelength across the visible spectrum. Another significant advantage of using colorimetry is that the CIE L* function common to both CIELUV and CIELAB is based upon psychometric lightness/darkness. It is referenced in almost all standards relating to color, whether in color difference or color appearance models. Conclusion Unfortunately, to date, no Technical Terms of Reference exist for assessing conformance with ADA recommendations for color contrast and nothing has been published in the public domain which conforms to the standard, CIE best practice for color measurement. While processes might be in place that individuals or companies are currently using, we do not believe that any of these practices has been technically certified. Investigations by the Department of Justice and the US Access Board dating back to 1991 reveal a fairly murky history and, indeed, cast some doubt concerning the methodology by which the 70% color contrast value came into existence. For example, the US Access Board s technical department has acknowledged that the original source of this information was flawed and currently has no value. In addition, they confirm that, at present, they have no recommendation on how to measure color contrast. For this very reason, the 70% contrast has remained an advisory clause in the 2004 and 2008 revisions of ADAAG. Contrary to the proposed amendment, therefore, the issue of contrast measurement cannot be addressed via the suggested metrics which previously have been rejected by the ANSI A117.1 Committee. Nevertheless, if a necessity truly exists to include a metric value for color contrast in the ADA recommendations for interior signage, then a process allowing for Terms of Reference using CIE nomenclature must first be established due to the complexity of applied color science and its necessary, technical scope. This process needs to meet the following goals to be successful: A metric Terms of Reference need to be established that can provide a consistent valuation across the total visible color spectrum based on a standard lighting and Standardized Observer function using define instrumentation The visual threshold required for color contrast and legibility must be based on scientific research where the measurement process is in conformance with color science methodologies

7 Appendix Perceptual Color Deficiencies There are three basic forms of color deficiency to be considered: Deuteranopia Deficient color vision of reddish-greenish components of the cones, but neither appears to be abnormally dim Protanopia Deficient color vision where the reddish-greenish component of the cones is reduced & the reddish component appears to be abnormally dim Tritanopia Deficient color vision where the bluish-yellowish components of the cones are absent Many studies have been published on the subject of color deficiency and it is not the intent of this document to recommend another, but simply to mention this in general. It is important to note however, many Observers who experience color deficiency tend to discriminated colors by their relative brightness, or lightness/darkness values rather then relative colorfulness (hue and chroma). It follows therefore, using psychometric values that highly correlate with the attributes of brightness or lightness/darkness would be a very good place to begin. That said we would prefer to make a case for including all chromatic visual attributes in such a study, rather than just lightness and darkness values. Metamerism The study should consider the effects of Metamerism, of which there are three, Observer Mesmerism, Lighting Metamerism, and Materials Metamersim. As with color deficiency, there have been multiple studies on this subject and it is not our intent to delve into these other than to say, they need be included in the measurement process. A simple metameric index based upon the magnitute of differences between colors using two CIE illuminants would most likely suffice here. Illumination Conditions It is important that one standard CIE illuminant is referenced, many industries use CIE D50, but other CIE illuminants can also be used if they are appropriate. Measurement Conditions & Color Space The Commission International L Eclairage (International Commission on Illumination) has a standardized color space know as CIELAB: this is an opponent color space used to communicate colorimetric and psychometric values based upon standardized CIE procedures for Colorimetry and is widely used in other industries where critical color communications is required. In

8 many cases a certified color palette such as the Munsell Color Checker can also be used to check consistency and repeatability of measurements, using differing instrumentation. So Technical Terms of Reference need to include the following: What standardized color reference Munsell Certified Color Scale for Numeric and Visual Representation What Spectrophotometers are to be used? Integrating Sphere (specula component included/excluded) or a 0/45 devise wavelength abridgement (10nm) What illumination CIE Illuminant D65 CIE Illuminant D50 Which CIE Standard Observers CIE º Standard Observer CIE º Standard Observer Then: CIE Tristimulus Values (XYZ) are: X (Rλ) (Sλ) (x-barλ) dλ (1) Y (Rλ) (Sλ) (y-barλ) dλ Z (Rλ) (Sλ) (z-barλ) dλ

9 Where (Rλ) is the reflectance factor of a color, (Sλ) is the Illumination condition, (x-barλ) (y-barλ) (z-barλ) is the Standard Observer function, and can be either the 2º or 10 model and dλ is the density of the color. Then: CIELAB Psychometrics are: and: L* = 116 (Y/Yn) 1/3-16 (2) a* = 500 [(X/Xn) 1/3 - (Y/Yn) 1/3 ] b* = 200 [(Y/Y 1/3 ) - (Z/Zn) 1/3 ] X/Xn, Y/Yn, Z/Zn > 0.01 C* ab = (a* 2 + b* 2 ) 1/2 h ab = arctan (b*/a*) CIE Color Difference is: ΔE * ab = [ΔL*) 2 + (Δa*) 2 + (Δb*) 2 ] 1/2 (3) Please note, there are several calculations for assessing CIE color difference, these equations are but one.