MPEG-21 Digital Item Adaptation for Color Vision Deficiency
Research for ISO/IEC JTC1/SC29/WG11 MPEG-21 International Standard Work
Related MPEG Activities
- í░MPEG-21 DIA for Color Vision Deficiencyí▒, MPEG Requirements Group, ISO/IEC JTC1/SC29/ WG11 M8303, Fairfax, May 2002
- í░Report on CE for Visual Accessibility - Part 1: Color Vision Deficiencyí▒, MPEG MDS Group, ISO/IEC JTC1/SC29/WG11 M8543, Klagenfurt, July 2002
- í░Color Image Dataset for CE on Color Vision Deficiencyí▒, MPEG MDS Group, ISO/IEC JTC1/SC29/WG11 M8544, Klagenfurt, July 2002
Color is a characteristic of a visible object or light source by which an observer may distinguish differences between two objects with the same size and shape. It also plays an important role in our daily life as a fundamental visual feature that gives richness to natural world. The color seems to be only for decoration, but it is frequently used as the primary means of informing people how to interpret information. Nowadays, the development of broadband telecommunication, multimedia information coding and processing, and color display technologies let user access easily the colored-visual contents anytime and anywhere. One can easily access the multimedia contents with high-quality color, as even using wireless personal communication devices such as cellular phone, PDA (personal digital assistants) and so on.
As the use of color to convey visual information in the multimedia content is more increasing, it becomes more crucial to perceive the color to get the visual information. Obviously the color works well for people with normal color vision, but not for people with deficient color vision. The use of rich color may even cause the color deficient people to misread the meaning of the information that it describes. Roughly 7 ~ 10% population has some kinds of color vision deficiency (CVD). Although there is no treatment for the CVD, many pictures, documents, and web pages on Internet have been designed without any consideration about the problem.
CVD arises from two causes, which are complete lack or modification of one of three classes of cone pigments. The former is called dichromacy, and the latter is called anomalous trichromacy. Both are called partial color blindness. There is also complete color blindness, called achromatopsia, who has no cone. Dichromacy has one of three photoreceptors, which are cones. There are therefore three types of dichromacy: protanopia, deuteranopia, and tritanopia. Protanopia lacks the long wavelength cone (L cone) or red pigments. There is an inability to see dark reds and there is typically confusion between reds and greens. Deuteranopia lacks the middle wavelength cone (M cone) or green pigments. They also confuse between reds and greens. Tritanopia lacks the short wavelength cone (S cone) or blue pigments. This is a rare condition and typically caused by acquired defects. There is confusion between blues and greens. All colors visible for normal trichromacy looks two monochromatic colors: blue and yellow for the protanope and the deuteranope, and red and cyan colors for the tritanope. Compared with dichromacy, anomalous trichromacy is caused by a variety of problems. The most frequent one is shifting of a cone. There are also three types of anomalous trichromacy: protanomaly, deuteranomaly, and tritanomaly. Anomalous trichromacy also has three classes of cone pigments but the peak sensitivity wavelengths of two classes are closer together than those for the normal color vision. Protanomaly has abnormal L cone which spectral absorption curve is shifted toward shorter wavelength (M cone). Deuteranomaly has abnormal M cone which spectral absorption curve is shifted toward longer wavelength (L cone). Tritanomaly has abnormal S cone. It is also acquired defects like tritanopia. It often occurs as a result of disease such as diabetes, injury usually to the eye or head, exposure to chemicals or medication, and age.
Figure 1. Comparison of normal and deficient color visions
The vision for MPEG-21 is to define a multimedia framework to enable transparent and augmented use of multimedia resources across different communities as well as a wide range of networks and devices. That is, everyone should be able to easily and equally access any kinds of digital item. In the MPEG-21, user accessibility is an important part of multimedia (or digital item) adaptation. Specially, MPEG-21 visual accessibility for colored-visual resource of digital item is proposed to give better accessibility of color information to people with color vision deficiency (CVD).
Figure 2. MPEG-21 Digital Item Adaptation for Color Vision Deficiency
In MPEG-21, a digital item is composed of resources and descriptions. So MPEG-21 DIA is composed of two modules: resource and description adaptation modules. Above figure shows DIA procedure in MPEG-21. As shown in the figure, an engine called 'DIA engine' performs the adaptation for digital item. The adaptation procedure for a digital item is as follows. Firstly, original digital item is delivered from digital item provider to DIA engine. The DIA engine performs the adaptation of the digital item, based on DIA description delivered from the digital item consumer (user). And then the adapted digital item is transferred to the digital item consumer. In the DIA engine, the description adaptation module adapts description (D in Fig) of the original digital item into a new or modified description (D' in Fig). The resource adaptation module adapts resource (R in Fig) in the original digital item into a new or modified resource (D' in Fig). To do so, the DIA engine needs DIA description containing user characteristics. In result, the DIA engine can provide equivalent accessibility of the digital item to user in any kind of environments.
When a class of cone pigment genes is absent or the genes are not expressed or not functional, the User is a dichromate and we use the TextualDegree "Severe". The "Mild" cases refer to anomalous trichromacy, where some trichromatic color vision is present because rearranged gene sequences (chimeric genes) lead to two classes of a remaining red or green cone type in the red-green confusion phenotype. At the time of this writing, the genotype corresponding to the blue-yellow confusion of the tritanomaly phenotype is unknown. Color blindness can also be acquired though disorders like glaucoma, diabetic retinopathy, and macular degeneration. It is also a symptom of exposure to certain toxic drugs and chemicals. When the User does not know her/his degree of color vision deficiency in a specific numeric value, i.e., which amino acids have been substituted in the genes, s/he can use a textual representation of "Mild" or "Severe". Note that a default value of "Mild" in TextualDegree is 0.3 in NumericDegree. Table 1shows that types in medical terms of color vision deficiency are represented by the descriptor of ColorVisionDeficiency (in parenthesis is the phenotype) and also relationship between TextualDegree and NumericDegree.
Table 1. MPEG-21 DIA description for color vision deficiency
The following example shows an instance of ColorVisionDeficiency, in which a description of visual accessibility characteristics of a User who has a certain type and degree of color vision deficiency, e.g., mild red-color deficiency (Protanomaly).
Figure 3. Example of DIA description for color vision deficiency
Below figure shows some experimental result to verify the usefulness of the proposed DIA description. We adapted colors on the images with DIA description for user with CVD.
Figure 4. Experimental result of color adaptation for people with color vision deficiency