*3.3. ColorTemp*

Recently, visual artworks have been reconstructed using 3D printers and various 3D transformation technologies to help the visually impaired rely on their sense of touch to appreciate works of art. However, while there is work in HCI on multimodality and cross-modal association based on haptic interfaces, such as vibrotactile actuators, thermal cues have not been researched to that extent. In that context [88,102], explored a way to use temperature sensation to enhance the appreciation of artwork.

Bartolome et al. [88] designed, developed, and implemented a color-temperature mapping algorithm to allow the visually impaired to experience colors through a different sense. The algorithm was implemented in a tactile artwork system that allowed users to touch the artwork. Temperature stimulation has some influence on image appreciation and recognition. An image presented along with an appropriate temperature is perceived as an augmented image by the viewer [103]. One VR device uses a small Peltier device to provide a temperature stimulus to maximize the sense of the field [104]. Lee et al. [105] explored the modal relationship between temperature and color focused on the spectrum of warm and cold colors. Bartolome et al. [102] expresses color and depth (advancing and retreating) as temperature in Marc Rosco's work using a thermoelectric Peltier element and a control board. An obvious way of conveying the warm or cold feeling of color to the visually impaired is to have a finger touch the temperature generating device (e.g., Peltier devices that are used in dehumidifiers and coolers) to identify the color. Temperature stimulation has some influence on image appreciation and recognition. An image presented along with an appropriate temperature is perceived as an augmented image by the viewer. Like sound, temperature is a modality that the visually impaired can use to enhance their appreciation of visual artwork. The modal relationship between temperature and color focused on the spectrum of warm and cold colors, including 3D printing techniques, interactive narration, tactile graphic patterns, and color-sensibility delivery through temperature. A temperature generator using Peltier element allows the visually impaired to perceive the color and depth in an artwork. The control unit, which controls the Peltier element, used an Arduino mega board, and a motor driver controlled the forward and reverse currents to manage the endothermic and heat dissipation of the Peltier element. Because constant voltage and current are important in maintaining the temperature of a Peltier device, a multi-power supply was used for stability. Twelve Peltier elements were densely placed in a 4 × 3 array, on top of which a thick paper coated with conductive ink was coated inside each cell except for the boundary of each cell. On top of that, relief-shaped artwork using swell paper was placed. The artwork is divided into 4 × 3 cells, providing the matched temperature for the color. The visually impaired feel a sense of temperature by touching the cell with their fingers, and they can obtain color and depth information corresponding to the temperature. Russian-born painter Marc Rothko is known for his color field works, Figure 5. If you touch a part of the artwork twice, the color of that part can be recognized more clearly through temperature and sound coding colors [36,88].

**Figure 5.** Peltier array and finished prototype with an artwork on top [88].

Chromostereopsis [106] is a visual illusion whereby the impression of depth is conveyed in two-dimensional color images. In this system, red and yellow are conveyed with warmth, and blue and green are conveyed with cold. Warm colors feel close, and cold colors feel far away, so music can be used to reinforce the cross-modal correlation between color and temperature. The thermoelectric element produced temperatures from 38 to 15 ◦C in 4◦ intervals, enabling six different colors or depths to be distinguished [102]. It is difficult to distinguish between bright and dark colors with temperature, so musical notes with different combinations of pitch, timbre, velocity, and tempo can be used to distinguish vivid, light, and dark colors. Mapping the depth of field and color-depth to temperature can help the visually impaired comprehend the depth dimension of an artwork through touch. Iranzo et al. [102] developed an algorithm to map color-depth to temperature in two different contexts: (1) artwork depth and (2) color-depth.

First, the temperature range was selected within a comfortable range. In general, the visual perceived distance between the extreme depth levels in a piece will be assessed, and the extreme temperatures will then be selected accordingly (higher temperature difference for larger distances). However, to simplify the algorithm, the extreme depth levels can consistently be linked to the extreme temperatures of 14 and 38 ◦C, regardless of their perceived relative distances. Second, the total number of perceived depth levels is counted. For example, an image with two people, one in front of the other, contains two depth levels, front and back. Third, the temperature is equally divided into as many segments as needed to assign a temperature to each depth level. The highest and lowest temperatures are always assigned to the nearest and farthest depth levels, respectively.

Fourth, if the difference between the temperatures of two consecutive depth levels is less than 3 ◦C, some of the levels can be clustered to make the temperature distinctions between levels easier to feel. The prototype was designed, developed, and implemented using an array of Peltier devices with relief-printed artwork on top. Tests with 18 sighted users and six visually impaired users revealed an existing correlation between depth and temperature and indicated that mapping based on that correlation is an appropriate way to convey depth during tactile exploration of an artwork [102].
