*2.1. Concept Design*

We propose the design of ColorWatch, which is a wearable wrist-worn analog tactile device for people with visual impairments (PVI). The concept of ColorWatch design includes two disks that can be rotated independently: one marked square disk which is on top of and smaller in size than a round disk, which functions as an hour hand in analog watches while the marked round disk functions as a minutes hand. Both disks are marked at one position each, with markers pointing to the reference positions for time. These disks and marked pointers can be touched by PVIs to convey tactile information. In addition to conventional time checking, the function of ColorWatch extends to represent object colors by the tactile interface. An integrated color sensor or smartphone camera can be used to detect color information of a reference object, which can then be wirelessly communicated to the ColorWatch. Hybrid smartwatches available in the market already exhibit wireless communication and control capabilities along with traditional watch hands. The ColorWatch design proposed a square and a round disk instead of conventional arms to enable PVIs to interact with them without external protective glass and minimizing the risk of damage or heavy touch to conventional arms. The control circuitry in ColorWatch can then direct the watch disks to point to the corresponding position associated with the detected color and color tone. A maintained contact push toggle switch can be used to toggle between timepiece and ColorWatch mode. The ColorWatch tactile design is effective for drawing less attraction to PVI, and for not being disruptive to others in contrast to talking watches. The analog disk design of ColorWatch also makes it easy to read, less fragile, and less susceptible to damage in contrast to a traditional analog watch hands. Figure 2a displays the schematic configuration and perspective view of the ColorWatch design concept, with Figure 2b outlining an application scenario for the ColorWatch. More features can theoretically be added to the ColorWatch; such as smartphone call notifications, incoming call pick and drop, and alarms through haptic feedback. The push button and mechanical dial of the ColorWatch can also hypothetically function as a tactile input method for smartphone scrolling. In this setting, PVI can wirelessly navigate smartphone features through ColorWatch dials discrete rotation, select desired options through one or two buttons or ColorWatch, and ge<sup>t</sup> audio feedback through smartphone speakers. However, this study focuses on the automatic spatial color translation framework for the PVI.

(**a**)

**Figure 2.** Perspective view of ColorWatch design concept; (**a**) PVI use scenario of ColorWatch during shopping (**b**).

### *2.2. Proposed Color Selection and Tactile Representation Scheme*

The tactile association of color proposed in this study considers six distinct hues namely red (R), orange (O), yellow (Y), green (G), blue (B), and purple (P) from Goethe's color triangle. These hues are represented by the round disk of the prototype which dynamically points to the reference color. It can be seen from Figure 3 that complementary colors are arranged on opposite ends to each other, and mixing any two primary colors results in the secondary color between them. An emerged tactile dot of half-sphere on edge of the round disk resembling braille embossment is used as a pointer for tactile color marking. These tactile-color associations are further expanded by Munsell color systems's three dimensions of light (L), saturated (S), and dark (D) as a color tone of each monochromatic basic color or hue from Goethe's color triangle. The color tones are represented by the square disk of the ColorWatch design, where the emerged tactile dot at one corner points to the reference color tones, marked 90 degrees apart at 0, 90, and 180 degrees for L, S, and D, respectively. The remaining position at 270 degrees of square disk pointer is used to represent achromatic colors. When a reference to achromatic color is detected on the square disk, the round disk represents each of the achromatic colors given by White, Gainsboro, Light Gray, Dark Gray, Dim Gray, and Black (Table 1). The arrangemen<sup>t</sup> of these achromatic colors, and the six color-hues for monochromatic colors on round disk, depending on the color mode is provided in Table 2.

The analog clock dial design holds twelve marks separated by 30 degrees universally. These six markers for round disk and four markers for square disk can be incorporated on the analog clock design as the common factor of twelve markers. This association of perceptual colors and their tactile placement can be very convenient for learnability and ease of use of users and the user-centric design.

**Figure 3.** ColorWatch pattern for color hues and color tones. Blue and black text represents monochromatic and achromatic color modes, respectively.


**Table 1.** Colors tones or color mode according to the angle of the square disk.

**Table 2.** Round disk angle chroma-lightness levels for monochromatic and achromatic colors (0–180° and 270° on the square disk, respectively).

