IDENTIFICACIÓN Y DETERMINACIÓN DEL PROBLEMA

The thumb’s natural range of movement is fairly limited while the hand is over a touch screen. A tiny (≈ 20∘) vertical movement determines if the thumb makes contact with the screen or not. This movement is well within the comfort zone of a human hand. In addition, a short range of horizontal movement (≈ 15∘ on either side of the natural position) is also within the comfort zone. We show how these movements can be integrated into the use of the multi-tap slider.

Figure 6.1: Placing the thumb onto the screen brings up the parameter menu. Scrolling with the index finger selects a set, lifting the thumb enters the parame- terization menu.

6.2.1 Parameter set menu

In our design we use the thumb for two distinct interactions. For the first, touch- ing and holding down onto the screen raising the parameter menu. This is a distinct mode, that the user maintains while the thumb makes contact with the screen. Fig- ure 6.1 show the parameter menu. When this menu is displayed, the index finger performs the selection. Raising the finger selects the set of parameters.

6.2.2 Undo/redo

The goal of this research is to encourage exploration of multi-dimensional param- eter spaces. Fine grained adjustment in the dimension of each parameter is carefully performed, while the visual focus is maintained on the target. Figure 6.2 shows how

small movements of the thumb are mapped to undo and redo operations. The precise position of the thumb region can be customized for each user. The operation can still be performed without looking at the interface. The flicks are an easy movement to perform. The inward undo movement takes less effort than the outward redo move- ment, as found by a study mapping the operation to back and forth in web Browsers [86].

Figure 6.2: Using the thumb for undo and redo operations

6.2.3 Integrated tool parameterization

Tools in design applications are loaded with a variety of customizable parameters. The most basic brush tool in Adobe Photoshop has the following parameters: brush type, size, hardness, opacity and flow. In the toolbox, the other tools (blur, sharpen, smudge, burn, dodge and sponge to name a few) have a similar set of parameters. During regular use of the tool, designers experiment with different parameter values. This requires frequent back and forth trips from the canvas to the parameter toolbar,

placed on the top of the screen by default. Even when the toolbar is placed closer to the canvas, it requires targeting of small items. The Springboard technique [42] addresses the problem of selection of the tool, we presents a solution for customizing parameters of each tool.

Figure 6.3: The finger pad follows the first touch point, which is shown here operating the brush tool. The dashed circle is the transparent finger pad region highlighted for visibility. Placing the middle finger on the screen raises the widget, allowing selection and adjustment of the stroke weight. Raising fingers from the finger pad makes the widget invisible, while the index finger continues operating the brush.

We modify our interaction technique to make the index finger operate as a tool brush, instead of the adjustment (see Figure 6.3). However, we make the finger pad follow the index finger as a transparent tracking toolbar (like the ToolGlass interface by Bier et al. [13]). The widget itself is not displayed. When required, placing a finger onto the finger pad will raise our widget. Now, the parameters of the tool can be selected and adjusted. Raising all fingers from the finger pad will make the widget disappear, reverting the index finger to operate as a tool again. This provides an in-context access to the tool parameters.

6.2.4 Bimanual control

We recognize the limitations of the slider to allow for only four parameters. There are operations that consist of more than four integral parameters, such as the split toning operation, which presents upwards of 8 different hues that could be altered. All eight of these hues are integral to the operation, grouping them in two groups of four breaks the mental model of the user. Switching between any of these eight parameters should be as simple as switching between the four parameters that our technique currently supports.

In cases that require more than four parameters, we use a secondary finger pad to be used with the non-dominant hand. The number of fingers placed on this secondary pad selects another four parameters within the operation, supporting a total of 16 parameters for a single integral operation. To select and adjust the sixth parameter, the user performs the following:

1. Using the non-dominant hand, place a finger on the secondary finger pad. 2. Using the dominant hand with the regular widget, place one finger on the

primary finger pad.

3. The index finger of the primary hand performs the adjustment.

However, it should be noted that juggling all sixteen parameters for a single operation would be overwhelming for the user. Care must be taken when deciding how many parameters must be grouped into an operation, and when possible group other parameters into another operation.