Mobile Blog: Video, Media, Augmented Reality, Rich Media, IVVR

photo credit: qthomasbower

Applications cannot enlarge a small screen visually, but they can implement techniques that virtually increase the size of the display. One way is providing horizontal or vertical scrolling of the user interface to make new information visible while hiding other content. Another idea is a Peephole display that shows a different portion of a bigger picture when the phone is moved to the left, right, up or down. Unfortunately, neither approach works well with IVVR (Interactive Voice & Video Response). There are no positional sensors usable with 3G-324M, and scrolling requires fast screen updates with the ability to hold a key as long as the user wants to scroll. High delays in the current 3G-324M deployment and lack of transmitting the information that a key is hold for a time prevent the implementation of such features. However, applications can have multiple layers, such as a deck of cards that can be shown or hidden depending on the user’s selection. Furthermore, designs can take advantage of the media- streaming capabilities and multimodal information channels by providing some information using speech output, some with pictures or text, and others by using video sequences.

Mobile users demand visually attractive user interfaces that are clearly readable and intuitive to use. Application flow design is beyond the scope of this thesis, and every application and game will have its own characteristics to model and challenges to overcome. Nevertheless, some basic guidelines for slide-based IVVR applications can be given.

Slide-based applications such as IVR (Interactive Voice Response) Supplements shown in Figure 6 are best visually designed using pixel-based image editors such as Adobe Photoshop. The video codecs used in 3G-324M work in the YUV420 colour space, and the target image size is 176 x 144 pixels (QCIF (Quarter Common Intermediate Format)). With basic understanding of chroma-subsampling and how spatial and temporal compression in video codecs works, designers can create slides that will compress well while maintaining sharpness where essential. A precondition is to align the slide’s layout to a raster of 16×16 pixels with one subdivision (8×8) as seen in the figure below:

Template with 16x16 grid

To ensure best readability despite video compression, designers should use sans-serif fonts. Moreover, the font colour and the background colour should have a high difference in luminance. The human eye can distinguish difference in luminance easier than in colour; this fact is used by video compressors and is the foundation of chroma subsampling. For instance, a white font on a light yellow background is already hardly readable without compression. After compression, however, with only half of information available for colour differences when using YUV420, the font will not be distinguishable from the background. The author’s experiments showed that especially Microsoft’s Calibri font creates a nice typeface even after compression. Calibri’s subtly rounded stems and corners are perfect for H.263 DCT-based compressors that create smooth edges. Note that the minimum font size is 18px when lossy compressed in order to be readable for mobile users. We can only hope that next-generation IVVR applications can use T.140 or similar ways to transmit ASCII-text directly, making readability considerations obsolete.