How User Quality Expectations Increase Over Time

The Optoelectronics Industry Development Association (www.oida.org) and the Video
Electronics Standards Association (www.vesa.org) help to establish standards for pixel
density/pixel spacing (resolution), refresh frequency, color depth, brightness, contrast
ratio, duty cycle (for example, phosphor degradation in phosphor displays), and
power budgets. Quality expectations are influenced by the other display devices that
we use each day. Looking back over time, an IBM VGA monitor in 1987 provided a 640
× 480 pixel display with 16 colors. By 1990, XGA monitors were typically 800 × 600
pixel with 16 million colors.
Table 4.8 shows how computer monitor resolution standards are evolving—partly
because technology makes the evolution possible (and gives marketing people something
new to sell) and partly because high resolution opens up new applications, for
example, medical images using Quad Extended Graphics Array (QXGA) resolution.
QXGA images are either 3 or 5 megapixels. A 5-megapixel image with a 24-bit color
depth produces an image bandwidth of 120 million bits. You would not want to send
too many of these to or from a digital cellular handset!
Table 4.9 shows typical LCD screen size and resolution options for laptop PCs. A21-
inch XGA monitor needs 9 million transistors—it is not surprising that LCDs constitute
about a third of the component cost of a laptop PC! The smaller the screen, the fewer
pixels you need to achieve the same resolution as a bigger screen. Small screens, however,
seem bigger if they have higher resolution. It’s not just the number of pixels but
rather the pixel density that’s important.

The other factor determining user expectations is digital TV. Present digital TV offerings
in the United States, Europe, and Asia do not provide recognizable improvements
in terms of image quality (actually because analog TV quality, certainly in Europe and
Asia, is already very good). In the longer term, high-definition television will increase
user quality expectations.
Digital TV does, however, have an impact on our perception of aspect ratio. A
square screen has an aspect ratio of 1:1, standard television sets are 4:3, and widescreen
digital TV is 16:9. The 16:9 ratio is chosen to match the typical aspect ratio of
human vision, which is supposed to be more comfortable and satisfying to look at.
Aspect ratio has a particular impact on pixel processing overhead—1:1 aspect ratio
screen use square pixels. On a 4:3 or 16:9 screen you have to use rectangular pixels (the
image pixel is wider than it is taller). The screen pixel information has to be distorted
to correct for this. 128