Text

Having captured our wideband (16 kHz) audio, we now want to add some text. Text
source coding has traditionally been realized using ASCII (American Standard for
Communications Information Interchange). These are 7-bit words that are used to
form a 7-bit alphabet used to describe letters of the alphabet, numbers, full stops, and
other text necessities.
ASCII works okay for Latin script (English, etc.) but runs out of address bandwidth
if a more complex language has to be described (for example, Japanese, with thousands
of characters). Japanese, Chinese, Arabic, or Hebrew SMS can be realized using
USC2 (Universal Multiple Octet Coded Character Set), a 16-bit/2-octet character
string, or UCS4, a 32-bit/4-octet character string.
ASCII, UCS2, and UCS4 all allow perfectly acceptable representation of text on a
grayscale LCD. However, we have said that we are beginning to see an increasing use
of high-definition high color depth displays. These displays provide us with the capability
to do text rendering by using pixel manipulation.
Pixel elements are made up of pels (picture elements) representing the singular red,
green, or blue value of an RGB pixel. Remember that the number of bits used per pixel
determines the amount of control you have over the color balance�"24 bits gives you
high color depth. The size of the image is the product of the number of pixels times the
number of bits per pixel.

Text rendering is effectively subpixel manipulation, borrowing subpixels from adjacent
whole pixels. The borrowed subpixels are always adjacent to their complementary
color pixels, which our eyes mix to form white. We can therefore use subpixel manipulation
to clean up jagged edges. Subpixel manipulation also only works on the horizontal
resolution of LCDs. Even so, this means we can do the following:
Emboldening (stretching text horizontally)
Ke rning (shifting text horizontally, that is, micro-justification)
Italicizing (slanting type by skewing it horizontally)
Subpixel manipulation only works for LCDs, not CRTs. CRTs are not addressable at
subpixel level, but then, as yet, no digital cellular handsets have CRT displays.
This means we can produce book-quality text on our screens, if we so desire. We
must be aware, however, that not all LCDs have the same ordering of RGB subpixels.
The rendering engine needs to know whether subpixels are arranged in forward or
reverse order. Also, text rendering only works for landscape not portrait aspect displays,
which means it is not really suitable for e-books, which would be an obvious
application. Text rendering is now, however, included in a number of software products
(Windows 2000 being one example) and will likely begin to appear further down
the portable product food chain at a later date. 169