DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

device pixels. However, a graphic subsystem may
resample by primitive means when faced with
a mismatch between framebuffer pixel count and
display device pixel count. If framebuffer count is
higher, pixels are dropped; if lower, pixels are replicated.
In both instances, image quality suffers.
CRT displays typically have a Gaussian distribution of
light from each pixel, as I will discuss in the next
chapter. The typical spot size is such that there is some
overlap in the distributions of light from adjacent pixels.
You might think that overlap between the distributions
of light produced by neighboring display elements, as in
a CRT, is undesirable. However, image display requires
a certain degree of overlap in order to minimize the
visibility of pixel structure or scan-line structure. I will
discuss this issue in Image structure, on page 43.
Two disparate measures are referred to as resolution in
computing:
• The count of image columns and image rows – that is,
columns and rows of pixels – in a framebuffer
• The number of pixels per inch (ppi) intended for image
data (often misleadingly denoted dots per inch, dpi)
An image scientist considers resolution to be delivered
to the viewer; resolution is properly estimated from
information displayed at the display surface (or screen)
itself. The two measures above all limit resolution, but
neither of them quantifies resolution directly. In Resolution,
on page 65, I will describe how the term is used in
image science and video.
42 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES