Image Processing Reference
measure 4 and 3 will be 5 units long. Multiply all the values by 3 to scale the diagonal to
15 inches and we learn that the width is 12 inches and the height is 9. This gives us a hor-
izontal and vertical resolution of 53.3 DPI. This assumes that the picture is adjusted to
exactly that size. But it is very likely it will under-scan slightly so the DPI value will be
slightly higher. If the display is not set up correctly, some nonlinear distribution of the
lines will cause resolution changes across the surface of the screen. This is a problem if you
use the monitor to draw accurate diagrams.
At this resolution, there are significant issues with raster size, storage, throughput,
and display. The solutions are all rather expensive. It is likely that this type of high-qual-
ity moving image will be useful to people making movies, compositing graphics assets,
and rendering special effects, but the average users are not likely to require this type of
output. Video editing is possible at much lower resolutions. Then, the edit decision list can
be moved to a craft-editing workstation to conform the edit on a master copy of the video.
Video Conferencing Formats
When video conferencing systems were being developed, the International Tele-
communications Union (ITU) defined a data rate and picture size that it thought was rea-
sonable to accommodate within the transmission mechanisms being deployed.
Common Intermediate Format
The baseline standard was called common intermediate format (CIF) and is a quarter of
the size of a generic TV display.
The ITU H.261 standard defined CIF to be a progressively scanned 352
with 4:2:0 chroma sub-sampling and a frame rate of 29.97 Hz. This is a strange combina-
tion because the size is based on the visible area of a 625-line TV service with the frame
rate from a 525-line service.
CIF is sometimes called Full CIF ( FCIF ) to distinguish it from a related standard that
defines a lower bit-rate service with a smaller display-image size. That standard is called
QCIF . This is misleading because it implies that the picture is full size and somehow dis-
tinct from CIF, which it is not.
Some implementations change the number of lines or frames per second according
to the geographic use. In PAL-based territories, the format is 352
288 and in NTSC terri-
tories, the line count is reduced to 240.
In some documentation the authors suggest that the “I” in CIF is short for inter-
change or image rather than intermediate. No common image format has ever been agreed
upon so you should avoid using the term “common image format.”
Quarter Common Intermediate Format
The quarter common intermediate format (QCIF or “quarter CIF”) requires a quarter of
the bit rate used by CIF image streams. It is designed to be suitable for video-conferencing
systems that transfer their bit streams via telephone lines.