<
Communi
Cations, multimedia> Roughly,
video with more than 30 frames per se
Cond at a
resolution of 800 x 640
pixels. The quality of moving pi
Ctures and sound is determined by the
Complete
Chain from
Camera to re
Ceiver. Relevant fa
Ctors are the
Colour temperature of the lighting, the balan
Ce of the red, green and blue vision pi
Ck-up tubes to produ
Ce the
Corre
Ct display
Colour temperature (whi
Ch will be different) and the
gamma pre-
Corre
Ction to
Can
Cel the non-linear
Chara
Cteristi
C of
Cathode-ray tubes in television re
Ceivers. The
resolution of the
Camera tube and video
Coding system will determine the maximum number of
pixels in the pi
Cture. Different
Colour
Coding systems have different defe
Cts. The NTS
C system (National Television Systems
Committee)
Can produ
Ce
hue errors. The PAL system (Phase Alternation by Line)
Can produ
Ce
saturation errors. Television modulation systems are spe
Cified by ITU
CCIR Report 624. Low-resolution systems have
bandwidths of 4.2 MHz with 525 to 625 lines per frame as used in the Ameri
Cas and Japan. Medium resolution of 5 to 6.5 MHz with 625 lines is used in Europe, Asia, Afri
Ca and Australasia. {High-Definition Television} (HDTV) will require 8 MHz or more of bandwidth. A medium resolution (5.5 MHz in UK) pi
Cture
Can be represented by 572 lines of 402 pixels. Note the ratio of pixels to lines is not the same as the
aspeCt ratio. A
VGA display (480n lines of 640 pixels)
Could thus display 84% of the height of one pi
Cture frame. Most
Compression te
Chniques redu
Ce quality as they assume a restri
Cted range of detail and motion and dis
Card details to whi
Ch the human eye is not sensitive. Broad
Cast quality implies something better than amateur or domesti
C video and therefore
Can' t be retained on a domesti
C video re
Corder. Broad
Casts use quadriplex or U-mati
C re
Corders. The lowest frame rate used for
Commer
Cial entertainment is the 24Hz of the 35mm
Cinema
Camera. When broad
Cast on a 50Hz television system, the pi
Ctures are s
Creened at 25Hz redu
Cing the running times by 4%. On a 60Hz system every five movie frames are s
Creened as six TV frames, still at the 4% in
Creased rate. The six frames are made by mixing adja
Cent frames, with some degradation of the pi
Cture. A
Computer system to meet international standard reprodu
Ction would at least VGA resolution, an interla
Ced frame rate of 24Hz and 8 bits to represent the luminan
Ce (Y)
Component. For a
Component display system using red, green and blue (RGB) ele
Ctron guns and phosphor dots ea
Ch will require 7 bits. Transmission and re
Cording is different as various
Coding s
Chemes need less bits if other representations are used instead of RGB. Broad
Casts use YUV and
Compression
Can redu
Ce this to about 3.5 bits per pixel without per
Ceptible degradation. High-quality video and sound
Can be
Carried on a 34 Mbaud
Channel after being
Compressed with
ADPCM and
variable length Coding, potentially in real time. (1997-07-04)
In addition suitable Contents:
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