[rec.video] TN30--Calculator Shortcuts for Television Engineers

poynton@vector.Sun.COM (Charles A. Poynton) (01/11/90)

TN30-Calculator Shortcuts for Television Engineers

Charles A. Poynton
Sun Microsystems, Inc.
90/01/10

Many different approximations to the values of various television 
parameters are in common use. However, the fact that television 
parameter values are based on ratios of small integers can be used to 
quickly compute exact parameter values, as an alternative to entering 
multi-digit approximations. 

Each line of the table on the following page gives the name of a 
parameter, a ratio of integers giving its precise value, the unit of the 
value, and its numerical value rounded to ten digits (unless the exact 
value is already expressed numerically). 

This table contains expressions for time periods (e.g. frame, field, 
line, subcarrier, and sample): invert the numerator and denominator of 
any ratio which defines a time period (duration) to obtain an exact 
expression for the corresponding frequency. 

The values derived are in scaled units (e.g. nanoseconds). The power-of-
ten scaling required to obtain a value expressed in its basic unit (e.g. 
seconds) is implied by the metric multiplier of its unit. For example, 
to convert the ratio for NTSC subcarrier period in nanoseconds (88/.315) 
to seconds, multiply by 10^-9. 

Even though all but two of the PAL values are simple integers, all 
values have been included to make the table useful even to neophytes. 
The number of subcarrier cycles per line in PAL (283.7516) is exact; 
this value is the sum of 1135/4 (exactly 283.75) which accomplishes the 
90 degree line-to-line subcarrier phase shift necessary for PAL, and 
1/625 (exactly 0.0016) which accomplishes the much-discussed (but not 
much celebrated) 25 Hz offset. 

Now that you have read this far, I can reveal that the true purpose of 
this document is not to reduce computation time but to increase 
accuracy. Television engineering has suffered on many occasions from 
inaccurate calculation (case studies are in Technical Note 19), and it 
is actually that problem which I hope this Technical Note addresses, 
through the back door. 


CCIR 601 Parameters

CCIR Y sampling period          1/.0135    74.074 074 07 ns
CCIR 8-bit Y quanta                3x73    219 levels
CCIR 8-bit U, V quanta             7x32    224 levels

525/59.94 Parameters

Sync amplitude                      2/7    0.285 714 285 7 V
Black-to-white excursion          37/56    0.660 714 285 7 V
Pedestal amplitude                 3/56    0.053 571 428 57 V
Blanking-to-white excursion         5/7    0.714 285 714 3 V
1 IEEE unit                       1/.14    7.142 857 143 mV
Frame period                    1001/30    33.366 666 67 ms
Field period                    1001/60    16.683 333 33 ms
Line period                       572/9    63.555 555 56 us

625/50 Parameters

Sync amplitude                      300 mV
Black-to-white,  
  blanking-to-white excursion       700 mV
1 IEEE unit                           7 mV
Frame period                         40 ms
Field period                         20 ms
Line period                          64 us

525/59.94 NTSC Parameters

Subcarrier cycles per line        455/2    227.5 cycles
Subcarrier period               88/.315    279.365 079 4 ns
Sample period (at 4xFsc)        22/.315    69.841 269 84 ns

625/50 PAL Parameters

Subcarrier cycles per line 1135/4+1/625    283.7516 cycles
Subcarrier period           64/.2837516    225.549 389 0 ns