Video reproduction apparatus having automatic black and white calibration

Claim 2

A demodulator for a frequency modulated (FM) video signal comprising; means for reproducing an FM video signal from recording media; integrator means for producing a ramp signal which varies substantially linearly over a predetermined integration period between first and second signal levels representing intensity limits of a scene; sample and hold means for sampling and holding the signal level produced by said integrator means; detector means for detecting the zero crossings of said reproduced FM video signal and for producing a pulse of fixed sampling period which terminates production of said ramp signal by said integrator means and which causes said sample and hold means to sample said integrator means signal level and to hold said sampled signal level after termination of said sampling pulse; switch means for resetting the signal level of said integrator means to a reset level less than said first signal level and for maintaining said reset signal level for a predetermined offset period; means for comparing first and second reference signal levels of said demodulated reproduced video signal with respective fixed first and second reference signal levels and for producing a first signal level correction signal for changing the slope of said ramp signal and a second signal level correction signal for changing the duration of said offset period as a function of differences in the compared reproduced reference video signal levels and said fixed reference levels so as to constrain said demodulated video signal between said fixed first and second signal levels.

Claim 3

The demodulator of claim 1 wherein said integrator means includes an integrating capacitor and an integrating current source means for supplying an integrating current to said capacitor and wherein said first signal level correction signal changes said integrating current to said integrating capacitor to constrain said demodulated video signal to said first signal level.

Claim 4

The demodulator of claim 1 including means for producing a reset signal, which actuates said switch means for the offset period of said reset signal, said reset signal producing means including an offset period timing capacitor and an offset current source means for supplying an offset current to said capacitor and wherein said second signal level correction signal changes said offset current to said offset period timing capacitor to change said offset period so as to constrain said demodulated video signal to said second signal level.

Claim 5

The demodulator of claim 1 wherein said reproducing means simultaneously reproduces from recording media both an FM video signal and a timing signal which are subject to corresponding flutter error components, and includes means for producing a flutter correction signal from said timing signal, and further includes means for applying said flutter correction signal (1) to said integrator means to change the slope of said ramp signal, and (2) to said switch means to change the duration of said offset period to cancel said flutter error in said demodulated video signal.

Claim 6

A multitrack magnetic tape video reproduction apparatus comprising: means for reading out an area imager in sequential blocks of a plurality of parallel channels of analog video information signals wherein each channel of video signal includes a reference period with white-and-black reference level signals followed by a video period with video information signals; a plurality of frequency modulator means for converting said plurality of analog video information signals into a plurality of frequency modulated video information signals; means for recording blocks of said plurality of frequency modulated video information signals on a plurality of parallel longitudinal tracks on magnetic tape so that a frame of video information is recorded in sequential blocks on said tape; means for simultaneously reproducing a plurality of parallel channels of FM video information signals from said magnetic tape; a plurality of FM demodulator means for demodulating said plurality of reproduced FM video information signals into a plurality of analog video information signals; wherein each of said plurality of FM demodulator means includes (a) integrator means for producing a ramp signal which varies substantially linearly over a predetermined integration period between first and second signal levels representing intensity limits of a scene; (b) sample and hold means for sampling and holding the signal level produced by said integrator means; (c) detector means for detecting the zero crossings of said reproduced FM video signal and for producing a pulse of fixed sampling period which terminates production of said ramp signal by said integrator means and which causes said sample and hold means to sample said integrator means signal level and to hold said sampled signal level after termination of said sampling pulse; (d) switch means for resetting the signal level of said integrator means for a reset level less than said first signal level and for maintaining said reset signal level for a predetermined offset period; (e) means for comparing first and second reference signal levels of said demodulated reproduced video signal with respective fixed first and second reference signal levels and for producing a first signal level correction signal for changing the slope of said ramp signal and a second signal level correction signal for changing the duration of said offset period as a function of differences in the compared reproduced reference video signal levels and said fixed reference levels so as to constrain said demodulated video signal between said fixed first and second signal levels; and wherein said reproduction apparatus further includes means for displaying said plurality of demodulated analog video information signals such that the white-to-black range of the displayed image is uniform.

Claim 7

A multitrack magnetic tape video reproduction apparatus comprising: means for reading out an area imager in sequential blocks of a plurality of parallel channels of analog video information signals wherein each channel of video signal includes a reference period with white-and-black reference level signals followed by a video period with video information signals; a plurality of frequency modulator means for converting said plurality of analog video information signals into a plurality of frequency modulated video information signals; means for recording blocks of said plurality of frequency modulated video information signals on a plurality of parallel longitudinal tracks on magnetic tape so that a frame of video information is recorded in sequential blocks on said tape; means for simultaneously reproducing a plurality of parallel channels of FM video information signals from said magnetic tape; a plurality of FM demodulator means for demodulating said plurality of reproduced FM video information signals into a plurality of analog video information signals; wherein each of said plurality of FM demodulator means includes (a) integrator means for producing a ramp signal which varies substantially linearly over a predetermined integration period between first and second signal levels representing intensity limits of a scene; (b) sample and hold means for sampling and holding the signal level produced by said integrator means; (c) detector means for detecting the zero crossings of said reproduced FM video signal and for producing a pulse of fixed sampling period which terminates production of said ramp signal by said integrator means and which causes said sample and hold means to sample said integrator means signal level and to hold said sampled signal level after termination of said sampling pulse; (d) switch means for resetting the signal level of said integrator means for a reset level less than said first signal level and for maintaining said reset signal level for a predetermined offset period; (e) means for comparing first and second reference signal levels of said demodulated reproduced video signal with respective fixed first and second reference signal levels and for producing a first signal level correction signal for changing the slope of said ramp signal and a second signal level correction signal for changing the duration of said offset period as a function of differences in the compared reproduced reference video signal levels and said fixed reference levels so as to constrain said demodulated video signal between said fixed first and second signal levels; and wherein said reproduction apparatus further includes means for displaying said plurality of demodulated analog video information signals such that the white-to-black range of the displayed image is uniform.

Claim 8

The apparatus of claim 5 wherein, in each of said demodulator means, said integrator means includes an integrating capacitor and an integrating current source means for supplying an integrating current to said capacitor and wherein said first signal level correction signal changes said integrating current to said integrating capacitor to constrain said demodulated video signal to said first signal level.

Claim 9

The apparatus of claim 5 wherein, each of said demodulator means includes means for producing a reset signal, which actuates said switch means for the offset period of said reset signal, said reset signal producing means including an offset period timing capacitor and an offset current source means for supplying an offset current to said capacitor; and wherein said second signal level correction signal changes said offset current to said offset period timing capacitor to change said offset period so as to constrain said demodulated video signal to said second signal level.

Claim 10

The apparatus of claim 5 wherein said reproducing means simultaneously reproduces from said magnetic tape both said plurality of channels of FM video information signals and a timing signal, said video information signals and said timing signal being subject to corresponding flutter error components; wherein said apparatus includes means for producing a flutter correction signal from said timing signal and means for applying said flutter correction signal to each of said demodulator means to change the slope of said ramp signal produced by said integrator means and to change the duration of said offset period of said switch means so as to cancel any flutter error in said demodulated video signal.