Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-02-02
1990-05-01
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
382 32, G01V 904, G06M 700, G06K 974
Patent
active
049220934
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and to a device for determining the number of people present in a determined space, and it is equally applicable to performing television audience surveys and to performing automatic suveillance of premises.
Apparatuses already exist for performing television audience surveys, these apparatuses are associated with respective television sets and they are capable of recording the times at which the television set is switched on and off, together with the channel that is selected, thereby making it possible, in combination with the times given by a time base, to accurately determine which programs are selected. A central computer uses the telephone network to interrogate apparatuses of this nature associated with television sets and thus to automatically determine audience ratings and hence the success of various broadcasts put out by different television channels. However, these prior apparatuses do not provide information concerning the number of people watching a program on a television set, indeed they do not even specify whether there is anybody actually watching a television set which happens to be switched on.
Devices are also known, in general for use in premises surveillance for security purposes, which make use of ultrasonic or Doppler effect detectors and which provide information on the presence or absence or people in a determined premises. Nevertheless, these prior devices do not specify how many people are present. To obtain the number of people present it is necessary to use means for counting people passing through the entrance and through the exit of a room. However, this requires the entrance to a room to be separated from its exit, and it also requires counting to be initialized. Further, such means would not be suitable for performing automatic television audience surveys since merely verifying the presence of a person in a room where a television set is present does not ensure that the person is actually watching a broadcast.
A particular object of the present invention is to mitigate these drawbacks of known devices.
The present invention provides a method and a device for determining the number of people present in a room, and in particular the number of people watching a broadcast on a television set.
To this end, the present invention provides a method of determining the number of people present in a determined space, the method being characterized in that it consists in forming an image of said space on a strip or set of photodetectors, in reading the gray levels of the points in said image at a determined read frequency, in comparing the gray levels of the same points in successive images, in determining the variations in gray levels which are caused by the movements of a person, and in deducing the number of people present in said space therefrom.
The method of the invention thus makes it possible not only to know the number of people present in a determined space at a given moment, but also to know the variations in this number and the departures and returns of the people present. The space in question may be a premises under surveillance, or that portion of a room which faces a television set and within which people may indeed be looking at the television.
In accordance with another characteristic of the invention, the method further consists in varying the frequency at which the photodetectors are read as a function of the intensity with which the determined space is illuminated in order to obtain a mean image gray level which is substantially independent of lighting conditions.
This avoids the photodetectors saturating, and comparison between images is facilitated.
The method of the invention also consists in recording the above-specified images at a frequency which is a submultiple of the read frequency, in comparing pairs of successive images which are separated from each other by a determined number of recorded images, and in determining the variations in gray levels by taking the difference between these images.
The method also consists in
REFERENCES:
patent: 3851096 (1974-11-01), Collins et al.
patent: 4045816 (1977-08-01), Cave
patent: 4258351 (1981-03-01), Shigeta et al.
patent: 4771333 (1988-09-01), Michaels
Dignac Jean P.
Drevon Jean M.
Fardeau Michel G. J.
Guern Yves F. C.
Bertin & Cie
Nelms David C.
Oen William
LandOfFree
Method and a device for determining the number of people present does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and a device for determining the number of people present, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and a device for determining the number of people present will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-831748