Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1990-06-12
1992-03-31
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Recording apparatus
358219, 35821319, H04N 530, H04N 5235, H04N 314, H04N 5335
Patent
active
051012758
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a video camera provided with an imaging system and an image transducing apparatus having an entry window, on which images of the pictures to be taken can be formed by this system, and is adapted to transform said images into electrical signals delivered to an output connection.
BACKGROUND OF THE INVENTION
In the current video cameras an iris diaphragm in the optical system is used for adapting the light intensity of the image formed on the entry window, which diaphragm is controlled by means of a control system responsive to the light intensity in such a manner that a substantially constant average light intensity is maintained.
Such a camera has several draw-backs. A first draw-back is that the mechanical control of the diaphragm has a given inertia, so that a lag in the light intensity control arises, which, particularly in the case of fast light changes, e.g. with a fast camera movement from light to dark and vice versa, will lead an objectionable image transition. A second draw-back is that such a control acts on the whole image, so that in the case of large light contrasts and depending on the manner of intensity measurement, some image regions will be over- or underexposed, with, as a consequence, reproduction losses in the image parts of these regions.
Although, for the first draw-back, possibly a solution might be found by increasing the speed of the diaphragm drive, there is no solution for the second objection in the case of a diaphragm-type light control.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a camera of the above-mentioned kind, by means of which these objections can be avoided. To that end the camera according to the invention is characterized in that the amplitude of the image signal derived from the signal output and corresponding with the light intensity of an image portion is transformed into a control signal for a control means for an additional image influencing element which, synchronously with the image line scanning, can influence the image signal in such a manner that the sensitivity in the image point in question during the image scanning is decreased at a large amplitude and is increased at a small amplitude.
Since, now, the sensitivity in any image point, or at least in groups of closely adjacent image points, can be adapted to the local light intensity, large light contrasts can be levelled or smoothed out and a good reproduction of the image portions can be obtained in the very bright and dark image portions.
The control should, of course, be so that not all the light contrasts will be suppressed, but only an adaptation to transitions in the light intensity will be obtained.
In a video camera with a transducer tube with electron beam scanning and a common electrode arranged behind the image window, the connection of which is, at the same time, the signal output, the voltage at this electrode can be controlled, according to the invention, in correspondence with the amplitude of the image signal during scanning.
It also possible, and in particular in so-called CCD transducers, to obtain such a control by arranging, in the light path to the transducer, i.e., between the imaging system and the transducer, a liquid crystal element or similar light control element, to which a HF voltage can be applied, the frequency thereof, and, thus, the transmittance of said element, being controlled in correspondence with the scanning.
Sometimes high intensity peaks will remain which cannot be completely suppressed by this control. In order to suppress also these peaks, it is possible, according to the invention, to send the image signal, if required after a preamplification, towards a threshold circuit which only passes the signal portions exceeding the chosen threshold, which portions, if required after adaptation of the amplitude thereof, will be subtracted from the original image signal in order to reduce the brighter portions accordingly, and, in particular, before said threshold circuit an inverter can be p
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Britton Howard W.
Copyguard Enterprises S.A.
Greening Wendy R.
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