Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2002-03-18
2003-10-28
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005030, C327S060000, C348S607000
Reexamination Certificate
active
06639656
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a distance measuring apparatus capable of measuring a distance to a target object, for example a human body, and also measuring its shape.
Conventionally, there has been a distance measuring apparatus available such that it gets a range image by an active method i.e. by using projected light and measures a distance to a target.
FIG. 18
shows a block diagram of such a conventional distance measuring apparatus A′. This conventional apparatus has a clock signal generator unit
1
which generates a clock signal CK to synchronize light irradiation and reception, a modulated light projector unit
2
which projects light Pt modulated in brightness and a predetermined frequency and synchronized with the signal CK, a light receiver unit
3
which receives reflected light from a target object TG such as a human body and transforms the received light to received-light-signal and outputs the signal to a demodulator unit
4
′ which will be used to form an image including information (namely a range image) showing distances of objects including the target object TG.
The demodulator unit
4
′ demodulates the received-light-signal which is synchronous with the clock signal CK, that is, the signal corresponding to modulated reflected-light Pt′. The light Pt′ originates in the modulated light Pt, and is also return-light from the target object TG and other objects after projection and reflection.
The light receiver unit
3
has a light receiving device of two dimension in which many image elements are arrayed in matrix. The unit
3
reads out signal charges corresponding to a received quantity of light from each image element, and gets received-light-signals by processing the signal charges.
The demodulator unit
4
′ comprises a microcomputer and memories, and executes above-mentioned demodulation process with a pre-installed program so as to extract signals corresponding to the reflected-light Pt′ from the above-mentioned received-light-signal which is output by the unit
3
.
Through the demodulation process, the unit
4
′ obtains the distance information to the objects in a form of signal level using the extracted signals based on the time differences, in other words, phase differences between the light Pt and the reflected-light Pt′, and forms the range image in which above-mentioned distances to the objects are expressed by using the signal levels. Hence a distance to the target object TG and its shape (two dimensional shape) are measurable by using this range image obtained in the demodulator unit
4
′. The range image is output to a display unit B to be displayed there.
Such a conventional apparatus A′ is configured, for example, by using optical system of lenses so that reflected-light from objects is fed onto the light receiving device in the light receiver unit
3
, and is used as a monitoring apparatus to monitor an invader, a target object TG, entering into the monitored area.
FIG. 19
shows signal levels along one horizontal line of a range image obtained by the demodulator unit
4
′. The signal level is defined in the manner that the near the object is, the higher the signal level is. This figure shows a situation that a target object TG having a spherical shape is at the forward center of the light receiving device.
In general natural light and/or reflected disturbing light Pn are received along with the reflected-light of modulated light Pt by the light receiver unit
3
as shown in FIG.
18
. Those components equivalent to the modulated light Pt results in noises which is superimposed on the range image. For example, as shown in
FIG. 19
, there can be seen noise components in the both sides of a half circle. The half circle is a shape image of the target object TG. The signal levels are largely changing in a small span because of noise.
As another case, if the quantity of light coming into the light receiver unit
3
is too small, the output signal level of the light receiving devise becomes so low that noise components are superimposed on the range image. Noises may be superimposed also on the waveform of the target object TG, and these are omitted in FIG.
19
.
Such noise components tends to increase when large fluctuation of the received quantity of light occurs. Followings are those cases that the quantity of light received by the light receiver unit
3
is small, the objects have various reflection coefficients, or near and far objects are mixed in the scene.
The range image on which noises are superimposed is uneasy to see when displayed by the display unit B. Besides the noises in the range image tends to obstruct many kind of data processing in the successive stages.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a distance measuring apparatus that can remove the noise components in a range image.
According to an aspect of the present invention, an apparatus for measuring a distance to a target object and a shape of the target object with a range image which is obtained beforehand and contains information of distances to objects including the target object comprises following two means.
One is a range image obtaining means which obtains the range image by irradiating light onto the objects and receiving reflected light from the objects by a light receiving device. The range image presents signal levels which changes according to the distances to the objects,
Another one is a range image processing means which divides the obtained range image into a number of unit-range-images so as to discard every unit-range-image as noise if variation of a signal level in the unit-range-image exceeds a pre-determined threshold, and to save every unit-range-image as usable range image if variation of signal levels in the unit-range-image dose not exceed the threshold.
Consequently, prevailing noise components in the range image can be removed by discarding the unit-range-images as noise in which the variation of the signal levels exceeds predetermined threshold. As the results, almost all noises are removed from the range image which is composed of unit-range-images such that the variation of the signal levels in them dose not exceeds predetermined threshold.
Thus, there is a technical advantage in this apparatus since it can be performed precisely without influence of noises to measure the distance to the target object and the shape of the target object.
According to a further aspect of the present invention, the range image processing means interpolates the discarded unit-range-images by using unit-range-images in which variation of signal levels does not exceed the threshold and which are next to the discarded unit-range-images, or by using an average value calculated from a plurality of unit-range-images in which variation of signal level does not exceed the threshold.
Consequently, a further technical advantage is achieved by the interpolation, that is, background information around the target object can be available, in other words, it is impossible to use background information if the discarded unit-range-images are left discarded without interpolation.
According to a further aspect of the present invention, the range image processing means defines a central-range-image locating in the middle of serial unit-range-images in which variation of signal levels does not exceed the threshold, and selects unit-range-images which has signal levels fall between a representative signal level of the central-range-image and a signal level calculated by adding a predetermined value to the representative signal level or by subtracting a predetermined value from the representative signal level.
Consequently, a further technical advantage is achieved that processing time can be reduced when the shape of the target object is substantially included in the above-mentioned selected unit-range-images and if it is enough to detect partially the target object.
According to a further aspect of the present invention, the range image p
Furukawa Satoshi
Hirono Atsuyuki
Ikari Motoo
Takada Yuji
Andrea Brian
Greenblum & Bernstein P.L.C.
Matsushita Electric & Works Ltd.
Tarcza Thomas H.
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