Solid-state imaging apparatus for motion detection

Television – Camera – system and detail – Camera image stabilization

Reexamination Certificate

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Details

C348S241000, C348S169000, C348S155000, C348S302000

Reexamination Certificate

active

06753904

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a solid-state imaging apparatus for motion detection which detects differences between frames of images. More specifically, the present invention pertains to an imaging apparatus for motion detection that compares a pixel output of pixels in an image frame to determine whether objects within the image move and to provide for error correction of false motion signals.
2. Description of the Related Art
Prior art processing apparatuses for motion detection sequentially transfer image data from a solid-state imaging apparatus and detect motion based on differences between frames of this image data.
FIG. 11
is representative of a prior art image processing apparatus for motion detection
100
. The image processing apparatus for motion detection
100
consists of a solid-state imaging apparatus
101
, an A/D conversion circuit
102
that converts the analog image signal from the solid-state imaging apparatus
101
into a digital signal, a first image memory
103
and a second image memory
104
that save digital signals from A/D conversion circuit
102
, and an image processing circuit
105
that compares the digital image data saved in the first and second image memories
103
,
104
against one another to detect motion.
In this motion detection apparatus
100
, a first frame image signal is first converted into a digital signal by the A/D conversion circuit
102
, and then saved in first image memory
103
.
Next a second frame image signal is also converted into a digital signal by the A/D conversion circuit
102
and saved in second image memory
104
.
The image processing circuit
105
then compares pixels of the digital signal saved in the first image memory
103
with pixels of the digital signal saved in the second image memory
104
. The processing circuit detects pixels that differ by more than a specified threshold value and generates a signal indicating detection of a moving object (hereafter the “moving object signal”).
In this manner, comparison of successive frames permits detection of motion of a subject. Nevertheless, the aforesaid conventional image processing apparatus for motion detection
100
is not ideal. The motion detection circuitry for the solid-state imaging apparatus
101
is complicated making the image processing apparatus for motion detection
100
overly large and costly.
Another defect of the prior art is that the image signal output from solid-state imaging apparatus
101
is an analog signal, which is supplied to A/D conversion circuit
102
. Therefore, the analog signal is conducted along a path presenting an opportunity to be easily affected by noise (interference), which causes the image processing circuit to erroneously generate the moving object signal.
Furthermore, in the motion detector apparatus
100
, the dynamic range of the analog image signal is limited by the A/D conversion circuit
102
. The input dynamic range of A/D conversion circuit
102
is usually narrower than the dynamic range of the solid-state imaging apparatus
101
. Therefore, there is a defect in that the wide dynamic range of solid-state imaging apparatus
101
cannot be effectively used in the course of detecting and processing a moving object.
Also, A/D conversion circuit
102
has a sample rate that may become out of phase with the successive frames provided by the imaging apparatus
101
. This type of phase shifting in inter-frame sampling timing can create a slight phase shift in the pixel position to be compared at the image processing circuit
105
. If this type of phase shift occurs, a stationary body may have inter-frame differences at its edge portions. Therefore, prior art solid-state imaging apparatuses do not provide the desired precision and reliability of moving object detection.
One proposal for avoiding these defects is to provide a memory to store the image signal for the immediately previous frame and the current frame in each pixel of solid-state imaging apparatus
101
, and to additionally provide each pixel with a comparison circuit to compare the image signal stored in this memory, and to generate a moving object signal for each pixel.
However, this design makes the structure of the unit pixel complicated, and reduces the numerical aperture and resolution of the solid-state imaging apparatus
101
. In addition, this design can output only the moving object signal from each pixel. Thus, this design can not simultaneously provide an image signal and a motion signal.
It is generally known that a solid-state imaging apparatus comprising a semiconductor device experiences charge fluctuations, which create shot noise. The magnitude of shot noise is proportional to the square root of the signal magnitude. Therefore, the brighter the subject and the higher the signal level, the greater the shot noise that is created.
As a result, in bright locations shot noise looms large in inter-frame differences. If shot noise occurs in inter-frame differences and exceeds the threshold value for a moving-object decision, erroneous motion detection may occur.
One proposal for avoiding erroneous detection due to shot noise is to set the comparison threshold value for differences between frames uniformly high. Nevertheless, this sort of countermeasure has the problem that sufficient motion detection cannot be performed for a low-contrast subject.
Another known problem of using a semiconductor imaging apparatus is that incorrect motion detection may occur when the field is extremely bright or extremely dark because motion signals can not be generated accurately. Also, in addition to the case described above, background differences between frames also occur, such as when tree leaves wave in a wind. This sort of motion is small motion in the background, and should be distinguished from motion of the intended subject that is being monitored.
SUMMARY OF THE INVENTION
The imaging apparatus for motion detection of the present invention includes an imaging unit that receives incident light on an array of pixel elements that provide a pixel output corresponding to the incident light thereby generating an output signal. The imaging apparatus compares sequential pixel output signals from a single pixel, and generates a motion signal which indicates in pixel units whether or not there is a change within the field of coverage. A motion signal processing circuit sequentially fetches the image signals and motion signals associated with the same pixel that were generated by the imaging unit, and determines whether to externally output the motion signals based on the image signals.
Because image signals and motion signals are generated simultaneously, and the motion signals an be controlled based on the image signals, various types of signal processing of the motion signal can be performed easily. Consequently, additional functions relating to the motion detection of an object in the field can be easily implemented.
For example, if the brightness level, or the color components of the desired subjects, or if the brightness level or the color components of objects that are to be excluded as subjects for motion detection are known, it is possible to determine whether or not to externally output a motion signal according to the brightness level and color components of the image signal. As a result, it is possible to reliably detect the motion of the desired subjects only.
Thus with an imaging apparatus for motion detection which compares the pixel output that is being continuously output from the same pixel and thereby generates a motion signal, if any noise is superimposed on an image signal corresponding to the pixel output, the effect of the noise will also appear in the motion signal, and stationary objects can be mistakenly detected as moving objects. However, because the motion signal can be disabled, any noise that is superimposed on the image signal can be reliably reduced, and the motion of objects in the field can be accurately detected.
In a preferred embodiment, the motion signal processing cir

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