Solid-state image-pickup devices and methods for motion...

Details Solid-state image-pickup devices and methods for motion... Solid-state image-pickup devices and methods for motion...

1998-11-24

2003-07-08

Vu, Ngoc-Yen (Department: 2615)

Television

Camera, system and detail

Solid-state image sensor

C348S243000, C348S208120, C250S208100

Reexamination Certificate

active

06590611

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to solid-state image-pickup devices (SSIPDs) with motion-detection capabilities and to associated drive methods. In particular, this invention pertains to SSIPDs that simultaneously output an image signal and a motion-detection signal.
BACKGROUND OF THE INVENTION
Solid-state image-pickup devices (SSIPDs) are typically used in electronic camera equipment such as camcorders, digital still cameras, and monitoring devices. SSIPDs measure light intensity at discreet locations to image a scene, and contain an array of pixels that convert light intensity into measurable voltage signals. These voltage signals are then processed to produce an output signal that may be stored or viewed on a video display.
It is sometimes desired to add a motion-detection capability to an SSIPD. Conventional motion-detection devices of this type typically detect motion by comparing the difference between frames of image data output by the SSIPD. A “frame” of image data comprises the output signals of all of the pixels in the array during the most recent output cycle. Conventional devices of this type typically provide frame-update rates of five or more frames per second.
FIG. 9
shows the major functional blocks of a motion-detection image-processing sequence commonly employed in a conventional motion-detection image-processing device
100
. The motion-detection image-processing device
100
comprises an SSIPD
101
, an analog-to-digital (A/D) converter
102
that converts the analog image signal output by the SSIPD
101
into a digital signal, a first-frame image memory
103
, a second-frame image memory
104
, and an image-processing circuit
105
that detects motion by comparing the digital image data stored in the first-frame and second-frame image memories
103
and
104
.
The motion-detection image-processing device
100
processes image data in the following sequence. During a first step, the analog image signals output by the pixels of the device during a first frame of image output are converted into corresponding digital signals (i.e., “digitized”)by the A/D converter
102
. The digital signals are stored in the first-frame image memory
103
. Next, the image signals obtained during a second frame, immediately subsequent to the first frame, are digitized by the A/D converter
102
, and stored in the second-frame image memory
104
.
In the image-processing circuit
105
, the digital signal stored in the first-frame image memory
103
and the digital signal stored in the second-frame image memory
104
are compared on a pixel-by-pixel basis to detect motion. For example, all of the digitized pixel-output values stored in the first image memory
103
may be subtracted from respective digitized pixel-output values stored in the second-image memory
104
; if the difference between any two corresponding pixel outputs exceeds a predetermined threshold, the pixel-output difference data may be stored in the image-processing circuit
105
. By comparing the frame images in this manner, it is possible to detect motion of a subject within the image being exposed.
There are several problems with the foregoing conventional approach to detecting motion using a SSIPD. The additional circuitry required for the first-frame and second-frame image memories
103
,
104
, and the image-processing circuit
105
increase the size of the device, making it more costly to manufacture. Also, A/D conversion normally causes a loss in signal quality. Because the pixels are arranged in a tightly packed array, the A/D converters must be located externally to the pixel array. The analog signals output by the pixels are easily affected by peripheral noise caused by high-frequency switching of thousands of MOS switches that are in close proximity to electrical pathways connecting each pixel output to the A/D converters. Thus, by the time the pixel-output signals reach the A/D converters, the signals typically no longer accurately reflect the respective signal values at the pixel outputs.
Moreover, in a conventional motion-detection image-processing device
100
, the dynamic range (bandwidth) of the image signal from a given pixel is limited by the respective A/D converter
102
. Normally, the bandwidth of an A/D converter
102
is narrower than the bandwidth of the SSIPD
101
. Consequently, the entire bandwidth of the SSIPD
101
cannot be effectively used for motion detection.
Conventional analog-to-digital processing is also subject to phase-shift errors that adversely affect the accuracy of motion detection. Each A/D converter
102
processes analog signals on a sequential basis in which the outputs from the pixels in a given horizontal row are processed before proceeding to the pixels in the next horizontal row. As a result, if the A/D conversion circuitry is not properly synchronized with the readout of the pixel outputs, the location of the data for a particular pixel (or sets of adjacent pixels) may be “shifted” in the first-frame or second-frame image memories. For example, suppose that the digitized pixel-output data for all of the pixels in the lower half of the pixel array produced during a first frame is shifted (out of phase) relative to the corresponding digitized pixel-output data produced during a subsequent second frame. In such a case, the difference of the output data produced between frames at a given pixel location in the lower half of the pixel array can no longer be accurately measured because the data corresponding to a particular pixel location in the first-frame image memory is shifted relative to the data of the particular pixel in the second-frame image memory. This phase shift reduces the accuracy of the motion-detection device.
A potential solution to the foregoing problems, which has been considered, is to store the image signals in digital form from the first and second frames in a memory, and route the first-frame and second-frame image signals for each pixel from the memory through a comparator to measure the difference between the frames on a pixel-by-pixel basis. Such a scheme could be implemented by placing local storage circuitry and a comparator in close proximity to each pixel, or by including storage and comparator circuitry with each pixel. The problem with these schemes is that the solid-state surface area required for each such pixel and its associated memory and comparator circuitry is increased, resulting in a corresponding decrease in resolution and/or aperture ratio of the SSIPD. Another problem is that only a motion-detection signal is produced without simultaneously outputting an image signal.
In addition, frame-by-frame comparison techniques as used in conventional motion-detection devices do not accurately detect the motion of a rapidly-moving body.
SUMMARY OF THE INVENTION
In view of the foregoing shortcomings of conventional devices, an object of the invention is to provide motion-detection solid-state image-pickup devices (SSIPDs) that provide an electronic shutter function without requiring external image-comparison processing for motion detection. Another object of the invention is to provide motion-detection SSIPDs capable of simultaneously outputting motion-detection signals and image signals. Yet another object is to provide motion-detection SSIPDs that can output a high-quality image signal from which “dark” signals have been removed. A further object is to provide motion-detection SSIPDs that can evaluate the motion of a body being imaged.
The invention is exemplified herein by several example embodiments that accomplish the foregoing objects by providing image-processing and motion-detection circuitry that simultaneously output an image signal and a motion-detection signal. The motion-detection circuitry compares the pixel outputs from a current frame and a previous frame, to determine if any motion has occurred between the frames, on a pixel-by-pixel basis. The image-processing circuitry subtracts “dark” signals from the pixel-output signals so as to output an image signal from which the dark signals have been removed.

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