Showing papers on "Image sensor published in 1997"

CMOS image sensors: electronic camera-on-a-chip

Abstract: CMOS active pixel sensors (APS) have performance competitive with charge-coupled device (CCD) technology, and offer advantages in on-chip functionality, system power reduction, cost, and miniaturization. This paper discusses the requirements for CMOS image sensors and their historical development, CMOS devices and circuits for pixels, analog signal chain, and on-chip analog-to-digital conversion are reviewed and discussed.

Catadioptric omnidirectional camera

Abstract: Conventional video cameras have limited fields of view that make them restrictive in a variety of vision applications. There are several ways to enhance the field of view of an imaging system. However, the entire imaging system must have a single effective viewpoint to enable the generation of pure perspective images from a sensed image. A new camera with a hemispherical field of view is presented. Two such cameras can be placed back-to-back, without violating the single viewpoint constraint, to arrive at a truly omnidirectional sensor. Results are presented on the software generation of pure perspective images from an omnidirectional image, given any user-selected viewing direction and magnification. The paper concludes with a discussion on the spatial resolution of the proposed camera.

Moisture sensor and windshield fog detector using an image sensor

Abstract: A control system for automatically detecting moisture on the windshield of a vehicle. The automatic moisture detecting system includes an optical system for imaging a portion of the windshield on to an image array sensor, such as a CMOS active pixel sensor. The voltages of each of the pixels which represents the illumination level is converted to a corresponding gray scale value by an analog digital converter. The gray scale values corresponding to the image are stored in memory. The spatial frequency composition of the gray scale values are analyzed to determine the amount of rain present. In order to provide a control signal to control the operation of the windshield wipers of the vehicle as a function of the amount of moisture present. The system is also adapted to detect the level of fog both on the interior of the windshield as well as the exterior of the windshield. By providing a system for automatically detecting the presence of fog on the interior and exterior of the windshield, serious performance limitations of known automatic rain sensors are eliminated.

Hand-held bar code reader with laser scanning and 2D image capture

Abstract: A hand-held bar code reader (100) includes a laser scanning module and a two dimensional image sensor and processing for reading a bar code. The laser scanner assists the 2D image processing by providing information on location, type, range, reflectivity, and presence of bar code for 2D reading. Additionally, the 2D imaging reading operation is improved by using the laser scan as a spotter beam for aiming.

Omnidirectional imaging apparatus

Abstract: An omnidirectional image apparatus (130) for sensing an image of a substantially hemispherical scene from a single viewpoint, including a truncated, convex, substantially paraboloid-shaped reflector (135) positioned to orthographically reflect an image of the substantially hemispherical scene, and an image sensor (110) positioned to receive the orthographically reflected image. An omnidirectional image projection apparatus for projecting an image of a substantially hemispherical scene as viewed from a single viewpoint, including a means for projecting a collimated beam of light modulated with the image, and a truncated convex substantially paraboloid-shaped reflector positioned to orthographically reflect the collimated beam of light modulated with the image to project the hemispherical scene.

Optical reader having improved interactive image sensing and control circuitry

Abstract: A hand-held optical reader for reading 2D bar code symbols. The reader includes an illuminating system for illuminating the symbol and an optical system for focusing an image thereof on a 2D image sensor. The image sensor is of the type which allows its imaging parameters, such as exposure, to be controlled by external circuitry. The reader also includes an image sensor processor which sets and changes the imaging parameters used by the image sensor as necessary to meet predetermined image quality criteria and to reduce the time necessary to complete a read operation.

Digital radiology using active matrix readout of amorphous selenium: Theoretical analysis of detective quantum efficiency

Abstract: A flat-panel x-ray imaging detector using a layer of amorphous selenium (a-Se) for direct conversion of x rays (to charge) and an active matrix for self-scanned readout is being investigated for digital radiology. A theoretical analysis of the spatial frequency dependent detective quantum efficiency (DQE(f )) of the self-scanned a-Se detector is performed based on a model of signal and noise propagation in a cascaded imaging system. Because of the high intrinsic resolution of a-Se and the pixelated active matrix readout method, such detectors are inherently undersampled and aliasing is present. The presampling modulation transfer function (MTF) and aliased noise power spectrum (NPS) of the detector were used in the analysis of DQE(f ). It is proven that the aliased NPS for the self-scanned a-Se detectors is white. Since the shape of DQE(f ) is determined by the ratio of MTF squared and the NPS, the shape of DQE(f ) follows the square of the presampling MTF of the detector as a result of the white NPS. The analysis also shows that DQE(0) is proportional to the pixel fill factor, i.e., the fraction of each pixel area used for image charge collection. The DQE analysis is applied to detector parameters for three x-ray imaging applications: mammography, chest radiography, and fluoroscopy. The effects of pixel fill factor, imaging geometry (i.e., incident angle of x rays), and various sources of electronic noise on the detector DQE(f ) are discussed. Strategies for maximizing detector DQE for each x-ray imaging application are proposed.

Serial analog-to-digital converter using successive comparisons

Abstract: A method for simultaneously performing bit serial analog to digital conversion (ADC) for a potentially very large number of signals is described. The method is ideally suited for performing on chip ADC in area image sensors. In one embodiment, to achieve N-bit precision, the method employs a one-bit comparator per channel (or set of multiplexed channels) and an N-bit DAC. To achieve N bits of precision, 2 N -1 comparisons are sequentially performed. Each comparison is performed by first setting the DAC output to the desired value and then simultaneously comparing each of the pixel values to that value. If a pixel value is greater than the DAC output value, its comparator outputs a one, otherwise it outputs a zero. By appropriately choosing the sequence of comparison values, the pixel values are sequentially generated. In another embodiment, the DAC is omitted and a continuous ramp signal is generated for comparison with the analog input.

On-focal-plane analog-to-digital conversion for current-mode imaging devices

Abstract: A current-mode analog-to-digital converter based on a current copier circuit with a constant bias current that is independent of the input signals. A second-order incremental Σ-Δ conversion configuration is implemented. An array of such analog-to-digital converters can be integrated onto the focal plane of an imaging sensor array to achieve column-wise parallel analog-to-digital conversion.

Virtual reality camera

Abstract: A method and apparatus for creating and rendering multiple-view images A camera includes an image sensor to receive images, sampling logic to digitize the images and a processor programmed to combine the images based upon a spatial relationship between the images

Pulse-based analog VLSI velocity sensors

Abstract: We present two algorithms for estimating the velocity of a visual stimulus and their implementations with analog circuits using CMOS VLSI technology. Both are instances of so-called token methods, where velocity is computed by identifying particular features in the image at different locations; in our algorithms, these features are abrupt temporal changes in image irradiance. Our circuits integrate photoreceptors and associated electronics for computing motion onto a single chip and unambiguously extract bidirectional velocity for stimuli of high and intermediate contrasts over considerable irradiance and velocity ranges. At low contrasts, the output signal for a given velocity tends to decrease gracefully with contrast, while direction-selectivity is maintained. The individual motion-sensing cells are compact and highly suitable for use in dense 1-D or 2-D imaging arrays.

A 0.8-/spl mu/m CMOS two-dimensional programmable mixed-signal focal-plane array processor with on-chip binary imaging and instructions storage

Abstract: This paper presents a CMOS chip for the parallel acquisition and concurrent analog processing of two-dimensional (2-D) binary images. Its processing function is determined by a reduced set of 19 analog coefficients whose values are programmable with 7-b accuracy. The internal programming signals are analog, but the external control interface is fully digital. On-chip nonlinear digital-to-analog converters (DAC's) map digitally coded weight values into analog control signals, using feedback to predistort their transfer characteristics in accordance to the response of the analog programming circuitry. This strategy cancels out the nonlinear dependence of the analog circuitry with the programming signal and reduces the influence of interchip technological parameters random fluctuations. The chip includes a small digital RAM memory to store eight sets of processing parameters in the periphery of the cell array and four 2-D binary images spatially distributed over the processing array. It also includes the necessary control circuitry to realize the stored instructions in any order and also to realize programmable logic operations among images. The chip architecture is based on the cellular neural/nonlinear network universal machine (CNN-UM). It has been fabricated in a 0.8-/spl mu/m single-poly double-metal technology and features 2-/spl mu/s operation speed (time required to process an image) and around 7-b accuracy in the analog processing operations.

A CMOS image sensor with analog two-dimensional DCT-based compression circuits for one-chip cameras

Abstract: This paper presents a CMOS image sensor with on-chip compression using an analog two-dimensional discrete cosine transform (2-D DCT) processor and a variable quantization level analog-to-digital converter (ADC). The analog 2-D DCT processor is essentially suitable for the on-sensor image compression, since the analog image sensor signal can be directly processed. The small and low-power nature of the analog design allows us to achieve low-power, low-cost, one-chip digital video cameras. The 8/spl times/8-point analog 2-D DCT processor is designed with fully differential switched-capacitor circuits to obtain sufficient precision for video compression purposes. An imager array has a dedicated eight-channel parallel readout scheme for direct encoding with the analog 2-D DCT processor. The variable level quantization after the 2-D DCT can be performed by the ADC at the same time. A prototype CMOS image sensor integrating these core circuits for compression is implemented based on triple-metal double-polysilicon 0.35-/spl mu/m CMOS technology. Image encoding using the implemented analog 2-D DCT processor to the image captured by the sensor is successfully performed. The maximum peak signal-to-noise ratio (PSNR) is 36.7 dB.

A 0.6 /spl mu/m CMOS pinned photodiode color imager technology

Abstract: The world's first submicron pinned photodiode CMOS image sensors have been produced by adding an optimized image sensor module to a 33 V, 06 /spl mu/m CMOS process The 4-transistor pixel cells achieve excellent blue response, low dark current, and good dynamic range A full-color imager with good color reproduction has been produced using this technology

Focal plane exposure control system for cmos area image sensors

Abstract: An electronic exposure control system for an active pixel CMOS image sensor includes a row decoder and a column decoder for respective row-wise and column-wise addressing of the image signal generating pixels. The decoders receive row and column addresses and control signals from a controller. The row addresses received by the row decoder are alternately switched between a predetermined row address for resetting the image signals of pixels in said row and another predetermined spaced apart row address for enabling the image signals of pixels in said selected row to be read out by the column decoder. By providing a predetermined sequence of row addresses, a “rolling shutter” can be created and/or the exposure time of the pixels can be selected to be different from the time to expose an entire frame. The image sensor can also be operated in an interlaced mode and/or specific areas on the image sensor can be selected to be reset and read out.

Scanning ink jet printer for electronic displays

Abstract: An attachable printer for use with a electronic camera having an image sensor which captures an image of a subject onto the image sensor is disclosed. The camera includes electronics coupled to the image sensor for storing a digital image of the subject; a display; and circuitry coupled to the display and responsive to the stored digital image and effective in a first condition for producing a correctly oriented image on the display and in a second condition for producing a mirror image on the display. The printer is effective when connected in operative relationship to the display and having a moveable carriage, and a scanner and an ink jet printhead mounted on the carriage, and being arranged so that as the carriage moves, the scanner scans the mirror image on the display and produces image signals; and the ink jet printhead being responsive to the signals produced by the scanner for producing a correctly oriented image onto the receiver sheet.

Digital radiology using active matrix readout of amorphous selenium: construction and evaluation of a prototype real-time detector.

Abstract: The goal of the present work is to develop a large area, flat-panel solid-state detector for both digital radiography and fluoroscopy The proposed detector employs a photoconductive layer of amorphous selenium (a-Se) to convert x rays into charge The charge image formed by the a-Se layer is electronically read out in situ using a two dimensional array of thin film transistors (TFTs), or active matrix Since the active matrix readout is capable of producing x-ray images in real-time, it can potentially be applied in both radiography and fluoroscopy In this paper, the imaging performance of this concept is investigated using a prototype x-ray imaging detector The designs for the active matrix, the peripheral electronic circuits, and the image acquisition system are described Measurements of x-ray imaging properties of the prototype detector, ie, x-ray sensitivity, presampling modulation transfer function (MTF), and noise power spectrum (NPS), were performed, and from which the spatial frequency dependent detective quantum efficiency (DQE) of the prototype was derived The experimental results are in agreement with the results of our theoretical analysis The factors affecting the imaging performance and methods of improvement in the future are discussed

CMOS active pixel sensor star tracker with regional electronic shutter

Abstract: A 64/spl times/64 element CMOS active pixel sensor (APS) for star tracker applications is reported. The chip features an innovative regional electronic shutter through the use of an individual pixel reset architecture. Using the regional electronic shutter, each star in the field of view can have its own integration period. This way, simultaneous capture of bright stars with dim stars is accommodated, enabling a large increase in tracker capability. The chip achieves 80 dB dynamic range, 50 e-rms read noise, low dark current, and excellent electronic shutter linearity.

Perceptual-based image fusion for hyperspectral data

Abstract: Three hierarchical multiresolution image fusion techniques are implemented and tested using image data from the Airborne Visual/Infrared Imaging Spectrometer (AVIRIS) hyperspectral sensor. The methods presented focus on combining multiple images from the AVIRIS sensor into a smaller subset of images white maintaining the visual information necessary for human analysis. Two of the techniques are published algorithms that were originally designed to combine images from multiple sensors, but are shown to work well on multiple images from the same sensor. The third method presented was developed specifically to fuse hyperspectral images for visual analysis. This new method uses the spatial frequency response (contrast sensitivity) of the human visual system to determine which features in the input images need to be preserved in the composite image(s) thus ensuring the composite image maintains the visually relevant features from each input image. The image fusion algorithms are analyzed using test images with known image characteristics and image data from the AVIRIS hyperspectral sensor. After analyzing the signal-to-noise ratios and visual aesthetics of the fused images, contrast sensitivity based fusion is shown to provide excellent fusion results and, in every case, outperformed the other two methods.

Electronic camera for initiating capture of still images while previewing motion images

Abstract: An electronic camera uses a relatively more complex digital image processing technique in a still image mode to produce high quality still images, and a relatively more simple image processing technique in a motion preview mode to produce preview images of acceptable quality prior to initiation of the still image mode. The more complex digital technique is done in software in a general purpose processor section 35, while the more simple digital technique is implemented in a fixed digital circuit in an application specific integrated circuit 27, which also implements timing and control functions. The motion preview mode uses a shorter image readout period than the still mode and further involves mapping image sensor pixels into a fewer number of color display pixels on a color LCD display 10. The mapping further converts color pixel signals from a mosaic array into a different color pattern on the color LCD display 10.

System and method for using a single intelligence circuit in both a digital camera and printer

Abstract: A simplified electronic camera and printer imaging system is provided that includes a single intelligence circuit preferably in the form of a PC card that is detachably connectable to either the camera or the printer for converting a data stream generated by the imaging sensor of the camera into stored data when connected to the camera, and converting the stored data into printer instructions, and relaying the printer instructions to the printhead when connected to the printer. The use of a single intelligence circuit to operate both a digital camera and printer advantageously simplifies the structure of the system, reduces costs, and enhances reliability by minimizing processing steps and circuit interfaces. In the preferred embodiment, the PC card containing the intelligence circuit includes a liquid crystal display and manual controls for displaying stored or real time images, capturing or erasing images, scrolling through stored images, and commanding a printer to render the images in hard copy form.

Image sensor with direct digital correlated sampling

Abstract: A CMOS image sensor is provided in which correlated double sampling is performed entirely in the digital domain. In an exemplary embodiment, the image sensor includes a plurality of imager cells arranged in rows and columns, where the imager cells of a particular column are coupled to a column data line of that column. Each active imager cell is capable of selectively providing a first output on an associated column data line indicative of a reset level during a first sampling interval. During a second sampling interval, each active imager cell provides a signal output on the associated column data line indicative of an amount of light incident upon that imager cell. At least one analog to digital (A/D) converter is coupled to the column data lines and converts the first and signal outputs on each column data line to first and second digital codes, respectively, to complete a correlated double sampling operation. The invention eliminates the need for analog capacitors to store the reset and signal levels.

Random addressable 2048/spl times/2048 active pixel image sensor

Abstract: In this paper, we discuss the design, design issues, fabrication, and performance of a 2048/spl times/2048 active pixel image sensor in a 0.5-/spl mu/m standard CMOS process. Each pixel, 7.5/spl times/7.5 /spl mu/m/sup 2/, consists of three transistors and a photo diode, resulting in a 12-million transistor chip with a die size of 16.3/spl times/16.5 mm. The pixel has a nonintegrating direct readout architecture, with a logarithmic light-to-voltage conversion. This allows the array to be fully random accessible, both in space and time. The sensor has eight analog outputs, each with a pixel rate of 4.5 MHz, which implies a maximum frame rate of eight full frames per second. Sub-sampling or windowing makes higher frame rates possible. The yield of the sensor is high if one accepts a small number of bad pixels.

Image sensor with dummy pixel or dummy pixel array

Abstract: Disclosed is an image sensor including one or more dummy pixels that produce a reference signal which is used to compensate for errors within the devices of the main pixel cells. In one embodiment, at least one dummy pixel is used in conjunction with other circuitry to correct for nonlinearities in the transfer characteristic of a source follower transistor within each pixel. In another embodiment, an array of dummy pixels is used to correct for leakage current within the pixels during an electronic shutter mode of operation. The two techniques can be combined whereby both threshold voltage mismatch and leakage current are compensated for.

Model-based planning of optimal sensor placements for inspection

Abstract: We report a system for sensor planning, GASP, which is used to compute the optimal positions for inspection tasks using known imaging sensors and feature-based object models. GASP (general automatic sensor planning) uses a feature inspection representation (the FIR), which contains the explicit solution for the simplest sensor positioning problem. The FIR is generated off-line, and is exploited by GASP to compute on-line plans for more complex tasks, called inspection scripts. Viewpoint optimality is defined as a function of feature visibility and measurement reliability. Visibility is computed using an approximate model. Reliability of inspection depends on both the physical sensors acquiring the images and on the processing software; therefore we include both these components in a generalized sensor model. These predictions are based on experimental, quantitative assessment. We show how these are computed for a real generalized sensor, which includes a 3-D range imaging system, and software performing robust outlier removal, surface segmentation, object location and surface fitting. Finally, we demonstrate a complete inspection session involving 3-D object positioning, planning optimal position inspection, and feature measurement from the optimal viewpoint.

Endoscope having elevation and azimuth control of camera assembly

Abstract: A surgical/diagnostic imaging device for use in interabdominal, interthoracic, and other surgical and diagnostic procedures includes an image sensor pivotally mounted at the distal end of a support. In use, the image sensor and support are contained within a disposable sterile sheath, and the distal portion of the sheath is inserted into the patient through an incision. The imaging device includes actuators to move the image sensor in elevation and azimuth.

Image sensor employing non-uniform A/D conversion

Abstract: Disclosed is an image sensor having A/D conversion circuitry coupled to column data lines of an image sensor array. The A/D conversion circuitry digitizes analog signals on the column data lines, each representing intensity of light incident upon an active imager cell. Higher resolution is provided for darker light levels than for bright light levels, such that a high resolution image is obtained with less storage data than would otherwise be required. In one embodiment, the A/D conversion circuitry includes a plurality of comparators, each having a first input coupled to one or more column data lines and a second input coupled to receive a time-varying reference signal, and a plurality of n-bit counters coupled to the comparator outputs. An n-bit to m-bit converter nonlinearly maps n-bit codes to m-bit codes and provides the m-bit codes to an m-bit D/A converter which produces the time-varying reference signal. In another embodiment, the A/D conversion circuitry is comprised of a non-uniform successive approximation A/D converter.

Motion tracking using image-texture templates

Abstract: Image templates are extracted from video images in real-time and stored in memory. Templates are selected on the basis of their ability to provide useful positional data, via position locator (2), and compared with regions of subsequent images to find the position giving the best match. From the position data, a transform model calculator (3) calculates a transform model. The tracking controller (1) tracks the background motion in the current image to accurately determine the motion and attitude of the camera recording the current image. A transform model confirmer (4) confirms the transform model by examining predefined image templates. Transform model data and camera sensor data are then used to insert images into the live video broadcast at the desired location in the correct perspective. Block updater (5) periodically updates stored templates to purge those that no longer give valid or significant positional data. New templates extracted from recent images are used to replace the discarded templates.

Printer receiving electronic camera

Abstract: Apparatus for capturing and printing images on photosensitive sheets includes an electronic camera having a display; and an image sensor means for producing a digital image of a subject. In response to the digital image, the electronic camera displays an image on the display. The printer includes a light tight storage structure for receiving the photographic sheets. The printer receives the electronic camera and includes optics for focusing the image on the display along a single optical path onto a photosensitive sheet at an exposure position. The printer further includes a shutter member having a shutter aperture for controlling the aperture to cause light from the display image to illuminate the photosensitive sheet.