Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J31/00—Cathode ray tubes; Electron beam tubes
  • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
  • H01J31/26—Image pick-up tubes having an input of visible light and electric output
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/50—Constructional details
  • H04N23/54—Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/58—Means for changing the camera field of view without moving the camera body, e.g. nutating or panning of optics or image sensors

Definitions

• the invention relates to an optoelectronic camera of the type specified in the preamble of claim 1.
• German patent application DE-37 33 593 AI describes a device for photographing an object, in particular for later display on the screen.
• an image pickup that is smaller than the image through the lens is slidably arranged in the image plane. Any section of the image field can be made visible by moving the image sensor in the image plane.
• the advantage here is that the particular made visible is displayed with very good reproduction quality and high resolution.
• the disadvantage of this device is that it is not possible to grasp the entire image field at a glance, that changing the image section requires a certain amount of time and that the dimensions and the weight are relatively high due to the required lenses with a large image field are.
• the image sensor is a 6.6 x 8.8 mm a large CCD chip with 580 lines of 499 elements.
• the pixels are approximately 11 x 17 ⁇ m 2 in size.
• the CCD matrix is covered by a shadow mask that only leaves an area of less than 3 x 3 ⁇ m a per pixel.
• the sensor can be moved horizontally in up to 6 intervals and vertically in 4 intervals, which increases the number of pixels by a factor of 24 to almost 7 million pixels.
• the gradual displacement of the sensor takes place by means of piezoelectric drives, which enable highly precise and fast scanning.
• Collector electrodes at the output of the individual channels of the microchannel plate collect the electrons and feed them to the processing via memory, transmission element and analog shift register.
• the resolution of image intensifiers is limited. When using microchannel plates, the resolution is determined by the center distance of the individual channels. It is currently around 20 ⁇ m. With microchannel plates, electron gain factors of 10,000 can be achieved.
• the invention is based on the object of creating an optoelectronic camera of the type mentioned at the outset which enables high-resolution images (for example up to approximately 500 pixels / millimeter) to be produced in real time without loss of sensitivity compared to known image sensors ⁇ time (25 frames / second).
• the reason for the low sensitivity of the image sensors, which operate according to the piezocontrolled aperture shift method, is the reduction in the effective pixel area by masking, which results in a reduction in the proportion of the sensitive area in the total area of the Sensor is connected.
• the sensitivity is indirectly further reduced in that the exposure time per pixel is limited in accordance with the image frequency and the number of steps per image. This results in
• the factor K for reducing the sensitivity compared to the unmasked sensor.
• an additional image intensifier is arranged between the components present in the recording unit of an optoelectronic camera, in a known manner, a shadow mask! and an image sensor.
• the image intensifier has a photocathode, which is followed, in particular, by a microchannel plate.
• a channel of the microchannel plate is directly assigned to each hole of the shadow mask. Due to the image brightness on the photo
• Electrons generated in the region of the individual holes of the shadow mask are preferably multiplied or accelerated under the effect of a high voltage source within the individual channels of the microchannel plate. After passing through the individual channels, the electrons corresponding to the image content hit the image sensor directly and generate a corresponding charge image there.
• the smallest part of the image that can be read out depends on the step pattern of the drives for aperture shifting and the diameter of the holes in the shadow mask.
• the invention is based on the knowledge that it is possible by means of an image intensifier to increase the amount of light reduced by the diaphragm arrangement to such an extent that it corresponds to a light yield that could be achieved without a diaphragm arrangement. This refuted the previously prevailing opinion that it can be assumed that only either the resolution or the sensitivity could be chosen to be large. With the measures of the invention, however, a high resolution can be achieved even with high sensitivity, so that the use of the generic optoelectronic camera is no longer - as was previously the case - restricted to fields of application with high light intensity.
• the lack of real-time capability at high resolution in the prior art was due to the limited data rate of the CCD image sensor and the fact that the entire image had to be read out at all times.
• the increase in the data rate also reaches technical and economic limits in image processing. With 25 frames / second, 25 million pixels and 8-bit gray value quantization, this results in a data rate of 5 gigabits / second.
• the high resolution for image processing is only partially necessary and sensible.
• the entire image can be captured with normal resolution and, on the other hand, sections of the image can be accessed, which means that the entire image does not have to be read out.
• the optoelectronic camera is provided with a selection circuit by means of which different image resolutions and sections can be freely selected taking into account the data processing capacity of the downstream processor.
• an increased resolution can be maintained while maintaining the sensitivity. Achieve similarity of comparable devices of the prior art.
• the resolution is reduced, the sensitivity is increased.
• a switch is preferably made to partial image reproduction at high resolution. This applies to the conditions of real-time transmission.
• the changing sensitivity is usually borrowed by changing the gain accordingly.
• this area can also be examined or measured more precisely with the highest sensitivity and in high resolution when the scanning rate is slowed down.
• the optoelectronic camera When the optoelectronic camera is operated, according to the method, in the "overall image acquisition” operating mode, essential parts of the image of the overall image are determined with a relatively low resolution, whereas in the "partial image acquisition” operating mode the previously determined or further image sections are acquired with a higher resolution.
• the resulting charge image of the xy-addressable image sensor is integrated and read out pixel by pixel during a complete cycle of mechanical scanning in the "total image acquisition” operating mode, so that the number of pixels of the keyed image corresponds to the number of pixels of the xy-addressable image sensor.
• the integration time is advantageously divided equally between the individual raster steps within a complete cycle of the mechanical scanning.
• the position and size of the restricted image parts read out in the "partial image acquisition" operating mode can be freely programmed.
• the device according to the invention and the method according to the invention thus enable the recording of images of an object with normal resolution and the recording of high-resolution partial images in real time with a minimum of image data.
• the new technical principle is comparable to that of the human eye.
• the entire object field is captured with a relatively low resolution.
• the essential parts of the image of the object are determined and recorded with a much higher resolution.
• the object is scanned by the eye with a "sharp view" that is locally limited in resolution.
• the visual process can be clearly followed when measuring with a ruler.
• the length of a line is determined by only bringing the start and end points of the line into line with marks of the ruler and reading the distance on the scale.
• the amount of data to be processed can be drastically reduced according to this principle in automatic image processing by preprocessing or selection.
• a picture section with variable size, position and resolution is made possible.
• the sensitivity of the optoelectronic camera can thus be adapted to the circumstances by variation within wide limits.
• the usable scope within the dependence on resolution, sensitivity, number of pixels and frame frequency is significantly expanded with the optoelectronic camera according to the invention. According to the requirements, the camera can be adapted to a wide variety of application conditions.
• the electronic selection of image sections can be implemented without any further mechanical aids, since the camera according to the invention has a much higher resolution than can be displayed on conventional monitors.
• the selection of the image section can be made, for example, from the overall image using a mouse or automatically, so that mechanical panning, tilting or zooming processes of the camera are eliminated.
• the invention is explained in more detail below in connection with the enclosed drawing using exemplary embodiments. Show it:
• FIG. 1 shows a representation of the device according to the invention in the main section
• FIG. 2 is an illustration of the method for operating the device according to the invention
• FIG. 3 shows a block diagram for the control of a device according to the invention
• FIG. 4 shows the time course of essential control signals in the overall image acquisition mode
• FIG. 5 shows the time course of essential control signals in the partial image acquisition mode
• FIG. 6 shows a schematic representation of an arrangement for the selection of the different operating modes of the camera according to the invention.
• the lens of an optoelectric camera designs the optical image of an object in its image plane 13.
• a shadow mask 1 which has a regular hole structure 2 with a hole diameter of 5 ⁇ m, has a hole spacing in the horizontal and vertical direction of 20 ⁇ m and a number of 512 x 512 holes.
• the shadow mask is applied to the photocathode 3 of an image intensifier, which also consists of a microchannel plate 4 with 512 x 512 microchannels, which are arranged such that a microchannel is assigned to each hole of the mask.
• an xy-addressable image sensor 6 On the output side of the image intensifier there is an xy-addressable image sensor 6, the pixels of which are designed as collector electrodes 5, which collect the electrons emitted by the individual microchannels and feed them to a storage capacitor. Each microchannel is assigned a collector electrode and thus a pixel of the image sensor.
• the image intensifier and the surface of the image sensor are in a vacuum.
• a high voltage source 7 supplies DC voltage pulses, the amplitude and position of which is variable. With these pulses, the image intensifier is operated in the manner of an electronic shutter, so that in this way the integration time becomes independent of the readout regime.
• Hole mask, image intensifier and xy-addressable image sensor are firmly connected to each other and are deflected by two piezo translators in the x and y directions at a maximum of 4 x 5 ⁇ m in steps, relative to the optical image of the object, in such a way that that the image is scanned without gaps.
• the pixels of the image sensor are addressed using an address decoder and MISFET switches.
• the xy-addressable image sensor has the special that the pixels can be reset together and regardless of whether they have been read out. In this way, partial images can also be read out or the readout process can be interrupted and restarted at any time if this is necessary within the scope of the invention.
• FIG. 3 schematically shows an arrangement for controlling the recording unit of an optoelectronic camera according to the invention (the modules analog amplifiers, filters, in particular suppression of the fixed pattern noise, and A / D converters are not explicitly designed) .
• the abbreviations used mean:
• VBV control voltage for the image intensifier
• ADBA pixel addresses of the image recorder ADBS ... memory addresses of the image memory T1, T2, T3 ... various clock signals
• the parameters during image recording are influenced by input variables shown on the left in FIG. 3.
• An aperture control device (PAD controller) 21 enables the controlled displacement of a shadow mask 22 via a shadow mask drive 23 (PAD - piezoelectric aperture displacement), which is arranged downstream of a lens 24.
• the input variables "step size" in the x and y directions can be used to scan the object and thus the number of light-sensitive objects areas of an image sensor 25 falling pixels that are to be recorded sequentially in time - and thus the resolution - vary.
• An image intensifier (BV) controller 26 can be used to influence the corresponding physical quantities of a downstream image intensifier 27 via the input control variables “shutter speed” and “amplification”.
• An address generator 28 can be used to control the selection of an image section via the input-large “position image section” and “size image section”, the addresses of the separately selectable light-sensitive areas (pixels) of the image sensor containing the relevant image parts being addressable .
• the above-mentioned modules are controlled under the control of a clock generator 29 with the input variables “clock” and “reset”.
• a data record (image data) containing the image information is available at the output of the image sensor.
• the image data are furthermore transferred to an image memory (not shown in FIG. 4) to which control signals ADBS from the address generator 28 are also supplied for image composition.
• the arrangement is operated in the following manner: For an image, an image area of 20 ⁇ m ⁇ 20 ⁇ m is meandered in 4 ⁇ 4 steps from each pixel stares. At the same time, the arrangement is subjected to high-voltage pulses, so that a charge image results from the integration of 16 sub-images in the image sensor.
• the integration time is determined exclusively by the microchannel plate operated as an electronic shutter. The result of the meandering scanning is that the arrangement between two sub-images only has to be moved one step (5 ⁇ m) - that is, its positioning time is minimized.
• the respective signals belonging to the modules indicated in FIG. 3 are given the corresponding designations in FIG. 4. While most of the signals are pulse-shaped signals, the signals "ADBA" and "ADBS" form digital addresses, which are designated by way of example in the figure.
• the x-y-addressable image sensor is read out regularly line by line in a downstream image memory 17 which is not part of the device according to the invention.
• the mutually assigned addresses of the pixels of the x-y-addressable image sensor and the memory cells of the image memory are identical except for the offset of the image memory area.
• the address is generated on the basis of the coordinate designating the image section (address of the upper left pixel of the sub-picture) so that after reading out a line of the sub-picture (128 pixels), the next line with an offset of 384 is jumped to.
• the address generation for the image memory is carried out in such a way that only every sixteenth memory cell is written to.
• the other 15 sub-images are read into the intermediate memory cells one after the other.
• the last 4 bits of the memory address thus correspond to the sequential number of the sub-picture within a picture with increased resolution. In this way, the sub-images in the image memory are interleaved to form an image with 16 times the resolution.
• the time-related loss of sensitivity is calculated from the reciprocal of the number of subpixels per picture element.
• the time-related loss of sensitivity is calculated as follows:
• T p readout time for one pixel
• T A recording time for a subimage
• FIG. 6 shows a device for selecting the operating mode of a camera according to the invention as a block diagram.
• the camera according to the invention can be influenced via an input unit 31 by inputting commands which trigger complex control sequences. These control sequences are stored in memory locations of a memory 32, which can be addressed by the selection made on the input unit. Practically different "control words" are present in the memory locations of the memory 32, which contain the input variables for the desired operating modes of the camera in accordance with the block diagram in FIG. 3. This means that every selection of sensitivity, resolution or image detail can already be stored in advance, so that the required control signals are provided with the selection made.
• the operation of an image computer 33 which receives the image data and the signal "ABDS" from FIG. 3, can also be controlled.
• This image calculator contains the necessary memories to buffer the image data for one or more images. With this computer, the vectorial arithmetic operations necessary for the measurement of images are also carried out. The recorded and processed image is then shown, for example, on a display 33, but can also be further processed in some other way and transmitted to a remote location, for example, by data transmission.
• a shadow mask with a hole diameter of 2.5 ⁇ m which enables the number of pixels to be increased by a factor of 64 with 8 x 8 grid steps.
• the image can be resolved into a maximum of 4096 x 4096 pixels " . 0.625 ms are available for each sub-image if 64 pixels are to be acquired step by step in 40 ms (25 Hz image frequency).
• this time is divided into the time for the relative movement of the hole ke by 2.5 ⁇ m, in the exposure time and in the readout time for the integrated image after a complete cycle of the mechanical scanning.
• a movement time of 0.2 ms per step an exposure time of 0.025 ms and a readout time of 25.6 ms per image, a step frequency of approx. 4.5 kHz and a pixel readout frequency of 10.24 MHz are required.
• Each pixel 10 can be assigned coordinates which identify its position within the coordinate system 9 of a pixel 11 and the position of this coordinate system in the reference coordinate system 8 of the semiconductor matrix structure. From the overall picture, parts of the picture are determined that are essential for the dimension to be determined. Only these parts of the image are captured with maximum resolution. With the determined coordinates of the relevant pixels, the dimension can be determined by means of vector calculation, as explained with reference to FIG. 6.
• pixel addressing in the image sensor takes place with the aid of digital shift ghost. These have the peculiarity of enabling forward and backward pushing. In the operating mode

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• 1990
  • 1990-10-08 DE DE4032193A patent/DE4032193A1/de active Granted
• 1991
  • 1991-10-08 WO PCT/DE1991/000802 patent/WO1992006560A1/de active Application Filing

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