JPS6013597B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging device using a CCD (charge coupled device) image sensor.

Conventionally, common methods for keeping the image signal output of an imaging device substantially constant include a method using an amplifier with automatic gain adjustment and a method using an optical aperture.

When using the former type of amplifier with automatic gain adjustment, the output level must be increased during low illuminance, resulting in a deterioration of the S/N ratio. In the latter case, it is necessary to adjust the aperture value of the optical system according to the output level, which has the disadvantage of being troublesome during manual adjustment or requiring a special optical system equipped with an automatic aperture device. In the case of a device using a CCD image sensor, since the scanning method is different from that of other sensors, it becomes possible to control the scanning frequency and keep the video signal output approximately constant, which has been difficult in the past. However, this method has the drawback that the scanning frequency changes in response to changes in the amount of light, and the time axis of the output signal corresponding to the position of the object in space changes. There is also a method of keeping the output of the video signal substantially constant by controlling the application time of the voltage necessary for photoelectric conversion while keeping the scanning frequency constant. In this method, it is difficult to maintain a constant amount of light even with large changes in light intensity due to charge leakage between the electrodes of the CCD that store photoelectrically converted charges and the electrodes that transfer charges. The present invention eliminates the above-mentioned drawbacks by controlling only the number of consecutive extractions of video signals, and provides a device that maintains the video signal output within a certain range even when the amount of incident light changes while keeping the scanning frequency constant. It is. According to the present invention, there is provided a photoelectric conversion means using a charge-coupled device that outputs a signal proportional to the amount of incident light, an average value detection circuit that detects the average value of the photoelectric conversion means, and an output of the average detection circuit that outputs a signal proportional to the amount of incident light. and a pulse generation circuit for converting the width into a pulse width, and controls the number of times the output signal of the photoelectric conversion means is taken out in response to the output of the pulse generation circuit, and changes the charge accumulation time of the photoelectric conversion means. A bran image device is obtained which is characterized by keeping the output of a video signal within a certain range.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram schematically showing an imaging apparatus of the present invention, and symbols 7 to 1 shown in the diagram correspond to symbols in the waveform diagram of each part in FIG. 2. In FIG. 1, reference numeral 1 denotes an imaging optical system, which forms an image on the light-receiving surface of the sensor 2. Horizontal and vertical scanning signals generated by a scanning signal generator 7 are applied to the sensor 2 through a scanning signal gate 10, and charges photoelectrically converted by a plurality of image sensing elements inside the sensor are synchronized with the scanning signals. is extracted as a video signal. This video signal is amplified to an unnecessary level by the video amplifier 3 and outputted as shown in FIG. 7, which is branched into two. Reference numeral 4 denotes a video signal gate A, which operates in synchronization with the vertical scanning signal of the scanning signal generator 7 to control the signal level for one screen necessary to maintain the signal level within a certain range by the output of the gate controller 9. 5 signals are selected and routed to a mean value detector of 5.

The signals selected by the video signal gate A of No. 4 are shown in FIG. 2A.

The average value detector 5 obtains an output proportional to the amount of light irradiated onto the sensor 2 by determining the average value of the input video signal as V shown in (c) through the process of FIG. 2(c). The output of the average value detector 5 is led to a pulse generator 6, and the average value output is compared with the chain tooth wave signal shown in FIG. After obtaining the pulse waveform shown in Figure 2, the pulse is extended by the vertical scanning signal of the scanning signal generator 7 until the scanning completes one screen, as shown in Figure 2, if scanning is in progress. Obtain the pulse waveform. The output of the pulse generator 6 is led to a scanning signal gate 1, and the number of times the scanning signal is supplied as shown in FIG. 2C is controlled as shown in FIG. 2C.

The waveform in Figure 3 shows that when the number of cycles of the scanning signal is controlled, the charge stored in the sensor is maintained within a certain range in response to a sudden increase in the amount of light. ) 11 is a video signal gate B, and a scanning signal gate 10
When the scanning signal is interrupted and then restarted, the video signal for one screen initially obtained is transferred to 12 video memo rivers.

The video signals selected by the 11 video signal gates B are shown in FIG.

The video memory 12 stores the video signal at the scanning speed of the sensor 2 using the scanning signal from the scanning signal generator 7, and reads the video signal at the normal television scanning speed using the signal from the synchronizing signal generator 8 to set the scanning frequency. Convert.

The video signal read from the video memory 12 is guided to a mixer 13, where horizontal and vertical synchronizing signals are mixed, resulting in the output of the imaging device shown in FIG.

14 indicated by a broken line in FIG. 1 is a peak value detector; 15
is a sample and hold circuit.

By replacing 14 or 15 with the average value detector 5, it is possible to maintain the video signal output corresponding to the peak light intensity of the image projected on the sensor, or the image light intensity at a certain point, within a certain range. It is.

Further, by synchronizing the scanning signal generator 7 with a signal supplied from the outside, it is possible to perform the same function even when a scanning signal having a scanning frequency matching the external device is applied to the sensor 2. As explained above, the present invention allows unnecessary charges to escape by increasing the number of times the video signal is taken out as the amount of incident light increases, without affecting the scanning frequency of the sensor and the video signal frame rate of the imaging device. This structure prevents charge leakage between the electrodes and maintains the output of the video signal within a certain range, allowing for rough integration with equipment such as televisions or video tape recorders that handle conventional video signals with a constant scanning frequency. It is particularly effective when the amount of light changes, especially when synchronization is required with an image processing device such as a computer that inputs and outputs data at a constant speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention;
FIGS. 2-2 are diagrams showing signal waveforms of various parts in the embodiment of FIG. 1, and FIG. 3 is a diagram showing waveforms of temporal changes in the amount of charge within the sensor when the amount of light changes. 1...Optical system, 2...Image sensor, 3...Video amplifier, 4...Video signal gate A, 5...Average Value detector, 6...Pulse generator, 7...Scanning signal generator, 8...
・Synchronization signal generator, 9...Gate controller, 10
......Scanning signal gate, 11...Video signal gate B, 12...Video memory, 13...
・Mixer, 14...Peak value detector, 15...
...Sample and hold circuit. Lower 1 Kanzu J figure Leopard 2 figure

Claims (1)

[Claims] 1. In an imaging device whose photoelectric conversion means is a charge-coupled device that outputs a signal proportional to the amount of incident light, the amount required for one full charge readout of the photoelectric conversion means for one imaging period in which an imaging signal is output from the imaging device. an average value detection circuit that detects the average value of an output signal taken out by reducing the time to at least half or less and giving a constant charge accumulation time to the photoelectric conversion element; and an output average value of the average value detection circuit. a pulse generating circuit that generates a pulse having a width close to the voltage-time width converted time width and corresponding to a time that is an integral multiple of a time for reading out the charges of all the elements at one time of the photoelectric conversion means; By reading and discharging the accumulated charge from the photoelectric conversion means a number of times corresponding to the output pulse width of the pulse generation circuit, the time ratio of discharge and charge accumulation during one imaging cycle is changed according to the amount of incident light, and the time ratio of discharge and charge accumulation from the photoelectric conversion means is changed depending on the amount of incident light. An imaging device characterized by obtaining a constant output signal.