JP2010166429A - Device for controlling exposure to light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a device for controlling exposure to light enabling an electronic camera or the like having an electronic shutter to capture an image whose proper luminance is maintained, while elaborately controlling the exposure to light upon capturing the image by imaging an object by the electronic camera or the like. <P>SOLUTION: An average level is calculated for video signals for one screen of a two-dimensional image imaged using an electronic shutter, to which an exposure time is set in units of steps according to a limitation on set resolution, and this average level is compared with a preset reference level of luminance to calculate its deviation. When deriving the exposure time to be set to the electronic shutter next time, the next exposure time determined by narrowing down from the present exposure time so as to further reduce the deviation is rounded in units of steps for the set resolution and set it to the electronic shutter. At the same time, regarding an exposure time less than the rounded set resolution, a video gain is calculated for correcting this, and video signals in the captured image are corrected by applying the video gain thereto. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photosensitive control device, and more particularly, to a photosensitive control device that performs control so that an image having a favorable luminance level can be maintained when an object is imaged using an electronic shutter.

  2. Description of the Related Art Conventionally, in an electronic camera or the like, a charge storage type element such as a CCD in which pixels are two-dimensionally arranged is used as an image sensor, and the charge storage time, that is, the photosensitive time is electronically used as a shutter. There is a method of controlling the exposure time of the electronic shutter using a controllable electronic shutter so that the level of the video signal output from the image sensor as an acquired image is stabilized within a predetermined range.

  Such an electronic shutter used together with an image pickup device in which pixels are two-dimensionally arranged is a read start timing generated after a predetermined time has elapsed from a vertical synchronization signal corresponding to an image acquisition period for one frame of the image pickup device. After the signal, the charges accumulated in the image sensor are sequentially erased at the period of the horizontal synchronizing signal corresponding to the period of one line. For this reason, the resolution of the exposure time set for the electronic shutter is almost the period of the horizontal synchronizing signal, and this resolution is the minimum unit for setting the exposure time and also the minimum value of the exposure time. .

  Therefore, the exposure time set for the electronic shutter may include an error due to resolution. In other words, the optimum value cannot be set as it is in the electronic shutter, and the optimum value is set after being rounded to a stepped step value considering the resolution. Even if the optimum value is set without rounding, the actual exposure time is limited by the resolution.

  Patent Document 1 discloses a method for correcting an exposure error of an imaging apparatus having an electronic shutter and a mechanical shutter.

JP 2000-98449 A (page 7, FIG. 2)

  As described above, when the exposure time is set for the electronic shutter, the exposure time is set by being rounded down due to the limitation of the resolution, and the minimum exposure time is also limited. Therefore, it is difficult to control the photosensitivity in such a fine unit as to be less than the resolution. Thus, even with a slight change in the amount of incident light, the luminance of the image changed greatly between frames.

  Furthermore, when the optimum value is located near the middle of the stepped set value, flickering of brightness called so-called flicker occurs between the frames of the acquired image by causing the set value to fluctuate between adjacent step values. The quality of the acquired image was not always sufficient. In particular, in such an image with unstable luminance, for example, there is a risk of hindering the visual recognition or extraction of the target or target in the subsequent stage.

  The present invention has been made in consideration of the above circumstances, and when an object is captured by an electronic camera or the like equipped with an electronic shutter and the image is acquired, an appropriate brightness is maintained while finely controlling the sensitivity. It is an object of the present invention to obtain a photosensitive control device that acquires a processed image.

  In order to achieve the above object, a photosensitive control device of the present invention includes an imaging unit that operates a electronic shutter based on a photosensitive time set in a predetermined step unit to acquire a two-dimensional image, and a set video gain. And a level control means for controlling the level of the video signal from the imaging means, and an average level of the obtained video signal after level control for one screen of the obtained two-dimensional image, and this average level is preset. Level deviation calculating means for obtaining a deviation from the reference level, and calculating a calculated value of the next exposure time to be applied to the electronic shutter based on the deviation and rounding the calculated value to the predetermined step unit; Is set for the electronic shutter, and based on the ratio between the calculated calculated value of the next exposure time and the set value of the exposure time. Calculating a next video gain applied to Le control means, characterized in that a control value setting means for setting the level control means.

  Further, when the average level of the video signal is calculated by the level deviation calculating means, a predetermined region in the screen including the imaging target that exists in one screen of the acquired two-dimensional image is targeted. It is characterized by calculating.

  According to the present invention, there is provided a photosensitive control device capable of acquiring an image with appropriate brightness maintained while finely performing photosensitive control when an object is captured by an electronic camera or the like equipped with an electronic shutter and the image is acquired. Obtainable.

1 is a block diagram showing the configuration of a first embodiment of a photosensitive control device according to the present invention. 2 is a flowchart for explaining the operation of the photosensitive control apparatus illustrated in FIG. 1. The block diagram which shows the structure of the 2nd Example of the photosensitive control apparatus which concerns on this invention. FIG. 4 is a flowchart for explaining the operation of the photosensitive control apparatus illustrated in FIG. 3. FIG.

  The best mode for carrying out the photosensitive control device according to the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing a configuration of a first embodiment of a photosensitive control device according to the present invention. As illustrated in FIG. 1, the photosensitive control device includes an imaging unit 10, a level control unit 20, a level deviation calculation unit 30, a reference value 40, and a set value calculation unit 50. The imaging unit 10 includes, for example, a charge storage type imaging device 11 such as a CCD in which pixels are two-dimensionally arranged, and an electronic shutter that electronically controls the charge storage time of the imaging device 11 as a photosensitive time in predetermined step units. 12 for obtaining a two-dimensional image and sending the video signal Vraw to the level control unit 20. One step of the exposure time of the electronic shutter 12 corresponds to the resolution of the exposure time.

As shown in Expression (1), the level control unit 20 controls the level of the video signal Vraw from the imaging unit 10 based on the video gain G set by the setting value calculation unit 50 to be described later, thereby correcting the corrected video signal. Send as V.

The level deviation calculation unit 30 calculates the average level Vμ for one screen of the corrected video signal output from the level control unit 20, and compares this with the luminance reference level Vref set to the reference value 40 in advance. Then, the deviation Vε as the difference is calculated as shown in Equation (2).

  Here, the level deviation calculation unit 30 includes an average level calculation unit 31 and a deviation calculation unit 32. The average level calculation unit 31 calculates an average level Vμ for one screen of the corrected video signal V from the level control unit 20 and sends it to the deviation calculation unit 32. The deviation calculating unit 32 calculates a deviation Vε between the average level Vμ and the reference level Vref of the luminance set to the reference value 40 according to the equation (2), and sends it to the set value calculating unit 50.

The set value calculation unit 50 calculates and sets the exposure time for the electronic shutter 12 based on the deviation Vε from the level deviation calculation unit 30 and sets the exposure time rounded when setting the exposure time for the electronic shutter 12. The video gain for the level control unit 20 is calculated and set so as to be interpolated. Here, the set value calculation unit 50 includes a photosensitive time calculation unit 51 and a video gain calculation unit 52. In this embodiment, the exposure time calculation unit 51, as shown in the equation (3), from the set value τ ⁿ app (the exposure time after rounding described later) of the exposure time (n) set for the electronic shutter 12 this time (n). Based on the deviation Vε, a time corresponding to a value corresponding to a value obtained by multiplying Vε and a constant k as a control gain is reduced to obtain a calculated value τ ^{n + 1} calc of the next exposure time.

Here, the control gain k is a constant corresponding to the time constant of the response time in the control system. As a primary control system, the control constant is generally a constant K, for example, τ ^{n + 1} = τ ⁿ −K · Vε. However, in the present invention, the entire exposure time is short and long. In order to make the control responsiveness uniform over the range, when the current (n) exposure time is long, the next (n + 1) exposure time is changed longer, and when the current exposure time is short The control constant is calculated in association with the set value of the current exposure time (n) so that the next exposure time is changed to be shorter.

Then, the calculated value τ ^{n + 1} calc of the next exposure time obtained is rounded to a step unit corresponding to the resolution of the electronic shutter 12 using the rounding function f as shown in the equation (4), and the set value of the exposure time is set. It is sent to the electronic shutter 12 as τ ^{n + 1} app. As the rounding function f, for example, rounding up to the step unit, rounding down, rounding off, etc. can be applied.

Further, the video gain calculation unit 52 calculates the exposure time calculated value τcalc and the exposure time set value τapp obtained each time by the exposure time calculation unit 51 so as to interpolate the exposure time rounded by the exposure time calculation unit 51. The ratio is calculated according to the equation (5), and this is sent to the level control unit 20 as the video gain G multiplied by the video signal Vraw.

  Next, the operation of the photosensitive control apparatus of the present embodiment configured as described above will be described with reference to the flowcharts of FIG. 1 and FIG. FIG. 2 is a flowchart for explaining the operation of the first embodiment of the photosensitive control apparatus illustrated in FIG.

Prior to the start of the operation, in the apparatus, including setting of the luminance reference level Vref to the reference value 40, initial setting of the exposure time τapp to the electronic shutter 12, and initial setting of the video gain G to the level control unit 20. Various initial settings are made (ST21). When the apparatus operation is started following these initial settings, incident light from the imaging target is input to the imaging device 11 of the imaging unit 10 and based on the photosensitive time τ ⁿ app set this time (n) in the electronic shutter 12. A video signal Vraw corresponding to the amount of light received by the image sensor 11 is sent to the level controller 20 (ST22). The level control unit 20 obtains a corrected video signal V by multiplying the video signal Vraw by the video gain G set this time (n) according to the equation (1). As described above, this video gain G is the luminance included in the video signal due to the control amount that could not be driven when the exposure time was set, such as the exposure time rounded when the exposure time was set for the electronic shutter 12. The deviation from the reference level is corrected so as to be interpolated. The corrected video signal V is sent from the level control unit 20 to the level deviation calculation unit 30 and is also used as a video signal corrected to an appropriate luminance level that more matches the reference level, for example, for a subsequent device. (ST23).

  Next, in the level deviation calculation unit 30, the average level Vμ for one screen of the corrected video signal V from the level control unit 20 is calculated in the internal average level calculation unit 31 and sent to the deviation calculation unit 32. In calculating the average level Vμ, for example, a method of calculating an average value of luminance levels of all pixels for one screen can be applied (ST24). The deviation calculation unit 32 calculates a deviation Vε between the average level Vμ and the reference level Vref of the luminance set to the reference value 40 according to the equation (2), and sends it to the set value calculation unit 50 (ST25).

Next, the set value calculation unit 50 obtains the photosensitive time set for the electronic shutter 12 next time (n + 1) and the video gain set for the level control unit 20 based on the deviation Vε of this time (n). First, in the exposure time calculation unit 51, based on the deviation Vε from the deviation calculation unit 32, the next time (n + 1) is calculated from the set value τ ⁿ app of the current (n) exposure time so that the deviation Vε becomes smaller. The calculated value τ ^{n + 1} calc of the next (n + 1) exposure time is obtained according to 3). Then, the rounding function f is applied to the calculated value τ ^{n + 1} calc according to the equation (4) to obtain the next (n + 1) exposure time setting value τ ^{n + 1} app. The exposure time obtained in this way is sent to the electronic shutter 12 as the set value of the next (n + 1) exposure time for the electronic shutter 12 (ST26).

On the other hand, the video gain calculation unit 52 calculates the ratio between the calculated value τ ^{n + 1} calc for the next exposure time and the set value τ ^{n + 1} app for the next exposure time obtained by the exposure time calculation unit 51 according to the equation (5). The video gain G is calculated. As described above, the video gain G is used to correct the deviation of the level of the video signal Vref caused by the rounding when the exposure time of the electronic shutter 12 is set, that is, the exposure time less than the resolution. Then, the calculated video gain G is sent to the level control unit 20 as the next (n + 1) video gain (ST27). Thereafter, the operation from step ST22 described above is repeated until the end of the operation is instructed (ST28).

  As described above, in this embodiment, the average level of the video signal for one screen of a two-dimensional image captured using an electronic shutter in which the photosensitive time is set in units of steps due to the setting resolution is determined. Is compared with a preset reference level of brightness to calculate the deviation. Then, when deriving the exposure time to be set for the next electronic shutter, the next exposure time, which is calculated by reducing the deviation from the current exposure time, is rounded to the set resolution step unit and set to the electronic shutter. In addition, a video gain for correcting the exposure time less than the rounded setting resolution is calculated, and this video gain is applied to the video signal of the acquired image.

  Accordingly, it is possible to finely control the exposure time less than the resolution, and continuously obtain an image with a proper brightness maintained with a smaller deviation from the reference brightness level. In particular, even when imaging is performed with a short exposure time that is close to the resolution of the exposure time of the electronic shutter, it is possible to acquire an image with good quality while performing fine exposure control.

  FIG. 3 is a block diagram showing the configuration of the second embodiment of the photosensitive control apparatus according to the present invention. FIG. 4 is a flowchart for explaining the operation of the second embodiment of the photosensitive control device. In the second embodiment, the same parts as those in the first embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted. The difference between the second embodiment and the first embodiment is that when calculating the average level of the acquired images, the first embodiment calculates the entire level of one screen. In this embodiment, the target of the imaging target existing in the image is detected and the peripheral area including the target is calculated as the target. Only the differences will be described below with reference to FIGS. 1 and 2 and FIGS.

  As illustrated in FIG. 3, the photosensitive control device includes an imaging unit 10, a level control unit 20, an area specifying unit 60, a level compilation calculation unit 70, a reference value 40, and a set value calculation unit 50. The imaging unit 10, the level control unit 20, the reference value 40, and the set value calculation unit 50 are configured in the same manner as in the first embodiment. The area specifying unit 60 detects the presence / absence of a target to be imaged from one screen of the corrected video signal output from the level control unit 20, and determines a predetermined area in the screen including the detected target as the corrected video signal. The average level calculation target area is specified and notified to the level deviation calculation unit 70. In detecting the target, for example, a method of determining based on the level or level change of the corrected video signal can be applied. As the target area, various geometric shapes such as a circular area having a radius of a predetermined number of pixels centered on the target and a rectangular area can be set in advance and applied.

  Based on the notification from the region specifying unit 60, the level deviation calculating unit 70 determines the average level Vμ for a specific region in one screen of the corrected video signal output from the level control unit 20 in the internal average level calculating unit 71. In addition, the deviation calculation unit 32 compares the calculation result with the luminance reference level Vref set to the reference value 40 to calculate a difference Vε as the difference, and sends it to the set value calculation unit 50.

  Next, the operation of this photosensitive control device will be described with reference to the flowchart of FIG. First, similarly to the first embodiment, an image to be imaged is acquired by the imaging unit 10, and the corrected video signal V whose level is controlled by the level control unit 20 is sent to the region specifying unit 60 (ST21 to ST23). Next, the area specifying unit 60 determines the presence / absence of a target to be imaged from one screen of the corrected video signal V, and when the target is detected, the average level is determined based on the position on the screen. An area around the target to be calculated is specified. The identified target area is notified to the average level calculation unit 71 in the level deviation calculation unit 70 (ST41).

  Next, the average level calculation unit 71 extracts the signal of the target region from one screen of the corrected video signal from the level control unit 20 in accordance with the notification from the region specifying unit 60, and calculates the average level Vμ. The calculated average level Vμ is sent to the deviation calculator 32 (ST42). Thereafter, as in the first embodiment, the deviation calculation unit 32 calculates a deviation from the reference value 40, and the set value calculation unit 50 sends the next exposure time and video gain to each unit based on this deviation. (ST25 to ST28).

  As described above, in this embodiment, when calculating the average level of the acquired image, the target of the imaging target existing in the image is detected and the peripheral region including the target is calculated. Yes. Thereby, in addition to the effect in the first embodiment, the target to be imaged can be made clear and can be visually recognized more reliably and easily.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

DESCRIPTION OF SYMBOLS 10 Image pick-up part 11 Image pick-up element 12 Electronic shutter 20 Level control part 30, 70 Level deviation calculation part 31, 71 Average level calculation part 40 Reference value 50 Setting value calculation part 51 Photosensitive time calculation part 52 Video gain calculation part 60 Area | region specific part

Claims (3)

An image pickup means for obtaining a two-dimensional image by operating an electronic shutter based on a photosensitive time set in predetermined step units;
Level control means for controlling the level of the video signal from the imaging means based on the set video gain;
Level deviation calculating means for calculating an average level of the video signal after level control for the obtained one-dimensional image of the two-dimensional image and obtaining a deviation between the average level and a preset reference level;
Based on the deviation, a calculated value of the next exposure time to be applied to the electronic shutter is obtained, rounded to the predetermined step unit, and then set to the electronic shutter as a set value of the exposure time. Control value setting means for calculating the next video gain to be applied to the level control means based on a ratio between the calculated value of the exposure time and the set value of the exposure time, and setting the level control means. Photosensitive control device.   The calculated value of the next exposure time obtained by the control value setting means is obtained by multiplying the deviation from the deviation calculation means by a constant as a control gain from the set value of the rounded exposure time set for the electronic shutter. 2. The photosensitive control device according to claim 1, wherein the time is calculated by subtracting a time corresponding to a ratio corresponding to the value.   When the average level of the video signal is calculated by the level deviation calculating means, it is calculated for a predetermined area in this screen including the imaging target that exists in one screen of the acquired two-dimensional image. The photosensitive control device according to claim 1 or 2, wherein

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