The present invention relates to a brightness detection system for measuring brightness based on the imaging data taken by an image sensor.
Conventionally, there is known an illumination control system that detects brightness by using an image sensor including a charge-coupled device (see, e.g., Japanese Patent Laid-open Publication No. 2004-501496). One example of imaging data is illustrated in FIG. 5. The imaging data obtained by an image sensor include brightness data corresponding to a multiplicity of pixels. Brightness is detected by calculating an average value of brightness data of the total pixels belonging to a designated brightness detection range among the imaging data. The illumination control system feedback controls an illumination device based on the brightness thus detected.
The average value of brightness data of the total pixels, typically an arithmetic average in the prior art, is calculated by performing a calculation in which the brightness data of the total pixels are added and then divided by the number of the total pixels. This means that the quantity of data to be calculated gets greater as the number of pixels increases. The present inventors have found through researches that a brightness index closer to the human sense and complying with the sense of brightness of a space can be obtained by use of a geometrical average. Depending on the kinds of illumination devices, the geometrical average rather than the arithmetic average is used as the average value of brightness data. As compared to the arithmetic average, however, the quantity of data to be calculated becomes vast in case of the geometrical average. This is because the geometrical average is calculated by multiplying the brightness data of the total pixels and finding the n-th root thereof where the n denotes the number of total pixels. In an illumination device that makes use of an image sensor, it is required that the average value of brightness data be calculated by an embedded microcontroller. Although small in size, the embedded microcontroller is slower in calculation speed than a large-sized computer. For that reason, it is sometimes the case that one hour or more is required for an embedded general-purpose 16-bit microcontroller to calculate a geometrical average from the brightness data of total pixels taken by a one-million-pixel image sensor.
Since the conventional brightness detection system for detecting brightness through the calculation of imaging data taken by the image sensor needs to calculate a vast quantity of data, it suffers from a prolonged calculation time and has a difficulty in feedback controlling an illumination device on a real-time basis. This makes it difficult to combine the brightness detection system with the illumination device.
In view of the above, the present invention provides an brightness detection system combined with an illumination device for measuring brightness through the calculation of imaging data taken by an image sensor, which is capable of shortening the calculation time and feedback controlling the illumination device on a real-time basis.
In accordance with an aspect of the present invention, there is provided a brightness detection system including an image sensor for generating imaging data formed of pixels; and a calculation unit for finding the brightness of an object by calculating the imaging data, wherein the calculation unit is designed to execute a calculation only for selected arbitrary pixels among the pixels of the imaging data and falling within a preliminarily designated brightness detection range.
With such configuration, the calculation unit performs a calculation only for the selected arbitrary pixels. This reduces the calculated data quantity, thereby shortening the calculation time. Thanks to this feature, it becomes possible to provide a brightness detection system combined with an illumination device, which is capable of performing feedback control on a real-time basis.
Preferably, the selected arbitrary pixels are so selected as not to adjoin to one another on their sides
With such configuration, the calculation unit executes no calculation with respect to the adjoining pixels having substantially the same brightness as that of the calculation target pixels. This makes it possible to calculate the imaging data of broad range while suppressing an increase in the calculated data quantity. Therefore, it is possible to achieve a balance between the reduction of calculated data quantity and the maintenance of calculation accuracy.
The selected arbitrary pixels may have brightness data equal to or greater than a predetermined value.
With such configuration, a calculation is executed only for the pixels whose brightness data are equal to or greater than a predetermined value. In other words, a calculation is performed with respect to the pixels falling within the area affected by external light but no calculation is executed for the pixels falling outside that area. This makes it possible to achieve a balance between the reduction of calculated data quantity and the maintenance of calculation accuracy required in correcting external light.
A brightness detection system in accordance with a first embodiment of the present invention will be described with reference to
The image sensor 11 includes an imaging element such as a CCD, a CMOS or the like and is designed to output the imaging data 12 by photoelectrically converting the light coming from an object. The calculation unit 13 includes an embedded microcontroller or the like and is configured to find the brightness of an object by calculating the imaging data 12 and to output brightness data.
The calculation unit 13 executes a calculation only for the selected arbitrary ones of the total pixels 14 of the imaging data 12 falling within the preliminarily designated brightness detection range (hereinafter abbreviated as detection range) 15.
The detection range 15 refers to the range over which the brightness is to be detected by the brightness detection system 1. The detection range 15 is designated and stored in the microcontroller of the calculation unit 13, e.g., when an illumination device incorporating the brightness detection system 1 is installed in place. The entire imaging area may be designated as the detection range 15.
The calculation unit 13 obtains the brightness of the detection range 15 by executing a calculation with respect to the selected pixels 14a. The brightness thus obtained is the arithmetic average or the geometrical average of the brightness data of the selected pixels 14a. The results of calculation are outputted as the brightness data of the detection range 15. The calculation time can be shortened by changing the ratio of the calculation target pixels 14a to the out-of-calculation pixels 14b. In an instance where the calculation target pixels 14a and the out-of-calculation pixels 14b are alternately selected (see
In the illumination device 2 configured as above, the brightness is detected by the brightness detection system 1. The illumination device 2 performs feedback control of reducing the load current if the brightness thus detected is greater than a control target value and increasing the load current if the brightness thus detected is smaller than the control target value. In an installation environment affected by external light, the illumination device 2 performs, through the feedback control, external light correction of reducing a dimming rate if the external light is too bright and increasing the dimming rate if the external light is too dark.
In the brightness detection system 1 of the present embodiment set forth above, the calculation unit 13 performs a calculation only for the selected arbitrary pixels 14a. This reduces the calculated data quantity, thereby shortening the calculation time. Reduction of the calculated data quantity makes it possible to perform the calculation through the use of the embedded microcontroller. Thanks to this feature, it becomes possible to provide a brightness detection system combined with an illumination device, which is capable of performing feedback control on a real-time basis.
The calculation unit 13 executes no calculation with respect to the adjoining pixels having substantially the same brightness as that of the calculation target pixels. This makes it possible to calculate the imaging data 12 of broad range while suppressing an increase in the calculated data quantity. Therefore, it is possible to achieve a balance between the reduction of calculated data quantity and the maintenance of calculation accuracy.
A brightness detection system in accordance with a second embodiment of the present invention will be described with reference to
The calculation speed of the calculation unit 13 can be increased by changing the ratio of the calculation target pixels 14c to the out-of-calculation pixels 14d. In the example shown in
Within the specific area in which the calculation target pixels 14c are selected, the brightness data of the pixels 14c become greater than a predetermined value. For example, the area affected by external light may be preliminarily selected from the detection range 15 by using the imaging data 12, and the pixels 14 falling within that area may be used as the calculation target pixels 14c. Dark objects such as black furniture and black electronic appliances are kept black regardless of the presence or absence of external light. Therefore, the area in which the image of dark objects is taken may be excluded from the calculation target. In addition, the selection of the out-of-calculation pixels 14d may be determined by setting a specified threshold value, e.g., by excluding from the calculation target the pixels 14 whose brightness data (Y-value) obtained by the image sensor 11 are equal to or lower than the 50-th level out of the 256 levels in total. The calculation unit 13 finds the brightness of the detection range 15 by executing a calculation only for the selected pixels 14c among the total pixels falling within the detection range 15.
In the brightness detection system of the present embodiment set forth above, a calculation is executed only for the pixels 14c whose brightness data are equal to or greater than a predetermined value. In other words, a calculation is performed with respect to the pixels 14c falling within the area affected by external light but no calculation is executed for the pixels 14d falling outside that area. This makes it possible to achieve a balance between the reduction of calculated data quantity and the maintenance of calculation accuracy required in correcting external light.
The present invention is not limited to the embodiments described above but may be modified in many different forms without departing from the scope of the invention defined in the claims. For example, the first embodiment and the second embodiment may be combined together, in which case the calculation target pixels are selected in an equal interval within the specific area containing the pixels whose brightness data is equal to or greater than a predetermined value.
Number | Date | Country | Kind |
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2008-263054 | Oct 2008 | JP | national |