JPH0342976A - Picture input device - Google Patents

Abstract

PURPOSE:To input a picture over a wide dynamic range by inputting one object with plural area sensors. CONSTITUTION:In order to input one and same object image to two area sensors, the optical path after passing through a lens is split into two by a half mirror and one object image is formed onto each area sensor. A glass plate 3 whose transmissivity is 0.1% is placed in front of the area sensors 2. Thus, the lightness of the object image formed on the surface of the area sensor 2 is smaller in the order of 3 digits than the object image formed on the surface of the area sensor 1. When the output current from a 1st area sensor reaches a saturated value, the output is switched into an amplified signal from a 2nd area sensor to realize a picture input device having a double dynamic sense.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an image input technology using a plurality of sensors, and more particularly to an image input device that inputs high-quality images with a wide dynamic range.

[Conventional technology]

The area sensor is a device that converts a subject image formed by a lens or the like into nine time-series electric signals using a two-dimensional light-receiving element array having an appropriate scanning means.

In an image input device using such an area sensor, one of the important conditions for inputting high-quality images is:
The goal is to widen the range between the lowest and highest levels of subject illuminance that can be extracted as a signal, that is, to widen the dynamic range.

Regardless of the type of area sensor, there is noise generated in the switching element used in the scanning means and the first stage amplifier, or dark current noise generated in the light receiving element.

When the signal component becomes smaller than these noise components as the illuminance of the subject decreases, the signal cannot be extracted. This is the factor that determines the minimum level of subject illuminance. On the other hand, as the subject illuminance increases, the signal also increases proportionally;
After a certain point, the signal no longer increases even if the subject illuminance increases. In other words, the output signal exhibits saturation characteristics, and the illuminance at which this saturation begins is the highest level that can be taken out as a signal.In a normal area sensor, the range between the minimum level and the maximum level, that is, the dynamic range, is 3.
It is about 10,000 digits.

If the difference in illuminance between the dark and bright parts of the object exceeds the dynamic range, it will no longer be possible to obtain an effective signal over the entire illuminance range. For example, when capturing an image of a person in the shadows in a place with a bright background, if you adjust the aperture of the lens to match the brightness of the background, the face of the person will become completely black, making it difficult to clearly recognize the shape of the face. arise. Also, if you match the brightness of the person in the shadow, the background will become pure white.

To solve the above problem, it is necessary to expand the dynamic range. As mentioned above, the dynamic range is determined by the noise level and saturation characteristics. this house.

The saturation characteristics are often caused by the structure of the light receiving element, and it is not easy to increase the saturation value. Therefore.

In the conventional method, noise is reduced using a dedicated circuit provided after the first stage amplifier, thereby lowering the minimum level and expanding the dynamo range.

[Problem to be solved by the invention]

In the conventional method described above, the dynamic range is expanded by reducing noise using a circuit, but the noise reduction that can be achieved by one circuit means is about one order of magnitude at most. Therefore, the expansion of the dynamic range is only about one order of magnitude, and the dynamic range is still insufficient for inputting high-quality images.

An object of the present invention is to enable input of images with a wide dynamic range.

[Means to solve the problem]

In order to overcome the above drawbacks of the conventional method, the image input device of the present invention inputs the same subject using a plurality of area sensors. Here, for the sake of simplicity, a method for solving the above problem according to the present invention will be explained assuming that the number of Eliasen lifetimes is 2.

Of the two area sensors, the first area sensor inputs a subject image according to a normal method.

Furthermore, an object that attenuates the light intensity is installed in front of the second area sensor.

Therefore, in the second quadrature sensor, the subject illuminance that can be input is entirely shifted to the high illuminance side. In this way, two area sensors are used, and the signal from the first area sensor is output for areas of the subject with low illuminance, and the signal from the second area sensor is output for areas of the subject where illumination is high. shall be. In this case, the signal from the second area sensor is amplified by an appropriate magnification.

[For production]

By doing this, in the case of the first area sensor, the range that was in the saturation region and could not be extracted as a valid signal.

It can be supplemented using the output from the second area sensor.

〔Example〕

1st grade A first embodiment of the invention is shown in FIG.

In FIG. 1, 1 and 2 are CCD area sensors, 3 is a glass plate with a transmittance of, for example, 0.1%, 4 is a half mirror whose transmittance and reflectance are equal, for example, 5 is a lens, 6 is a subject, 71. 72 is an A/D converter, and 8 is a signal processing section.

In this embodiment, the number of area sensors is two. In order to input the same subject image to the two area sensors, the optical path after passing through the lens was divided into two by a half mirror, and the same subject image was formed on each area sensor. However, a glass plate 3 with a transmittance of 0.1% was installed in front of the area sensor 2. Therefore, the brightness of the subject image formed on the surface of area sensor 2 is three orders of magnitude smaller than that of the subject image formed on the surface of area sensor 1. After converting into bit digital signal.

The signal is sent to the signal processing section 8. The signal processing section 8 processes the signals from both sensors as follows. First, if the magnitude of the signal from the area sensor 1 is less than the highest gradation of 255, the signal from the area sensor 1 is directly used as an output signal. if,
If the signal from the area sensor 1 is 255, which is the highest gradation, the signal obtained by adding 255 to the signal from the area sensor 2 is set as the output signal.

The effect obtained by the above means will be explained with reference to FIG.

FIG. 2 shows the dependence of the area sensor output current on the subject illuminance, where the horizontal axis shows the subject illuminance and the vertical axis shows the output current of the area sensor. Here, both the horizontal axis and the t74 axis are expressed in logarithms.

Figure 2 (a) shows the subject illuminance dependence when a conventional single area sensor is used, and Figure 2 (b) shows the subject illuminance dependence according to the present invention when two area sensors are used. . As shown in Figure 2 (Q)), the subject illuminance dependence of the output current of the second area sensor is due to the object installed in front of the area sensor that attenuates the light intensity, so the subject illuminance that can be input is generally high. Shift to the brightness side. Therefore, the second area sensor can extract a portion of the subject with high illuminance, which is a saturated region and cannot be extracted as a valid signal with the first area sensor. FIG. 2(C) shows the characteristics when the output from the second area sensor is amplified by an appropriate magnification and made continuous with the output from the first area sensor.

If you use these two area sensors and decide to switch the output to the amplified signal from the second area sensor when the output current from the first area sensor reaches the saturation value, you can An image input device having twice the dynamic range as an image input device using an area sensor can be realized.

With the above configuration and signal processing, this embodiment achieves a dynamic range approximately twice as large as that of a conventional image input device using a single area sensor.

2 挌 1 A second embodiment of the present invention has a configuration in which the glass plate 3 installed in front of the area sensor 2 in the first embodiment shown in FIG. 1 is omitted. Instead, the ratio of transmittance and reflectance of the half mirror 4 is set to, for example, 1000:1. Therefore, as in the first embodiment, the brightness of the subject image formed on the surface of area sensor 2 is three orders of magnitude smaller than that of the subject image formed on the surface of area sensor l. The method of processing signals from is the same as in the first embodiment.

In this embodiment as well, the range of the image input device ξ is doubled compared to the conventional image input device using a single area sensor.

In the above, only two embodiments of the present invention have been described.2 It goes without saying that various changes can be made without departing from the spirit of the present invention.For example, in the above embodiment, 2
Although several area sensors were used, if the number of area sensors used is increased, the dynamic range can be further expanded according to the number of area sensors. Further, although a single lens system is used in the above embodiment, it is also possible to install a lens system for each area sensor. Further, in the above embodiment, the output from the area sensor 2 is amplified by the signal processing section after A/D conversion, but it is also possible to amplify it before the signal processing section or at the analog signal stage.

〔Effect of the invention〕

According to the present invention, depending on the number of area sensors used,
It is possible to expand the dynamic range and realize a high-quality image input device. Further, as shown in the above embodiment, the gradation can be made small on the low illuminance side and coarse on the high illuminance side. This exactly matches the visual characteristics of the human eye, and is an effective way of obtaining information for the human eye.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a first embodiment of the present invention. FIG. 2 is an explanatory diagram of the concept and effects of the present invention. 1.2...CCD area sensor. 3...Glass plate, 4...Half mirror
5...Lens, 6...Subject. 71 72...A/D converter. 8...Signal processing section.

Claims (1)

[Scope of Claims] An optical system having a plurality of sensors that capture the same subject image, and configured such that the brightness of the subject image formed on these sensors differs for each sensor, An image input device characterized in that outputs of the plurality of sensors are combined to realize a wide dynamic range.