JPH04318978A - Image sensing device - Google Patents

Abstract

PURPOSE:To set an optimum reference voltage level corresponding to an exposure distribution of an image sensing signal by measuring the distribution of at least one of a plurality of image sensing signals, and deciding a reference voltage level to become a reference of comparison of a level of the signal. CONSTITUTION:Memories 3, 4 for storing a plurality of image sensing signals, and a circuit 5 for measuring an exposure distribution of at least one of the plurality of image sensing signals and deciding a reference voltage level, are provided. The reference level is compared with levels of the signals from the memories 3, 4 by a comparator 6. A switching circuit 7 for selecting at least one from the plurality of signals of different exposure conditions to be outputted from the memories 3, 4 according to the comparison result, is provided. Thus, if the level of the signal is equal to or larger than the reference level, the signal having a small exposure amount is selected, while if the level of the signal is smaller than the reference level, the signal having a large exposure amount is selected, and combined.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device, and more particularly to an imaging device that combines a plurality of imaging signals with different exposure conditions to form an imaging signal.

0002

2. Description of the Related Art There is an imaging apparatus that combines a plurality of imaging signals with different accumulation times (exposure times) to form an imaging signal in order to expand the dynamic range or the like.

FIG. 5 is a block configuration diagram showing a conventional imaging device, in which 1 is an image sensor, 2 is a signal processing circuit that processes the output signal of the image sensor 1, and 3 is a signal processing circuit that processes the output signal of the image sensor 1 (
4 is a frame memory (hereinafter abbreviated as F.M.) that stores one screen's worth of signals (low-speed shutter signals); M. It is. 9 compares a certain fixed threshold level with the level of the luminance signal (obtained from the output signals of FM 3 and FM 4). M. 3, F. M. Among the output signals of F.4, the dark parts of the subject are detected by F.4. M. 3 output signal is selected, and the bright part of the subject is set to F.3. M. 8 is a signal processing circuit that selects and synthesizes the output signal of circuit 9, and 8 is a signal processing circuit that converts the output signal of circuit 9 into a video signal.

0004

However, in the above-mentioned conventional imaging device, the F. M. 3,F
．． M. Since one of the four output signals is selected and synthesized, there is a problem in that depending on the subject, the connection between bright and dark areas of the screen may be discontinuous, resulting in an unnatural appearance.

[0005]

[Means for Solving the Problems] An imaging device of the present invention is an imaging device that combines a plurality of imaging signals having different exposure conditions to form an imaging signal, and includes a memory means for storing the plurality of imaging signals; means for determining a reference voltage level by measuring the exposure distribution of at least one of the plurality of image signals; and comparing the reference voltage level with the signal level of the at least one image signal from the memory means. and signal selection means for selecting one imaging signal from a plurality of imaging signals output from the memory means with different exposure conditions based on the comparison result, the signal level of the imaging signal being equal to or higher than the reference voltage level. In this case, an imaging signal with a small amount of exposure is selected, and when the signal level of the imaging signal is smaller than the reference voltage level, an imaging signal with a large amount of exposure is selected and combined.

[0006]

[Operation] In selecting and composing a plurality of imaging signals having different exposure conditions, the present invention sets a reference voltage level, which is a reference for comparison of the signal levels of the imaging signals, to the reference voltage level of at least one of the plurality of imaging signals. By measuring and determining the exposure distribution, it is possible to set an optimal reference voltage level corresponding to the exposure distribution of the imaging signal.

[0007] In this application, exposure conditions refer to conditions such as exposure time (storage time), light amount adjustment using an aperture, presence or absence of a flash, etc. For example, an image signal with a small exposure amount is an image signal with a short exposure time. , an image signal with a reduced amount of light using an aperture, etc., an image signal without a flash, etc. In the embodiments described later, a case where the exposure time (storage time) is different is explained as an example, but it is needless to say that the exposure conditions are not limited to such.

In the present invention, the reference voltage level is
If the voltage level corresponds to the minimum value of the exposure distribution of the imaging signal or a value in the vicinity thereof, it is possible to switch to an imaging signal with a different exposure amount (for example, exposure time) in an area where the exposure distribution is small, and it is possible to change the brightness of the screen. The dark areas can be connected almost continuously.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention. Reference numeral 1 denotes an image pickup element, and numeral 2 denotes an F. M. 3 is a signal processing circuit that converts the input signal into an input signal to F. M. , 4 serves as a memory means for storing signals with shorter storage time for one screen. M. It is. 5 is F. M. 3, F. M. Measure the exposure distribution of the signal (corresponding to the brightness distribution of the subject) from the output signal of step 4,
This is a circuit that determines the optimum threshold hold level (Vth) to be the reference voltage level, and outputs the optimum threshold hold level (Vth) to the comparator circuit 6. The comparator circuit 6 determines the optimum threshold/hold level (Vt
h) and F. M. 3, F. M. F.4 is compared with the output signal of F.4. M. 3, F. M. If the luminance signal obtained from the output signal of F.4 is equal to or higher than Vth, F. M. Select the output signal of F.4 and if it is smaller than Vth. M. In order to select the output signal No. 3, a switching control signal is output to the switching circuit 7 serving as signal selection means. Luminance distribution measurement and threshold
The signals synthesized by the hold level determination circuit 5, the comparison circuit 6, and the switching circuit 7 are input to the signal processing circuit 8 and converted into a video signal. Figures 2 and 3 are diagrams showing the frequency distribution with respect to the brightness of the subject. Here, the voltage corresponding to the minimum value of the brightness value of the subject (here, the frequency is 0) is defined as the threshold level (Vth). . FIG. 2 shows a case where the subject has many dark parts, and FIG. 3 shows a case where the proportion of bright and dark parts of the subject is almost equal. Here, since the imaging signal is switched to a different exposure time when the frequency is 0, there is no discontinuity in the connection between the bright and dark parts of the screen. It goes without saying that the present invention is not limited to the case where the power is 0 as in this embodiment.

In the embodiment described above, the brightness distribution measurement and threshold/hold level determination circuit 5 includes an F
．． M. 3, F. M. The brightness distribution was measured by inputting the output signal of F.4, but as shown in FIG. M. The luminance distribution may also be measured from the output signal of the output signal, and the same effect as the above-mentioned embodiment can be obtained. Furthermore, regarding the accumulation time, the luminance distribution may be measured from the imaging signals obtained during three or more accumulation times, the optimal threshold/hold level may be determined, and the three or more imaging signals may be combined.

[0011]

As described above in detail, according to the imaging apparatus of the present invention, when selecting and combining a plurality of imaging signals with different exposure conditions, a standard is provided that serves as a reference for comparing signal levels of imaging signals. By determining the voltage level by measuring the exposure distribution of at least one of the plurality of imaging signals, it is possible to set an optimal reference voltage level corresponding to the exposure distribution of the imaging signal.

Further, in the present invention, if the reference voltage level is set to a voltage level corresponding to the minimum value of the exposure distribution of the image pickup signal or a value in the vicinity thereof, the exposure amount (for example, the exposure time ), the bright and dark areas of the screen can be connected almost continuously, and a good image can be formed even when photographing a subject with a large dynamic range.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of an imaging device of the present invention.

FIG. 2 is a diagram showing a frequency distribution with respect to the brightness of a subject.

FIG. 3 is a diagram showing a frequency distribution with respect to the brightness of a subject.

FIG. 4 is a block diagram showing another embodiment of the imaging device of the present invention.

FIG. 5 is a block configuration diagram showing a conventional imaging device.

[Explanation of symbols]

1 Image sensor 2 Signal processing circuit 3 Frame memory (F.M.) 4 Frame memory (F.M.) 5 Brightness distribution measurement and threshold/hold level determination circuit 6 Comparison circuit 7 Switching circuit 8 Signal processing circuit

Claims (2)

[Claims] 1. An imaging apparatus that combines a plurality of imaging signals having different exposure conditions to form an imaging signal, comprising: a memory means for storing the plurality of imaging signals; and at least one imaging signal of the plurality of imaging signals. means for determining a reference voltage level by measuring the exposure distribution of the memory means; means for comparing the reference voltage level with the signal level of at least one imaging signal from the memory means; and signal selection means for selecting one imaging signal from a plurality of imaging signals with different exposure conditions output from the imaging signal, and when the signal level of the imaging signal is equal to or higher than the reference voltage level, the imaging signal with a small exposure amount is selected. If the signal level of the imaging signal is smaller than the reference voltage level,
An imaging device characterized by selecting and combining imaging signals with a large amount of exposure. 2. The imaging apparatus according to claim 1, wherein the reference voltage level is a voltage level corresponding to a minimum value of an exposure distribution of the imaging signal or a value in the vicinity thereof.