JP2715464B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an imaging device such as a video camera.

[Conventional technology]

A method of synthesizing image signals under different exposure conditions to expand a substantial dynamic range is disclosed in, for example, Japanese Patent Application Nos. 143884 to 143887 in 1987. Hereinafter, the method A ² C (Advanced Adaptive Compand
er) method. In the A ² C method, an image sensor is driven alternately for each field with two types of charge accumulation times.
In odd fields, shooting is performed at a low shooting speed (for example, 1/60 second), and in even fields, high shooting speed (for example, 1/250 second) is used.
Seconds). Then, in a normal scene, a video signal (hereinafter, referred to as an _SL signal) in low-speed shooting is employed, and in a high luminance portion, a high-speed video signal (hereinafter, referred to as an _SH signal) is employed. The pixels that are white compression is generated by excessive exposure to the S _L signal, so as to switch to S _H signals, exchange data in units of pixels, overexposure also underexposure is prevented from occurring in captured image . That is, a substantial dynamic range can be expanded.

[Problems to be solved by the invention]

However, in the conventional A ² C method, the calculation for the image synthesis processing for exchanging pixel data was very complicated. If the arithmetic processing is simplified by adopting a look-up table method, the image quality becomes unsatisfactory. For example, if simple pixel data exchange is performed, the gray scale is reversed, and a screen that looks very unnatural appears. To prevent this grayscale inversion, multiply by an appropriate coefficient and
Although a configuration for adding two data has been proposed, it is difficult to set the coefficient, and the configuration of a look-up table for these calculations becomes complicated.

Accordingly, an object of the present invention is to provide an A ² C-type imaging device having a simple circuit configuration that does not cause grayscale inversion.

[Means for solving the problem]

An imaging apparatus according to the present invention includes an imaging unit that outputs image signals obtained by shooting under different exposure conditions in a predetermined order, and a detection unit that detects an image portion having a predetermined luminance level from an image signal under a predetermined exposure condition in the image signals. And synthesizing means for synthesizing an image signal under another exposure condition with the image signal under the predetermined exposure condition according to a detection result of the detecting means, wherein an image under another exposure condition to be synthesized by the synthesizing means is provided. Signal
The modification is performed according to the detection level of the detection means.

[Action]

As described above, when the image signal under the other exposure condition is modified at the time of the composition, inversion of the gradation in the composite portion does not occur. In addition, since synthesis is performed for a portion having a predetermined luminance level, circuit processing is simplified, and the circuit configuration can be simplified.

〔Example〕

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

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 10 is a subject, 12 is a taking lens, 14
Is an aperture, and 16 is an image sensor. Light rays from the subject 10 incident from the photographing lens 12 are regulated in light quantity by the aperture 14 and enter the photoelectric conversion surface of the image sensor 16. The output of the image sensor 16 is converted by the camera signal processing circuit 18 into an image signal.
The camera signal processing circuit 18 outputs a luminance signal Y and a color difference signal C. The luminance signal Y is applied to an A / D converter 30Y and a gate circuit 24, and the color difference signal C is applied to an A / D converter 30C. The aperture adjustment circuit 20 controls the aperture 14 according to the output of the gate circuit 24. Further, the speed switching circuit 26 is provided with a shutter speed (for example, 1/60 second and 1/25 second) that alternates between fields.
At 0 seconds), a timing pulse for driving the image sensor 16 is applied to the drive circuit 22. The gate circuit 24 extracts only a signal under a specific exposure condition (for example, a photographing signal at a 1/60 second shutter speed) under the control of the speed switching circuit 26.

Output data of the A / D converters 30Y and 30C are applied to signal processing circuits 32Y and 32C, respectively. The signal processing circuits 32Y and 32C perform an operation for synthesizing pixel data to be described later, and the output is applied to the output processing circuit 36 via the D / A converters 34Y and 34C. The output processing circuit 36 forms a composite video signal from the input signal and outputs the composite video signal.

FIG. 2 shows details of the signal processing circuit 32Y, and FIG. 4 shows a timing chart thereof. Under the control of the speed switching circuit 26, the image sensor 16 outputs a video signal ( _SL signal) at the time of low-speed accumulation in an odd field, and outputs a video signal ( _SH signal) at the time of high-speed accumulation in an even field. Therefore, the digital data is supplied from the A / D converter 30Y alternately in the field. The switches 50 and 52 are switched by a pulse signal (1/2 VD) of the frame frequency, and are connected to the a contact in an odd field and to the b contact in an even field. That is, the output of the A / D converter 30Y in odd fields (S _H signal) is written into the field memory 54. The data read from the memory 54 at the same time as the writing is the data of the screen of the previous field, and is applied to the D / A converter 34Y via the a contact of the switch 56 and the b contact of the switch 64.

S _H signal written in the memory 54 in the odd field is read out at the next even field, it is applied to the secondary differential circuit 56. The secondary differentiating circuit 56 calculates a difference twice from the adjacent pixel data (that is, a difference between the difference data) and applies the difference to the coefficient unit 58. The coefficient unit 58 outputs a coefficient k to the output of the second differentiation circuit 56.
(0 ≦ k ≦ 1). The coefficient k takes a value corresponding to the output of the high luminance detector 68. FIG. 5 shows the detection characteristics of the high luminance detector 68, and FIG. 6 shows the value of the coefficient k with respect to the output of the high luminance detector 68. Since the input range is 1 to 256, the range of ± 255 for one difference and the range of ± 510 for two differences. However, since it is necessary to keep this change component within a narrow specific range, k is reduced for values above a predetermined level.
The reason why k = 0 near zero is to make it possible to practically ignore a constant slope portion near the switching point between H and L of the output of the high-intensity detector 68 by a so-called coring effect.

The adder 60 adds the output of the coefficient unit 58 and the signal of the even field from the contact b of the switch 50. In the even field, the switch 50 is connected to the contact b, S _L signal is applied to the adder 60, the switch 52 is also connected to the contact b, the output of the adder 60 is written to the field memory 54. In this way, the second derivative signal of the high-speed accumulation signal is superimposed on the high-luminance area in the low-speed accumulation signal.

In the even field, the image data synthesized by the adder 60 is applied to the D / A converter 34Y via the b contact of the switch 62 and the b contact of the switch 64. The output of the adder 60 is also applied to the memory 54 via the b contact of the switch 52,
The written signal is read out to the odd field as described above, so that the same screen continues in two fields of the even field and the odd field. In order to use the synchronization signal from the camera signal processing circuit 18, the switch 64 is connected to the contact a during the synchronization signal period.

The high-intensity detector 66 of FIG.
A circuit for processing, the constant S _H signal threshold Th-C
Compare with This threshold Th-C is the threshold Th of the high-intensity detector 68.
It is set lower than -Y. By the way, the threshold value Th-C, Th-
Y is input at 100% linear, and is set to around 200% color and 400% luminance.

FIG. 4 shows a timing chart of a series of operations in FIG. FIG. 4A shows a field discrimination signal.
Indicates an odd field, and L indicates an even field. FIG. 3B shows a VD signal, which falls to L only during each blanking period. The (c) shows the charge accumulation of the image pickup device 16, in a _n high speed accumulation operation, shown immediately after the b _n is a slow accumulation operation. (D) is a signal output from the camera signal processing circuit 18 at a television rate, and includes a ₁ , a ₂ , a ₃ ,
...... corresponds to S _{H signal, b 1, b 2, b} 3, corresponding to ...... S _L signal. 2E shows a signal written to the field memory 54, FIG. 2F shows a signal read from the field memory 54, and FIG. 2G shows an output of the adder 60. The field memory 54 is a type of memory that can be read out simultaneously with writing.

Next, details of the signal processing circuit 32C for processing the color difference signal will be described with reference to FIG. A digital video color signal is input from the A / D converter 30C. The color signals may be I, Q signals subjected to quadrature two-phase modulation, or may be in the form of color difference signals in which RY data and RY data are set. switch
70 and 72 are switched by a pulse signal (1/2 VD) of the frame frequency, and are connected to the a contact in an odd field and to the b contact in an even field. That is, in the odd field output of the A / D converter 30C (S _H signal) is written into the field memory 74. The data read from the memory 74 at the same time as the writing is the data of the screen of the previous field, and is applied to the D / A converter 34C via the contact a of the switch 78 and the contact b of the switch 80.

S _H signal written in the memory 74 in the odd field is read out at the next even field, it is applied to a contact point of the color data conversion switch 76. Switch 76 is switched according to the output of the high brightness detector 66 of the signal processing circuit 32Y, usually, since the connection to the contact b in the even field, S _L signal from the contact b of the switch 70 is selected I have. In the present embodiment, the high-luminance detector 66 is provided to independently provide the threshold value Th-Y for color signal processing lower than the threshold value Th-C for luminance signal processing. The switch 76 may be controlled using a high-brightness determination signal for a high-brightness color suppression process that is generally performed. The switching of the switch 76, the data of the color suppression portion in S _L signal is replaced with the color data in S _H signals. The combined image replaced by the switch 76 in the even field is applied to the D / A converter 34C via the b contact of the switch 78 and the b contact of the switch 80.

The combined data from the switch 76 is applied to the memory 74 via the contact b of the switch 72 and written. Since the written data is read to the next odd field as described above, the same screen continues in two fields of the even field and the odd field. In order to use the synchronization signal from the camera signal processing circuit 18, the switch 80 is connected to the contact a during the synchronization signal period.

FIG. 7 is a waveform chart showing the effect of the embodiment of FIG. FIG. 7A shows an original waveform. In the case of the prior art, although the original waveform is limited by the threshold value Th _0, according to this embodiment, the threshold value Th ₁ high-intensity part of over (<Th ₀₎ (period t _H), the image of the high-speed shooting Since the signals are superimposed, the waveform shown in FIG. 7 (c) can be obtained, and the dynamic range can be substantially expanded without grayscale inversion.

FIG. 8 shows a modification of the signal processing circuit 32Y. In this modified example, a substantial change amount is calculated for the combined portion, and the level is adjusted. That is divided by a predetermined value N to S _L signal from the b contact of the switch 50 in the divider 82, by applying a division result to the subtracter 84 subtracts from the output of the field memory 54. N is the low shutter speed and high shutter speed
Determined by speed ratio. For example, 1 "60 seconds and 1/25
In the case of 0 seconds, N = (1/60) ÷ (1/250) ≒ 4.

FIG. 9 shows still another modification of the signal processing circuit 32Y.
When S _H signals odd field is written into the memory 54,
The average luminance value of the screen is calculated by the average value calculating circuit 86, and the level is adjusted by subtracting the average luminance value from the output of the memory 54 by the subtracter 88. As a result, the level change in the synthesized portion can be made natural.

In the embodiment shown in FIG. 1, only the characteristics of the high-luminance portion are improved, but the characteristics of the low-luminance portion can be improved by the same concept. Also, in order to make improvements in both the high brightness area and the low brightness area, the standard shutter speed (for example, 1/100
Second), this allows for a faster shutter speed (eg, 1/500 second) and a slower shutter speed (eg, 1
/ 60 seconds), high-luminance area and low-luminance area are detected from the photographing signal of the standard shutter speed, and the high-luminance area is synthesized using the video signal by high-speed shooting as in the above embodiment. Then, in the low-luminance area, synthesis may be performed as in the above-described embodiment using the video signal obtained by the low-speed shooting.

〔The invention's effect〕

As can be easily understood from the above description, according to the present invention, dynamic inversion is substantially achieved without inversion of gradation.
The range can be expanded. Further, there is an effect that it can be realized with a simple circuit configuration without requiring a complicated arithmetic algorithm.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.
FIG. 3 is a block diagram showing the configuration of the processing circuit 32Y in FIG. 1, FIG. 3 is a block diagram showing the configuration of the processing circuit 32C in FIG. 1, and FIG.
FIG. 5 is a detection characteristic diagram of the high-intensity detector 68, FIG. 6 is a characteristic diagram of the coefficient unit 58, and FIG.
FIG. 8 is an improved waveform diagram, FIG. 8 is a modified example of FIG. 2, and FIG. 9 is another modified example of FIG. 10 ... Subject, 12 ... Shooting lens, 14 ... Aperture, 16 ...
Image sensor, 32Y, 32C processing circuit, 26 speed switching circuit

Claims (1)

(57) [Claims] An imaging unit for outputting image signals obtained by shooting under different exposure conditions in a predetermined order; a detection unit for detecting an image portion having a predetermined luminance level from an image signal under predetermined exposure conditions among the image signals; In accordance with the detection result of the detection means, the image signal of the predetermined exposure condition, the image signal of another exposure condition is provided with a synthesis means, and the image signal of another exposure condition to be synthesized by the synthesis means, An image pickup apparatus, wherein the correction is performed according to a detection level of the detection means.