JPH02125589A - Picture quality correction system for image pickup device - Google Patents

Abstract

PURPOSE:To suppress the deterioration in the picture quality by supplying a luminance signal formed by a matrix circuit forming a luminance signal from a color signal obtained by the pickup at an image pickup element to a luminance correction circuit so as to expand the intermediate brightness between the minimum and maximum brightness. CONSTITUTION:For example, a luminance signal Y as shown in figure (a) is a signal Y1 attenuated by 1/K1 at an attenuation circuit 20, and becomes a signal Y2 amplified nonlinear by a nonlinear amplifier circuit 21. Then the polarity of the signal Y2 is inverted by an inverting circuit 22 to form a signal Y3. The signal Y3 and the original luminance signal Y are added by an adder circuit 23 to form a signal Y4. Moreover, the signal Y4 and the original luminance signal Y are added by an adder circuit 24 to form a new luminance signal Yc. Thus, since a luminance signal correction circuit emphasizes intermediate brightness and the change in the brightness at a black and white levels is suppressed, the picture quality of a main object and a background is improved in the state of rear light and spot light scene.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an imaging device such as an electronic camera, and particularly in a so-called backlit situation where the surrounding brightness is relatively high relative to the main subject, or when the main subject is So-called spots where the brightness of
The present invention relates to an image quality correction method for properly photographing a main subject and a background in a light scene.

[Conventional technology]

2. Description of the Related Art Conventionally, imaging devices such as electronic still cameras and video tape recorders (VTRs) have been equipped with an imaging system shown in FIG. First, to explain the configuration, in the figure, 1 is an imaging optical system consisting of a photographing lens, an aperture, a shutter, etc. Behind the imaging optical system 1, there is a charge accumulation solid-state image sensor (CCD), etc. An image sensor 2 is arranged, and the light-receiving surface of the image sensor 2 is colored with red (R) corresponding to the pixel, for example.
).

Blue (B) and green (G) color filters 3 are provided. The image sensor 2 photoelectrically converts the optical image of the object and outputs video signals generated in each pixel by so-called horizontal scanning and vertical scanning readout in time series, and this video signal has an amplitude level that can be processed by the amplifier 4. is amplified to.

The time-series video signal output from the amplifier 4 is separated into red (R) and blue (B) by the color separation circuit 5.

The signal is separated into green (G) color signals, and the amplitude level of each color signal is adjusted by a white balance circuit 6 in order to obtain the optimum white color when an image is reproduced from these color signals. be done. Furthermore, the color signal output from the white balance circuit 6 passes through a T correction circuit 7 for correcting the gradation characteristics of the cathode ray tube, and is converted into a luminance signal Y1 and color difference signals R-Y and B-Y by an IJ circuit 8. converted. Then, these ° signals Y, RY, and B-Y are recorded on a magnetic recording medium or supplied to a monitor, television, etc. for image reproduction.

[Problem to be solved by the invention]

By the way, such imaging devices automatically adjust the exposure amount by adjusting the aperture and shutter speed.
Automatic exposure function that optimally sets the amount of light incident on the image sensor (
AE function).

This AE function detects the intensity of light received from a subject within the field of view, and automatically adjusts the aperture etc. to enable photographing under the optimum photoelectric conversion characteristic conditions of the image sensor.

However, even with such a function, if the brightness of the background scene B of the main subject A is high, as shown in FIG. 7, the main subject A that you most want to photograph will be dark and the image will be unclear. Furthermore, if the amount of light received from the main subject is increased, the background scenery will become completely white. On the other hand, when photographing a person wearing white clothes as the main subject in a dark background, there is a problem in that the clothes come off and the texture is lost.

[Means to solve the problem]

The present invention has been made in view of such problems,
An object of the present invention is to provide an image quality correction method for an imaging device that clearly photographs each subject even when high-luminance and low-luminance subjects coexist within the same angle of view.

In order to achieve this object, the present invention provides an output for a luminance signal input of the minimum luminance and an output for a luminance signal input of the maximum luminance with the same linear characteristic within a preset range of minimum luminance and maximum luminance. The luminance signal within the range of the minimum brightness and maximum brightness is output by outputting the brightness signal input within the range of the minimum brightness and maximum brightness with an appropriate non-linear characteristic having a larger amplification factor than the linear characteristic. Equipped with an expanding brightness correction circuit.

FIG. 1 is a diagram illustrating the principle of the present invention, and FIG. 2 is a diagram illustrating the principle of the present invention. On the right side of these figures, the color-separated color signals R (red), B (blue), and G (green) are processed by a matrix circuit 9 of the prior art to generate a color difference signal RY.

B-Y and luminance signal Y, and further converts the luminance signal Y into a second
A new luminance signal Yc is generated through the luminance signal correction circuit 10 having the input/output characteristics shown in the figure, and these color difference signals R-
Y, BY and the luminance signal Yc are used as signals for image reproduction. As shown in FIG. 2, the minimum brightness Y corresponds to the preset darkest state. and the maximum brightness Y corresponding to the brightest state) in the range of 1, the minimum brightness Y. For the luminance signal input with the maximum luminance YM, a new luminance signal Yc is output with the same linear amplification factor, and the minimum luminance Y
For a luminance signal input between 0 and the maximum luminance YM, a new luminance signal Y is generated using a preset nonlinear amplification factor characteristic.
Output c. Note that this nonlinear amplification factor is determined by the minimum brightness Y0
By setting the amplification factor to a value higher than the amplification factor at maximum luminance Y and 4, the intermediate luminance signal is expanded.

[Effect]

In the present invention having such a configuration, since the intermediate brightness between the minimum and maximum brightness is extended, it is possible to emphasize the brightness of the subject in low illumination and to take good pictures of the main subject. Since the brightness of the darkest and brightest states remains the same, blacks remain black and whites remain white, which prevents deterioration in image quality such as black areas turning white or relatively high-brightness areas disappearing. Also, since only the luminance signal is processed, there is no white balance shift.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the configuration of an imaging system when applied to an electronic still camera or a VTR. First, to explain the configuration, in FIG. 3, 11 is an imaging optical system consisting of a photographing lens, an aperture, a shutter, etc. Behind the imaging optical system 11 is an imaging device 12 such as a charge storage solid-state imaging device (CCD).
are arranged, and color filters 13 of, for example, red (R), blue (B), and green (G) corresponding to the pixels are provided on the light receiving surface of the image sensor 12. The image sensor 12 photoelectrically converts the optical image of the object, and outputs video signals generated in each pixel by so-called horizontal scanning and vertical scanning readout in time series, and this video signal has an amplitude level that can be processed by the amplifier 14. is amplified to.

The time-series video signal output from the amplifier 14 is separated into red (R), blue (B), and green (G) by the color separation circuit 15.
Further, when an image is reproduced from these color signals, the amplitude level of each color signal is adjusted by a white balance circuit 16 in order to obtain the optimum white color. Further, the color signal output from the white balance circuit 16 passes through a γ correction circuit 17 for correcting the gradation characteristics on the cathode ray tube, and is converted by the matrix circuit 18 into a luminance signal Y1 and color difference signals R-Y and B-Y. Ru.

Reference numeral 19 denotes a luminance signal correction circuit, which generates a new luminance signal Yc from the luminance signal Y formed by the matrix circuit 18 using an internal nonlinear circuit. The nonlinear circuit has the configuration shown in FIG. 4, and the amplitude of the luminance signal Y is 1/
an attenuation circuit 20 that attenuates the attenuated signal, and a nonlinear amplification circuit 21 that amplifies the attenuated signal with a preset nonlinear amplification factor.
An inversion circuit 22 that inverts the signal output from the nonlinear amplifier circuit 21 is provided. The nonlinear amplifier circuit 21 has an amplification factor kI (reciprocal of the attenuation factor) at the minimum brightness and maximum brightness, and the amplification factor within the range of the minimum brightness and maximum brightness has a nonlinear characteristic of less than 1. have For example, the nonlinear characteristic may be made similar to a characteristic curve in the case where T (gamma) is 1 or more in the well-known gamma characteristic, or a characteristic curve experimentally detected under various imaging conditions may be used.

Furthermore, the nonlinear circuit includes adder circuits 23 and 24, the adder circuit 23 adds the signal Y3 output from the inverting circuit 22 and the luminance signal Y to form a signal Y4, and the adder circuit 24 adds the signal Y3 output from the inverting circuit 22 and the luminance signal Y to form a signal Y4. By adding the signal Y, a new luminance signal Yc is generated.

Next, the operation of the luminance signal correction circuit 19 will be explained based on FIG. For example, the luminance signal Y shown in FIG. 5(a) becomes the signal Y1 which is attenuated to 1/1 by the attenuation circuit 20 [see FIG. 5(b)], and the signal Y1 is attenuated by the nonlinear amplifier circuit 21. The signal Y2 is linearly amplified [see FIG. 5(C)]. Here, the amplitude corresponding to the minimum and maximum brightness of the signal Y2 is restored to a level equal to the amplitude of the minimum and maximum brightness of the original brightness signal Y, but the brightness signal between the minimum and maximum brightness is nonlinearly attenuated. waveform.

Next, the polarity of the signal Y2 is inverted by the inverting circuit 22,
A signal Y3 shown in FIG. 5(d) is formed.

By adding the signal Y3 thus formed and the original luminance signal Y in the adder circuit 23, a signal Y4 indicating only the nonlinearly amplified portion is formed, as shown in FIG. 5(e). , further adds the signal Y and the original luminance signal Y to the adding circuit 24
A new luminance signal Yc as shown in FIG. 5(f) is formed by adding the luminance signals Yc. That is, the new luminance signal Yc shown in FIG. 5(f) corresponds to the one formed by the characteristics shown in FIG.

As described above, according to this embodiment, the luminance signal formed by the matrix circuit is further enhanced by the luminance signal correction circuit having predetermined non-linear input/output characteristics, and the luminance of the black part and the white part is adjusted. Since it has 11 control over changes in the amount of light, it is possible to improve the image quality of the main subject and background in backlit and spotlight scenes.

〔Effect of the invention〕

As explained above, according to the present invention, non-linear processing is performed to expand the luminance signal formed by the matrix circuit to an intermediate luminance between the minimum and maximum luminance, so the luminance of a low-luminance object is emphasized and the main The subject can be photographed well, while the darkest and brightest conditions remain the same brightness, so black remains black and white remains white.
It is possible to suppress deterioration in image quality such as black parts turning white and relatively high-luminance parts disappearing, and it is also possible to take clear images without white balance deviation.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the configuration of the present invention; Figure 2 is a diagram explaining the principle of the invention; Figure 3 is a diagram showing the configuration of an embodiment of the invention; Figure 4 shows the configuration of the brightness correction circuit in Figure 3. Block diagram; FIG. 5 is an explanatory diagram for explaining the operation of the brightness correction circuit; FIG. 6 is a block diagram for explaining the configuration of a conventional example; FIG. 7 is an explanatory diagram for explaining the problem to be solved. In the figure: 9.18; Matrix circuit 10.19; Brightness correction circuit 11; Imaging optical system 12; CCD 15; Color separation circuit 16; White balance circuit 17; T correction circuit 20; Attenuation circuit 21: Nonlinear amplifier circuit 22 .23; Addition circuit

Claims (1)

[Claims] In an imaging device equipped with a matrix circuit that forms a luminance signal from a color signal obtained by imaging with an image sensor, within a preset range of minimum and maximum luminance, the minimum luminance is The output for the luminance signal input and the output for the maximum luminance luminance signal input are generated with the same linear characteristic, and the luminance signal input within the range of the maximum, minimum luminance and maximum luminance is generated with an appropriate amplification factor larger than the above linear characteristic. a brightness correction circuit that expands a brightness signal within the range of the minimum brightness and maximum brightness by outputting it with a non-linear characteristic; the brightness signal formed by the matrix circuit is supplied to the brightness correction circuit; An image quality correction method for an imaging device characterized by forming a linearly amplified luminance signal.