JP3094231B2 - Signal processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to luminance signal processing for a color video camera, a color still video camera, and the like.

[Conventional technology]

In the single-panel color solid-state imaging device, each pixel is provided with a specific color filter, and a signal obtained through these is subjected to appropriate signal processing to finally obtain a luminance signal Y and two types of signals. Color difference signals RY, BY
Have gained.

Generally, the luminance signal Y is obtained as follows when interlaced reading is performed using, for example, an image sensor equipped with a complementary color filter shown in FIG. That is, reset noise is removed from the read four signals of magenta (Mg), green (Gr), cyan (Cy), and yellow (Ye) by a correlated double sampling (CDS) circuit, and automatic gain adjustment ( After the gain is appropriately adjusted by an AGC circuit, gamma (γ) conversion and white compression (knee) of a high-luminance portion are performed, and finally, band limitation is performed by a low-pass filter.

[Problems to be solved by the invention]

However, when trying to obtain a luminance signal by the above-described method, one horizontal scanning period (hereinafter, 1H) is performed due to band limitation in the horizontal direction.
And referred) every, and Y ₁ signal Mg + Gr obtained by averaging the Mg and Gr,
Although so that the Cy and Ye averaged Y ₂ signal Cy + Ye is obtained, not necessarily the luminance signal Y ₁ and Y ₂ is always equal due to the difference of the spectral characteristics of the color filters. Therefore, when an image is reproduced using the two types of luminance signals as they are, a so-called luminance step occurs in which a bright luminance line and a dark luminance line are generated every 1H, which causes a problem that the image quality of the reproduced image is significantly deteriorated. Such a luminance step occurs not only in a complementary color filter but also in a pure color filter. For example, as shown in FIG. 4, leakage from red (R) and blue (B) occurs in a filter having the arrangement of FIG. By Green G
Since the spectral characteristics of 1 and G2 are slightly different, this difference causes a luminance step, and a luminance step easily occurs in the R or B portion, deteriorating the image quality of a reproduced image. In order to solve this problem, (i) averaging of luminance signals by band limitation in the vertical direction, and (ii) using the difference signal in the vertical direction as a vertical aperture (VAPC) signal, performing a certain amplitude limitation such as a base clip,
Means such as adding to the luminance signal before correction are conceivable, but (i) tends to damage the high-frequency component and blurs the edge portion, and (ii) specifies the threshold value for amplitude limitation because it is constant. Although the effect is effective for the color, there is a problem that the amplitude limit is excessively applied to other colors or the amplitude is not perfect.

Further, the luminance step is conspicuously different depending on the magnitude of the luminance level. That is, the signal output from the image sensor is
Both the luminance signal and the chrominance signal are normally subjected to gamma correction as shown in FIG. 11 in order to match the gamma characteristics of the receiver shown in FIG. 10, so that the luminance at the output end of the image sensor is almost inconspicuous. Even with the step, there is a problem that the step is emphasized in the low luminance part after the gamma correction than in the high luminance part.

For example, in the case of a television receiver, since the gamma characteristic is such that the output signal Q is normally Q = ^{12.2 with} respect to the input signal I, the camera performs gamma correction such that Q ′ = I ′ ^0.45 . Therefore, the luminance step in the low luminance portion is enhanced about three times after the gamma correction.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a signal processing device capable of obtaining an image with less noticeable luminance steps.

[Means for solving the problem]

In order to achieve the above object, in the present invention, the signal processing device is configured as in the following (1) to (5).

(1) A signal processing device that generates a luminance signal and a color signal from an output of an imaging device, comprising: a hue determination unit that determines a hue of the color signal; and a vertical aperture correction unit that performs vertical aperture correction on the luminance signal. The vertical aperture correction unit performs a nonlinear process of performing a nonlinear process on a correction signal for vertical aperture correction of the luminance signal using a nonlinear characteristic that suppresses a level lower than a predetermined level among output levels of the signal. A signal processing device comprising: means for controlling a nonlinear characteristic of the nonlinear processing means in accordance with a determination output of the hue determination means.

(2) In the signal processing device according to (1), when the hue determining unit determines that the hue has a luminance step, the characteristic of the nonlinear processing unit is such that the luminance step is removed. A controlled signal processor.

(3) In a signal processing device that generates a luminance signal and a color signal from an output of an image sensor, a luminance level determining unit that determines a luminance level of the luminance signal, and a vertical aperture correction unit that performs vertical aperture correction of the luminance signal. Prepared,
The vertical aperture correction unit performs a nonlinear process of performing a nonlinear process on a correction signal for vertical aperture correction of the luminance signal using a nonlinear characteristic that suppresses a level lower than a predetermined level among output levels of the signal. A signal processing device comprising: means for controlling a nonlinear characteristic of the nonlinear processing means in accordance with a determination output of the luminance level determination means.

(4) In the signal processing device according to (3), when the luminance level determining unit determines that the luminance level has a luminance step, the nonlinear processing unit removes the luminance step so as to remove the luminance step. A signal processing device whose characteristics are controlled.

(5) The signal processing device according to any one of (1) to (4), wherein the nonlinear characteristic of the nonlinear processing unit is a base clip characteristic.

[Action]

According to the configurations of (1), (2) and (5), the luminance step based on the hue is removed, and the (3), (4),
According to the configuration of (5), the luminance step based on the luminance level is removed.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 shows a "signal processing apparatus" according to a first embodiment of the present invention.
It is a block diagram of.

This embodiment shows an example in the case of performing interlaced scanning of an image pickup device equipped with the color filter shown in FIG. As shown in the figure, an image signal formed on an image sensor (CCD) 101 through a lens 100 is read out from the CCD 101 for each pixel by interlaced scanning, and a correlated double sampling (CDS) circuit 102 After the reset noise is removed, the gain is adjusted by an automatic gain adjustment (AGC) circuit 103, and luminance signal processing and chrominance signal processing are performed.

The color signal processing in FIG.
Is input to a color signal processing circuit 107, and the circuit 107 performs normal synchronization, conversion to RGB signals, white balance, gamma conversion, and the like. Finally, two types of color difference signals R- Y, BY signals are obtained.

The output of the automatic gain adjustment circuit 103 is first input to the γ and Knee conversion circuit 104 in order to perform luminance signal processing. In the circuit 104, after gamma conversion and white compression of the high-luminance portion are performed, the band in the horizontal direction is limited by the low-pass filter 105, and the luminance step is removed by the luminance step removing circuit 106. Is output.

The characteristics of the luminance step removing circuit 106 are controlled by an output signal of a hue detecting circuit 108 which receives the color difference signals RY and BY output from the color signal processing circuit 107 as input signals.

Next, operations of the luminance step removing circuit 106 and the hue detecting circuit 108 will be described. Since the luminance step is conspicuous in the specific color (hue), the detection (determination) of the deviation to the specific color is performed from the output signal of the color signal processing circuit 107. From the experience so far, it is considered that the particularly noticeable colors of the luminance step are red and blue, so the positions of R and B shown in FIG. 5 are detected by the hue detection circuit shown in FIG.

The hue detection circuit determines R when the condition of RY>ref1> 0, ref2 <BY <0 in FIG. 5 is satisfied, and ref3 <RY <0, BY>ref4> When the condition of 0 is satisfied, B is determined. That is, the comparators 601 to 606 determine whether or not the above condition is satisfied, and then output R detection and B detection signals to the gate circuits 607 and 607. Further, the output of the gate circuit 609 outputs as a hue detection signal whether or not the hue requires the luminance step removal.

The hue detection signal thus obtained is input to the luminance step removing circuit 106, and becomes a control signal for removing the luminance step. The luminance step is removed by the circuit configuration shown in FIG. When the output signal of the low-pass filter 105 is input to the luminance step removing circuit 106, a vertical aperture (VAPC) circuit 701
Although not shown, a VAPC signal is obtained using a 1H delay line,
The signal is input to the base clip circuit 702 having the characteristics shown in FIG.

The base clip circuit 702 compares the VAPC signal with the clip level α and performs a so-called base clip process. The hue detection signal controls the clip level α of the luminance signal so that the base clip is applied in a hue with a noticeable luminance step. It should be noted that if the clip level α is set to an excessively large level, the edge component may be damaged.

Next, an example in which a gain adjustment method as shown in FIG. 8 is used as the luminance step removing means instead of the base clip method of FIG. 7A will be described as a second embodiment of the present invention. This embodiment is configured in the same manner as the first embodiment except for the luminance step removing circuit. In FIG. 8, when there is a luminance step in the input luminance signal, the luminance signal is output by switching to the gain control amplifier 802 and the terminal e for outputting nothing at every 1H. When there is no luminance step, the input signal is connected to the terminal e and output as it is, and the terminal d is connected to the terminal c to keep the input terminal of the gain control amplifier 802 at a certain potential. This switch 801 is controlled by 1H switching. A signal and a hue detection signal are input signals, which are output from the gate circuit 805, and a switch is switched every 1H only in a portion having a luminance step. The gain of the gain control amplifier 802 is adjusted for each color using the R detection signal and the B detection signal shown in FIG. 6 to adaptively remove the luminance step according to the color.

Next, an example of removing a luminance step when a pure color type filter as shown in FIG. 3 is used as a color filter will be described as a third embodiment of the present invention. This embodiment is configured as shown in FIG. As shown in FIG.
The image signal which is color-separated by the color filter 101b through 0 and formed on the CCD 101 is read out by interlaced scanning, and
Through the S circuit 102 and the automatic gain adjustment circuit 103, luminance signal processing and chrominance signal processing are performed.

In the color signal processing, processes such as gamma conversion and white balance which are usually performed in the color signal processing circuit 907 are performed, and the color difference signals RY and BY are processed by appropriate matrix processing.
Get. The color difference signals RY and BY are input to a hue detection circuit 906, as in the case of the complementary color, and are determined as R or B in a vector diagram as shown in FIG. A hue detection signal of the B detection signal is output and used as a control signal for the base clip circuit 904.

In the luminance signal processing, after performing gamma conversion and white compression of a high-luminance part in a gamma conversion circuit 901, a vertical aperture circuit
The VAPC signal is obtained in 902, the band is appropriately limited in the vertical direction by the low-pass filter 903, and input to the base clip circuit 904.

The base clip circuit 904 controls the characteristic (α) in FIG. 7 (b) based on the hue detection signal, performs appropriate base clip processing according to the hue of the image, and outputs the result to one terminal of the adder 905. Since the other terminal of the adder 905 receives a luminance signal including a luminance step after the gamma processing,
By adding the luminance signals after the base clip that have been appropriately processed according to the hue, a luminance signal Y without a luminance step can be obtained at the output terminal.

In this embodiment, the base clip processing is used for removing the luminance step. However, similar to the first embodiment, after the gamma processing, the luminance adjustment of the luminance level may be performed for each 1H as shown in FIG. good.

In each of the above embodiments, since the hue detection is performed by a combination of the comparator and the gate circuit, the base clip and the amplifier gain can be controlled only digitally. However, the hue detection is performed in an analog manner using appropriate discrete components. To control the base clip and the amplifier gain in an analog manner. At this time, the setting may be made so that the removal of the luminance step is not limited to R or B, but can be performed with an arbitrary hue.

Further, instead of the color difference signal, an RGB signal after white balance adjustment in the color signal processing may be used as the hue detection circuit.

Next, an example in which attention is paid to the fact that the degree of the luminance step differs depending on the magnitude of the luminance level will be described as a fourth embodiment of the present invention. In the present embodiment, the configuration is the same as that of the first embodiment except for the luminance step removing unit that removes the luminance step in the configuration of FIG. In FIG. 12, reference numeral 121 denotes a luminance level detection circuit,
It is configured as shown in Figure 4.

When the luminance signal including a luminance step component is input to the luminance level detecting circuit in FIG. 14, the comparator 141 and 142 is compared with the low luminance detection level y _L and high luminance detection level y _h as shown in FIG. 13, detecting the brightness level range 0 to y _L a prominent luminance step, it is output to the output terminal of the detection circuit 121 of Figure 12.

This level detection signal is input to the luminance step removing circuit 122, and performs control as a control signal of the above-described base clip circuit (or 1H gain adjusting circuit).

Thus, the luminance signal Y output from the luminance step removing circuit 122 is output as a luminance signal from which the luminance step generated due to the influence of the gamma correction has been removed.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reduce the luminance step based on the hue or the luminance level, and obtain an image in which the luminance step is inconspicuous.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a diagram showing an example of arrangement of complementary color filters, FIG. 3 is a diagram showing an example of arrangement of pure color filters, and FIG. FIG. 5 is a view showing a position of a specific color in which a luminance step is conspicuous,
FIG. 6 is a circuit diagram of a hue detection circuit, FIG. 7A is a block diagram of a luminance step removing circuit of the first embodiment, FIG. 7B is a characteristic diagram of a base clip circuit, and FIG. FIG. 9 is a block diagram of a third embodiment of the present invention, FIG. 10 is a gamma characteristic diagram of a receiver, and FIG. 11 is a gamma correction characteristic of a camera. FIG. 12 is a block diagram of a main part of a fourth embodiment of the present invention, FIG. 13 is an explanatory diagram of a luminance level detecting circuit, and FIG. 14 is a circuit diagram of the luminance level detecting circuit. 106: Luminance level difference removal circuit 108: Hue detection circuit

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 9/04-9/11 H04N 9/64-9/78

Claims (5)

(57) [Claims] 1. A signal processing apparatus for generating a luminance signal and a color signal from an output of an image pickup device, comprising: a hue determination unit that determines a hue of the color signal; and a vertical aperture correction unit that performs vertical aperture correction on the luminance signal. Wherein the vertical aperture correction means performs a non-linear process on a correction signal for vertical aperture correction of the luminance signal by using a non-linear characteristic that suppresses a level lower than a predetermined level among output levels of the signal. A signal processing apparatus comprising: a non-linear processing unit, wherein a non-linear characteristic of the non-linear processing unit is controlled in accordance with a judgment output of the hue judgment unit. 2. The signal processing apparatus according to claim 1, wherein when the hue determining means determines that the hue has a luminance step, the nonlinear processing means has a characteristic so as to remove the luminance step. Is controlled. 3. A signal processing apparatus for generating a luminance signal and a chrominance signal from an output of an image sensor, comprising: a luminance level judging unit for judging a luminance level of the luminance signal; and a vertical aperture correcting unit for vertically aperture correcting the luminance signal. The vertical aperture correction means, the correction signal for vertical aperture correction of the luminance signal, using a non-linear characteristic to suppress a level lower than a predetermined level of the output level of the signal, A signal processing apparatus comprising: a non-linear processing unit for performing processing, wherein a non-linear characteristic of the non-linear processing unit is controlled according to a determination output of the luminance level determination unit. 4. The signal processing apparatus according to claim 3, wherein when the luminance level determining means determines that the luminance level has a luminance step, the non-linear processing means removes the luminance step. A signal processing device whose characteristics are controlled. 5. The signal processing device according to claim 1, wherein the non-linear characteristic of said non-linear processing means is a base clip characteristic.