JP2698404B2 - Luminance signal processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance signal processing device for an imaging device such as a color video camera or a color still video camera equipped with a color separation filter.

[Conventional technology]

In the single-panel color solid-state imaging device, a specific color filter is mounted on each pixel, and a luminance signal Y and a luminance signal Y are finally obtained by performing appropriate signal processing on a color signal obtained through these pixels. Two types of color difference signals R-Y, B-
Y has been obtained.

In general, color signal processing in the case of using a complementary color filter generally involves performing arithmetic processing on a signal that is a result of subtracting outputs from pixels that are horizontally adjacent to each other and that have a different complementary color filter. Is common.

For example, in the case of a sensor equipped with a color filter shown in FIG. 3, the respective color signals of Mg, Gr, Cy, and Ye output from the sensor show equal responses to white by an automatic gain control (AGC) circuit. The gain is adjusted as described above, and A / D conversion is performed by the A / D converter. Then, in order to extract a signal as a luminance signal, γ conversion is performed by the γ conversion unit, and
Knee transform is performed, and finally a luminance signal is obtained by band-limiting with a low-pass filter.

[Problems to be solved by the invention]

However, for example, when interlaced scanning is performed on the color filter array shown in FIG. A luminance signal obtained by averaging Mg, Gr, and a luminance signal as shown in Thus, two types of luminance signals, such as a luminance signal obtained by averaging the luminance signals of Cy and Ye, are obtained. However, due to the difference in spectral characteristics between each color filter, The two types of luminance signals are not always equal. Therefore, if an image is reproduced using the two types of luminance signals as they are, every line Therefore, there is a problem that a bright line and a dark line are generated for each horizontal line in the vertical direction, and a so-called luminance step occurs. To solve this problem, there is a method of averaging the luminance signal in the vertical direction by applying a low-pass filter in the vertical direction.However, this method alone solves the luminance step and the problem. There was a problem that the image was blurred. SUMMARY OF THE INVENTION It is an object of the present invention to provide a luminance signal processing device that solves the problem of the luminance step without losing the original image information.

[Means for solving the problem]

In order to achieve such an object, a luminance signal processing apparatus according to the present invention includes: an image pickup unit provided with a color separation filter; a unit for detecting a high-frequency component in a vertical direction of a signal obtained from the image pickup unit; When the high frequency component detected by the detection means is less than a predetermined level, the luminance step between the horizontal line signals obtained from the imaging means is reduced by reducing the high frequency component in the vertical direction of the luminance signal obtained from the imaging means. Frequency switching means for reducing the frequency characteristic.

[Action]

Therefore, an averaged luminance signal is output in a portion where a low-frequency component is relatively conspicuous, and an original luminance signal is output as it is in a portion where a high-frequency component is not conspicuous. In addition, the luminance step can be eliminated at the same time.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

<First Embodiment> FIG. 1 shows an embodiment of the present invention in the case of interlaced scanning of a CCD equipped with, for example, a color filter as shown in FIG.

The CCD sensor 101 is equipped with, for example, four types of color filters as shown in FIG. The image signal read out for each pixel by interlaced scanning from the sensor 101 is first gain-adjusted by an automatic gain adjuster 102 so that each signal shows an equal response to white, and then A / D The A / D conversion is performed by the converter 103 at a timing synchronized with the read clock. For color processing to be performed later, the A / D converter 103 has good linear characteristics, and it is desirable to perform the processing with 8 bits or more from the viewpoint of quantization error.

The color signal processing in FIG. 1 is one example.
The output signal of the D converter 103 is input to the interpolation filter 110, and each of the color signals Mg, Gr, Cy, Ye is
Are being synchronized. Next, the synchronized color signals Mg, Gr,
Cy and Ye are input to the RGB conversion unit 111, converted into RGB signals, and then input to the white balance unit 112 to obtain white-balanced RGB signals. Furthermore, white balance section 1
The RGB signal output by 11 is input to the γ conversion unit 113,
After γ conversion by table conversion, color difference matrix section
114, and is subjected to a matrix operation to obtain color difference signals R-Y, B
-Y is obtained. Finally, each color difference signal is D / A converted by D / A converters 115 and 116 and output.

On the other hand, the output of the A / D converter 103 is first input to the γ conversion unit 104 for performing the luminance signal processing. The luminance signal subjected to γ conversion in the γ conversion section 104 is input to the Knee conversion section 105 and
Is converted. The conversion order of the γ conversion unit 104 and the Knee conversion unit 105 may be changed. The luminance signal subjected to the γ conversion and the Knee conversion is averaged by a low-pass filter 106 for the luminance signal in the horizontal direction. The luminance step correction unit 107 is configured, for example, as shown in FIG. 2, and this output is a luminance signal which does not impair the original image information and eliminates the luminance step generated for each line. Further, the example of FIG. 2 is characterized in that the aperture correction in the vertical direction is performed at the same time. Next, a description will be given of the luminance step correction unit shown in FIG.

Assuming that the output from the sensor 101 is interlaced, the output of the A / D converter 103 is, for example, when the color filter shown in FIG. 3 is used, the (Mg / Gr) line and the (C
(y / Ye). Therefore, when the luminance signal is averaged in the horizontal direction by the low-pass filter 106, every 1H Line with a luminance signal of These two types of luminance signals are input signals to the luminance level difference correction unit 107.
The luminance step correction unit shown in FIG. 2 includes a vertical low-pass filter unit formed by 1H delays 201 and 202, coefficient multipliers 203, 204 and 205, and an adder 211, a 1H delay 201 and 202, and a coefficient multiplier 2
06, 207, 208 and a V-APC obtained by high-pass filtering and a high-pass filter formed by the adder 212.
This is roughly constituted by three blocks of a switch 214 for switching between an original luminance signal by a (vertical aperture) and a luminance signal averaged in the vertical direction by a low-pass filter. For example, if the coefficients of the coefficient multipliers 203 and 205 are set to 1/4 and the coefficient of 204 is set to 1/2, the output of the adder 211 Luminance signal and its surrounding And the luminance signal of And the luminance signal of Luminance signal and its surrounding And the luminance signal of Are alternately output every 1H. In this manner, Y ₁ Y _{2 is obtained} by the low-pass filtering in the vertical direction, and the luminance signals in the vertical direction are averaged. When the coefficients of the coefficient units 206 and 208 are set to -1/2 and the coefficient of 207 is set to 1, the output of the adder 212 is Luminance signal and its surrounding Averaged the luminance signal of V-APC signal and Luminance signal and its surrounding Averaged the luminance signal of V-APC signal is output alternately every 1H.

Switch 214 is the luminance signal Y ₃ subjected to vertical edge enhancement in the luminance signal Y ₁ and the original luminance signal obtained by the vertical low-pass filtering is input to, a portion where the low-frequency component is large and luminance step noticeable the selected output Y ₁ of the low-pass filtering adders 211, high-pass filter as an output Y ₃ of the adder 213 high-frequency components in the hard portion noticeable many luminance step of performing edge enhancement in the vertical direction are selected The output of the adder 212 obtained by the ring, that is, VA
The switch is controlled by the PC signal. The determination of the amount of the high-frequency component is performed, for example, by using a predetermined reference voltage Vre using the comparator 210.
This can be easily done by comparing f with the V-APC signal.

To perform the vertical edge enhancement, the V-APC signal output from the adder 212 may be added to the original luminance signal by the adder 213 through, for example, the coefficient multiplier 209. The use of the edge-enhanced luminance signal enables the reproduced image to be a sharp image. The degree of vertical edge enhancement can be easily set by controlling the V-APC signal by arbitrarily changing the coefficient of the coefficient multiplier 209.

As described above, the luminance signal subjected to the luminance step correction and the vertical contour enhancement by the luminance step correction unit 107 is subjected to horizontal contour enhancement at 108, and is finally D / A converted and output by the D / A converter 109. Is done.

<Second Embodiment> The present invention is effective even if a luminance signal is generated with a configuration as shown in FIG. 4, so an embodiment in this case will be described.

In the example shown in FIG. 4, the output luminance signal of the vertical low-pass filter and the original luminance signal or a luminance signal obtained by performing contour enhancement in the vertical direction on the original luminance signal are added at an arbitrary ratio and output. Things. For example, the output of the adder 211, which is the output of the low-pass filter in the vertical direction, is Y _LPF , the original luminance signal or the luminance signal _subjected to contour enhancement is Y _apc , and the coefficients of the coefficient doublers 401 to 404 are K ₁ , K ₂ , 1−K ₁ , 1−K ₂ , K ₁ >
Switch by a suitable switching-by setting the K ₂
Y ₁ in the output of _{214 = K 1 Y LPF + (} 1-K 1) Y apc or Y ₂ = K ₂ Y
A luminance signal of _LPF + (1−K ₂ ) Y _apc is obtained. As in the first embodiment, the switch 214 is a V-AP which is the output of the comparator 210.
Since it is controlled by the C signal, the Y _LPF is used for an image signal having many low frequency components, and the original luminance signal or a luminance signal obtained by performing edge enhancement in the vertical direction for an image signal having many high frequency components. _Adder 405 with coefficients set to include many _apc ,
406 outputs are each selected. The number of coefficient units is the fourth
It is not necessary to provide two adders for each of the adders 211 and 213 as in the example shown in the figure, and the number may be increased or decreased for each adder as necessary.

Third Embodiment In the above description, the case where two 1H delays are used has been described. However, even when one 1H delay or a frame memory is used, the luminance signal averaged in the vertical direction and the original luminance signal are used. Alternatively, the present invention is effective similarly to the first and second embodiments in that it has a luminance signal on which contour enhancement has been performed in the vertical direction and generates a final luminance signal under the control of the V-APC signal.

In the above description, the color filter arrangement shown in FIG. 3 has been described as an example. However, a mosaic filter or a G stripe R / B line sequential as shown in FIGS. (G is arranged in a stripe every other row,
The present invention is similarly effective as long as its luminance signal is formed from the sum of different color filters for each 1H, even if it is a pure color mosaic type such as R and B alternately arranged for each row). It is.

Further, in the above configuration, the low-pass filter and the outline enhancement are performed digitally, but may be configured by an analog circuit.

〔The invention's effect〕

As described above, according to the present invention, the luminance signal and the original luminance signal that have been subjected to low-pass filtering in the vertical direction in the low-frequency region where the luminance step is conspicuous and the high-frequency region that is relatively inconspicuous using the vertical contour signal are used. Is output by switching or adding at an arbitrary ratio, thereby eliminating the luminance step without impairing the image quality of the input image information.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a block diagram showing an example of the configuration of a luminance step correction unit, FIG. 3 is a diagram showing an example of a color filter array, and FIG. Block diagrams of the second embodiment, FIGS. 5 and 6 are diagrams showing examples of other color filter arrangements. 101: Sensor 107: Luminance level difference correction unit 201, 202: 1H delay 203 to 209: Coefficient multiplier 210: Comparator 211 to 213: Adder 214: Switch 401 to 404: Coefficient multiplier 405, 406 … Adder

Claims (1)

(57) [Claims] 1. An imaging device equipped with a color separation filter, a detection device for detecting a high-frequency component in a vertical direction of a signal obtained from the imaging device, and the high-frequency component detected by the detection device is specified. A frequency characteristic switching unit that reduces a luminance step between horizontal line signals obtained from the imaging unit by reducing a vertical high-frequency component of the luminance signal obtained from the imaging unit when the level is less than the level. Processing equipment.