JPH077738A - Color signal processing circuit for single-chip color camera using solid-state image sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to suppress the false color signal generated near the Nyquist frequency when a horizontal high frequency signal component or a vertical high frequency signal component is incident. [Structure] A solid-state image sensor capable of independently reading out image information of all pixels, and a basic lattice formed by repeating two pixels in each of horizontal and vertical directions, and a pixel having the same spectral sensitivity characteristic in this unit lattice In a single-chip color camera having a color filter array arranged on a solid-state image pickup device having two existing color arrangements, three primary color signals are separated from each color signal of four pixels of a unit grid, and the color difference is detected. While converting into a signal, at least one of a horizontal high-frequency signal component and a vertical high-frequency signal component is detected based on each color signal of two pixels having the same spectral sensitivity characteristic among each color signal of four pixels of the unit grid, The gain of the color difference signal is controlled according to the signal level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal processing circuit for a single-chip color camera, and more particularly to a color signal processing circuit for a single-chip color camera using a solid-state image sensor capable of independently reading out image information of all pixels. Regarding

[0002]

2. Description of the Related Art In a single-chip color camera, a color filter array is arranged on a single solid-state image pickup device in order to generate a color signal. As a single-chip color camera of this kind, a color filter that repeats every two pixels in the scanning direction is used, and a coefficient corresponding to the signal corresponding to the first or second pixel of the two repeating pixels or the signal corresponding to the first pixel is used. The coefficient is set so that the difference from the value obtained by multiplying by 0 becomes 0 in the white portion of the subject image, and signal processing is performed to add or subtract the difference to or from the signals corresponding to the first and second pixels. As a result, it is known that the false color signal generated at the boundary between the diagonal line and the colored portion is corrected (see, for example, JP-A-60-62789).

[0003]

However, the conventional single-chip color camera as described above can correct the false color signal generated at the boundary between the diagonal line and the colored portion, but can reduce the pixel pitch in the horizontal direction. Assuming that Px is the vertical pixel pitch and Py is the vertical pixel pitch, as shown in FIG. 7, frequency components 1 / Px and 1 / Py near the horizontal and vertical Nyquist frequencies are obtained.
When a signal component having is input, a strong color false signal is generated, and no consideration has been given to this type of color false signal.

Therefore, the present invention provides a color signal processing circuit for a single-chip color camera capable of suppressing a false color signal generated near the Nyquist frequency when a horizontal high frequency signal component or a vertical high frequency signal component is incident. The purpose is to provide.

[0005]

In order to achieve the above object, a color signal processing circuit according to the present invention comprises a solid-state image pickup device capable of independently reading out image information of all pixels and a horizontal and vertical direction. A single plate comprising a repeating unit of two pixels as a basic lattice, and a color filter array arranged on a solid-state image sensor having a color array in which two pixels having the same spectral sensitivity characteristic are present in the unit lattice. In a color camera, primary color separation means for separating three primary color signals from each color signal of four pixels of a unit grid obtained from an output signal of a solid-state image pickup device, color difference conversion means for converting the three primary color signals into color difference signals, and unit grid 2 with the same spectral sensitivity characteristics of each color signal of 4 pixels
A high-frequency signal detecting means for detecting at least one of a horizontal high-frequency signal and a vertical high-frequency signal based on each color signal of the pixel and outputting a control signal corresponding to the signal level, and in accordance with the control signal The configuration is such that the gain of the color difference signal is controlled.

[0006]

In the color signal processing circuit according to the present invention, the three primary color signals are separated from the color signals of the four pixels of the unit grid, and the three primary color signals are converted into color difference signals, while the color signals of the four pixels of the unit grid are converted. At least one of the horizontal high frequency signal component and the vertical high frequency signal component is detected based on each color signal of two pixels having the same spectral sensitivity characteristic, and a control signal corresponding to the signal level is obtained. Then, the gain of the color difference signal is controlled according to this control signal. As a result, it is possible to suppress a false color signal generated near the Nyquist frequency when a horizontal high frequency signal or a vertical high frequency signal is incident.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a color signal processing circuit according to the present invention. In the figure, as the solid-state image sensor 1, a so-called all-pixel independent readout type solid-state image sensor capable of independently reading out image information of all pixels is used. A color filter array 2 is arranged on the solid-state image sensor 1. As the color filter array of this color filter array 2, one having three basic types of color filters'A ',' B ', and'C' with horizontal two repetitions and vertical two repetitions as a basic repetition cycle is used. Of this color filter array, as shown in FIG. 2, color filters'A 'that transmit a certain color light are arranged in a mosaic pattern,
The mosaic line-sequential color filter array in which the color filters'B 'and'C' are arranged line-sequentially has an excellent feature that high horizontal and vertical resolutions can be obtained.

In FIG. 2 which shows the mosaic line sequential type color filter array in a general form, the color filter'A ',
As shown in FIG. 3, as'B 'and'C', Ye mosaic, Mg, Cy are used by using color filters of'Ye (yellow) ',' Mg (magenta) ', and'Cy (cyan)'.
Color coding with line-sequential array (a) and G using'G (green), 'Ye', and'Cy 'color filters
Color coding with mosaic, Ye, Cy line sequential array (b) is conceivable. In this embodiment, as the color filter array of the color filter array 2, the Ye mosaic, Mg, Cy line-sequential type shown in FIG. 3A is used. From the solid-state imaging device 1 in which the color filter array 2 is arranged, two outputs Ye ₁ and Ye ₂ are obtained for the color filter'Ye 'with respect to the unit lattice, so four color signal outputs corresponding to the colors of the respective color filters are obtained. That is, the output Mg, the output Ye ₁ , the output Ye ₂ and the output Cy are respectively derived. The four color signal outputs are supplied to the luminance signal synthesizing circuit 3 and the primary color separating circuit 4, and of the four color signal outputs, the color signal outputs Y of two pixels arranged in a mosaic pattern.
e ₁ and Ye ₂ are supplied to the color false signal suppression control circuit 5.

The luminance signal synthesizing circuit 3 obtains a luminance signal Y by synthesizing the four outputs of the solid-state image pickup device 1. The luminance signal Y is γ-corrected by the γ-correction circuit 6 and becomes one input of the adder 7. The primary color separation circuit 4 is for separating the three primary color signals of R (red), G (green) and B (blue) from the respective color signals of three colors of Ye, Cy and Mg. The R, G, B three primary color signals separated by the primary color separation circuit 4 are
It is supplied to the color difference matrix circuit 10 via the white balance amplifiers 8R, 8G, 8B and the γ correction circuits 9R, 9G, 9B, respectively. The color difference matrix circuit 12 generates color difference signals (RY) and (BY) in the color television format based on the three primary color signals. The color difference signals (RY) and (BY) are added to each other by the adder 13 after passing through the 3.58 MHz quadrature two-phase modulators 11 and 12, and are supplied to the variable gain amplifier 14.

In the color false signal suppression control circuit 5, the color signal outputs Ye _{1 of} two pixels arranged in a mosaic pattern,
Ye ₂ is directly applied to the horizontal / vertical high frequency signal detection circuit 15 and further 1H (H is a horizontal scanning period) delay lines 16 and 17.
Is supplied via. In FIG. 2, when the pixel pitch in the horizontal direction is Px and the pixel pitch in the vertical direction is Py, the horizontal / vertical high frequency signal detection circuit 15 outputs the color signal outputs Ye ₁ and Y 2.
The horizontal high frequency signal component (center frequency 1/2 Px) and the vertical high frequency signal component (center frequency 1/2 Py) are detected based on the 1H delay signal of each e ₂ and the original signal before delay. That is, in FIG. 4, for example, the detection of the vertical high-frequency signal component V _{H (n + 1)} of (n + 1) rows is performed by V _{H (n + 1)} = Ye _{2 (n + 1)} − (Ye _{1 ( n)} + Ye _{1 (n + 2)} ) / 2. Further, for example, the horizontal high frequency signal component H _{H (m + 1)} of the (m + 1) column is detected by H _{H (m + 1)} = Ye _{2 (m + 1)} − (Ye _{1 (m)} + Ye _{1 (m + 2)} ) / 2.

The horizontal and vertical high frequency signal components H _{H and} V _H thus detected are converted into absolute values by absolute value circuits 18 and 19, respectively, and further passed through variable gain amplifiers 20 and 21, and then a post-adder 22. Are added together. The addition output of the adder 22 becomes the gain control signal of the variable gain amplifier 14 through the slice control circuit 23. In the variable gain amplifier 14, gain control is performed according to the signal levels of the horizontal and vertical high frequency band signal components H _{H and} V _H so that the gain of the color difference signal is lowered when the signal level is high. The gain-controlled color difference signal becomes the other input of the adder 7, is added to the luminance signal Y which is one input of the adder 7, and is output as a video signal.

As described above, the horizontal high frequency signal component (center frequency 1/2 Px) and the vertical high frequency signal component (center frequency 1) are generated based on the color signal outputs Ye ₁ and Ye ₂ of the two pixels arranged in a mosaic pattern. By detecting (/ 2Py) and controlling the color difference signal level according to these signal levels, it is possible to suppress the false color signal generated when the horizontal high frequency signal component or the vertical high frequency signal component is incident.

In the above embodiment, the case where the color filter array of the color filter array 2 is mosaic line sequential coding (see FIG. 2) has been described. However, stripe line sequential coding as shown in FIG. It is also possible that Specifically, as shown in FIG.
Color coding using the Ye stripe, Mg, Cy line sequential arrangement (a) and color coding using the G stripe, Ye, Cy line sequential arrangement (b) are conceivable. In the case of the stripe line sequential color coding, since the horizontal high frequency signal component (center frequency 1 / 2Px) cannot be detected, only the vertical high frequency signal component (center frequency 1 / 2Py) is used for the vertical high frequency signal component. It suffices to suppress the color false signal at the time of input.

In the above embodiment, the gain of the color difference signal is controlled by controlling the gain of the variable gain amplifier 14 that amplifies the color difference signal. However, the place where the gain control is performed is separated into three primary color signals. It is possible to suppress the color false signal by finally controlling the gain of the color difference signal based on at least one of the horizontal high frequency signal component and the vertical high frequency signal component.

[0015]

As described above, in the color signal processing circuit according to the present invention, the three primary color signals are separated from the color signals of the four pixels of the unit grid and converted into color difference signals, while the four color signals of the unit grid are converted. At least one of the horizontal high frequency signal component and the vertical high frequency signal component is detected based on the color signals of the two pixels having the same spectral sensitivity characteristic among the color signals of the pixel, and the gain of the color difference signal is determined according to the signal level. Since the control is performed, there is an effect that a color false signal generated near the Nyquist frequency when a horizontal high frequency signal component or a vertical high frequency signal component is incident can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a color signal processing circuit according to the present invention.

FIG. 2 is a diagram showing a general form of mosaic line-sequential coding of horizontal 2-repeat and vertical 2-repeat color filters.

FIG. 3 is a diagram showing a specific example of the coding in FIG. 2, in which (a) shows Ye mosaic, Mg, Cy line sequential coding, and (b) shows G mosaic, Ye, Cy line sequential coding.

FIG. 4 is a diagram showing a part of the configuration of a color filter array when the coding shown in FIG. 3 (a) is used.

FIG. 5 is a diagram showing a general form of stripe line sequential coding of a horizontal 2-repeat color filter and a vertical 2-repeat color filter.

6 is a diagram showing a specific example of the coding of FIG.
(A) shows Ye stripe, Mg, Cy line sequential coding, (b) shows G stripe, Ye, Cy line sequential coding.

FIG. 7 is a horizontal spatial frequency-vertical spatial frequency characteristic diagram showing a frequency of an input signal in which a strong color false signal is generated.

[Explanation of symbols]

 1 Solid-state image sensor 2 Color filter array 3 Luminance signal composition circuit 4 Primary color separation circuit 5 Color false signal suppression control circuit 8R, 8G, 8B White balance amplifier 9R, 9G, 9B γ correction circuit 10 Color difference matrix circuit 14, 20, 21 Variable Gain amplifier 15 Horizontal / vertical high frequency signal detection circuit

Claims (1)

[Claims] 1. A solid-state image sensor capable of independently reading out image information of all pixels, and a basic lattice formed by repeating two pixels in each of horizontal and vertical directions. The unit lattice has the same spectral sensitivity characteristic. A single-chip color camera comprising a color filter array arranged on the solid-state image sensor having a color array having two pixels, wherein four pixels of the unit lattice obtained from an output signal of the solid-state image sensor. Primary color separation means for separating three primary color signals from each color signal, color difference conversion means for converting the three primary color signals into color difference signals, and two pixels having the same spectral sensitivity characteristic among the color signals of the four pixels of the unit grid. A high-frequency signal detecting means for detecting at least one of a horizontal high-frequency signal component and a vertical high-frequency signal component based on each color signal and outputting a control signal corresponding to the signal level, Color signal processing circuit, characterized in that Flip and adapted to control the gain of said color difference signals.