JPS61227490A - Method for reducing false color signal in color video camera - Google Patents

Abstract

PURPOSE:To decrease the secondary effect on a color signal by separating a false signal component included in a color signal and decreasing the false component. CONSTITUTION:Output signals (b, c) corresponding to filters E, F when a strip- shaped object comprising a light part and a dark part comes to a position shown in a figure A are fed to input terminals 10, 11, the signal (c) is delayed by a delay circuit 12 to match the phase, and a difference signal is formed by a subtraction circuit 13, then a false color signal shown in the hatched part in a figure D appears at the edge of the picture. A clip circuit 14 eliminates a negative false signal (E4-F4), a sample-and-hold circuit 15 and a low-pass filter circuit 16 extract the low frequency component to obtain a signal E'. The signal whose phase is matched by a delay circuit 17 is subjected to clip for a signal higher than the signal level shown in E' by a clip circuit 18 to obtain a signal F'. A positive false signal portion (E2-F2) is eliminated from the signal F' and a color signal with less false signal is obtained through a low-pass filter 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color video camera, and more particularly to a method for reducing false color signals occurring at the bright and dark edges of an imaging screen.

[Background of the invention]

In a single-chip color video camera using a solid-state image sensor, which has become popular in recent years, a mosaic color separation filter as shown in FIG. 1, for example, is arranged on each pixel of the solid-state image sensor. A solid-state image sensor scans the signals of each pixel arranged on the light receiving surface using pulses applied from the outside and outputs them in an orderly manner. For example, in the case of an image sensor that can read two lines at the same time, as shown in FIG. 2, white (W) is displayed during one horizontal scan.

Cyan (CY), white, cyan,... and yellow (Ye)
.

Two lines of signals: white, yellow, white, etc. are read out at the same time.

The luminance signal, red (R), and blue (B) signals necessary to obtain the NTSC composite color signal are obtained from these two lines of signals.
reproduces the signal by calculating W-Ye.

However, when reproducing signals using such calculations, if the bright and dark edges of the subject are located between the W and Cy, or W and Ye filters, as shown in Figure 3, false colors that are not present in the subject may be generated. A signal is generated.

Degrades image quality.

For this reason, color video cameras that use mosaic filters, which have been commonly used in the past, use a color signal canceling circuit that attenuates color signals using the edge signals of the subject.

FIG. 4 shows an example of a conventionally used false color erasing circuit.

1 is a subtraction circuit, which is a circuit for detecting edges of an image. A wideband video signal A and a narrowband video signal B are applied to this subtraction circuit 1, and an edge signal is detected by taking the difference between A and B.

The edge signal extracted in this manner is applied to a false color signal suppression circuit 3 via a low-pass filter 2. A modulated chroma signal C of 3.58 MHz is applied to the false color signal suppression circuit 3, and the amplitude of C is modulated according to the amplitude of the edge signal. As a result, in the portion where the edge signal exists, the chroma signal is suppressed and the saturation is reduced.

This method of suppressing false color signals suppresses all color information near the edges, so depending on the subject, it may appear unnatural.
This will lead to image quality deterioration.

[Purpose of the invention]

An object of the present invention is to provide a false color signal reduction method that causes fewer side effects on color signals by separating and reducing false signal components contained in color signals.

[Summary of the invention]

A solid-state camera using complementary color filters calculates color signals from signals corresponding to two types of color filters. As a result, negative color signals that do not actually exist may be generated at edge portions of one image. In the present invention, false color signals are reduced by detecting and deleting such abnormal portions. .

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 6 shows an example circuit that satisfies the gist of the present invention. FIG. 5 is a diagram for explaining the mechanism of false color signal generation, and the operation of the circuit in FIG. 6 will be explained using this diagram.

Figure 5 (a) is a diagram in which only one horizontal line of color filters is extracted, and E and F indicate two types of color filters that transmit different colored light components, and E transmits more polychromatic light than F. Assume that

Here, assuming that a strip-shaped object consisting of bright and dark areas is placed at the position shown in FIG. 5 (a), the output signals corresponding to filters E and F are (b).

Add the signals (B) and (C) to the input terminals 10 and 11 in Fig. 6, delay the signal (C) in the delay circuit 12, match the phases of E and F, and perform subtraction. When a difference signal between the two is generated in the circuit 13, the signal shown in FIG. 5(d) is changed.

In this way, a color video camera that uses a complementary color filter obtains a color signal by calculating two types of signals, but at the edge of the image, the false color signal shown in the shaded area in Figure 5 (d) is generated. Hail, which significantly degrades image quality.

The circuits shown at 14 to 19 in FIG. 6 eliminate or reduce this spurious signal. The circuit 14 is a circuit that clips a negative signal, and the function of this circuit is to generate a negative false signal, that is, as shown in FIG.
(d) Remove (E4-F4). On the other hand, a positive false signal (
Et-Fi) is connected to the adjacent signal (El-F) and (E, -F
3) To achieve a higher level, (F□−F□) and (
By deleting signals that exceed the average value of Es - F 3), positive false signal components can also be significantly reduced.

Sample hold circuit 15. Low pass filter circuit 16
is a circuit for extracting the low-frequency component of the output signal of the circuit 14, which converts a signal (FIG. 5(e)) close to the average value of adjacent pixels. The delay circuit 17 receives the output signal of the circuit 14 and the output signal of the circuit 1.
The signal whose phase has been matched with the output signal of the delay circuit 17 is sent to the clip circuit 1.
At step 8, the signal having a higher level than the signal level shown in FIG. 5 (e) is clipped to obtain the signal shown in (f). This signal (to) is the positive false signal part of the signal (d) (E yo - F,)
is removed, so by passing this signal through the one-pass filter 19, a color signal with less false signals can be obtained.

In addition, after the signal output terminal 20 in FIG. 6, there is a 15° 1-6.
By connecting the circuits of 17, 18, and 19 and performing the above signal manipulation again, positive false signals can be further reduced.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to efficiently reduce false color signals of a solid-state image sensor equipped with a complementary color filter, and therefore it is possible to eliminate image quality deterioration due to false signal removal.

[Brief explanation of drawings]

Figure 1 is a plan view showing an example of a mosaic color separation filter, Figure 2 is a diagram showing signals when two lines are read simultaneously, Figure 3 is an explanatory diagram showing the state of generation of false color signals, and Figure 4. 5 is a block diagram showing an example of a conventional false color signal erasing circuit, FIG. 5 is an explanatory diagram of a false color signal generation mechanism, and FIG. 6 is a block diagram showing an embodiment of the present invention. 12...Delay circuit, 13...Subtraction circuit, 14...
Clip circuit, 15... Sample hold circuit, 16
...Low pass filter, 17...Delay circuit, 18.
・・Chryso゛・、↓、・ 1st Figure 5 Old Sakazuki H-ko times] 11H Diagram H Correct H Co[R

Claims (1)

[Claims] A solid-state image pickup device in which a plurality of types of filter elements that pass light in different wavelength ranges is regularly arranged in row and column directions, and video signals corresponding to the plurality of color filter elements are output from the solid-state image pickup device. A color video camera equipped with a reading means and a signal processing circuit that processes the read video signal to obtain a color signal, which is compatible with at least two color filters among the plurality of types of color filters mentioned above. a first means for obtaining a difference signal of signals; a second means for cutting out a negative signal component of the difference signal; a third means for extracting a low frequency component of an output signal of the second means; A false color signal reduction method for a color video camera, characterized in that the color signal is demodulated using the output signal of the third means using a fourth means for deleting an unnecessary portion of the output signal of the second means.