JPS58195390A - Color television camera - Google Patents

Abstract

PURPOSE:To improve the color reproducibility due to the difference of lightness of red signal, by using a matrix circuit and decreasing the deterioration in the S/N ratio of a luminance signal. CONSTITUTION:A red signal is separated at an addition circuit 20 from a high frequency signal extracted at a BPF17 by using a 1HDL19 and utilizing the correlation of signals at two horizontal scanning periods, a blue signal is separated at a subtraction circuit 21, the red and blue signals are detected at detection circuits 22, 23, they are converted into a low frequency signal at a narrow band LPF. The low frequency signal is subtracted from a low frequency signal outputted from an image pickup tube through an LPF26 having the same band as said LPF at subtraction circuit 24, 25 to form color difference signals R-Y and B-Y. The R-Y signal between the color difference signals is clipped at a clip circuit 27 for the negative signal, to form a positive signal, i.e., the red signal only, a low frequency signal separated and outputted at an LPF18 is subtracted from the red signal at a subtraction circuit 28, a luminance signal is formed, said carrier chrominance signal and the synchronizing signal are summed at an addition circuit 29 to form an NTSC signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to improve the color reproducibility of a single-tube camera using a color stripe filter, especially a color television camera using a single frequency separation method. Among the three elements of brightness and brightness, the purpose is to approximate the brightness, that is, the characteristics of the brightness signal in the NTSC system, to ideal characteristics with less deterioration of the S/N ratio.

FIG. 1 shows a general signal processing block in a single frequency separation type color television camera. The operation of each block is briefly explained as follows.

The signal current output from the image pickup tube 1 is amplified by a preamplifier 2, spatially modulated by a color stripe filter placed on the face plate of the image pickup tube, and then subjected to bandpass filtering of photoelectrically converted high frequency components. The low-frequency components separated by a wave filter (hereinafter referred to as B, P, and F) 3 and photoelectrically converted without undergoing spatial modulation by the color stripe filter are passed through a low-pass filter (hereinafter referred to as P and F). (abbreviated) 4 and is used as a luminance signal.

The high frequency components separated by the B, P, and F 3 are sent to an adder circuit 7 and a subtracter circuit using a one horizontal scanning period delay line (hereinafter abbreviated as 1HDL) 6 and utilizing signal correlation between two horizontal scanning periods. 8, it is separated into red and green signals. The separated signals are detected by detectors 9 and 10, and narrow band beams, P,
After passing through F, L#PeF with the same frequency band
The luminance signal added through 5 is subtracted by subtracting circuits 11 and 12 to produce a color difference signal, which is converted into a carrier color signal by a modulator 13. The luminance signal and the synchronization signal are added together by an adder circuit 14 to produce an NTSC output signal. ing.

The color stripe filter of such a single frequency separation type color television camera generally has a configuration as shown in FIG. In Figure 2, ye is a yellow transmission filter, Cy hasian transmission filter, W is a transparent filter, and in the n-th horizontal scanning period, a green transmission part where yellow and cyan overlap, and a transparent part where transparent and transparent overlap. are arranged continuously, and the output signal from the image pickup tube when white light is incident is S[nH
)"G+ (R+B)'+R+, = ωt+Bs1n
It becomes ωt.

\Next, in the (n+'1.)th horizontal scanning period, a 1-yellow transparent area where yellow and transparent overlap, and a cyan transparent area where cyan and transparent overlap are consecutively arranged. 1 from the image pickup tube when white light is incident. If, the force signal is S(n+1)H=G+-z(R+B)+Rs
i. (ωt+90°) + Bs1n (ωt −90
0). In addition, the cyan and yellow spectral characteristics of a color stripe filter generally have the characteristics shown in Figure 3, and the spectral characteristics of this filter, the spectral sensitivity characteristics of the image pickup tube, and the infrared cut filter are similar. The overall characteristics determine the characteristics of the signal output from the image pickup tube. As mentioned above, this type of color television camera uses a low frequency signal component photoelectrically converted without undergoing spatial modulation by a color stripe filter as a luminance signal, so the luminance signal is YH= G17 (R-1-B
), which is the ideal characteristic of NTSC YH=
0.59G-4-0,3OR+o,11B, the ratios of green, let, and blue are different, and the characteristics of the three primary color signals are the S/N A of the luminance signal and color signal in the color streak filter. In order to improve □, a complementary color filter with high transmittance is used, so it has ideal characteristics 1.

Due to reasons such as the fact that
As shown in Figure 1, the characteristics of the luminance signal differ from the ideal characteristics of NTSC. When such a luminance signal is used, for example, when reproducing red colors on the long wavelength side, the brightness increases and becomes a whitish red, resulting in the drawback that subtle color differences due to brightness differences are not expressed. Similar results occur for signals on the short wavelength side, but human visual sensitivity characteristics are less sensitive to short wavelength/long side blues than red, so they are more acceptable than red color reproduction. As a means of bringing the spectral sensitivity characteristics of such a luminance signal close to ideal characteristics, the high frequency signal that has been photoelectrically converted after being spatially modulated by a color stripe filter is separated, and the low frequency red and blue signals are processed by a signal processing circuit. A method has been considered to obtain a luminance signal by matrixing the low-frequency signal output from the image pickup tube with the light and blue signal after forming the signal, but the S/N ratio of the luminance signal is significantly reduced due to the signal matrix. This deterioration leads to the disadvantage that the purpose of increasing the sensitivity of a color television camera by using a complementary color filter as a color stripe filter is defeated.

It has a matrix circuit that improves the color reproducibility of red signals by approximating the spectral sensitivity characteristics to the ideal characteristics using a method that does not cause practical problems on the screen due to deterioration of the S/N ratio of the luminance signal due to the signal matrix. The configuration of the present invention is shown in FIG.

The signal output from the image pickup tube 16 is amplified by the preamplifier 16, then spatially modulated by a color stripe filter as in the conventional example, and then photoelectrically converted by the image pickup tube, and the high frequency components are converted into B-. At F17, the low frequency component photoelectrically converted in the image pickup tube without being subjected to the spatial island tone by the color strip drive filter is separated at L, P and F1a, respectively.

The high frequency signal taken out at B@PJ17 is I HDL
Using the correlation between the signals in two horizontal scanning periods using the signal l9, the adder circuit 20 separates the red signal and the subtractor circuit 21 separates the red signal into a blue signal. These red and blue signals are detected by the detection circuit 22゜23
The waves are detected at the respective narrowband gates P and F, and converted into low frequency signals through the narrowband signals P and F, and the subtraction circuits 24 and 26 generate the L fist P*F having the same band as P−F.
The color difference signals R-Y and B-Y are generated by subtracting the low frequency signal output from the image pickup tube that has passed through 26. This 2
The two color difference signals are modulated by a modulator 30 and added to form a carrier color signal. Also, for one of the two color difference signals, the R---Y signal, a clipping circuit 27 clips the negative direction signal to produce only a positive direction signal, that is, a red signal. The red signal obtained in this way is subtracted from the above-mentioned low frequency signal separated and outputted to the P-F 18 by a subtraction circuit 28 to produce a luminance signal, and the carrier color signal and synchronization signal are added to an addition circuit 29. The configuration is such that the signals are added together to form an NTSC signal.

Changes in luminance characteristics when using the matrix circuit according to the present invention are shown in the shaded area in FIG.

In FIG. 4, M is an ideal characteristic, and B is a characteristic of a conventional example.

The spectral sensitivity characteristics shown in Figure 6 represent a red signal, but
The shaded portion of the luminance signal characteristic corresponds to this red signal. In other words, in terms of spectral characteristics, the matrix circuit of the present invention has a shape that approximates the ideal characteristics by reducing the red signal component in the luminance signal, similar to the previous example, but for matrix circuits When creating a red signal, a color difference signal is used, so there is no red signal for the matrix in an achromatic signal, so the S/N of the luminance signal is
The matrix circuit works only when the luminance signal corresponds to a chromatic color signal (red signal), reducing the ratio of the red signal in the luminance signal to approximate the ideal luminance signal. . In this way, the color reproduction characteristics of red signals are improved from those due to brightness differences, and the deterioration of the S/N ratio of luminance signals due to the signal matrix occurs only when photographing chromatic objects (red lights only), but generally speaking In a color ten vision camera using a single frequency separation method like the present invention,
Since the S/N ratio of the color signal is worse than the S/N ratio of the luminance signal, even if the S/N ratio of the luminance signal corresponding to the red subject image deteriorates due to the matrix, the output image is It has the advantage of being difficult to detect, and since no matrix is used for achromatic objects, the S/N of the luminance signal is low.
The ratio remains unchanged.・ ：：・1゜・More than −+ of the present invention! When creating one luminance signal using the J, p 2 circuit and improving color reproducibility, select the half value of the infrared cut filter mentioned above to be on the longer wavelength side than the ideal value, and reduce the luminance signal and red signal. S
/N ratio can be improved. As explained earlier, when choosing half the value of conventional infrared cut filters, the ratio of the red signal component in the luminance signal is almost always NTS.
The brightness signal was selected in such a way as to prevent the red signal from increasing away from its ideal value and causing poor reproducibility of the red signal (brightness increases too much), but the matrix circuit of the present invention makes it easy to correct the brightness signal. This is for the purpose of

Although the matrix circuit described above is not shown in this configuration example, it can perform similar correction for blue signals, and can also be used in color television cameras that use color stripe filters to obtain luminance signals and color difference signals in the same way. ,
It goes without saying that it can also be used, for example, in a two-frequency separation method.

As described above, according to the present invention, it is possible to reduce the deterioration of the S/N ratio of the luminance signal and improve the color reproducibility due to the brightness difference of the red signal.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional color television camera, Figure 2 is a principle diagram of a color stripe filter in a single frequency separation method, Figure 3 is a spectral characteristic diagram of a same color stripe filter, and Figure 4 is a luminance signal. FIG. 6 is a block diagram of a color ten vision camera according to an embodiment of the present invention, and FIG. 6 is a spectral sensitivity characteristic diagram of a red light. 16...Image tube, 17...B-P・F
119...1HDL, 18.26...Mark L...
P@F, 22, 23, river...detection circuit, 24, 25.2
8... Subtraction circuit, 27... Clip circuit, 29... Addition circuit, 3o... Modulator.

Claims (1)

[Claims] It is created by adding or subtracting two color signals obtained from a high-frequency signal that is spatially modulated using a color stripe filter and converted into an electrical signal by an image pickup tube, and another color signal obtained from a low-frequency signal. A color television camera characterized in that a brightness signal is created by adding or subtracting the red and blue signals obtained by suppressing the positive or negative direction of the two color difference signals and the low frequency signal.