JP2667496B2 - Color television transmission luminance signal correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an improvement of a color television transmission luminance signal correction circuit in the NTSC system.

(Prior Art) In the color television broadcasting system by NTSC,
The gamma correction circuit provided on the image sending side is configured so that faithful color reproduction is performed on the image receiving side.

FIG. 5 is a circuit diagram showing a conventional color television transmission luminance signal correction circuit.

That is, the image from the subject is supplied to the color separation circuit 1 such as a dichroic mirror via the lens of the camera.
Each image sensor separated into three primary colors R (red), G (green), and B (blue)
It is converted into an electric signal by 2R, 2G, 2B.

The outputs of the image sensors 2R, 2G, 2B are supplied to first gamma correction circuits 3R, 3G, 3B composed of process amplifiers, for example, γ ′
Gamma correction signals R ', G', B'of (= 1 / γ) = 0.45 are derived.

These gamma-corrected signals are supplied to the first matrix circuit 4, where they are converted into luminance signals Y ', I signals I', and Q signals Q ', respectively. Further, among these signals after the gamma correction, a luminance signal Y 'is branched and supplied to an addition circuit 5 and a subtraction circuit 6, and the I signal I' and the Q signal Q 'are 0-1.5 MHz and 0-1.5 MHz, respectively. 0.5MHz as pass band
It is supplied to LPFs (low-pass filters) 7,8. The signals I 'and Q' which have passed through the LPFs 7 and 8 are modulated by the subcarrier,
It is combined with the luminance signal Y'passed through the adder circuit 5 and transmitted as an NTSC signal.

In the NTSC signal, I signals I 'and Q after gamma correction
The signal Q 'originally contains the luminance component Y'.

Moreover, these signals pass through the LPFs 7 and 8,
Since a luminance component in a high frequency region included in I 'and Q' is cut off, a compensation circuit for compensating for the cut-off luminance component is added as a television signal.

That is, as this compensation circuit, gamma correction circuits 3R, 3G, 3B
Output signals from the corresponding inverse gammas (γ = 2.2)
It is supplied to the correction circuits 9R, 9G, 9B, and the original three primary color signals R, G,
B is derived. These three primary color signals R, G, B are supplied to the second matrix circuit 10 and are supplied to the linear luminance signal Y represented by the following equation.
Is obtained.

Y = 0.3R + 0.59G + 0.11B (1) The linear luminance signal Y is subjected to correction (Y ^0.45 ) of γ ′ = 0.45 corresponding to γ = 2.2 on the picture tube side by the correction gamma circuit 11, It is compared with the gamma-corrected luminance signal Y ′ from the first matrix circuit 4 and subtracted. The difference signal (Y ^0.45 −Y ′) by this subtraction is I ′ and Q ′
, The luminance signal components included in I ′ and Q ′
Area that passes at least in common to the signals of
Since z) is included, the frequency domain excluding the passband, that is, the signal component of 0.5 MHz or more is added to the luminance signal and corrected.

Therefore, the difference signal (Y ^0.45 -Y ') is the HPF 12 having a cutoff frequency of 0.5 MHz and the high frequency amplifier 13 for amplification adjustment.
Are sequentially supplied to the adder circuit 5, and the lacking luminance signal component in the luminance signal Y'is corrected.

However, in such a conventional color television transmission luminance signal correction circuit, the HPF 12 has a configuration in which a band of 0.5 MHz or more in the signal from the subtraction circuit 6 is corrected. Beyond 0.5MHz,
Since the luminance signal component in the middle region in the range of 0.5 to 1.5 MHz is transmitted as it is in the NTSC signal without any interruption, the luminance signal in the range of 0.5 to 1.5 MHz is excessively compensated. As a result, faithful color reproduction was hindered. For this reason, there has been a defect that the outline of the reproduced subject image and characters such as red with high accuracy are not clear.

To avoid this, set the cutoff frequency of HPF12 to 1.5
On the other hand, if the frequency is set to MHz, the range of 0.5 to 1.5 MHz has a shortage of the luminance signal, and similarly, an appropriate color reproduction cannot be obtained.

(Problems to be Solved by the Invention) In the conventional color television transmission luminance signal correction circuit, the signal component corrected to the gamma correction luminance signal does not always correspond exactly to the frequency characteristics of the gamma correction I and Q signals. However, there is a disadvantage that an appropriate luminance signal over a wide frequency range is not obtained on the image receiving screen, and the reproduced color signal is distorted.

Accordingly, an object of the present invention is to provide a color television transmission luminance signal correction circuit that can obtain a good reproduced image by forming a correction signal that is more faithful to the frequency characteristics of the I and Q signals of gamma correction. And

[Structure of the Invention] (Means for Solving the Problems) A color television transmission luminance signal correction circuit according to the present invention performs first gamma correction of each color signal from an image sensor.
A gamma correction circuit, a first matrix circuit for converting and deriving each gamma-corrected color signal from the gamma correction circuit into a luminance signal and I, Q signals, and a gamma-corrected I signal from the first matrix circuit; A plurality of low-pass filters into which the Q signals are respectively introduced, a subtraction circuit and an addition circuit into which the luminance signal from the first matrix circuit is branched and supplied, respectively, and each color signal from the first gamma correction circuit is introduced. An inverse gamma correction circuit for converting the original luminance signal into an original color signal, a second matrix circuit for introducing a signal from the inverse gamma correction circuit to derive a linear luminance signal, and a gamma correction for the linear luminance signal from the second matrix circuit A second gamma correction circuit to be supplied to the subtraction circuit; and a difference signal between the luminance signal and the linear luminance signal from the subtraction circuit. And a plurality of high-pass filters for supplying the filter characteristics, and a filter characteristic combined by the plurality of high-pass filters has a combined filter characteristic in which each cut-off region by the plurality of low-pass filters is a pass region. It is characterized by.

(Function) The color television transmission luminance signal correction circuit according to the present invention is configured to obtain a correction signal by passing each cutoff region of a low-pass filter that determines a transmission band of each of the gamma-corrected I and Q signals. A plurality of high-pass filters having the combined filter characteristics described above are provided, and a difference signal between the gamma correction signal and the linear gamma correction signal is passed through the high-pass filter having the plurality of configurations.

Therefore, since it is a high-pass filter having a plurality of configurations,
Compensation filter characteristics corresponding to two LPFs can be configured,
For example, a plurality of filter characteristics of 0.5 MHz or more and 1.5 MHz or more can be provided.

From this, it is possible to adopt a configuration directly adapted to a high-pass filter corresponding to the frequency characteristics of each of the two LPFs, so that a corrected luminance signal capable of faithfully compensating for the insufficient signal component in the cutoff frequency characteristics of the LPF is derived. be able to.

(Embodiment) An embodiment of a color television transmission luminance correction circuit according to the present invention will be described below in detail with reference to the drawings. In addition,
The same components as those shown in FIG. 5 are denoted by the same reference numerals, and detailed description will be omitted.

That is, an image from a subject is supplied to the color separation circuit 1 via a lens, and is then converted into an electric signal by each of the imaging devices 2R, 2G, and 2B. The outputs of the image sensors 2R, 2G, 2B are supplied to first gamma correction circuits 3R, 3G, 3B, and gamma correction signals R ', G', B 'after correction are derived at γ' = 0.45.

Each of these gamma-corrected signals is converted and derived by the first matrix circuit 4 into a luminance signal Y ', an I signal I', and a Q signal Q '.

The luminance signal Y 'is branched and supplied to an addition circuit 6 and a subtraction circuit 7, and the I signal I' and the Q signal Q 'are supplied to LPFs 7, 8 having pass bands of 0 to 1.5 MHz and 0 to 0.5 MHz, respectively. After being subjected to modulation by the subcarrier, it is combined with the luminance signal and derived as an NTSC signal. For NTSC signals,
Although the I signal I 'and the Q signal Q' originally contain the luminance component Y 'as described above, by passing through the LPFs 7 and 8,
The luminance component in the high frequency region is cut off. Therefore, in order to compensate for these blocked luminance components, first, the output signals from the gamma correction circuits 3R, 3G, 3B are supplied to the corresponding inverse gamma correction circuits 9R, 9G, 9B, and γ (= 2.2 ), The original three primary color signals R, G, B are derived. These three primary color signals R, G, B are supplied to the second matrix circuit 10, and the linear luminance signal Y represented by the above equation (1) is obtained.

Here, the linear luminance signal Y is subjected to correction of .gamma. '= 0.45 corresponding to the picture tube by the correction gamma circuit 11, and the subtraction circuit 6 combines and subtracts the gamma corrected luminance signal Y' from the first matrix circuit 4 with the luminance signal Y '. Is done. The difference signal (Y
^0.45 -Y ') includes the areas (0 to 0.5 MHz) and (0 to 1.5 MHz) transmitted as the luminance signals as they are, so that the reduced luminance signals in each area are corrected and added. The HPFs 14 and 15 are supplied to the correction addition circuit 16 via the high-frequency amplifiers 16 and 17 connected in cascade to the HPFs 14 and 15 respectively.

HPF14 and 15 are respectively, as shown in FIG. 2 and FIG. 3, respectively.
In correspondence with the filter frequency characteristics of the LPFs 7 and 8, these filter characteristics have a filter characteristic that complements the luminance frequency band deficient by the LPFs 7 and 8. As a result, these filter outputs are combined in the correction addition circuit 18, so that a combined filter characteristic as shown in FIG. 4 is obtained.

The high-frequency amplifiers 15 and 17 adjust the amplification of each passing signal with respect to the passing signals of the correction filter characteristics shown in FIGS. This can be an optimum luminance signal component Y '.

As described above, the color television transmission luminance signal correction circuit according to the present invention has the narrow band I'and Q'of the NTSC signal.
Since the luminance signal component that is insufficient due to the signal is appropriately complemented as it is, a good image with clear and faithful color reproduction can be obtained on the image receiving side.

[Effects of the Invention] The color television transmission luminance signal correction circuit according to the present invention can reduce the luminance signal components deficient due to the I 'and Q' signal filter characteristics by forming a plurality of HPFs, thereby making these deficiencies appropriate. As a result, the color tone of the subject image captured on the image transmitting side can be transmitted to the image receiving side as it is, and the effect is particularly large when adopted in the NTSC system.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a color television transmission luminance signal correction circuit according to the present invention, and FIGS.
The figures are frequency characteristic diagrams showing the HPF characteristics of the circuit shown in FIG. 1, respectively. FIG. 4 is the composite frequency characteristic diagram of the HPF of the circuit also shown in FIG. 1, and FIG. 5 is a conventional color television transmission luminance signal. FIG. 3 is a circuit diagram illustrating a correction circuit. 1 color separation circuit 2R, 2G, 2B image sensor 3R, 3G, 3B first gamma correction circuit 4 first matrix circuit 5 addition circuit 6 subtraction circuit 7, 8 LPF 9R, 9G, 9B: inverse gamma correction circuit 10: second matrix circuit 11: second gamma correction circuit 14, 16, HPF 18: correction addition circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Taizo Nishino 1 Komukai Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Komukai Plant (72) Inventor Masataka Shimada Masayuki Shimada Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa 1. In the Toshiba Komukai Plant (72) Inventor Junichi Yamanaka 1 In the Komukai Toshiba Town, Koyuki-ku, Kawasaki City, Kanagawa Prefecture 1 In the Toshiba Komukai Plant (56) References JP-A-57-99089 (JP, A) 1988-67889 (JP, A)

Claims (1)

(57) [Claims] 1. A first gamma correction circuit for gamma-correcting each color signal from an image sensor, and a first matrix for converting and deriving each gamma-corrected color signal from the gamma correction circuit into a luminance signal and I and Q signals. Circuit, a plurality of low-pass filters into which gamma-corrected I and Q signals from the first matrix circuit are respectively introduced, and subtraction circuits from which the luminance signal from the first matrix circuit is branched and supplied, respectively. And an adder circuit, an inverse gamma correction circuit for introducing each color signal from the first gamma correction circuit and converting it into an original color signal, and a second for introducing a signal from the inverse gamma correction circuit to derive a linear luminance signal. The matrix circuit and this second
A second gamma correction circuit for gamma-correcting the linear luminance signal from the matrix circuit and supplying the same to the subtraction circuit; and a difference signal between the luminance signal and the linear luminance signal from the subtraction circuit are introduced and supplied to the addition circuit. A plurality of high-pass filters, and a filter characteristic synthesized by the plurality of high-pass filters has a synthetic filter characteristic in which each cut-off region by the plurality of low-pass filters is a pass region. Color television transmission luminance signal correction circuit.