JPH02253790A - Color television transmission luminance signal correction circuit - Google Patents

Abstract

PURPOSE:To suitably complement the deficiency of luminance signal component by constituting plural HPFs for a deficient luminance signal component by I' (luminance signal) and Q' signal filter characteristics. CONSTITUTION:The correction of gamma'=0.45 corresponding to a television receiver tube is loaded to a linear luminance signal Y by a correction gamma circuit 11 and the signal Y is synthesized and subtracted with a luminance signal Y', for which the gamma correction is executed from a first matrix circuit 4 by a substracting circuit 6. Then, the signal is successively passed through plural HPFs 14 and 15, which are respectively correspondent, and high frequency amplifiers 15 and 17, to which cascade connection is respectively executed and supplied to a correction adder circuit 16 so that a reduced luminance signal to be corrected and added in each area. The high frequency amplifier 15 and 17 adjusts the amplitude of each passing signal to the passing signal of a correction filter characteristic and the amplitude characteristic of LPFs 7 and 8 in an interruption frequency is made coincident and defined as an optimum luminance signal component Y'.

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 brightness signal correction circuit in the NTSCrj system.

(Prior Art) In the NTSC color television broadcast system, a gamma correction circuit provided on the image sending side is configured to reproduce faithful colors on the receiving side.

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

That is, the image from the object is supplied via the camera lens to a color separation circuit 1 using a dichroic mirror or the like;
It is separated into primary colors R (red), G (green), and B (blue) and converted into electrical signals by each image sensor 2R, 2G, and 2B.

The output of each @image element 2R, 2G, 2B is supplied to a first gamma correction circuit 3R, 3G, 3B consisting of a process amplifier, and for example, a gamma correction signal R' of T' (=1/γ)=0.45, G' and B' are derived.

These gamma-corrected signals are supplied to the first matrix circuit 4, where the luminance signal Y', I signal 1', Q signal @Q'
are converted and derived respectively. Further, among these gamma-corrected signals, the luminance signal Y' is branched and supplied to the addition circuit 5 and the subtraction circuit 6, and
' are supplied to LPFs (low pass filters) 7 and 8 whose passbands are 0 to 1.5 Hz and Q-, -0.5 Hz, respectively. The signals @I' and Q' that have passed through the LPF 7.8 are combined with the luminance signal Y' that has been modulated by the subcarrier and the luminance signal Y' that has passed through the adder circuit 5, and is transmitted as an NTSC signal.

In the above NTS, C signals, the I signal 1' and the Q signal Q' after gamma correction originally contain a luminance component Y'.

Furthermore, by passing each of these signals through each LPF7.8, the luminance components in the high frequency region included in I' and Q' are blocked, so the television signal contains the luminance components corresponding to the blocked luminance components. A compensation circuit is added to compensate.

That is, as this compensation circuit, gamma correction circuits 3R, 3G
, 3B respectively correspond to the corresponding inverse gamma (γ
= 2.2) Supplied to correction circuits 9R, 9G, 9B,
The original three primary color signals R, G, B are derived. These 3
The primary color signals R, G, and B are supplied to the second matrix circuit 1°, and a linear luminance signal Y expressed by the following equation is generated.

Y=O13R+0.59G+0.11B
(1) This linear luminance signal Y is subjected to a correction (YO·45) of γ' = 0.45 corresponding to γ-2,2 on the picture tube side in the correction gamma circuit 11, and then in the subtraction circuit 6 to the first matrix It is compared with and subtracted from the gamma-corrected luminance signal Y' from circuit 4. The difference signal (YO・”'-
Y') represents the luminance signal component included in 1' and Q', but since it includes a region (0-0,5Hi1z) that passes through at least in common with the signals of 1' and Q', This is to add and correct signal components in the frequency domain excluding the pass region, that is, 0.5) IHz or higher to the luminance signal.

Therefore, the difference signal (YO-45-Y') is 0.5Hz
The signal is sequentially supplied to the adder circuit 5 via the H P F 12 having a cutoff frequency of , and the high frequency amplifier 13 for adjusting the fixed amplitude, and the insufficient luminance signal component in the one-time signal @Y/ is corrected.

However, in such a conventional color television transmission brightness signal correction circuit, the HPF 12 is configured to correct the signal from the subtraction circuit 6 for a band of 0.58B2 or more. In LPF7,
Since the luminance signal components in the intermediate range exceeding 0.5 Hz and in the range of 0.5 to 1.5 Hz are not blocked in any way and are transmitted as they are in the NTSC signal, the 0.5 to 1.5 Hz range is transmitted as is. Luminance signals in the 5H11z range were overcompensated, hindering faithful color reproduction. This has resulted in the drawback that the contours of the reproduced object image and the highly detectable characters, such as characters of different colors, are not clear.

Also, in order to avoid this, if the cutoff frequency of I-IPF12 is changed to 1°5H1lz, conversely O45~1.5M1
The lZ range was the main star of the luminance signal, and proper color reproduction could not be obtained as well.

(Problems to be Solved by the Invention) In the conventional color television transmission brightness signal correction circuit,
Since the signal components corrected into the gamma-corrected luminance signal did not necessarily correspond accurately to the frequency characteristics of the gamma-corrected I and Q signals, the correct luminance signal over a wide frequency range was not obtained on the receiving screen. However, there was a drawback that distortion occurred in the reproduced color signal.

Therefore, this invention provides 1. of gamma correction. It is an object of the present invention 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 each Q signal.

[Structure of the Invention] (Means for Solving the Problems) A color television transmission luminance signal correction circuit according to the present invention includes a first gamma correction circuit that gamma-corrects each color signal from an image sensor, and a first gamma correction circuit that gamma-corrects each color signal from an image sensor; A first matrix circuit that converts and derives each gamma-corrected color signal into a luminance signal and I, Q signals, and a plurality of low frequency bands into which the gamma-corrected 1 signal and Q signal from the first matrix circuit are respectively introduced. A pass filter, a subtraction circuit and an addition circuit to which the luminance signal from the first matrix circuit is branched and supplied, respectively, and inverse gamma correction to which each color signal from the first gamma correction circuit is introduced and converted into the original color signal. a second matrix circuit that introduces a signal from the inverse gamma correction circuit to derive a linear luminance signal; and a second gamma circuit that gamma-corrects the linear luminance signal from the second matrix circuit and supplies it to the anti-pruritic circuit. a correction circuit; and a plurality of high-pass filters that respectively introduce difference signals between the luminance signal and the linear luminance signal from the subtraction circuit and supply them to the addition circuit, and the plurality of high-pass filters perform synthesis. The obtained filter characteristic is characterized in that it has substantially a composite filter characteristic in which each cut-off region of the plurality of low-pass filters is a pass region.

(Function) In order to obtain a correction signal, the color television transmission brightness signal correction circuit according to the present invention passes through each cutoff area of the low-pass filter that determines the transmission band of each gamma-corrected I and Q signal. A difference signal between a gamma correction signal and a linear gamma correction signal is passed through a plurality of high-pass filters having a synthesis filter characteristic.

Therefore, since it is a high-pass filter with multiple configurations, it is possible to configure filter characteristics for correction corresponding to two LPFs,
For example, it is possible to provide a plurality of filter characteristics of 0.5 MHz or higher and 1.58 H2 or higher.

From this, it is possible to create a configuration that is directly adapted to the high-pass filter corresponding to the frequency characteristics of each of the two LPFs, so a corrected brightness signal that can faithfully compensate for the insufficient signal component in the cut-off frequency characteristics of the LPF can be created. can be derived.

(Embodiment) Hereinafter, an embodiment of the color television transmission brightness correction circuit according to the present invention will be described in detail with reference to the drawings. Components that are the same as those shown in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

That is, the image from the object is passed through the lens to the color separation circuit 1.
(changed) is converted into an electrical signal by each image sensor 2R, 2G, 2B.Each image sensor 2R, 2G, 2B
The output of is supplied to the first gamma correction circuits 3R, 3G, and 3B, and the gamma correction signal @R' after correction with γ' = 0.45.
eG'B' is derived.

These gamma-corrected signals are sent to the first matrix circuit 4 as a luminance signal Y', a signal I', and a Q signal Q.'
are converted and derived respectively.

The luminance signal Y' is branched and supplied to the addition circuit 6 and the subtraction circuit 7, and the 1 signal 1' and the Q signal Q' are
~1.5 MHz and O~0.5) It is supplied to LPFs 7 and 8 with a pass band of IH2, is modulated by a subcarrier, is combined with the luminance signal, and is derived as an NTSC signal. In the NTSC signal, ■signal I' and Q signal Q'
originally includes the luminance component Y' as mentioned above, but
By passing through each LPF 7, 8, luminance components in a high frequency region are blocked. Therefore, in order to compensate for these blocked luminance components, first, gamma correction circuits 3R, 3G, 3
The inverse comma correction circuit 9R, to which the output signal from B corresponds,
9G and 9B, each undergoes gamma correction of γ (=2.2), and the original three primary color signals R, G, and B are derived. These three primary color signals R, G, and B are supplied to the second matrix circuit 10, and a linear luminance signal Y expressed by the above equation (1) is generated 1q.

Here, the correction gamma circuit 11 applies a correction of γ' = 0.45 corresponding to the picture tube to the linear luminance signal @Y, and the subtraction circuit 6 applies the gamma-corrected luminance signal from the first matrix circuit 4. It is combined and subtracted with Y'. The difference signal (YO・"-Y') resulting from this subtraction includes areas (O~O, 5) IH2) and (O~
1.5MH2), so in order to correct and add the reduced luminance signals of each area, a plurality of corresponding one
-(pH 4, 15 and the high frequency amplifiers 16 and 17 connected in cascade to these, respectively, are sequentially supplied to the correction and addition circuit 16.

As shown in FIGS. 2 and 3, HP F1a and 15 each have filter characteristics that correspond to the filter frequency characteristics of 1PF7.8 and complement the luminance frequency band that is insufficient with LPF7.8. be. As a result,
In the correction and addition circuit 18, these filter outputs are combined, so that a combined filter characteristic as shown in FIG. 4 is obtained.

Furthermore, the high frequency amplifiers 15 and 17 adjust the amplitude of each passing signal with the corrected filter characteristics shown in FIGS. 2 and 3 to match the approximate width characteristics at the cutoff frequencies of the LPFs 7 and 8. , which can be made into the optimal luminance signal component Y'.

As described above, the color television transmission brightness signal correction circuit according to the present invention is capable of correcting narrow bands I' and Q of an NTSC signal.
Since the luminance signal component lacking in the 'signal is appropriately supplemented as it is, on the receiving side, it is possible to produce 1q of good images with clear and faithful color reproduction.

[Effects of the Invention] The color television transmission brightness signal correction circuit according to the present invention corrects the brightness signal components that are insufficient due to the 1' and Q' signal filter characteristics by configuring a plurality of HPFs. As a result, the color tone of the subject image captured on the image sending side can be transmitted as is to the image receiving side.Special feature 1: It is highly effective when adopted in the NTSC system.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a color preview transmission brightness signal correction circuit according to the present invention, and FIGS.
The figures are a frequency characteristic diagram showing the I-I P characteristics of one circuit shown in Fig. 1, and Fig. 4 is a frequency characteristic diagram showing the I-I P characteristic of the circuit shown in Fig. 1.
FIG. 5 is a circuit diagram showing a conventional color television transmission luminance signal correction circuit. 1... Color separation circuit 2R, 2G, 2B... Image pickup device 3R, 3G, 3T... First gamma correction circuit 4... First matrix circuit 5... Addition circuit 6... Subtraction Circuit 7.8...9R, 9G, 9B...inverse gamma correction circuit 10...in LP...
Second matrix circuit 11...Second gamma correction circuit 1416...HPF 1.8...Correction addition circuit Figure 4 Agent Patent attorney Norihiro Ogo No. 5 r! A

Claims (1)

[Claims] a first gamma correction circuit that gamma-corrects each color signal from the image sensor; a first matrix circuit that converts and derives each gamma-corrected color signal from this gamma correction circuit into a luminance signal and I and Q signals; a plurality of low-pass filters into which gamma-corrected I and Q signals from the first matrix circuit are respectively introduced, and a subtraction circuit and an addition circuit into which the luminance signal from the first matrix circuit is branched and respectively supplied; an inverse gamma correction circuit into which each color signal from the first gamma correction circuit is introduced and converted into the original color signal; a second matrix circuit into which the signal from the inverse gamma correction circuit is introduced and derives a linear luminance signal; A second gamma correction circuit gamma-corrects the linear luminance signal from the second matrix circuit and supplies it to the subtraction circuit; and a second gamma correction circuit that inputs a difference signal between the luminance signal and the linear luminance signal from the subtraction circuit to the addition circuit. The filter characteristic synthesized by the plurality of high-pass filters is approximately the synthesized filter characteristic with each cut-off region of the plurality of low-pass filters as a pass region. A color television transmission brightness signal correction circuit comprising: