JP2000115583A - Gamma correction discriminating system for crt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically discriminate whether an inputted video signal has already been subjected to CRT gamma correction. SOLUTION: The inputted video signal is first converted to the digital signal of 8 bits by an AD converting circuit 18. The video signal converted to the digital signal like this is inputted to ROM 2 and the level of the video signal is coordinated with the address of a table housed in ROM. Thus, when the level of the signal is >=1 and <=20, the inputted video signal is discriminated to be a signal without receiving CRT gamma correction and the detected result signal is outputted from an output terminal 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for automatically determining whether an input video signal has been subjected to CRT gamma correction in a television receiver.

[0002]

2. Description of the Related Art The light emission characteristics of a CRT (cathode ray tube) of a television receiver are not proportional to the level of a video signal input to the CRT, but are proportional to the gamma power of the level. Therefore, conventionally,
When the transmitting side performs inverse characteristic processing of the light emission characteristic of the CRT such that the image signal is raised to the power of 1 / γ and transmits the image signal, the television receiver receives the image signal and reproduces the image on a CRT display. In addition, the light emission characteristic of the received video signal has a proportional relationship with that of the received video signal, so that the linearity of gradation at the time of displaying an image is maintained. Hereinafter, performing the inverse characteristic processing of the light emission characteristic of the CRT, such as raising the video signal to the power of 1 / γ, is referred to as CRT gamma correction processing.

[0003] Today, the evolution of displays is remarkable,
In addition to CRT displays, many large-screen, thin, and high-definition displays have appeared. The light emission characteristics of these displays are different from the light emission characteristics of a CRT display and have linearity. Therefore, in these displays, the CRT gamma correction processing applied to the video signal is unnecessary, and if the signal subjected to the CRT gamma correction processing is reproduced on such a display, the halftone level may be reduced to the original level. It floats more than the gradation and causes a great loss of contrast. Therefore, a CRT that gives a CRT gamma characteristic to a video signal obtained on the receiver side is used.
A process for returning to an image signal before the CRT gamma correction process is performed by performing a process reverse to the gamma correction process. Hereinafter, the process of returning the image signal subjected to the CRT gamma correction process to the image signal before the CRT gamma correction process is performed is referred to as CRT gamma correction return process.

In recent years, in order to transmit a large amount of information in a narrow frequency band, a transmission method of compressing a video signal to be transmitted has been actively used. In such a transmission system, since the encoding process and the decoding process are complicated, the transmitting side transmits a video signal having a linear characteristic without performing the CRT gamma correction process, and the receiving side decodes the received video signal. After that, the CRT gamma correction process is performed.

At this time, if the display for reproducing the video is a flat display other than the CRT display, the CRT gamma correction processing is unnecessary, so that
The CRT gamma correction process can be omitted. Also, since the video signal is a signal that has not been subjected to CRT gamma correction processing, CRT gamma correction return processing is not required.

[0006]

However, since the transmitted video signal is not unified to a signal that has not been subjected to the CRT gamma correction processing, the signal that has been subjected to the CRT gamma correction processing and the signal that has not been subjected to the CRT gamma correction processing have not been standardized. , The ON / OFF of the CRT gamma correction return process must be manually switched according to each signal.

An object of the present invention is to provide a CRT gamma correction determination system that can automatically determine whether an input video signal has been subjected to CRT gamma correction processing.

It is an object of the present invention to provide a CRT gamma correction discrimination system that can operate correctly even when noise is superimposed on the video signal.

The present invention provides a CR which can operate correctly even when an unnecessary DC component is superimposed on the video signal.
An object of the present invention is to provide a T gamma correction discrimination system.

[0010]

CRT according to claim 1
The gamma correction determination system determines whether or not the video signal is subjected to the CRT gamma correction process based on whether or not the input video signal is at a level within a specific range, and determines the result of the determination. C to be output as a determination result signal
It is characterized by having an RT gamma correction determining means.

In such a CRT gamma correction determination system, when a video signal is input, the
The D-converted signal is input to a ROM as an n-bit digital signal, and a determination result signal corresponding to the input digital signal is output using a table stored in the ROM in advance.

According to a second aspect of the present invention, there is provided the CRT gamma correction determining system according to the first aspect, wherein the input video signal is converted to n by the AD converter.
When converted into a digital signal of bits, the level within the specific range is not less than 1 and not more than (2 ⁿ -1) ^{1.2 / 2.2} , and the CRT gamma correction determining means determines that the level of the video signal is the specific level. C that determines that the video signal at a level within the range has not been subjected to the CRT gamma correction processing.
It is an RT gamma correction determining means.

In such a CRT gamma correction determining system, when a video signal is input, the video signal is
It is D-converted and input to the ROM as an n-bit digital signal. Further, when the video signal is a video signal subjected to the CRT gamma correction processing, 1 or more (2 ⁿ -1)
Since there is no video signal having a digital signal of a level of ^{1.2 / 2.2} or less, a value of 1 or more (2 ⁿ -1) is previously stored in the ROM.
By storing a table that outputs a High determination result signal when a digital signal having a level of ^{1.2 / 2.2} or less is input, a determination result signal corresponding to the input digital signal is output, and the video signal is output to a CRT. It can be determined whether or not gamma correction processing has been performed.

According to a third aspect of the present invention, there is provided a CRT gamma correction determining system according to the first aspect, further comprising a noise component detecting circuit for detecting a noise component included in the video signal. When the noise component detected by the noise component detection circuit is N, the level within the specific range is ^{equal to} or more than (1 + N) ((2 ⁿ −
1) The CRT gamma correction judging means judges that the video signal whose level is within ^{1.2 / 2.2} -N) or less and whose level is within the specific range has not been subjected to the CRT gamma correction processing. And CRT gamma correction determining means.

In such a CRT gamma correction discrimination system, when a video signal whose noise component is N is input, an n-bit digital signal obtained by AD-converting the video signal is passed through a noise component detection circuit. After detecting the noise component, the digital signal and the detection result are input to two comparators. When the two comparators output High when the level is ^equal to or more than (1 + N), the first comparator and the first comparator output level ((2 ⁿ -1)).
^{1.2 / 2.2-} N) A second comparator that outputs High when the output is less than or equal to N ^/ N, and the outputs of the two comparators are connected to an AND circuit, so that CRT gamma correction in which noise components have been removed from the input video signal A determination process can be performed.

According to a fourth aspect of the present invention, in the CRT gamma correction determining system according to the third aspect, the noise component detecting circuit detects a maximum value of a signal level during a pedestal period. The circuit is characterized in that the circuit has a maximum value of the signal level during the pedestal period as a noise component.

According to a fifth aspect of the present invention, there is provided a CRT gamma correction determination system according to the first or second aspect, wherein the unnecessary DC component of the video signal is removed and the unnecessary DC component is removed. And an unnecessary DC component removing circuit for sending the video signal from which CRT has been removed to the CRT gamma correction means.

In the CRT gamma correction determination system having such a configuration, the input video signal is AD-converted.
After the unnecessary DC component is removed by passing the bit digital signal through an unnecessary DC component removing circuit, the digital signal from which the unnecessary DC component has been removed is input to the ROM. When this video signal is a video signal that has been subjected to CRT gamma correction processing, one or more (2
^n- 1) By storing a table that outputs a High determination result signal when digital data of ^{1.2 / 2.2} or less is input, a determination result signal corresponding to the input digital data is output, and a video signal is output. Can be determined whether or not CRT gamma correction processing has been performed.

According to a sixth aspect of the present invention, there is provided a CRT gamma correction determination system according to the third or fourth aspect, wherein the unnecessary DC component of the video signal is removed and the unnecessary DC component is removed. An unnecessary DC component removing circuit for sending the video signal from which the noise has been removed to the noise component detecting circuit.

In such a CRT gamma correction discrimination system, the noise component when unnecessary DC components are removed is N
When such a video signal is input, first, an unnecessary DC component is removed by passing an n-bit digital signal obtained by AD-converting the video signal through an unnecessary DC component removal circuit,
Further, after the noise component is detected by the noise component detection circuit, the digital signal and the detection result are input to two comparators. These two comparators are a first comparator that outputs High when the level is ^equal to or higher than (1 + N) and a second comparator that outputs High when the level is equal to or lower than ((2 ⁿ -1) ^{1.2 / 2.2} -N), and By connecting the outputs of the two comparators to the AND circuit, it is possible to perform a CRT gamma correction determination process in which noise components have been removed from the input video signal.

According to a seventh aspect of the present invention, there is provided a CRT gamma correction determining system according to the fifth or sixth aspect, wherein the unnecessary DC component removing circuit comprises an average of signal levels during the pedestal period. And a subtraction circuit for subtracting the average value of the signal level during the pedestal period calculated by the average value calculation circuit from the input video signal. And

The CRT gamma correction determining system according to claim 8 is the CRT gamma correction determining system according to any one of claims 1 to 7, wherein the CRT gamma correction determining system holds the determination result signal output from the CRT gamma correction determining unit. When the video signal is not input and when the video signal is not input, the determination result signal in the hold circuit is determined to be the video signal when the video signal is subjected to the CRT gamma correction process. Is initialized to the determination result signal of

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a CRT gamma correction determination circuit used in the present embodiment. FIG. 10 shows the level x of the quantized signal from 0 to 255 and the signal of this level x is further converted to CRT.
9 is a table showing a relationship between a gamma correction process and a signal level y when quantized. Further, x and y have a relationship as in the following equation (1).

[0024]

(Equation 1)

The CRT gamma correction determination circuit used in this embodiment has an input terminal 1 to which a video signal is input, and an A / D converter for converting the video signal into an 8-bit digital video signal.
A D conversion circuit 18, a ROM 2 for detecting from the output of the A / D conversion circuit 18 whether or not the video signal has been subjected to gamma correction processing, and an output terminal 3 for outputting a 1-bit determination result signal from the ROM 2 It is composed of ROM
Reference numeral 2 stores an output table for outputting from the output terminal 3 an output corresponding to the level of the video signal input from the input terminal 1.

By the way, as shown in FIG. 10, when the level x of the video signal not subjected to the gamma correction processing is 0 on the transmitting side, the video signal is quantized after being subjected to the CRT gamma correction processing. The signal level y becomes 0. Similarly, on the transmitting side, when the level x of the video signal not subjected to the CRT gamma correction processing is 1, when the video signal is quantized after the CRT gamma correction processing is performed, the level y of the signal becomes 21. Becomes Therefore, CR
When an A / D conversion is performed on a video signal that has been subjected to the T gamma correction process, the level of the video signal cannot take a value of 1 or more and 20 or less.

Therefore, as shown in the table example of FIG.
A table stored in the ROM 2 so as to output High when the digital data input to the OM 2 is 1 or more and 20 or less and to output Low when the digital data is 0 or 21 or more and 255 or less. Set.
By setting in this manner, the video signal whose level is in the range of 1 or more and 20 or less is AD
It is determined whether or not CR is input to the input terminal 1 after conversion.
Whether the signal is a signal subjected to the T gamma correction processing is determined by comparing the signal with a table stored in the ROM 2, and
A 1-bit signal is output from the output terminal 3 as the determination result signal.

A second embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows the C used in the present embodiment.
FIG. 3 is a block diagram illustrating a configuration of an RT gamma correction determination circuit. FIG. 3 is a diagram showing a configuration of a video signal. Also, FIG.
3 is a block diagram showing an internal configuration of the unnecessary DC component detection / correction circuit 4 in FIG.

The CRT gamma correction judging circuit used in this embodiment includes an input terminal 1 to which the video signal is input, and an A / D converter for converting the video signal into an 8-bit digital video signal.
An AD conversion circuit 18 for D-conversion, an unnecessary DC component detection / correction circuit 4 connected to the AD conversion circuit 18, and a video signal in which the unnecessary DC component has been corrected by the unnecessary DC component detection / correction circuit 4 are input. And an output terminal 3 for outputting a 1-bit determination result signal from the ROM 2. The unnecessary DC component detection / correction circuit 4 includes an average value calculation circuit 5 for detecting an unnecessary DC component.
And a subtraction circuit 6 that corrects the video signal by subtracting the unnecessary DC component calculated by the average value calculation circuit 5 from the original video signal.

The input video signal is composed of signals of three periods of a horizontal synchronizing signal period, a pedestal period, and a video signal period as shown in FIG. When an unnecessary DC component is superimposed on such a video signal, a signal whose level has changed by the level of the DC component appears in a pedestal period in which the level is originally 0 level. Therefore, unnecessary DC components can be detected by averaging the signal levels during the pedestal period.

The unnecessary DC component detection / correction circuit 4 shown in FIG. 4 will be described based on the above concept. The video signal converted into an 8-bit digital signal by the AD conversion circuit 18 is input to the average value calculation circuit 5. Then, the average value calculation circuit 5 calculates the average value of the signal train during the pedestal period.

As described above, the average value calculation circuit 5 calculates the average value of the signal during the pedestal period, and calculates as an unnecessary DC component of the video signal during one horizontal scanning period immediately after the pedestal period. After that, the unnecessary DC component is subtracted from the video signal input to the input terminal 1 by the subtraction circuit 6 to perform correction during the video signal period. From the subtraction circuit 6,
A video signal having the unnecessary DC component corrected is output, and the video signal is input to the ROM 2. The operation after the video signal is input to the ROM 2 is the same as the operation in the first embodiment, and thus the detailed description is omitted.

A third embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows C used in the present embodiment.
FIG. 3 is a block diagram illustrating a configuration of an RT gamma correction determination circuit. The CRT gamma correction determination circuit used in this embodiment includes an input terminal 1 to which the video signal is input, an AD conversion circuit 18 that converts the video signal into a video signal that is an 8-bit digital signal, A maximum value detection circuit 7 for detecting a maximum value of a level of a signal during a pedestal period;
And AND circuits for performing an AND operation on the signals from the comparator circuits 8 and 9
It comprises a circuit 10 and an output terminal 3 for outputting an output from the AND circuit 10 as a determination result signal.

In the CRT gamma correction determining circuit having such a configuration, the video signal, which is an 8-bit digital signal that has been AD-converted by the AD converter circuit 18, is supplied to the comparator 8,
9 and the maximum value detection circuit 7. The maximum value detection circuit 7 obtains the maximum value NM of the input video signal during the pedestal period, and supplies the maximum value to the comparators 8 and 9 as the maximum noise amount in one horizontal scanning period immediately after the pedestal period.

The comparator 8 compares the input video signal with (1 + NM) and determines that the video signal is (1 + NM).
High is output in the above case, and Low is output in the case of less than (1 + NM). Further, the comparator 9 compares the video signal with (20-NM), and when the video signal is equal to or less than (20-NM), High and conversely (20-NM).
If it is larger than NM), Low is output. The AND circuit 10 outputs High when the signals input from the comparators 8 and 9 are both High.
9 when one of the signals input from L is Low.
ow is output.

When a video signal on which noise is superimposed is input to the CRT gamma correction determination circuit as described above, and the maximum value detection circuit 7 detects that the maximum value of the pedestal period signal is 2, the video If the level is 3 or more and 18 or less in the signal period, it is determined that the video signal has not been subjected to the CRT gamma correction processing, and High is output.

When the noise of the noise amount 2 is superimposed on the input video signal as described above, the level of the video signal is a level obtained by adding ± 2 to the originally transmitted level. Therefore, similarly to the case where the noise is not superimposed, when it is determined that the CRT gamma correction processing has not been performed for the video signal between 1 and 20 inclusive, the video signal originally transmitted with its level set to 0 is added to the video signal. Since noise is superimposed on the image signal, the image signal may be input as a 1 or 2 level video signal. Therefore, the video signal on which the CRT gamma correction processing has been performed is erroneously determined as a video signal on which the processing has not been performed. This means that when the level is 20,
The same can be said. Therefore, in the present embodiment, when the noise amount is determined to be NM, it is (1 + NM) or more (20−N
M) A video signal having a level below is determined as a video signal that has not been subjected to CRT gamma correction processing.

A fourth embodiment of the present invention will be described with reference to the drawings. FIG. 6 shows C used in the present embodiment.
FIG. 3 is a block diagram illustrating a configuration of an RT gamma correction determination circuit. The CRT gamma correction determination circuit used in the present embodiment includes an input terminal 1 to which the video signal is input, an A / D conversion circuit 18 that performs A / D conversion of the video signal into a video signal that is an 8-bit digital signal, An unnecessary DC component detection / correction circuit 4 connected to the conversion circuit 18; a maximum value detection circuit 7 connected to the unnecessary DC component detection / correction circuit 4 for detecting the maximum value of the level in the pedestal period; Comparator circuits 8 and 9 to which the corrected video signal is input and connected to the maximum value detection circuit 7;
An AND circuit 10 for performing a logical AND operation on the signals from the comparator circuits 8 and 9 and an output terminal 3 for outputting an output from the AND circuit 10 as a determination result signal.

In the CRT gamma correction determining circuit having such a configuration, the unnecessary DC component detection / correction circuit 4 is the same as the unnecessary DC component detection / correction circuit 4 used in the second embodiment. It comprises an arithmetic circuit 5 and an adder circuit 6. For the detailed operation of this circuit,
Since the operation is the same as that described in the second embodiment, the description is omitted. By passing the unnecessary DC component detection / correction circuit 4, a video signal in which the unnecessary DC component has been corrected is output, and the video signal is sent to the comparator circuits 8 and 9 and the maximum value detection circuit 7.

The operation after the unnecessary DC component corrected video signal is sent from the unnecessary DC component detection / correction circuit 4 to the comparator circuits 8 and 9 and the maximum value detection circuit 7 is described in the third embodiment. Since the operation is the same as the operation performed by the comparator circuits 8 and 9 and the maximum value detection circuit 7 used in the embodiment, detailed description is omitted. That is, if the noise of the noise amount NM is confirmed, when the level of the video signal is equal to or more than (1 + NM) and equal to or less than (20-NM), it is determined that the CRT gamma correction process is not performed on the video signal, High is output from the AND circuit 10.

A fifth embodiment of the present invention will be described with reference to the drawings. FIG. 7 shows C used in the present embodiment.
FIG. 2 is a block diagram illustrating a configuration of an RT gamma correction determination system. FIG. 8 is a flowchart for closing the operation of the CRT gamma correction determination system. The CRT gamma correction determination system used in the present embodiment includes an input terminal 1 to which the video signal is input, and an AD conversion circuit 18 that performs AD conversion of the video signal into a video signal that is an 8-bit digital signal.
And the input terminal 1 to which the video signal is input to the AD conversion circuit 18 and the video signal input to the input terminal 1
C for determining whether or not RT gamma correction processing has been performed
An RT gamma correction discriminating circuit 11, a video input discriminating circuit 13 connected to the input terminal 1 and discriminating whether or not the video signal has been input to the input terminal 1, and a discrimination result signal from the CRT gamma correction discriminating circuit 11 It comprises a hold circuit 12 which is sent out and from which a video input identification signal is sent out by the video input identification circuit 13, and an output terminal 3 which outputs a judgment result signal held by the hold circuit 12.

In such a CRT gamma correction discrimination system, the CRT gamma correction discrimination circuit 11 performs the operation described in any one of the first to fourth embodiments, whereby the image input to the input terminal 1 is obtained. It is determined whether or not the signal has been subjected to CRT gamma correction processing, and a signal corresponding to the result is sent to the hold circuit 12. The hold circuit 12 receives a video input identification signal indicating whether or not the video signal sent from the video input identification circuit 13 has been input.

The operation of the hold circuit 12 will be described below with reference to the flowchart shown in FIG. First, when a video signal is input to the input terminal 1, Hi indicating that a video signal has been input from the video input identification circuit 13.
When the video input identification signal of gh is sent to the hold circuit 12, the process proceeds to Step 3, and when the video input identification signal is Low, the process proceeds to Step 2 (STEP 2).
1). In step 2, the hold circuit 12 is initialized with Low being given as a signal indicating that the video signal has been subjected to CRT gamma correction processing. In step 3, when the determination result signal sent from the CRT gamma determination circuit 11 is High, the process proceeds to step 4 and the Low signal held in the hold circuit 12 is subjected to the CRT gamma correction processing of the video signal. The signal is replaced with a High signal indicating that the signal is not stored. Conversely, when the determination result signal is low, the process returns to step 1.

In a video signal that has not been subjected to the CRT gamma correction processing, a video signal having a level of 1 to 20 is input relatively frequently. Taking advantage of such characteristics, once the High-level signal is input to the hold circuit 12 when the video signal of the level 1 to 20 is input, even if a signal of a level other than 1 to 20 is input. The CRT gamma correction determination system does not output Low until the input of the video signal is completed.

A sixth embodiment of the present invention will be described with reference to the drawings. FIG. 9 shows the C used in the present embodiment.
FIG. 2 is a block diagram illustrating a configuration of a video signal processing device 16 which is an application system using an RT gamma correction determination system. Such a video signal processing device 16 includes a signal source 14 or C that transmits a video signal that has been subjected to CRT gamma correction processing.
An input terminal 17 to which a video signal transmitted from a signal source 15 for transmitting a video signal which has not been subjected to RT gamma correction is input; and a video signal input to the input terminal 17 is converted from an analog signal to an 8-bit digital signal. And an A / D conversion circuit 18 for converting the A / D conversion into

The video signal processing device 16 operates when the video signal transmitted from the signal source 14 is input, and receives the video signal transmitted from the signal source 15. A CRT gamma correction determination circuit 11 that determines whether or not a video signal sent from the AD conversion circuit 18 has been subjected to CRT gamma correction processing, and a CRT gamma correction determination circuit A hold circuit 12 for holding a determination result signal sent from the display circuit 11; a video input identification circuit 13 for sending a result of identifying whether or not a video signal has been input to the hold circuit 12; It has a multiplexer 21 for switching contacts and a video signal reproducing circuit 22 for converting an output signal from the multiplexer into a luminance signal or a chrominance signal. .

An image is reproduced on a flat display such as a liquid crystal display by the luminance signal and the color signal output from the image signal device 16. When a video signal subjected to CRT gamma correction processing is input from a signal source 14 to an input terminal 17 of the video signal processing device 16, the video signal is converted into a digital signal by an AD conversion circuit 18, and the video signal processing is performed. The digital signal is input to the circuits 19 and 20, the CRT gamma correction determination circuit 11, and the video signal input identification circuit 13.

The CRT gamma correction discriminating circuit 11, the hold circuit 12, and the video signal input discriminating circuit 13 perform operations in accordance with the flowchart of FIG. A Low determination result signal indicating that the corrected video signal has been input is held. When such a determination result signal is output to the multiplexer 21, the video signal processing circuit 19 and the video signal reproduction circuit 22 are connected by short-circuiting to the contact a side. In the video signal processing circuit 19, a CRT gamma correction return process is performed on the video signal.

Conversely, when a video signal that has not been subjected to CRT gamma correction processing is input from the signal source 15 to the input terminal 17 of the video signal processing device 16, the video signal is converted into a digital signal by the AD conversion circuit 18. The digital signal is input to the video signal processing circuits 19 and 20, the CRT gamma correction determination circuit 11 and the video signal input identification circuit 13.

At this time, the CRT gamma correction determining circuit 1
1. Hold circuit 12 and video signal input identification circuit 13
However, by performing the operation according to the flowchart of FIG. 8 shown in the fifth embodiment, the hold circuit 12
A High determination result signal indicating that a video signal that has not been subjected to the RT gamma correction processing is input is held. When such a determination result signal is output to the multiplexer 21, the video signal processing circuit 20 and the video signal reproduction circuit 22 are connected by short-circuiting to the contact b side. In the video signal processing circuit 20, an operation for expanding the video signal is performed.

Although the present embodiment has been described with reference to an example of a video signal processing device to which a digital video signal is input, the video signal device to which an analog video signal is input may be used for the CRT gamma correction determination as described above. A system may be used.

[0052]

According to the CRT gamma correction judging system according to the first aspect, whether the video signal is subjected to the CRT gamma correction processing based on the level of the digital signal obtained by converting the input video signal by the AD converter. Can be automatically and easily determined, and by making a determination in this way, C can be determined according to the video signal.
Whether or not to perform the RT gamma correction return process can be automatically determined.

According to the CRT gamma correction determination system according to the second aspect, the digital signal obtained by converting the video signal subjected to the CRT gamma correction processing by the AD converter is 1 or more (2 ⁿ -1) ^{1.2 / 2.2.} Since there is no digital data of a level in the following range, it is possible to easily determine that a video signal when a digital signal of a level in this range is input is not subjected to CRT gamma correction processing.

According to the CRT gamma correction judging system according to the third aspect, after detecting a noise component, it is determined whether or not the input video signal has been subjected to the CRT gamma correction process in consideration of the noise component. Since the determination is made, the determination can be made more accurately.

According to the CRT gamma correction determination system of the fourth aspect, the maximum value of the level of the input video signal is detected from the signal in the pedestal period in which the level at the time of transmission is 0 among the input video signals. By using the maximum value as a noise component, it is possible to accurately determine the presence or absence of CRT gamma correction for noise with a simple configuration.

According to the CRT gamma correction judging system according to the fifth aspect, by removing unnecessary DC components superimposed on an input video signal from the video signal, the CRT gamma correction processing is performed on the video signal. It can be determined more accurately.

According to the CRT gamma correction discrimination system according to the sixth aspect, the input video signal is converted into a CRT signal in consideration of noise components while eliminating unnecessary DC components.
Since it is determined whether or not the gamma correction process has been performed, the determination can be made more accurately than when the unnecessary DC component removing circuit and the noise component detecting circuit are separately used.

According to the CRT gamma correction judging system according to the seventh aspect, an average value of signal levels of a signal in a pedestal period in which the level at the time of transmission is 0 among input video signals is calculated. By making the average value an unnecessary DC component, the unnecessary DC component can be detected more easily, and by using a subtraction circuit, the detected unnecessary DC component can be simply subtracted from the video signal to thereby simplify the detection. With such a configuration, the presence or absence of CRT gamma correction can be accurately determined for unnecessary DC components.

According to the CRT gamma correction discrimination system according to the present invention, when it is determined that a video signal that has not been subjected to CRT gamma correction processing has been input even once while a video signal is being input, this determination result is obtained. By storing the signal in the hold circuit while the video signal is being input, a fixed determination result can be output without being influenced by the level of the input video signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a CRT gamma correction determination system used in a first embodiment.

FIG. 2 is a block diagram illustrating a configuration of a CRT gamma correction determination system used in a second embodiment.

FIG. 3 is a diagram showing a configuration of a video signal.

FIG. 4 is a block diagram showing the inside of an unnecessary DC component detection / correction circuit.

FIG. 5 is a block diagram illustrating a configuration of a CRT gamma correction determination system used in a third embodiment.

FIG. 6 is a block diagram illustrating a configuration of a CRT gamma correction determination system used in a fourth embodiment.

FIG. 7 is a block diagram illustrating a configuration of a CRT gamma correction determination system used in a fifth embodiment.

FIG. 8 is a flowchart showing the operation of a CRT gamma correction determination system used in the fifth embodiment.

FIG. 9 is a block diagram showing a configuration of an application system of a CRT gamma correction determination system used in a sixth embodiment.

FIG. 10 is a table showing a relationship between a level x of a quantized signal and a level y of the signal after CRT gamma correction processing and quantization.

FIG. 11 is a table showing a table stored in a ROM.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 ROM 3 output terminal 4 unnecessary DC component detection / correction circuit 5 average value calculation circuit 6 subtraction circuit 7 maximum value detection circuit 8, 9 comparator circuit 10 AND circuit 11 CRT gamma correction determination circuit 12 hold circuit 13 video input identification Circuits 14, 15 Signal source 16 Video signal processing device 17 Input terminal 18 AD conversion circuit 19, 20 Video signal processing circuit 21 Multiplexer 22 Video signal reproduction circuit

Claims (8)

[Claims] 1. Determine whether or not a video signal is subjected to CRT gamma correction processing based on whether or not an input video signal is at a level within a specific range, and determine the result of the determination. A CRT gamma correction determination system, comprising CRT gamma correction determination means for outputting as a result signal. 2. An A / D converter converts an input video signal to n
When converted into a digital signal of bits, the level within the specific range is not less than 1 and not more than (2 ⁿ -1) ^{1.2 / 2.2} , and the CRT gamma correction determining means determines that the level of the video signal is the specific level. The video signal at a level within the range is CR
2. The CRT gamma correction determination system according to claim 1, wherein the CRT gamma correction determination unit determines that the T gamma correction has not been performed. 3. A noise component detection circuit for detecting a noise component included in the video signal, wherein the noise component detected by the noise component detection circuit is N
When the level in the specific range is not less than (1 + N) and not more than ((2 ⁿ -1) ^{1.2 / 2.2} -N), the CRT gamma correction determining means determines that the level of the video signal is not less than the specific level. The video signal at a level within the range
2. The CRT gamma correction determination system according to claim 1, wherein the CRT gamma correction determination unit determines that the T gamma correction has not been performed. 4. The circuit according to claim 1, wherein the noise component detection circuit detects a maximum value of a signal level during the pedestal period and uses the maximum value of the signal level during the pedestal period as a noise component. CRT according to item 3
Gamma correction system. 5. An unnecessary DC component removing circuit for removing an unnecessary DC component included in the video signal and transmitting the video signal from which the unnecessary DC component has been removed to the CRT gamma correction unit. The CRT gamma correction determination system according to claim 1 or 2. 6. An unnecessary DC component removing circuit for removing an unnecessary DC component included in the video signal and sending the video signal from which the unnecessary DC component has been removed to the noise component detecting circuit. The CRT gamma correction determination system according to claim 3 or 4. 7. An average value calculating circuit for calculating an average value of a signal level during the pedestal period, the unnecessary DC component removing circuit; and an average value of a signal level during the pedestal period calculated by the average value calculating circuit. The CRT gamma correction determination system according to claim 5, further comprising: a subtraction circuit configured to subtract from the input video signal. 8. A holding circuit for holding the judgment result signal output from the CRT gamma correction judging means, and when no video signal is input, the judgment result signal in the hold circuit is output. 8. The CRT gamma correction determination system according to claim 1, wherein the video signal is initialized to a determination result signal when it is determined that the video signal is a video signal when the CRT gamma correction process is performed. .