JPH0697782B2 - Video signal automatic white compression circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a white compression circuit in a television camera of a system in which a video signal is digitalized and processed.

[Prior art and its problems]

At present, the dynamic range that can be given to the image pickup system and the signal processing system of the television camera is far short of the light amount change range of the image pickup target.

Therefore, in particular, in order to deal with the shortage of the dynamic range in the signal processing system, the white compression processing has been widely adopted conventionally. That is, if this white compression processing is not performed,
This is because a bright portion in the video signal that exceeds a certain fixed level is clipped, and so-called white underexposure occurs.

This situation will be described with reference to FIG.

In FIG. 3, the characteristic i _(X) is the input characteristic of the video signal processing system, and the output level Y is fixed to W when the input level is X _W or higher. Therefore, this level W becomes the white clip point. , The dynamic range of input X is 0XX _W.

Therefore, in order to widen the input dynamic range and reduce the white crushing, the characteristic Ki _(X) of FIG. 3 is given. That is, the characteristic i _(X) is compressed from the level KP to a value lower than the white clip level W by a predetermined value to obtain the characteristic Ki _(X) ,
This will change the dynamic range of input X to 0XKX
Be able to spread to This is the white compression process.

Here, the level KP of the output Y at which compression starts is called a white compression point, and the slope KS of the characteristic Ki _(X) is called a white compression ratio. And
This characteristic Ki _(X) is expressed as follows.

Ki _(X) ＝ i _(X)・ ・ ・ (1) However, i _(X) <KP Ki _(X) ＝ (i _(X) −KP) KS ＋ KP ・ ・ (2) However, i _(X) KP In recent years, the progress of digital signal processing related technology has been remarkable, and in connection with this, even in television cameras,
A so-called digital camera, which uses a digital technique for processing the video signal, has appeared and is widely adopted.

In this digital camera, for example, a method of using a LUT (Look up Table) for nonlinear processing of a video signal such as gamma correction is often used. That is, the gamma correction is a process of giving the transfer characteristic shown in FIG. 4 to the video signal, and the LUT is the predetermined function f of the address value for the data to be stored at each address ai, as shown in FIG. ₍ ai ₎ is a data conversion table memory, and as shown in FIG. 6, by inputting a digitalized video signal to the address terminal 2 of this LUT1, the output terminal 3 outputs the data as shown in FIG. , A video signal processed according to an arbitrary conversion characteristic can be obtained.

Note that, as one related to the processing of a digital video signal using such a LUT, there is, for example, Japanese Patent Laid-Open No. 59-211394.
The gazette can be mentioned.

Therefore, it is used in such digital cameras.
In order to realize the above white compression processing by the method using the LUT, it is sufficient to prepare the LUT that gives the input / output characteristic Ki _(X) of FIG.

By the way, this white compression process is not particularly necessary when the subject is dark as a whole, and for a subject having a very high contrast, the white compression may occur even with such white compression.

Therefore, this white compression point KP is changed according to the nature of the video signal, and even if there is a bright portion in the image, it is always reproduced correctly and an appropriate white compression is automatically obtained so as not to be clipped. It is desirable to do so.

For example, as shown by the characteristic Ki ′ _(X) in FIG. 7, a white portion is compressed in the range of the input level X of 0XX _{1 and} a highlight portion exceeding X ₁ is entered in a part of the screen. When it comes, the signal in this part will be white clipped. To prevent this, the video signal level somewhere on the screen
Detects that exceeds X _1, characteristics of the white compression characteristic Figure 7
It is necessary to change it as shown by Ki ▲ _{″ (X)} ▼. A circuit for such processing is called an automatic white compression circuit, which is as shown in FIG. LUT
In order to realize it with a digital system circuit using, the video signal level is detected by the detection unit 5 by the configuration shown in FIG. 8, and the result is input to the central processing unit 6 and processed as follows. Software is required.

(1) Calculate appropriate white compression characteristic data according to the detected video signal level.

(2) Rewrite the LUT4 data with the data obtained in (1).

In the automatic white compression circuit of FIG. 8, 7 is a video signal input terminal and 8 is an output terminal.

Therefore, in the circuit shown in FIG. 8, it is necessary to perform the data rewriting processing of the LUT4 at high speed, which causes a problem that the cost is significantly increased, and there is a drawback that the practical application is difficult. .

〔Purpose〕

According to the present invention, in order to eliminate the above-mentioned drawbacks of the circuit, the white compression point is held in the register, the white compression is processed by hardware, and the automatic white compression is obtained only by rewriting the white compression point held in the register. The purpose is to provide an automatic white compression circuit having sufficient response characteristics at a low cost.

〔Example〕

Hereinafter, the automatic white compression circuit according to the present invention will be described in detail with reference to the illustrated embodiment.

FIG. 1 shows an embodiment of the present invention. The video signal input from the input terminal 7 is divided into two, one of which is input to the level detecting section 9. The data detected by the level detector 9 is
The white compression point setting unit 10 inputs the white compression point setting unit 10
Indicates that the data in the register 11 should be rewritten, and the data in the register 11 is input to the gain adjusting unit 12. The other input of the gain adjusting section 12 is a signal from the full-term input terminal 7. The output is connected to the output terminal 8.

Next, the operation of this embodiment will be described. First, the first
It is assumed that the white compression point input X _KP is set in the register 11 in the figure. Then, the gain adjustment unit 12 uses the register 11
And the video signal input from the input terminal 7 are compared.
When the video signal level is lower than the white compression point input X _KP, it is converted by the characteristic of the straight line a (output = input) and output to the output terminal 8 as shown in FIG. If it is larger than the white compression point X _KP, it is output to the output terminal 8 with the characteristic of the straight line of b.

As shown in FIGS. 9 and 10, the gain adjusting unit 12 has a hardware configuration including an adder, a subtracter, and a switch, and will be described in more detail below with reference to these figures. .

First, in FIG. 9, a video signal is input to the input terminal 7 and is connected to one input of the switch 17. This corresponds to the conversion by the straight line a shown in FIG. The input terminal 13 has a register holding the white compression point KP described above.
The output of 11 is connected, and the subtractor 14 subtracts this data from the video signal from the input terminal 7. When this is multiplied by the white compression ratio KS in the gain converter 15 and added to the white compression point KP input from the register 11 by the adder 16, the transfer characteristic given to the video signal obtained by the adder 16 is It becomes like the straight line b in FIG. The gain converter 15 may be configured by the LUT described in FIG. 6, but the white compression ratio KS
Is (KS = 1 / 2n: n = positive integer), as shown in Fig. 11, the video signal Di given by digital data is
This can be achieved very easily by arithmetically bit shifting N and discarding unnecessary bits. Note that FIG. 11 is an example when n = 1.

Therefore, the output of the adder 16 is connected to the other input of the switch 17.

The switch 17 is composed of an electronic switch or the like having a number of circuits equal to or greater than the number of bits of the video signal, and performs switching operation according to the polarity of the signal input from the subtractor 14 to the control input C. The signal of is output to the output terminal 8.

Therefore, when the output of the subtractor 14 is negative, the switch 17 is switched to the upper side as shown in the figure to select the characteristic a, and when the output of the subtracter 14 is positive, the switch 17 is switched to the lower side opposite to that shown in the figure. If you select b, output terminal 8
From, it is possible to obtain a video signal that has been subjected to white compression processing according to the characteristics shown by the solid line in FIG.

Next, the example of FIG. 10 will be described. The difference from the previous example is that the output of the subtractor 14 is multiplied by (1-KS) by the gain converter 15, and the switch 17 selects when the output of the subtractor 14 is positive. Also,
When the output of the subtractor 14 is negative, 0 is selected so that the output of the switch 17 is subtracted from the video signal from the input terminal 7 by the subtractor 18. In this way, the video signal output having exactly the same characteristics as the previous example can be obtained from the output terminal 8.

Returning to FIG. 1, as described above, according to this embodiment, the white compression according to the characteristics shown in FIG. 2 can be obtained with the data set in the register 11 as the white compression point KP. become.

By the way, the data of this register 11 is stored in the white compression point setting unit 10
The level detection unit 9 rewrites each time a predetermined condition is satisfied according to the video signal supplied to the input terminal 7. The data rewriting of the register 11 will be described below.

The level detection unit 9 is composed of a digital peak hold circuit or the like, and has a function of latching each field of the video signal supplied to the input terminal 7 or the maximum value in each frame in real time.

On the other hand, the white compression point setting unit 10 includes a microcomputer (microcomputer), sequentially takes in the data latched by the level detection unit 9, and calculates the data X _P that is averaged over a predetermined number of fields or a predetermined number of frames. . Then, as shown in FIG. 2, the deviation between the output Y _P and the white clip W due to the data X _P is examined, and when Y _P −W = α takes a positive value and reaches a predetermined value or more, Rewrite the data X _KP previously set in register 11 to a value smaller by a predetermined value, and if Y _P −W = α takes a negative value and becomes a value greater than the predetermined value, set it in register 11 until then. It operates so as to rewrite the existing data X _KP by a predetermined value.

By the way, in this embodiment, the value X _{KP of the} input that gives the white compression point KP in FIG. 2 is determined by the data X _KP set in the register 11, and accordingly, According to the embodiment, the automatic white compression operation described with reference to FIG. 7 can be obtained.

Further, according to this embodiment, since the processing required for switching the white compression characteristic is only the rewriting processing of the register 11, high speed processing can be easily performed and an automatic white compression circuit can be easily realized at low cost. .

〔effect〕

As described above, according to the present invention, since it is possible to easily switch the white compression characteristic, the drawbacks of the prior art are eliminated.
An automatic white compression circuit with excellent responsiveness can be provided easily and at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic white compression circuit according to the present invention, FIG. 2 is a characteristic diagram for explaining its operation, FIG. 3 is an explanatory diagram of white compression processing, and FIG. Characteristic diagram,
FIG. 5 is an explanatory diagram of the Luck-up table, FIG. 6 is an explanatory diagram of signal processing by the Luck-up table, an explanatory diagram of automatic white compression processing in FIG. 7, and FIG. 8 is a Luc-up table. A block diagram showing an example of an automatic white compression circuit using the, FIG. 9 and FIG. 10 are block diagrams showing an embodiment of a gain adjusting unit in the present invention, and FIG. 11 is a description of a signal compression process by bit truncation. It is a figure. 7 ... input terminal, 8 ... output terminal, 17 ... switch.

Claims (1)

[Claims] 1. An automatic white compression circuit, wherein white compression processing of a digitized video signal is performed by at least one of a table search processing by an input digital video signal and a bit truncation processing of the digital video signal. The maximum level is fetched at every predetermined cycle, and a new predetermined voltage level is sequentially set according to this level and written in a predetermined register means. The level of the video signal is compared with the voltage level held in the register means, and the transfer characteristic for this video signal is at least the linear characteristic, the compression characteristic given by the table search processing and the compression characteristic given by the bit truncation processing. A gain adjusting means consisting of a hardware configuration for switching to one side is provided. Automatic white compression circuit level of the video signal, characterized by being configured so as to be controlled automatically when the gain adjusting means the transfer characteristic is switched.