JPS5820096A - Digital gamma compensating circuit - Google Patents

Abstract

PURPOSE:To improve the S/N and at the same time to avoid the deterioration of the image resolution to perform the ideal gamma compensation, by dividing the digitized video signal into plural parts corresponding to the levels and providing the frequency characteristics corresponding to the sampled signals. CONSTITUTION:The primary color video signal supplied through an input terminal 4 is converted into a digital signal through an A/D converter 5 and then applied to the digital comparators 6a-6n corresponding to the signal levels to be divided into (n) units of signals. The outputs of the comparators 6a-6n are fed to the filters 7a-7n and limited to the range of each prescribed frequency characteristics. The outputs of the filters 7a-7n are fed to the nonlinear circuits 8a-8n, and the gamma compensation is carried out through the circuits 8a-8n. The outputs of the circuits 8a-8n are shinthesized by a shinthesizer 11. Then the S/N is improved by providing the frequency characteristics, and at the same time the deterioration is avoided for the image resolution. Thus the ideal gamma compensation is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital gamma correction circuit that changes frequency characteristics in accordance with the level when gamma correction is performed by digitizing each encoded primary color video signal. .

In general, on the color receiver side, the change in luminance on the fluorescent surface with respect to the input video signal is not linear, and its electrical and optical conversion characteristics have a gamma of approximately 2.2, as shown in Figure 1. ing. Therefore, on the image sending side, the characteristics of this, that is, gamma, on the television camera 2 side are x7zz+! , < s (see Figure 2).

This makes it possible to faithfully reproduce colors in the Cica-to-Tele, Gamma 1 as a comprehensive vision system, receiver, and wingman.

However, when gamma correction is performed, the start-up time is approximately 3 to 4 times higher at low levels of the video signal. When a low-level video signal is amplified by 11 times, the noise component is amplified at the same rate as the video component, which is very small compared to the video signal at the specified level. Ratio of signal component to noise component (hereinafter referred to as B/N
, called it,) Tsumagan! Thousands of corrections 3-4
(The regulation of the noise component is low, so it refers to the noise in the complement.) Generally, in the case of color television V-jima, the measurement of the rule is from frequency - fi 100Kt cycles to 4.2 megacycles. This is done by measuring the effective value of the frequency characteristics of the band. The VN ratio is one of the important factors for improving image quality, and if the 8A ratio decreases, noise will become noticeable on the screen, which will seriously affect the image quality.

Therefore, in order to transmit high-quality images, it is desirable to perform processing to reduce the deterioration of the hair as much as possible.

Simply Tsujigan! Although it is possible to lower the high-frequency components of the frequency characteristics during correction, this will result in a decrease in resolution.

Ideally, the frequency characteristics when performing gamma correction should be such that low-level portions of the video signal are transmitted by lowering the high-frequency 0 frequency characteristics, and high-level portions of the video signal are transmitted as they are. For example, if the output of a sweep oscillator is used as an input signal, when the level is low, it will have the frequency characteristics as shown in Figure 3 O, and when the frequency 4# is high, it will have the frequency characteristics as shown in Figure 4. This is equivalent to having the frequency characteristic of Ka at the specified level as shown in FIG. 5.

With this kind of frequency characteristic, the O noise component is reduced at low levels, so it is possible to reduce this deterioration during gamma correction, and at high levels, the N wave number characteristic is flat, so There are almost no negative effects such as resolution deterioration.

In actual gamma correction circuits, it is normal to use the analog-a-da method, but an example is shown in No. 6 WJ. After that, resistor R1 and diode D1% resistor Oisetsu and Mayo FD.

As shown in Figure 7, in the series circuit of , the gamma correction has been recently performed with a polygonal characteristic and the output is output from output terminal 1. However, the frequency characteristic line at low level It could not be said that Ka was sufficient to lower the high frequency components and flatten the frequency characteristics at high levels. Note that Rm also represents resistance.

It is difficult to realize such frequency 4I characteristics, and even if it is possible to approximate it, there are problems such as troublesome adjustment.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and it involves dividing a digitized video signal into a plurality of parts according to the level, and giving frequency characteristics corresponding to each of the extracted parts. Yes, the ratio is good and the resolution is O.
An object of the present invention is to provide a digital yamma correction circuit that is free from adverse effects such as deterioration.

Hereinafter, embodiments of the digital gamma correction circuit of the ζO invention will be described with reference to the drawings. It is a four-dimensional diagram showing the structure of an embodiment of the eighth expansion.

In FIG. 8, each primary color signal is processed and expanded, so the explanation will be given by taking the green channel as an example.

The green video signal introduced into the input terminal 4 is converted into a digital signal by an anada digital converter J (hereinafter referred to as a digital converter). In general, when converting a 1 TV signal to a digital compensation signal, @'
It is sufficient to perform Sansol at tF or more.

Next, this digital signal is introduced into the digital comparator C, and at this time, corresponding to the level of the digital signal, the INK digital comparator-a is inputted to a predetermined level. It is divided into digital comparators (mlf (an integer greater than or equal to mlf3)) so as to be introduced for each range.In this way, digital comparators #a to tap
c) Each divided and extracted video signal is introduced into the filters Fa to Fm1C of the filters FO, and each is subjected to a predetermined frequency characteristic O limit.') K
t 9.

These filters Fa to rm are, for example, low-frequency components Hiroso O1.
This can be achieved using a digital eye if it is a filter that transmits t and reduces high-frequency components. These filters Fa~r-Hiro, HFF (-ia 4, X
The filter) can be easily configured (by means of a digital filter) which may flatten the frequency 41 characteristic without a middle or high frequency filter.

The output of the comparator 0, which corresponds to the low level of the video signal, passes through a four-pass filter, and the output frequency q# of the comparator corresponding to the high level is equalized by It is designed to be introduced into each of the nonlinear circuits 8 to 8M& of the linear circuit 8. ' The gamma correction non-direct i11 circuit low1m converts the input linear signal to a gamma of 0.450 as shown in FIG.
Although we are talking about Ik conversion, there is a method of approximating Ka, for example, using a polygonal line, or preparing a wing MK conversion table in advance, supplying the input signal to the IIAM address, and converting the gamma-corrected one. Gamma correction can be easily performed by extracting the image from the data section.

In FIG. 8, a case will be described in which the outputs of the filters Fa to 1m are introduced into the multiplication circuit as non-linear circuits 81 to 8m.

In each multiplication circuit, the predetermined coefficients are multiplied by an arithmetic operation, or by combining them in a synthesizer 11.
It is possible to construct a gamma correction circuit using a polygonal line approximation.

(The arithmetic circuit is an r-digit multiplier or an 8-m MC) It is easy to use the conversion cheedel. With these), a nine-gamma correction circuit can be realized by changing the frequency according to the level.

In the example of FIG. 8 of Jin, the filters Pa to Fb and the non-direction Im!
As explained in the description of the multiplication circuit section as circuit I, it is also possible to reverse this order and design the multiplication circuit section 0 and the filter section next.

#E9E indicates another example of this release 9110
It is a four-dimensional diagram. In Figure 9 of H, Mori, digital comparator -
A gamma correction circuit section J using a backup method that passes through a filter 1 and a synthesizer 11, for example, a wing-shaped transformation.
- Shows the configuration by - In this case, 4 icILAMcln! It goes without saying that the correction circuit unit 10 may first perform gamma correction 9, then provide the comparator 6, and then provide the 74 lter r.

As described above, according to the digital gamma correction circuit of the invention, when gamma correcting the digitized primary color 1 image signal of the TV and camera 2, the digitized primary color Wk image signal O level is adjusted. Since the frequency characteristics are corrected in response to this, it is an ideal table gun that has a good BIN ratio and does not cause resolution deterioration! It can be used as a correction circuit.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the luminance between 1 and 1L with respect to the input video signal in a general color receiver; Fig. 2 is a diagram showing the relationship between the output signal and the input video signal after conventional gamma correction; Figure 3 shows the frequency characteristics at low level when the sweep oscillator O output is used as the input signal in 11 after gamma correction is performed, and the sweep oscillator IIO output is used as the input signal when performing the fourth solid gamma correction. Figure 5 is a diagram showing the frequency at high level when using f7ma correction, and Figure 5 is a diagram showing the frequency characteristics when O is properly input and the output is bell when the sweep oscillator O output is used as an input signal when performing f7ma correction. , 6th WA is a circuit diagram of an eye-major correction circuit using the conventional analogue system, and FIG. A diagram showing the relationship between the output signal and the polygonal input video signal from the correction circuit. FIG. 9 is a diagram showing the configuration of one embodiment of the correction circuit, and FIG. 9 is a diagram showing another embodiment of the digital gamma correction circuit according to the invention. 1-~heavy liquid exchange-1-96-~σn-digital comparator,
r e F a~F mm74 J'&I, a e#a
~am...Nonlinear circuit, 1e-gamma correction circuit section, 11-synthesizer. Applicant's attorney Takehiko Suzue Figure 1 > v Shibobu iJag -el Figure 2 ~ Koma & Jre 3 eI Figure 3 Takara Kai - IN4 Figure i school □

Claims (1)

[Claims] Dili! a first means for dividing each of the nine primary color video signals into a plurality of pieces corresponding to horizontal lines; A digital gamma correction circuit which synthesizes each of the primary color video signals by imparting a frequency characteristic to change the frequency characteristic corresponding to the level.