JPH0693771B2 - Beam current control circuit for electronic beam recorder - Google Patents

Description

The present invention relates to a beam current control circuit for an electron beam recording apparatus.

[Conventional technology]

Conventionally, an electron beam recording device (hereinafter referred to as an electron beam recording device for recording a television image on a photographic film using the electron beam as a stylus)
(Abbreviated as EBR) is known. Then, in the conventional EBR, the beam current is controlled in order to compensate for the fluctuation of the beam current due to the temperature change of the EBR in the initial stage of operation. First, a conventional EBR beam current control circuit will be described with reference to FIGS. 3 and 4.

FIG. 3 shows an example of a conventional EBR current control circuit. Third
In the figure, (1) is an EBR, and the recording electron beam Br is emitted from the filament (2) toward the film F loaded in the EBR, and the beam current amount of the electron beam Br is changed to the grid (3). It is controlled by the voltage of.
(4) is a beam current detection electrode called a Faraday cage, which is used for recording electron beam Br only during the blanking period.
Is deflected toward the detection electrode (4), and the beam current Bb flows into the electrode (4). (5) is a power supply for filament (2), and (6) is an exhaust port. In addition,
Focusing, deflecting, accelerating means and the like for the electron beam are well known, and therefore illustration and description thereof are omitted.

The video signal to be recorded is supplied to the grid (3) of the EBR (1) via the input terminal (10) and the amplifier (11). (12) is a bias control circuit, (13) is a minimum value detection circuit, and the output of the bias control circuit (12) is an EBR.
In addition to being supplied to the grid (3) of (1), the output of the minimum value detection circuit (13) is supplied to the bias control circuit (12) as a control signal. The output of the detection electrode (4) of the EBR (1) is supplied to the minimum value detection circuit (13) via the amplifier (14).

Thus, the electron beam B during the blanking period of EBR (1)
b, an amplifier (14), Yotsute servo loop L _A is formed to the minimum value detection circuit (13) and the bias control circuit (12), the minimum value of the electron beam Bb is controlled to be constant. If the time constant ^τ _A of the servo loop L _A is appropriately selected, the bias control similar to the blanking period is performed on the electron beam Br in the non-blanking period, that is, the recording period, and the minimum electron beam Br The value is controlled to be constant corresponding to, for example, the black level of the video signal.

Another example of the conventional EBR current control circuit is shown in FIG. In FIG. 4, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and redundant description will be omitted.

In FIG. 4, (15) is a gain control amplifier, (16) is a maximum value detection circuit, and the gain control amplifier (15) is inserted between the input terminal (10) and the amplifier (11), The output of the maximum value detection circuit (16) is used as a gain control signal for this amplifier (1
5) supplied to. Further, the output of the amplifier (14) is supplied to the maximum value detection circuit (16).

Thus, the electron beam B during the blanking period of EBR (1)
The servo loop L _B is formed by b, the amplifier (14), the maximum value detection circuit (16), the gain control amplifier (15) and the amplifier (11), and the maximum value of the electron beam Bb is controlled to be constant. To be done. By properly selecting the time constant ^τ _B of the servo loop L _B , the maximum value becomes constant not only for the blanking period but also for the electron beam Br in the recording period, corresponding to, for example, the white level of the video signal. Such control is performed.

The above two current control circuits can be used together.

[Problems to be solved by the invention]

When the recording beam current Br fluctuates due to a temperature change in the initial operation of the EBR (1) or replacement of the filament (2), the beam current control circuit as described above is used to control the recording beam current Br. The maximum value and the minimum value can be kept constant corresponding to, for example, the white level and the black level of the video signal.

However, each level of the halftone of the video signal E ₁ , E ₂ ...
For each intermediate value I ₁ , I _{2 of} the beam current Br corresponding to, the above-mentioned beam current control circuit does not work effectively, and each intermediate value of the beam current Br fluctuates to I ₁₁ (≠ I ₁ ), I ₁₂ (≠
I ₂ ) …… It becomes like this. Due to this variation, the gradation of the recorded image differs from the gradation of the original image, and there is a problem that the recording cannot be performed correctly.

In view of these points, the object of the present invention is to automatically control the beam current of the EBR so that the gradation of an image is correctly recorded without being affected by the temperature change in the initial operation. The present invention proposes a beam current control circuit for an electron beam recording apparatus which can be used.

[Means for solving problems]

The present invention has a beam current control means (3) for controlling the beam current of the electron beam and a beam current detection means (4) for detecting the controlled beam current, and the beam current control means (3) on the film F. Of the electron beam recording device (1) for recording an image corresponding to the video signal applied to the beam current detecting means (4) and the beam current detecting means (4) during the blanking period of the video signal applied to the beam current control means (3). A first control circuit (12) for controlling the beam current control means (3) so that the minimum value of the beam current becomes constant corresponding to the black level of the video signal based on the minimum value of the output; A gamma correction circuit (17) configured to perform gamma correction on a signal and change the gamma correction characteristic according to the correction signal, and a video signal output from the gamma correction circuit (17) to the beam current control means. Mark (3) In addition, the maximum value of the beam current is kept constant corresponding to the white level of the video signal based on the maximum value of the output of the beam current detection means (4) during the blanking period of the applied video signal. The second control circuit (1) for controlling the beam current control means (3) so that
5) and a level reference signal including a plurality of levels between the black level and the white level of the input video signal, and the level reference signal is supplied to the gamma correction circuit (17) during the blanking period of the input video signal. Each level of the level reference signal supplied to the signal generation circuit (19) and the gamma correction circuit (17) and the output of the beam current detection means (4) obtained by supplying the level reference signal to the gamma correction circuit (17) Of the level reference signal supplied to the gamma correction circuit (17) and the beam current detection means. A beam current control circuit for an electron beam recording apparatus, characterized in that a gamma correction characteristic is changed by a correction signal so that each output level of (4) becomes correspondingly equal.

[Action]

According to the present invention, the input / output characteristics of the gamma correction circuit (17) are automatically controlled according to the characteristics of the beam current of the electron beam recording apparatus (1).

〔Example〕

An embodiment of the beam current control circuit of the electron beam recording apparatus according to the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, parts corresponding to those in FIGS. 3 and 4 are designated by the same reference numerals, and redundant description will be omitted.

In FIG. 1, (17) is a gamma correction circuit, which is inserted between the common contact (18c) of the switching switch (18) and the gain control amplifier (15). One fixed contact (18a) of the switch (18) is connected to the input terminal (10). (19)
Is a staircase wave generator, and (20) is a level comparator, and the output of the staircase wave generator (19) (n-step linear staircase voltage) is the other fixed contact (18b) of the switching switch (18). ) And the level comparator (20). The output of the detection electrode (4) of the EBR (1) is supplied to the level comparator (20) via the amplifier (14), and the output of the level comparator (20) is supplied to the gamma correction circuit (17). . In this embodiment, the conventional current control circuit described with reference to FIGS. 3 and 4 is also provided, but the description thereof will be omitted.

FIG. 2 shows a specific configuration example of the above-mentioned gamma correction circuit (17). In FIG. 2, diode D ₁ and semi-fixed resistor R ₁
And the semi-fixed power supply E ₁ are connected in series to form a first control branch, which is connected in parallel with the second to nth control branches having the same structure to form a known polygonal line approximation circuit. To be done. S _{1 to} S _n are switches for distributing control signals, and the output of the level comparison circuit (20) supplied from the terminal CTL via the switches S _{1 to} S _n is a semi-fixed resistor of each control branch. R ₁
To R _n and semi-fixed power supplies E _{1 to} E _n are sequentially supplied.

The operation of this embodiment is as follows.

First, the switching switch (18) is switched to the switching state shown in the figure, and the reference staircase wave voltage S _R is supplied from the staircase wave generator (19) to the gamma correction circuit (17). The reference staircase wave voltage S _R has n unit steps S _u (S _{u1 to} S _un ) of the same amplitude and the same time width T.
Composed of.

Assuming that the initial input / output characteristic of the gamma correction circuit (17) is linear, the reference staircase voltage S _R is equal to the gain control amplifier (15).
And via the amplifier (11) to the grid (3) of the EBR (1). The beam current of the EBR (1) is designed to flow into the detection electrode (4) in conjunction with the switching switch (18).
Time for each width T of S _u, staircase wave current is obtained nonlinearly its value increases with the gamma characteristic of the EBR (1). The staircase wave current i _s obtained at the detection electrode (4) is supplied to the level comparator (20) as the staircase wave voltage e _s via the amplifier (14) and corresponds to the reference staircase wave voltage S _R. The levels are compared for each unit staircase S _{u1 to} S _un . Unit stairs of level comparator (20)
The comparison output E _{c for} each of S _{u1 to} S _un is supplied to the gamma correction circuit (17) and, via the distribution switches S _{1 to} S _n , the semi-fixed resistors R _{1 to} R _n and the half of the control branches. are sequentially supplied to the fixed power source E ₁ to E _n, the amplifier becomes a corresponding unit step each at equal level with the staircase wave voltage e _s and the reference staircase wave voltage S _R which is the output (14), the level comparator (20 unit as stairs output of each is zero), the semi-fixed resistors R ₁ to R _n and semi-fixed power supply E ₁ to E _n
To control.

Thus, the input / output characteristics of the gamma correction circuit (17) are EBR.
When it is set in conformity with the input / output characteristics of (1), the switching switch (18) is connected in a state opposite to that shown, and the video signal from the input terminal (10) is switched to the switch (18) and the gamma correction circuit ( 17) is supplied to the grid (3) of the EBR (1) through the gain control amplifier (15) and the amplifier (11), and the electron beam B
It is recorded on the film F with r as a stylus. In this case, the maximum and minimum values of the beam current are kept constant as described above, and the intermediate value is determined by the input / output characteristics of the gamma correction circuit (17) set as described above. Since it is regulated, it is not affected by the temperature change of the EBR (1) at the initial stage of operation.

The gamma correction circuit (17) described above can be configured by using an operational amplifier in addition to the one shown in FIG. Further, instead of the staircase wave, a sawtooth wave can be used as a reference signal for gamma correction.

〔The invention's effect〕

According to the present invention described above, the gamma correction is automatically performed in advance each time the electron beam recorder is used, and the maximum and minimum values of the beam current are automatically maintained constant during the recording operation. Therefore, the fluctuation of the intermediate value of the beam current due to the temperature change in the initial operation is automatically removed, and the gradation of the image can be recorded correctly.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a beam current control circuit of an electron beam recording apparatus according to the present invention, and FIG. 2 is a connection diagram showing the essential parts of the embodiment shown in FIG. 1, FIGS. FIG. 3 is a block diagram showing a configuration example of a conventional electron beam recording apparatus. (1) is an electron beam recorder, (3) is an input electrode,
(4) is a detection electrode, (13) is a minimum value detection circuit, (16) is a maximum value detection circuit, (17) is a gamma correction circuit, (19) is a reference level signal generator, and (20) is a level comparison circuit. Is.

Claims (1)

[Claims] 1. A video signal applied to the beam current control means on a film, comprising beam current control means for controlling the beam current of an electron beam and beam current detection means for detecting the controlled beam current. And an electron beam recording apparatus for recording an image according to the above, and the minimum value of the beam current based on the minimum value of the output of the beam current detection means during the blanking period of the video signal applied to the beam current control means. Is a first control circuit for controlling the beam current control means so as to be constant corresponding to the black level of the video signal, and gamma correction is applied to the input video signal, and the gamma correction is performed according to the correction signal. A gamma correction circuit adapted to change the correction characteristics, and an image signal output from the gamma correction circuit are applied to the beam current control means for driving, and Based on the maximum value of the output of the beam current detection means during the blanking period of the applied video signal, the beam current is adjusted so that the maximum value of the beam current becomes constant corresponding to the white level of the video signal. A second control circuit for controlling the control means, and a level reference signal including a plurality of levels between the black level and the white level of the input video signal, the level reference signal being used for the blanking period of the input video signal. Of the beam current detecting means for supplying the gamma correction circuit to the gamma correction circuit, each level of the level reference signal supplied to the gamma correction circuit, and the level reference signal supplied to the gamma correction circuit. A level comparison signal which is supplied to the gamma correction circuit, and a comparison circuit which generates a correction signal of the gamma correction circuit by comparing each output level. Beam current control of an electron beam recording apparatus characterized in that the gamma correction characteristic is changed by the correction signal so that each level and output level of the beam current detecting means are correspondingly equal. circuit.