JPS6220749B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for correcting shading of an image signal such as a facsimile signal.

In a facsimile transmitter in which a plurality of solid-state scanning elements are arranged in rows and an image to be captured is formed on the solid-state scanning elements by a lens system, even if the entire image is uniformly white, the image formed by the lens system is is not uniform, and the resulting image signal is large at the center and small at the periphery, depending on the characteristics of the lens. For example, in an optical system that performs divided scanning using four lenses and four solid-state scanning elements, shading as shown in FIG. 1a occurs. Furthermore, even when shading due to lens characteristics can be ignored, when a linear light source such as a fluorescent lamp is used as a light source for illuminating the original, the tube length of the fluorescent lamp may be compared to the original due to mechanical constraints. If it cannot be made long enough, due to the influence of both ends of the fluorescent lamp, even if the entire image is uniformly white, the image signal obtained will be large in the center and small in the periphery, as described above. Shaded groin as shown in Fig. 1b occurs.

Correction of such shading is generally processed optically, but the structure of the apparatus is complicated and relatively large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized shading correction signal with a simple structure by electrically processing the shading correction.

FIG. 2 is a circuit diagram showing an embodiment of the first invention of the present invention, in which 1 is an input terminal, 2 is a positive DC power supply terminal, 3 is ground, and 4 is a capacitor which together with a variable resistor 5 forms a differential circuit 6. Configure. Transistor 7 and resistor 8 constitute a slice circuit 9. 10 is a variable resistor, 11 is a monostable multivibrator, and the pulse width is determined by a capacitor 12 and a variable resistor 13. 14 is a NAND circuit which together with the monostable multivibrator 11 constitutes an input pulse generation circuit.
15 is a resistor, and transistor 16 is a capacitor 1.
7 in parallel. 18 is a transistor, 1
A resistor 9 is connected in series between one end 21 of the constant voltage power supply 20 and one end 22 of the capacitor 17. One end 22 of the capacitor 17 is connected to the input terminal of an amplifier 23 with a gain of 1. Output terminal 24 of amplifier 23
is connected to the input terminal of an inverting amplifier 26 via a resistor 25. 27 is a resistor, and 28 is a variable resistor. The output terminal of the inverting amplifier 26 is connected to the capacitor 29
is connected to the base of transistor 18 via. Resistor 30 and resistor 31 provide base bias for transistor 18. The output terminal of the amplifier 23 is further connected to one end of the constant voltage power supply 20 and the buffer amplifier 3.
Connected to the second input terminal. A variable resistor 33 is connected together with the variable resistor 10 to the input terminal of the summing amplifier 34. 35 and 36 are resistors. 37 is a video amplifier, and 38 is an input terminal for a video signal before shading correction. 39 is an amplification factor control terminal 40 is an output terminal.

Next, the operation of this embodiment will be explained for the case of correcting shading groin as shown in FIG. 1b. Assuming that the input _gate pulse C shown in _FIG . As a result, the differential waveform signal d shown in FIG. 3b is obtained. This differential waveform signal D is sliced below the zero level by a slicing circuit 9 consisting of a transistor 7 and a resistor 8, resulting in a signal E shown in FIG. The slice circuit 9 also acts as a buffer amplifier. On the other hand, the input gate pulse is input to the monostable multivibrator 11, and the capacitor 12,
It has a pulse width determined by a variable resistor 13,
Figure 3 d with the same starting point t ₁ as the input gate pulse
A pulse signal shown in is obtained at the output terminal of the monostable multivibrator 11. This output signal and the input gate pulse are input to the NAND circuit 14, and the output terminal of the NAND circuit 14 receives a predetermined time delay determined by the capacitor 12 and the variable resistor 13 from the starting point _t1 of the input gate pulse. point in time
The start point is at t ₃ and the end point is the end point of the input gate pulse
The signal t shown in FIG. 3e, which coincides with t ₂ , is obtained. This signal is input to an image signal shading correction waveform generation circuit 41 located on the right side of the scanning section, which will be described next. Next, when the signal G is supplied to the base of the transistor 16 through the resistor 15, the transistor 16 remains in the low level while the signal G is at the low level.
becomes non-conductive, and the resistor 19,
A charging current I that charges the capacitor 17 flows through the transistor 18 . This charging current I causes the voltage Ec at one end 22 of the capacitor 17 to rise.
This voltage Ec is amplified by an amplifier 23 with a gain of 1 and appears as it is at the output terminal 24 of the amplifier 23. Here, the voltage E ₂₁ at one end 21 of the constant voltage power supply 20
increases by the charging voltage E _c and becomes E ₂₁ =E + E _c , but the current I flowing through the resistor 19 and transistor 18 is I = E ₂₁ -E _c /R = E/R (where R is the resistance 19 and transistor 18). The composite impedance of the emitter-collector impedance of transistor 1 is
If the impedance between the emitter and collector of 8 is constant, the capacitor 17 will always be charged with a constant current I during the low level period of the signal G, and a sawtooth wave signal with good linearity will be obtained at the terminal 24. . However, the signal appearing at the terminal 24 is inverted and amplified and passed through the capacitor 29 to the transistor 1.
8, the impedance between the emitter and the collector of the transistor 18 becomes smaller as the charging start time _t3 of the capacitor 17 approaches the charging end time _t2 . Since the impedance changes over time to become smaller, the charging current I of the capacitor 17 increases as it approaches the charging end time _t2 from the charging start time ₃ , contrary to the impedance between the emitter and collector of the transistor 18. As a result, the waveform appearing at the terminal 24 deviates from the straight line as shown in FIG. . The deviation of the sawtooth signal Q from the straight line can be varied by adjusting the gain of the inverting amplifier 26 using the variable resistor 28 and adjusting the amount of feedback to the base of the transistor 18. Next, the signal Q is amplified by a buffer amplifier 32 with a gain of 1, and this signal Q and the signal H shown in FIG. A shading correction signal having a shading correction waveform of the image signal is obtained. By the way, the waveform and amplitude of the waveform of the shedding correction signal of the image signal on the left side of the scanning section can be varied by adjusting the variable resistor 5 and the variable resistor 10, and the waveform and amplitude of the shedding correction signal of the image signal on the right side of the scanning section can be varied by adjusting the variable resistor 5 and the variable resistor 10. , the variable resistor 28, and the variable resistor 33, the waveform and amplitude can be varied, and the waveforms of the shading correction signals of the image signals on the left and right sides of the scanning section can be adjusted independently for the left and right sides. By supplying the shading correction signal RI to the amplification factor control terminal 39 of the video amplifier 37, controlling the gain of the video amplifier 37 according to the amount of shading of the image signal, and controlling the output amplitude of the video amplifier 37, accurate shading correction can be achieved. The resulting image signal is obtained at the output terminal 40 of the video amplifier 37.

If four sets of shading occur in one scanning section in the optical system using four sets of lenses and a solid-state scanning element as shown in Fig. 1a, as shown in Fig. 4, 4 having the same configuration as the shading correction waveform generation circuit block 42 shown in FIG.
2A, 42B, 42C, and 42D are connected to the input terminals of the four-column summing amplifier 34 as shown in FIG. 4, and each input gate pulse signal null shown in FIG. .about.W is supplied to each input terminal 1A, 1B, 1C, 1D, the shading of the image signal within each divided scanning section _t1 to _t4 ...... _t6 to _t2 is corrected, respectively. The shading correction signal C shown in FIG.

In the above two embodiments, in order to correct the shading of the image signal on the left side of the scanning section, the input gate pulse corresponding to the scanning section is directly differentiated to obtain waveform D. As shown in the figure, the differentiating circuit 6 may be placed after the monostable multivibrator 11 to differentiate the Q output of the monostable multivibrator 11.

FIG. 7 shows an embodiment of the second invention in which the present invention is applied when the characteristics of the lenses corresponding to each divided scanning section are the same when correcting the shading waveform A shown in FIG. 1a. In the figure, the input gate pulses corresponding to the divided scanning sections t ₁ to t ₄ and t ₆ to t ₂ shown in FIG.
When supplied to the input terminal of the monostable multivibrator 11A, . . . 11D, the signal curve shown in FIG. When these signals C to C are supplied to the input terminal of the OR circuit 43, the signal C shown in FIG. 5C is obtained. Each NAND circuit 14A, 14B, 1
The output signal circuits of 4C and 14D are as shown in FIG.
The signal wave shown in is obtained at the output terminal of the AND circuit. Therefore, from each output signal of the OR circuit 43 and the AND circuit 44, the fifth
Since the shading correction signal c shown in FIG. f is obtained, the circuit can be simplified.

Further, in FIG. 7, a NAND circuit may be used instead of the OR circuit 43 to supply the output signals of the monostable multivibrators 11A, 11B, 11C, and 11D to each input terminal.

Incidentally, in the above description, the present invention is applied to shading correction of facsimile signals, but it goes without saying that it can be applied to shading correction of other image signals such as television signals.

As described above, according to the present invention, it is possible to electrically achieve shedding correction easily and satisfactorily from the input gate pulses corresponding to the scanning section, and the apparatus can be downsized and simplified.

[Brief explanation of the drawing]

FIGS. 1a and 1b are waveform diagrams showing an example of an image signal including shading of a facsimile transmitter, FIG. 2 is a circuit diagram of an embodiment of the first invention, and FIGS. 3a to 3g are FIG. 2 is a waveform diagram of each part of the shading correction circuit, FIGS. 4 and 6 are circuit diagrams showing other embodiments of the first invention, and FIG. 7 is an embodiment of the second invention of the present invention. An exemplary circuit diagram, FIGS. 5a to 5f, is a waveform diagram of each part of the circuit diagram shown in FIGS. 4 and 7. In the figure, 6 is a differential circuit, 9 is a slice circuit, 11, 11A, 11B, 11C, 11D are monostable multivibrators, 14, 14A, 14
B, 14C, and 14D are NAND circuits, 16 is a transistor, 17 is a capacitor, 18 is a transistor as a variable impedance element, 26 is an inverting amplifier, 41 is a shading correction waveform generation circuit for the image signal on the right side of the scanning section, and 34 is an addition circuit. amplifier,
37 is a video amplifier, 42 is a shading correction waveform generation block, 43 is an OR circuit, and 44 is an AND circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Shading on the starting end side of the horizontal scanning period of the video signal by differentiating an input gate pulse signal corresponding to the horizontal scanning period of the video signal or a rectangular wave signal having the same starting point as this signal pulse signal. Means for obtaining a correction signal, inputting the output of a monostable multivibrator triggered by the input gate pulse signal and the gate pulse signal, from a point delayed by a predetermined period from the start point of the gate pulse signal to the end point of the gate pulse signal. a pulse generating circuit that outputs an input pulse that is at zero level for a period of , a switch element that is controlled by the input pulse and becomes non-conductive only during the zero-level period, and a switch element that is connected in parallel to this switch element and whose impedance is variable during the non-conductive period. A capacitor that is charged by a constant voltage power supply through the element, an inverting amplifier that outputs a change in the charging voltage of the capacitor as a control signal of opposite polarity, and means for controlling the variable impedance element using the control signal. A gain is achieved by means for obtaining a shading correction signal on the end side of the horizontal scanning period of the video signal, an adder circuit for outputting a shading correction signal obtained by adding both the shading correction signals on the start end side and the end side, and the shading correction signal. Shading correction circuit with controlled video intensifier. 2. Means for dividing one horizontal scanning section of the video signal into a plurality of small sections and generating a plurality of gate pulse signals corresponding to each of these divided scanning sections; An input pulse that takes as input the output of a monostable multivibrator triggered by a gate pulse signal and each of the above gate pulse signals, and is at zero level for a period from a point delayed by a predetermined period from the start point of the pulse signal to the end point of the gate pulse signal. a first logic circuit that inputs the output of each of the monostable multivibrators and outputs a pulse train that is at a positive level for a predetermined period from the starting end of each gate pulse signal; and each of the above pulse generation circuits. a second logic circuit that inputs the output of the video signal and outputs a pulse train that determines the width of the shading correction signal at the end of each divided scanning section of the video signal, and differentiates the output of the first logic circuit to calculate the video signal. means for obtaining a shading correction signal on the starting end side of each divided scanning section in the horizontal scanning period; a switch element that is controlled by the output pulse of the second logic circuit and becomes non-conductive only during the zero level period; A capacitor connected in parallel and charged by a constant voltage power supply through the variable impedance element during the non-conducting period, an inverting amplifier that outputs a change in the charging voltage of this capacitor as a control signal of opposite polarity, and the control signal. means for controlling the variable impedance element, means for obtaining a shedding correction signal on the end side of each divided scanning section in the horizontal scanning period of the video signal, and adding both the shedding correction signals on the starting end side and the end end side. A shading correction circuit comprising: an adder circuit that outputs a shading correction signal; and a video amplifier whose gain is controlled by the shading correction signal.