JPS607278B2 - Digital image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus in which an image display means used in a scanning electron microscope or the like is configured digitally.

In electron beam devices such as scanning electron microscopes, various images are often displayed or photographed using a cathode ray tube (CRT). In this case, the video signal printed on the CRT is generally treated as an analog signal and amplified by a linear amplifier, but the frequency characteristics (functions) of the amplifier are adjusted to express the part to be emphasized. It is necessary to incorporate an image processing circuit to adjust input and output functions. There are various types of image processing circuits, but in order to make fine adjustments, it is necessary to use complex and expensive circuits. The present invention has been made in view of these points, and it is an object of the present invention to process a desired video signal with a relatively simple circuit configuration by digitally processing the video input signal. The present invention is characterized in that various signal processing is performed during AD conversion and DA conversion of video signals, and input/output characteristics are controlled by changing the combination of resistors in the AD conversion means.

The present invention will be explained in detail below according to embodiments. FIG. 1 is a schematic diagram showing the configuration of an apparatus according to an embodiment of the present invention.

In the figure, 1 indicates an input video signal terminal, and as the video signal, for example, in the case of a scanning electron microscope, a detection signal of secondary electrons generated from a sample by electron beam irradiation is used. The signal is C for displaying the wife of a scanning electron microscope.
It is used as an RT brightness modulation signal. The video signal from input terminal 1 is first amplified by amplifier 3 and then sent to AD converter 4.
and is divided into, for example, eight stages depending on the signal strength. The separated signal is processed by a processing means such as a filter circuit 5 for removing noise, and then sent to a DA conversion circuit 6.
is outputted to the output terminal 2 via the adder 7. With this kind of circuit configuration, an analog input signal is converted into a digital video signal, but the brightness modulated image actually displayed on a CRT screen has eight gradations of brightness, and compared to an analog image, it is hardly visible to the naked eye. It is barely distinguishable.

However, depending on the observation sample, a fine structure may be required, so in the apparatus shown in Figure 1, the amplifier 3
The output is applied to an adder circuit 7 via an attenuator 8. FIG. 2 shows a generation circuit for a comparison reference signal applied to a comparator 9 used in the AD converter 4 in the device shown in FIG.
, 12 are connected to terminals P, Q, and R, respectively, to change the input/output characteristics.

That is, by switching the changeover switches 10, 11, and 12, the connection of the resistor group having the values shown in the figure changes, so that the combination of dividing resistors that divides the reference voltage of 15V is 3.
The input terminals a, b, c, d, e,
The potentials applied to f and g also change. Also, comparator 9 is 7
Using the potentials applied to the input terminals as a comparison standard, it is compared to which range of each reference potential the level of the input signal falls, and the results are a', b', c', d', e'? f',
Output to one of the eight types of g. An example of this relationship is shown in FIG. 3, in which the dashed line A represents the so-called y (gamma -) control curve. Therefore, by changing the resistance values of the dividing resistors and their combinations in the circuit shown in Fig. 2, a, b, c, d, e,
Since the positions of f and g can be changed freely, the shape of the broken line can be changed arbitrarily. For example, in addition to the above-mentioned y control, it is also possible to form a compander as shown by B and C in Figure 4 by combining input/output linearity compression (compressor) and expansion (expander). can. In the circuit shown in FIG. 2, if the terminals of the changeover switches 10, 11, 12 are connected to Q, the output terminals a, b, c, d, e of the comparator 9? f,
Since the resistance values between g are all equal to 1000, the input/output characteristic becomes a straight line. Next, the switch 10, 11,
When the 12 terminals are connected to P, a 1000 resistor is connected in parallel between the c terminal of the comparator 9 and the power input (5V), and a 700 resistor is connected between the e terminal of the comparator 9 and the ground potential. Since these are connected in parallel, the input/output curve has a steep slope at the center, as shown by broken line B in FIG. Conversely, if the terminals of changeover switches 10, 11, and 12 are connected to R, comparator 9
Since 500 resistors are connected in parallel between terminals c and f of , the central portion has a gentle slope as shown by broken line C in FIG. Conventional input/output characteristic adjustment circuits that handle analog signals had to be constructed using diodes, capacitors, and other elements in addition to resistors. It is understood that this is a simplification. Furthermore, in the embodiment shown in FIG. 1, the frequency characteristics of the filter circuit 5 can also be advantageously adjusted.

In other words, in conventional analog signal processing, when performing high-frequency attenuation, if the waveform is distorted, that distortion is directly reflected on the CRT screen, impairing the sharpness of the edges in the image. In the apparatus shown in FIG. 1, even if the Takagi information is attenuated, waveform distortion can be suppressed to zero, and edge sharpness is maintained. On the other hand, when it is desired to emphasize a high frequency region, analog processing increases noise in the CRT image, making it difficult to observe, but digital processing eliminates unnecessary noise from the beginning, so this drawback does not occur. It should be noted that the present invention is not limited to the above-described embodiments, but can be modified in various ways.

For example, as a comparison reference signal generation circuit for a comparator used in the AD converter 4 in the device shown in FIG.
The circuit shown in the figure can also be used. The circuit in Figure 5 is 1
A needle resistor r jump is connected in series, and the output value of the terminal e,, e2......e,2 provided at each connection point is compared with 12 comparison circuits (not shown). 6), an output Eo as shown in FIG. 6 is obtained for the video input signal e. Three curved turtles 3, 14, shown in FIG.
15 is the resistance value of the variable resistor R in FIG. 6, respectively.
. It represents the ``linear'', ``expander'', and ``compander'' characteristics that can be obtained when 3, 3, and 3 are used. Similarly, the resistance values RA and RB of the variable resistor in the circuit of FIG.
The combination of (RA=7r~RB=), (RA=1
The input/output characteristics obtained when RB=r), (RA=r, RB=12) are expressed as 16, 17, and 17 in Figure 8.
This is shown by the curve No. 18. As described above, according to the present invention, it is possible to ideally perform image signal processing in a scanning electron microscope with an extremely simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, FIG. 2 is a schematic diagram showing the main parts of the device in FIG. 1, and FIGS. 3 and 4 are diagrams for explaining the operation of the device in FIG. 1. 5 and 7 are schematic diagrams, and FIG.
8 and 8 are schematic diagrams for explaining the functions of the circuits shown in FIG. 5 and FIG. 7, respectively. 1: input terminal, 2: output terminal, 3: amplifier, 4: AD converter, 5: filter circuit, 6: DA converter, 7: addition circuit, 8: attenuator, 9: comparator. Next “Figure Z Figure Next 3 Figure Next A Figure Next Figure *6 Figure Next 7 Figure Next 8 Figure

Claims (1)

[Claims] 1. Means for performing various signal processing during AD conversion and DA conversion of the input video signal is provided, and the AD conversion means is configured using a comparison circuit to which a plurality of comparison reference signals are applied, and a plurality of dividing resistors. 1. A digital image processing device, wherein a reference voltage signal divided by a voltage converter is used as the comparison reference voltage, and a plurality of combinations of the plurality of dividing resistors can be selected.