ON ONE METHOD FOR EXTRACTING IMAGE CONTOURS

N. F. KUCHER, O. G. MATUSHKIN

(Presented by the scientific seminar of the Department of Computer Engineering)

One of the most important problems facing designers of information display systems is the problem of timely perception, by the operator, of the image on the screen of an information system. In a number of cases, the rate at which images change on the screen exceeds a certain threshold of human perception. Therefore the functions of recognizing these images are assigned to automatic devices.

Fig. 1. Image generator

It is known [1] that the most informative feature of any image is the contour of that image under a definite gradation of brightness. Human perception of images takes place precisely at the level of contours. Preliminary processing of the information arriving at the screen of a display system makes it possible to display only the contours of the image, facilitating the perception of images not only by a human—

Fig. 2. Contour-extraction circuit

… but also by a recognizing automaton. We have developed one variant of a system for extracting an image contour. The experiment was carried out on an RLS indicator system of the RBP-4 type.

The video signal was generated by means of an image generator proposed by B. S. Ryabyshkin, operating on the principle of a running beam. A block diagram of the generator is shown in Fig. 1.

A mask bearing an image in the form of transparent and blackened areas was placed on the screen of one of the three station indicators operating synchronously in the radial-circular scanning mode. The screen of indicator tube 1 glows with constant brightness. When the screen of indicator 1 is scanned, the beam successively passes over the light and blackened areas of the mask, and the photomultiplier located behind the mask is illuminated accordingly when the beam passes through the light areas of the mask.

Fig. 3. Ordinary image

The signal from the output of the photomultiplier is fed to a cathode follower, whose output signal goes to the beam-brightening circuit of indicator 2 and to the contour-extraction circuit. On the screen of indicator 2 an image is displayed that fully corresponds to the pattern of the mask.

A block diagram of the contour-extraction device is shown in Fig. 2.

The video signal from the image generator is amplified by a video amplifier and subjected to limiting by means of a Schmitt trigger at a specified brightness level. From the output of the Schmitt trigger there is taken—

Fig. 4. Contour image.

A video signal is obtained, consisting of a sequence of rectangular pulses whose duration is equal to the duration of the sweep of indicator beam 1 over the light region of the mask. This signal is fed to a device that produces the modulus of the derivative of the rectangular pulses. The resulting pointed pulses, corresponding to the beginning and end of the sweep of indicator beam 1 over the light region of the mask, trigger a shaping blocking oscillator, which generates pulses of standard duration and amplitude. These pulses are supplied to the illumination of indicator beam 3, on which the contour image is displayed.

Figures 3 and 4 show photographs from the screens of indicators 2 and 3, on which the ordinary and contour images are displayed. As can be seen from these photographs, the accuracy of reproducing the contour is quite good; moreover, with proper adjustment of the contour-extraction circuit, the quality of the contour image can be improved.

REFERENCES

1. B. F. Lomov. Man and Technology. Sovetskoe radio, Moscow, 1966.