Security television system with expanded dynamic range in computer image recording mode.

Security television system with expanded dynamic range in computer image recording mode..

Security television system with dynamic range expansion in computer image recording mode

SMELKOV Vyacheslav Mikhailovich, Candidate of Technical Sciences, Associate Professor

Source: Magazine «Special Equipment» No. 6 2007

In [1], an analytical assessment of the method for expanding the dynamic range of a security television system with multichannel «light-signal» conversion in a television camera was proposed. The difficulties of the fundamentally necessary combination of the image of the observed scene with the television rasters of photodetectors on matrix CCDs lead to the practical implementation of this method only with two-channel parallel conversion [2, 3, 4]. However, even for two-channel «light-signal» conversion, this combination of rasters remains an optical-mechanical problem with obvious difficulties, both in the process of manufacturing the television system and in the process of its operation.

According to leading domestic experts [5, p. 23], at present, there is a fusion of computer technology, television and communications, characteristic of the second stage of the solid-state revolution in television. An obvious trend of this process is the counter movement towards television on the part of computer technology developers. As an example of this phenomenon, we can name the presence on the market of a product of the AverTV series, consisting of a tuner board with an installation CD, which can turn the user's computer into a real multimedia center, since it can be used to watch TV programs, conduct video conferences, take pictures and video recordings.

Below is proposed a technical solution for a television-computer system capable of solving the problem of expanding the dynamic range of recorded images with two-channel sequential conversion of «light-signal» using a single photodetector on a CCD matrix in a television camera and with the AverTV product installed in a computer.

In this solution, two consecutive shots of a composite video signal from a television camera are recorded into a computer, with the video signal itself prepared for shooting and consisting of two periodic sequences following with a time interval between shots. The frame components of each sequence are formed at two different photodetector accumulation durations, which are optimal or close to optimal values, respectively, for the light and dark details of the transmitted scene fragments.

The structural diagram of the system is shown in Fig. 1.

Fig. 1. Structural diagram of the television-computer system

It consists of a TV camera (1) and a computer (2) connected in series via a composite video signal. The TV camera contains a lens (1-1) and a TV signal sensor (1-2) located in series and optically connected, as well as an RS trigger (1-3) and a sync pulse selector (1-4), a counter-divider (1-5) and a preset and switching unit (PSU) (1-6) connected in series. The «S» input of the RS trigger (1-3) is the «Start» input, and the «R» input of the RS trigger (1-3) is the «Stop» input of the TV camera (1).

Note that control pulses to the «S» and «R» inputs of the RS trigger (1-3) can be supplied from the computer (2) via the RS-232 or RS-485 interface coupling unit (1-7) installed in the TV camera (see. Fig. 1).

As a sensor (1-2), as in solution [3], a VSI-746 frameless camera, proposed by the Russian company EVS (St. Petersburg), can be used. It is based on a CCD matrix with a number of elements of 582 x 752 and a target size of a diagonal of ½ inches.

The sensor (1-2) is characterized by the presence of the first and second control inputs. For the VSI-746 device, the first control input is pin 20 of the CXD2463R microcircuit. If it is necessary to enable automatic accumulation time adjustment (AAT), it is necessary to apply logical «0» to this pin, and logical «1» in TTL levels to switch to manual control mode.

The second control input of the VSI-746 device is formed by pins 11, 12, 13 of the CXD2463R microcircuit. For operation in the AAT mode, these pins must «hang in the air», since the corresponding potentials in the range of 1.3 — 3.5 Volts are applied to them using high-resistance resistive dividers. If it is necessary to switch eight values ​​of fixed exposures in the range from 10 μs. up to 10 ms, then code combinations of zeros («0») and ones («1») specified in Table 1> below must be supplied to them.

This solution uses two code combinations: «000», corresponding to the minimum accumulation time of the photodetector, equal to 10 μs, and «111» — the maximum time of 10,000 μs. The presetting of these codes is provided in the BPC block (1-6) of the television camera.

Table 1