GB1560682A

GB1560682A - Method of scanning infrared images

Info

Publication number: GB1560682A
Application number: GB2781268A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-07-11
Filing date: 1968-06-11
Publication date: 1980-02-06

Description

(54) METHOD OF SCANNING INFRARED IMAGES (71) I, JOSEF-FERDINAND MENKE, a German Citizen of 27, Fördes- trasse, 2392, Giiicksburg, Ostee, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of scanning infrared images, particularly thermal images, using a row of receiving elements or receivers.

With such a method it is desirable to keep image sequence frequency as low as possible, with a view to a small bandwidth and in part to large time constants of a receiver, whilst reproducing a stationary and if possible flicker-free image on the screen.

It is known to scan infrared images by means of a row of receivers disposed one immediately below another, wherein an image passes the row of receivers by the scanning movement of a mechanical/optical system, and a multiline image is produced according to the number of receivers.

This method requires a large number of separate parts, with correspondingly high cost, if good image quality and a sufficient number of lines are to be obtained for a given image.

It is an object of the invention to provide, for a given image sequence frequency, an acceptable relationship as between i) the number of receivers, ii) the bandwidth of the system, and iii) a suitable number of lines.

According to the invention there is provided a method of scanning an infrared image by means of receivers arranged in a row, wherein each receiver is used for successively scanning two or more lines, the parts of the original image scanned by individual receivers being combined to form the desired whole image.

The receivers may be spaced apart a distance which is a whole multiple of the height of the lines.

Preferably the number of receivers, and the number of lines to be scanned by each receiver, are such that the number of parts of the image is adapted to the requirements of the bandwidth, the number of scanning or image points to be transmitted per unit of time, and the scanning frequency.

The method of the invention has the advantage that the number of receivers may be substantially reduced for a given number of lines. In this way a favourable compromise can be reached, in accordance with the time constant can be reached, in accordance with the time constant of the receiver, between the cost of the mechanical scanning device and of the electronics.

Since the parts of the image overlap, flickering during reproduction is reduced.

The method can be further improved by using the advance and return of the line scanning device in a like manner for scanning different lines.

In this way it is possible to reduce by half the number of complete scanning movements of the mechanical optical systems, consisting of a forward and reverse movement, under otherwise equal conditions, or to increase the number of scanning operations to twice the value with the same number of complete scanning movements.

Use of the forward and reverse movement of the line scanner for scanning different lines may be realised in a simple manner by tilting the scanner perpendicularly to the line at the end of the forward movement and then at the end of the reverse movement by tilting in the opposite direction.

Further details of the method, and the arrangement preferably used for performing it, will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagram showing scanning for producing two parts of an image; Figure 2 is a diagram showing a similar arrangement for producing four parts of an image; and Figure 3 is a circuit diagram of the receiving elements.

With two parts of an image (Figure 1), the individual receivers or receiving elements 21, 22, 23, 24 are spaced at a distance equal to the height of a receiver. By means of a mechanical scanning system, the image is so passed over the receivers that they describe relative loop-like motions, indicated in respect of receiver 21 by lines 11, 12; in respect of receiver 22 by lines 13, 14. Lines 11 and 13 are described during forward scanning and lines 12 and 14 during reverse scanning. In this manner lines 1, 3, 5 and 7 are formed during forward scanning and during reverse scanning, lines 2, 4, 6 and 8.

In this arrangement, after termination of forward scanning, the image (not shown) is moved by the height of one line (corresponding to the height of a receiver), so that scanning by all the receivers is displaced by one line.

The reverse scanning is then used for scanning the second part of the image (i.e.

the lines 12, 14). In this way the time required for scanning the whole image is reduced to substantially half the time hitherto required.

With four parts (Figure 2), the distance between the individual receivers 21, 22, 23 is three times the height. The individual parts are scanned in the sequence 11, 13, 12, 14, or 15, 17, 16, 18 etc. Here, during advance of the image from line 1 to 3 and from line 2 to 4 the image is tilted by two line heights and during the return from line 3 to 2 by one line height, and from 4 to 1 by three lines.

The distance between the receivers may also be increased to seven times the height of a receiver. However, this may be performed only with receivers with very small time constants.

The scanning electronics should switch, with a row of a large number of receivers, from one receiver to the next with the lowest possible signal levels and with a minimum of deterioration of the signal-tonoise ratio. PbS cells are suitable for this purpose. Several circuits are possible in this connection.

Figure 3 shows an arrangement for carrying out the method. The receivers are shown at 21, 22, 23 and 2n. A low noise preamplifier is connected to each receiver.

These preamplifiers are shown at 31, 32, 33 and 3n; Conveniently these preamplifiers are d.c. voltage coupled miniaturised amplifiers which are particularly adapted to the PbS cell. The preamplifiers are necessary because the signals received may be only a little above the noise level.

Gate circuits 41, 42, 43 to 4n are connected to the preamplifiers. The outputs 51, 52, 53 and Sn of the gate circuits are connected by a common lead 25 to a common video amplifier 10 and are successively actuated by a ring video amplifier 10 and are successively actuated by a ring pulse generator 20. In this way the individual signal voltages are serially scanned.

The ring pulse generator may be an arrangement of flip flops, which are electrically so connected to a ring that only one at a time of the n stages can assume a given state (to which it is switched by a transistor). A pulse produced by a timing generator 30 passes via leads 2829 to the input of the ring pulse generator 20, causing the gate circuits 41 to 4n to be successively opened. The signal passes for brightness control through the video amplifier 10 to the Wehnelt cylinder of an oscillograph 27.

For producing the line deflecting voltage, transmitted through a lead 69 to the oscillograph, the input pulse of the first switching pulse generator is used in a line deflecting generator 26 for producing, by means of a capacitance, a saw tooth wave form which is applied through suitable final amplifiers to the vertical deflector plates of the oscillograph. Another saw tooth generator 36, whose rise and fall times are adjustable within wide limits for matching with the mechanical movement of the scanning system, produces the horizontal deflector voltage applied through a lead 70 to the oscillograph. The saw tooth generator 36 may be synchronised externally by a marking derived from the movement of the scanning system.

For suppressing beam flyback, both line and picture flyback pulses are applied to the Wehnelt cylinder as black control.

WHAT WE CLAIM IS: 1. Method of scanning an infrared image by means of receivers arranged in a row, wherein each receiver is used for successively scanning two or more lines the parts of the original image scanned by the individual receivers being combined to form the desired whole image.

2. Method according to claim 1, wherein the number of receivers and the number of lines to be scanned by each receiver are chosen according to the required bandwidth, or the number of scanning points to be transmitted per unit of time.

3. Method according to claim 1 or claim 2, wherein line scanner advance and return are used in like manner for scanning different lines.

4. Method according to claim 3, wherein scanning of different lines during forward scanning and reverse scanning is achieved by tilting the scanner perpendicularly to the lines.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. producing two parts of an image; Figure 2 is a diagram showing a similar arrangement for producing four parts of an image; and Figure 3 is a circuit diagram of the receiving elements. With two parts of an image (Figure 1), the individual receivers or receiving elements 21, 22, 23, 24 are spaced at a distance equal to the height of a receiver. By means of a mechanical scanning system, the image is so passed over the receivers that they describe relative loop-like motions, indicated in respect of receiver 21 by lines 11, 12; in respect of receiver 22 by lines 13, 14. Lines 11 and 13 are described during forward scanning and lines 12 and 14 during reverse scanning. In this manner lines 1, 3, 5 and 7 are formed during forward scanning and during reverse scanning, lines 2, 4, 6 and 8. In this arrangement, after termination of forward scanning, the image (not shown) is moved by the height of one line (corresponding to the height of a receiver), so that scanning by all the receivers is displaced by one line. The reverse scanning is then used for scanning the second part of the image (i.e. the lines 12, 14). In this way the time required for scanning the whole image is reduced to substantially half the time hitherto required. With four parts (Figure 2), the distance between the individual receivers 21, 22, 23 is three times the height. The individual parts are scanned in the sequence 11, 13, 12, 14, or 15, 17, 16, 18 etc. Here, during advance of the image from line 1 to 3 and from line 2 to 4 the image is tilted by two line heights and during the return from line 3 to 2 by one line height, and from 4 to 1 by three lines. The distance between the receivers may also be increased to seven times the height of a receiver. However, this may be performed only with receivers with very small time constants. The scanning electronics should switch, with a row of a large number of receivers, from one receiver to the next with the lowest possible signal levels and with a minimum of deterioration of the signal-tonoise ratio. PbS cells are suitable for this purpose. Several circuits are possible in this connection. Figure 3 shows an arrangement for carrying out the method. The receivers are shown at 21, 22, 23 and 2n. A low noise preamplifier is connected to each receiver. These preamplifiers are shown at 31, 32, 33 and 3n; Conveniently these preamplifiers are d.c. voltage coupled miniaturised amplifiers which are particularly adapted to the PbS cell. The preamplifiers are necessary because the signals received may be only a little above the noise level. Gate circuits 41, 42, 43 to 4n are connected to the preamplifiers. The outputs 51, 52, 53 and Sn of the gate circuits are connected by a common lead 25 to a common video amplifier 10 and are successively actuated by a ring video amplifier 10 and are successively actuated by a ring pulse generator 20. In this way the individual signal voltages are serially scanned. The ring pulse generator may be an arrangement of flip flops, which are electrically so connected to a ring that only one at a time of the n stages can assume a given state (to which it is switched by a transistor). A pulse produced by a timing generator 30 passes via leads 2829 to the input of the ring pulse generator 20, causing the gate circuits 41 to 4n to be successively opened. The signal passes for brightness control through the video amplifier 10 to the Wehnelt cylinder of an oscillograph 27. For producing the line deflecting voltage, transmitted through a lead 69 to the oscillograph, the input pulse of the first switching pulse generator is used in a line deflecting generator 26 for producing, by means of a capacitance, a saw tooth wave form which is applied through suitable final amplifiers to the vertical deflector plates of the oscillograph. Another saw tooth generator 36, whose rise and fall times are adjustable within wide limits for matching with the mechanical movement of the scanning system, produces the horizontal deflector voltage applied through a lead 70 to the oscillograph. The saw tooth generator 36 may be synchronised externally by a marking derived from the movement of the scanning system. For suppressing beam flyback, both line and picture flyback pulses are applied to the Wehnelt cylinder as black control. WHAT WE CLAIM IS:

1. Method of scanning an infrared image by means of receivers arranged in a row, wherein each receiver is used for successively scanning two or more lines the parts of the original image scanned by the individual receivers being combined to form the desired whole image.

5. Method according to claim 4, wherein

the scanner is tilted by more than one line between forward and reverse scanning.

6. Method according to any preceding claim. wherein signal voltages are successively scanned at the output of the individual receivers, or at the output of preamplifiers, by an electronic switching circuit and then applied to a common video amplifier.

7. Method according to claim 6, wherein the electronic switching circuit is controlled by an electronic ring pulse generator.

8. Method according to claim 7, wherein the vertical deflection for the beam of a cathode ray tube is derived from the impulses of the ring pulse generator.

9. Method according to claim 8, wherein the output signal of the video amplifier causes brightness modulation of the beam which is deflected vertically in saw tooth form according to the switching frequency of the electronic switching, and horizontally according to the scanning function of the optical/mechanical scanning system.

10. Method of scanning infrared pictures substantially as herein described, with reference to the accompanying drawings.