DE2207526A1 - IMAGE TRANSFER SYSTEM WITH SELECTIVE CONTRAST CONTROL - Google Patents

Description

Image transmission system with selective contrast control The present The invention relates to an improved image transmission system, and more particularly to one improved image transmission transmitter and an improved image transmission receiver each of which with transmitters and receivers of the same kind but without the improved ones Circuits of the present invention is compatible.

Image transmission systems are used in various applications to scan a paper or document in one place and document signals to one remote place where the scanned Paper or document is reproduced. Such an image transmission system is in the US patent application, Serial number 669.315 * disclosed. Such image transmission systems are used to reproduce all kinds of documents including photographs, typewritten or printed material or other information. Although previously known image transmission systems have worked more or less satisfactorily, has been made by the inventors of the present invention found that such systems do have some disadvantages. For example, it has been found2 that in a given image transmission system some a photograph or document with all shades of gray between white and Black scans the overall sensitivity of the system d. H. the curve of "gray output" to "gray input" should be as linear as possible. With such a linear sensitivity also includes the photograph reproduced on the image transmission receiver all shades of gray between white and black and can be a very faithful and provide exact reproduction. However, if there is printed information or similar material scanned for reproduction at a remote location has been determined that a non-linear sensitivity of the system is more desirable. This is based on because a non-linear sensitivity creates a sharper contrast between whites and dark in which to be reproduced Document created so that typewritten or written material very sharp with a white background and sharp appears in dark or black letters. The characteristic or type of transmission medium between the image transmission sender and receiver is closely related to both of these problems together.

The object of the present invention is a new and To provide improved image transmission equipment2 which includes an image transmission transmitter and an image transmission receiver including both the image transmission receiver as well as the image transmission transmitter with image transmission, or

Recipients that do not include the present invention can be used and yet include improved operation and resulting improved provide for reproduced document.

These and other objects are achieved in accordance with the present invention in an image transmission sender achieved with a heavily modified step carrier circuit between the point at which electrical signals are provided by a scanning device and coupled to the point in the electrical circuit is where the signals are converted into frequency-modulated signals.

The Schmitt carrier circuit is a feedback circuit in the form of a rectifier, understand that a more linear operation for image scanning provides. The input of the SchEitt carrier is provided with a rectifier for Improvement of the sensitivity for use with documents made of carbon paper can be reproduced. The circuit is with controls that understand the threshold level and adjust the saturation level of the transmitted signal. A switch is provided which makes the circuit sensitive to either a photograph or a printed one Copy can adjust appropriately. The exit of the step door is with upper and lower fixed clamping circuits provided to shift the frequency swing to a selected one Limit area. In an image transmission receiver according to the present invention Invention is an improved circuit between the point at which frequency modulated Signals are demodulated and provided to the output to the converters. This improved Circuit arrangement uses a diode rectifier in shunt between the demodulated signals and the converter with the required transfer function of the gray scale in the receiver component. Also a wave control circuit is provided so that the operator at the image transceiver when reproducing written or printed documents, the sensitivity threshold can be adjusted so that a sharp and clear transition between white and black is provided whereby signals of a low level are suppressed, which are very annoying could be. There is also a background control for the distance between the pens and the slightest transition time effects of the pens Set copy to reduce horizontal shifts during the printing process to a minimum and a saturation control to be able to set the gray level above which the copy will be black. The independent Setting these controls compensates for tolerance problems in the manufacture of such controls Machines with a consequent reduction in their costs.

The invention is now based on a preferred embodiment in Described in detail in connection with the accompanying drawings.

It shows: Fig. 1 is a schematic perspective view an image transmission system incorporating the improved circuitry of the present invention Invention in an image transmission transmitter and in an image transmission receiver can use; Fig. 2 is a block diagram showing the electrical circuitry an image transmission transmitter in accordance with the present invention; 3 shows a block diagram of an electrical circuit arrangement of an image transmission receiver, using the present invention; Fig. 4 is a complete electrical circuit diagram of the improved circuit arrangement according to the invention in the image transmission transmitter of Fig. 2; Figure 5 is a complete electrical schematic of the improved electrical Circuit arrangement according to the invention, which is used in the image transmission receiver of Fig. 3 is used; FIGS. 6 to 12 are graphic representations of various transfer functions in known plants; Figures 13 through 37 are graphs showing Transfer functions in the improved system of the present invention in FIG illustrate different operational locations in a qualitative way.

In Fig. 1 is an image transmission system having two image transmission machines 10, 11, which are connected via a telephone system 12. Fig. 1 represents an acoustic coupling to the telephone line, an inductive coupling or ebie direct coupling can also be used. Usually both are image transfer engines 10, 11 arranged so that each machine is used for sending or receiving can be.

In Fig. 1, it has been assumed that the image transfer engine 10 is used as a transmitter for scanning a document transmitted by the Image transfer machine 11 is to be reproduced, so that the image transfer machine 11 is used as a receiver. The image transmission machines 10, i 11 are known and may be of the type shown in the above-mentioned application, so that they are only briefly described. When used as a transmitter, the image transmission machine scans 10 a document, for example with a moving light spot and used a photosensitive device for manufacturing electrical Signals' indicative of the specific area scanned on the document are. These electrical signals can take several forms, although the present invention as intended for the o-like signals; H. Signals2 the can be obtained from an image. The transmitter 10 converts the electrical signals into frequency-modulated signals with a tone frequency around that for the relative brightness or darkness of the document surface being scanned are indicative.

These frequency-modulated signals are through a cable 13 to a acoustic coupling 14 connected to a loudspeaker or the like having acoustic transducer which converts the electrical signals into audible signals converts.

The audible signals are sent to the mouthpiece of an ordinary telephone receiver 15 directed. The telephone receiver 15 is connected to the telephone system 12. By Prior local or remote connections, a person at the transmitter 10 can connect with a telephone receiver 16 at the location of the receiver 11. Even though the telephone system 12 is shown with simple open wire connections it is evident that the system 12 can use any conventional communication facility, such as cables, cable carriers or radio carriers.

The telephone receiver 16 on the telephone at the receiver 11 is through an acoustic coupling 17 and a cable 18 are connected to the receiver 11. If the acoustic coupling 17 is used in the reception mode, are the audible signals generated by the earpiece of the telephone handset 16 directed at a microphone in acoustic coupling 17. The microphone in the acoustic coupling 17 converts these audible signals into electrical signals, which are fed to the receiver 11 through a cable 18. The receiver 11 has suitable electrical circuits for converting the electrical signals into mechanical ones Functions that make marks on a document. If the recipient 11 is exactly synchronized with the transmitter 10, is that produced by the receiver 11 Document a fairly faithful and complete reproduction of the information in the transmitter 10 scanned document.

However, as mentioned above, by the inventors herein present Invention found that current image transmission transmitters and receivers a faithful reproduction of photographs or documents that have gray shadows in them do not produce as desired. It has also been found2 that current picture broadcasters and recipients a good, clean and crisp printed document do not provide.

Thus, there is an improved operation of the current image transmission facilities are desirable, especially from the standpoint of the user or quality.

Figure 2 illustrates an overall block diagram of the present invention containing electrical circuitry to scan a document and frequency modulated Produce signals indicative of the document being scanned.

This circuit contains a transducer that is insensitive to scanning or a photocell 20, the signals of which are typically DC signals. These Signals are chopped or decomposed for simplified amplification and in the chopper and amplifier 21 amplified. The amplified video signals are then rectified and filtered to produce DC signals that are between selected levels vary e.g. B. from 0 to 7 volts.

In this selected area, 0 volts represents white voltages above 0 volts represent darker shadows and 7 volts represent black. This Rectifying and filtering takes place in a rectifier and filter 22, its Output circuit then to a signal circuit 23 according to the present invention is coupled. This signal circuit 23 is shown in detail in FIG and will be further described. This circuit modifies the DC signals they have different sensitivity to shadows from white to black to leave and has a switch for changing the circuit 23 to printed To transmit material that is a more desirable implementation for these types of signals used. Signals fall from the signal circuit 23 of the present invention still in the direct current range between 0 and 7 volts and become a voltage controlled oscillator 24 supplied. The oscillator 24 uses the DC signals in order to produce frequency modulated signals which, for example, between 1500 and 2450Hz vary, depending on the applied DC control voltage.

These frequency modulated signals are the acoustic coupling 14 in Fig. 1 which it converts into audible signals for application to the Telephone receiver 15 and for transmission to the receiver 11.

3 shows a block diagram showing the one used in the receiver 11 represents electrical circuit for receiving the frequency-modulated signals. These signals are produced as audible signals by the telephone handset 16 and the acoustic coupling 17 which converts the audible signals into electrical Signals converts, which is typical for the frequency-modulated signals between 1500 and 2450 Hz are. These signals are fed via a demodulator 30 for frequency modulation, which converts the signals into direct current signals in a range between 0 and + 7 volts implements, which can vary in this area in quotas that z. B. between Direct current and 1260 Hz are indicative. These DC signals become a Signal circuit 31 supplied, which according to the present invention, the signals further modified to make the sensitivity for the entire system more linear when signals indicative of an image are transmitted. The same circuit creates when fed by the transmitter, d. H. in the mode of printing a Sensitivity of the entire system which provides a high contrast for a "DrucdL copy results and which can also be modified to adjust the white level to any desired Set the threshold or background and the gray level that will be printed, d. H. adjust the saturation level. This circuit 31 is detailed in Fig. 5 and will be explained more fully. The DC signals from the circuit 31 have enough power to operate output transducers 32 which are electrical Signals in appropriate implement mechanical or physical movement, which cause the production of a mark on a document or the document to mark. This marking is carried out by a pencil or by ink or, as in the present invention, preferably by pressing against a piece of carbon paper which is held against a paper which becomes the copied document. The pressure this pressing causes the carbon paper to leave a mark, which represents a portion of the image scanned at the transmitter 10.

4 is a circuit diagram of a signal circuit 23 of the present invention Invention shown. Basically, this circuit 23 contains a modified one SehEitt-Trerschaltung, the two NPN transistors coupled together in a known manner Q 1 and Q 2. Signals from the rectifier and filter 22 are passed through a Resistor R 1 and a potentiometer R 2 are fed to the base of transistor Q 1. A DC power source with a positive voltage B and a negative voltage B- is provided on busbar 40 and 41, respectively. A reference bus 42 which a ground or a reference potential can be connected is also provided. The collector of the transistor Q 1 is connected to the positive via a resistor R 3 Bus bar 40 coupled. The output from transistor Q 1 is coupled via a resistor R 4 to a potentiometer R 5, whose movable Tap connected to the base of transistor Q 2. The potentiometer R 5 is coupled to the negative busbar 41 via an additional resistor R 6. The collector of the transistor Q 2 is connected to the positive via a resistor R 7 Bus bar 40 is coupled and the emiter of transistor Q 2 is across a resistor R 8 coupled to the negative busbar. The output of transistor Q 2 becomes at its collector and is connected to an amplifier transistor via a resistor R 9 Q 3 coupled which is an NPN transistor. The collector of transistor Q 3 is coupled to the positive bus bar 40 via a resistor R 10 and the The emiter of the transistor Q 3 is connected to the negative busbar via a resistor R 11 41 coupled. Output signals are related to the emiter of transistor Q 3 derived from the reference busbar 41 for application to the voltage controlled oscillator 24.

The circuit described so far is more or less conventional. In accordance with the present invention, multiple circuitry and feedback are shared arrangements provided, which the processing of the image and Improve pressure derived signals, change the gray scales and maintain the level the output voltage. These circuits are when related with improvements to U.S. patent application filed March 3, 1969, serial number 803,609 a vastly improved overall image transmission system is used result. The first of these circuits contains a resistor R 12 and a diode rectifier D 1 those in the feedback circuit of the switch between the emiter of transistor Q 2 and the emiter of transistor Q 1 are connected. It is it has been found that this feedback circuit has the resistor R 12 in parallel with the diode rectifier D 1 a method of generating the desired conversion of the signal from the filter 22 and thus gives a signal that is more faithful Provides reproduction of the scanned copy. The diode D 1 is as actual shown consisting of four diode rectifiers connected in series are although it is to be understood that a single diode rectifier or other Varistor (which is a semiconductor device with two terminals the non-linear Voltage current characteristics) with the necessary tension Current property instead of the four individual diode rectifiers shown as well as the other diodes shown in the circuits can. It has also been found that where carbon paper is used to make a Document in the receiver 11 to mark a certain charcoal transfer characteristic between the exciting signal and the transfer of the coal to the desired one There is a controlled way of pressing in the marking. About this characteristic to compensate, according to the invention, a circuit is provided on the transmitter, the one resistor R 13 and one between the base of the transistor Q 1 and the Reference bus 42 coupled diode rectifier D 2 contains. The reason for the inclusion of this compensating circuit in the transmitter instead of in the receiver is to create a better signal-to-noise ratio as later in the discussion will emerge more clearly. Those skilled in the art will appreciate that the diode rectifier D 2 can contain only a single element instead of the two elements shown if such a single element has the necessary characteristics. This circuit in connection with R 1, R 2 and the switch S 1 sees a procedure for the required change in the sensitivity of the circuit of the filter 22 on the voltage controlled oscillator 24 before.

As already mentioned, it is desirable that documents with print or similar information has a fairly white background with sharp dark letters or have lines. Where printed information is known to be transmitted a switch S 1 can be moved from its photo position to its pressure position are to short-circuit or bridge the resistor R 1. When the resistance R 1 is short-circuited, the input signals from the filter 22 are attenuated less and thus cause the overall transfer function to be greatly changed with a resulting change in the gray scale by one to the receiver 11 make a more desirable print copy. It is also highly desirable to have one at the same time high signal-to-noise ratio and / or signal-to-noise ratio of which one or both will in future be referred to as the signal-to-noise ratio when the copy is transmitted the machine is in print or photo mode. This is achieved by dealing with the modulation index M and the differentials M of the modulation index (with the accompanying spectral changes) which develop the desired gray scale of the copy along with maintaining compatibility between old and new machines.

Higher amounts of the modulation index M is equal to Df / f index center ( where DF equals the deviation due to a swing from two different gray levels and f index center is equal to the average transmitted frequency) from an FM system increase the signal-to-noise ratio of the system. If the signal-to-noise ratio is poor, will the individual spots that are required in the received copy to a ge - make reproduction set back and forth. The one printed letter defining spots would thus be shifted (at or near the edge) around the print dissolve at the edge and give it an unpleasant appearance or completely unusable close. These effects are generally noticeable on edge lines or fine Details; the darker or more indistinct the transmission of the gray of the question the coming edge, the more obvious the effect due to the contrast ratio.

The Df index output of the voltage controlled oscillator 24 is a direct function of the DE from the signal circuit 23 which in turn has a function the D index g is equal to g minus g index 2 - level is who the Photo cell are supplied (gray level 1 to gray level 2 differential). To the recipient the reverse is true where a large moculation index M has a raw DE per D index g results in which the signal causes generally to be large compared to that Noise, and thus the printed Dg, is less ambiguous.

It is therefore obvious that the type of curve DE versus Dg not only affects the "gray output" against the "gray input" of the l; pie, but also affects the signal spectrum and the resulting signal-to-noise ratio the plant.

In the following it will be noted that MM is a function of that range the gray scale will change which is transmitted at some point in time. So do we notices that f index center as well as Df changes.

The original machine had the following characteristics before the change of the transfer functions which control the gray scale of the system: Fig. 6 and 7 show linear and logarithmic representations of the voltage input of the improved Transmitter circuitry of the present invention as a function of gray, i.e. H. of the gradations from white to black of the copy, which the photocell scans. Similarly, Figures 8 and 9 show the gray output of the gradations from white to black on the copy paper at the receiver as a function of the voltage input to the output transducer is. Again, they are both linear and logarithmic representations shown, as can be seen in Fig. 7, the photocell has a 0 output when black is presented and the print heads like to be maximally aroused when black printing is required. The drive of the print heads could be such that is printed black if the input to the write amplifier was 0. If the Input to the write amplifier was a maximum could be the drive in the mind Be 0. An alternative would have to have heads withdrawn from the coal would have to be in order to write in white. Instead of the above solutions, the voltage output from the photocell E index fz reversed and a 7 volt level added. The exit of the base wall panel was as shown in Figs. 10 and 11, presumably resulted in the overall sensitivity of the system shown in FIG.

The effect of this known system illustrated in FIGS. 6 to 12 is and summarized in Fig. 12, the photographs consisted of distorting the Greatly reduce gray scales. For photognophia, the gray scale should be the overall marking be linear. There were other accompanying difficulties in the tolerance of the plant caused by small differences in their individual circuit sensitivities through the circuit designs and the steepness of the "gray output - gray input" System sensitivity. The settings of the plant could change the variance during The manufacture of the machine was only available after a great effort overcome.

Even if there were no mechanization problems it can be noticed that in the near white area of Fig. 6 the slope of the curve is greatest. Likewise, for the receiver illustrated in FIG. 8, the curve has its greatest slope in the nearby white area. There is a small D on the transmitter Index g gives rise to a large DE if it is the voltage-controlled oscillator 24 this gives a large Df. Since the modulation index is directly proportional too Df is in those areas where the disturbance can easily be seen a high modulation index (and a high M) which is the bed of a good Signal-to-noise ratio. From the gray index against gray index a curve gives it a spin benefit. Pictures are rather badly treated and the print is handled very well. It is worth noting that although the signal to noise ratio is improved and that the sensitivity curve of the overall system for the printed Copy is reasonably satisfactory. Much of the great slope of the Gray curve of Fig. 12 is based on the receiver transfer function. The signal-to-noise ratio would be even better if everything of great inclination took place at the transmitter uhd the receiver transfer function from the solid line of Fig. 13 and 14 are converted into the dashed curves would. The original system had the successive transmission properties, illustrated in FIGS. 15, 17, 16, 22, 32 and 31. In an attempt one to get high signal-to-noise ratio and develop high contrast reproductions for a pressure mode as well as linear Erhpfin: (iliciikeit for a photo Operating mode, the system was further changed by the sequence of sensitivities which is shown in FIGS. i5, 18, i9, 20, 33 and 21. In this wide Sequence of graphically steep, steep curves in Figs. 18, 19 and 21 represent two curves one representing the print mode and the other representing the photo mode.

These two operating modes coincide in the remaining curves.

For the print mode it should be noted that a high M and M results in essentially the same overall sensitivity curve for the system to give the gray scale but due to the fact that everything of great inclination and If saturation occurs on the sending side, the overall system has a higher level Signal-to-noise ratio. When photo information is sent it is linear as desired Gray index output versus gray index input curve reached.

Figures 23, 24 and 25 illustrate the plant sensitivity when an unmodified transmitter supplies information to a receiver, which does not has been modified in accordance with the teachings of the present invention. In the tc'ge of three curves, the solid line represents an installation without the improvements of the present invention operates and the dashed lines illustrate the sensitivity of the system using improved receiver circuitry. Thus z. B. the linear solid line of Fig. 23 only that the Signal circuit 31 of Fig. 3 has a linear sensitivity and the dashed Line of Fig. 23 shows that the improved receiver signal circuit is not one linear Has sensitivity, as discussed in relation to FIG. 5, this non-linearity is distributed to the receiver signal circuit 31 through Providing the amplifier therein with a non-linear feedback circuit. The case of transferring from a new machine to an old machine is in 26, 27 and 25 shown. These changes are due to changes in the Signal circuit 31.

Figs. 26, 27 and 34 subsequently illustrate what the transfer functions happens when the combination of the old transmitter and the new receiver from Fig. 23, 24 and 25 or 26, 27 and 25 replaced by a new transmitter-new receiver system will. Thus, the straight, solid line in Fig. 26 indicates only gnphically that the signal circuit 23 of Fig. 2 was previously a linear amplifier and in the improved system is non-linear as illustrated by the dashed line. Again, this non-linearity is intentionally introduced into the system by design non-linear feedback in the circuit of Fig. 4. Of course, the transmitter sensitivity is of Figs. 26, 27 and 34 indicative of its operation only during the photo mode.

When making these changes in the sender and recipient identification data the machine is agreed with the old machines.

When transferring from a new machine to an old machine, There are two modes of operation, print mode and photo mode, which make a copy at a high level Contrast or a linear reproduction result.

When a new machine receives from an old machine, the Copy essentially halfway between a high contrast and a linear one Reproduction.

When transferring from a new machine to an old machine, is the copy of a high contrast in the mode of printing and is not as linear in reproduction as when received by a new machine.

Some carbon paper transfer characteristics are of the type that more gray scale changes Force / device in the white part of the transmission property is required to get one linear overall curve g index output against g index input of the system. This change could take place at either the transmitter or the receiver, if However, if it takes place at the transmitter, then the system will have a high Modulation index M and therefore have a high signal-to-noise ratio, furthermore the background plus as a result Eliminate stains, dirt, or other unwanted low-level markings two actions are taken.

1. The threshold of the transmitter is one Dg above the established one automatic background set.

2. The threshold of the receiver is one Dg above the transmitted Background set in the transmitted white level.

The threshold at the transmitter can be kept just above the background and when the threshold is reached there is a high M and M which good is. Small unwanted errors in the background gray level are added to the Transfer prevented.

The threshold at the receiver can have small errors in the white level frequency (1500) Compensate for errors in the setting of the receiver (E index output at 1500) and it also reduces the effect of noise and interference on the telephone line Of the initial detected threshold in the transfer functions of the circuit of Fig. 4 shown in Figs. 28 and 29 is controlled by the setting of R 5, which works in a way similar to the other Schmitt circuits. The initial one rapid rise of the upward convex part of the two curves is mainly due to R 13 controlled, which works in conjunction with D 2. When the voltage E index c is small, the bypass effect of R 3 and D 2 on R 2, R1 and R 2 is negligible. Above a certain input voltage, E index c Z1. «Is tamedly weakened when the current in D 2 builds up to a final certain value R 13, R 1 and R 2 or R 13 and R l as determined by the position of switch S 1. Of the concave upward part of the curves is caused by R 12 and D 1. This circuit represents a non-linear positive feedback that increases the gain of the Overall circuit with E index c increased. The rate of rise to one saturated level is controlled by R 2 in the case of the print mode and in the case of photo mode through R 1 in connection with R 2. The function here is mainly one of the gain.

The controlled threshold is for the purpose of suppression all Markings such as spots below a certain gray level and only works on gray levels above a selected background level.

The initial convex shape of the curve is for the purpose of levels above of the selected threshold value quickly.

This is necessary to avoid certain threshold effects in the carbon paper transfer properties overcome by different types of carbon paper.

The saturation level is adjusted by R 2 for the purpose of adjustment the gray level at which the resulting copy will be completely black.

As known to those skilled in the telephone art, the typical telephone transmission line has or the transmission circuit has certain transmission spectral energy limits as a result of the system's signal line. To these limitations not by the sender and to allow the full range between white and can be reproduced dark is according to the present invention in the transmitter of Fig. 4, a clamping circuit is provided, which the output voltage to a desired selected level limited or stuck in this case between minus 0, 25 and plus 7 volts which causes the maximum transmitted frequency To be 2450 Hz. This clamp circuit includes a series circuit of the one Has resistor R 14 connected to the positive bus bar 40. One with that Resistor R 14 connected potentiometer R 15 and a ten-electrode or rectifier Z 1 connected between the potentiometer R 15 and the reference busbar 43. A diode rectifier D 3 is connected to the base of transistor Q 3 and the potentiometer R 15 is connected and a resistor R 16 is between the base of the transistor Q 3 and the negative bus bar 41 are coupled. The setting of the movable Tap on the potentiometer R 15 sets the upper limit for the direct current voltage a, which can be made by transistor Q 3. A diode rectifier D 4 is coupled between the emiter of transistor Q 3 and reference bus 42 around the lower limit of the DC output voltage generated by transistor Q 3 to adjust. This clamping circuit limits the range of the DC voltage which can be generated and ensures that the direct current voltage to the Frequency limits the phone line is kept and represents the full range between white (0 volts) and black (+ 7 volts).

Fig. 5 shows an electrical schematic of the signal circuit it 31 of the present invention is shown in the block diagram shown in FIG is used and is typical of the circuitry in the receiver 11 of FIG. Figure 5 is again a positive DC power source, a negative DC power source and a reference provided. The positive source is called a voltage B + on a positive busbar 50 and the negative voltage is considered a negative Voltage B supplied on a negative busbar 51. The point of the reference potential or the ground is connected to a reference bus 52. In Fig. 5 will / will Signals from demodulator 30 to the base electrode of an NPN amplifying transistor Q 9 supplied. The base is attached to the reference bus 52 through a resistor R 25 connected and the emiter and collector are through the resistors R 26 and R 27 are connected to the positive bus bar 50 and the negative bus bar 51. Output voltage from the transistor Q 9 is through a resistor R 28 and a Potentiometer R 33 and a diode rectifier D 5 to a current or summing Collectors 53 supplied. This bus bar 53 is connected to an amplifier of the three llansistors Q12 Q 13 Q 14 contains which are PNP transistors and which by corresponding resistances between the positive busbar 50 and the negative bus bar 51 are connected. The exit from the last Transistor Q 14 is drained off at its emiter and the write heads or output transducers 32 supplied. The circuit described so far is more or less conventional and amplifies the DC voltage supplied from the demodulator 30 for digestion the write heads or output transducers 32 according to the present invention is one Threshold control circuit is provided which comprises a PNP transistor Q 10 and a Includes NPN transistor Q 11. This threshold control circuit sees a current to the summing busbar 53, in operation with a diode rectifier D 6 between the potentiometer R 33 and the diode D 5 and the Referenzssammeisehiene 52 is connected. Signals from the emiter of transistor Q 9 are passed through a Resistor R 29 in transistor Q 10 is supplied. The collector of transistor Q 10 is via a resistor R 31 to the base of transistor Q 11 to the connection point 54 coupled to the diode rectifiers D 5, D 6.

That corresponds to point 8 on FIG. 5 from demodulator 30 on FIG. 3 supplied Signal is in the range from 0 to + 7 volts. In the input 0 or a value below is a given amount called the threshold, Q is 10 in one conductive state.

The conductive state of Q 10 is caused by the voltage on it its base relative to the voltage at its emiter. The forward bias level is set by the voltage divider R 34 and R 30. The line condition of Q 10 causes Q 11 to conduct through the voltage divider R 31 R 32 to be. Power from bus 51 becomes the reference bus through Q 11 R 35 and D 6 52 supplied. This causes the diode D 6 to be in a low impedance state be. As long as the diode is in a conductive state, the rail 54 is attached prevented from becoming positive. If point 5 is the base of Q 9 and consequently the Emiters of Q 9 become positive by a sufficient amount (the threshold level), transistor Q 10 becomes non-conductive (this is made possible by the voltage drop at R 28) whereby its collector is caused to go in a negative direction. A quotient of this change becomes the base of Q 11 via the resistor divider R. 31 R 32 supplied. This in-negative going voltage blocks Q 11. The current that through the transistor Q 11 from the busbar 51 via the resistor R 35 to Diode D 6 is closed is on the diode D 6 no longer conducts and consequently their clamping action on the connection point 54 is terminated. The connection point 54 can now rise according to the bidding of the emitter of Q 9 and consequently according to the entrance from the demodulator 30.

If connection point 54 rises, then D 5 causes it to rise the busbar53. The busbar 53 is an input node point to a Function amplifier Q 12 and Q 13 Q 14 with feedback via R 38, R 39 consequently the collector rail 53 rises very little. Input 8 is converted into a current input Via R 28, R 33 its level is controlled by the saturation control R 33.

Before the input reaches a threshold value, the bus bar becomes 53 only by the feedback through R 38, R 39 and the injection current level from R 36, R 37 controlled. This level of injection current causes a background current to flow into the output converter 32. The setting of the background level is independent from junction 54 because of the non-conductive state of D 5 when the Input 8 is below the threshold. Likewise can when setting the threshold can be adjusted without the line to that Impact output transducer 32 if input 8 is below the threshold value lies.

In addition to the improved threshold control circuit, is an improved feedback circuit from the output to the output transducers 32 and the busbar 53 are provided. This is the feedback circuit contains two resistors R 38, R 39 which are shunted by a capacitor C 6 are. The connection point 55 of the resistors R 38, R 39 is via a diode rectifier D 7 (actually represented by four diode elements) driven to earth. This Feedback.

circuit sees a more linear sensitivity to the gray scale of the Facility so that when photographs are reproduced they are more faithful than without this feedback circuit could be achieved.

13 illustrates the effect of the feedback circuit R 38, R 39, D 7 '<the capacitor C 6 is attached because of the circuit atability) the concave sensitivity is caused by the fact that when the input current level (to the busbar 53) increases in magnitude the output to the Output converter 32 becomes negative. It is a resulting negative feedback current to busbar 53 caused by R 38, R 39. When this feedback level increases, the voltage at the junction point 55 becomes negative this circumstance eventually causes the diode D 7 to conduct to a greater or lesser extent, thus reducing the degree of negative feedback and thus the gain of the Circuit is modified. If the input is 8 larger, the gain becomes (the slope of the transfer function increases with the level of input 8) des entire circuit larger. This effect causes the voltage to be transferred from Fig. 30 E index B to E index 8 to be established which in turn the entire System transfer causes to be modified, as shown in FIG.

When sending a photocopy, the transmission function of the sender modified via the circuit of Fig. 4 as shown in Fig.

18 shown. This effect plus that of the previous one The circuit of Fig. 5 as shown in Fig. 23 causes the Plant curve "gray output" versus "gray input" becomes linear, as shown in FIG. The dislocation found in FIG is variable and is made by caused the threshold value selected by the controller R 34.

When sending a print copy, the transmission function of the sender modified via the circuit of FIG. 4 as shown in FIG. This Effect plus that produced by the previous circuit of Fig. 5, as shown in Fig. 25 shown causes the curve at the "gray output" against '| gray input " of the plant to be that in FIG. The displacement effect is caused by the Threshold level that is selected via control R 34.

In any of the above cases, the level at which saturation may be reached (above which the output is completely black) can be set via R 33 (R 28 and R 33 are responsible for the conversion of input 8 as on Emiter from Q 9 detected an input current level to the connection point 54) and via R 2 if both the new receiver and transmitter are in use, as well as R 33 or R 2 if one machine in a working pair is a new machine is.

It can thus be seen that the present invention improved Circuits for an image transmission system, and in particular improved circuitry for an image transmission transmitter and for an image transmission receiver. At best Both the transmitter and the receiver should use the circuits of the present Invention included so that the best possible operation for all types of documents can be reached. A customer who has used the improved circuits of the present However, invention in its equipment can be sent to or from a customer Customers of their equipment will not receive the improved circuits of the invention having. The customer who can have the improved circuits of the invention however, provide better operational or broadcast signals to the customer who owns the circuits of the invention does not own. Or a customer with the improved circuitry of the Invention can reproduce better documents from a customer or a sender without the improved circuitry of the invention. Therefore see the circuits of the present invention improved image transfer operation for either one Transmitter or a receiver, or for both a transmitter and a receiver before. Although it is preferred that the transmitter and receiver all be enhanced Circuits of the invention will be understood by those skilled in the art that this is not absolute is essential. Only parts of the improved Circuits can will be installed to provide improved operation. Professionals will continue Recognize that the switch is triggered by one of several non-linear saturation amplifier circuits can be replaced and the phrase "a circuit similar to the step-tri @ ger is intended to encompass these claims

Claims (24)

Claims .Nna = Ms1 == 1. Image transmission transmitter with a device for scanning a document to be transmitted and for producing electrical signals, which are indicative of the information scanned from the document n z e i c h n e t d u r c ii a) input ports for receiving electrical signals, which are indicative of the information scanned from a document b) a a step tri @ ger circuit with first and second electron flow devices, which are coupled together between an input circuit and an output circuit wherein the devices have a non-linear feedback coupled therebetween s circuit have c) an arrangement that the input circuit of the step-tri @ gers d) couples at least one waristor to the feedback circuit to the input connections is coupled to improve the property of the electrical signals e) and a Arrangement which is coupled to the output circuit and suitable for a voltage controlled oscillator (24) coupled to be used to create the Signals to it for transmission. 2. Transmitter according to claim 1, characterized by a resistor in series between the Scwitt Trager Input circuit and the input terminals is coupled and an optionally operable switch for short-circuiting the resistor. 3. Transmitter according to claim 1, characterized by a clamping circuit arrangement which is connected to the output circuit of the Step-Trassger Circuit is coupled to limit the DC voltage variation of the Step triger Output. 4. Transmitter according to claim 1, characterized by a clamping circuit which is connected to the output circuit of the Schmitt Tragers is coupled to limit the DC voltage variation thereof and a series connected resistor and diode rectifier connected between the input circuit of the Step - wearer and is coupled to a reference potential point 5. Transmitter according to claim 1 geken n ze i cne t- by an arrangement for optionally increasing the gain factor Step -trker -Circuit when the input increases. 6. Transmitter according to claim 5 because d u r c h gek e n n z ei c h n e t that the arrangement for increasing contains a parallel resistance-waristor coordination, which is connected between the emitters of the first and second electron flow devices is 7. Transmitter according to claim 1, characterized by an arrangement for optionally reducing the gain factor Step -Trer -Circuit when the input level increases 8. Transmitter according to claim 7 d a d u r c it is noted that the detachable assembly includes a resistor and a series waristor connected between the input of the first electron current device and is coupled to a reference potential point 9. Transmitter according to claim 8 gek enn z ei ch ne t by a resistor between the input of the Schitt-Tragers and coupled to the input terminals and a selectively operable switch connected in parallel with the resistor for selectively shorting the resistor 10. Image transmission transmitter having a device for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from the document characterized by a) input terminals for receiving electrical signals indicative of the information scanned from a document b) a one ; IJ Schmitt - TrXger Similar circuit with first and second electron current devices which are coupled together between an input circuit and an output circuit, the devices having an intermediate feedback circuit c) an arrangement for coupling the input circuit of the Step -trkgers to the input terminals containing a resistor and a selectively operable switch in parallel with the resistor for selectively short-circuiting the resistor d) an arrangement which is coupled to the output circuit and suitable to be coupled to a voltage-controlled oscillator for applying the signals to it for transmission 11. Image transmission receiver with an arrangement for receiving electrical signals and producing an output on a document which is indicative of the information scanned from a document at a remote location is g e k e n n n z e i c h n e t d u r c a) Input connections for receiving electrical Signals indicative of the information scanned from a document b) an amplifier circuit having an input coupled to the input terminals and with an output that is suitable to be coupled to a converter, which converts electrical signals into information on a document c) and a Feedback circuit comprising a series resistor and waristor which are coupled are to increase the amplification factor of the amplifier w0.nn the input level increases 12. Receiver according to claim 11 g e k e n n n z e i c h n e t by a threshold value circuit with strombe limiting devices and a waristor, which is connected to the feedback circuit is coupled 13. Receiver according to claim 11 g e k e n n n z e i c h n e t through a Voltage divider potentiometer, which is a current control device of the amplifier connected 14. Receiver according to claim 11 g e k e n n n z e i c h n e t by an adjustable resistor in series between the output and the input two adjacent current control devices of the amplifier is connected 15th Receiver according to claim 11 g e k e n n n z e i c h n e t d u r c h current limiting end Devices and a waristor coupled to the feedback circuit to provide a threshold control and a voltage divider potentiometer, coupled to an electron current control device of the amplifier for background control to be provided 16. Receiver according to claim 11 g e k e n n n z e i c h n e t by current limiting Devices and a varistor coupled to the feedback circuit are to provide threshold control and an adjustable resistance of the in series between the output and input of two adjacent current control devices of the amplifier, is coupled to provide saturation control 17th Receiver according to claim 11 g e k e n n z e i c h n e t d u r c h a voltage divider Potentiometer coupled to an electron flow control device of the amplifier is to provide background control and an adjustable resistor in series between the output and input of two adjacent current control devices of the Amplifier is coupled to provide saturation control 18. Receiver according to claim 11 g e k e n n n e i c h n e t d u r c h current-limiting devices and a Varistors coupled to the feedback circuit for threshold control Provide a voltage divider potentiometer which connects to an electron current control device of the amplifier is coupled to provide basic control and an adjustable Resistance, -ler in series between the output and input of two be.naclll, artell Electron flow control devices of the amplifier are coupled to control saturation to be provided 19. Image transmission system d u r c h e k e k e n n n z e i n t d u r c h: a Transmitter with an arrangement for scanning a document to be transmitted and for Producing electrical signals for the 'sampled information The transmitter includes: a) Input terminals for receiving electrical Signals indicative of the information scanned from a document b) a circuit similar to Schwitt-Triger with first and second electron current devices which are coupled together between an input circuit and an output circuit and have a non-linear feedback circuit coupled therebetween c) an arrangement that connects the input circuit of the Schmitt carrier to the input terminals d) couples at least one rectifier device to the feedback circuit is coupled to improve the property of the electrical signals e) and a Arrangement, which is coupled to the output circuit and heated to a voltage controlled To be coupled to the oscillator in order to feed the signals for transmission there f) and a receiver with an arrangement for receiving electrical signals and for generating an output on a document for the scanned by the sender Information is indicative where the receiver contains g) input terminals to the Receiving electrical signals relevant to the of a document Sensed information indicative of h) an amplifier circuit having a Input which is coupled to the input terminals and to an output of the r; e is suitable to be coupled to a converter that converts electrical signals into information on a document implements i) and a feedback circuit with a series resistor and a rectifier arrangement which are coupled by the amplification factor of the amplifier when the input level increases 20. Procedure for Transfer Image information is not shown: optical scanning of an original document the conversion of the thus scanned optical information in electrical signals the non-linear amplification in one of a number of selectable Types of electrical signals where the gain provided by the amplifier for larger electrical signals, the transmission of the amplified by the electrical signals is higher Information represented by electrical signals to a remote location is the non-linear Amplify the signals thus received, the overall effect of the two being non-linear No gain levels is linear and reproducing a transmitted image of the original document from the amplified signals 21. Image broadcast transmitter as indicated by: a) a scanning device for optical scanning an information-bearing document b) a first transducer arrangement for Umwanin the light energy into electrical signals indicative of the information c) a analog signal processing arrangement that is responsive to the electrical signals and is operable in a first mode of operation to provide the electrical signals a first way of amplifying non-linearly and operable in a second mode of operation is to amplify the electrical signals nonlinearly in a second way, thereby the first and second types of output signals give those for both max. and minimum amounts of the electrical signals are identical and non-identical output signals for all values between the maximum and minimum values and d) a second Transducer assembly responsive to the amplified electrical signals in order for to produce energy signals indicative of the information 22. Transmitter according to claim 21 g e k e nNnnz e i c h n e t d u r c h a clamping arrangement for Limiting the size of the amplified signals. 23. Image transmission transmitter with a device for scanning a document to be transmitted and generation of electronic signals that are used by Information scanned on the document is indicative of the indicia t d u r c h: input terminals for receiving electrical signals used by Information that has been scanned in a document is indicative. a step-carrier-like circuit of the first and second electric lesson devices the z its amnien between an input circuit and an output circuit the devices are coupled to a non-linear feedback circuit afweis, which is coupled to analog output signals responsive to Analog input signals provide an arrangement that controls the input circuit of the Step Trkger circuit couples to the input terminals and one to the Output circuit coupled arrangement which is suitable for a voltage controlled To be coupled to the oscillator in order to feed the signals to it for transmission. 24. A transmitter according to claim 23 characterized by a device for changing the sensitivity of the one Step straps similar circuit.