Black and white runs of scanned image signals are encoded into binary information at a transmitting station, transmitted over a transmission link and received by apparatus at a receiving station. Jitter introduced during the transmission is detected by the apparatus prior to the decoding of the received signal to produce an error indicating pulse which is utilized to effect erasure of the image signals of the line scan in which the jitter has occurred to leave the line as a white run. As an alternative, the erased line is filled with the signals on the next line scan to thereby visually improve the quality of reproduced image.
An optical radio system includes a host device, an end device, and a repeater. The host device and the end device communicate with each other via the repeater by use of optical radio. The repeater includes a section for receiving a first light signal from one of the host device and the end device, a section for converting the received first light signal into a first electric signal, a section for frequency-converting the first electric signal into a second electric signal, and a section for generating a second light signal in response to the second electric signal and transmitting the generated second light signal. The repeater also includes a section for demodulating one of the first electric signal and the second electric signal into a baseband signal, a section for detecting a quality of the baseband signal, and a section for enabling transmission of the second light signal only when the detected quality of the baseband signal is equal to or greater than a predetermined quality.
In facsimile transmission by means of a redundancy reducing coding, for example run-length coding, a distance affects the entire remaining portion of the picture line. End-of-line control characters are therefore transmitted for line synchronization. As these characters are possibly also disturbed and the picture lines to be printed would then completely be lost, a fixed number of different end-of-line control characters are used in cyclic sequence from line to line. This enables the recognition of various successive disturbed picture lines, lost end-of-line control characters as well as end-of-line control characters artificially produced by a disturbance, so that the correct number of picture lines is always printed. Corrected picture lines are printed instead of the picture lines which were received in a disturbed manner, for example by taking over the contents of adjacent picture lines.
A jitter measuring apparatus forms a circuit for detecting the jitter component found in an input signal. A jitter indicating line signal is generated in response to the detected jitter component. At least one reference line signal is generated at a time point which deviates from the jitter indicating line signal. The jitter indicating line signal is supplied to a television receiver which displays it as a line which extends vertically and sways horizontally on the picture screen. The reference line signal is supplied to the television receiver where it is displayed as a reference line extending vertically at a reference position, for the jitter indicating line on the picture screen.
In facsimile transmission the sequences of picture elements having the same luminance are transmitted in coded form. The code words have, in general, different lengths and no ambiguous beginning or end marking respectively. Consequently, in case of a disturbance during the transmission not only the luminance values are generally falsified but also the plurality of successive picture elements so that in situ of the receipt picture lines appear which are too long or too short. In accordance with the invention it is now proposed in the case of a picture line which was received in a disturbed manner to compare it to one or both adjacent picture lines respectively, to take-over the portions having an adequate correlation, and, as regards the place of the disturbed portion to shift the end of the disturbed picture line in such a way that the definite line gets the prescribed length and to replace the portions of insufficient correlation by the corresponding information of one of the two adjacent picture lines. This comparison can be done relative to the two ends of the disturbed picture line. It is particularly favorable for the comparison that the picture elements of each picture line are grouped in equal groups and to check if the ratio of the number of, for example, black picture elements having a corresponding position in adjacent lines relative to the total number of black elements in the groups of the two lines together, remains below a given threshold value (decorrelation).
Buffers 101 and 103 are provided in an input and an output of a signal processing circuit 102 for performing a data transformation between a first digital data signal and a second digital data signal, respectively, and data of one of the first and second digital data signals is interpolated by a data interpolation circuit 106 on the basis of a deviation between sampling frequencies of the first and second digital data signals detected by an out-of-sync detection circuit 104 on the basis of two clocks driving the buffers 101 and 103. Further, an amount of jitter between the two clocks driving the respective buffers 101 and 103 is detected by a jitter detection circuit 105 and the amount of interpolation data is controlled in the data interpolation circuit 106 on the basis of the amount of jitter.
