DE2364629A1 - SYSTEM FOR CODING VIDEO SIGNALS ACCORDING TO THE SO-CALLED DIFFERENTIAL SIGNAL PROCEDURE - Google Patents

Description

ROBERT BOSCH FERNSEHANLAGEN GMBH, 61 Darmstadt, Robert-Bosch-Str. 7 C 00 HO Z

Rl.-No. 1609/73 PLI / Go / Me

December 21, 1973

System for coding video signals using the so-called differential signal method

The invention relates to a system for coding video signals according to the so-called difference signal method which the difference signal is quantized and, depending on the presence of edges, the quantization characteristic is controlled will.

When coding video signals, in order to obtain the smallest possible bit flow, the aim is to use a bit flow that is as coarse as possible Perform quantization. In areas a rough one makes itself However, quantization is noticeable through so-called contouring. Here, brightness transitions that take place gradually, when a quantization threshold is exceeded, this is shown as brightness jumps, in the case of excessively coarse quantization appear disturbing. In the case of a small number of fine quantization levels, however, this is the case Differential signal method not possible, signal jumps that caused by the scanning of edges, fully transferable. It is therefore known, the characteristic of quantizers ever to switch over after the presence of edges at which the coarser quantization does not appear disruptive.

In order to determine whether or not there is an edge at the corresponding point in the document being scanned, it is already known to delay the respective signals by one line and to compare them with the signal, which occurs in the next line and thus again an edge signal derives. However, these known methods do not give satisfactory results if the edges are not perpendicular

509827/0765

ROBERT BOSCH FERNSEHANLAGEN GMBH

Rl. -No. 1609/73 -2- 236462 *

run to the direction of the line. This is true when the sampling frequency is coupled to the line frequency in the so-called zero offset. With the so-called zero offset, this is Sampling frequency is a whole-line multiple of the line frequency, so that the respectively scanned image points of successive Lines are next to each other perpendicular to the direction of the line. In the case of operation without a zero offset, on the other hand, the vertical edges are not, but edges of a certain inclined position recognized. , "

For scanning below the Nyquist sate and for combing out of the spectra with comb filters, however, it is necessary to use a so-called half-line offset to be sampled, in which the Sampling points from line to line each by half the width of a sampling interval are shifted.

The object of the present invention is to provide a system by which when scanning with any offset both vertical and inclined chews are appointed will.

The system according to the invention is characterized in that a Edge signals is derived when assigned to a row of at least three adjacent pixels Dxfferenzsignalen at least one exceeds a predetermined value, and that the contour signal is delayed and in the next line is used to control the quantization characteristic.

When using the system according to the invention, at If there is an edge, the quantization characteristic curve during the scanning of several pixels for the transmission of the Edge switched. In practice, however, this does not mean a disadvantage, as the so-called contrast masking in the In the immediate vicinity of edges, the human eye is relatively insensitive to a falsified reproduction of the contrast.

509827/0765

ROBERT BOSCH FERNSEHANLAGEN GMBH 7 36 4 6 2

Rl.-No. 1609/73 - 3 -

In a preferred embodiment, there are five adjacent Pixels used to form the edge signal. On the one hand, it is possible here to still run relatively obliquely To detect edges, and on the other hand, the area of the gray levels in front of and behind an edge is not exactly reproduced still sufficiently small.

The invention is explained in more detail with reference to the figures. Of these shows: -

Fig. 1 schematically shows a number of sampling points, two consecutive lines in the case of zero offset and

2 shows an embodiment of a system according to the invention.

In Fig. 1 are a few sampling points of two temporally successive lines, which are denoted by n-1 and η schematically are shown. The following consideration becomes one Time at which a transmission of the dem Difference signal assigned to sampling point χ, i.e. the difference in values between point χ and point f, should take place. If the template now contains a black and white jump, which is indicated by line 1, it is required to run the quantizer before transmitting the To switch the difference signal for the pixel χ to a quantization characteristic suitable for the transmission of signal jumps. This switchover takes place according to the known method

which

by an edge signal, by comparing the signal for the Point d and that for point g is obtained. However, an edge represented by line 2 is not considered to be such recognized.

In the system according to the invention, there is now an edge signal derived, for example, from five difference signals which are assigned to adjacent pixels, at least one of them exceeds a predetermined value. In the case of scanning an original with a jump in brightness in the Line 1 is this criterion for the first time in the - 4 -

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BATH

ROBERT BOSCH FERMSEHANLAGEN GMBH
Rl.-No. 1609/73 - 4 -

Sampling of point c given. At this moment, as will be explained in more detail later in FIG. 2, an edge signal arises, that by one line minus two pixel sampling intervals is delayed so that it turns on the so-called edge quantization characteristic before the point f is sampled. at In this last-mentioned example, this happens two pixels before the scanning of line 1 in line η, what but does not appear disturbing because of the so-called contrast coverage effect.

In the case of scanning an original with an inclined edge, as symbolized by the line 2, takes place in of line n-1 the formation of an edge signal only at the Scanning of the pixel d. Then occurs during the line η the delayed edge signal before the sampling of point g on just in time to transfer the quantization curve of edge 2 to switch.

Line 3 symbolizes an edge that runs in contrast to edge 2. This also creates an edge signal, when the pixel e is scanned. This edge signal is again reduced by one line minus the sampling interval of two Delayed pixels, so that it is still before the scanning of the pixel x, so before the quantization of the dem Image point χ associated difference signal occurs. Fig. 2 shows an embodiment for the system according to the invention. At 11 the system receives the so-called difference signal, which is the difference between the last and the current Sample corresponds, supplied. This signal can either be present in analog form or already in digital form Form, which, however, is achieved through the use of very small quantization levels and thus includes a larger number of binary digits, usually eight. This difference signal is the known comparators 12, 13, 14 and 15 supplied. In the case of an analog differential signal, the comparators each consist of a differential amplifier.

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ROBERT BOSCH FERNSEHANLAGEN GMBH
RL no. 1609/73. - 5 - 236462 '

Whether analog or digital comparison is being made, in any case ■ a reference value corresponding to the quantization to be used is fed to the other input of each comparator. When switching the characteristic curve of the quantizer, which is known per se, the comparison voltages are switched, which is done in the exemplary embodiment shown for the comparators 12, 13, 14 and 15 by the switches 16, 17 and 18. Assume that the switches. 16, 17 and 18, in their upper position, supply direct voltages to the comparators, which correspond to a coarse quantization and, in their lower position, lead to a finely graduated quantization characteristic.

A constant comparison value, for example 15% of the entire amplitude range of the difference signal, is fed to the comparator 15. The output signal of the comparator 15 is passed one after the other via a delay device which delays the signal by the duration of a sampling interval. These delay devices are denoted by 20, 21, 22 and 23 in FIG. At the switching points 24, 25, 26, 27 and 28, signals are thus generated at the same time which correspond to five adjacent and temporally consecutive scanned image points, provided that their difference signal is greater than 15 % . These signals are fed to the inputs of an OR circuit 29, at the output of which a signal is emitted when one of the aforementioned signals is present, ie when one of the difference signals assigned to one of the five pixels exceeds the value of 15%. This edge signal is fed to a delay device 30 which delays the edge signal by one line minus the duration of two pixels. The output voltage of this delay device 30, ie the delayed edge signal, now controls the changeover switches 16, 17 and 18 in such a way that when an edge signal occurs, the switches are brought to the upper position, which results in a coarse quantization characteristic. The output signals of the comparators 12, 13, 14 and 15 are sent to an encoder - 6-

⁵⁰⁹ ° BAD ORIOiMAL

ROBERTBOSCHFERNSEHANLAGENGMBH
Rl.-No. 1609/73 -6- .236

31 supplied, which in a manner known per se converts the information contained therein into a form suitable for transmission brings.

The number and height of the quantization levels is usually selected depending on the requirements for the transmission quality or the type of signals to be transmitted. In Fig. 2 are For the sake of clarity, only four quantization levels are shown by way of example.

509827/0765 ORTCUNAL

Claims (4)

ROBERT BOSCH FERNSEHANLAGEN GMBH Rl.-No .: 1609/73. _ 7 _ Claims 1. System for coding video signals according to the so-called Differential signal method in which the differential signal is quantized and. depending on the presence of edges, the quantization characteristic is controlled, characterized in that that an edge signal is derived when from 'the a row of at least three adjacent pixels associated difference signals at least one exceeds a predetermined AYert and that the edge signal is delayed and in the next line to control the quantization characteristic is used. 2. System according to claim 1, characterized in that the predetermined value is approximately 15 % of the maximum possible value. 3. System according to claim 1 or 2, characterized in that an edge signal is derived when one of five adjacent pixels associated with the difference signals exceeds the specified value. 4. System according to claim 1, characterized in that the difference signals are fed, inter alia, to a coraperator are at the output of several delay elements in series each with the delay time of a sampling interval are connected, 'that the outputs of these delay elements and the output of the comparator each with an input an OR circuit are connected and that the output of the Or — connection to the input of another delay device is connected, the delay time of which is one line minus half of the total through which to the output the delay elements connected to the comparator circuit corresponds to the delay that has taken place. 509827/076 5 Blank page