EP0603226B1 - Process and device for driving matrix displays - Google Patents

Abstract

The object of the invention is to solve the problem that consists in reducing the ratio ft/Za, where ft stands for a signal-processing clock frequency and Za stands for the number of lines to be displayed in a matrix display. For that purpose it is proposed to expand the time interval available for executing signal-processing algorithms that drive a matrix display into time intervals in which a transmitted video-signal contains no information. The invention is preferably used for driving LCD-displays.

Description

The present invention relates to a method for controlling a matrix display according to the preamble of the main claim and a device suitable for carrying out the method according to the preamble of the first subject claim.

It is known, for example from GB-A-2 179 185, that so-called matrix displays, also called matrix displays, are used to an increased extent in addition to cathode ray tubes for image reproduction. These can be designed as a liquid crystal display (LCD display), plasma display (plasma display) or the like.

Matrix displays consist of an arrangement of M * N pixels, so-called pixels. M is the number of these pixels per line and N is the number of lines.

The control of the pixels is usually done line by line, i.e. An analog video signal, which contains the information of a picture line, is first scanned M times. It is also conceivable that the M samples from previous signal processing are already available.

The sample values are converted in series / in parallel, so that all M sample values are simultaneously available for driving a display line. The corresponding display line is addressed, which means that the sample values available in parallel can be transferred to the corresponding display line.

The clock frequency ft, for controlling signal processing devices, which among other things carry out the above-mentioned series / parallel conversion and control the matrix display, is based on a number M 'of pixels to be displayed per line. $${\text{ft = M ′ / T}}_{\text{Za}}\text{.}$$

T _Za is the time duration of the video signal to be displayed within one line.

The aforementioned document GB-A-2 179 185 presents an interface in which a period of time for carrying out signal processing algorithms for driving a matrix display is extended into periods in which a video signal transmitted by a transmitter or a storage medium does not contain any image information.

For this purpose, the image data of a transmitted video signal are written into a memory with a first high clock frequency and the image data for controlling the matrix display are read out with a second clock frequency that is lower than the first clock frequency. However, the known interface does not allow the number of lines to be added to be increased compared to the number of lines transmitted.

mit

• ft: Taktfrequenz für die Signalverarbeitung und für die Ansteuerung von Matrixdisplays, und
• Za: Anzahl von anzuzeigenden Zeilen,

derart zu vermindern, daß die Anzahl Za von darzustellenden Zeilen erhöht wird.It is the object of the present invention, the ratio $$\text{ft / Za}$$

With

• ft: clock frequency for signal processing and for controlling matrix displays, and
• Za: number of lines to be displayed,

to be reduced in such a way that the number Za of lines to be displayed is increased.

This object is achieved in a generic method by the features of the main claim and in a device suitable for carrying out the method according to the invention by the features of the first claim.

The invention is based on the following knowledge.

To drive cathode ray tubes, such as are used in conventional image display devices, such as television sets, monitors and the like, the electron beam must be returned to the beginning of the next image line after writing each image line. This return takes a certain amount of time. A horizontal blanking period is therefore provided within each line in which there is no active video signal from which the image to be displayed is derived.

Furthermore, when driving a cathode ray tube after writing the last line of each image, the electron beam must be returned to the beginning of the first line. The duration required for this is referred to as the vertical blanking period and is taken into account in the video signal to be processed by invisible return lines.

Furthermore, overwriting in the horizontal and vertical directions is customary in the case of cathode ray tubes due to tolerances which result from the manufacturing process, aging, etc., as a result of which the image area to be displayed is reduced both in the horizontal and in the vertical direction.

When controlling a matrix display, however, it is not necessary to take the horizontal and vertical blanking periods into account.

These time periods are thus available for the signal processing algorithms mentioned and the number Za of lines to be displayed can be increased without a corresponding increase in the clock frequency ft.

The invention has the advantage that the increase in the number of controlled lines leads to a reduction in the visible line structure.

When using a matrix display with, for example, 560 lines and when processing a video image in accordance with the M standard (US standard) with approximately 482 active lines, the image to be displayed can be expanded to 560 lines.

This results in a lower visibility of the line structure, as well as a better utilization of a possibly given matrix display with a larger number of available lines. When using an optic geared towards the maximum number of lines on the display, the control of the entire matrix display results in an increase in the luminous efficacy.

Fig. 1:

den Verlauf eines gebräuchlichen Farb-Videosignales,

Fig. 2:

einen zeitlichen Bildaufbau gemäß dem Stand der Technik,

Fig. 3:

ein erstes Ausführungsbeispiel gemäß der erfindungsgemäßen Vorrichtung,

Fig. 4:

ein zweites Ausführungsbeispiel gemäß der erfindungsgemäßen Vorrichtung,

Fig. 5:

einen zeitlichen Bildaufbau gemäß dem zweiten Ausführungsbeispiel,

Fig. 6:

symbolisch Speicher- und Lesevorgänge gemäß dem zweiten Ausführungsbeispiel.

Further features, advantages and details of the invention are explained in the following exemplary embodiments with reference to the drawing. Show:

Fig. 1:

the course of a common color video signal,

Fig. 2:

a temporal image structure according to the prior art,

Fig. 3:

a first embodiment according to the device according to the invention,

Fig. 4:

a second embodiment according to the device according to the invention,

Fig. 5:

a temporal image structure according to the second embodiment,

Fig. 6:

symbolically storing and reading operations according to the second embodiment.

1 symbolically shows the course of a video image line 10 known per se, which is composed of an active part 11 and a non-active part 12. The total duration of line 10 is Tz, of which the active part 11 takes the duration Tza.

2 shows the temporal structure of a video picture or field when using interlaced signals. This consists of a total number Z of rows, of which Za are active, i.e. Image information included.

Each of these lines has a course as symbolically shown in Fig. 1. The time duration of each of the lines mentioned is Tz. If only those lines that receive image information are considered, their number is Za and the duration for the transmission of the active lines is Tba.

erfolgt bei Bildwiedergabegeräten mit Elektronenstrahlröhren die Rückführung des Elektronenstrahls zu dem Beginn der folgenden Zeile.In the period hatched in FIG. 2, which results from the difference $$\text{Tz - Tza}$$

In the case of image display devices with electron beam tubes, the electron beam is returned to the beginning of the following line.

erfolgt bei Bildwiedergabegeräten mit Elektronenstrahlröhren die Rückführung des Elektronenstrahls zum Beginn der ersten Zeile.In the period hatched twice in FIG. 2, which results from the difference $$\text{Tb - Tba}$$

In the case of image display devices with electron beam tubes, the electron beam is returned to the beginning of the first line.

The lines indicated in FIG. 2 can also have a course other than that shown in FIG. 1. It is only essential that, in addition to an active part, a non-active part is provided which, depending on the respective television standard, can contain synchronization pulses such as "sync", "burst", etc.

A device according to a first embodiment is shown in FIG. 3. An image source 13, which processes a signal transmitted by a recording medium or a transmitter and has, for example, a receiver, a color decoder and an analog / digital converter, outputs a video signal line by line to the data input of a line memory 14. This has a first control input 15 and a second control input 16.

A first line control signal S1 is present at the first control input 15, by means of which the storage (writing) of video line data is controlled. A second line control signal S2 is present at the second control input 16, by means of which the reading out of video line data is controlled.

The signal read out from the line memory 14 is output to a signal processing device 17. The signal processed by the signal processing device 17 reaches a line-serial / parallel converter 18, the output signal of which drives a matrix display 19 line by line.

Since, as described at the beginning, no times for the return of a beam have to be provided for the control of matrix displays, the time periods shown in hatched lines in FIG. 2 can additionally be used for the control of a matrix display for the execution of signal processing algorithms and for the control of the Matrix displays 19.

By only using the horizontal blanking interval Tz-Tza, the time that is additionally available for image processing algorithms can be increased by a factor
k1 less than or equal to 1.23
be expanded.

To control the matrix display 19, an initialization time Ti per line must also be taken into account. This results in the available time Tza * for reading out, processing and displaying a line $$\text{Tza * = Tz - Ti}$$

The number M 'of pixels to be displayed per line in this exemplary embodiment is identical to the number M of pixels per line determined by the geometry of the matrix display.

The first line control signal S1 thus has a first clock frequency ft, the value of which results from $$\text{ft = M / Tza.}$$

bzw. $$\text{ft′ = ft / k1.}$$

d.h. $$\text{Tza* = Tza * k1}$$

The second line control signal S2 has a first reduced clock frequency ft ', the value of which results from $$\text{ft ′ = M / Tza *}$$

respectively. $$\text{ft ′ = ft / k1.}$$

ie $$\text{Tza * = Tza * k1}$$

The clock frequency required for the stages 17, 18 for driving the matrix display 19 thus becomes lower given the same number Za of lines to be displayed.

The device of a second embodiment is shown in FIG. 4. Means that perform the same function As in the first exemplary embodiment in FIG. 3, the same characteristic numbers are used as there and they are only dealt with to the extent necessary for understanding.

The image source 13 outputs its output signal to an image memory 20 which has a first control input 21 and a second control input 22.

At the first control input 21 is a first image control signal S1 ', which controls the storage (writing) of video image data. At the second control input 22 there is a second image control signal S2 'which controls the reading out of video image data.

The versions of the control signals S1 ', S2' can be used to implement different versions.

If both the horizontal and the vertical blanking interval are taken into account, the time available for signal processing is increased by up to 33%, which is a factor
k2 less than or equal to 1.33
corresponds.

• der Taktfrequenz ft, entsprechend $$\text{ft = M/Tza; und}$$
  
• einer Zeilenfrequenz fz, entsprechend $$\text{fz = Z / Tb;}$$
  
     dabei ist die Bilddauer Tb = 1/fB und fB ist die Bildfrequenz (üblicherweise 50 bzw. 60 Hz).

For this purpose, controlled by the first image control signal S1 ', the active signal emitted by the image source 13 is written into the image memory 20 with the following values:

• the clock frequency ft, accordingly $$\text{ft = M / Tza; and}$$
  
• a line frequency fz, corresponding $$\text{fz = Z / Tb;}$$
  
  the image duration is Tb = 1 / fB and fB is the image frequency (usually 50 or 60 Hz).

The reading of the image data takes place, controlled by the second image control signal S2 ', now extended into the vertical blanking period.

The time available for displaying Za lines is designated Tba '. $$\text{Tba ≦ Tba ′ - Tb}$$

Since the time to display before Za lines has been increased, this results in a reduction in the line frequency.

und damit als reduzierte Zeilenfrequenz fz′ $$\text{fz′ = 1/Tz′.}$$

Since the number Za of lines with image information is less than the number Z of lines transmitted overall by a video signal (see FIG. 2), the result is an extended duration Tz 'for a line to be displayed $$\text{Tz ′ = Tba ′ / Za.}$$

and thus as a reduced line frequency fz ′ $$\text{fz ′ = 1 / Tz ′.}$$

For the control of the matrix display with one line, the total available line duration is Tza + $$\text{Tza ′ ≦ Tz ′ - Ti}$$

The reduced clock frequency ft 'suitable for this exemplary embodiment is $$\text{ft ′ = M / Tza ′.}$$

It should be noted that the reduced clock frequency ft 'is an integer multiple of the reduced line frequency fz'.

An image structure according to the second exemplary embodiment is shown in FIG. 5.

It can be seen that for the image information to be displayed, which results from the active parts 11 of each line 10 (see FIG. 1) and the number Za of lines with image information, almost the entire original image duration Tb is available.

It should be noted that the time Tb (corresponds to the total framed area of hatched and non-hatched area) is the same in FIGS. 2 and 5.

From Fig. 5 it can also be seen that the time TB does not necessarily have to be divided into an even number of lines TB / Tz '.

In a variant of this exemplary embodiment, only the vertical blanking interval Z-Za (see FIG. 2) is taken into account. This increases the time Tza⁺ available for signal processing algorithms compared to that of previously known systems by a factor k3 less than or equal to 1.09. $$\text{Tz⁺ = Tz * k3.}$$

It follows for the corresponding clock frequency ft⁺ $$\text{ft⁺ = ft / k3.}$$

In this variant, the first image control signal S1 'with the clock frequency ft and the second image control signal S2' is modulated with the reduced clock frequency ft⁺.

If the image area that is lost in cathode ray tubes by overwriting the image area is also dispensed with, a further increased time is available for driving the matrix display 19 for a reduced image content, whereby a further reduction in the clock frequency is possible.

FIG. 6 symbolically shows storage and reading processes for the image memory 20 of FIG. 4.

As already mentioned, the storage takes place at a higher frequency than the reading. During the entire image duration Tb, image information is only present within an active image duration and is stored in this duration.

In a system with the reduction of the clock frequency by the factor k2 = 1.33, the active image duration is to be understood as the time corresponding to the non-hatched area in FIG. 2.

The reading out, however, takes place during a period of time that can essentially correspond to almost the entire image duration Tb, particularly taking into account the initialization time Ti.

The required size of the image memory depends on the area in which the image is enlarged in the vertical direction. That is the area $$\text{Tb - Tba.}$$

Based on a progressive 625 line system with 575 active lines, this corresponds to a maximum area of approximately 50 lines to be saved.

Another exemplary embodiment provides that the clock frequency ft is not reduced to the extent that was described in the previous exemplary embodiments. Instead, however, the video information stored in the image memory 20 is to be displayed over a larger number of lines compared to the number Za of lines which contain image information, which corresponds to a vertical upward interpolation of the number of lines Za.

For example, an active video image that contains image information can be read into and read out of the memory 20 at the same clock frequency.

The periods for beam return are additionally available for processing by stages 23, 24 and for display by the matrix display 19. These time periods can now be used to control more lines of the matrix display than is provided by the relevant television standard, which leads to a reduction in the visible line structure.

To reduce or avoid image distortion, the image to be displayed can be stretched, for example, in its horizontal dimensions. Parts that thereby go beyond the horizontal dimensions of the matrix display 19 can be trimmed.

The following application is also conceivable.

When using a matrix display with, for example, 560 lines and when processing a video image in accordance with the M standard (US standard) with approximately 482 active lines, the image to be displayed can be expanded to 560 lines.

This results in a lower visibility of the line structure, as well as a better utilization of a possibly given matrix display with a larger number of available lines. When using an optic geared towards the maximum number of lines on the display, the control of the entire matrix display results in an increase in the luminous efficacy.

• für eine indirekte Ansteuerung des Matrixdisplays 19 können Speichermittel vorgesehen sein, die das zeitlich "gedehnte Bild" abspeichern und deren ausgelesene Informationen zu einer Ansteuerung des Matrixdisplays 19 dienen;
• die Anzahl M′ von darzustellenden Bildpunkten entspricht nicht der durch die Geometrie des Matrixdisplays 19 vorgegebenen Anzahl M von Bildpunkten pro Zeile. Stattdessen kann ein Abspeichern und/oder Auslesen des Videosignals in den Zeilen- bzw. Bildspeicher mit geringerer Auflösung erfolgen. Mit dadurch erhaltenen Bildinformationen können benachbarte Bildpunkte des Matrixdispalys 19 gemeinsam angesteuert werden, so daß dieses auf nahezu seiner gesamten Fläche ein Videobild mit geringerer Auflösung anzeigt. Denkbar ist weiterhin, daß die Bildinformationen nur einem Teilbereich des Matrixdisplays 19 zugeführt werden, wie es beispielsweise bei "Bild-in-Bild" Systemen der Fall ist.
  Analog kann auch die vertikale Auflösung verringert werden;
• statt der Abspeicherung eines einzigen Videobildes (bzw. Teilen davon) können mehrere Videobilder abgespeichert werden, die anschließend über meherere Matrixdisplays angezeigt werden können oder aufgezeichnet werden können.
• statt einer direkten Ansteuerung des Matrix-Displays ist ebenfalls eine indirekte Ansteuerung möglich. Unter direkter Ansteuerung wird in diesem Zusammenhang verstanden, daß die durch das Videosignal übertragenden Bildinformationen "online" angezeigt werden. Bei einer indirekten Ansteuerung erfolgt eine Aufzeichnung der Bildinformationen hinter dem Speicher 14 bzw. 20 und eine spätere Ansteuerung des Matrixdisplays 19.

Further versions of the exemplary embodiments mentioned can have at least one of the following variants:

• For indirect control of the matrix display 19, memory means can be provided which store the temporally "stretched image" and whose information read out is used to control the matrix display 19;
• the number M 'of pixels to be displayed does not correspond to the number M of pixels per line given by the geometry of the matrix display 19. Instead, the video signal can be stored and / or read out in the line or image memory with a lower resolution. With the image information obtained in this way, adjacent pixels of the matrix display 19 can be controlled jointly, so that the latter displays a video image with a lower resolution on almost its entire surface. It is also conceivable that the image information is only supplied to a sub-area of the matrix display 19, as is the case, for example, with "picture-in-picture" systems.
  Similarly, the vertical resolution can also be reduced;
• Instead of storing a single video image (or parts thereof), multiple video images can be saved, which can then be displayed or recorded on several matrix displays.
• instead of direct control of the matrix display, indirect control is also possible. Under In this context, direct control means that the image information transmitted by the video signal is displayed “online”. In the case of indirect control, the image information is recorded behind the memory 14 or 20 and the matrix display 19 is controlled later.

Claims (6)

1. Method for controlling a matrix display with a multiplicity of picture elements, in which active parts of a transmitted video signal containing picture information are scanned and stored using a first rate which corresponds to the density of predetermined picture information contained in the active parts and to the duration of the active parts of the transmitted video signal, and is read out at a second rate which results from the density of picture information to be displayed and from the time available for its display, characterised in that the density of picture information to be displayed is determined by the number of picture elements to be controlled, in which the number of controlled lines of the matrix display is greater than the number of lines of the video signal transmitted.
2. Method according to claim 1, characterised in that the transmitted video signal corresponds to the M-norm (US-norm).
3. Method according to claim 1 or 2, characterised in that the number of lines of the matrix display to be controlled is 560.
4. Apparatus for controlling a matrix display (19) in which a store (14,20) is provided, controlled by a first pre-determined control signal (S1) in such a way that active parts of a transmitted video signal from a picture source (13) containing picture information are stored using a first rate which corresponds to the density of predetermined picture information contained in the active parts and to the duration of the active parts of the transmitted video signal, and is read out by means of a second pre-determined control signal (S2) at a second rate which results from the density of picture information to be displayed and from the time available for its display, characterised in that the density of picture information to be displayed is determined by the number of picture elements to be controlled, and that a signal processing device (17) is provided which processes the picture information to be displayed such that the number of controlled lines of the matrix display is greater than the number of lines of the video signal transmitted.
5. Apparatus according to claim 4, characterised in that the transmitted video signal corresponds to the M-norm (US-norm).
6. Apparatus according to claim 4 or 5, characterised in that the number of lines of the matrix display to be controlled is 560.

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