Device for the insertion of a first image in a second image on a screen.

The invention relates to a device for superimposing a first image into a second image on a screen<ul id="ul0001" list-style="dash"><li>with a first digital image processing stage for generating first analog image signals for the first image, which has means for generating the first image and an image storage device for intermediate storage of this first image as well as a digital-analog conversion stage provided on the output side,</li><li>with a second image processing stage for generating second analog image signals for the second image,</li><li>with a switching device which can be switched between the first and second image signals and at whose output terminals the first and / or second image signals can be tapped,</li><li>and with a control device for controlling the first image processing stage, the second image processing stage and the switching device.</li></ul>

Such a device is known for example from Siemens Components Issue 1, 1990. As an essential component, this arrangement has a picture-in-picture processor (SDA 9088) from Siemens, which enables a reduced picture to be superimposed on a larger main picture. Both image sources can be chosen completely independently with regard to the television standard and synchronization. The picture-in-picture processor takes over the image reduction, the intermediate storage of this reduced image in an integrated image memory and the output of the image data of this reduced image via a digital-to-analog conversion stage, so that the image signal for the reduced image at the output of the image in the image processor in analog form.

The second image processing stage, which provides image signals for the second image from a second video signal source, can in principle be constructed in an analog or digital manner. The structure and operation of such a second image signal processing stage in digital form is described, for example, in Siemens Components Issue 6, 1988 on pages 240 to 245. In this known system, analog image signals can be tapped at the output of this second image processing stage. A switching device at the output of the first and second image processing stage ensures a timely switching between the image signals for the reduced first image and the second main image, so that a small image shown in a large image becomes visible on the television screen.

It has been shown that this arrangement is problematic with regard to differences in the amplitudes of the first image signals and second image signals. In the picture-in-picture display, undesirable contrast differences between the small picture and the large picture can occur, which are unpleasant and disturbing for the viewer. In addition, it was not possible for the viewer of the screen in the picture-in-picture display according to the concept described so far to adjust the contrast of the small picture according to his individual wishes, for example via his remote control.

One way of making the contrast of a small picture adjustable has already been described in Funkschau, Issue 21, 1989, on pages 53 to 55. There, the contrast setting is made in the digital color decoder and thus at the input of the digital signal processing of the image signals, which is only complex to implement in terms of circuitry.

Another possibility for adjusting the contrast would be to provide an amplitude control for both the first and the second image signal in the switching device. However, this would inevitably lead to a switching device which is complex in terms of its circuitry structure and which is therefore expensive.

In the publication Patent Abstracts of Japan, Volume 10, No. 125 (E-402) [2182], a television set with picture-in-picture fade-in is shown, in which the amplitude of the picture to be faded in only after its digital-analog Conversion, but before the image is faded into the main image. An analog-converted control signal is used for the control, on which a corresponding control signal for the main picture is superimposed.

In the publication Patent Abstracts of Japan, Volume 6, No. 222 (E-140) [1100], an analog-to-digital converter for digital TV input signals is shown, in which the amplitude of the output signal is adjustable. For this purpose, a plurality of current paths connected in parallel on the output side are provided, each having two transistors and a resistor arranged between them. One of the transistors is controlled by one bit of the digital TV signal, the other transistors are controlled jointly by a voltage supplied by an analog adjustable resistor.

The invention is therefore based on the object of developing the device described at the outset in such a way that it can be implemented in a simpler manner than in the previous possibilities and that digital control of the contrast setting of the second image is made possible.

This object is achieved in that the digital-to-analog conversion stage provided for the first image processing stage can be supplied with at least one variable reference signal for setting the output amplitude of the first analog image signals, in that the reference signal is a reference voltage which can be tapped at the connection point of a voltage divider connected between supply terminals. and that this reference voltage can be set by the control device in accordance with digital control signals, in that at least one resistor can be connected in parallel to one branch of the voltage divider by means of control by one of the digital control signals.

Developments of the invention are the subject of the dependent claims.

Due to the simple solution according to the invention, it is possible to either automatically adjust the contrast of the superimposed image to the large image or to adjust the viewer z. B. via his remote control to give the opportunity to adjust the contrast individually. The digital control of the reference signals of the digital-to-analog conversion stage provides maximum flexibility for setting the contrast.

In the present invention - as already mentioned at the beginning - image sources of the most varied types can be used for the first and second images, for example television programs, video cameras or video recorders. But it is also possible to use subtitles e.g. B. for hearing impaired in a main picture, as is currently possible in connection with the teletext or teletext signals broadcast by the television stations.

It is thus achieved in a simple manner with the device according to the invention that the contrast of the first image can be adjusted or the contrast of the second image can be adjusted individually. This is particularly advantageous in the case of picture-in-picture display, but is also useful for successive picture sequences. For example, after viewing a television program, the television viewer can switch to a teletext table in which the contrast can be individually adjusted, regardless of how the contrast of the television program is selected. When "jumping back" to the television program, the contrast for the television program is automatically set again on the television.

In order to be able to receive such teletext signals naturally, the device must be suitable for receiving information in the form of coded characters which can be converted into image signals via a character generator. Integrated circuits for receiving such teletext signals are known, for example, from Siemens as SDA 5243.

The invention is explained in more detail below on the basis of the picture-in-picture overlay in connection with two figures. Show it:<dl id="dl0001"><dt>FIG 1</dt><dd>a basic circuit diagram for picture-in-picture overlay with a first image processing stage with a digital-to-analog conversion stage provided on the output side and a second image processing stage as well as a downstream switching device and</dd><dt>FIG 2</dt><dd>a circuit arrangement for setting the reference signal, which is supplied to the digital-to-analog conversion stage according to FIG. 1.</dd></dl>

1 shows the basic circuit diagram for picture-in-picture overlay with a first image processing stage 1 and a second image processing stage 2. The first image processing stage 1 has input terminals 3, 4 for applying first video signals Video 1 and associated sync signals Sync 1. The second image processing stage 2 is provided with input terminals 5, 6 for second video signals video 2 and second synchronization signals sync 2. First analog image signals R1, G1, B1 can be tapped at output terminals of first image processing stage 1 and second analog image signals R2, G2, B2 at output terminals of second image processing stage 2.

The first and second image signals R1, G1, B1; R2, G2, B2 arrive at a switching device 7, which switches between the first image signals R1, G1, B1 and second image signals R2, G2, B2 at the correct time. A control device 8 is connected via multi-core connecting lines a, b, c to the first image processing stage 1, second image processing stage 2 and switching device 7 and provides suitable control signals for the correct control of the individual components.

The first image processing stage 1 has a picture-in-picture processor, e.g. B. the integrated circuit SDA 9088 from Siemens, which is used via a signal processing stage 9, the image reduction, the intermediate storage of the digital image data in an integrated image memory and the output of the digital image data of the reduced image to digital-to-analog conversion stage 10. According to the invention, the digital-analog conversion stage 10 can be supplied with a variable reference signal from a reference signal stage 11, this reference signal being adjustable by the control device 8 in accordance with digital control signals b. The digital-to-analog conversion stage 10 is preferably a D / A converter with switchable current sources, as is described as such from Tietze-Schenk, Semiconductor Circuit Technology, 5th edition, 1980, under item 24.2.2.

2 shows the reference signal stage 11 in detail. A reference voltage V serves as the reference signal_ref, which is supplied to the digital-to-analog conversion stage 10. This reference voltage V_ref, is tapped at the connection point P of a voltage divider, which is connected between a supply voltage source V₊ and reference voltage V₋, here ground. The voltage divider consists of a connected to the supply voltage source V₊ MOS transistor 14, the control terminal of a voltage V_S lies, with series connected resistors R3 and R8. The connection point P is also connected to an output terminal 12 of the first image processing stage 1. At this output terminal 12 there is an external resistor R connected to reference potential V₋_ref connect, whereby the reference voltage V_ref is initially roughly defined. Connected to the connection point P are at least two further resistors 15, here a total of four resistors, each of which has their respective other connections via a semiconductor switch 13 at reference potential V₋, the control connections of the semiconductor switches being connected to terminals to the control signals b1, b2, b3, b4 of the control device 8 can be applied. These resistors can be switched on and off via the control device 8 shown in FIG. As a result, the reference current of the current mirror shown in FIG. 2, which changes the reference voltage V_ref the digital-to-analog conversion stage. The resistance values ​​R_n the resistors 15 are made accordingly<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>R</mtext></mrow><mrow><mtext>n</mtext></mrow></msub><msup><mrow><mtext> = R · 2</mtext></mrow><mrow><mtext>(n-1)</mtext></mrow></msup></mrow></math><img file="EP0443064B1_D0001.tif" /></maths> chosen. In the example shown in FIG. 2, the resistors 15 have the values ​​R, 2R, 4R and 8R. With the control signals b1, b2, b3 and b4, for example, a contrast variation of ± 20% is thus achieved in 16 steps. By changing the reference voltage of the digital-to-analog conversion stage 10 there is a uniform change in the output current without the properties of the digital-to-analog conversion stage 10 changing significantly.

With the present invention, the contrast of the image to be faded in can be set in a particularly simple manner via a keyboard on the television set or the associated remote control, as provided with the reference number 20 in FIG. In addition, the contrast setting of the image to be faded in can be adjusted automatically depending on the main image. For this purpose, only the amplitude of the second image signals R2, G2, B2 in FIG. 1 has to be detected and the amplitude of the first image signals R1, G1 and B1 have to be adjusted accordingly.