MXPA00007900A - Processing of digital picture data in a decoder - Google Patents

Abstract

A decoder for a digital audiovisual transmission system, the decoder comprising a processor means for decompressing and displaying compressed still picture data and a memory (66, 67) characterised in that the memory (66, 67) comprises a storage memory (66) allocated to receive from the processor decompressed digital image data representing a plurality of still picture images (63, 64, 65) and at least one display memory (67) adapted to hold contemporaneously data representing multiple still picture images (68, 69, 70, 71) readable by the processor means prior to display, data representing the plurality of images being copied from the storage memory (66) to the display memory (67) for subsequent display.

Description

PROCESSING OF DIGITAL IMAGE DATA IN A DECODER The present invention relates to a decoder for a digital audiovisual transmission system, the decoder comprising a processor element for decompressing and displaying compressed digital image data and a memory element. 10 The transmission of digital data broadcasts is well known in the field of paid television systems, where disturbed audiovisual information is sent, usually via a satellite or a satellite / cable link, to several subscribers, each subscriber having a capable decoder to wake up the transmitted program to see it subsequently. The digital terrestrial transmission systems are also known. Recent systems have used the transmission link to transmit other data, in addition to, or as well as, audiovisual data, such as computer programs or interactive applications At the most basic level of functionality of these systems, the digital audio and video data related to the television program are transmitted in a compressed format, for example, according to the standard of MPEG-2 compression. The decoder receives and decompresses this data in order to regenerate the televised program.

In addition to simple data from televised programs, it is becoming increasingly common for the decoder to be required to handle other image data or compressed graphics. For example, in the case where the decoder includes network finder capabilities, the decoder processor may be required to receive and decompress data from copied digital images, eg, fixed video images, and with graphics, etc. . This image information can be displayed on the images of normal televised programs. This data of still or moving images can typically be received in one of several compressed formats that are currently used in the context of personal network-based search engines. By For example, an image can be formatted and compressed according to the well-known GIF or PNG standards, where an image is described by means of a color look-up table that defines a color table and an array of pixel values relating to this table, the data of the matrix according to a known compression method for preparing the GIF / PNG image. Alternatively, the image can be formatted and compressed as a MPEG or JPEG still image, in which each pixel is directly associated with a red / green / blue color value. It is an object of the present invention to provide a element to efficiently handle these copied still image files. In accordance with the present invention, a decoder for a digital audiovisual transmission system is provided, the decoder including a processor for decompressing and displaying compressed still image data and a memory, characterized in that the memory comprises a storage memory allocated to receive from the processor decompressed data representing a plurality of fixed representative images, and at least one display memory adapted to store data representing multiple fixed representative images readable by the processor before displaying them, the data representing the plurality of representation of still images which are being copied from the storage memory to the display memory for subsequent display. This division of the memory into storage areas and display memory introduces a degree of flexibility in the display of still image data, in particular allowing the data representing a given fixed representative image to be stored at the same time both in the element of storage as in the exhibition. Data representing one or more still images can be stored indefinitely in the storage memory as long as there is a possible requirement for this data, even after the J & k ** This is an image that has been removed from the screen when erasing the data from the display memory. In some cases, the decompressed image data can simply be copied "as is" in the display memory. However, in some cases, the digital image data copied from the storage memory in the display memory is modified or duplicated during the copying step, for example, in order to adapt the size of the digital image or copy the image. same image several times in a display memory. Preferably, the processor element is adapted to process image data in the display memory since a layer between a plurality of layers over imposes one over the other when displayed. As discussed above, the image data can be superimposed on a top layer during, for example, normal televised images representing audiovisual information. However, in one embodiment, the image data in the display memory may be displayed in a layer normally used by the processing element to display transmitted audiovisual information. This may be the case, for example, when the decoder changes from a "television" mode, in which a transmitted broadcast is displayed, to a "network finder" mode, in which the image data copied from the Internet are displayed instead of the programs • L? A £ ?. ToeáB * televised normal. Advantageously, the memory comprises a second display memory readable by the graphic processor element and corresponding to a second layer of displayed image data, the data being copied from the storage memory to the second display memory for subsequent display thereof. in the second layer of image data. Again, as before, the digital image data copied from the storage memory to the second display memory can be modified during the copy step. In one embodiment, for example, when the decoder switches between a television and search mode, the image data in the second display memory can be displayed in the lowermost background layer normally used by the processing element to display fixed audiovisual information. of transmission. Preferably, the partial image data is copied from the storage memory to a display memory under the control of an application running inside the decoder in a manner that allows to display a part of an image. This may be desirable, for example, when the decompression and copying of an image in the storage memory by the processor proceeds in several stages. In one embodiment, the image data is copied from the storage memory into a first or second display memory under the control of a high level application running in the processor. Alternatively, this process can be handled automatically by a lower level application associated for example with the general handling of received image data. The compressed digital image data is preferably stored in a buffer before decompression by the processor. It is not necessary that this buffer element be a single integral block of the memory particularly if the data arrives in several blocks of information. In particular, in one embodiment, the buffer comprises a plurality of buffer elements. Each memory element may correspond, for example, to a block of data copied in the decoder. Preferably, the decompression and transfer of image data from the buffer elements to the storage memory, and from the storage memory to a display memory, is controlled by the processor so that the image information present in the memory storage is transferred to the display memory at the end of the decompression of the content of each intermediate element. It may be the case, for example, that the information corresponding to an image will be scattered over a number of buffer elements. As each buffer is emptied and decompressed, the information ready for display is immediately transferred to the display memory, enabling a partial display of the complete image. In addition, or alternatively, the decompression and transfer of a group of images in a single image file from the buffer to the storage memory, and from the storage memory to the display memory, is controlled by the processor. Thus, the image information is transferred from the storage memory to the display memory at the end of the decompression of each image in the image file. As mentioned above, the image data can be sent in any number of formats. In one embodiment, the processor is adapted to decompress data from images sent in a compression standard, such as GIF or PNG, which uses a color look-up table. In addition or alternatively, the processor is adapted to decompress data from images sent in a compression standard, such as MPEG or JPEG, which uses a red / blue / green color value associated with each pixel. All functions of decompression, display and so on can be integrated into a single processor.

Alternatively, the processor in the decoder does not necessarily need to be integrated into a single chip but can be divided, for example, into a general processor that handles data decompression and a graphics processor to prepare the decompressed data for display. Similarly, although the application may refer to a storage memory, a display memory, etc., it will be understood that they do not need to correspond to typically separate memory devices (direct access memory, read-only memory, FLASH, etc.). .) but may correspond to one or more areas assigned for this purpose by a control application and divided among one or more physical memory devices. The present invention has been discussed above in connection with a decoder apparatus. The present invention also extends to a method of processing digital images within a decoder, corresponding to the general and preferred aspects of the invention discussed above. In the context of the present application the term "digital audiovisual transmission system" refers to all transmission systems for transmitting or broadcasting mainly digital audio-visual or multimedia data. Although the present invention is particularly applicable to a digital transmission television system, the present , aa¿¿ -K - ÉM * a- «i | 1 ^^ Í! ft. ~, .s ^ aaam ^ ji, ^^^ invention can also be used to filter data sent by a fixed telecommunications network for multimedia Internet applications, etc. Similarly, the term "decoder" is used to apply to an integrated receiver / decoder to receive and decode a transmission encoded in cryptic language, the receiver and decoder elements of this system are considered separately, as well as a capable receiver. to receive transmissions that are not encoded in cryptic language. The term likewise covers decoders that include additional functions, such as network finders, together with decoders integrated with other devices, for example, integrated VHS / decoder devices, digital televisions or the like. The term MPEG refers to the data transmission standards developed by the working group of the International Standard Organization "Motion Pictures Expert Group", and notably the MPEG-2 standard developed for digital television applications and presented in ISO 13818 documents -1, ISO 13818-2, ISO 13818-3 and ISO 13818-4. In the context of the present patent application, the term includes all variants, modifications or developments of the basic MPEG formats applicable to the field of digital data transmission. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a global view of a digital television system. Figure 2 shows the elements of the receiver / decoder of Figure 1. Figure 3 shows a flow diagram of the computer system of the receiver / decoder. Figure 4 shows in layer form the image data processed by the graphics processor of Figure 2. Figure 5 shows the operations carried out in the memory for image data to be displayed in the MPEG layer of Figure 4; and Figure 6 shows the operations carried out in the memory for the partial display of image data of the MPEG layer. A general view of a digital television system 1 according to the present invention is shown in Figure 1. The invention includes a mostly conventional digital television system 2 which uses the known compression system MPEG-2 to transmit compressed digital signals. In more detail, the MPEG-2 compressor 3 in a transmission center receives a stream of digital signals (typically a stream of video signals). The compressor 3 is connected to a multiplexer and a disturber 4 via a link 5. The multipultor 4 receives a plurality of additional input signals, assembles the transport current and transmits the compressed digital signals to the transmitter 6 of the transmission center via the link 7, which can of course take a wide variety of forms, including telecommunications links. The transmitter 6 transmits electromagnetic signals via the upper link 8 to a satellite transmitting transmitter 9, where they are processed electronically and transmitted via a downward notional link 10 to the terrestrial receiver 12, conventionally in the form of a proprietary satellite dish. rented by the end user. The signals received by the receiver 12 are transmitted to an integrated receiver / decoder 13 owned or rented by the end user, and connected to the television set of the end user 14. The receiver / decoder 13 decodes the MPEG-2 signal compressed into a television signal for the television set 14. Other transport channels for the transmission of data are of course possible, such as terrestrial transmission, cable transmission, combined satellite / cable links, telephone networks, etc. In a multi-channel system, multiplexer 4 handles audio and video information received from several parallel sources and interacts with the transmitter 6 to transmit the information along a corresponding number of channels. In addition to audiovisual information, messages or applications or any other kind of digital data may be produced in some or all of these interlaced channels with the audio and digital video information transmitted. A conditional access system 15 is connected to the multiplexer 4 and the receiver / decoder 13, and is located partially in the transmission center and partly in the decoder. This allows the end user to have access to digital television broadcasts from one or more broadcast providers. A smart card, capable of deciphering messages related to commercial offers (this , one or more television programs sold by the transmission provider), can be inserted into the receiver / decoder 13. Using the decoder 13 and the smart card, the user can buy commercial offers, either in the subscription mode or a mode of payment to see. As mentioned above, the programs transmitted by the system are disturbed in the multiplexer 4, the conditions and the cryptic encoding keys applied to a given transmission are determined by the access control system 15. The transmission of disturbed data of this way is well known in the field of systems of paid television. Typically, the disturbed data is transmitted together with a control word to awaken the data, the control word itself being cryptically encoded by an operation key and transmitted in a cryptic manner. The mixed data and the control word in cryptic language are received by the decoder 13 having access to an equivalent of the operating key stored in the smart card inserted in the decoder to decode the coded control word in cryptic form and after that will awaken the transmitted data. A paid subscriber will receive, for example, in the Monthly Rights Control Message (ECM) the exploitation key needed to decode the control word encoded cryptically to allow viewing of the transmission. An interactive system 16, also connected to the multiplexer 4 and the receiver / decoder 13 and again located partially in the transmission center and partially in the decoder, enables the end user to interact with several applications via a modem back channel 17. The Modem back channel can also be used for communications used in the conditional access system 15. An interactive system can be used, for example, to enable the viewer to immediately communicate with the .Í2. & -. transmission center to request authorization to see a particular event, copy an application, etc. With reference to Figure 2, the elements of the receiver / decoder 13 in the upper case adapted to be used in the present invention will now be described. The elements shown in this figure will be described in terms of functional blocks. The decoder 13 comprises a central processor 20 that includes associated memory elements and adapted to receive input data from a serial interface 21, a parallel interface 22, a modem 23 (connected to a rear modem channel 17 of the Figure 1), and switch contacts 24 on the front panel of the decoder. The decoder is further adapted to receive inputs of an infrared remote control 25 via a control unit 26, and also has two smart card readers 27, 28 adapted to read bank or subscription smart cards 29, 30, respectively. The subscriber smartcard reader 28 is connected to an inserted subscription card 30 and to a conditional access unit 29 to supply the necessary control word for a demultiplexer / wake-up device 30 to enable the cryptically encoded transmitted signal to be awakened. . The decoder also includes a conventional tuner 31 and demodulator 32 for receiving and ^^^^^ MW ^^^ ffit ^^^^ demodulate the satellite transmission before being filtered and demultiplexed by the unit 30. The data processing within the decoder is generally handled by the central processor 20. The software architecture of the central processor corresponds to a virtual machine that interacts via an interface layer with a lower level operating system implemented in the hardware components of the decoder. This will now be described with reference to Figure 3. For the purposes of this description, an application is a piece of computer code for controlling high-level functions of the receiver / decoder 13. For example, when the end user places the focus of the a remote controller on a button object seen on the fixed television screen and press a validation key, the instruction sequence is associated with the button is to execute. An interactive application proposes menus and executes commands to the final user's request and provides data related to the purpose of the application. The applications can be either resident applications, that is, stored in the read-only memory (or FLASH or other non-volatile memory) of the receiver / decoder 13, or they are transmitted and copied into the direct access memory FLASH memory of the receiver / decoder 13. The applications are stored in the memory locations in the receiver / decoder 13 and are represented as resource files. Resource files include files for graphical object description units, variable block unit files, instruction sequence files, application files, and data files. The receiver / decoder contains the memory divided into a direct access memory volume, a FLASH volume and a read-only memory volume, but this physical organization is distinct from the logical organization. The memory can also be divided into memory volumes associated with several interfaces. From one point of view, memory can be considered part of the hardware; from another point of view, the memory can be considered as supporting or containing the entire system shown apart from the hardware. Referring to Figure 3, the computer system can be considered as centered in a runtime machinery 40 forming part of a virtual machine 41. This is coupled to the applications on one side (the "high level" side) , and, on the other side (the "low level" side), via several intermediate logical units discussed below, to the receiver / decoder hardware 42. The receiver / decoder hardware can be considered to include several ports corresponding to the commented functional blocks in relation to Figure 2 (the £ - -Aflfc- »--rt« »- É ^ -M« «interface 26 for the manual device 25, the MPEG 30 current interface, the serial interface 21, the parallel interface 22, the interfaces to the readers of cards 27, 28 and interface 23 to the back channel with modem 17). Several applications 43 are coupled to virtual machine 41. Some of the most commonly used applications may be more or less permanently resident in the system, as indicated in 44, while others will be copied into the system, for example, from the MPEG data stream or other ports as required. The virtual machine 41 includes, in addition to the runtime machinery 40, some resident library functions 45 which includes a toolbox 46. The library contains miscellaneous functions in C language used by the machinery 40. These include such data manipulation. as compression, expansion or comparison of data structures, line drawing, and so on. The library 45 also includes information about device units 49 in the non-modifiable programs of the receiver / decoder, such as the numbers of hardware and software versions and the available direct access memory space, and a function used when copying a device. new device 47. Functions can be copied to the library and stored in FLASH memory or direct access memory. - é 'm ^^^ r ^^^^ ^ s ... tei ... sliii.

The runtime machinery 40 is coupled to a device manager 48 which is coupled to a set of devices 47 which are coupled to the device units 49 which in turn are coupled to the ports or 5 interfaces. In general terms, a device unit can be considered as defining a logical interface, so that two different device units can be coupled to a common physical port. A device will typically be attached to more than one device unit; if a The device is coupled to a single device unit; the device will normally be designed to incorporate the full functionality required for communication, so that the need for a separate device unit is omitted. Certain devices can communicate with each other.

As will be described later, there are three forms of communication between the devices 47 to the runtime machinery: by means of variables, buffers, and events which are passed to a set of event queues. 20 Each function of the receiver / decoder is represented as a device 47. The devices can be local or remote. Local devices include smart cards, SCART connector signals, modems, serial and parallel interfaces, an MPEG audio and video player and a MPEG section and table extractor. Remote devices executed in a remote location, they differ from the local devices in which a port and procedure must be defined by the system authority or the designer, rather than by a device and the device unit provided and 5 designated by the receiver manufacturer / decoder. The runtime machinery 40 is run under the control of the microprocessor and a common application programming interface. It is installed in any receiver / decoder so that all the receivers / decoders are identical from the point of view of the application. The machinery 40 executes applications 43 in the receiver / decoder. It executes interactive applications and receives events from outside the receiver / decoder, exhibits graphs and text, calls devices for services and uses functions of the library 45 connected to the machinery 40 for specific calculations. Runtime machinery 40 is an executable code installed on each receiver / decoder, and includes an interpreter to interpret and execute applications. The machinery is adaptable to any operating system, including a single-task operating system (such as MS-DOS). The machinery is based on process sequencer units (which take several events such as pressure from key, to carry out several actions), and contains your «Aa8te = -86aa_ = te-a-sáa.aÉa own programmer to handle event queues from different hardware interfaces. It also handles the display of graphics and text. A process sequencing unit comprises a set of action groups. Each event causes the process sequencer unit to move from its current action group to another action group depending on the character of the event, and executes the actions of the new action group. The machinery 40 comprises a code loader for load and copy applications 43 into the memory of the receiver / decoder. Only the necessary code is loaded into the direct access memory or FLASH memory, in order to ensure optimal use. The copied data is verified by an authentication mechanism to avoid any modification of an application 43 or the execution of any unauthorized application. The machinery 40 further comprises a decompressor. As the application code (a form of intermediate code) is compressed to save space and fast copy of the MPEG stream or via a mode integrated receiver / decoder, the code must be decompressed before loading it into direct access memory. The machinery 40 also comprises an interpreter to interpret the application code to update various variable values and determine status changes, and a error verifier. afc-aeJ > »^» A-wa ^ J * - ««. A - »-...- ÍJ-.

Before using the services of any device 47, a program (such as a sequence of application instructions) has to be declared as a "client", that is, a logical path to the device 47 or the device manager 48. The administrator gives the client a customer number that is referenced in all accesses to the device. A device 47 can have several clients, the number of clients for each device 47 is specified depending on the type of device. A client is introduced to device 47 by a procedure "Device: Open Channel". This procedure assigns a customer number to the customer. A client can be removed from the list of clients 48 of the device manager by means of a procedure "Device: Close Channel". The access to the devices 47 provided by the device manager 48 may be either synchronous or asynchronous. For synchronous access, a "Device: Call" procedure is used. This is a means of accessing data which are immediately available or a functionality that does not involve waiting for the desired response. For asynchronous access, a "Device: Input / Output" procedure is used. This is a means of accessing data that involves waiting for the response, for example by scanning tuner frequencies to find a multiplex or returning to a table for MPEG stream.

When the requested result is available, an event is placed in the machinery queue to signal its arrival. Another procedure "Device: Event" provides a means to handle unexpected events. As noted above, the main cycle of the runtime machinery is coupled with a variety of process sequencing units, and when the main cycle encounters an appropriate event, the control is temporarily transferred to one of the process sequencing units. In this way, it can be seen that the computer system implemented in the processor 20 provides a platform that gives considerable flexibility in enabling an application to communicate with a variety of devices. Returning to Figure 2, the processing of sound and image data by each of the associated processors will now be described in detail. In the case of received audio and video signals, the MPEG packets containing these signals will be demultiplexed and filtered to pass real-time audio and video data in the form of an elementary packet stream (PES) of audio and video data to dedicated audio and video processors or decoders 33, 34. The converted output of the audio processor 33 passes to a preamplifier 35 and thereafter via the audio output of the receiver / decoder. The converted processor output - ^ üa,. »^ - ..? - .. aaa», ^ i? t -... of video 34 passes via a graphics processor 36, and PAL / SECAM 37 encoder to the video output of the receiver / decoder. The video processor may be of a conventional type, such as the ST 3520 A of SGS Thomson. The graphic processor 36 additionally receives graphic data for its display (such as generated images, etc.) from the central processor 20 and combines this information with information received from the video processor 34 to generate an on-screen display combining images in movement along with superimposed text or other images. An example of a graphics processor adapted to carry out this type of operation is the CL 9310 of C-CUBE. In the case of received teletext and / or subtitle data, the conversion of elementary current data in packages to generate the appropriate images can also be handled by dedicated processors. However, in most conventional systems, this is carried out by the general processor 20. In fact, many of the functions associated with the elements, such as the graphic processor 36, the video 34, the central processor 20, etc., can be combined or divided in different ways, for example, to integrate the central and graphic processors as a single processor element, etc. Referring now to Figure 4, the functionality of the graphics processor 36 will now be described.

«^,. ^ And y -,» - ^^ As discussed above, the graphics processor receives and processes video data in real time from the video decoder 34 together with graphic data received from the general processor 20 for the purpose to generate a screen display superimposed. As shown in Figure 4, the graphics processor 36 is adapted to process input data divided into four distinct layers; a background layer 50, an MPEG layer 51, a graphic layer 52 and a cursor layer 53. As will be understood, the background layer 50 corresponds to the lowest layer of the screen display, the other layers progressively overlapping with varying degrees of translucency or opacity on this layer. In the case where the decoder is configured to display a transmitted video signal, the background and MPEG layers 50, 51 correspond to the data stream received from the video decoder 34, the layer 50 corresponding to the MPEG still images received from the decoder 34 and layer 51 corresponding to a moving video MPEG signal received from the decoder. The division of a video signal into a fixed part and a changing part is a known feature of MPEG compression. Other configurations of the decoder are possible, for example, where the background and MPEG 50, 51 layers are completed by image data in any number of formats received from the processor 20. For example, in the case where the decoder is operating in a network finder configuration, the processor 20 can supply still and / or moving image data to complete the layers 50, 51. The layer 50 may also correspond, for example, to a background color and the layer 51 to one or more windows displayed on the background and containing, for example, information, and moving cones or the like. The operation of the system in handling image data will be discussed in more detail below with reference to Figures 5 and 6. The data of still and moving images of the background layers and MPEG 50, 51 are mixed together by a processor graph 36, as represented by element 54, and a combined output provided. The information mixture of the MPEG layer 51 on the background layer 50 by the graphics processor can be carried out using the so-called alpha mixing factor to allow a greater or lesser degree of translucency of the pixels in the image of the MPEG layer. In the case of moving video image received from the video decoder 34, the same mixing factor is used for all the pixels within the video sequence. In the case of image data from the central processor 20, the value of the blend factor for layer 51 may be different for different parts of the screen. . ^ tá ^^^ tj ^^ & The graphic layer 52 is used for texts, forms, icons, etc. that will be displayed on the screen on the images taken from the layers 50, 51, for example, to allow the display of a moving icon or something similar generated by the processor 20 on a real-time video sequence taken from the video decoder 34. In a manner similar to the mixing carried out for the layers 50, 51, the element 55 performs mixing of the graphic layer 52 with the combined output of the layers 50, 51. 10 Different regions within the graphic layer 52 can be assigned a different mixing factor and a corresponding different level of translucency depending on the characteristics of the data within each region. A final layer, the cursor layer, is shown at 15 53 and represents an opaque, hardware-generated cursor image under the control of the central processor 20 and superimposed on all the previous layers. As shown at 56, this layer is combined with the summed output of the combination of all the previous layers to generate a final combined output 20 sent to the encoder 37 for subsequent display. Unlike the previous layers, the cursor presents a continuously opaque appearance and overlaps the combined layers without any mixing. With reference to Figures 5 and 6, the operation 25 of a device 47 of the kind shown in Figure 3 and a ^ ~ - ^^ g ^] «pflrtftill -Sjf -B. ^ .iM ^ t S > ^ ---- ^ _ Affect. adapted to decompress and display representative images copied in the MPEG layer 51 will now be described. In the following description, the term representation is used to describe a compressed digital image. Typically, the 5 kinds of representation formats used may include MPEG fixed representation, JPEG format representation, PNG format representation, GIF format representation, and so on. Although the following description will focus on the processing and display of a single image, a sequence of still images can be displayed one after the other in order to generate a sequence of moving images. Referring to Figure 5, the copied compressed image data 60, 61, 62 is initially stored in a buffer section of the decoder direct access memory indicated at 63. This buffer can be of the type initialized and managed by a high-level application 43 responsible for decoding and displaying images, or a memory area handled by he device manager 48 shown in Figure 3. Each type of image file or group of image files includes a header indicating the format of the image file (GIF, MPEG, etc.) as well as the information necessary to decompress the file of pictures. By For example, a file in GIF 62 format comprising more than one image has a global header that describes the size of the global area where the two decompressed images will be displayed and a specific heading for each image describing its size and location coordinates within the global area. After copying a compressed image into a buffer section 63 of the memory, a decompression of the image data will be performed by the device in response to a PICTURE_DECOMPRESS command received from the application. The decompressed image data subsequently 63, 64, 65 is stored in a separate storage section of the direct access memory indicated at 66 and reserved for image data that will eventually be displayed in the MPEG layer. Each uncompressed image or image sequence is given an image identity reference Idl, Id2, Id3 by the device, this ID value is supplied to the high level application and is used for all subsequent operations that are carried out about these data. Unlike the compressed image data temporarily stored in the application buffer 63, the decompressed image data 63, 64, 65 can be stored indefinitely in the storage memory 66 until such time as the application decides to erase the information.

The storage of decompressed image data in a different allocated memory area allows the data to be manipulated in various ways before being displayed. For example, an adaptation to the size of the image can be carried out, either by the device itself, the device manager or by a higher level application. Likewise, the image can be duplicated in order to be displayed in several positions on the screen. The conversion of color data associated with the image, for example for compensate for limitations in the functionality of the graphics processor, it can also be carried out on the image. Modified or unmodified data stored in memory 66 are passed, in response to a PICTURE_DISPLAY command from the application, in an access memory section separately assigned 67 for the images to be displayed in the MPEG 51 layer (see Figure 2). The layer of the display memory 67 corresponds to the screen area. As shown, the Idl and Id2 images are displayed at 68 and 69, while the image or sequence of the Id3 images is displayed. duplicates and is displayed at positions 70, 71. The information from the memory section 67 is fed to the graphics processor 36 in order to create the MPEG 51 layer, as shown in Figure 2. In addition to transferring the information from picture between the storage area 66 and the display area 67, it may carry out a second transfer to copy the information stored in the storage area 66 into a memory area (not shown) associated with the image display in the background layer 40 of Figure 2. For example, a single image it can be replicated and displayed several times in the background layer in order to cover the screen in a mosaic manner. The information stored in the memory area associated with the background layer is accessed by the graphics processor in the same way as the MPEG display area 67. As will be understood, the memory sections 63, 64, 65 do not need to physically match the uninterrupted memory zones in a single direct access memory or other memory element. In particular, the memory area 63 can be divided among several buffers. Figure 6 shows the steps associated with decompressing a file 80 that contains two compressed images 81, 82 previously loaded into 4 associated buffer elements or buffer lists 83, 84, 85, 86. Each buffer list corresponds to buffer areas in which a block of data has been copied from the MPEG stream. The buffer list itself can designate a number of separate buffer areas depending on availability as the information is copied. In step 87, the application sends a PICTURE_DECOMPRESS 87 command to initiate the decompression process. The device assigns a group image identifier and begins reading the buffers. Once the start of the image is found in step 88, the device assigns an image identifier and decompression of the image begins. In step 89, the end of the first buffer list is reached and the application sends a PICTURE_ADD_DATA command in step 90 to command the device to read the following buffer list in the series. At this time, only part of the image of the first image 81 has been decompressed and stored in the memory storage area 66. The application however may decide to immediately transfer the partial image to the display memory area 67. The decompression of the the remaining part of the image 81 continues until the start of the next image is found at 91. At this time, the total of the first image 81 has been decompressed and stored in the memory area 66. The application can then update the content of the display memory area 67 by copying the entire image in the display area 67. In this way, the total of the first image 81 can be displayed before the second image has been decompressed. In step 92, the device reports the application of the end of the second buffer list 84 and the application sends a second command of ICTURE_ADD_DATA 93 to begin reading the next buffer list 85. The process is repeated at the end of the third buffer list 85 and the fourth list of intermediate memory 5 starts by means of steps 94, 95. Again, each time the end of a buffer is reached at 92, 94, the application can copy the data which have already been decompressed from the storage area 66 in the display area 67. 0 In step 96, the end of the file is reached and both images 81, 82 have been decompressed and loaded into the storage memory 66. At this point , the device informs the application of the successful decompression of the complete file and the application again copies the contents of the storage memory 66 into the display memory 67 to display the conjunct or full of images.

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Claims (18)

1. A decoder for a digital audio-visual transmission system, the decoder including a processor for decompressing and displaying data of compressed still images and a memory, characterized in that the memory comprises a storage memory allocated to receive decompressed data representing a plurality of the processor from the processor. of images of fixed representations, and at least one display memory adapted to store data at the same time as representing multiple images of fixed representations readable by the processor before the display, the data representing the plurality of images of fixed representations that are being copied from storage memory to the display memory for its subsequent display.

2. A decoder as claimed in claim 1 in which the digital image data copied from the storage memory in the display memory is modified or duplicated during the copying step.

3. A decoder as claimed in claim 1 or 2 wherein the processor is adapted to process display memory image data as a layer between a plurality of layers superimposed one on top of the other as they are displayed.

4. A decoder as claimed in claim 3 in which the processor is adapted to display the image data in the display memory in a layer normally used by the processor element to display transmitted audiovisual information.

5. A decoder as claimed in any preceding claim wherein the memory comprises a second display memory readable by the processor element and corresponding to a second layer of displayed image data, the data being copied from the storage memory to the second display memory for its subsequent display in the second layer of image data.

6. A decoder as claimed in claim 5 in which the digital image data copied from the storage memory to the second display memory is modified or duplicated during the copying step.

7. A decoder as claimed in any preceding claim, wherein the image data is copied from the storage memory to a display memory to allow the display of part of an image.

8. A decoder as claimed in any preceding claim, in which the image data is . .. ^ .tja ** afc¿áM. «i.aiá ^ copied from the storage memory in a first or second display memory under the control of a high-level application running on the processor.

9. A decoder as claimed in any preceding claim, wherein compressed digital image data is stored in the buffer element before decompression by the processor.

10. A decoder as claimed in claim 9, wherein the buffer element 10 comprises a plurality of buffer element. A decoder as claimed in claim 10, wherein the decompression and transfer of image data from the buffer elements to the storage memory, and the memory of the 15 storage to the display memory, is controlled by the processor so that the image information present in the storage memory is transferred to the display at the end of the decompression of the content of each buffer element. 12. A decoder as claimed in any preceding claim, wherein the decompression and transfer of a group of images in a single image file from the buffer to the storage memory, and from the storage memory to 25 an exhibition memory, is controlled by the element ^^ tógtegg ^^ M ^ sgágtóMßj jte ^^^^^^^^^^^^^^^^^^^ processor so that the image information is transferred from the storage memory to the display memory at the end of the decompression of each image in the image file. 13. A decoder as claimed in any preceding claim, wherein the processor is adapted to decompress image data sent in a compression standard using a color look-up table. 14. A decoder as claimed in any preceding claim, wherein the processor is adapted to decompress image data sent in a compression standard using a red / blue / green color value associated with each pixel. 15. A decoder as claimed in any preceding claim, wherein the processor comprises a general processor for decompressing digital image data and a graphics processor for preparing the decompressed data for display. 16. A method of processing digital images in a decoder for a digital audiovisual transmission system, the decoder comprising a processor for decompressing and displaying compressed still image data characterized in that the decompressed digital image data representing a plurality of rendering images fixed data received from the processor are transmitted to a storage memory and thereafter copied from the storage memory to a display memory which at the same time stores the data representing the multiple image representations, the data being read by the processor for its subsequent display of these multiple representations of images. 17. A decoder for a digital audiovisual transmission system substantially as described herein. 18. A method of processing digital images in a decoder for a digital audio-visual transmission system substantially as described herein.