MXPA05011876A - Reverse trick modes on non-progressive video using special groups of pictures - Google Patents

Abstract

The invention concerns a method (200) and system (100) for performing a reverse trick mode. The method includes the steps of receiving (212) a non-progressive video signal and encoding (214) the non-progressive video signal into at least one group of pictures having at least one prediction source picture and at least one non-prediction source picture. All the non-prediction source pictures are predicted from the at least one prediction source picture such that no non-prediction source picture is predicted from another non-prediction source picture. The method also includes the step of, in response to a reverse trick mode command, altering (220) the display order of the group of pictures to permit the group of pictures to be displayed in a reverse order.

Description

MODES INVERSE TRICK IN NON PROGRESSIVE VIDEO USING SPECIAL GROUPS OF IMAGES BACKGROUND OF THE INVENTION 1. Technical Field The inventive arrangements refer, in general, to video systems, and more particularly to video systems that record or reproduce digitally encoded video sequences. 2. Description of Related Art Devices that facilitate video playback are gaining popularity in the consumer electronics market to date. For example, many consumers have purchased digital video disc players (DVDs) for the purposes of watching pre-recorded programs or recording their favorite programs. A DVD player or recorder typically contains a Motion Picture Expert Group (MPEG) decoder to decode the digitally encoded multimedia data that is stored on the discs that play the recorder or the player. The MPEG video signal to be decoded is comprised of a plurality of groups of images (GOP), each of which typically contains an intra (1) image, a plurality of predictive images (P) and a plurality of bidirectional predictive images. (B) If the digital video recorder or player is connected to certain televisions, the digitally encoded signal will be decoded by the MPEG decoder of the digital video recorder or player before being presented on television. Significantly, however, many digital televisions (DTV) contain their own MPEG decoders. As such, if a digital video recorder or player is connected to a DTV, the video signal read from the disc is decoded remotely by the DTV decoder. This type of decoder is considered a passive decoder since the microprocessor of the digital video recorder or player has no control over the decoder. This configuration can be referred to as a remote decoder system. During the reproduction of a video signal, some viewers may wish to develop certain trick modes. A trick mode can be any video playback in which playback is not done at a normal speed or in a forward direction. As an example, a reverse trick mode can be started to allow the viewer to locate the portions of video that have already been played and that the viewer wants to see again. The reverse trick mode can be at a normal speed or the images in a GOP can be skipped to produce a fast reverse trick mode. In addition, duplicates of the images in a GOP can be inserted into the GOP to generate a slow reverse trick mode. To perform a reverse trick mode on an MPEG video signal, the decoder of the DVD can decode the images in a GOP in a forward direction. Once these images are decoded, the decoder is instructed to present the images in reverse order and, if necessary, add duplicate images to the GOP or skip the images in the GOP. A remote decoder system, however, is not particularly suitable for performing reverse trick modes. The reason for this disadvantage is that the microprocessor of the digital video recorder or player can not instruct the decoder to present the images in reverse. As such, a reverse trick mode in such an arrangement is typically limited to merely sending to a decoder in an inverse order the I images in all or some GOPs of the video signal.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a method for performing a reverse trick mode. The method includes the steps of receiving a non-progressive video signal and encoding the non-progressive video signal in at least one group of images having at least one prediction source image and at least one non-prediction source image. All non-prediction source images are predicted from the at least one prediction source image such that no non-prediction source image is predicted from another non-prediction source image. further, the method may include the steps of recording the non-progressive video signal in a storage medium and reproducing the non-progressive video signal. The method also includes the step of, in response to a reverse trick mode command, altering the display group order of images to allow the group of images to be presented in reverse order. The method also includes the step of modifying at least the number of non-prediction source images in the group of images in response to the inverse trick mode command. In one arrangement, the prediction source image may be an intra image. In addition, at least a portion of the non-prediction source images can be bidirectional predictive images or predictive images. As an example, each of the bi-directional predictive images can be unidirectional bidirectional predictive images. In one aspect of the invention, the modification step may include the step of skipping at least one non-prediction source image in the group of images. Alternatively, the modification step may include the step of inserting a duplicate of at least one non-predicted source image into the image group. In another aspect, the at least one skipped non-predicted source image may be a predictive image being the last image in order of presentation in the group of images. In addition, the method may further include the step of converting a previous immediate non-prediction source image, in the order of presentation in the group of images, into a predictive image unless the previous immediate non-prediction source image is a predictive image In another arrangement, each of the prediction source images and the non-prediction source images may contain a presentation indicator, and the method may further include the step of modifying the presentation indicator of at least a portion of the images of prediction source and non-prediction source images to reflect a projected presentation order. As an example, the presentation indicator can be a temporary reference field. This step of modifying the presentation indicator may be done after the alteration step or the modification step of the number of non-prediction source images. The method may also include the step of, after the alteration step, converting the last non-prediction source image in the altered group of images into a predictive image unless the last non-prediction source image in the altered group of images is a predictive image. In addition, the method may include the step of, after the alteration step, selectively converting in bidirectional predictive images, the non-prediction source images in front of, in order of presentation, the prediction source image. It is also understood that the method may include the step of carrying out the steps of receiving and encoding in a remote decoder system. Additionally, the method may include the step of encoding at least a portion of the prediction and non-prediction source images into field images. The present invention also relates to a system for performing a reverse trick mode. The system includes a processor for encoding a non-progressive video signal in at least one group of images having at least one prediction source image and at least one non-prediction source image. All non-prediction source images are predicted from the at least one prediction source image such that no non-prediction source image is predicted from another source image of non-prediction. The system also includes a decoder to decode the non-progressive video signal. The processor is further programmed to, in response to a reverse trick mode command, alter the display group order of images to allow the group of images to be presented in a reverse order. The system also includes the appropriate software and electronic circuit to implement the methods described above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 A is a block diagram of a system that can encode a video signal in special GOPs and develop a reverse motion trick mode, in accordance with the inventive arrangements herein. FIG. 1 B is a block diagram of another system that can encode a video signal in special GOPs and develop a reverse movement trick mode, according to the inventive arrangements. FIG. 2 is a flow chart illustrating a method for encoding a video signal in special GOPs and developing a reverse motion trick mode, according to the inventive arrangements. FIG. 3 illustrates an example of a special GOP, according to the inventive provisions. FIG. 4A illustrates the GOP of FIG. 3 in reverse order, according to the inventive provisions. FIG. 4B illustrates the GOP of FIG. 4A with modified presentation indicators, according to the inventive provisions. FIG. 4C illustrates the GOP of FIG. 4B with a converted image, according to the inventive arrangements. The F1G 4D illustrates the GOP of FIG. 4C with another converted image, according to the inventive provisions. FIG. 5A illustrates an example of skipping images in the GOP of FIG. 4D, according to the inventive provisions. FIG. 5B illustrates an example of inserting duplicate images into the GOP of FIG. 4D, according to the inventive provisions. FIG. 5C illustrates another example of skipping images in the GOP of FIG. 4D, according to the inventive provisions.

FIG. 5D illustrates yet another example of skipping images in the GOP of FIG. 4D and the modification of the indicators of presentation of any of the remaining images, in accordance with the inventive provisions. FIG. 6 is a flow diagram illustrating an alternative method for encoding a video signal in special GOPs and carrying out a reverse motion trick mode use, in accordance with the inventive arrangements. The F1G 7A illustrates a GOP of trick mode in slow advance, according to the inventive provisions. FIG. 7B illustrates a GOP containing field images, according to the inventive arrangements. The F1G 7C illustrates the GOP of FIG. 7B in reverse order of presentation, in accordance with the inventive provisions. FIG. 7D illustrates the GOP of FIG. 7C with several of the images in the GOP having been converted into other types of images, according to the inventive provisions. FIG. 7E illustrates an example of inserting duplicate images into the GOP of the F1G. 7D, according to the inventive provisions.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES It is shown in the form of a block diagram in FIG 1A, a system 100 for implementing the different characteristics of advanced operation according to the inventive provisions. However, the invention is not limited to the particular system illustrated in FIG. 1A, since the invention can be practiced with any other system capable of receiving a video signal, processing the signal and emitting the signal to any convenient component, such as a display device. In addition, the system 100 is not limited to reading data from or writing data to any particular type of storage medium, since any storage medium capable of storing digitally encoded data can be used with the system 100. The system 100 may include an encoder 1 10 for encoding an incoming video signal, and a microprocessor 1 12 for instructing the encoder 1 10 to encode the video signal according to different techniques, some of which will be explained later. All or parts of the encoder 1 10 and the microprocessor 1 12 can be considered as a processor 1 14 within the perspective of the present invention. The encoder 1 10 can be located in the same apparatus as the microprocessor 1 12 oralternatively, it can be placed in a device that is remote from the apparatus housing the microprocessor 1 12. If the encoder 1 10 is remotely located, the encoder 1 10 is not necessarily under the control of the microprocessor 1 12. The system 100 can also be including a driver 1 16 for reading data from and writing data to a storage medium 1 18. For example, the data may be a digitally encoded video signal. The system 100 may also have a decoder 120 for decoding the encoded video signal when it is read from the storage means 1 18 and transferring the decoded video signal to a convenient component, such as a display device. The decoder 120 can be mounted in the same apparatus that contains the encoder 1 10 (if the encoder 1 10 is not remotely positioned), the microprocessor 1 12 and the controller 1 16 or can be mounted in a separate device, such as is found. in a remote decoder system. Control and data interfaces can also be provided to allow the microprocessor 1 12 to control the operation of the encoder 1 10 (as noted above), the controller 1 16 and the decoder 120. Suitable software or firmware can be provided in the memory for conventional operations performed by the microprocessor 1 12. In addition, program routines can be provided for the microprocessor 1 12, in accordance with the inventive arrangements. In operation, the encoder 1 10 can receive and encode an incoming non-progressive video signal. As is known in the art, this type of video signal is comprised of images that have been scanned non-progressively, that is, the images were created through an interconnected scanning technique. In accordance with the inventive arrangements, the microprocessor 112 can instruct the encoder 1 10 to encode the incoming video signal in one or more GOPs that are particularly useful for developing trick modes. Examples of such GOPs will be presented below. The encoder 1 10 can then transfer the encoded video signal to the controller 1 16, which can record the signal in the storage medium 1 18. In the case where the encoder 1 1 0 is remotely located, the encoder 1 10 can encoding the incoming non-progressive video signal, but the encoding instructions are not necessarily received from the microprocessor 1 12. If the microprocessor 1 12 receives a playback command, the microprocessor 1 12 can instruct the controller 1 16 to read the encoded video signal from the storage medium 1 18. The controller 1 18 can transfer the signal to the microprocessor 1 12, which can send the signal to the decoder 120. The decoder 120 can decode the video signal and emit the signal for presentation in a convenient device. If the microprocessor 1 12 receives a trick mode command, the microprocessor 1 12 can skip images in the GOPs, insert duplicates of the images in the GOPs or cause the display of any combination of images in a reverse order. As alluded to above, there may be some examples in which the decoder 120 performing the decoding step is located in a device separate from the apparatus containing the microprocessor 1 12. An example of such an arrangement, or of a remote decoder system, it is illustrated in FIG. 1B, in which the decoder 120 is in a deployment device 122, separated from a multimedia device 124 that can house the microprocessor 1 12. In this case, the decoder 120 may not be under the control of the microprocessor 1 12. However, trick modes can still be developed in this system 100, in which the microprocessor 1 12 alters the order of presentation of the images in the GOP before decoding to allow the images to be presented in a reverse order. further, the microprocessor 1 12 can delete images or insert duplicates of the images in the GOP before being decoded by the decoder 120 in the presentation device 122. It is understood that the encoder 1 10 in this type of system can be remotely located as well. In another embodiment, during the encoding step, the images in the non-progressive video signal may be encoded in field images, which may help to avoid the vibration artifact, which will be described later. The coding of non-progressive images in field images may allow the microprocessor 1 12 to transmit the field images to a decoder located remotely in a way that can help control such a vibration problem. Such a process will be discussed later. In any of the provisions discussed in relation to FIGS. 1A and 1B, the GOPs created during the encoding process will facilitate the effective implementation of a reverse trick mode. The total operation of the invention will be discussed in detail below.

With reference to FIG. 2, a method 200 is illustrated which shows a way to develop a trick mode in a non-progressive video signal using special GOPs. The method 200 can be practiced in any convenient system capable of encoding and decoding a video signal. The method 200 may begin, as shown in step 210. In step 212, a non-progressive video signal may be received. As noted above, a non-progressive video signal contains images that have been progressively scanned, that is, they are scanned through an interconnected scanning technique. As shown in step 214, the non-progressive video signal can be encoded in at least one GOP having at least one prediction source image and at least one non-prediction source image. In one arrangement, all non-prediction source images can be predicted from the prediction source image, such that no non-prediction source image is predicted from another non-prediction source image. With reference to FIG. 3, an example of such a process is shown. In this particular arrangement, the video signal can be encoded in one or more GOPs 300. The GOPs 300 are displayed in order of presentation. Each of the GOPs 300 may include at least one prediction source image 310 and at least one non-prediction source image 312. These images are non-progressive images having at least one upper field and one lower field. The images are shown in full: the illustration does not show them separately in their respective fields. A prediction source image is an image in a GOP that is not predicted from another image, however, it can be used to predict other images in the GOP. In addition, a non-prediction source image can be any image in a GOP that can be predicted from a prediction source image in that GOP. As an example, the prediction source image 310 can be an I image, and the non-prediction source images 312 can be B and / or P images. Each of the non-prediction source images 312 can be predicted from the prediction source image 310, which in this example is correlated with each of the images B and P that are predicted from the image I. Because the P images can serve as non-prediction source images 312, it must it will be apparent that a non-prediction source image 312 is not limited to images from which other images can not always be predicted, such as images B. However, according to the inventive provisions, each of the source images of non-prediction 312 can be predicted from the prediction source image 310 only. In one arrangement, the B images can be unidirectional prediction images, such that the B images prior to, or in front of, the I image (in order of presentation) can be retro-predicted from the I image, and the images B behind the image I (in order of presentation) can be predicted in advance of the image I. The numbers subscripts incorporated in the prediction source images 310 and the non-prediction source images 312 can indicate the order in which each of these images will be presented - in relation to the other images in the GOP - at a normal playback speed (in advance). As noted above, the GOP 300 is displayed in order of presentation. The order of transmission is slightly different in that the prediction source image 310, in this example, image l3, can first be transmitted to a decoder followed by the non-prediction source images 312 to be predicted from the source image of prediction 310. It is important to note that the invention is not limited in any way to these particular GOPs 300, since they merely represent an example of a GOP structure in accordance with the inventive arrangements. In fact, any GOP in which all the non-prediction source images in the GOP can be predicted from a prediction source image in that GOP, is within the perspective of the inventive provisions. In addition, although only two GOPs 300 are shown in FIG. 3 in which each GOP 300 has a prediction source image 310 and six non-prediction source images 312, it is understood that the received video signal can be encoded at any convenient number of GOPs 300 having any convenient number of images of prediction source 310 and non-prediction source images 312. Also, if more than one prediction source image 31 0 is in the GOP 300, any B image in the GOP 300 can be predicted bidirectionally. As an example, more than one prediction source image 310 can be placed in the GOP 300 and some of the non-prediction source images 312 can be predicted from these prediction source images 310. As such, the source images of prediction 310 can be transmitted to a decoder before the non-prediction source images 312 that are dependent on these prediction source images 310 for prediction. Referring again to method 200 of FIG. 2, in step 215, the non-progressive video signal containing the GOPs can be recorded in a convenient storage medium. Once recorded, the non-progressive video signal containing the GOPs can be played back, as shown in step 216. In step 21 8, a reverse trick mode command can be received. In response, the order of presentation of the GOP may be altered to cause the GOP to be presented in a reverse order, as shown in step 220. An example of such a step is illustrated in FIG. 4A. Here, each of the GOPs300, as represented first in FIG. 3, is shown with the prediction source images 310 and the non-prediction source images 312 in reverse order. Again, these non-progressive images are shown as being intact, since they have not been separated in their respective fields. Altering the order of presentation of the images in the GOP 300 can be useful to perform a reverse trick mode, especially in a remote decoder system. The reason that such a process is particularly useful in this type of system is that the decoder in a remote decoder system can not receive instructions directing it to the presentation images in a reverse order. However, it should be understood that the method 200 is in no way limited to the application in a remote decoder system. The prediction source images 310 and the non-prediction source images 312 shown in FIG. 3 may contain presentation indicators. In one arrangement, the presentation indicator can be a temporary reference field. A temporal reference field is typically a ten-bit field located in the image header of digitally encoded images. Some decoders depend on the temporal reference field to determine when a particular image in a video signal will be displayed in relation to other images in the video signal. This field normally has an integer value. As an example, referring again to FIG. 3, each GOP 300 contains seven images. The sub-index numbers for the images in each GOP 300 may correspond to the integer values for each time reference field of the respective image. For example, the time reference field of the first non-prediction source image 312, or image B0, may have an integer value of zero, which indicates that this particular image will be the first in each GOP 300 to be presented. The temporal reference field of the image B-, the next image to be presented, can have an integer value of one. Therefore, the integer value of the temporal reference field for each subsequent image to be presented may be larger by one, until the image P6, whose temporal reference field can have an integer value of 6. For convenience, the phrase "integer value of the temporal reference field" can also be referred to as "integer value". When the order of presentation of the images in the GOP 300 is altered to allow the GOP to be presented in a reverse order, as shown in FIG. 4A, the original presentation indicators or integer values are no longer valid. As such, referring again to method 200 of FIG. 2, the display indicators of the prediction source images and the non-prediction source images can be modified to reflect a projected display order, as shown in step 222. An example of the result of this step is illustrated in FIG. FIG. 4B. Here, the new integer values that reflect the new order of presentation are displayed. The original integer values are shown in parentheses. Although the integer value for the prediction source images 310 in this example do not change, it should be noted that the invention is not limited in this respect; it may be necessary, based on the GOP structure, to modify the integer value of the prediction source image 310 as well.

It is understood that the invention is not limited to this particular example, since other forms may be developed, in any other convenient way, to modify the integer values of the relevant temporal reference fields to reflect a projected display order. Furthermore, it should be noted that the invention is not limited to the use of a temporal reference field, since any other suitable presentation indicator can be modified to reflect a projected presentation order in any of the modalities discussed above. Referring once again to method 200 of the F1G 2, in decision block 224, it can be determined whether the last non-prediction source image in the altered GOP is a P-image. For purposes of the invention, the term "GOP" altered refers to a GOP in which the The order of presentation of the images in the GOP has been altered to allow the GOP to be presented in a reverse order. If yes, the method 200 can be summarized in step 228. Otherwise, the last non-prediction source image in the GOP can be converted to a P image, as shown in step 226. An example of this process is shown in the F1G 4C. The last non-prediction source image 312 in the GOP 300, which was originally image B6, has been converted into a P image, or P6 image. The last reason for this conversion is that the specification for MPEG video requires that the last image in a GOP is a P image or an I image. As an example, a B image can be converted to a P image by setting the values of the P image the following parameters located in the header of the image of image B: image_coding_type; vector_to_back_full_plete; and back_code_f. Additionally, the following variable length codes can be set for macroblock type for the values of the image B: cant_macroblock; forward_movement_macroblock; backward_macroblock movement; macroblock pattern; intra_macroblock; temporal_temporal_weight_code_flag; and permissible temporal_heavy_classes. This step can instruct the decoder to decode the image as an image P. As such, according to the inventive arrangements, the order of presentation of a GOP can be altered to allow the GOP to be presented in a reverse order without violating the MPEG requirement of that the last image in a GOP is a picture P. Referring again to method 200 of FIG. 2, in decision block 228, it can be determined whether all non-predicted source images in the altered GOP that are in front of, in order of presentation, the prediction source image, are B-images. If they are, method 200 may continue in decision block 232 through a hop circle A. If not, then such non-prediction source images may be converted to images B, as shown in step 230. For example, referring to FIG. 4D, after the alteration of the order of presentation, the first non-prediction source image 312 was an image P, or image P0, which is shown in parentheses. According to step 228, image P0 can be converted to image B0. In one arrangement, an image P can be converted into a B image by setting the following parameters located in the header of the image P in the values of image B: image_coding_type; vector_to_back_full_plete; and back_code_f. Additionally, the following variable length codes can be set for macroblock type for the values of the image B: cant_macroblock; forward_movement_macroblock; backward_macroblock movement; macroblock pattern; intra_macroblock; temporal_temporal_weight_code_flag; and permissible temporal_heavy_classes. Because the previous non-prediction source images 312 (in order of presentation) the prediction source image 310 can be backward predicted images, the conversion of such P images into B images improves the prediction scheme of the GOP 300, how the P images can not be predicted backwards; they can only be predicted forward. The prediction scheme to be used with the altered GOP is shown in FIG. 4D. In this way, until now, the GOP 300 has been described in relation to a reverse trick mode in which the images in the GOP 300 are presented in a reverse order at a normal playback speed (normal playback speed is 1X). However, there are certain cases in which viewers may wish to see vide in reverse at speeds other than 1X, such as a slow reverse or fast reverse trick mode. Typically, the video speed can be changed by either adding images to or skipping images in the video. Referring again to FIG. 2, it can be determined whether the number of non-predicted source image images in the altered GOP are to be modified, as shown in decision block 232 through jump circle A. If not, method 200 may terminate in step 224. If the number of images in the altered GOP is to be modified, such a process may be performed in step 234. Several examples are shown in FIGS. 5A to 5D. With reference to FIG. 5A, each of the altered GOPs 300 (as illustrated in FIG 4D), is displayed with several 312 non-predicted source images removed or skipped. Specifically, the images B0, B2, B and P6 in the GOP 300 on the left can be skipped, while the images B1 t B4 and P6 in the GOP 300 on the right can be skipped. Skipping of such non-prediction source images 312 may cause the reverse reproduction rate to increase. Here, the number of non-predicted 312 source images skipped, half of all the images in the two GOPs 300, is correlated with a playback speed that is twice the normal playback speed, or 2X. In accordance with the inventive arrangements, any of the non-prediction source images 312 in the GOPs 300 may be skipped to increase the reverse reproduction rate of the video signal without affecting the prediction of any remaining non-prediction source image 312 in GOPs 300. This feature is made possible, through the coding process described above. One step for placing the 300 GOPs according to the standard MPEG, for example, will be discussed later. Of course, it is understood that the invention is not limited to the example described in relation to FIG. 5A, since the ability to skip all of the non-prediction source images 312 in any order during a fast reverse trick mode applies to any other GOP in which the non-prediction source images 312 are predicted from an image of prediction source 310. Also, the entire GOP 300 can be skipped to produce faster playback. Referring again to FIG. 2, modification step 234 may also include the step of inserting into the altered GOP a duplicate of at least one prediction source image or source image. no prediction to produce a slow reverse trick mode. An example of such an operation is shown in FIG. 5B. Here, a duplicate of each prediction source image 310 and non-prediction source image 312 can be inserted into the altered GOP 300 (for convenience, only one GOP 300 is shown). This particular example can produce a reproduction speed of 1 / 2X. The letter subscript "d" represents the image to which it is associated as a duplicate of the preceding immediate image. Similar to the original non-prediction source images 312, duplicates of such images can be predicted from a prediction source image 310 (according to the MPEG standard, the last image in the GOP 300, the duplicate image P6d, can predict from the image immediately preceding P, which in this case is the image P6). In addition, the original non-prediction images 312 and their duplicates can be predicted from the duplicate of a prediction source image 310. The example presented in FIG. 5B is explained as follows: all non-prediction source images 312 and their duplicates in front (in order of presentation) of the original prediction source image 310, or image l3, can be predicted from image l3. Additionally, the original non-prediction source images 312 and their duplicates behind the (in order of presentation) duplicate of the original prediction source image 310, or l3d image, can be predicted from the duplicate image l3d (with the exception of the duplicate image P6 (J) - However, it is understood that this particular arrangement is merely an example, since the non-prediction source images 312 and their duplicates can be predicted from any other convenient prediction source image 310, including any duplicate of a prediction source image 310. In another arrangement, one or more of the duplicate images inserted in the GOP 300 may be fictitious B-pictures or fictional P. A fictitious B-picture or fictional P is a B or P picture, respectively, in which the motion vectors of the dummy image are set to zero and their residual signal is set to zero or not encoded, for example, the duplicate of the image was The prediction data 310 (image 13) in the altered GOP 300 may be a fictitious image P instead of another image I, such as the l3d image. Similarly, the duplicate for the last non-prediction image 312 (image P6) can be a fictitious image P instead of a conventional image P, such as the duplicate image P6d. By using fictional B or P images during a reverse trick mode, the bit rate of the video signal may decrease, which may be necessary in certain circumstances, particularly when the method 200 is being performed in a remote decoder system. Referring again to the F1G. 2, in decision block 236, it can be determined whether the last non-prediction source image in the altered GOP has been skipped. Otherwise, method 200 may be summarized in step 242. If yes, it may be determined in decision block 238 whether the source image of immediate non-prediction, above in order of presentation in the altered GOP is a P image. thus, method 200 may continue in step 242. If not, then the source image of no immediate prediction, previous in the altered GOP may become a P image, as shown in step 240. An example of this operation is illustrated in FIG. 5C. As mentioned above, the specifications for MPEG video require that the last image in a GOP be a P image or an I image. Therefore, if the image P6 in the altered GOP 300, a non-prediction source image 312, was skipped during a fast reverse trick mode, the last image in the GOP 300 (if it is not skipped) would be the image B5 , a violation of the MPEG standard. To satisfy the MPEG requirement, the previous immediate non-prediction source image 312, in this case, image B5l can be converted to an image P, or image P5. This conversion has been previously treated, and it is unnecessary to present it in the present. As such, the last image in an altered GOP 300 can be skipped if it violates the MPEG requirement that the last image in a GOP is an image P (or an image I). Referring again to method 200 of FIG. 2, in step 242 (similar to step 222) the display indicators of the prediction source images and the non-prediction source images can be modified. Modifying the display indicators of these images may reflect a projected display order of the altered GOP when any of the prediction or non-prediction source images are skipped or duplicated. When, for example, a non-predicted source image is skipped, the order of presentation is no longer valid. Accordingly, the display indicators of the prediction source images and the non-prediction source images following the skipped image can be modified to indicate an appropriate presentation order. This feature is also applicable if the duplicates of the prediction source images or the non-prediction source images, they are inserted into the altered GOP. As an example, referring to the F1G. D, if the Bi image in the GOP 300 is skipped, then the integer values of the prediction source images 310 and the non-prediction source images 312 that follow this image can be decreased by a value of one. Therefore, the integer value of the temporal reference field of the image B2 can be modified from two to one, the integer value of the temporal reference field of the image l3 can be modified from three to two, and so on. In this particular example, the new integer values are shown, the skipped image B-i is represented by a dashed line and the old integer values are in parentheses. This modification process may continue until the end of the altered GOP 300 is reached and can ensure that the remaining images in the altered GOP are presented in an appropriate order. Each time a prediction source image 310 or a non-prediction source image 312 in an altered GOP is skipped, the integer values of the temporal reference fields of the remaining images in that GOP that follow the skipped image may be decrease by a value of one. Also, if the images in the altered GOP are duplicated, the integer values of the images following the added duplicates can be increased by a value of one each time a duplicate is added. Referring again to FIG. 2, method 200 may be stopped at step 244. Referring to FIG. 6, a method 600 demonstrating another way of performing a reverse trick mode on a non-progressive video signal using special GOPs is illustrated. Similar to method 200 of FIG. 2, method 600 may begin in step 610, and a non-progressive video signal may be received, as shown in step 612. Also as in step 214 of method 200, non-progressive video may be encoded in at least a GOP having at least one prediction source image and at least one non-prediction source image in which all non-prediction source images can be predicted from the prediction source image, as shown in step 614. In this arrangement, the encoded non-progressive video signal may eventually be encoded in a remote decoder system. As noted above, in a remote decoder system, the components used to encode and read from a storage medium, the non-progressive video signal, have no control over the decoder. This lack of control over the decoder can cause problems with the presentation of non-progressive video, particularly during a slow trick mode. Before explaining the problems associated with performing trick modes in such a system, a brief interconnected exploration explanation, the technique by which non-progressive images are generated, is guaranteed. Under the interconnected scanning format, a video signal is typically divided into a predetermined number of horizontal lines. During each field period, only one half of these lines are explored; Generally, odd-numbered lines are scanned during the first field period, and even-numbered lines are scanned during the next field period. Each sweep is referred to as a field, and when combined, the two fields form a complete picture or picture. For an NTSC system, sixty fields are displayed per second, resulting in a speed of thirty frames per second. As a moving object moves across the screen on an interconnected scanning television, each field will only present a portion of the moving object. This partial presentation occurs because the field only presents every other horizontal line of the total image. For example, for a particular field n, only the horizontal lines with odd numbers are scanned, and the portion of the moving object that will be presented in the field n is the portion that is scanned during the sweep of the horizontal line with odd numbers for the field n. The next field, field n + 1, is created 1/60 of a second later and will present the horizontal lines with even numbers of the image. In this way, the portion of the moving object that occurs in the n + 1 field is the portion that is scanned during the horizontal line sweep with even number for the field n + 1. Although each field is temporarily different, the human eye perceives the sequential presentation of the fields as a plane movement due to the speed at which the fields appear. If a viewer activates a trick mode, the trick mode video signal may contain repeated images, images that are recorded under the interconnected scan format. For example, if the viewer initiates a slow reverse scan mode in a particular image, then that image can be repeatedly transmitted to and decoded and displayed on a digital television, for example, containing the remote decoder. The presentation of the repeated images, however, is in accordance with the normal presentation of non-progressive images, that is, the fields, upper and lower, which form the non-progressive image are presented alternatively. These fields are presented alternatively based on the slow trick mode playback speed. For example, for a reproduction speed of 1 / 3X (1X represents normal playback speed), each field will be presented three times in an alternate way. If a moving object appears in the images recorded under the interconnected scan format, each field will present the moving object at a specific position. In this way, as the fields of a frame or picture are alternately presented during the slow reverse trick mode, the moving object in the presentation moves rapidly back and forth from the position in the presentation to the other; indeed, the object in motion seems to vibrate. This vibration is created because the interconnected fields are temporarily different, and the moving object appears in a different position for each field. For example, FIG. 7A illustrates the GOP 300 of FIG. 3 in which non-progressive images are shown separated in their respective fields. The prediction scheme used in this example is the same as that discussed in relation to FIG. 3 and does not require an additional description here. In this case, each of the non-prediction source images 312 and the prediction source image 310 may have an upper field and a lower field. The letter subscript "t" designates the particular field to which it is associated as an upper field; similarly, the letter subscript "b" designates the particular field to which it is associated as a lower field. Here, a duplicate of each of the images in the GOP 300 has been added, and the altered GOP 300 represents a GOP in reverse trick mode. The letter subscript "d" represents that a particular field is a duplicate field. As an example, the image B0 may include an upper field Bot and a lower field B0b, while the duplicate of the image B0 the image Bo, may have an upper field B0t and a lower field Bobd. As shown, the upper and lower fields are presented in an alternate manner. If a moving object appears in these fields, that object will appear to vibrate due to the way in which the fields are presented. For example, if a moving object appears in a place in the Bot field and in another place in the Bo field, the object will appear to jump back to the previous place (as shown in the Bt image) when the duplicated Botd field is presented . When the next field, the duplicate Bobd field, is shown, the object will appear to jump back to the first place presented in picture B0b- Therefore, the moving object seems to vibrate when duplicate images are added to the GOP 300. This vibration effect will continue as long as the duplicate images are inserted into one or more GOPs 300 during the slow trick mode. Referring again to method 600 of FIG. 6, another encoding step can be executed to overcome the vibration artifact, which can appear when certain trick modes are initiated in a remote decoder system. In step 615, the non-prediction source images and the prediction source images can be encoded in field images. As will be explained below, when coding these images in field images, the display of the field images can be carried out in accordance with a way that helps to control the vibration problem. An example of this coding step is shown in FIG. 7B. In this example, the GOP 300 of FIG. 3 is shown with the original non-progressive images, encoded in field images. For example, image B0, which originally contained fields B0t and B0b, has been encoded in field images Bot and B0b-Field images that originally comprised non-prediction source images 312 can also be considered non-prediction source images 312. Similarly, the field images that originally comprised the prediction source image 310 may be considered prediction source images 310. Therefore, for purposes of the invention, when reference is made to the terms "source images" of prediction "or" source images of non-prediction ", it is understood that such terms may refer to field images, even though the word" field "is not expressly used as a modifier for the terms. In this particular example, any of the prediction source images 310, i.e., the field images l3t and l3b, can be used to predict any of the non-prediction source images. A suitable example is shown in which the field image l3t (a prediction source image 310) predicts all the non-prediction source images 312 in front (in order of presentation) of the l3t image. In addition, the field image l3b (also a prediction source image 310) can predict all the non-prediction source images 312 behind (in order of presentation) of the image l3b. Of course, the invention is not limited to this particular example, since other suitable prediction schemes may be employed. Referring again to method 600 of FIG. 6, in step 616, the non-progressive video signal containing the GOPs can be recorded in a convenient storage medium. As shown in step 617, the non-progressive video signal containing the GOPs can be reproduced, and in step 618, a reverse trick mode command can be received. Similar to step 220 of FIG. 2, the order of presentation of the GOPs can be altered to allow the GOPs to be presented in a reverse order, as shown in step 620 in FIG. 6. Additionally, in step 622, the display indicators of the field images in these GOPs can be modified to reflect a projected display order. An example of GOP 300 of FIG. 7B following these steps is shown in FIG. 7C. The original designations are shown in parentheses. In addition, because the field images are to be displayed in reverse, each lower field image may be presented before its corresponding upper field image. The decision blocks 624, 628, and steps 626 and 630 of FIG. 6 are respectively similar to decision blocks 224, 228 and steps 226 and 230 of FIG. 2. That is, referring to method 600, the last pair of non-predicted field images in the altered GOP can be converted into field images P, and the field images P in front of, in order of presentation, the image of source of prediction, can be converted into field images B. Referring to FIG. 7D, an example of the GOP 300 of FIG. 7C after the previous steps is shown. The original designations are shown in parentheses. The process for converting B images into P images and vice versa has already been explained and does not guarantee additional description in the present. An example of a convenient prediction scheme is also shown in FIG. 7D. Referring back to FIG. 6, in decision block 632 (of hop circle A), it can be determined whether the number of non-prediction source images (field) in the GOP is to be modified for purposes of producing a reproduction rate less than or greater than normal playback speed. Otherwise, method 600 may be stopped in step 644. If yes, such a process may be executed in step 634. As an example, referring to FIG. 7E, the GOP 300 of FIG. 7D is displayed with duplicate field images inserted in the GOP 300 (original designations in parentheses are no longer displayed). Although this particular example focuses on a slow reverse trick mode, it is understood that the modification step may include skipping the images as well. This particular GOP 300 is illustrated as a GOP of slow inverse trick mode with a reproduction speed of 1 / 2X. That is, a duplicate of each field image has been inserted into the GOP 300; the duplicates of the field images can also be field images themselves. As reflected in FIG. 7E, the field images are displayed in such a way that an upper field image and its duplicate are displayed in succession before the upper field image after and its duplicate. For example, the field image B0b and its duplicate, field image B0bd, are displayed in succession and are followed by the presentation of the field image B0t and its duplicate, field image B0td- Thus, if a moving object in the field images Bob and BQt, the insertion of duplicate field images will not lead to a vibration arti because the field image, duplicated, lower, B0bd, will be presented before the original upper field image , B0t, and its duplicate, Botd- This manner of presentation in which the groups of field images are displayed before other groups of images have a different parity becomes possible when the prediction source image 310 and the images of Source of non-prediction 312 are encoded in field images. Specifically, when encoding the non-progressive images in field images, the field images can be transmitted to a decoder located remotely in an order that allows them to be presented in a successive manner, similar to the one illustrated above. For example, for a slow reverse trick mode 1 / 2X, a higher field image and its duplicate can be transmitted to a remote decoder for decoding and display, and subsequently, the corresponding upper field image and its duplicate can be transmitted to the remote decoder . In order to accommodate the requirement of presentation that field images of different parities must follow each other, the parity of these field images, as indicated in the image header, may be modified. For example, if a lower field image is located at a position where a higher field image is normally displayed, the parity of that lower field image may be modified such that the lower field image is actually defined as an image. of superior field. However, changing the parity of an image does not affect the content of the image. As a more specific example, the parity of the duplicate image B0b, a lower field image in a location where a higher field image would normally be, can be modified in such a way that this image is actually defined as a higher field image. In addition, the parity of the field image B0t, a higher field image in a location where a lower field image is typically displayed, can be modified to define the Bot image as a lower field image. This concept can be applied to the remaining field images in the GOP 300. However, the process of modifying the parities of these images does not affect the removal of the vibration arti. A prediction technique suitable for the GOP trick mode in FIG. 7E is also illustrated. The field image l3b can also be used to predict any of the non-prediction source images 312 (including the duplicate field images) placed in front (in order of presentation) of the l3b image. As those skilled in the art will appreciate, the use of the l3 image to predict these particular images is useful because the l3b image was used to predict the original non-predicted source images 312 in front of the l3b image.

In addition, the field image l3td can be used to predict any of the non-prediction source images 312 behind (in order of display) of the image I3td- The image l3td is useful for predicting these images due, in accordance with the above discussion , as regards the parity change of certain images, the image l3td is defined as a lower field image in this example; A lower field image was the type of image used to predict the original non-source prediction images 312 behind the image l3td. To further improve the prediction scheme of this example, the P6b and Pbd images can be converted into B6b and B6bd images, with the above designations shown in parentheses. As will be apparent to those skilled in the art, the conversion of these P field images into B field images can prevent the prediction of the last two field images, Pßt and Petd, from being negatively affected. This conversion has been previously illustrated. As an option, one or more of the duplicate images inserted into the GOP 300 can be fictional B or dummy field images P, which can help to decrease the bit rate of the video signal contained in the GOP 300 during a trick mode, including slow and fast forward trick modes. The addition of dummy field images B or P can be particularly useful in a remote decoder system. The remaining steps illustrated in method 600 of FIG. 6 are similar to the steps presented in method 200 of FIG. 2. Therefore, the steps of the 600 method do not require a deep discussion. In decision block 636, if the last pair of non-predicted source field images in the GOP has been skipped, method 600 may continue in decision block 638. If not, the method may terminate in block 638. decision 642. In decision block 638, it can be determined whether the immediate pair of previous non-prediction source field images are P field images. If they are, then method 600 may proceed to step 642. If they are not, , the immediate pair of source field images of non-prediction can be converted into a pair of P field images, as shown in step 640, a process described above. In step 642, the display indicators of the field images can be modified. Finally, the method may terminate at step 644. Although the present invention has been described in conjunction with the embodiments described herein, it is to be understood that the aforementioned description is intended to illustrate and not limit the scope of the invention as defined. through the claims.

Claims (36)

1. CLAIMS 1. A method for performing a reverse trick mode, comprising the steps of: receiving a non-progressive video signal; encoding the non-progressive video signal in at least one group of images having at least one prediction source image and at least one non-prediction source image, wherein all the non-prediction source images are predicted of at least a prediction source image such that no non-prediction source image is predicted from another non-prediction source image; and in response to a reverse trick mode command, alter the order of presentation of the group of images to allow the group of images to be presented in a reverse order. The method according to claim 1, further comprising the steps of: recording the non-progressive video signal in a storage medium; and, play the signal! of non-progressive video. The method according to claim 1, further comprising the step of modifying at least the number of non-prediction source images in the group of images in response to the inverse trick mode command. 4. The method according to claim 1, characterized in that the prediction source image is an intra image. The method according to claim 1, characterized in that at least a portion of the non-prediction source images are bidirectional predictive images. The method according to claim 1, characterized in that at least a portion of the non-prediction source images are predictive images. The method according to claim 5, characterized in that each of the bidirectional predictive images are bidirectional unidirectional predictive images. The method according to claim 3, characterized in that said modification step comprises the step of skipping at least one source image of non-prediction in the group of images. The method according to claim 3, characterized in that said modification step comprises the step of inserting in the image group a duplicate of at least one non-prediction source image. The method according to claim 8, characterized in that the at least one skipped non-predicted source image is a predictive image that is the last image in order of presentation in the group of images, and wherein said method further comprises the step of converting a previous non-prediction source image in order of presentation in the image group into a predictive image unless the previous immediate non-prediction source image is a predictive image. eleven . The method according to claim 1, characterized in that each of the prediction source images and the non-prediction source images contain a presentation indicator and the method further comprises the step of modifying the presentation indicator of at least one part of the prediction source images and the non-prediction source images to reflect a projected presentation order. The method according to claim 1, characterized in that the presentation indicator is a temporary reference field. The method according to claim 3, characterized in that each of the prediction source image and the non-prediction source image contains a presentation indicator and the method further comprises the step of modifying the presentation indicator to minus one part of the prediction source images and the non-prediction source images to reflect a projected presentation order. The method according to claim 13, characterized in that the presentation indicator is a temporary reference field. The method according to claim 1, after said alteration step, further comprising the step of converting the last non-prediction source image in the altered group of images into a predictive image unless the last source image of non-prediction in the altered group of images is a predictive image. 16. The method according to claim 1, after said alteration step, further comprising the step of selectively converting into bidirectional predictive images, the non-prediction source images in front of, in order of presentation, the prediction source image. The method according to claim 1, further comprising the step of carrying out said steps of reception, encoding and alteration in a remote decoder system. 18. The method according to claim 17, further comprising the step of encoding at least a portion of the prediction and non-prediction source images into field images. 19. A system for performing a reverse trick mode, comprising: a processor for encoding a non-progressive video signal in at least one group of images having at least one prediction source image and at least one non-source image. prediction, wherein all the non-prediction source images are predicted from the at least one prediction source image such that no non-prediction source image is predicted from another non-prediction source image; and, a decoder for decoding the group of images, wherein the processor is further programmed to, in response to a reverse trick mode command, alter e! order of presentation of the group of images to allow the group of images to be presented in a reverse order. The system according to claim 1 9, further comprising a controller for recording the non-progressive video signal in a storage medium and reproducing the non-progressive video signal. twenty-one . The system according to claim 19, characterized in that the processor is further programmed to modify at least the number of non-prediction source images in the group of images in response to the inverse trick mode command. 22. The system according to claim 19, characterized in that the prediction source image is an intra image. 23. The system according to claim 19, characterized in that at least a portion of the non-prediction source images are bidirectional predictive images. The system according to claim 19, characterized in that at least a portion of the non-prediction source images are predictive images. 25. The system according to claim 23, characterized in that each of the bidirectional predictive images are bidirectional unidirectional predictive images. 26. The system according to claim 21, characterized in that the processor is further programmed to skip at least one source image of non-prediction in the group of images. 27. The system according to claim 21, characterized in that the processor is further programmed to insert a duplicate of at least one non-predicted source image into the group of images. 28. The system according to claim 26, characterized in that the at least one source of non-predicted source is a predictive image that is the last image in order of presentation in the group of images, and wherein the processor it is further programmed to convert an earlier immediate non-prediction source image in order of presentation in the group of images, into a predictive image unless the previous immediate non-prediction source image is a predictive image. The system according to claim 1 9, characterized in that each of the prediction source images and the non-prediction source images contain a presentation indicator and the processor is further programmed to modify the presentation indicator of minus one part of the prediction source images and the non-prediction source images to reflect a projected presentation order. 30. The system according to claim 29, characterized in that the presentation indicator is a temporary reference field. 31 The method according to claim 21, characterized in that each of the prediction source image and the non-prediction source image contains a presentation indicator and the processor is further programmed to modify the presentation indicator of at least a part of the prediction source images and the non-prediction source images to reflect a projected presentation order. 32. The method according to claim 31, characterized in that the presentation indicator is a temporary reference field. The system according to claim 19, characterized in that the processor is further programmed to selectively convert the last non-prediction source image in the altered group of images in a predictive image to at least the last non-prediction image in the group. Altered images is a predictive image. 34. The system according to claim 19, characterized in that the processor is further programmed to selectively convert bidirectional predictive images, non-prediction source images in front of, in order of presentation, the prediction source image. 35. The system according to claim 19, further characterized in that the processor and the decoder are part of a remote decoder system. 36. The system according to claim 35, characterized in that the processor is further programmed to encode at least a part of the prediction and non-prediction source images in field images.