Method for replacing parts of a digitally coded picture, and device for carrying out the method

Abstract

A method for replacing parts of a digitally coded picture ( 11 ) is proposed. The digitally coded picture ( 11 ) may correspond to a sub-picture which is displayed on the screen of a television set ( 10 ). In the method, each line of the picture ( 11 ) is run length-coded. The replaceable parts of a line of the picture are run length-coded separately. The part which replaces the replaceable, original part of a line of the picture ( 11 ) is run length-coded in such a way that it has the same number of data units (data bytes) as the original part of this line of the picture ( 11 ). The replacement of the data for the run length coding words is carried out in a memory device ( 51 ). The replacement is possible in a simple manner by virtue of the fact that the original part of a line of the picture and the new part of the line of the picture have the same number of data units. Moreover, a device for carrying out the method is also proposed.

1. Method for replacing parts of a digitally coded picture, the method comprising the following steps:
 a) run length-coding each line of the picture wherein each replaceable part of a line of the picture is run length-coded separately; 
 b) run length-coding the part which replaces the replaceable, original part of the line of the picture such that the associated run length coding words take up the same number of data units as the run length coding words of the original part of this line of the picture; and 
 c) replacing the data for the run length coding words in a memory device. 
 
     
     
       2. Method according to  claim 1 , wherein the digitally coded picture is a sub-picture and further comprising the step of displaying the digitally coded picture on the screen of a display device. 
     
     
       3. Method according to  claim 2 , further comprising the step of holding the digitally coded picture in the form of two fields, interleaved in one another, each having half the number of lines in the memory device. 
     
     
       4. Method according to  claim 3 , further comprising the steps of signaling the field which is being respectively decoded, and allowing replacement of parts of the lines only in that field which is currently not being decoded. 
     
     
       5. Method according to  claim 1 , further comprising the step of holding the digitally coded picture in the form of two fields, interleaved in one another, each having half the number of lines in the memory device. 
     
     
       6. Method according to  claim 5 , further comprising the steps of signaling the field which is being respectively decoded, and allowing replacement of parts of the lines only in that field which is currently not being decoded. 
     
     
       7. Device for replacing parts of a digitally coded picture, comprising:
 a) a first memory device, in which run length coding words of lines of a picture can be stored, each replaceable part of a line of the picture being run length-coded separately, 
 b) a second memory device, in which the run length coding words of the correspondingly run length-coded parts of the lines of the picture for the replacement of the replaceable parts of the lines can be stored, 
 c) a control unit, which performs the replacement of the replaceable parts of the lines of the picture which are stored in the first memory device. 
 
     
     
       8. Device according to  claim 7 , in which the first memory device has separate memory areas for two fields of the picture which are interleaved in one another, and the second memory device has separate memory areas for the corresponding parts of the fields which are interleaved in one another. 
     
     
       9. Device according to  claim 8 , comprising a signaling device, which indicates which field of the picture ( 11 ) is currently being decoded. 
     
     
       10. Device according to  claim 9 , comprising control means, which prevent replacement of the replaceable parts of the lines of that field which is marked by the signaling device as being currently subjected to the decoding operation. 
     
     
       11. A machine readable storage device, in particular an optical disc, having recorded thereon a sub-picture unit for displaying sub-pictures when played back in a play back device, wherein the sub-picture unit includes the following:
 a sub-picture unit header,   a pixel data field,   a display control sequence table,   
       wherein each line of the sub-picture is run length coded, and run length-coded pixel data is contained in the pixel data field, a sub-picture line is divided into a number of replaceable parts and the pixel data field contains a number of separately run-length-coded data fields for each replaceable part of the line. 
     
     
       12. The machine readable storage device according to claim 11, wherein each replaceable part of a line of the sub-picture is run length-coded separately to allow replacement of a replaceable part with run length coding words that take up the same number of data units as the run length coding words of the original part of this line of the sub-picture. 
     
     
       13. Method for digitally coding a picture, the method comprising the following steps:
 dividing the lines of the picture into a number of replaceable parts,   run-length coding each line of the picture wherein each replaceable part of a line of the picture is run length-coded separately to allow replacement of the replaceable part with run length coding words that take up the same number of data units as the run length coding words of the original part of this line of the picture.   
     
     
       14. Method according to claim 13, wherein the picture is a sub-picture that can be displayed on a display device in addition to a main picture.