The present invention relates to a method for generating an index of Data Units of a Variable Length Coded (VLC) image. The method comprises categorizing Data Unit lengths, DU-lengths, as non indexed DU-lengths, categorizing DU-lengths not categorized as non-indexed DU-lengths as indexed DU-lengths, generating a value indicating the number of subsequent DU-lengths categorized as non-indexed in a sequence of subsequent DU-lengths categorized as non-indexed, generating a value indicating the number of subsequent DU-lengths categorized as indexed in a sequence of subsequent DU-lengths categorized as indexed, generating data representing the DU-length of each DU in the sequence of DU-lengths categorized as indexed, storing said generated values and data in the index of Data Units, and associating said index of Data Units with the VLC image. Further the invention relates to a method for retrieving Data Unit lengths, DU-lengths, from an image associated with an index of DU-lengths. This method comprises linearly reading data from the index, when the data is a value indicating a number of subsequent Data Units categorized as not having indexed DU-lengths then these Data Units is sequentially processed from the image for retrieving the length of each data unit, and when the data is a value indicating a number of subsequent Data Units categorized as having indexed DU-lengths then the corresponding number of DU-lengths are retrieved from the index.