Method for encoding of quality values of a data structure, whereby said data structure comprises a set of genomic reads, wherein the method comprises the following steps executable by a data processing system: ascertain the quality values of each read covering a certain index locus, —determine a codebook identifier identifying a specific codebook from a plurality of codebooks for said certain index locus based on the ascertained quality values of said certain index locus, whereby each code-book provides a mapping from a quality value of said quality value alphabet to a corresponding quantized quality value of a quantized quality value alphabet, —quantizing all ascertained quality values at said certain index locus using the specific codebook identified by the codebook identifier at said certain index locus in order to obtain for each quality value at said certain index locus a corresponding quantized quality value, and —encode all determined codebook identifiers using a first entropy encoder and encode all quantized quality values using a second entropy encoder or a set of encoders.