1. A method of compressing a texel block comprising multiple texels each having a respective texel value, said method comprising: determining, based on at least a portion of texel values of said multiple texels, a first value codeword representing a first texel value and a second value codeword representing a second texel value; determining, based on at least a portion of said texel values of said multiple texels, a first line codeword representing a first line for a first direction and a second line codeword representing a second line for a second direction; determining a function codeword representing a function that varies in two dimensions and reflects a change in texel values when traveling along said first direction and said second direction in said texel block; and storing, in a memory, a compressed texel block as a compressed representation of said texel block, said compressed texel block comprises said first value codeword, said second value codeword, said first line codeword, said second line codeword and said function codeword, wherein determining said first line codeword and said second line codeword comprises: determining said first line codeword to comprise a first angle codeword representing an angle α 1 of said first line relative a fixed direction and a first translation codeword representing a translation parameter C 1 , wherein A 1 =cos(α 1 ) and B 1 =sin(α 1 ) and said first line is defined as A 1 x+B 1 y+C 1 =0 and A 1 2 +B 1 2 =1; and determining said second line codeword to comprise a second angle codeword representing an angle α 2 of said second line relative said fixed direction and a second translation codeword representing a translation parameter C 2 , wherein A 2 =cos(α 2 ) and B 2 =sin(α 2 ) and said second line is defined as A 2 x+B 2 y+C 2 =0 and A 2 2 +B 2 2 1.