A method of detecting tiling or blockiness in an image comprising the steps of: generating a column vector of edge values for the image; determining from the column vector a first power value for the column vector and a second power value for each of a group of predetermined frequencies, each of the predetermined frequencies being associated with respective block sizes, wherein determining comprises the steps of: calculating the first power value, wherein calculating the first power value comprises: determining a mean value for the column vector from the edge values; subtracting the mean value from each edge value in the column vector to produce an AC component of the column vector; and producing the first power value for the column vector as the sum of the squares of the values for the AC component of the column vector; calculating component power values for an in-phase component and a corresponding quadrature component of the AC component of the column vector at each of the predetermined frequencies; and summing the component power values for the I and Q components of each predetermined frequency to produce the second power value for each predetermined frequency; and combining the first power value and the second power value to produce a tiling or blockiness value for each of the predetermined frequencies. generating a column vector of edge values for the image; determining from the column vector a first power value for the column vector and a second power value for each of a group of predetermined frequencies, each of the predetermined frequencies being associated with respective block sizes, wherein determining comprises the steps of: calculating the first power value, wherein calculating the first power value comprises: determining a mean value for the column vector from the edge values; subtracting the mean value from each edge value in the column vector to produce an AC component of the column vector; and producing the first power value for the column vector as the sum of the squares of the values for the AC component of the column vector; calculating component power values for an in-phase component and a corresponding quadrature component of the AC component of the column vector at each of the predetermined frequencies; and summing the component power values for the I and Q components of each predetermined frequency to produce the second power value for each predetermined frequency; and calculating the first power value, wherein calculating the first power value comprises: determining a mean value for the column vector from the edge values; subtracting the mean value from each edge value in the column vector to produce an AC component of the column vector; and producing the first power value for the column vector as the sum of the squares of the values for the AC component of the column vector; determining a mean value for the column vector from the edge values; subtracting the mean value from each edge value in the column vector to produce an AC component of the column vector; and producing the first power value for the column vector as the sum of the squares of the values for the AC component of the column vector; calculating component power values for an in-phase component and a corresponding quadrature component of the AC component of the column vector at each of the predetermined frequencies; and summing the component power values for the I and Q components of each predetermined frequency to produce the second power value for each predetermined frequency; and combining the first power value and the second power value to produce a tiling or blockiness value for each of the predetermined frequencies.