A digital image processing determining the extent of blocking and
contouring artifacts in a digital image includes the steps of: determining
the extent of blocking artifacts using the column and row difference
arrays; determining the extent of contouring artifacts based on an
estimated DC quantization step size; and, determining a composite artifact
measure as a function of the extent of blocking artifacts and extent of
contouring artifacts. A digital image processing method determining the
extent of contouring artifacts in the digital image includes the steps of:
forming a column difference image; averaging the values in the columns in
the column difference image to produce a column difference array;
computing the average of the values in the column difference array that
are separated by one block width to produce a block averaged column
difference array; locating the peak value in the block averaged column
difference array; repeating the above mentioned steps in the row
direction; locating block boundaries based on the locations of peak values
of column and row difference arrays; calculating DC value for each block;
generating a histogram of the block DC values; calculating the Fourier
transform of the histogram; locating the first non-DC peak in the Fourier
transform domain; calculating a DC quantization step size based on the
frequency of the first non-DC peak; and, employing the DC quantization
step size as a measure of the extent of the contouring artifacts in the
digital image.
