Techniques are described that can be used to identify blocking artifacts in both vertical and horizontal directions. For blocking artifacts in a vertical direction, a horizontal gradient is determined for a pixel. Gradient smoothing is performed for pixels in the row of the pixel. A ratio of the horizontal gradient over the gradient smoothing is determined. Any pixel with a ratio above a threshold and in a segment with a length that exceeds a threshold length as potentially having block artifacts. Each column with pixels that potentially have block artifacts is inspected to determine whether a number of block artifacts in the column are a local maximum and whether there is a sufficient number of blocking artifacts in the column. Columns that satisfy both conditions are considered to include blocking artifacts.