Method and apparatus for determining a sharpness metric of an image

An apparatus for determining a sharpness metric (S) of an image (im), comprising

• an weight generator unit adapted for generating weights for pixels and assigning the weights to pixels;
• a contrast metric determining unit adapted for determining a value representing a contrast metric C of the image;
• a calculating unit adapted for calculating at least a first threshold t1, a second threshold t2 and a third threshold t3 from the determined contrast metric C, wherein the first, second and third thresholds are related by a constant factor m according to t1=C, t2=m*t1 and t3=m*t2, wherein m is greater than one;
• a counter unit adapted for determining an amount of first level edge pixels (B1) being pixels having a gradient value of at least the first threshold t1,
• determining an amount of second level edge pixels (B2) being pixels having a gradient value of at least the second threshold t2, and
• determining an amount of third level edge pixels (B3) being pixels having a gradient value of at least the third threshold t3;
• and
• a calculation unit adapted for determining the sharpness metric S from the factor m, a relationship S2 between the amounts of second level and first level edge pixels and a relationship S3 between the amounts of third level and first level edge pixels.