This paper presents a new operator for corner detection. This operator uses a variant of the morphological closing operator, which we have called asymmetrical closing. It consists of the successive application of different morphological tranformations using different structuring elements. Each of these structuring elements used to probe the image under study is tuned to affect corners of different orientation and brightness. We found that this kind of approach, based on brightness comparisons, leads to better quality results than others and is achieved at a lower computational cost.