A method of auto-focusing comprising: acquiring an image; acquiring, for each of N frequency bands of the image, a Focus Value, FV, corresponding to each of focal points during a focusing process, wherein the N frequency bands form a set, and the N is a positive integer greater than 1; characterized in that the method further comprises acquiring, for a lowest frequency band in the set, an interested focal point which corresponds to a maximum FV for the lowest frequency band; determining, for each of other frequency bands than the lowest frequency band in the set, whether the FV corresponding to the interested focal point is a maximum FV for the other frequency band or not; on the condition that the FV corresponding to the interested focal point for each of the other frequency bands is the maximum FV, determining that the interested focal point is an in-focus point; and on the condition that the FV corresponding to the interested focal point for any one of the other frequency bands is not the maximum FV, updating the set by deleting at least one frequency band including the lowest frequency band from the set, wherein the FV corresponding to the interested focal point reaches maximum for the at least one frequency band, acquiring, for a new lowest frequency band in the updated set, a new interested focal point which corresponds to a maximum FV for the new lowest frequency band, and repeating the above determinations based on the new interested focal point. acquiring an image; acquiring, for each of N frequency bands of the image, a Focus Value, FV, corresponding to each of focal points during a focusing process, wherein the N frequency bands form a set, and the N is a positive integer greater than 1; characterized in that the method further comprises acquiring, for a lowest frequency band in the set, an interested focal point which corresponds to a maximum FV for the lowest frequency band; determining, for each of other frequency bands than the lowest frequency band in the set, whether the FV corresponding to the interested focal point is a maximum FV for the other frequency band or not; on the condition that the FV corresponding to the interested focal point for each of the other frequency bands is the maximum FV, determining that the interested focal point is an in-focus point; and on the condition that the FV corresponding to the interested focal point for any one of the other frequency bands is not the maximum FV, updating the set by deleting at least one frequency band including the lowest frequency band from the set, wherein the FV corresponding to the interested focal point reaches maximum for the at least one frequency band, acquiring, for a new lowest frequency band in the updated set, a new interested focal point which corresponds to a maximum FV for the new lowest frequency band, and repeating the above determinations based on the new interested focal point. updating the set by deleting at least one frequency band including the lowest frequency band from the set, wherein the FV corresponding to the interested focal point reaches maximum for the at least one frequency band, acquiring, for a new lowest frequency band in the updated set, a new interested focal point which corresponds to a maximum FV for the new lowest frequency band, and repeating the above determinations based on the new interested focal point.