Technology for removing noise from a frame group on a timeline such as a moving image is conventionally known. For example, Patent Literature 1 (JP 2007-323480A) discloses technology for removing noise from a frame group, by dividing the frame group into units of a plurality of frames along a timeline, and averaging the frames in the units into which the frame group is divided. In Patent Literature 1, in deciding the number of frames to serve as a unit for averaging, a difference value is calculated for each pair of adjacent frames included in the frame group, a histogram of these difference values is created, and the total number of difference values that are greater than or equal to a predetermined threshold is calculated, after which the number of frames to serve as a unit for averaging is decided according to the calculated total number.
Incidentally, a frame group such as a moving image may be recorded in a manner such that the same frames appear successively in roughly the same numbers on a timeline, depending on shooting and recording conditions and the like. For example, this may occur when the frame rate of the recording apparatus is higher than the frame rate of the image capture apparatus. To give a more specific example, if the frame rate of the image capture apparatus is 1 FPS and the frame rate of the recording apparatus is 30 FPS, roughly thirty each of the same frame will be arranged successively on the timeline of the recorded frame group.
However, the plurality of frames of image data that were recorded of the same frame may not be exactly the same due to various types of noise. In this sense, what are referred to as the “same” frame are, strictly speaking, “similar” frames, due to the difference arising from the noise component. Under such circumstances, these similar frames can be utilized to remove noise.
However, the apparatus of Patent Literature 1 does not function adequately under such circumstances. This is because the apparatus of Patent Literature 1 decides the number of frames to serve as a unit for removing noise in the abovementioned manner, and is thus not able to correctly evaluate a succession of similar frames. Note that this problem applies not only to the case where the only difference in similar frames arises clue to the noise component but also to all situations where similar frames appear successively in roughly the same numbers along a timeline.