An image encoding method includes, using an image as input, determining a first mode suited to encode the image in accordance with a first processing procedure; using the image as input, determining a second mode suited to encode the image in accordance with a second processing procedure; selecting one of first mode and the second mode as a final mode; encoding the image, using the final mode; and calculating a cost of using the second mode to encode the image. The second processing procedure is implemented by a reconfigurable circuit. In the selecting, the first mode is selected when the cost calculated in the calculating is higher than a first predetermined value, and the second mode is selected when the cost is lower than or equal to the first predetermined value.