The present invention provides a method of obtaining image data for an image sensing system. The image sensing system includes a sensing area having a plurality of sensing pixels. The method includes the steps of: scanning at least two groups of sensing pixels among the plurality of sensing pixels with at least two integration times, respectively, to obtain a plurality of sensing results; obtaining a selected integration time from one of the at least two integration times according to the plurality of sensing results; and scanning the plurality of sensing pixels except for the at least two groups of sensing pixels with the selected integration time, to obtain the image data.