1. A method performed under control of a gesture-based game system, comprising: capturing, by an image capture unit, an image of a first player and an image of a second player; cropping, from the image of the first player and the image of the second player, a first sub-image of at least part of the first player and a second sub-image of at least part of the second player, respectively; determining whether to adjust the first sub-image and the second sub-image; if it is determined to adjust the first sub-image and second sub-image, adjusting the first sub-image and the second sub-image; and merging the first adjusted sub-image and the second adjusted sub-image into an output image.