1. A region growing method, comprising: selecting a seed point of a current frame as an initial growing point of a region in the current frame; referring to a planar surface detection result to check if a neighboring pixel belongs to a detected planar surface, and accordingly generating a checking result, wherein the neighboring pixel is blocked from being included in the region when the checking result indicates that the neighboring pixel belongs to the detected planar surface; determining a background confidence value at the neighboring pixel around the seed point, wherein the neighboring pixel is not a seed point of the region when determining the background confidence value is executed, when the background confidence value is determined to be a first value, it indicates that the neighboring pixel is more likely to be one background pixel, and when the background confidence value is determined to be a second value lower than the first value, it indicates that the neighboring pixel is less likely to be one background pixel; and utilizing a processing unit for checking if the neighboring pixel is allowed to be included in the region according to at least the background confidence value.