There is provided a method of grouping pixels in a 2D digital image that assigns labels to regions of objects to differentiate between objects separated in the input image and groups a region of an object having the same label into one group when pattern recognition and image process are performed on the 2D digital image. A method of grouping pixels in a 2d digital image according to an aspect of the invention may include: determining whether a target pixel in an input image is included in a labeling section; determining whether the target pixel is connected to a previous pixel of the target pixel and an upper pixel located adjacent to and above the target pixel to perform a labeling process, and renewing a label table while saving a labeling result in a line memory when the target pixel is included in the labeling section and is a valid pixel including object information; and grouping pixels of the input image using the labeling result and the renewed label table, and renewing a group.