17. One or more non-transitory computer readable storage media comprising a sequence of instructions, which, when executed cause a processor to perform operations, the sequence of instructions comprising: first instructions to create a plurality of sets of positions automatically, by at least performing comparisons using multiple pluralities of pixels hereinafter compared pixels that are located in an image at corresponding positions comprised in the plurality of sets of positions; wherein a first set in the plurality of sets of positions is created without using in any comparison, a plurality of pixels hereinafter skipped pixels that are located in the image at additional positions comprised in the first set; wherein a first region identified by the first set is contiguous in the image, the first region comprising the compared pixels and the skipped pixels identified respectively by the corresponding positions and the additional positions; wherein a second region is contiguous in the image, the second region being identified by positions in a second set, in the plurality of sets of positions created by the creating; second instructions to check, whether a test is satisfied by a first attribute of the first region and a second attribute of the second region; third instructions to prepare a merged set comprising the positions in the first set and the positions in the second set, based on at least an outcome of said test; and fourth instructions to store in at least one memory, the merged set.
17. One or more non-transitory computer readable storage media comprising a sequence of instructions, which, when executed cause a processor to perform operations, the sequence of instructions comprising: first instructions to create a plurality of sets of positions automatically, by at least performing comparisons using multiple pluralities of pixels hereinafter compared pixels that are located in an image at corresponding positions comprised in the plurality of sets of positions; wherein a first set in the plurality of sets of positions is created without using in any comparison, a plurality of pixels hereinafter skipped pixels that are located in the image at additional positions comprised in the first set; wherein a first region identified by the first set is contiguous in the image, the first region comprising the compared pixels and the skipped pixels identified respectively by the corresponding positions and the additional positions; wherein a second region is contiguous in the image, the second region being identified by positions in a second set, in the plurality of sets of positions created by the creating; second instructions to check, whether a test is satisfied by a first attribute of the first region and a second attribute of the second region; third instructions to prepare a merged set comprising the positions in the first set and the positions in the second set, based on at least an outcome of said test; and fourth instructions to store in at least one memory, the merged set. 18. The one or more non-transitory computer readable storage media of claim 17 wherein the sequence of instructions comprise: fifth instructions to low-pass filter the image, hereinafter original image, prior to execution of the first instructions, to obtain a low-pass image; wherein comparisons performed by execution of the first instructions are performed using pixels located adjacent to one another in the low-pass image, thereby to exclude from the comparisons the skipped pixels of the original image.