#cython: cdivision=True #cython: boundscheck=False #cython: nonecheck=False #cython: wraparound=False import numpy as np import warnings cimport numpy as cnp """ See also: Christophe Fiorio and Jens Gustedt, "Two linear time Union-Find strategies for image processing", Theoretical Computer Science 154 (1996), pp. 165-181. Kensheng Wu, Ekow Otoo and Arie Shoshani, "Optimizing connected component labeling algorithms", Paper LBNL-56864, 2005, Lawrence Berkeley National Laboratory (University of California), http://repositories.cdlib.org/lbnl/LBNL-56864 """ DTYPE = np.intp # Short int - could be more graceful to the CPU cache ctypedef cnp.int32_t INTS_t cdef struct s_shpinfo ctypedef s_shpinfo shape_info ctypedef int (* fun_ravel)(int, int, int, shape_info *) # For having stuff concerning background in one place ctypedef struct bginfo: ## The value in the image (i.e. not the label!) that identifies ## the background. DTYPE_t background_val DTYPE_t background_node ## Identification of the background in the labelled image DTYPE_t background_label cdef void get_bginfo(background_val, bginfo *ret) except *: if background_val is None: warnings.warn(DeprecationWarning( 'The default value for `background` will change to 0 in v0.12' )) ret.background_val = -1 else: ret.background_val = background_val # The node -999 doesn't exist, it will get subsituted by a meaningful value # upon the first background pixel occurence ret.background_node = -999 ret.background_label = -1 # A pixel has neighbors that have already been scanned. # In the paper, the pixel is denoted by E and its neighbors: # # z=1 z=0 x # ----------------------> # | A B C F G H # | D E . I J K # | . . . L M N # | # y V # # D_ea represents offset of A from E etc. - see the definition of # get_shape_info cdef enum: # the 0D neighbor # D_ee, # We don't need D_ee # the 1D neighbor D_ed, # 2D neighbors D_ea, D_eb, D_ec, # 3D neighbors D_ef, D_eg, D_eh, D_ei, D_ej, D_ek, D_el, D_em, D_en, D_COUNT # Structure for centralised access to shape data # Contains information related to the shape of the input array cdef struct s_shpinfo: INTS_t x INTS_t y INTS_t z # Number of elements DTYPE_t numels # Number of of the input array INTS_t ndim # Offsets between elements recalculated to linear index increments # DEX[D_ea] is offset between E and A (i.e. to the point to upper left) # The name DEX is supposed to evoke DE., where . = A, B, C, D, F etc. INTS_t DEX[D_COUNT] # Function pointer to a function that recalculates multiindex to linear # index. Heavily depends on dimensions of the input array. fun_ravel ravel_index cdef void get_shape_info(inarr_shape, shape_info *res) except *: """ Precalculates all the needed data from the input array shape and stores them in the shape_info struct. """ res.y = 1 res.z = 1 res.ravel_index = ravel_index2D res.ndim = len(inarr_shape) if res.ndim == 1: res.x = inarr_shape[0] res.ravel_index = ravel_index1D elif res.ndim == 2: res.x = inarr_shape[1] res.y = inarr_shape[0] res.ravel_index = ravel_index2D elif res.ndim == 3: res.x = inarr_shape[2] res.y = inarr_shape[1] res.z = inarr_shape[0] res.ravel_index = ravel_index3D else: raise NotImplementedError( "Only for images of dimension 1-3 are supported, got a %sD one" % res.ndim) res.numels = res.x * res.y * res.z # When reading this for the first time, look at the diagram by the enum # definition above (keyword D_ee) # Difference between E and G is (x=0, y=-1, z=-1), E and A (-1, -1, 0) etc. # Here, it is recalculated to linear (raveled) indices of flattened arrays # with their last (=contiguous) dimension is x. # So now the 1st (needed for 1D, 2D and 3D) part, y = 1, z = 1 res.DEX[D_ed] = -1 # Not needed, just for illustration # res.DEX[D_ee] = 0 # So now the 2nd (needed for 2D and 3D) part, y = 0, z = 1 res.DEX[D_ea] = res.ravel_index(-1, -1, 0, res) res.DEX[D_eb] = res.DEX[D_ea] + 1 res.DEX[D_ec] = res.DEX[D_eb] + 1 # And now the 3rd (needed only for 3D) part, z = 0 res.DEX[D_ef] = res.ravel_index(-1, -1, -1, res) res.DEX[D_eg] = res.DEX[D_ef] + 1 res.DEX[D_eh] = res.DEX[D_ef] + 2 res.DEX[D_ei] = res.DEX[D_ef] - res.DEX[D_eb] # DEX[D_eb] = one row up, remember? res.DEX[D_ej] = res.DEX[D_ei] + 1 res.DEX[D_ek] = res.DEX[D_ei] + 2 res.DEX[D_el] = res.DEX[D_ei] - res.DEX[D_eb] res.DEX[D_em] = res.DEX[D_el] + 1 res.DEX[D_en] = res.DEX[D_el] + 2 cdef inline void join_trees_wrapper(DTYPE_t *data_p, DTYPE_t *forest_p, DTYPE_t rindex, INTS_t idxdiff): if data_p[rindex] == data_p[rindex + idxdiff]: join_trees(forest_p, rindex, rindex + idxdiff) cdef int ravel_index1D(int x, int y, int z, shape_info *shapeinfo): """ Ravel index of a 1D array - trivial. y and z are ignored. """ return x cdef int ravel_index2D(int x, int y, int z, shape_info *shapeinfo): """ Ravel index of a 2D array. z is ignored """ cdef int ret = x + y * shapeinfo.x return ret cdef int ravel_index3D(int x, int y, int z, shape_info *shapeinfo): """ Ravel index of a 3D array """ cdef int ret = x + y * shapeinfo.x + z * shapeinfo.y * shapeinfo.x return ret # Tree operations implemented by an array as described in Wu et al. # The term "forest" is used to indicate an array that stores one or more trees # Consider a following tree: # # 5 ----> 3 ----> 2 ----> 1 <---- 6 <---- 7 # | | # 4 >----/ \----< 8 <---- 9 # # The vertices are a unique number, so the tree can be represented by an # array where a the tuple (index, array[index]) represents an edge, # so for our example, array[2] == 1, array[7] == 6 and array[1] == 1, because # 1 is the root. # Last but not least, one array can hold more than one tree as long as their # indices are different. It is the case in this algorithm, so for that reason # the array is referred to as the "forest" = multiple trees next to each # other. # # In this algorithm, there are as many indices as there are elements in the # array to label and array[x] == x for all x. As the labelling progresses, # equivalence between so-called provisional (i.e. not final) labels is # discovered and trees begin to surface. # When we found out that label 5 and 3 are the same, we assign array[5] = 3. cdef DTYPE_t find_root(DTYPE_t *forest, DTYPE_t n): """Find the root of node n. Given the example above, for any integer from 1 to 9, 1 is always returned """ cdef DTYPE_t root = n while (forest[root] < root): root = forest[root] return root cdef inline void set_root(DTYPE_t *forest, DTYPE_t n, DTYPE_t root): """ Set all nodes on a path to point to new_root. Given the example above, given n=9, root=6, it would "reconnect" the tree. so forest[9] = 6 and forest[8] = 6 The ultimate goal is that all tree nodes point to the real root, which is element 1 in this case. """ cdef DTYPE_t j while (forest[n] < n): j = forest[n] forest[n] = root n = j forest[n] = root cdef inline void join_trees(DTYPE_t *forest, DTYPE_t n, DTYPE_t m): """Join two trees containing nodes n and m. If we imagine that in the example tree, the root 1 is not known, we rather have two disjoint trees with roots 2 and 6. Joining them would mean that all elements of both trees become connected to the element 2, so forest[9] == 2, forest[6] == 2 etc. However, when the relationship between 1 and 2 can still be discovered later. """ cdef DTYPE_t root cdef DTYPE_t root_m if (n != m): root = find_root(forest, n) root_m = find_root(forest, m) if (root > root_m): root = root_m set_root(forest, n, root) set_root(forest, m, root) def _norm_connectivity(connectivity, ndim): """ Takes the value of the connectivity parameter, validates it and converts it to a value that the subsequent algorithm may use as-is safely. Parameters ---------- connectivity : int The following should be true: -ndim < connectivity < 0, or 0 < connectivity <= ndim. Returns ------- connectivity : int Connectivity, 0 < connectivity < ndim """ if connectivity == 0: raise ValueError( "Connectivity of 0 or above %d doesn't make sense" % ndim) if not -ndim <= connectivity <= ndim: raise ValueError( "Connectivity below %d or above %d is illegal." % (-ndim, ndim)) if connectivity < 0: # Just as we say in the docs connectivity += ndim + 1 return connectivity # Connected components search as described in Fiorio et al. def label(input, neighbors=None, background=None, return_num=False, connectivity=None): r"""Label connected regions of an integer array. Two pixels are connected when they are neighbors and have the same value. In 2D, they can be neighbors either in a 1- or 2-connected sense. The value refers to the maximum number of orthogonal hops to consider a pixel/voxel a neighbor. 1-connectivity 2-connectivity diagonal connection close-up [ ] [ ] [ ] [ ] [ ] | \ | / | <- hop 2 [ ]--[x]--[ ] [ ]--[x]--[ ] [x]--[ ] | / | \ hop 1 [ ] [ ] [ ] [ ] Parameters ---------- input : ndarray of dtype int Image to label. neighbors : {4, 8}, int, optional Whether to use 4- or 8-connectivity. In 3D, 4-connectivity means connected pixels have to share face, whereas with 8-connectivity, they have to share only edge or vertex. **Deprecated, use ``connectivity`` instead.** background : int, optional Consider all pixels with this value as background pixels, and label them as -1. (Note: background pixels will be labeled as 0 starting with version 0.12). return_num : bool, optional Whether to return the number of assigned labels. connectivity : int, optional Maximum number of orthogonal hops to consider a pixel/voxel as a neighbor. Accepted values are ranging from 1 to input.ndim. Negative values from -input.ndim to -1 are also accepted. Negative connectivity value :math:`x` is equivalent to the positive connectivity value :math:`x + input.ndim + 1`. For example in 2D, -1 and 2 = -1 + 2 + 1 are equivalent, values. Returns ------- labels : ndarray of dtype int Labeled array, where all connected regions are assigned the same integer value. num : int, optional Number of labels, which equals the maximum label index and is only returned if return_num is `True`. Examples -------- >>> x = np.eye(3).astype(int) >>> print(x) [[1 0 0] [0 1 0] [0 0 1]] >>> print(m.label(x, connectivity=1)) [[0 1 1] [2 3 1] [2 2 4]] >>> print(m.label(x, connectivity=2)) [[0 1 1] [1 0 1] [1 1 0]] >>> x = np.array([[1, 0, 0], ... [1, 1, 5], ... [0, 0, 0]]) >>> print(m.label(x, background=0)) [[ 0 -1 -1] [ 0 0 1] [-1 -1 -1]] """ cdef cnp.ndarray[DTYPE_t, ndim=1] data cdef cnp.ndarray[DTYPE_t, ndim=1] forest # Having data a 2D array slows down access considerably using linear # indices even when using the data_p pointer :-( data = np.copy(input.flatten().astype(DTYPE)) forest = np.arange(data.size, dtype=DTYPE) cdef DTYPE_t *forest_p = forest.data cdef DTYPE_t *data_p = data.data cdef shape_info shapeinfo cdef bginfo bg get_shape_info(input.shape, &shapeinfo) get_bginfo(background, &bg) if neighbors is None and connectivity is None: # default connectivity = -1 elif neighbors is not None: depr_msg = ("The argument 'neighbors' is deprecated, use " "'connectivity' instead") DeprecationWarning(depr_msg) # fail if neighbors != 4 and neighbors != 8: msg = "Neighbors must be either 4 or 8, got '%d'.\n" % neighbors raise ValueError(msg) else: # backwards-compatible neighbors recalc to connectivity, nei2conn = {4: 1, 8: -1} connectivity = nei2conn[neighbors] connectivity = _norm_connectivity(connectivity, shapeinfo.ndim) scanBG(data_p, forest_p, &shapeinfo, &bg) scan3D(data_p, forest_p, &shapeinfo, &bg, connectivity) # Label output cdef DTYPE_t ctr ctr = resolve_labels(data_p, forest_p, &shapeinfo, &bg) # Work around a bug in ndimage's type checking on 32-bit platforms if data.dtype == np.int32: data = data.view(np.int32) res = data.reshape(input.shape) if return_num: return res, ctr else: return res cdef DTYPE_t resolve_labels(DTYPE_t *data_p, DTYPE_t *forest_p, shape_info *shapeinfo, bginfo *bg): """ We iterate through the provisional labels and assign final labels based on our knowledge of prov. labels relationship. We also track how many distinct final labels we have. """ cdef DTYPE_t counter = bg.background_label + 1, i for i in range(shapeinfo.numels): if i == bg.background_node: data_p[i] = bg.background_label elif i == forest_p[i]: # We have stumbled across a root which is something new to us (root # is the LOWEST of all prov. labels that are equivalent to it) data_p[i] = counter counter += 1 else: data_p[i] = data_p[forest_p[i]] return counter cdef void scanBG(DTYPE_t *data_p, DTYPE_t *forest_p, shape_info *shapeinfo, bginfo *bg): """ Settle all background pixels now and don't bother with them later. Since this only requires one linar sweep through the array, it is fast and it makes sense to do it separately. The result of this function is update of forest_p and bg parameter. """ cdef DTYPE_t i, bgval = bg.background_val, firstbg # We find the provisional label of the background, which is the index of # the first background pixel for i in range(shapeinfo.numels): if data_p[i] == bgval: firstbg = i bg.background_node = firstbg break # And then we apply this provisional label to the whole background for i in range(firstbg, shapeinfo.numels): if data_p[i] == bgval: forest_p[i] = firstbg # Here, we work with flat arrays regardless whether the data is 1, 2 or 3D. # The lookup to the neighbor in a 2D array is achieved by precalculating an # offset and adding it to the index. # The forward scan mask looks like this (the center point is actually E): # (take a look at shape_info docs for more exhaustive info) # A B C # D E # # So if I am in the point E and want to take a look to A, I take the index of # E and add shapeinfo.DEX[D_ea] to it and get the index of A. # The 1D indices are "raveled" or "linear", that's where "rindex" comes from. cdef void scan1D(DTYPE_t *data_p, DTYPE_t *forest_p, shape_info *shapeinfo, bginfo *bg, DTYPE_t connectivity, DTYPE_t y, DTYPE_t z): """ Perform forward scan on a 1D object, usually the first row of an image """ # Initialize the first row cdef DTYPE_t x, rindex, bgval = bg.background_val cdef INTS_t *DEX = shapeinfo.DEX rindex = shapeinfo.ravel_index(0, y, z, shapeinfo) for x in range(1, shapeinfo.x): rindex += 1 # Handle the first row if data_p[rindex] == bgval: # Nothing to do if we are background continue join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) cdef void scan2D(DTYPE_t *data_p, DTYPE_t *forest_p, shape_info *shapeinfo, bginfo *bg, DTYPE_t connectivity, DTYPE_t z): """ Perform forward scan on a 2D array. """ cdef DTYPE_t x, y, rindex, bgval = bg.background_val cdef INTS_t *DEX = shapeinfo.DEX scan1D(data_p, forest_p, shapeinfo, bg, connectivity, 0, z) for y in range(1, shapeinfo.y): # BEGINNING of x = 0 rindex = shapeinfo.ravel_index(0, y, 0, shapeinfo) # Handle the first column if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) # END of x = 0 for x in range(1, shapeinfo.x - 1): # We have just moved to another column (of the same row) # so we increment the raveled index. It will be reset when we get # to another row, so we don't have to worry about altering it here. rindex += 1 if data_p[rindex] == bgval: # Nothing to do if we are background continue join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) # Finally, the last column # BEGINNING of x = max rindex += 1 if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) # END of x = max cdef void scan3D(DTYPE_t *data_p, DTYPE_t *forest_p, shape_info *shapeinfo, bginfo *bg, DTYPE_t connectivity): """ Perform forward scan on a 2D array. """ cdef DTYPE_t x, y, z, rindex, bgval = bg.background_val cdef INTS_t *DEX = shapeinfo.DEX # Handle first plane scan2D(data_p, forest_p, shapeinfo, bg, connectivity, 0) for z in range(1, shapeinfo.z): # Handle first row in 3D manner # BEGINNING of y = 0 # BEGINNING of x = 0 rindex = shapeinfo.ravel_index(0, 0, z, shapeinfo) if data_p[rindex] != bgval: # Nothing to do if we are background # Now we have pixels below join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_en]) # END of x = 0 for x in range(1, shapeinfo.x - 1): rindex += 1 # Handle the first row if data_p[rindex] == bgval: # Nothing to do if we are background continue join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_el]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_en]) # BEGINNING of x = max rindex += 1 # Handle the last element of the first row if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_el]) # END of x = max # END of y = 0 # BEGINNING of y = ... for y in range(1, shapeinfo.y - 1): # BEGINNING of x = 0 rindex = shapeinfo.ravel_index(0, y, z, shapeinfo) # Handle the first column in 3D manner if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eh]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_en]) # END of x = 0 # Handle the rest of columns for x in range(1, shapeinfo.x - 1): rindex += 1 if data_p[rindex] == bgval: # Nothing to do if we are background continue join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ef]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eh]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_el]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_en]) # BEGINNING of x = max rindex += 1 if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_em]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ef]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_el]) # END of x = max # END of y = ... # BEGINNING of y = max # BEGINNING of x = 0 rindex = shapeinfo.ravel_index(0, shapeinfo.y - 1, z, shapeinfo) # Handle the first column in 3D manner if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eh]) # END of x = 0 # Handle the rest of columns for x in range(1, shapeinfo.x - 1): rindex += 1 if data_p[rindex] == bgval: # Nothing to do if we are background continue join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ec]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ek]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ef]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eh]) # BEGINNING of x = max rindex += 1 if data_p[rindex] != bgval: # Nothing to do if we are background join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eb]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ed]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ej]) if connectivity >= 2: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ea]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_eg]) join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ei]) if connectivity >= 3: join_trees_wrapper(data_p, forest_p, rindex, DEX[D_ef]) # END of x = max # END of y = max