class Blob: Represents a blob. def init (self) Constructs an empty blob self num

Question

class Blob: Represents a blob. def init (self) Constructs an empty blob self number of pixels self. x x-coordinate of center of mass self. y y-coordinate of center of mass def add (self, i, j): Adds pixel (i j) to this blob def mass (self) Returns the number of pixels added to this blob le its mass def distanceTo (self, other) Returns the Euclidean distance between the center of mass of this blob and the center of mass of other blob def str (self) Returns a string representation of this blob return '9 d (96. 4f, 95. 4f) (self P, self. x, self y)

Explanation / Answer

class Blob(): def __init__(self): # construct an empty blob self.pixels = [] #def __str__(self): #return "blob mass = %d" % (self.mass()) def add(self, i, j): #add a pixel (i, j) to the blob self.pixels.append((i,j)) def mass(self): # return number of pixels added = its mass self.mass = len(self.pixels) return self.mass def distanceTo(self, b): # return distance between centers of masses of this blob and b x1 = self.centerOfMass()[0] x2 = b.centerOfMass()[0] y1 = self.centerOfMass()[1] y2 = b.centerOfMass()[1] dist = ((x2 - x1)**2 + (y2 - y1)**2)**0.5 return dist def centerOfMass(self): # return tuple of (x,y) values for this blob's center of mass # format center-of-mass coordinates with 4 digits to right # of decimal point x = 0 y = 0 for coord in self.pixels: x += coord[0] y += coord[1] x_avg = x/(len(self.pixels)) y_avg = y/(len(self.pixels)) return [x_avg, y_avg] #def __repr__(self): #return "" % (self.mass, self.centerOfMass) def monochrome(picture, threshold): """loops over the pixels in the loaded image, replacing the RGB values of each with either black or white depending on whether its total luminance is above or below some threshold passed in by the user""" black = (0, 0, 0) white = (255, 255, 255) xsize, ysize = picture.size temp = picture.load() for x in range(xsize): for y in range(ysize): r,g,b = temp[x,y] if r+g+b >= threshold: temp[x,y] = black else: temp[x,y] = white #return picture def fill(picture, xsize, ysize, xstart, ystart): """keep a list of pixels that need to be looked at, but haven't yet been filled in - a list of the (x,y) coordinates of pixels that are neighbors of ones we have already examined. Keep looping until there's nothing left in this list""" queue = [(xstart,ystart)] blobby = Blob() while queue: BLACK = (0,0,0) RED = (255,0,0) x,y,queue = queue[0][0], queue[0][1], queue[1:] if picture[x,y] == BLACK: picture[x,y] = RED blobby.add(x,y) if x > 0: queue.append((x-1,y)) if x < (xsize-1): queue.append((x+1,y)) if y > 0: queue.append((x, y-1)) if y < (ysize-1): queue.append((x, y+1)) return blobby def count(picture): """scan the image top to bottom and left to right using a nested loop. when black pixel is found, increment the count, then call the fill function to fill in all the pixels connected to that one.""" xsize, ysize = picture.size temp = picture.load() LstOfBlobs = [] result = 0 BLACK = (0,0,0) RED = (255,0,0) for x in range(xsize): for y in range(ysize): if temp[x,y] == BLACK: LstOfBlobs.append(fill(temp,xsize,ysize,x,y)) return LstOfBlobs def BlobFinder(picture, tau): #Tau of 180 works for milk, 600 works for run4. """ picture = picture from file. tau = brightness threshold used in monochrome. Uses the monochrome function to invert the picture color so that the count function can then be called which runs through each pixel, finding a blob, filling it, then appending it to a list. """ float(tau) monochrome(picture, tau) #create list of blobs from picture. LstOfBlobs = count(picture) #return list return LstOfBlobs def countbeads(P,lst): """ P = minimum mass of a blob for it to be considered a 'bead'. lst = List of Blobs gained from BlobFinder function. countbeads takes the list of blobs of all sizes from the BlobFinder function and itterates through each blob and appends them to a new list if the blob has a mass (number of pixels) greater than P. This eliminates any one pixel 'noise' particles in the picture. The resulting list of 'Big Blobs' can also be reffered to as a list of 'beads'. The function then returns the length of the list to see how many beads are present in the picture. """ #initialize list LstOfBigBlobs = [] #itterate through list. for b in lst: #find mass of each blob. x = b.mass() if x >= P: #append blob to new list if mass is greater than the value P given by the user. LstOfBigBlobs.append(b) return len(LstOfBigBlobs) def getbeads(P,lst): """ P = minimum mass of a blob for it to be considered a 'bead'. lst = List of Blobs gained from BlobFinder function. get takes the list of blobs of all sizes from the BlobFinder function and itterates through each blob and appends them to a new list if the blob has a mass (number of pixels) greater than P. This eliminates any one pixel 'noise' particles in the picture. The resulting list of 'Big Blobs' can also be reffered to as a list of 'beads'. The function then returns the list of beads (LstOfBigBlobs). """ #initialize list LstOfBigBlobs = [] #itterate through list. for b in lst: #find mass of each blob. x = b.mass() if x >= P: #append blob to new list if mass is greater than the value P given by the user. LstOfBigBlobs.append(b) return LstOfBigBlobs

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