How to Determine the Size of an Object in Python

Finding size of the object in python (OpenCV)?

It is primitive method. Convert to grayscale and check which points have value bigger then some "bright" color ie. 21 and it gives array True/False - using .any(axis=0) you can reduce every row to single value, using .any(axis=1) you can reduce every column to single value and then using sum() you can count how many True was in any row or column (because True/False is converted to 1/0)

import cv2

img = cv2.imread('image.png')
img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
#print(img)

print('height, width, color:', img.shape)

#cv2.imshow('image', img)
#cv2.waitKey(0)
#cv2.destroyAllWindows()

print('width:', sum((img > 21).any(axis=0)))
print('height:', sum((img > 21).any(axis=1)))

For your image it gives me

width: 19
height: 27

For my image (below) it gives me

width: 23
height: 128

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EDIT: Version with small change.

I set mask = (img > 21) to

• calculate size

• create Black&White image which better shows which points are
  used to calculate size.

BTW: code ~mask inverts mask (convert True to False and False to True). It can be used also to invert image - ~img - to create negative for RGB, Grayscale or B&W.

Code:

import cv2

for filename in ['image-1.png', 'image-2.png']:

    img = cv2.imread(filename)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

    print('height, width, color:', img.shape)

    mask = (img > 21)

    # display size 
    print(' width:', sum( mask.any(axis=0) ))
    print('height:', sum( mask.any(axis=1) ))

    # create Black&White version 
    img[  mask ] = 255 # set white
    img[ ~mask ] = 0   # set black

    # display Black&White version
    cv2.imshow('image', img)
    cv2.waitKey(0)
    cv2.destroyAllWindows()

    # write Black&White version
    cv2.imwrite('BW-' + filename, img)

--->

--->

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EDIT: The same result using cv2.boundingRect() instead of sum(mask.any()) - but it still needs img[ mask ] = 255 to create Black&White image.

import cv2

for filename in ['image-1.png', 'image-2.png']:
    print('filename:', filename)

    img = cv2.imread(filename)
    #print('height, width, color:', img.shape)

    img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    #print('height, width, color:', img.shape)

    mask = (img > 21)

    # create Black&White version 
    img[  mask ] = 255 # set white
    img[ ~mask ] = 0   # set black

    x, y, width, height = cv2.boundingRect(img)

    # display size 
    print(' width:', width)
    print('height:', height)

    # display Black&White version
    #cv2.imshow('image', img)
    #cv2.waitKey(0)
    #cv2.destroyAllWindows()

    # write Black&White version
    #cv2.imwrite('BW-' + filename, img)

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_imgproc/py_contours/py_contour_features/py_contour_features.html#bounding-rectangle

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EDIT: The same result using cv2.boundingRect() and cv2.threshold() - so it doesn't need mask

import cv2

for filename in ['image-1.png', 'image-2.png']:
    print('filename:', filename)

    img = cv2.imread(filename)
    #print('height, width, color:', img.shape)

    img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    #print('height, width, color:', img.shape)

    ret, img = cv2.threshold(img, 21, 255, cv2.THRESH_BINARY)  # the same 21 as in `mask = (img > 21)`
    x, y, width, height = cv2.boundingRect(img)

    # display size 
    print(' width:', width)
    print('height:', height)

    # display Black&White version
    cv2.imshow('image', img)
    cv2.waitKey(0)
    cv2.destroyAllWindows()

    # write Black&White version
    #cv2.imwrite('BW-' + filename, img)

https://docs.opencv.org/3.4/d7/d4d/tutorial_py_thresholding.html

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_imgproc/py_thresholding/py_thresholding.html

https://www.learnopencv.com/opencv-threshold-python-cpp/

https://www.geeksforgeeks.org/python-thresholding-techniques-using-opencv-set-1-simple-thresholding/

Find out how much memory is being used by an object in Python

There's no easy way to find out the memory size of a python object. One of the problems you may find is that Python objects - like lists and dicts - may have references to other python objects (in this case, what would your size be? The size containing the size of each object or not?). There are some pointers overhead and internal structures related to object types and garbage collection. Finally, some python objects have non-obvious behaviors. For instance, lists reserve space for more objects than they have, most of the time; dicts are even more complicated since they can operate in different ways (they have a different implementation for small number of keys and sometimes they over allocate entries).

There is a big chunk of code (and an updated big chunk of code) out there to try to best approximate the size of a python object in memory.

You may also want to check some old description about PyObject (the internal C struct that represents virtually all python objects).

python. get size of an object

Considering that type(json.dumps(something))==str you should be able to literally just use len.

Consider the following

obj = {'content' : 'something goes here'}
json_obj = json.dumps(obj)
json_size = len(json_obj)

serialized_size = len(serialized_object)

if json_size < serialized_size:
  print "I'd use the JSON with this..."

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