Image outline using python/PIL

Question

I have a color photo of apple, how can I show only its outline (inside white, background black) with python/PIL?

Answer 1

If your object and background have fairly well contrast

from PIL import Image
image = Image.open(your_image_file)
mask=image.convert("L")
th=150 # the value has to be adjusted for an image of interest 
mask = mask.point(lambda i: i < th and 255)
mask.save(file_where_to_save_result)

if higher contrast is in one (of 3 colors), you may split the image into bands instead of converting it into grey scale.

if an image or background is fairly complicated, more sophisticated processing will be required

Answer 2

Something like this should work.

from PIL import Image, ImageFilter

image = Image.open('your_image.png')
image = image.filter(ImageFilter.FIND_EDGES)
image.save('new_name.png') 

If that doesn't give you the result you are looking for then you try implementing either Prewitt edge detection, Sobel edge detection or Canny edge detection using PIL and Python and other libraries see related question and the following example .

If you are trying to do particle detection / analysis rather than just edge detection, you can try using py4ij to call the ImageJ method you link to give you expect the same result, or try another Particle Analysis Python library EMAN alternately you can write a Particle detection algorithm using PIL, SciPy and NumPy.