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pythonarraysnumpymultidimensional-array
Ajay Soman
Ajay Soman

Reputation: 1651

Max value of a 3d array in python

I want to find the max value of a 3d array in python. I tried

image_file1 = open("lena256x256.bmp","rb")
img_i = PIL.Image.open(image_file1)
pix = numpy.array(img_i);
maxval= max(pix)

but i am getting an error

 File "test.py", line 31, in <module>
    maxval= max(pix)
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I cannot catch my mistake here, please help me.

Upvotes: 7

Views: 30121

Answers (4)

Janne Karila
Janne Karila

Reputation: 25197

You are using the builtin max function that does not understand multidimensional NumPy arrays. You must instead use one of:

These are also faster than the builtin in the case of 1D NumPy arrays.

Upvotes: 11

nvlass
nvlass

Reputation: 685

In accordance to what georgesl wrote, you can use flat to get an iterator for the array and then do something like

m = reduce(max, ar.flat)

Edit: removed the lambda, the default max should be OK.

Upvotes: 0

Bas Jansen
Bas Jansen

Reputation: 3343

Max is expecting a single value, the error message should be quite clear, you want to use amax instead.

maxval = numpy.amax(pix)

Upvotes: 4

lucasg
lucasg

Reputation: 11002

The np.max function works for vectors, not matrices (or along an axis). To have the max element a multi-dimensionnal array, you can use flatten() : maxval= pp.max( pix.flatten() )

Upvotes: -3

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