How to normalize a NumPy array to within a certain range?

audio /= np.max(np.abs(audio),axis=0)
image *= (255.0/image.max())

Using /= and *= allows you to eliminate an intermediate temporary array, thus saving some memory. Multiplication is less expensive than division, so

image *= 255.0/image.max()    # Uses 1 division and image.size multiplications

is marginally faster than

image /= image.max()/255.0    # Uses 1+image.size divisions

Since we are using basic numpy methods here, I think this is about as efficient a solution in numpy as can be.

In-place operations do not change the dtype of the container array. Since the desired normalized values are floats, the audio and image arrays need to have floating-point point dtype before the in-place operations are performed. If they are not already of floating-point dtype, you’ll need to convert them using astype. For example,

image = image.astype('float64')

Related Posts:

  1. Root mean square of a function in python
  2. Sorting arrays in NumPy by column
  3. Import Error: No module named numpy
  4. ValueError: setting an array element with a sequence
  5. Numpy ValueError: setting an array element with a sequence. This message may appear without the existing of a sequence?
  6. numpy: Invalid value encountered in true_divide
  7. How do I create an empty array/matrix in NumPy?
  8. numpy matrix vector multiplication
  9. How do I read CSV data into a record array in NumPy?
  10. How do I read CSV data into a record array in NumPy?
  11. Factorial in numpy and scipy
  12. Convert pandas dataframe to NumPy array
  13. size of NumPy array
  14. ValueError: all the input arrays must have same number of dimensions
  15. TypeError: cannot unpack non-iterable int objec
  16. ValueError: setting an array element with a sequence
  17. Using Numpy Vectorize on Functions that Return Vectors
  18. How to raise a numpy array to a power? (corresponding to repeated matrix multiplications, not elementwise)
  19. Is there a NumPy function to return the first index of something in an array?
  20. Numpy/Python Array Value error
  21. initialize a numpy array
  22. Overflow Error in Python’s numpy.exp function
  23. load csv into 2D matrix with numpy for plotting
  24. How to access the ith column of a NumPy multidimensional array?
  25. Dump a NumPy array into a csv file
  26. Python: find position of element in array
  27. numpy with python: convert 3d array to 2d
  28. Python: slicing a multi-dimensional array
  29. How to remove specific elements in a numpy array
  30. Add single element to array in numpy
  31. Overflow Error in Python’s numpy.exp function
  32. How to normalize a 2-dimensional numpy array in python less verbose?
  33. Make list of arrays in python
  34. Understanding NumPy’s einsum
  35. Moving average or running mean
  36. How to fix “TypeError: len() of unsized object”
  37. TypeError: Invalid dimensions for image data when plotting array with imshow()
  38. Numpy.dot TypeError: Cannot cast array data from dtype(‘float64’) to dtype(‘S32’) according to the rule ‘safe’
  39. How to get the unit vector from a numpy array
  40. Moving average or running mean
  41. Official abbreviation for: import scipy as sp/sc
  42. numpy-equivalent of list.pop?
  43. Using numpy to build an array of all combinations of two arrays
  44. Efficiently sorting a numpy array in descending order?
  45. How to plot an array in python?
  46. TypeError: only integer arrays with one element can be converted to an index 3
  47. How to create a numpy array of all True or all False?
  48. How to create a numpy array of lists?
  49. Removing nan values from an array
  50. IndexError: index 2 is out of bounds for axis 0 with size 2
  51. ImportError in importing from sklearn: cannot import name check_build
  52. How to add a new row to an empty numpy array
  53. What are the differences between numpy arrays and matrices? Which one should I use?
  54. Compute a confidence interval from sample data
  55. Numpy – add row to array
  56. ImportError: cannot import name NUMPY_MKL
  57. Is there any numpy group by function?
  58. Mean Squared Error in Numpy?
  59. Numpy Resize/Rescale Image
  60. numpy array concatenation error: 0-d arrays can’t be concatenated
  61. Convert a 1D array to a 2D array in numpy
  62. inverting image in Python with OpenCV
  63. How to print the full NumPy array, without truncation?
  64. TypeError: zip argument #2 must support iteration
  65. numpy/scipy/ipython:Failed to interpret file as a pickle
  66. How to declare an array in Python?
  67. numpy max vs amax vs maximum
  68. What is the purpose of meshgrid in Python / NumPy?
  69. why numpy.ndarray is object is not callable in my simple for python loop
  70. numpy division with RuntimeWarning: invalid value encountered in double_scalars
  71. Most efficient way to find mode in numpy array
  72. ImportError: numpy.core.multiarray failed to import
  73. ImportError: numpy.core.multiarray failed to import
  74. Python List vs. Array – when to use?
  75. numpy array concatenate: “ValueError: all the input arrays must have same number of dimensions”
  76. ‘DataFrame’ object has no attribute ‘sort’
  77. Is arr.__len__() the preferred way to get the length of an array in Python?
  78. convert nan value to zero
  79. TypeError: ‘DataFrame’ object is not callable
  80. LinAlgError: Last 2 dimensions of the array must be square
  81. What does axis in pandas mean?
  82. TypeError: list indices must be integers or slices, not str
  83. 3-dimensional array in numpy
  84. How do I calculate percentiles with python/numpy?
  85. How to have an array of arrays in Python
  86. ‘list’ object has no attribute ‘shape’
  87. What is the difference between np.mean and tf.reduce_mean?
  88. What does ‘index 0 is out of bounds for axis 0 with size 0’ mean?
  89. What does ‘index 0 is out of bounds for axis 0 with size 0’ mean?
  90. ValueError: x and y must be the same size
  91. Saving a Numpy array as an image
  92. NumPy List Comprehension Syntax
  93. Linear regression with matplotlib / numpy
  94. Numpy extract submatrix
  95. RuntimeError: module compiled against API version a but this version of numpy is 9
  96. Matplotlib: TypeError: can’t multiply sequence by non-int of type ‘numpy.float64’
  97. How to add column to numpy array
  98. Coalesce values from 2 columns into a single column in a pandas dataframe
  99. How do I compute derivative using Numpy?
  100. Installing scipy for python 2.7

Leave a Comment