I have an image in PIL Image format. I need to convert it to byte array. Now I need the roiImg as a byte array. Answer Thanks everyone for your help. Finally got it resolved!! With this i don’t have to save the cropped image in my hard disc and I’m able to retrieve the byte array from a PIL
Tag: arrays
How to copy a 2D array into a 3rd dimension, N times?
I’d like to copy a numpy 2D array into a third dimension. For example, given the 2D numpy array: convert it into a 3D matrix with N such copies in a new dimension. Acting on arr with N=3, the output should be: Answer Probably the cleanest way is to use np.repeat: Having said that, you can often avoid re…
Computing the correlation coefficient between two multi-dimensional arrays
I have two arrays that have the shapes N X T and M X T. I’d like to compute the correlation coefficient across T between every possible pair of rows n and m (from N and M, respectively). What’s the fastest, most pythonic way to do this? (Looping over N and M would seem to me to be neither fast
How to get a list of all indices of repeated elements in a numpy array
I’m trying to get the index of all repeated elements in a numpy array, but the solution I found for the moment is REALLY inefficient for a large (>20000 elements) input array (it takes more or less 9 seconds). The idea is simple: records_arrayis a numpy array of timestamps (datetime) from which we wa…
Sum slices of consecutive values in a NumPy array
Let’s say I have a numpy array a containing 10 values. Just an example situation here, although I would like to repeat the same for an array with length 100. I would like to sum the first 5 values followed by the second 5 values and so on and store them in a new empty list say b. So b
Set numpy array elements to zero if they are above a specific threshold
Say, I have a numpy array consists of 10 elements, for example: a = np.array([2, 23, 15, 7, 9, 11, 17, 19, 5, 3]) Now I want to efficiently set all a values higher than 10 to 0, so I’ll get: [2, 0, 0, 7, 9, 0, 0, 0, 5, 3] Because I currently use a for loop, which is
How do I find the position of a value in a pandas.DataFrame?
I want to search for ‘row3’ in the index of the DataFrame below, which should be 2 for a zero-based array. Is there a function which return the row number of ‘row3’? Thanks in advance for any help. Answer You could use Index.get_loc (docs): But this is a somewhat unusual access pattern…
How to pass Python list to C function using Cython
I am using a Raspberry Pi to interface with custom hardware connected to the GPIO. The controlling software is written in Python, and the interface to the custom hardware is written in C, as it is a much faster C implementation. I now need to start calling my C functions from my Python, and have recently been…
How to return 0 with divide by zero
I’m trying to perform an element wise divide in python, but if a zero is encountered, I need the quotient to just be zero. For example: I could always just use a for-loop through my data, but to really utilize numpy’s optimizations, I need the divide function to return 0 upon divide by zero errors…
Display numpy array in a for loop using matplotlib imshow
I have a numpy array whose elements are updated in a for loop: I want to display the array at each iteration, but imshow() doesn’t work, it just displays the image once the loop terminates. ps. I’m using an Ipython notebook I found different things on the web but none of them work on my computer (…