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I'm doing a little physics experiment where I send numpy arrays to a manufacturer library that is written in C++.

Currently, the code looks as follows:

import ctypes
import numpy as np

is_rgba = ctypes.c_uint(1)

# Load DLL
ctypes.cdll.LoadLibrary("\path_to_dll")
slm_lib = ctypes.CDLL("Blink_C_wrapper")


# Phase is the input array with data type np.uint8 and shape (1920, 1200)
# Here I only print parts of it

phase = [[137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137
  137 137 137 137 137 137 137 137 137 137 137 137]
 [118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118
  118 118 118 118 118 118 118 118 118 118 118 118]
 [100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
  100 100 100 100 100 100 100 100 100 100 100 100]
 [ 82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82
   82  82  82  82  82  82  82  82  82  82  82  82]
 [ 63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63
   63  63  63  63  63  63  63  63  63  63  63  63]
 [ 45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45
   45  45  45  45  45  45  45  45  45  45  45  45]
 [ 27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27
   27  27  27  27  27  27  27  27  27  27  27  27]
 [  9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9
    9   9   9   9   9   9   9   9   9   9   9   9]
 [246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246
  246 246 246 246 246 246 246 246 246 246 246 246]
 [228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228
  228 228 228 228 228 228 228 228 228 228 228 228]
 [210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210
  210 210 210 210 210 210 210 210 210 210 210 210]
 [191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191
  191 191 191 191 191 191 191 191 191 191 191 191]
 [173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173
  173 173 173 173 173 173 173 173 173 173 173 173]
 [155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155
  155 155 155 155 155 155 155 155 155 155 155 155]
 [137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137
  137 137 137 137 137 137 137 137 137 137 137 137]
 [118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118
  118 118 118 118 118 118 118 118 118 118 118 118]
 [100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
  100 100 100 100 100 100 100 100 100 100 100 100]
 [ 82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82
   82  82  82  82  82  82  82  82  82  82  82  82]
 [ 63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63
   63  63  63  63  63  63  63  63  63  63  63  63]
 [ 45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45
   45  45  45  45  45  45  45  45  45  45  45  45]
 [ 27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27
   27  27  27  27  27  27  27  27  27  27  27  27]
 [  9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9
    9   9   9   9   9   9   9   9   9   9   9   9]
 [246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246
  246 246 246 246 246 246 246 246 246 246 246 246]
 [228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228
  228 228 228 228 228 228 228 228 228 228 228 228]
 [210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210
  210 210 210 210 210 210 210 210 210 210 210 210]
 [191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191
  191 191 191 191 191 191 191 191 191 191 191 191]
 [173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173
  173 173 173 173 173 173 173 173 173 173 173 173]
 [155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155
  155 155 155 155 155 155 155 155 155 155 155 155]
 [137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137
  137 137 137 137 137 137 137 137 137 137 137 137]
 [118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118
  118 118 118 118 118 118 118 118 118 118 118 118]
 [100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
  100 100 100 100 100 100 100 100 100 100 100 100]
 [ 82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82
   82  82  82  82  82  82  82  82  82  82  82  82]
 [ 63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63
   63  63  63  63  63  63  63  63  63  63  63  63]
 [ 45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45
   45  45  45  45  45  45  45  45  45  45  45  45]
 [ 27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27
   27  27  27  27  27  27  27  27  27  27  27  27]
 [  9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9
    9   9   9   9   9   9   9   9   9   9   9   9]
 [246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246 246
  246 246 246 246 246 246 246 246 246 246 246 246]
 [228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228 228
  228 228 228 228 228 228 228 228 228 228 228 228]
 [210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210 210
  210 210 210 210 210 210 210 210 210 210 210 210]
 [191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191 191
  191 191 191 191 191 191 191 191 191 191 191 191]
 [173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173 173
  173 173 173 173 173 173 173 173 173 173 173 173]
 [155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155
  155 155 155 155 155 155 155 155 155 155 155 155]
 [137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137 137
  137 137 137 137 137 137 137 137 137 137 137 137]
 [118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118 118
  118 118 118 118 118 118 118 118 118 118 118 118]
 [100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
  100 100 100 100 100 100 100 100 100 100 100 100]
 [ 82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82  82
   82  82  82  82  82  82  82  82  82  82  82  82]
 [ 63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63  63
   63  63  63  63  63  63  63  63  63  63  63  63]
 [ 45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45  45
   45  45  45  45  45  45  45  45  45  45  45  45]
 [ 27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27  27
   27  27  27  27  27  27  27  27  27  27  27  27]
 [  9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9   9
    9   9   9   9   9   9   9   9   9   9   9   9]]

# Write to SLM
matrix = phase.ravel()
c = matrix.ctypes.data_as(ctypes.POINTER(ctypes.c_uint8))


success = slm_lib.Write_image(c, is_rgba)

I do not have access to Write_image. The header is

BLINK_C_WRAPPER_API int Write_image(unsigned char* image_data, int is_8_bit);

From what I record in the experiment, it seems as if there is a flip along the horizontal axis, i.e. what actually gets written to my machine is np.flip(phase, axis=0). I know that Python is row-major and so is C++, so it shouldn't be the case.

My question is:

  • Is my use of ctpyes correct?
  • Is it possible that somewhere in this code snippet a flip happens?
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