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python - 如何堆叠多个图像numpy ndarray

问题描述

我从opencv得到图像numpy数组，然后我想把32张图像堆叠在一起，我想得到的最终形状是(3, 32, image_height, image_width)，下面是代码片段：

import cv2
import numpy as np
video_path = 'xxxx.mp4'
frame_buffer = np.array([])
frame_index = 0
frame_buffer_num = 0
cap = cv2.VideoCapture(video_path)
while True:
  ret, image_np = cap.read()
  print(image_np.shape)
  if frame_index == 0:
    frame_buffer = image_np  # initialize empty frame_buffer
    frame_index += 1
    frame_buffer_num += 1
    continue

  frame_index += 1
  frame_buffer_num += 1
  frame_buffer = np.stack(frame_buffer, image_np)
  if frame_buffer_num == 32:
      print(frame_buffer.shape)
      break

我运行它但出现以下错误：

Traceback (most recent call last):
  File "/home/weidawang/Python/temp.py", line 19, in <module>
    frame_buffer = np.stack(frame_buffer, image_np)
  File "<__array_function__ internals>", line 6, in stack
  File "/home/weidawang/miniconda3/lib/python3.7/site-packages/numpy/core/shape_base.py", line 430, in stack
    axis = normalize_axis_index(axis, result_ndim)
TypeError: only size-1 arrays can be converted to Python scalars

- - - - - -更新 - - - - - - -

感谢@abe 的启发，以下代码有效：

import cv2
import numpy as np
video_path = 'xxxx.mp4'
frame_index = 0
frame_buffer_num = 0
cap = cv2.VideoCapture(video_path)
width = cap.get(cv2.CAP_PROP_FRAME_WIDTH)  # float
height = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)
frame_buffer = np.zeros((3, 32, int(height), int(width)))
while True:
  ret, image_np = cap.read()
  image_np = image_np.reshape(3, int(height), int(width))
  print(image_np.shape)
 
  frame_buffer[:, frame_buffer_num, :, :] = image_np
  frame_index += 1
  frame_buffer_num += 1

  if frame_buffer_num == 32:
      print(frame_buffer)
      print(frame_buffer.shape)
      break

标签： pythonnumpynumpy-ndarrayopencv-python

解决方案

你为每一帧得到的图像都有一个形状，(3, H, W)对吗？你想堆叠其中的 32 个。然后，您可以先重塑image_np为image_np = image_np.reshape((3, 1, H, W))，然后使用 的第一个重塑实例初始化np.append(frame_buffer, image_np, axis=1)where 。这应该会产生一个形状的张量frame_bufferimage_np(3, 32, H, W)

或者，您可以初始化frame_buffer = np.zeros((3, 32, H, W))并在每次迭代时，frame_buffer[:, i, :, :] = image_np

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