【PYTHON OPENCV】blobFromImage and imagesFromBlob

 """

Understanding cv2.dnn.blobFromImage() and also cv2.dnn.imagesFromBlob() in OpenCV """ # Import required packages: import cv2 import numpy as np from matplotlib import pyplot as plt def show_img_with_matplotlib(color_img, title, pos): """Shows an image using matplotlib capabilities""" img_RGB = color_img[:, :, ::-1] ax = plt.subplot(1, 4, pos) plt.imshow(img_RGB) plt.title(title) plt.axis('off') def get_image_from_blob(blob_img, scalefactor, dim, mean, swap_rb, mean_added): """Returns image from blob assuming that the blob is from only one image""" images_from_blob = cv2.dnn.imagesFromBlob(blob_img) image_from_blob = np.reshape(images_from_blob[0], dim) / scalefactor image_from_blob_mean = np.uint8(image_from_blob) image_from_blob = image_from_blob_mean + np.uint8(mean) if mean_added is True: if swap_rb: image_from_blob = image_from_blob[:, :, ::-1] return image_from_blob else: if swap_rb: image_from_blob_mean = image_from_blob_mean[:, :, ::-1] return image_from_blob_mean # Load image: image = cv2.imread("face_test.png") # Call cv2.dnn.blobFromImage(): blob_image = cv2.dnn.blobFromImage(image, 1.0, (300, 300), [104., 117., 123.], False, False) # The shape of the blob_image will be (1, 3, 300, 300): print(blob_image.shape) # Get different images from the blob: img_from_blob = get_image_from_blob(blob_image, 1.0, (300, 300, 3), [104., 117., 123.], False, True) img_from_blob_swap = get_image_from_blob(blob_image, 1.0, (300, 300, 3), [104., 117., 123.], True, True) img_from_blob_mean = get_image_from_blob(blob_image, 1.0, (300, 300, 3), [104., 117., 123.], False, False) img_from_blob_mean_swap = get_image_from_blob(blob_image, 1.0, (300, 300, 3), [104., 117., 123.], True, False) # Create the dimensions of the figure and set title: fig = plt.figure(figsize=(16, 4)) plt.suptitle("cv2.dnn.blobFromImage() visualization", fontsize=14, fontweight='bold') fig.patch.set_facecolor('silver') # Show the created images: show_img_with_matplotlib(img_from_blob, "img from blob " + str(img_from_blob.shape), 1) show_img_with_matplotlib(img_from_blob_swap, "img from blob swap " + str(img_from_blob.shape), 2) show_img_with_matplotlib(img_from_blob_mean, "img from blob mean " + str(img_from_blob.shape), 3) show_img_with_matplotlib(img_from_blob_mean_swap, "img from blob mean swap " + str(img_from_blob.shape), 4) # Show the Figure: plt.show()