def im_list_to_blob(ims):將圖像轉換成適合caffe輸入的blob數據結構（但是本質上還是python的np.ndarray）, 也就是N * C * H * W的四維結構
def im_list_to_blob(ims):
"""Convert a list of images into a network input.
Assumes images are already prepared (means subtracted, BGR order, ...).
"""
# ims裏不同圖片的shape可能不一樣，取出其最大值
max_shape = np.array([im.shape for im in ims]).max(axis=0)
num_images = len(ims)
blob = np.zeros((num_images, max_shape[0], max_shape[1], 3),
dtype=np.float32)
for i in xrange(num_images):
im = ims[i]
blob[i, 0:im.shape[0], 0:im.shape[1], :] = im
# Move channels (axis 3) to axis 1
# Axis order will become: (batch elem, channel, height, width)
channel_swap = (0, 3, 1, 2)
blob = blob.transpose(channel_swap)
return blob
def prep_im_for_blob(im, pixel_means, target_size, max_size)該方法主要是求取圖像的縮放比例，然後將圖像resize，
def prep_im_for_blob(im, pixel_means, target_size, max_size):
"""Mean subtract and scale an image for use in a blob."""
im = im.astype(np.float32, copy=False)
im -= pixel_means
im_shape = im.shape
im_size_min = np.min(im_shape[0:2])
im_size_max = np.max(im_shape[0:2])
im_scale = float(target_size) / float(im_size_min)
# Prevent the biggest axis from being more than MAX_SIZE
if np.round(im_scale * im_size_max) > max_size:
im_scale = float(max_size) / float(im_size_max)
im = cv2.resize(im, None, None, fx=im_scale, fy=im_scale,
interpolation=cv2.INTER_LINEAR)
return im, im_scale