Python - 加载多个图像的更快方法？

Question

我的项目中的任务之一是加载数据集（chars74k）并为每个图像设置标签。在这个实现中，我已经有一个包含其他图像的矩阵和一个带有各自标签的列表。为了做任务，我写了下面的代码：

#images: (input/output)matrix of images 
#labels: (input/output)list of labels 
#path: (input)path to my root folder of images. It is like this: 
# path 
# |-folder1 
# |-folder2 
# |-folder3 
# |-... 
# |-lastFolder 

def loadChars74k(images, labels, path): 
    # list of directories 
    dirlist = [ item for item in os.listdir(path) if os.path.isdir(os.path.join(path, item)) ] 

    # for each subfolder, open all files, append to list of images x and set path as label in y 
    for subfolder in dirlist: 
     imagePath = glob.glob(path + '/' + subfolder +'/*.Bmp') 
     print "folder ", subfolder, " has ",len(imagePath), " images and matrix of images is:", images.shape, "labels are:", len(labels) 
     for i in range(len(imagePath)): 
      anImage = numpy.array(Image.open(imagePath[i]).convert('L'), 'f').ravel() 
      images = numpy.vstack((images,anImage)) 
      labels.append(subfolder) 

它工作正常，但它花费的时间太长（约20分钟）。我想知道是否有更快的方式来加载图像并设置标签。

问候。

Answer 1

经过一番研究，我能改善这样的代码：

def loadChars74k(images, labels, path): 
    # list of directories 
    dirlist = [ item for item in os.listdir(path) if os.path.isdir(os.path.join(path, item)) ] 

    # for each subfolder, open all files, append to list of images x and set path as label in y 
    for subfolder in dirlist: 
     imagePath = glob.glob(path + '/' + subfolder +'/*.Bmp') 
     im_array = numpy.array([numpy.array(Image.open(imagePath[i]).convert('L'), 'f').ravel() for i in range(len(imagePath))]) 
     images = numpy.vstack((images, im_array)) 
     for i in range(len(imagePath)): 
      labels.append(subfolder) 

    return images, labels 

我敢肯定它可以提高甚至更多，但它的确定，现在！现在需要33秒！