如何使用多处理并行处理OpenCV的图像? [英] How can I process images with OpenCV in parallel using multiprocessing?

问题描述

我要使用某些OpenCV函数预处理的文件夹中有一组图像.函数

I have a set of images in a folder that I want to preprocess using some OpenCV functions. The function

detectAndaligncrop

拍摄一个图像路径，使用OpenCV对其进行预处理，然后返回utput图像. 我可以使用:

takes an image path preprocesses it using OpenCV and returns the utput image. I am able to do it using:

for image_path in files_list:
   cropped_image, _=detectAndaligncrop(im)
   cv2.imwrite("ouput_folder/{}".format(os.path.basename(image_path)),cropped_im*255.)

但是这不起作用:

jobs=[]
for im_no, im in enumerate(files_list):
    p=multiprocessing.Process(target=saveIm,args=[im])
    jobs.append(p)
    p.start()
for j in jobs:
    j.join()

其中saveIm是:

im,lm=detectAndaligncrop(im_path)
        fname="output_path/cropped2/{}".format(os.path.basename(im_path))
        cv2.imwrite(fname,im)

我已经验证它调用了detectAndaligncrop函数，但是没有处理从其中的行开始的图像

I have verified that it calls the detectAndaligncrop function, but does not process image starting from the line where

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

在detectAndaligncrop内部被调用，因为每个图像都调用"before cvtColor"，而"cvtColor after"则不是:

is called inside detectAndaligncrop, because "before cvtColor" is called for every image, while "after cvtColor" is not:

def detectAndaligncrop(impath):
    image=cv2.imread(impath)
    image_float=np.float32(image)/255.0
    print ("before cvtcolor")
    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    print ("after cvtcolor")
    return gray, 1

我也尝试过:

with ThreadPoolExecutor(max_workers=32) as execr:
    res=execr.map(saveIm,files_list)

此方法有效，但仅比运行for循环快.是因为GIL吗?

This works but no faster than simply running a for loop. Is it because of GIL?

推荐答案

经过几次实验后发现错误: 基本上，错误在于将读取的图像转换为灰度图像的方法. 如果我使用:

After a few experiments found the error: Basically, the error is in the method to convert the read image into a grayscale one. If I use :

gray = cv2.imread(impath,0)

代替

image = cv2.imread(impath)
image_float = np.float32(image)/255.0
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

代码工作正常，

在MultiProcessing中使用cv2.cvtColor可能存在一些问题.有人可以阐明原因.与可腌制性有关吗?

Perhaps there is some problem in using cv2.cvtColor in MultiProcessing. Someone can shed light on the reasons. Is it about picklability?

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