以 python/linux 方式比较两个图像 [英] Compare two images the python/linux way

问题描述

尝试解决防止重复上传图片的问题.

Trying to solve a problem of preventing duplicate images to be uploaded.

我有两个 JPG.看着它们，我可以看到它们实际上是相同的.但是由于某种原因，它们的文件大小不同(一个是从备份中提取的，另一个是另一个上传的)，因此它们具有不同的 md5 校验和.

I have two JPGs. Looking at them I can see that they are in fact identical. But for some reason they have different file size (one is pulled from a backup, the other is another upload) and so they have a different md5 checksum.

我如何才能有效且自信地比较两个图像，就像人类能够看到它们明显相同一样?

How can I efficiently and confidently compare two images in the same sense as a human would be able to see that they are clearly identical?

示例:http://static.peterbe.com/a.jpg 和 http://static.peterbe.com/b.jpg

更新

我写了这个脚本:

import math, operator
from PIL import Image
def compare(file1, file2):
    image1 = Image.open(file1)
    image2 = Image.open(file2)
    h1 = image1.histogram()
    h2 = image2.histogram()
    rms = math.sqrt(reduce(operator.add,
                           map(lambda a,b: (a-b)**2, h1, h2))/len(h1))
    return rms

if __name__=='__main__':
    import sys
    file1, file2 = sys.argv[1:]
    print compare(file1, file2)

然后我下载了两个视觉上相同的图像并运行了脚本.输出:

Then I downloaded the two visually identical images and ran the script. Output:

58.9830484122

谁能告诉我合适的截止时间应该是多少?

Can anybody tell me what a suitable cutoff should be?

更新二

a.jpg和b.jpg的区别是第二个已经用PIL保存了:

The difference between a.jpg and b.jpg is that the second one has been saved with PIL:

b=Image.open('a.jpg')
b.save(open('b.jpg','wb'))

这显然应用了一些非常非常轻的质量修改.我现在已经解决了我的问题，将相同的 PIL 保存应用到正在上传的文件而不对其进行任何操作，现在它可以工作了！

This apparently applies some very very light quality modifications. I've now solved my problem by applying the same PIL save to the file being uploaded without doing anything with it and it now works!

推荐答案

有一个 OSS 项目，就是用 WebDriver 截屏然后对比图片看有没有问题(http://code.google.com/p/fighting-layout-bugs/)).它通过将文件打开到流中然后比较每一位来实现.

There is a OSS project that uses WebDriver to take screen shots and then compares the images to see if there are any issues (http://code.google.com/p/fighting-layout-bugs/)). It does it by openning the file into a stream and then comparing every bit.

您可以使用 PIL 做类似的事情.

You may be able to do something similar with PIL.

经过更多研究，我发现

h1 = Image.open("image1").histogram()
h2 = Image.open("image2").histogram()

rms = math.sqrt(reduce(operator.add,
    map(lambda a,b: (a-b)**2, h1, h2))/len(h1))

在 http://snipplr.com/view/757/compare-two-pil-images-in-python/ 和 http://effbot.org/zone/pil-comparing-images.htm

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