Python Pillow image quality different in linux

Question

I have a bot that plays an online game that is driven by selenium. It works by utilizing image recognition (finding subimages). In Windows, my bot works fine; however, my bot does not work in Ubuntu.

The bot works like this:

1. takes a screenshot of an element in selenium
2. uses pillow to load the screenshot
3. finds a subimage (a local image) in the larger screenshot

I've traced the issue to the function I'm using to find a subimage. It doesn't work because the screenshot image quality is different on Ubuntu, and it can't do a pixel by pixel match.

A working needle and haystack image set from Windows works fine on Ubuntu, and the inverse is also true -- a non-working needle and haystack image set created from Ubuntu does not work on both Windows and Ubuntu.

My screenshot is always ~6KB in Windows and ~5KB in Ubuntu.

When I open my local "needle" image in PIL and save it, it goes from 1.7KB to 1.5KB and doesn't work as a result. This is the non 500 line version of the code:

# imports and everything else here..

browser.save_screenshot("haystack.png") # selenium screenshot
haystack = Image.open("haystack.png")
needle = Image.open("needle.png") # the needle is a local file

haystack.save("haystack_new.png","PNG",quality=100) # DEBUGGING
needle.save("needle_new.png","PNG",quality=100) # DEBUGGING

# call "needle in a haystack" locator function here

Can someone tell me what's going wrong? Why are the linux screenshots lower quality? Should I install a different version of zlib or just use opencv instead?

Answer 1

不同的浏览器（可能还有操作系统/窗口管理器）以不同的方式实现颜色渲染 - 因此显示的像素值可能具有不同的R，G，B值强度，这些值对于人眼是不可见的，但是它们之间的屏幕截图进行跨平台像素比较。浏览器/平台无效。