有时，当使用我们的电脑时，会发生一些非常奇怪的事情，完全没有意义……比如把一个简单的图像复制到剪贴板上，电脑就因此冻结了。图像就是图像，对吗？今天的超级用户帖子回答了一个困惑读者的难题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

原始图像由维基媒体提供。

问题

超级用户读者Joban Dhillon想知道为什么将图像复制到他电脑上的剪贴板会使其冻结：

I was messing around with some height map images and found this one:

(http://upload.wikimedia.org/*********/comm***/1/15/Srtm_ramp2.world.21600×10800.jpg)

The image is 21,600*10,800 pixels in size. When I right click and select “Copy Image” in my browser (I am using Google Chrome), it slows down my computer until it freezes. After that I must restart. I am curious about why this happens. I presume it is the size of the image, although it is only about 6 MB when saved to my computer. I am also using Windows 8.1

为什么一个简单的图像在复制到剪贴板后会冻结Joban的电脑？

答案

超级用户贡献者Mokubai为我们提供了答案：

“Copy Image” is copying the raw image data, rather than the image file itself, to your clipboard.

The raw image data will be 21,600 x 10,800 x 3 (24 bit image) = 699,840,000 bytes of data. That is approximately 700 MB of data your browser is trying to copy to the clipboard.

JPEG compresses the raw data using a lossy algorithm and can get pretty good compression. Hence the compressed file is only 6 MB.

The reason it makes your computer slow is that it is probably filling your memory up with at least the 700 MB of image data that your browser is using to show you the image, another 700 MB (along with whatever overhead the clipboard incurs) to store it on the clipboard, and a not insignificant amount of processing power to convert the image into a format that can be stored on the clipboard.

Chances are that if you have less than 4 GB of physical RAM, then those copies of the image data are forcing your computer to page memory out to the swap file in an attempt to fulfill both memory demands at the same time. This will cause programs and disk access to be sluggish as they use the disk and try to use the data that may have just been paged out.

In short: Do not use the clipboard for huge images unless you have a lot of memory and a bit of time to spare.

Like pretty graphs? This is what happens when I load that image in Google Chrome, then copy it to the clipboard on my machine with 12 GB of RAM:

It starts off at the lower point using 2.8 GB of RAM, loading the image punches it up to 3.6 GB (approximately the 700 MB), then copying it to the clipboard spikes way up there at 6.3 GB of RAM before settling back down at the 4.5-ish you would expect to see for a program and two copies of a rather large image.

That is a whopping 3.7 GB of image data being worked on at the peak, which is probably the initial image, a reserved quantity for the clipboard, and perhaps a couple of conversion buffers. That is enough to bring any machine with less than 8 GB of RAM to its knees.

Strangely, doing the same thing in Firefox just copies the image file rather than the image data (without the scary memory surge).

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