blocks|key|2990367|text|如果不实际下载图像(如使用带宽)，则很可能无法执行此操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2990368|也就是说，您可以使用FastImage+gem为您完成此操作。|offset|length|2990369|require+'fastimage'

FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
=>+[266,+56]++#+width,+height|code-block|syntax|javascript|2990370|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/sdsykes/fastimage^0|0|A|9|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

You will most likely not be able to do so without actually downloading the image (as in using the bandwidth). 

That being said, you can use the <a href="https://github.com/sdsykes/fastimage" rel="noreferrer">FastImage</a> gem to do this for you.

<pre><code>require 'fastimage'

FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
=&gt; [266, 56] # width, height
</code></pre>

blocks|key|5112776|text|"Validating+or+reading+a+remote+image+type+in+javascript“几乎涵盖了您需要了解的内容。它可能比你真正需要的要深一点，但它已经解释得很好了。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5112777|否则，您可以创建一个服务器端控制器来只执行一次此操作。你可以从任何地方读取图像和它们的尺寸。当用户获取图像时，尺寸将从您的服务器“缓存”中读取，而无需再次下载图像大小。如果关于该特定图像的信息不可用，您将获取它并存储尺寸和URL。这可以节省大量带宽。|5112778|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/11962445/validating-or-reading-a-remote-image-type-in-javascript^0|1|1J|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

"<a href="https://stackoverflow.com/questions/11962445/validating-or-reading-a-remote-image-type-in-javascript">Validating or reading a remote image type in javascript</a>" covers pretty much what you need to know. It might be a bit deeper then you really need but it's well explained.

Otherwise, you can create a server-side controller to do this only once. You can read the images and their dimensions from wherever you get them. When users fetch images, the dimensions will be read from your server 'cache' without downloading the image size again. If the information about that particular image is not available you will fetch it and store the dimensions and URL. This could save a lot of bandwidth.

blocks|key|5203710|text|仅使用HTTP标头请求不会对您有所帮助|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5203711|$+http+-h+get+"http://cdn.sstatic.net/stackoverflow/img/sprites.png"
HTTP/1.1+200+OK
Cache-Control:+max-age=604800
Connection:+close
Content-Length:+16425
Content-Type:+image/png
Date:+Fri,+19+Oct+2012+13:39:15+GMT
ETag:+"0d1523d7cadcd1:0"
Last-Modified:+Thu,+18+Oct+2012+22:02:18+GMT
Server:+NetDNA-cache/2.2|code-block|syntax|javascript|5203712|因此，您需要一些HTTP响应正文。但是一些图像文件格式在顶部有标头来描述分辨率(尽管jpeg没有)。因此，也许您可以为该位发出部分HTTP请求(range请求)。|5203713|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

A HTTP header only request won't help you

<pre><code>$ http -h get "http://cdn.sstatic.net/stackoverflow/img/sprites.png"
HTTP/1.1 200 OK
Cache-Control: max-age=604800
Connection: close
Content-Length: 16425
Content-Type: image/png
Date: Fri, 19 Oct 2012 13:39:15 GMT
ETag: "0d1523d7cadcd1:0"
Last-Modified: Thu, 18 Oct 2012 22:02:18 GMT
Server: NetDNA-cache/2.2
</code></pre>

So you will need some of the HTTP response body. But some image file formats have header at the top describing the resolution (although jpeg doesn't). So maybe you could make a partial HTTP request (range request) for that bit.

I need to get the size of an image in Ruby on Rails. The image is in a remote URL.
I dont want to download the entire image.

Get the width and height of an image without downloading it

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我需要在Ruby on Rails中获得图像的大小。图像位于远程URL中。我不想下载整个图像。

问无需下载即可获取图片的宽度和高度
EN

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问无需下载即可获取图片的宽度和高度EN