19

How do I resize an existing image to, say "260x180?"

I am using Carrierwave and Rmagick currently to upload images to my Amazon S3 storage bucket, and it creates 2 versions of the image: the original, and the thumb version( 70x70).

Now, I know that I can create another version so that three versions would be created, including the 260x180, but I felt like that was over-clogging the storage database, and I was wondering if I could do it on a view level.

I tried 

<%= image_tag(@syllabus.image_url, :size => "260x180") %>

but it seems like it's not working - the images are not identical sizes.

Also, if the image is smaller than my desired output, do I need to do something different than to images that are bigger? For example, do I need to cut the bigger ones, but expand the smaller ones, or will it automatically scale to the desired size?

kibaekr
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4 Answers4

34

Like @Yosep said, there's nothing magical of rails going on here. <%= image_tag %> generates an <img> tag in the result html. if you pass a :size => '260x180', the result <img> tag will have its width and height set to 260 and 180.

Here comes the answer for your question. the best way of providing another image size, is the way you turned down at the beginning. You need to resize those images in the backend and store them somewhere.

Resizing image by setting the width and height of <img> tag will not keep the image's original aspect ratio. if the original ratio is 260:180, then it's fine. But if not, the result will be ugly. Besides, there's another drawback of doing so, which is the same reason that you should not resize image using CSS also. Resizing large images into smaller ones at client side will eventually be a huge waste of your network, and doing so will slow your site's rendering. That's one of YSlow's rules.

To resize image using CSS, you can use max-width and max-height, larger images will be resized accordingly, smaller ones will not be resized.

nil
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  • thank you! unfortunately I can't vote up yet because I lack reputation points... (lame) So that brings up my other question of how I would use one uploader for multiple models without resizing unnecessary photos. (http://stackoverflow.com/questions/10458324/carrierwave-single-uploader-for-multiple-models) – kibaekr May 05 '12 at 05:01
6

All Rails does, when seeing your code, is to turn

<%= image_tag(@syllabus.image_url, :size => "260x180") %>

into something like

<image tag="image.jpg" width="260" height="190" ../>

on the page (HTML).

That said, if your code does not look like it's working, try to assign a CSS class to it:

.image-size {
  max-width: 300px;
  max-height: 200px;
}
Yosep Kim
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3

If you want you can use our automatic image resizing in the cloud. For example, the following command would resize the image to fill a 260x180 rectangle.

<%= cl_image_tag("my_image.png", :size => "260x180", :crop => :fill) %>

This blog post describes how to use CarrierWave while all images are stored in the cloud, delivered through a fast CDN and all transformations are dynamically done in the cloud (no need to install RMagick).

Cloudinary
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1

In a view, without processing a new image? By convention, you'd use CSS.

.image_container img {
  width: 260px;
  height: 180px
}

And here are some interesting ways to crop with CSS: http://cssglobe.com/post/6089/3-easy-and-fast-css-techniques-for-faux-image

Kyle Macey
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  • is this assuming I have a class named "image_container" wrapped around the image tag in my view? – kibaekr May 05 '12 at 04:17