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HTML Responsive Images Image Delivery with Srcset and Sizes Adding Sizes

Thomas Dimnet
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Thomas Dimnet
Python Development Techdegree Graduate 43,629 Points
Posted by Thomas Dimnet
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Thomas Dimnet
Python Development Techdegree Graduate 43,629 Points

Sizes values: need some help!

Ok, so I went to the MDN docs and see this:

<img 
  src="clock-demo-thumb-200.png" 
  alt="Clock"
  srcset="clock-demo-thumb-200.png 200w,
               clock-demo-thumb-400.png 400w"
  sizes="(min-width: 600px) 200px, 50vw"
>

It means: when the (min-width: 600px) media condition matches, the image will be 200px wide. Otherwise it will be 50vw wide (50% of the viewport width).

In our case, when Nick writes that:

<img 
  sizes="50vw, (min-width: 1024px) 512px"
>

It means: the image will be 50vw wide but the media condition matches. If the media condition matches, it will be 512px wide. Am I correct?

If yes: when do the sizes of the image change? I do not get it.

Thomas.

3 Answers

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

:point_right: Remember that sizes does not change the dimensions of the image.

The actual image dimensions is controlled by the CSS width (or min-width or max-width) setting.

All the sizes attribute does is provide information to the browser to help choose which of the srcset images to use.

Thomas Dimnet
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.a{fill-rule:evenodd;}techdegree seal-36
Thomas Dimnet
Python Development Techdegree Graduate 43,629 Points
Thomas Dimnet
.a{fill-rule:evenodd;}techdegree seal-36
Thomas Dimnet
Python Development Techdegree Graduate 43,629 Points

Thanks Steven, I just get it a few minutes ago! The other thing I have to keep in mind: "Chrome will always use the largest image available in the cache"! So if I resize the browser window, it is perfectly normal to have some issues :) (for now!)

Ran ShemTov
Ran ShemTov
14,148 Points
Ran ShemTov
Ran ShemTov
14,148 Points

If you use max-width 100% you'll usually end up with an image scaling up to it's parent div.