I found a similar question here, with the answer: "you should always define the width and height in the image tag." But it is from 2009.
In the meantime, many things has changed on frontend. We are all doing responsive page design now, for many devices and sizes simultaneously (mobile, tablet, desktop...).
So, I wonder is it still necessary to specify the width and height attributes, and for what reason (for responsive, page speed, SEO...)?
An img element has width and height attributes, but they're not required under any DOCTYPE.
Width and height attributes were only 'required' or relevant to reserve the space on the page and prevent the page moving around as it loads - which is important. This can be achieved using CSS instead providing the CSS loads quickly enough - it is likely to load before the images anyway, so all should be good.
It is also possible (and valid) to specify just one attribute, width or height and the browser will calculate the omitted value in order to maintain the correct aspect ratio.
You can specify percent values in the attributes if required. You don't need to use CSS for this, if that is what you are implying.
Also, it is relevant to add - Under HTML5 the width and height can only take a pixel value, in other words a valid non-negative integer.
Whether you use the width and height attributes can depend on your design. If you have lots of differently sized images, do you want to lump all the dimensions in the CSS or include them with the img?
YES, you want to declare the width and the height of an image in 2016.
To make them retina-ready
If you want your image to be retina-ready, you should define a width and an height lower than the actual pixels. If the image is 800x600 specify <img width="400" height="300" />.
To avoid page jump
Without the width and the height the image does not know how large it is, which causes an unwanted jump in the page as it loads (it reflows). Declaring height and width solves this problem.
Note that:
Images with a defined width and height can still be responsive. Simply add max-width and max-height to your CSS. This will cause the image to scale down (not up) when it does not fit the screen (see this sweet retina-ready, responsive kitten). Defining a min-width and min-height will do the opposite.
Adding a huge amount of compression to your JPG (around 50%) to keep the file size low is recommended when you use a single (relative large) image for all screen sizes.
Well, the basic answer to this question (as with most coding issues) is this: it depends on the situation at hand.
I would say that the “best practice” of always specifying the height and width attributes of images making a significant difference to page rendering speeds hark back to the days when designers laid out their websites using tables and spacer GIFs. We have come a long way since then.
An indication for the future is the introduction of the new picture element being drafted into HTML. The picture element is effectively a wrapper for the existing img element, which allows you to specify several images of different sizes via a source element, and the user-agent itself actually determines which version is used.
<picture>
<source media="(min-width: 64em)" src="high-res.jpg">
<source media="(min-width: 37.5em)" src="med-res.jpg">
<source src="low-res.jpg">
<img src="fallback.jpg" alt="This picture loads on non-supporting browsers.">
<p>Accessible text.</p>
</picture>
As you can see from this example code above (taken from the Intel Developer Zone's article on the HTML5 picture element) there are no height or width attributes on the img element itself.
Here are a selection of resources that will help you to decide the most appropriate method of declaring image sizes:
Responsive Images Community Group
W3C Working Group Note: Use Cases and Requirements for Standardizing Responsive Images
WHATWG HTML Living Standard: The picture element
Good standards are always worth a recommendation. With a little extra code it's quite easy to merge static (px) values of the img tag and generic (em, %) values supplied by CSS. And simpler still, get rid of the img tag altogether and set the picture as background of a div with a unique ID. If you have multiple images, use sprites and assign each picture to its corresponding div. Your mark-up sources would then look something like <div id="image_001"></div> - that's all. Scales all by itself; no need for bloatware like JQuery, etc.
If we're talking 'bout responsive, you may use bootstrap (if not, start doing this).
When working with images, you should add the class img-responsive, this will modify the width of the image if necessary and the height will be auto, so if width decreases, height will decrease too.
You will always have an image that keeps the same % of its container and will never loose the aspect ratio.
There's no relation with SEO and image size declarations.
Page speed will be the same always, so if the image is 800 x 600 px, you'll load the full image, even if you declare it as 60 x 40 px.
You must think that, even using img-responsive, the max width and height of this image will be the real size of the image. So if we have a 800 x 600 px image, it will not enlarge it (because it'll become loosing quality).
So in 2016, it's recommendable to NOT declare height and width of an image. Instead use bootstrap's img-responsive class, other responsive framework class that gets the same result, or hand-made the proper jquery and css to reach the same.
Hope it helps!
Yes, It is still relevant to specify width and height attribute on images in HTML.
Images often take longer to load than the HTML code that makes up the rest of the page. It is, therefore, a good idea to specify the size of
the image so that the browser can render the rest of the text on the
page while leaving the right amount of space for the image that is
still loading.
Hence, specifying width and height attribute on image will improve the webpage performance by protecting from delay in loading.
Yes, it is necessary to add height and width attributes to the img tag along with the src and alt attributes to prevent page-jumping. When our page loads, the specified space will be preserved for the image so that the it can occupy that place peacefully.
But, there is another problem that will arise here Responsiveness.
Once we give height and width attribute to img tag, the image will tend to stay in the same height for all screen-sizes which will make the image to shrink.
To avoid this, we need to add height: auto; to the image in the CSS file.
I want to create a page using only "em" for font size.
The page is going to have a grid (tiles) with each cell having one image with some text above and below the image. The images are all in 200px X 200px in size. The Grid Cell would be somewhat larger than the image to accommodate the text areas.
How should I go about setting the height and width of the Div and Img tag, given that I want to rely only on "em" and not "px" for font size.
em is a relative unit of measurement that inherits its value from the font size of the parent element, so to apply consistent widths to your img elements using em you'll need to define a font size somewhere in your document structure using a measurement in px and inherit from that.
For reference's sake, where 1em equals 16px, an image with a width of 200px would be 12.5em wide- 200 / 16.
You'll want to specify your own measurement in px at least once in any case to ensure cross-browser compatibility. Not every browser uses the same default font size and it's possible that users have manually changed the default font size of their browser. If you rely on defaults, you very likely won't get consistent results, and it will be detrimental to your grid design.
If only one of the attributes height or width is set for an img element, most browsers seem to keep the proportions of the image.
This is from the HTML 4.01 reference:
When the object is an image, it is scaled. User agents should do their
best to scale an object or image to match the width and height
specified by the author.
http://www.w3.org/TR/html401/struct/objects.html#edef-IMG
Would it be wrong of a browser to scale the image non-uniformly, that is changing only the height or the width of an image?
Update 2015-08-12: Dillo (version 3.0.4) is an example of a browser which does not keep the proportions of an image if only height or only width is set.
If you look at what Bootstrap does with the .img-responsive class, it only sets height and max-width. http://getbootstrap.com/css/#images-responsive
If a browser didn't auto scale the width based on the height, this widely used CSS package would fail.
I can't speak for the spec authors, but from my PoV as a web developer if you scale non-uniformly your user agent is broken and none of my sites will render properly for you. Why would I ever want a non-uniform scaling? Especially one where one side is just determined by whatever size the image happens to be?
I would like to resize an image on my website. I know how to do it by either resizing the image before or calculating the width and height and setting the values in pixels. But I use the same picture multiple times with different dimmensions, so it would take me less time if I could resize the image relatively to its own size.
<img src='images/logo-beta.png' id="logo" height="75%" width="75%"/>
I have tried this, however the problem is that the size is set relative to its parent element.
There's no way to do what you want automatically using HTML or CSS alone. You'll need to use JavaScript to get the image's dimensions, then calculate a percentage of those dimensions and reapply them to the image in pixels
There is a method, but it isn't perfect. It requires a wrapping element whose display is set to 'inline-block' and the image is resized using 'max-width'.
The issue is that the parent element retains the image's original width, which could cause problems depending on your requirements.
Example: http://jsfiddle.net/amustill/GnEw5/
I want to load some photos from a server and display each of them in an own box such that the box is filled and the image centered (not stretched), if it is to big. Can I achieve this for example with CSS without knowing the size of each image? Maybe with max-width or so?
Here is an example of what I want:
You could use the CSS3 background-size property.
Specifically, you would use either background-size:contain or background-size:cover.
From the spec:
Values have the following meanings:
‘contain’
Scale the image, while preserving its intrinsic aspect ratio
(if any), to the largest size such that both its width and its height
can fit inside the background positioning area.
‘cover’
Scale the image, while preserving its intrinsic aspect ratio
(if any), to the smallest size such that both its width and its height
can completely cover the background positioning area.
Source: http://www.w3.org/TR/css3-background/#the-background-size
Which one you used would depend on the aspect ratio of the original images you are using.
Scroll down on this resource to see some examples: http://www.css3.info/preview/background-size/
The quickest thing that you can do is to put the image as a background image that is centered:
style="background: url(images/42.png) 50% 50% no-repeat"
Images smaller than the box will be centered in the box. Images that are larger will experience cropping.
The downside is, there is no scaling.
For scaling, you would have to know the dimensions, employ some math to calculate a scaling amount that will preserve the aspect ratio and use an actual element that is inside a cropping container that uses "overflow: hidden".
Here what you do. If for instance the image is inside a DIV with an ID called "boxer" You'll now create a CSS that will automatically re-size every image that's inside the DIV with the ID "boxer" The CSS will look like this
#boxer img {
Width: 600px
Height: 600px;
}
The above CSS will automatically re-size whatever image you put inside to the specifications in the CSS. This will fit the box with the ID "boxer" precisely if the dimensions corresponds to that of the CSS. You could just do 100% for both the width and the height, that way it fits the box.