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?
Related
I'm new to html so I'm a bit lost when I read that we can change the dimensions of the images through CSS or the width, height attribute.
For the width height attribute, some posts say that only pixels are accepted. But somehow, percentage also seems to work fine for my code.
However, when I tried using vw and vh, the image sized strangly.
so,
What are the accepted units for width and height attribute?
Is CSS recommended over width and height, for changing the dimensions of the images?
Many thanks.
The accepted units for the width and height attributes of an HTML img element are pixels. You give the number of pixels, but don't put the 'px'.
From MDN
width
The intrinsic width of the image in pixels. Must be an integer without a unit.
It is possible to get confused between these attributes and the use of CSS properties of the same names. While the attributes had more use probably when load times were longer (they allowed the correct space for the img to be saved in the page) they may be making a comeback, see https://developer.mozilla.org/en-US/docs/Web/Media/images/aspect_ratio_mapping which ends with:
— eliminating another piece of jank from web layout! There is no need for a web developer to do anything special to their code to take advantage of this, besides returning to the habit of using width and height attributes in their HTML.
I am trying to make a website with a fluid layout. So to do this I am trying to use percentages as measurements. If I am not mistaken, the percentages are calculated from the parent element. Since the html tags does not have any set width, how does the body tag calculate 100% width? does 100% means the full resolution of the screen that you are viewing the page?
thanks
You have to read the specs to find the answer to your question:
https://www.w3.org/TR/CSS22/visudet.html#x3 says about percentage widths:
<percentage>
Specifies a percentage width. The percentage is
calculated with respect to the width of the generated box's containing
block.
About containing blocks:
https://www.w3.org/TR/CSS22/visudet.html#containing-block-details says:
The position and size of an element's box(es) are sometimes calculated
relative to a certain rectangle, called the containing block of the
element. The containing block of an element is defined as follows:
The containing block in which the root element lives is a rectangle
called the initial containing block. For continuous media, it has the
dimensions of the viewport and is anchored at the canvas origin;
(...)
The root element is <html> (https://www.w3.org/TR/html-markup/html.html).
The screen is considered a continuous media.
The relationship between viewport and canvas is simple:
https://www.w3.org/TR/CSS22/visuren.html#viewport
https://www.w3.org/TR/CSS22/intro.html#canvas
User agents for continuous media generally offer users a viewport (a
window or other viewing area on the screen) through which users
consult a document. User agents may change the document's layout when
the viewport is resized (see the initial containing block).
When the viewport is smaller than the area of the canvas on which the
document is rendered, the user agent should offer a scrolling
mechanism.
So, trying to simplify this, the canvas size considers the content size even if it doesn't fit on the browser window.
The browser window contains the viewport (considered without menus, scrolling bar and status bar).
So, if <body> has 100% width, that means it would be the same width as the <html> element, which width is equal to the viewport's width.
You can easily find the viewport width by inspecting the css for <html> element on Chrome.
100% width for the body tag means 100% of the html width, which again is the full width of the viewport, which on desktops will be the browser window, on mobile devices the screen width.
Using just HTML and CSS would not suffice to get the width, you would need to use Javascript, or even better, a framework like jQuery that would help you get the body's width.
Using jquery the code would look something like this:
$(document).width();
You can find out more about it here.
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'm validating my HTML 5 pages and I get a lot of errors because I specified the width and height of my images in percentage. I though that this was the best way because if I specify it in pixels it won't resize when the site is viewed on a smaller device.
What's the correct way to specify the width and height of an image in HTML?
Thanks
If the original image is the aspect ratio that you want then just specify the with % and the height will change automatically. Make sure that the height of the parent div does not have a specified height as that may cause some problems. Also positioning of the rest of the page should be relative.
I am trying to create a completely fluid layout in CSS (everything in %), which would work seamlessly across platforms (desktop/mobile/tablets like iPad).
With Fluid Layouts, can an image be made completely fluid? For example:
img { max-width:100%; }
Does this mean it will adjust/fit to any extent or window size?
Also can this be applied to background images as well ?
Does this property have any limitations in terms of browser implementation or anything ?
The snippet you provide says that the maximum width for the image is 100%. This could mean no wider than the browser window or device viewport. It could also mean no wider than a relatively postitioned parent node. But, if the window is big enough, the image will render at it's native size.
It can't be applied to background images, because the background image itself is tiled or positioned based on it's original size. The max-width trick is mostly useful for content images, not so much layout or styling images.
It is limited, in that IE6 doesn't support it at all. However, that market is rather small and shrinking, so maybe you can ignore that issue.
Your code means the size of the image relative to it's parent's width. So lets say the div that the image is in is 500px wide, then the image may be a maximum of 500px wide, or smaller, not larger. for more info on max-width: W3.org max-width
For backgrounds this works a little different, you can use background-size: x y; for this. It's CSS3 and is not supported by older browsers. for more info on background-size: W3.org background-size