I came to know that, if we dont give width and height attr. in image tag there will be a performance isssue.
I have a div element for which i'm setting width and height in percentages. Also the same div is having a background image of fixed size say 140px * 140px.
Here, will there be a perfromance issuse?.
markup example:
<div style="width:50%;background:url('imgofsize140*140') no-repeat"> </div>
Thanks
This isn't a one-size-fit-all case - Therefore we have to look at it case by case.
There are a lot of variables that we must keep in mind - User's internet connection speed, image size, computer capabilities, etc.
I found a few questions on SO that are somewhat relevant to this question. I will include them as I see it beneficial. I am NOT claiming to be absolutely correct.
BGIMG vs IMG
Performance Argument
AFAIK, browsers cache images the same whether they're in a DIV or an
IMG. In any case, I think this one of those cases where specific
performance is defined as an implementation detail internal to each
rendering engine (and possibly the browsers built around them). As
such, it's both out of our control as designers/developers and subject
to change from browser to browser and version to version. In other
words, I wouldn't spend too much time worrying about it.
Context
Technical differences yes, most notably you can set the width/height
of an IMG tag and it will stretch the image, which can be useful in
some situations.
The main thing you've got to keep in mind though is the context of the
image within the HTML document. If the image is content, say an image
in a gallery, I'd use a IMG tag. If it is just part of the interface I
might use a div instead.
- By Paul
And the response to that is just as important.
That said, you bring up an excellent point about the semantic
difference: an IMG is usually the better choice when the image is a
material part of the page's content, while a CSS technique is usually
preferred when the image is just decorative or for formatting.
This is not performance related directly - More about semantics and accessibility. By - Mr. W.
Then one more for Performance OFF of SO which I feel is directly related to your question.
Page Load Test
The version with background images actually gave me a “Document
Complete” after .0225 seconds – while the fully loaded page load time
was roughly the same as the inline image version. Could using all
background images speed up firing of $.document(ready)? It turns out
background-images are only downloaded after the element (containing
div, span etc) is available. This prevents blocking from all the round
trips required to get images.
results: inline image test page
results: background image test page
I wouldn't think there would be a performance issue in the same way as not specifying height and width on a img tag, since that forces the browser to repaint the whole page and that's where the performance issue is.
http://code.google.com/speed/page-speed/docs/rendering.html#SpecifyImageDimensions
tl;dr
You will not get a performance penalty (which is really small in the other case as well).
Some more details:
You shouldn't care (unless you work for Google) about the performance "penalty" you'd get from not specifing a width & height, but more about the layout flickering you might get.
Not specifing a width and height will make the browser display an initial box, as it doesn't know beforehand how much space the image will take, and after the image is loaded it will do a reflow - which means it will have to recalculate the layout of some elements which will be affected by the size change. But, this is actually going to happen very fast (and you're probably triggering reflows in lots of other places).
There is no reflow necessary for the background image.
I don't think this will effect perfomance.
If you combine your background images into one image and position it as and when you need to that will help speed up performance as you're only loading the one image rather than multiple images.
The background image will be displayed as 140x140 unless the div width has smaller size than 140px.
You might also want to check the result in older browsers such as InternetExplorer 6-7-8 just to ensure if there is any other performance issue.
Depends on the browser. I learned today that Chrome currently redraws the canvas as you scroll with an absolute position bg image. Firefox handles it just fine. This should be fixed in a future Chrome release.
On the contrary, specifying the img height and will cause the performance issue.
Because by specifying them, you tell the browser to resize the img first, then render the image. For example, storing thumbnail image is much better than resize the image on the fly.
If your image is already the specified size you want their is no need to specify the Height and Width in the attributes. Also, there will be no performance issue in using the background image.
Related
According to
http://www.w3schools.com/html/html_images.asp
Always specify the width and height of an image. If width and height are not specified, the page will flicker while the image loads.
Personally I have tried testing it and never noticed it happening. Anyone seen it before and know why it happens?
w3schools is not known for their accurate information, and historically was so bad that http://w3fools.com was created to explain just how bad the information was.
The "flicker" that w3schools is referring to is probably the content shifting that happens when an image changes sizes after it loads. Browsers have generally optimized this shifting to mostly go away, but it can still occur depending on how images are loaded and styles are handled.
The main point being to use [width] and [height] attributes to inform the browser of what size the content is expected to be to make correct rendering as fast as possible.
I was told that specifying inline width and height for all images will be good for SEO and also helps the site loads faster, like so:
<img src="http://www.example.com/images/free-size.jpg" width="200" height="400" alt="random image" />
Although I can still overwrite the inline setting using height:auto;.
So that images re-size properly when in different display platforms.
But just before I go ahead and doing this just want to reassure if these statements are true. Personally I feel dubious about fixing the inline dimension and overwriting using external CSS, just sound a bit hacky to me.....
I was told that specifying inline width and height for all images will
be good for SEO and also helps the site load faster.
Yes. This has traditionally been true (at least the "site loads faster" part).
By specifying the height and width attributes of an <img> the browser reserves a space matching those dimensions for the image while it continues parsing the rest of the HTML document. Then when the browser loads the image, the reserved space is waiting and there is no need to reflow the document.
Providing this sizing data results in a faster rendering process.
In contrast, if the width and height attributes are omitted, the browser will not know the size of the image until the download is complete, which forces the browser to reflow the document, slowing down the rendering process.
Now imagine a page with 50 images with no defined width and height attributes. The performance hit could be very noticeable.
The practice above represents the traditional view of image loading.
In contrast, some people are now saying that for responsive design the width and height attributes should be avoided.
Responsive Design does not normally use any width or height attributes
The majority of responsive websites do not use width or
height because they want the images to adapt to the screen size and by
using fixed width and height using <img> which would dampen user
experience and Google has declared this one of the most important
factors.
source: https://webmasters.stackexchange.com/a/68494
So there are arguments on both sides and the decision most likely depends on your individual case. As you make your decision here are some more details:
Specifying image dimensions to improve browser performance
Image width/height as an attribute or in CSS?
I was told that specifying inline width and height for all images will
be good for SEO and also helps the site loads faster.
No, it does help loading the site faster. It helps avoid flickering when rendering the page. If you want to load your images faster, make sure they have the same size as specified in the page and use a service like kraken.io to reduce the corresponding file size.
About SEO, it's improper image size and width for the screen size that can hurt your SEO. Google may consider you site as not user-friendly and/or not smartphone friendly.
If you do not tell the browser the size of your images then it must "build" the page not once, but twice (or more times depending on how many images you have on the page). It will build it once to display all the text, and then it will wait until an image is downloaded. When one image is downloaded the browser can now determine the size of the image and will rebuild the page to wrap the text around that image. This process will happen for every image on your page.
If you just specify the image dimensions, it will already know the size of the images and can use that information to shape the page. It won't have to rebuild the page a million times.
The best approach I think is to use the aspect ratio in css.
.img-container {
max-width: 500px;
aspect ratio: 2/1;
overflow:hidden;
}
The above css will reserve a container space for the image to load and prevent reflow.
Is it okay to set the width and height of the img tag performance wise knowing that the original image is much smaller?
The articles I've read usually say that setting width and height solves the performance issues, but its not clear, if I set the width and height and they are different from the native image size, is it "ok"?
Or Do I have to always set the same width and height as the image itself?
Unless you're anticipating your site used on slow/limited devices like smartphones you shouldn't bother about performance in this specific case.
However, if you specify size that is larger than the actual image size then the image will look bad.
From my experience specifying an image size is useful to avoid page layout change when an image is not loaded immediately; in this case the browser initially doesn't know what the size will be and won't reserve the needed space for it. Later when the image is loaded the page contents may "jump" because the size of the image will change for the browser.
I don't have benchmarks at hand, but I think it won't be a problem at all if you set a width/height different than the original one. The browser renders the image, and that's it. The rendering action is usually not expensive in terms of performance AFAIK. By the way you are not supposed to be afraid of things like this, unless you are doing something very fancy (i.e. an image 99999x99999 or rendering 2,000 images in a single page).
Anyway, if you can avoid that, it's probably better.
When I was first learning HTML a very long time ago, I was told that it was important to always set the dimensions of your images in your HTML, so that browsers could draw an empty box where the image should go, render your page, and then download and render the images where they belong. If you didn't set width and height values for your images, the browser would have to download the images first to discover their dimensions, and it would slow page loading for people with crappy connections.
For the past few years I've been using CSS, I always put a width and height declaration in my img tags in my HTML. My question is, is setting width and height in the style sheet, and no longer adding these HTML attributes, just as good? It certainly makes my spartan HTML look even cleaner without them.
The problem you mention with the image not being downloaded immediately also applies to your CSS.
The difference is that without the rest of the CSS the whole layout may not make sense. In other words, if the rest of the CSS hasn't loaded then the fact that the image dimensions are also missing won't really be that noticeable.
So personally I think it's fine to put the dimensions in the CSS.
This is a good question, but it's a bit subjective and may lead to more discussion than is generally advised on SO.
Back in the 90's, browsers were slow, and so was the internet. 56k took a while to transfer medium sized images. During that time, the layout would resize to fit the image.
Fast-forward a decade, and internet speeds are much faster, rendering times are much faster. People are used to layouts that change a bit in the first half-second of page load. It's not bad to not specify an image size, as long as you understand the layout of the page may shift during loading.
CSS is parsed before the page is loaded, so specifying the height & width in CSS will work just as well as specifying it inline.
One thing to keep in mind is that inline styles (and that includes height and width declarations) always trump CSS in specificity. If you specify heights and widths of images inline, you may have to go back through every page where an image is present if you want to adjust the size of the images.
Personally I'd suggest using CSS, as it keeps all your styles in the same place.
Yes, setting these properties in CSS will work just as well.
I don't know that it affects page rendering speed in any manner, however. The little effect it does have, is that layout that depends on the image will appear to jump around on the page until the image is loaded and allocates all the space it eventually will.
This is not a practice I follow myself.
A similar question has already been discussed and answered here:
Image width/height as an attribute or in CSS?
It should be defined inline. If you
are using the img tag, that image
should have semantic value to the
content, which is why the alt
attribute is required for validation.
If the image is to be part of the
layout or template, you should use a
tag other than the img tag and assign
the image as a CSS background to the
element. In this case, the image has
no semantic meaning and therefore
doesn't require the alt attribute. I'm
fairly certain that most screen
readers would not even know that a CSS
image exists.
This is also helpful:
If it's part of your site template,
I'd place it in the CSS file.
If it's just on one page, it should be
inline (or defined in a block of
page-specific CSS at the top).
I think the only difference is that css can (yeah it's possible!) not to be read, so <img> attributes are used.
But I'm not sure, I'm going to check that.
EDIT: http://www.mezzoblue.com/archives/2005/05/10/image_attrib/
While you can use CSS to clean up the layout, if your layout messes up by inability to load a single image you should fix that first.
Modern layouts should be controlled by divs and CSS, images in the layout should be supplied only in the form of a background-image:
The reason for always putting the dimensions into HTML code back in the day was due to loading times -- on a 14.4K modem, even relatively small image files would load noticably after the main HTML document had loaded.
These days this is much less of an issue. If it is an issue, it's worth noting that a CSS file will load after the main HTML document, so if you only specify your dimensions there you could potentially suffer the same problem, but CSS files are typically fairly small, so the effect should be minimised.
The other point is that old-school HTML design was very focused on layout, and image sizes were often a critical part of that - if the images were the wrong size, the layout of the whole page would often be completely wrong.
Modern page design approaches things very differently, putting minimal of any layout information into the HTML, and abstracting it all to the stylesheet. Therefore on a typical modern site, until the stylesheets have loaded, the site will just be a series of blocks, and be completely lacking in design. In fact, often the graphics themselves - not just their dimensions - are defined in the stylesheet.
So the answer is that to follow modern page design methods, you should put it in the stylesheet.
Obviously it's critical for most sites these days that the stylesheets load quickly, but it isn't just the size of the graphics that it'll affect.
I was wondering what is the better/faster way to resize an image.
Normally I would resize an image with CSS, but a college told me that by using the width attribute, e.g.
<img width="size" [..]>
the browser would render the page faster.
Anyone know if this is true?
It would be even faster if you resized the actual image, and not the dimensions you want the browser to render it to.
You should set width and height properties of each img tag. It speeds up rendering page because browser doesn't wait for css files and images loaded.
width and height are semantic in the case of imges and objects. They provide metadata for images so it is completely fine IMO to rely on those attributes in order to tell the user agent that it should presize the element to X dimensions prior to the image fully rendering.
If we stick with presentation vs. structure, I'd put your image sizes in CSS. Speed really doesn't matter these days, the browser has to wait for the images to be loaded anyway, so the speed it takes to compose and render the page isn't really measureable, well unless your CSS fails to load...
Bit difficult to give definitive answers for very general questions like this, but I think it’s generally better not to resize images in HTML or CSS — make the image file the right dimensions.
Ignoring that, I don’t think there’s likely to be any perceptible difference between the two.