I have never thought of this before, but am really curious. So here is the html:
<img src="/employees/img/uploads/users/2013-09-12-115644edif.jpg" alt="Employee" class="user_img" />
and here is the css:
.user_img{
width: auto;
max-height: 200px;}
The original picture is like 1.5 MB in size, so after the css is applied, the visual size of it really decreases. What I wonder is if user's browser needs to load the full sized picture in this case, or will it only load the small one?
CSS is applied by the user's web browser, which is running on their local PC. After the web browser downloads the image, it only then applies the CSS scaling to display it smaller than the actual image size.
As a result, the answer is no. The user must download the entire file, even if CSS is used to resize it smaller.
To make the image smaller before sending, you can use a server-side language such as PHP, and generate a thumbnail of the image that is the appropriate final display size. This not only will make your page load faster, but will reduce bandwidth requirements as well.
The scaling via CSS happens when the browser is rendering the page, AFTER it has downloaded the full image, so no.
HTML, CSS and JavaScript are client-side languages. Everything is transfered to the client and then the transformations are made.
If you want to reduce the size of the image before sending it to the client, you must use a server-side language such as PHP.
The fact that you resize the picture (scale it down) doesn't affect the image 'physical' size. Otherwise everyone would use css sizing as 'file' resizing technique.
No, CSS only scales your picture down(or up), but size of file is never changed.
Related
I need to implement image previews via thumbnails. Now I'm not certain how to implement it.
One option would be to do it straight with CSS, so something like this:
.thumbnail {
background-image: url(path/to/image);
background-size: 300px, 400px;
}
Is that practical? Are there any performance issues?
If you scale image in CSS to be smaller than it it actually is, browser still have to download the same amount of data. You should create separate file with the thumbnail.
With images, you need to focus on three things: size, format and the src attribute.
Image size
Oversized images take longer to load, so it’s important that you keep your images as small as possible. Use image editing tools to:
Crop your images to the correct size. For instance, if your page is 570px wide, resize the image to that width. Don’t just upload a 2000px-wide image and set the width parameter (width=”570”). This slows your page load time and creates a bad user experience.
Reduce color depth to the lowest acceptable level.
Remove image comments.
Image format
JPEG is your best option.
PNG is also good, though older browsers may not fully support it.
GIFs should only be used for small or simple graphics (less than 10×10 pixels, or a color palette of 3 or fewer colors) and for animated images.
Do not use BMPs or TIFFs.
Src attribute
Once you’ve got the size and format right, make sure the code is right too. In particular, avoid empty image src codes.
In HTML, the code for an image includes this:
When there’s no source in the quotation marks, the browser makes a request to the directory of the page or to the actual page itself. This can add unnecessary traffic to your servers and even corrupt user data.
Pro Tip: Take time to re-size your images before uploading them. And always include the src attribute with a valid URL.
To ensure your images load quickly, consider adding the WP Smush.it plugin to your website.
from: http://blog.crazyegg.com/2013/12/11/speed-up-your-website/
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.
A website that I'm currently working on has a number of slideshows. The issue is that the page loads and then the slideshow loads a second later. How do I improve loading speeds of the images? The site is hosted on Amazon. The url is http://gatehouse75.com to see what I mean.
There are a few ways you can do this:
Optimise image sizes. For example, images used on the front banner are 1920x1610. However, most screens are not that large. Use different sizes based on view port (screen size).
Reduce image sizes by changing compression and/or using a different format.
Preload images when the users visit certain parts of the site. That way when users get to a page with a gallery the images get served from the browser cache.
Finally, you can put a "loading" notice while images load if none of the above suggestions help. This is good for usability.
Convert your jpgs to lower quality and your logo (in png) to gif in grayscale. This should save a lot of space.
Right now the home page slideshow images are scaled to 1349 X 429 for me. I am using a laptop. The actual size of the images on the server is 1920 X 610 (at least the one that I inspected). This means two things: (1)The image served is a larger filesize than need be which takes bandwidth, and (2)that the served image needs to get scaled down which takes client time.
What is the max width for this slideshow? It is a fullscreen slideshow, so I understand why the chose to use the bigger image. Though maybe you can take the original compress and resize in a way that is acceptable?
You can also consider having a loading .gif in place while the content loads.
Also, go through and minify linked files... css, js.
1. Follow image file optimization best practices.
2. Use a fast CDN combined with a smart caching strategy.
3. Put your above-the-fold image refs (especially large "hero" images) in an inline stylesheet, immediately inside the <head> tag, in the html element selector, like this:
<head>
<style> html { background: url(/hero.jpg) no-repeat -9999px -9999px; }
</style>
This will get you the fastest time-to-visible for the images that impact perceived page speed the most.
I just started using the chrome developer tools for some basic html websites and I used the audit tool.
I had two identical images, one with the height and width attribute, and one without. On the Resources section, both the latency and the download time were identical. However, the Audit showed
Specify image dimensions (1)
A width and height should be specified for all images in order to speed up page display.
Does this actually help? And are there any other ways to speed up page time?
This is only a splash page for the website I am building and as such it is only html, no css or javascript or anything. I have already compressed the images but I want to speed up load time even more. Is there a way?
Generally speaking: If you specify the image dimensions in the <img> tag, the browser will know how much space to allot for it and will proceed to render the rest of the page while simultaneously downloading the image. Otherwise, the browser will have to wait a few more milliseconds to get the size of the image from the image itself before rendering the rest of the page.
Since you have only a splash page, I doubt that there will be anything else for the browser to render, so it doesn't much matter whether you specify dimensions or not.
If I have a logo image, and I want to use it on another page where I require it to be a smaller size, it is my instinct to create a new image, resized with a graphics editor. However, I am hearing that it is better for the user if I instead refer to the original image and resize it with the browser by changing the height and width in the image tag.
So I ask the crowd, what is the best practice here?
Thank you for your time,
-- Henry
My default response would be "Resize it in a graphics application", but it depends on how you're using it.
When you leave image resizing to the browser, the original (full-size) image has to be downloaded before the browser can display it at a smaller scale. This means that you use more bandwidth and your webpage takes longer to load. However, if you mainly use the larger image throughout your site, then it will be faster to always use this image, since the browser can cache it.
If you're concerned about image quality, you would get better results and would have more control over the downsampling process using a dedicated graphics application to resize the image.
It's fine to resize images with CSS or the height and width tags. The only thing you want to be careful of is making really large images small because it obviously doesn't decrease the download size.
Doing this would work best when you're effectively caching your images so it doesn't get downloaded a second time. Then you will be getting a tangible benefit from doing so. I usually just append the last modified time of the image to the URL, eg:
<img src="/images/log.png?1233454568">
and then set the Expires header to a year from now. If the image changes, the mtime changes and it will force the browser to reload it.
That's suggested for images, Javascript and CSS files.
If the browser resizes the image for you by using height/width tag, you might end with a lesser quality image, really depends on the image type (like photo vs. simple graphics), so try it out in some common browsers. But resizing the image in a graphics editor is the only way to ensure a high-quality resize operation.
Create the smaller image in a graphics editor, for several reasons:
If users have not already cached the larger image, they will be downloading the larger file unnecessarily.
Resizing the image client-side results in some unpredictable scaling quality.
Doing it in HTML is ill-advised anyway, for presentational issues (such as element sizes) you should do it via CSS.