mod_pagespeed does this nifty image-resizing, but only if "width= and height= attributes on the tag or an inline style= attribute" are set. This gets a bit problematic if you have e.g. an image blog with hundreds of posts and one day in the future might want to change the stylesheet, resulting in a new width for images.
So, is there a way to get both mod_pagespeed image-resizing and be able to specify the image width in a stylesheet? The insert_image_dimensions flag to mod_pagespeed isn't really helpful, since I can't specify image height, resulting in oddly stretched images.
The blog is running Wordpress, so perhaps there's some Wordpress-specific solution.
No, there is no support for cascading CSS styles into the page in mod_pagespeed. This is a really tricky rewriter to implement, since by definition it would require implementing a full cascade model + block the output of HTML on CSS processing. That's not to say it's impossible...
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I am a newby to design and looking now into the use of background instead of foreground images, which is a common practice.
I look at the techniques used, and see that:
you usually need to explicitly state the dimensions of the image (and set the foreground element to these dimensions)
you need to make the foreground element to somehow disappear with css tricks.
All this looks really hackish. So, I wonder, why on earth do all this instead of just using the native element? I am sure there is a good answer
(I did go through this When to use IMG vs. CSS background-image? , and could not figure out a clear answer)
One thing to consider as a benefit to using CSS for images is that you can load all your design images (images for UI elements, etc) with one http request rather than an http request for each individual image using a sprite. One large image that contains a grid of all your images.
As its been stated before, content images should use the img tag which also helps for people using various accessibility options when visiting your site/app. For example, if they are using a screenreader, the screenreader knows its an image and can read the img alt name or title, but if its just a div with a background image they get nothing.
The main difference is that in the img tag the image is hardcoded.
With CSS you can create different designs, switch between them, redesign the page, without altering the source code. To see the power of CSS, check http://www.csszengarden.com/, all the pages use the same HTML source, but with different CSS layout.
As #Shmiddty noted, if img is for embedded images (actual content, for example a gallery, or a picture for an article), and CSS is for design.
Also, the question you referred to, has nice list of all the use-cases: When to use CSS background-image.
The goal is to separate content from presentation. HTML should contain just content, and all presentation should be moved to the CSS. Once you achieve that, you gain a few useful side effects:
The CSS (presentational code) is cached by the user's browser, and each HTML file requested is smaller. This also has some SEO benefits (decreased code fluff).
Screen readers have to muddle through less when interpreting your page for visually impaired users. Making sure your HTML contains just content means visually impaired users reach what they're looking for much quicker.
CSS makes it possible to display the same content in different visual configurations, which is the cornerstone of the responsive web design movement. Properly delineating your content and presentation means being able to use the same HTML files across multiple platforms (desktop, tablet, smartphone).
However, there are times when images are content on a specific page. In those cases, you want to use an IMG tag, and moving the image to the CSS is actually a wrong move. A great discussion of when and where to use text to image replacement is at When to use IMG vs. CSS background-image? Basically, my personal litmus test is something like: Is this image going to be used multiple times on the site? If it is, it's probably part of the design. Once-off images are generally content.
If you're looking to move your design images to the CSS, congratulations :-p You've adopted a healthy amount of work, but started doing something worthwhile to the long-term health of your website as part of the web ecosystem. I would highly recommend looking into using the SASS/Compass system to manage your design images as sprites (see A List Apart:CSS Sprites and Spriting with Compass).
One of the main points of image replacement is to use your site title in a h1 tag for good SEO, and then hiding the text and replacing it with a custom logo.
This also makes your site more accessible. Say for example, your user has CSS disabled for whatever reason (screenreaders, maybe). They would still see the textual representation of your site title, whereas normal users would see the custom graphic.
I've been playing around with WordPress. As a programmer, the media library seems a little strange to me - but I'm keen to understand how I can achieve what I need with the framework. Cue WordPress enthusiasts...
I need to force my WordPress post images to be a certain size. I'm not talking about the thumbnail size, which I've found can be easily manipulated within the loop, but the images that actually get inserted into a post, amongst the writing and the other media. I have a fixed content width, and I would like the images to reflect that width (uncropped).
Obviously, I could run some sort of Regular Expression that could identify the image tags, and replace them with new sizes, but is there really no other way of forcing image sizes within the post while retaining there position amongst the formatted writing that comes with it?
So far, I'm guessing that there is a CSS property out there that is used by WordPress in all images. At a push, I'm willing to go with this - whatever it may be (answer needed). But I was hoping that their might be some more involved code (perhaps something I could plop into the functions.php file) which could actually force any inserted post images to be a certain width.
Any thoughts on this would be much appreciated.
If that's only about limiting the max width of an image and prevent an image from overflow, you could use the $content_width variable in your theme:
https://wordpress.stackexchange.com/questions/6499/how-to-create-a-conditional-content-width-for-a-wordpress-theme
I am a hobbyist webdesigner, use html and CSS for testing various website designs. However one particular thing that always confuse me is the decision to make use of image as tag or to use it as background via css or html.
Is their any rule of thumb for this ?
As one of the answers pointed out, you need to make the difference between content and actual page style.
Let me elaborate on that. The purpose of the background-image property is used to define the look of a certain block of your page, be it a div or a p, the key point to take home is that you're defining the page's look. And images in the context of defining the page's design (be that patterns, logos, gradients etc.) should almost never take the explicit form of an img tag. That tag is used to define content images, something linked to the news at hand - something that is unique to a story you're trying to portray.
It's very crucial to differentiate these two concepts because it'll allow you to contemplate a good design independent of the underlying content - as it should be. Uniformal, elegant and precise.
So, in review. Use background-image to define the look of the various blocks that comprise your website and use the classic img tag when you want to add visual content that is context-specific.
The question is it Content or Styling is a good place to draw the line on images.
Will this image be reused? etc.
Do you want the image be part of the document flow, give descriptions to the search engines (alt-text)? Use the img tag.
If you want to place other elements over the image (like text, copyright info), use a background image. You can even combine it by placing an image with transparency over the background image to get some effect.
Furthermore a lot of examples exist where the positioning of background images is used to get performance benefits ("sprites").
In other topics I've found that IE/FF doesn't print background images by default. Now that's a shame, because background images add some possibilities that are very difficult to reproduce with classical <img> tags:
You can align them both horizontally and vertically
You can crop them if they are larger than the target element (which also enables the idea of CSS sprites)
Now, it's not impossible to do, but it will require me to have different HTML layouts for printing and normal page, and the printing layout will be quite overcomplicated (since I'll have to use <table>s to achieve vertical alignment). Also, the benefits of CSS sprites will be lost.
Is there any hope? I gather that #media print doesn't help, but isn't there something else, maybe browser-specific, that would allow one to say: "Yes, this isn't a normal background, it really needs to be there even in print view"?
Not possible. You would have to some how convert your background images to img or use Canvas. Of course using canvas depends on which IE you supporting.
Its a browser setting which restricts the printing of background images. I think the logic behind it was that the vendors wanted to give the users the option of printing background images and ensure that the web developer could not alter these settings through some sort of script.
As a general rule, background images should be reserved for adding to the page design but aren't essential to understanding the content. Therefore it shouldn't matter if they are missing when the page is printed. If something (such as a product shot) is important, then it should be included as an actual image (which has the added bonus of being more accessible).
Could you look at including the image, then hiding it using CSS and duplicating is as a background image (perhaps dynamically using JS)? That way, you can ensure the image itself shows in your print stylesheet, and you get the benefits that having a background image brings. I've created a very simple example here.
I've observed that often the websites use only one background image which contains multiple images on it. For example, instead of using separately icons, all of the icons are put on one image and then the different parts of image are used in different section.
Is there any advantage to this?
How can this be used?
For example, for the following Stack Overflow sprite, how would I display just one of the images?
The technique is called CSS Sprites. Basically you use CSS's background-position property and fixed height or width for your element.
If your elemnts are fixed width and fixed height at the same time you can freely create a more compact image. See this site for more complex examples.
You are talking about CSS sprites, in which the background position changes on hover. Learn more here:
http://css-tricks.com/css-sprites/
Change the css property background-position.
yes , using sprites is good for website performs because every single component on website send different http request .So, when we use sprites images the http request become less & website performance increase.That rule is also apply on css also less css files less http request. you can yourself with the help of safari web inspector.
for more better performance download "yslow"
And with CSS sprites is also possible to make e.g. menu button hover effect without waiting until second image loads. see
It has the advantage that only one image needs to be loaded so that things like hover (roll-over) effects are faster. The technique is usually called "CSS sprites". Google for it.
It has been common for a while to put two images on one sprite sheet, but the tendency has been moving towards combining ALL of your background images on the same sprite sheet to load just one file for all of them. There's a rather good tutorial here.