i want to know about sprite technology used in css regarding fast accessing of the web pages.
They are cool because you can minimize http requests with them and make your page's performance improve. They are considered good in terms of SEO as well. Check out this for more info:
CSS Sprites: What They Are, Why They’re Cool, and How To Use Them
This page gives a pretty good overview.
Essentially it puts all of the page's images into one large image file and then uses CSS to display only parts of that file (to give the effect of multiple images). This has the advantage of only requiring the browser to make one request for all the images rather than a bunch of individual requests (each of which has an overhead).
If you have the group of icons for example , you are creating one jpg or png file and adding the images one after another. Then you just creating the backgrounds based on only one image and fixing it in percentage / pixels view. It makes your code organized and saves images loading time . For example , you have a window and it has close , unfold icon. You can create a png file named windowControlSprite.png that contains two icons one after another , then you can create properties in your css to this element. #somediv {background-position:0px -20px;}
Also, you can find CSS sprite X and Y easily with tools like http://www.getspritexy.com/
Otherwise you need to use image editors like Photoshop or use Firebug to find X and Y coordinates.
Related
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.
1) First, should I order the images in my spritesheet a certain way?(like biggest to smallest images, or images that appear at the top of the page to bottom of the page?)
2) Say I have a css spritesheet that contains before and after images. Like the image shows a cow, but when the image is hovered, it shows a cow with wings. Is it in my best interest to not use css spritesheet for that then? Does the css load all the pictures in my spritesheet at once?
3) Is a spritesheet better in terms of caching? Unrelated, but what does it take for a browser to cache something? I mean if it's only after a single page view, perhaps it's not worth it.
4) Lastly, I want to start a forum. I don't know anything about forums yet, but I plan to start one soon. I'm thinking of just having like a default set of 40 images that people can only choose from as their avatars. Should I even make a spritesheet for those images (if it's even possible)?
I know this is a lot of questions, so please answer any that you have knowledge of. Thanks!
A 'spritesheet' is just one large image. So...
1) Doesn't matter.
2) Again, it's just one image. If not all users will want to activate the 'after' feature, then you can save them some bandwidth my making the afters a separate sprite. If most people will want to use the after feature, then you can save them bandwidth by making it all one sprite. (Though note if we're talking really large images, there will be a practical limit to how much you want to stick into one sprite. No one is going to wait to download 1mb file, for instance).
3) Again, a sprite is just an image. It has the same caching pros/cons as any image.
4) 40 hits on the server is a lot compared to 1 sprite. So, based solely on that, a sprite would be useful. But if it's rare that you'll get more than 10 or so of those avatars on one page, then the sprite would be a detriment, as it's loading such a large file.
Just on the ordering of images, I have a sprite file for a site I’m working on that contains various browser logos with version numbers added to them. As such, there’s quite a lot of repetition in visual information in the file.
I was quite surprised to find that the direction of the repetition could have a big effect over the file size I could achieve for the image when saving as a PNG. When I had similar logos in columns, the file came out at about 120 KB; whilst when I arranged them as rows, it came out at 41 KB.
Once the project’s live I’ll post the actual images. It’s probably quite rare to have such similar images repeated in a sprite file; normally your images would be different, or you’d just use the same image repeatedly. (Indeed, I might end up refactoring my sprites so that the varying bits are in their own file.) But I hadn’t realised that such supposedly similar images could be encoded in two files of such varying sizes, purely based on the geometric arrangement of the elements in the image file.
1) Not sure, but I don't think it would matter much, if at all.
2) The best way to do this is with CSS image rollovers.
3) Spritesheets would be better for caching, since it's only a single image, instead of the web server having to connect, send an image, disconnect, send again, send another image, disconnect, etc...
4) I would just use single images. There's really no reason to use a spritesheet in that situation.
Is there any application to merge small images into a single one in a web application in order to make less HTTP request and have the page load faster?
GWT does this automatically and makes proper images + CSS styles to show those images. When I have a plain HTML + CSS is there a helper application which given HTML + CSS + a bunch of small images, outputs a proper HTML + CSS + Single Image?
See for example this Google image.
The technique you're looking for is called CSS sprites (take note of this name the next time you talk about it).
Although what you're asking for (give them your code, get back same code with sprites applied) is a little too much, some online generators do come close - they will automatically calculate the most optimal image placement and give you the CSS needed for this. Googling for CSS Sprite Generator gets back some very good ones, like http://spritegen.website-performance.org/.
You should note that these generators are not perfect, and for static sites you will need to do this ever ytime you want to tweak the graphics on the site.
You could give SpriteMe a try
Has anyone seen tooling, or even a process concept to generate css sprites from an existing website's images, and css during the build process?
I should think the steps would be:
walk an images directory
create a single sprite file from all the images in that directory
for each image
find any css classes using that image
update the css class to use the new sprite file
I'll using asp.net so something in msbuild would be awesome. However, I'm finding little out there even coming close.
You could use this http://spritegen.website-performance.org/ which is BSD licensed code. (see the download link on the right hand side.)
An automatic process like that only works well if you have a few simple images. There are several reasons to do the process manually:
Some image formats work better than others for sprites. If you try to make sprites out of JPEG images the compression will easily bleed from one image to another causing artifacts. Index color formats like GIF and 8-bit PNG has a limited number of colors, so if you put images with too varying color palettes together you will lose colors.
You may want to repeat an image horisontally or vertically, which makes it harder to combine the sprite image.
If the image is smaller than the element that you use it in, you would have to pad the image with transparent pixels. If the size of the element is dynamic in any way, the automatic process would not even know how much padding the image would need.
Is the only benefit of using css image sprites that there is less http requests?
Or is there other benefits?
Also is there an easy way of detiming which area of a sprite to show?
Like you said, one of the main advantage is to reduce the number of requests to the server, improving the response time (especially if you're loading a large amount of small images). But this is not the only reasons people use sprites.
If you don't use sprites for a "mouse over" display, the user will see the image disappear for a second... and it looks really bad. This is because if you change the image instead of just moving the sprite around it will load a new image and the loading time can be visible to the end user.
.bad{
background:url(abc.jpg);
}
.bad:hover{
background:url(abcHover.jpg);
}
.good{
background:url(abc.jpg) 0px 0px;
}
.good:hover{
background-position:15px 0px;
}
Another advantage of sprites is that you can keep all your images in one location and in some cases it makes more sense (for menus and so on).
To determine which area of a sprite to show, just use photoshop or any other image editing software.
The primary benefit is your pages load faster, mainly because of reduced HTTP requests.
You could generate your sprite using a tool.
Disclaimer - I wrote this tool.
It is much easier to get image placement (especially next to text) the same cross-browser. You can adjust images up/down/left/right with out using vertical-align and padding.
I find it easier to keep track of all the images if they are in a single file. Especially since I usually have a transparent png images and and then use gif images for ie6. I save my png sprite map as a gif and add one line with background-image in my ie6 css and my images are switched.
I use photoshop or gimp to get approximate locations in the sprite map and then use firefox to fine-tune the placement.
Yes, there is another benefit. Every image file has his own headers, describing image type, colors etc. So when you combine images to a single sprite, you win some kb.
But as you said before, mostly you win by reducing HTTP requests count.
In terms of determining the area to show, I will typically place my elements on pixels that are multiples of 100. So if there's a sprite with a bunch of 64x64 pixel icons, I'll typically have them at (0, 100), (0, 200), (0, 300), etc.
This way, I don't have to type in an exact measurement (or any other developer for that matter) and save keystrokes when setting all my background-position properties.