Image Performance

Jan 22 2014, 5:47am CST | by

Image Performance

By Lara Swanson

Images make up the majority of most sites’ page weight. Thanks to their size and the number of image requests made by an average site, optimizing images is arguably the easiest big win when it comes to improving your site’s page load time.

Let’s start by looking at the various image types available, and then work through the various options you have for optimizing them.

Image File Types

You have a range of file types to choose from when creating images for your site. When generating an image, ask yourself:

* How compressed can this image be?
* How many colors are needed?
* Do I need transparency?/>/>

When you need transparency in your image, PNG is your best choice. GIFs also support transparency, but they tend to be much heavier than PNGs. PNG-8 contains a maximum of 256 colors within the image, and generally result in a smaller file size. If you have a small number of colors in your image, PNG-8 will likely be your best option of all image file types, thanks to its small size. While Photoshop supports exporting PNG-8 with binary transparency, it also supports creating PNG-24 images with partial transparency as well as millions of colors. This naturally results in a larger file size.

Use JPEG for photos and other images with tons of colors. JPEGs do not support transparency. JPEG is a lossy compressed file format, unlike PNGs, which are lossless. While you can use PNGs for photos, they will often be five to ten times larger in file size than JPEGs because they are lossless. Since you're aiming for the smallest file size to decrease page load time, and web images typically have more than 256 colors, it's no surprise that the majority of the images analyzed by HTTP Archive are JPEGs.

Optimizing Image Request Size

If you use Photoshop, test out a few different qualities and file types in the Save for Web workflow. You’re aiming for a happy medium of acceptable quality and small file size. Most people find that for JPEGs, 80-90% quality works well, but it’s important to play with the file size and see what level of compression is noticeable. Look for artifacts, inaccurate contrast between elements, and blurry details and text.

After you’ve exported the image, run it through a tool like ImageOptim, which finds the best compression technique for a variety of file types. There’s also SmushIt, which is an online lossless image optimizer. These tools can save you a ton of additional file size by finding ways to reduce the image size without visibly reducing the quality of the image.

Optimizing the Number of Image Requests

In addition to decreasing your images’ file sizes, it’s also important to decrease the number of image requests on the page to improve page load time. One way to do this is to combine images into sprites. Your page weight might increase slightly because you’ll have one large image file and additional CSS to position the site elements, but it’s likely that combining images into a sprite will be a huge win for page speed.

Another way to decrease image requests is to replace them with CSS3 gradients. CSS3 gradients (aka visuals):

* Can handle transparency
* Can be overlaid on a background color
* Eliminate an image request
* Are super easy to re-edit/>/>/>

CSS3 can be a great, performant replacement for images. Don’t worry about the extra page weight from the vendor-prefixes in CSS3 syntax; if you arent’ already, you should be using GZIP on your site, which will take care of optimizing this code. Even though you will be loading more CSS, it’ll still be a faster-loading option than an image request.

You can do some pretty amazing things with CSS3 gradients because of the control over where colors begin and end. That being said, be careful how your CSS affects repaint times, as there can be a cost to using a lot of CSS3. A repaint is an expensive operation performance-wise and can make your page look sluggish. If you find that your user interface does become sluggish, especially upon scrolling, you may have a CSS3 or JavaScript repaint issue and will want to diagnose what’s causing it using tools from JankFree.org.

Optimizing images is likely the biggest win for performance on your site. As you take a look at the images on your site, ask yourself:/>/>

* Can I save any file size by choosing a different image format?
* Have all of my images been run through a lossless compression tool?
* Can any of my image requests be replaced with gradients or sprites?
* Is there any UI slugishness that could be due to repaint times?/>/>/>

In the next post, we’ll cover optimizations you can make to the HTML and CSS of your site such as creating design patterns that can be repurposed, identifying the best naming patterns for your elements, and caching assets correctly.

Additional Resources

This post originally appeared on O’Reilly Programming (“Image Performance“). It’s republished with permission.

Source: Forbes Business

 
 

Don't miss ...

 

<a href="/latest_stories/all/all/30" rel="author">Forbes</a>
Forbes is among the most trusted resources for the world's business and investment leaders, providing them the uncompromising commentary, concise analysis, relevant tools and real-time reporting they need to succeed at work, profit from investing and have fun with the rewards of winning.

 

blog comments powered by Disqus

Latest stories

Climate change threatens global health security: UNEP
San Juan, Nov 1 (IANS/EFE) The rapid propagation in recent years of infectious diseases such as Malaria, Chikungunya and even Ebola is one more example of how climate change threatens global health security.
 
 
US-Japan joint rain radar mission to end next year
Washington, Nov 1 (IANS) After 17 years of groundbreaking 3-D images of rain and storms, the joint NASA and Japan Aerospace Exploration Agency Tropical Rainfall Measuring Mission (TRMM) will come to an end next year, the US space agency said in a statement.
 
 
Al Qaeda threatens to disrupt Australian fuel supplies
Sydney, Nov 1 (IANS) Al Qaeda has urged Islamic militants to attack oil tankers in maritime hotspots that supply Australia with up to 70 percent of its petrol, a media report said Saturday.
 
 
Insomnia triples risk of motor accident deaths
London, Nov 1 (IANS) Developing a healthy sleeping habit could be a life saviour as researchers have found that insomnia significantly increases risk of death caused by motor vehicle crashes and other unintentional fatal injuries.
 
 
 

Latest from the Network

Al Pacino considered name change
Al Pacino considered changing his name to ''Sonny Scott'' when he started acting. The 74-year-old star was advised to alter his moniker when he began working in the movie industry because any stars with an ''ethnic...
Read more on Movie Balla
 
How to increase your popularity on Twitter
London, Nov 1 (IANS) Having a large number of followers on Twitter is a more efficient strategy to gain popularity on the social networking site than increasing your number of tweets, said a study. Messages from...
Read more on Celebrity Balla
 
US-Japan joint rain radar mission to end next year
Washington, Nov 1 (IANS) After 17 years of groundbreaking 3-D images of rain and storms, the joint NASA and Japan Aerospace Exploration Agency Tropical Rainfall Measuring Mission (TRMM) will come to an end next year,...
Read more on Politics Balla
 
Sexist slur against Nikki Haley; media calls it only a 'gaffe'
Washington, Nov 1 (IANS) Reflecting the falling standard of US politics, the Democratic opponent of South Carolina's Indian-origin Governor Nikki Haley called her a "whore", but more shockingly the mainstream US media...
Read more on Politics Balla
 
Users Facing Wi-Fi Connectivity Issues in the New OS X Yosemite
The OS X Yosemite, the latest version of the operating system for Macs, might have been affected by a bug, as its users are continuing to be frustrated by the Wi-Fi connectivity issue.According to Apple Insider, the...
Read more on Apple Balla
 
Wear your sweatshirt right
Los Angeles, Nov 1 (IANS) A sweatshirt is a must-have item in your autumn-winter wardrobe. Mix it up with jeggings or team it up with hot pants to jazz up the look. Sweatshirts are not only comfortable and cosy, but...
Read more on Celebrity Balla
 
Undergo seaweed body wrap for a beautiful you
London, Nov 1 (IANS) Try seaweed body wraps in a spa for improved skin elasticity and reduction of cellulite. A seaweed wrap is typically made by combining seaweed with hot water and sometimes essential oils, clay and...
Read more on Celebrity Balla
 
When Jake Gyllenhaal went out with real nightcrawlers
Los Angeles, Nov 1 (IANS) Actor Jake Gyllenhaal, who features in "Nightcrawler", found it a "dangerous" experience to venture out in the dark to prepare for his role in the movie. But he found it to be exciting too!...
Read more on Celebrity Balla