How to Optimize Web Images for the Best User Experience
While it’s easy enough to remember Google’s biggest algorithm changes in recent years and the far-reaching effects of each, you may not realize that Google’s famous proprietary algorithm changes hundreds of times per year.
Taking time to optimize images is a win-win for both SEO and user experience. As with every other aspect of web design, image optimization is partly intuitive, partly data-driven best practice, and overall A/B-testable. Web designers should follow these five image optimization best practices:
1. Move image optimization into the initial design phase of the project.
Making decisions about size, complexity, and selection of images at this stage can help ensure that pages aren’t overly “heavy” when they launch.
For example, while not specifically an “image” optimization, the use of a large number of web fonts can add greatly to page load time as browsers load these assets. For an optimal UX, limit your selection of web fonts.
2. Select the appropriate file format for the type of image you have.
The number one mistake designers and developers make is using either the wrong or the same image format for every image on a site. Follow these suggestions to determine the correct format for a given image:
- Photographs should almost always be JPEG files, as should other complex images with thousands (or millions) of colors, subtle color gradations, and no need for image transparency.
- Vector images with minimal complexity are often best served as SVG (Scalable Vector Graphics), which offers the bonus of being able to scale images for desktop, tablet, mobile, and retina displays with no loss of quality using a single web asset.
- Logos, illustrations, icons, and similar images that have fewer than 256 colors are typically best optimized in GIF, as long as they require only mask-based transparency.
- The versatile PNG format is necessary for images that require alpha transparency and layering. PNG files tend to be larger than the other formats, depending on how well they are optimized.
- Simple motion without sound — and smaller than a few hundred pixels in height and width — are often best produced as an animated GIF rather than a video file.
- A large library of vector-based icons that change infrequently may be best served as a CSS2 web font in a format such as TTF/OTF or WOFF.
3. Optimize images by eye.
Once you’ve chosen the appropriate format, eyeball it to make sure that the image is as compressed as possible without sacrificing quality.
JPEG files employ lossy compression, which means that you must balance quality and file size when optimizing. The difference between a “maximum” 100 percent quality JPEG and a “low-quality” 30 percent JPEG can be astounding. Try taking the quality down low and then dialing it up 10 percent at a time until you reach an acceptable level. Be sure to double-check against the original asset for a final test.
To optimize GIF files by eye, use the minimum number of colors necessary to display your image and test different color palette sizes for quality. The difference between a 16-color GIF and a 256-color GIF can be many kilobytes. Depending on the image, you may be able to reduce the palette a bit further to save space.
When optimizing PNG files, try to use PNG-8 formats wherever possible. These limit you to a 256-color palette, but with the benefit of a significantly smaller file size than a PNG-24 file. Recent tools, such as ImageAlpha, optimize alpha transparency in PNG-8 images, in part by converting them to PNG-8 images that include alpha transparency.
In addition to your typical design tools, ImageOptim is an exceptional application for optimizing PNG, GIF, and JPEG images. Using this tool can easily cut your total image load time in half.
4. Determine what’s best for your website.
Every website, scenario, and audience is different, so there isn’t a specific number that your images should add up to.
Having said that, use images under 200KB when possible — smaller file size is always better! Try to get your total page weight well under 1 megabyte.
5. Give those images meaningful names.
Even though we are primarily talking about file size optimization for images, don’t forget the basics. Website images named “red-shiny-car-part.jpg” contain more SEO information than “image1.jpg.”
Effective image optimization looks like a high-performing, quick-loading, mobile-responsive user experience. Other than that, it depends on the site. Engaging, compelling websites like Wolf-Gordon, Bryan Cave, and Winston & Strawnmake use of optimized images throughout for an exceptional UX. While great image optimization impacts site performance and factors in SEO, most companies are most concerned with making a positive impression on their visitors. As with any first impression, the most appealing experiences starts with optimal imagery.
Jaron Rubenstein is the founder and president of Rubenstein Technology Group. His experience, deep technical expertise, and passion for design empowers creative partners to identify opportunities, manage complex projects, and maintain the integrity of their work from concept through launch. Rubenstein Technology Group is the leading technology partner for top creative firms. Brands ranging from Bloomberg to Edgewell to Nizuc have benefited from his design-led engineering focus on empowering user experience.
This article originally appeared in HOW.