Image compression and WebP conversion

What Is Image Compression and Why It Matters for Site Speed

Image compression is the process of reducing file size while keeping the image looking the way it should to the human eye. There are two types: lossless, where data is simply packed more efficiently, and lossy, where details the human eye is least likely to notice are discarded. For photos on a website, lossy compression is almost always the better choice, since it produces a file many times smaller with a difference few people notice.

A large image is the most common culprit for a slow site. A 4 MB hero image can delay content display by several seconds, especially on mobile internet. Google measures this through Core Web Vitals, primarily LCP (Largest Contentful Paint), and that metric affects both your search ranking and whether a visitor will even wait to see the page.

Compression tools work in two ways: they reduce image dimensions (width and height in pixels) and they reduce encoding quality. Both are necessary. A 4000 px wide image displayed at 800 px is pure waste, no matter how well it is compressed.

How to Compress Images for Your Website Without Losing Quality

The process is simple and requires no tool expertise:

1. Choose a width that matches where the image is displayed. For large banner images up to 1920 px, for in-text images 800 to 1200 px, for thumbnails 300 to 600 px.
2. Set quality to around 80 percent. That is the point where savings are large and the difference is invisible.
3. Choose a format: WebP for broad support, AVIF when you want the smallest file.
4. Download the file and compare it with the original at 100 percent zoom, especially on areas with text and sharp edges.

A practical trick: if an image contains a lot of text, thin lines, or a logo, lower the quality more carefully or use lossless compression. Photos with natural detail tolerate more aggressive compression without visible artifacts.

WebP or AVIF: Which Format to Choose

WebP is the safe choice today. All modern browsers support it, it is smaller than JPEG at the same visual quality, and it supports transparency. AVIF goes a step further and often produces an even smaller file, but on some older devices and browsers it may fail to display or decode more slowly.

A practical rule: use WebP as your base format, and AVIF where your priority is the smallest possible page weight and where you have a fallback. If you do not want to think about compatibility, WebP is enough for the vast majority of websites.

Expert tip: do not convert an already compressed WebP to AVIF and back. Every new lossy conversion adds artifacts. Always start from the original or from the highest-quality saved file.

Most Common Image Compression Mistakes

• Lowering quality before reducing dimensions. First scale the image to the required width, then compress it. The reverse order gives a worse result.
• The same quality for every image. Portraits and product shots need more detail than background images and illustrations.
• A forgotten srcset. One large image for all screens is a miss. Offer multiple widths and let the browser choose.
• Compressing logos in a lossy format. For graphics with sharp edges, SVG or PNG is better.
• Ignoring cache and CDN. The best compression does not help if the image is downloaded again every time a page is opened.

Expert tip: check the result in a performance measurement tool, not just by eye. Sometimes an image looks good but is still heavy because its dimensions remained too large.

If you have hundreds or thousands of images, manual compression becomes tedious. That is where automation within the build process or CMS helps, and EVI Solutions can help when the problem is bigger than a single tool.