Image Compression Guide — How to Reduce Photo Size Without Losing Quality

Large image files slow down websites, fill up storage, and frustrate users. This guide explains how image compression works, the difference between the most common formats, and how to choose quality settings that shrink your photos while keeping them visually sharp.

What is image compression?

Image compression is the process of reducing the number of bytes needed to store a picture. Compression algorithms look for redundant or visually unimportant information inside the image data and remove or simplify it. The result is a file that looks almost identical to the original but takes up a fraction of the disk space and bandwidth. Compression is what makes it practical to share high-resolution photos over slow mobile networks and to display rich image galleries on a web page that still loads in under a second.

Lossy vs. lossless compression

There are two broad families of compression. Lossless compression preserves every single pixel exactly as it was captured; the decompressed image is byte-for-byte identical to the original. PNG uses lossless compression, which is why it is the preferred format for graphics, screenshots and logos where crisp edges matter. Lossy compression, used by JPEG and most WEBP outputs, permanently discards detail that the human eye is unlikely to notice — subtle colour gradients, fine texture in flat areas, high-frequency noise. In exchange, lossy files can be ten to twenty times smaller than the originals with no visible difference on a normal screen.

Understanding quality settings

When you pick a quality value between 1 and 100 for a JPEG, you are telling the encoder how aggressively it may discard visual information. A quality of 90 or above produces files that are virtually indistinguishable from the source and are ideal for portfolio photography and printed materials. A quality around 70 to 80 is the sweet spot for the web: file sizes drop dramatically while artefacts stay invisible to the casual viewer. Values below 60 start to introduce visible blockiness and banding, so they are best reserved for thumbnails or preview images where size matters more than fidelity.

Choosing the right format

Each format has a purpose. JPEG is the universal choice for photographs and natural scenes with smooth colour transitions; it offers an excellent size-to-quality ratio and is supported everywhere. PNG supports transparency and lossless detail, making it perfect for logos, icons and UI screenshots. WEBP combines the strengths of both, often producing files 25 to 35 percent smaller than equivalent JPEGs or PNGs, although older browsers may not support every variant. PhotoShrinker exports optimised JPEGs by default because that format delivers the most reliable quality-to-size balance for everyday photos shared online.

Why browser-side compression matters

Traditional online compressors upload your photos to a remote server, process them, and send them back. That round trip is slow, consumes mobile data, and — most importantly — means your private images leave your device. PhotoShrinker performs every step of compression directly in your browser using Web Workers, so your photos never touch a server. The processing is faster, completely private, and works without an account or an internet connection once the page has loaded.