Image Compressor and Converter

Lossy and lossless compression

Image files are compressed in one of two ways. Lossy compression (JPEG, and WebP or AVIF in lossy mode) throws away detail that is hard to see, which makes files much smaller; the quality setting decides how much is thrown away. Lossless compression (PNG, and WebP in lossless mode) keeps every pixel exactly, so files are larger but text and sharp edges stay crisp.

MDN’s advice is a good rule of thumb: photographs and other continuous-tone images usually tolerate lossy compression, while screenshots, diagrams, logos and line art are better lossless, because blurring and coloured fringes around text are easy to see.

Format	Compression	Transparency	Good for
JPEG	Lossy	No	Photos
PNG	Lossless	Yes	Screenshots, logos, graphics with text
WebP	Lossy or lossless	Yes	Photos and graphics on websites
AVIF	Lossy or lossless	Yes	Photos, in browsers that support it

web.dev says WebP and AVIF generally compress better than the older formats and should be used where possible. If your website platform cannot serve WebP, a well-compressed JPEG is still a good choice for photos.

Resize before you compress

The biggest saving often comes from the dimensions, not the quality. A 4000 × 3000 pixel photo from a phone has 12 million pixels; the same photo at 1600 × 1200 has 1.92 million, 16% as many. If a page only ever shows the image 800 pixels wide, the extra pixels are downloaded and thrown away. Google’s Lighthouse audit flags images that are larger than the size they are shown at, and says a page should ideally never serve an image larger than the version rendered on screen.

To choose a maximum width, find the largest size the image appears at on your site and allow for high-density screens: web.dev explains that doubling a screen’s resolution quadruples the number of pixels. Then set Fit within a maximum width and height and the tool shrinks larger images while keeping their proportions. It never enlarges an image.

How to read the results

• Original → new size and the percentage smaller are shown for each image, and the total for the batch at the top.
• Original kept means that re-saving the image in the same format and size would have made it larger, so your original file is offered unchanged. Untick the option in the settings if you would rather have the re-encoded file.
• Larger than the original appears when a conversion or setting increased the size, for example turning a small JPEG into a PNG. Try a lower quality or another format.
• Compare opens a before-and-after slider. Tick Show at actual size to look closely at faces, text and gradients, where compression artefacts show first.

Metadata and privacy

Photos from phones and cameras often carry EXIF metadata, and Apple explains that iPhone photos can include the coordinates of where they were taken. This tool draws each image again from its pixels, so new files do not include that metadata. That is useful before you publish photos online, but it also removes details you may want to keep, such as the date taken and copyright notes, so keep your originals.

Next steps

Once your images are smaller, run your pages through the website speed test to see what else slows them down. To crop or straighten a photo first, use the photo editor; for profile pictures, covers and adverts, the social media image resizer gives you each platform’s sizes. If you would like a website that handles all of this for you, see our website design and development service.