Compress images without wrecking them

Why your photos are so much bigger than they need to be

A picture straight out of a phone is built for a future you might never need. Twelve megapixels, full colour depth, and enough detail to print it a metre wide. Then it goes into a web page where it will be shown four hundred pixels across, or into a form that only ever displays it as a thumbnail. Everything past that point is weight with no purpose.

This is why capping the longest edge often does more than any quality setting. Cutting a photo from 4000 pixels wide to 1600 removes about eighty four percent of the pixels before a single detail is thrown away, and on screen the two look identical. Squeezing quality on top of that is a second, smaller saving rather than the main event.

The part people get wrong

Most people reach straight for the quality slider and drag it to the floor. That is the one move guaranteed to produce the mottled, watery patches that make a photo look cheap. Resize first, compress gently second, and the same file size arrives with a far better picture attached.

What quality really controls

JPEG and WebP both work by grouping pixels into blocks and describing each block approximately rather than exactly. The quality number decides how rough that approximation is allowed to be. High numbers keep fine variation, low numbers flatten it.

Detail hides the damage. Grass, brick, hair and foliage stay convincing at settings that would ruin a plain wall, because your eye has too much going on to notice a little imprecision. Smooth areas are where compression shows itself, which is why skies, skin, studio backdrops and flat brand colours are the first places to check.

Seventy eight is the default here because it clears the limits most forms impose while leaving photographs looking like photographs. If you are unsure, run your most difficult picture at two settings and compare. That takes twenty seconds and beats guessing.

Picking the right format

JPEG

The safe choice. Every browser, every email client, every upload form and every ancient piece of government software opens a JPEG without complaint. It cannot store transparency, so anything see through comes out white. For ordinary photographs it remains an excellent option.

WebP

Typically twenty five to thirty percent smaller than a JPEG of the same visual quality, and it keeps transparent backgrounds. Every current browser supports it. The catch is older desktop software and the occasional submission portal that still refuses anything but JPG or PNG. Use WebP on your own website, use JPEG when someone else decides what is acceptable.

PNG

PNG records every pixel exactly, which is perfect for screenshots, logos, diagrams and anything with crisp text or hard edges. It is a poor container for photographs, and a photo saved as PNG can easily be five times larger than it needs to be. If a picture is a photo in a PNG wrapper, changing the format is the single biggest saving available to you.

The limits you are probably up against

Compression is rarely done for fun. Something refused a file, and these are the usual culprits.

• Upload forms. Visa applications, job portals and council websites commonly cap each image at 1 or 2 MB, and some go as low as 500 KB. They frequently cap dimensions as well, so a small file that is still 4000 pixels wide can be rejected too.
• Page speed. Images are usually the heaviest thing on a web page. A gallery of untouched phone photos can put twenty megabytes in front of a visitor, and on a mobile connection that visitor leaves before the page finishes.
• Email. Most services stop somewhere around twenty five megabytes for the whole message. Ten holiday photos will pass that on their own.
• Storage that is filling up. Not a hard limit, but a real one. Shared drives quietly fill with originals nobody will ever need at full size.

If the file that has to shrink is a document rather than a picture, our PDF compressor handles that side, and you can put several documents together first with Merge PDF.

Working through a batch sensibly

When you have thirty photos to get through, a few habits save time and regret.

• Keep your originals. Compression is a one way street. Work on copies and leave the untouched files somewhere safe, because you cannot recover detail once it has gone.
• Test on the worst one first. Find the picture with the largest area of plain sky, wall or skin. If that survives the settings, everything else will.
• Do not compress twice. Each pass discards what the last one kept, and the losses accumulate. Go back to the original and use a lower number instead of stacking two rounds.
• Match the width to the destination. A full width banner rarely needs more than 1920 pixels. A photo inside an article rarely needs more than 1280. Thumbnails need far less again.
• Check the result at full size. A thumbnail hides everything. Open the saved file properly before you send a batch you cannot easily redo.

Compressing without handing your pictures to anyone

Almost every online image compressor works the same way. Your photos are uploaded to a server, processed there, and offered back as a download. For holiday snaps that is fine. For a passport scan, a medical form, a photograph of your children or unreleased product shots, it means your files sat on somebody else’s machine for as long as their policy says, and you have no way to check what happened in between.

This tool never sends them. The page uses your browser’s own image decoder to open each picture and writes the new versions back out in the same tab. Open the network panel in your developer tools and watch while it runs. Nothing leaves. It also means the tool keeps working if your connection drops after the page has loaded, and that there is nothing to delete afterwards, because nothing was ever stored.