Compress JPEG images online, free

This is also why quality 100 is not lossless. The transform and rounding still run at the top of the range, so a small amount of data is discarded. A quality 100 JPEG is merely a JPEG that discards very little. If you need a truly identical copy of an image, JPEG is the wrong container no matter what number you choose.

What artifacts look like when you push quality too low

Because the encoder works on those 8 by 8 blocks independently, the first thing you notice at low quality is blocking. Smooth areas like skies, skin, or a plain wall break into visible square tiles, each a slightly different flat shade. Once you can see the grid, you have gone too far for that image.

The second artifact is ringing, sometimes called mosquito noise. Sharp edges, such as a tree branch against a bright sky or black text on white, pick up a faint shimmer or halo alongside them. A hard edge needs those high-frequency coefficients to stay crisp, and quantization is exactly what removes them.

The third is color banding. JPEG stores color at lower resolution than brightness, so gentle gradients can collapse into stepped bands of color, most visible in sunsets and studio backdrops.

These three problems show up at different quality levels depending on the picture. A photo of grass and foliage hides artifacts well because the eye already expects chaos there. A portrait against a soft gray background shows banding and blocking early, because the eye is trained to read faces and smooth tones. When you compress, glance at the busiest edges and the smoothest gradients, since that is where the damage appears first.

Recommended quality ranges for real jobs

For photos you publish on a website, quality 75 to 82 is the working range. It cuts file size by half or more against a high-quality original while keeping artifacts below the threshold most people notice on a normal screen. A full-width hero photo can sit at the top of that band, around 82, since it gets viewed large. A product shot in a grid can sit at the bottom, around 75, because it displays small.

Thumbnails and preview images live happily at quality 60 to 70. At the size a thumbnail occupies, often a couple hundred pixels wide, the artifacts that would bother you at full size become invisible, and if you resize the image first the savings across a large gallery add up fast. For archival copies or images you plan to edit again, stay at quality 90 or above to preserve as much detail as possible.

One thing worth internalizing: above roughly quality 85, file size keeps climbing but the visible improvement flattens out. The encoder is now spending bytes on high-frequency detail your screen and your eye cannot resolve at normal viewing distance. For anything bound for the web, settings of 90 and above mostly buy bigger files, not better pictures. Reserve the high end for masters and archives, not for the version you ship.

Generation loss: why you should always start from the original

JPEG compression is not idempotent. Every time you open a JPEG, edit it, and save it again as JPEG, the encoder runs the transform and quantization steps over a picture that was already quantized once. The new rounding compounds the old rounding.

Detail that survived the first save can vanish on the second, and artifacts you could not see at first start to stack up. This is generation loss, the photographic equivalent of photocopying a photocopy.

The rule that follows: always compress from the highest-quality source you have, ideally the file straight off the camera or the original export from your editor. Compressing a JPEG already saved at quality 60 will not make it meaningfully smaller, but it adds a fresh layer of artifacts on top of the old ones. If you keep a master in a lossless format like PNG or your camera's raw file, generate your JPEGs from that master each time instead of re-saving an existing JPEG.

When JPEG is the wrong tool

JPEG was designed for photographs, meaning images full of soft gradients and natural texture. It is a poor fit for several common image types, and forcing them into JPEG produces ugly results no quality setting can fix.

Logos, line art, and icons with large flat areas and crisp edges suffer badly. The ringing artifact attacks every hard boundary, so a clean logo picks up a dirty halo. Screenshots with text are the same story: the high-contrast edges of letters are exactly what JPEG handles worst, and small text turns fuzzy. For both, PNG keeps edges sharp and is usually smaller too, so the compress-png tool is the better home.

Anything that needs transparency cannot use JPEG at all, since the format has no alpha channel and fills transparent areas with solid color. To move a JPEG photo to a transparency-capable or generally smaller format, you can convert to WebP, which often beats JPEG at the same visual quality. The png-to-jpg tool handles the reverse trip when you need it.

EXIF, location data, and your privacy

Photos taken on a phone carry a hidden payload called EXIF metadata. It records the camera or phone model, the exposure settings, the date and time down to the second, and very often the exact GPS coordinates where the shot was taken. Post such a photo to a forum, a marketplace listing, or a public profile, and anyone who downloads it can read the location of your home or workplace straight out of the file.

Re-encoding a JPEG strips that metadata as a side effect. When imgkilo runs your photo through the Canvas API, it builds a fresh image from the pixels alone, and the EXIF block does not survive the trip. GPS coordinates, timestamps, and camera model are gone from the output.

You get this for free on every compress, so a quick pass through the tool before sharing a photo publicly removes the location trail with no extra steps. Because the whole process runs in your browser, the original photo with its location data never reaches a server in the first place.

A batch workflow for catalogs, email, and forms

When you have many images to handle, consistency matters more than squeezing every last byte. Pick one quality setting for the whole set and apply it across the batch. A catalog compressed at a single quality level gives you predictable file sizes and even page-load behavior, which beats hand-tuning each photo to its own number. imgkilo processes up to 100 files at once, each up to 50 MB, and compresses them on separate threads so a large batch finishes without locking up the page.

For e-commerce, quality 75 to 80 usually lands product shots comfortably under 300 KB, keeping storefront pages quick even with dozens of images on screen. For email, work backward from the limit: most mail servers reject attachments over about 10 MB, so a setting that brings each photo to 500 KB or 1 MB lets you attach several without trouble.

Job portals and government forms often set strict caps. The quality slider gets you close, but when the rule is a hard ceiling like 100 KB or 200 KB, you can compress to an exact KB size, which searches for the right quality automatically and lands at or under your target. Drop the batch, set your number, download the ZIP, and the whole set is done in one pass.