Reduce image file size without visible quality loss

The three things that set an image's file size

Most advice about shrinking images jumps straight to the quality slider. That is the weakest lever you have. File size comes from three factors, in this order of impact:

1. Pixel dimensions. A 12-megapixel phone photo is 4032 × 3024 pixels. Stored raw at three bytes per pixel, that is about 36 MB of data before any compression happens. Every format is just a strategy for packing those pixels tighter, so the pixel count sets the baseline.
2. Format. At similar visual quality, WebP typically comes in 25–35% smaller than JPG, and AVIF can reach roughly half the size of JPG.
3. Quality setting. The 0–100 slider. Useful for fine-tuning, but push it too far and you get artifacts long before you get the savings you wanted.

So when a photo is too big for an email or a web page, the first question is not "how low can I set quality?" but "how many pixels does this image actually need?"

Resizing vs compressing

Resizing throws pixels away: 4032 wide becomes 1600 wide. Compressing keeps every pixel but stores them more efficiently, discarding detail the eye is unlikely to miss. Both make the file smaller, but they behave very differently.

File size scales roughly with pixel count, and pixel count scales with the square of the width. Cap that 4032 × 3024 photo at 1600 pixels wide and you get 1600 × 1200, or 1.9 million pixels, about 16% of the original. That step alone usually cuts the file to a fifth or a sixth of its size, and on a laptop or phone screen nobody can tell, because those screens never display 4032 pixels across in the first place.

Compressing alone, without resizing, forces you to crank quality way down to hit the same target, and that is where blocky skies, halos around edges and waxy skin come from.

Sensible pixel targets:

• Viewing on screens, sharing, email: 1600–2048 pixels on the long edge.
• Web pages: twice the displayed width, so the image stays sharp on high-density (Retina) screens. An image shown 800 px wide wants a 1600 px file.
• Printing: keep the original. A 4 × 6 inch print at 300 dpi needs 1200 × 1800 pixels, and larger prints need more.

JPG vs PNG vs WebP vs AVIF

How big is the gap in practice? For a typical photo at matched visual quality, if the JPG is 400 KB, expect WebP around 260–300 KB and AVIF somewhere near 170–220 KB. The exact numbers move with the content: AVIF shines on smooth areas like skies and skin, and its lead shrinks on fine, noisy texture like foliage or gravel.

The classic mistake is saving photos as PNG "to avoid quality loss." Lossless compression cannot do much with the grain and gradients of a real photo, so a 12 MP PNG can easily exceed 15 MB. The reverse mistake is saving a text-heavy screenshot as low-quality JPG, which smears ringing artifacts around every letter.

Which quality setting to use

• 75–85: the sweet spot for photos. At 80, most images are indistinguishable from the original at normal viewing size.
• 90 and up: files grow fast for gains you will struggle to see. Worth it only if the image will be edited again.
• Below 60: banding and blocks start showing up, first in skies, plain walls and gradients.

Two caveats. Quality numbers are not comparable across formats: every encoder uses its own scale, so WebP at 80 is not "the same" as JPG at 80. Judge by looking, not by the number. And lossy formats lose a little more every time they are re-saved, so always compress from the original file, never from a copy that has already been compressed.

Compressing a photo for email

Major email providers generally cap attachments somewhere around 20–25 MB per message, and above that they switch to a cloud link. What catches people out is that attachments are encoded for transport and grow by roughly a third, so 20 MB of photos may not fit under a 25 MB limit.

The fix is resizing, not crushing quality. A phone photo capped at 1600–2048 pixels wide and saved as JPG at quality 80 usually lands well under 1 MB, which means a couple of dozen photos fit in a single message. Stick with JPG for email, since you don't know what the recipient will open it with.

For messaging apps the logic flips. WhatsApp and most chat apps recompress photos sent as photos, scaling them down and lowering quality on their side; "HD" modes recompress less but still recompress. Pre-compressing saves little and stacks two rounds of loss. If the image must arrive untouched, send it as a document, but remember that a document keeps all its metadata, including GPS.

iPhone HEIC photos

iPhones save photos as HEIC by default, a format that takes roughly half the space of a comparable JPG. Size isn't the problem, compatibility is: plenty of Windows software, web forms and corporate systems still reject it.

• Shoot JPG instead: Settings › Camera › Formats › Most Compatible. Photos take more space on the phone.
• Let the phone convert on transfer: Settings › Photos › Transfer to Mac or PC › Automatic delivers JPGs over a cable. It doesn't cover every path, such as uploading from the Files app.
• Convert afterwards: the image compressor has a HEIC to JPG tab. The decoder (about 3 MB) downloads the first time and the conversion runs on your device, with the same quality and width controls as the main mode.

Expect the JPG to be bigger than the HEIC if you keep the full resolution. That is normal; JPG is the less efficient format. Cap the width in the same pass if size matters.

EXIF, GPS and what your photos give away

A phone photo carries the camera model, the exact date and time, exposure settings and, if location is enabled for the camera, GPS coordinates accurate enough to find the building. Some social networks strip this on upload, but files sent by email, posted to forums or shared as documents usually arrive with everything intact.

The Utiliobox compressor does not keep EXIF. Re-encoding through the browser produces a clean file with no GPS, no timestamp and no color profile. Two honest footnotes:

• If re-encoding to the same format with no width cap would make a file bigger, the tool hands back the original and marks it "unchanged" in the results table. That original still has its metadata. Switching format or enabling the width cap forces a clean re-encode.
• Dropping the color profile means photos shot in a wide-gamut profile such as an iPhone's Display P3 can show very saturated colors slightly muted. On ordinary photos it isn't noticeable.

Orientation is preserved: the image is rotated according to its EXIF before saving, so portrait shots don't come out sideways once the tag is gone.

Worked example

These figures are an illustrative example, not a guarantee. Every photo compresses differently depending on detail and noise, but the proportions below are what you will typically see with an outdoor phone shot.

Changing format alone stops at 1.5 MB. Capping the width takes it to a few hundred kilobytes. Format and quality are the finishing touches; pixels do the heavy lifting.

One practical detail: the tool's width field caps width, not the long edge. A portrait photo of 3024 × 4032 with a 1600 cap becomes 1600 × 2133. If you want portrait shots at 1600 on the long side, set the cap to 1200. Images already narrower than the cap are left alone. If you need to frame the shot first, run it through the image cropper and then compress.

Why not upload private photos to a random compressor

Many online compressors work by uploading your file to their server, processing it there and sending it back. For a product shot that's fine. For a scanned passport, photos of your kids or a screenshot of your bank app, you have no idea how long the file is kept, who can access it or which country the server sits in, and the photo travels with its metadata.

The Utiliobox image compressor does all the work in your browser: decoding, resizing and encoding happen on your device and nothing is sent to a server. It reads JPG, PNG, HEIC and TIFF, outputs WebP, AVIF or JPG, handles up to 100 images per batch and bundles the results in a .zip. A before-and-after slider lets you drag across the image itself to check for artifacts before you download. One limitation: creating AVIF requires a recent Chrome or Edge, since Firefox and Safari can't yet encode AVIF from a web page; if your browser can't, the option is disabled rather than silently producing something else.

The order that works: decide how many pixels you need, pick the format for where the image is going, leave quality near 80, and compare before you call it done.