What Actually Happens When You Hit "Compress"

Most compressor pages never explain this part, so here it is in plain terms. When you drop a photo into this tool, your browser draws it onto an invisible canvas — a feature built into every modern browser called the Canvas API. From that canvas, the browser re-encodes the pixels into a new file using whatever quality level you picked. Lower the quality number, and the encoder throws away more of the fine detail a viewer is unlikely to notice; raise it, and it keeps more of the original information at the cost of a bigger file.

Because this whole process runs on your device's own processor, there's no upload step, no server queue, and no size cap tied to a free-tier limit. It also means the tool keeps working even on a slow connection, since the only network activity is loading the page itself. The one exception is the optional ZIP download, which briefly pulls in a small packaging library to bundle multiple files together — everything else, including the compression itself, never leaves your machine.

How to Use This Tool (Quick Version)

Understanding the Compression Levels

The five buttons above the quality slider aren't arbitrary — each maps to a quality percentage tuned for a different priority:

• Best Quality (92%) — barely compresses the file at all. Use this for images you'll print, zoom into, or edit further later.
• Recommended (80%) — the setting most people should leave alone. It's the point where file size drops sharply while the image still looks untouched on a normal screen.
• Small File (60%) — a noticeably smaller file with a very slight softness that's hard to spot unless you're comparing side by side.
• Smallest (35%) — for situations where size matters more than looks, like a thumbnail or a placeholder image.
• Custom — drag the slider anywhere from 1–100% for full control, which the tool switches to automatically the moment you touch the slider.

If you're compressing images for a form, application, or upload portal that lists an exact size limit — say, "photo must be under 100 KB" — skip the presets entirely and switch on Target an exact file size. Rather than guessing at a quality number, the tool tests multiple quality levels behind the scenes and lands on the highest one that still fits under your limit. This is one of the more genuinely useful long-tail features here: most free compressors only offer a quality slider and leave you to guess-and-check manually.

Choosing a Resize Mode

Resizing and compressing are two different jobs, and combining them properly is where the biggest file-size savings usually come from. This tool offers three resize modes, each suited to a different scenario:

• Fit Within — set a maximum dimension (say, 1920px) and any image larger than that gets scaled down proportionally, while smaller images are left alone. This is the fastest option for batch jobs where your photos come from different cameras at different sizes.
• Scale % — shrink every image by the same percentage, useful when you already know your photos are roughly uniform in size and just need them all a bit smaller.
• Exact Size — type a precise width and height, with the aspect-ratio lock keeping the proportions correct as you adjust one field. This is the one to reach for when a platform demands a specific pixel size, like a 500×500 profile photo or a 1200×630 social share image.

A rule that holds up in practice: resize to the dimensions your image will actually display at before you touch the quality slider. A photo that's 4000 pixels wide but only ever shown at 800 pixels on a page is carrying data nobody will see — shrinking the dimensions first, then compressing, produces a smaller and sharper result than compressing alone ever will.

JPEG vs. PNG vs. WebP: Picking the Right Output

The format you choose affects file size more than almost any other setting. Here's the short version of how the three behave:

A quick way to remember it: WebP for a website when you can, since it typically lands 25–35% smaller than a JPEG at matching quality. JPEG when you need a format every device and platform will open without question. PNG only when transparency or perfectly sharp text and edges actually matter — using it for an ordinary photo just means carrying extra weight for no visual benefit.

Matching Settings to What You're Actually Doing

Rather than a generic settings table, here's how this tends to play out for the situations people actually land on this page for:

Selling on a marketplace or storefront. Buyers zoom in, so keep quality around 80–85% and resize to roughly 1200–1600px on the longest side — sharp enough to inspect, light enough to load fast on mobile data.

Attaching photos to an email or online form. Many inboxes and portals cap attachments at 5–25 MB total, and some application forms specify an exact per-photo limit. This is exactly what the target-size feature is for — set the number the form asks for and let the tool find a quality level that fits.

Publishing on a blog or content site. Convert to WebP, fit within 1920px for full-width hero images, and keep quality at 75–80%. Search engines increasingly reward pages that load quickly, and images are usually the heaviest thing on the page.

Uploading a headshot, ID photo, or avatar. Use Exact Size to match the pixel dimensions the platform specifies exactly, rather than letting it get auto-cropped or stretched after upload.

Archiving or backing up a personal photo library. Stick closer to 90%+ quality. The point of compression here isn't maximum savings — it's trimming the excess without giving up anything you'd notice years later.

Common Mistakes That Leave a File Bigger Than Expected

If you've compressed a photo and the size barely moved, the setting probably wasn't the problem — something upstream usually was. A few patterns show up constantly:

• Compressing a PNG photograph instead of converting it first. PNG is lossless, so it has very little left to trim once it's already a photo. Switch the output format to JPEG or WebP before compressing anything that isn't a logo or screenshot.
• Skipping the resize step. A full-resolution camera photo displayed small on a page is storing far more pixel data than anyone will see — resize first, then compress.
• Leaving the quality slider near 90%+ by habit. That range barely compresses anything; most of the real savings sit between 70% and 85%.
• Re-compressing a file that's already been compressed once. There's a practical floor — running an already-lossy file through compression again rarely shrinks it further.

For a deeper, reason-by-reason breakdown of exactly why a file refuses to shrink — including hidden metadata, color profiles, and chroma subsampling settings most tools never mention — see why your image might still be large after compression.

Frequently Asked Questions

About This Tool

This tool was built for online sellers, bloggers, job applicants, students, and anyone who needs a smaller image file without installing software. It relies on standard browser APIs — Canvas, Blob, and File — to resize and re-encode images entirely on your device, the same underlying approach used by professional image-optimization pipelines, just without the upload step.

• web.dev — Learn Images: formats, compression & performance
• MDN — Canvas API Reference
• Google Developers — WebP Image Format
• MDN — Image File Type and Format Guide