A 4 MB photo straight off a phone is overkill for almost everything you’d use it for online — a blog post, a product listing, an email attachment. Compression shrinks that file dramatically, and in most cases you won’t be able to see the difference. Here’s what’s actually happening when you compress an image, and how to do it without wrecking the result.
Why images get so large in the first place
Modern phone cameras capture more detail than most screens can even display. A 12-megapixel photo has more than enough resolution to fill a laptop screen twice over, and the camera saves all of that detail at a high quality setting by default. That’s great for editing or printing, but wasteful for a web page someone will scroll past in two seconds.
Lossy vs. lossless compression
JPEG and WebP use lossy compression: they throw away some image data to shrink the file, using patterns in how the human eye perceives color and detail to decide what to discard. Done carefully, you lose almost nothing visible. PNG is lossless — it never discards data, which is why PNG files compress much less and why a photo saved as PNG is often 5–10x larger than the same photo saved as JPEG.
This is the single most common mistake people make: saving photographs as PNG. PNG is the right choice for screenshots, logos, and graphics with flat colors and sharp edges. For photos, use JPEG or WebP.
How much quality is “enough”?
Quality settings usually run from 0–100 (or 0–1 as a decimal). In practice:
- 90–100%: Visually identical to the original. Minimal savings.
- 70–85%: The sweet spot for most photos. Files shrink by 60–80% with no visible difference at normal viewing sizes.
- 40–60%: Noticeably smaller files, useful for thumbnails or background images where size matters more than fine detail.
- Below 30%: Visible blockiness and color banding start to appear, especially in photos with smooth gradients like skies.
There’s no universal “correct” number — it depends on the image’s content and how it’ll be displayed. A good approach is to compress at 75%, look at the result at the size you’ll actually use it, and adjust from there.
A quick workflow
- If the file is a PNG photo, convert it to JPEG or WebP first — this alone often cuts the size by 80% or more before you even touch the quality slider.
- Compress at around 75% quality.
- Resize the dimensions down to what you’ll actually display it at — a 4000px-wide image displayed at 800px wide is wasting three-quarters of its file size on detail nobody will ever see.
- Check the result. If it still looks sharp, you’re done; if you spot artifacts, nudge the quality back up.
Our batch image compressor does this entirely in your browser — nothing gets uploaded to a server — and you can process multiple images at once. If you’re starting from PNGs, run them through the image converter first, and use the batch image resizer to cut dimensions down before compressing.