Images are why bundled apps are big
HTML, CSS and JavaScript compress to roughly a quarter of their size inside an Android package. Images do not compress at all — they are already compressed — so they arrive in your app at full weight. In practice, a site's images account for most of the difference between a 5 MB app and a 30 MB one.
WebP is the cheapest fix available. Android has supported it since 4.0, every current browser reads it, and it typically produces files 25–35% smaller than JPEG and considerably smaller than PNG at the same visual quality.
What you can expect
| Source | Typical saving | Notes |
|---|---|---|
| JPEG photo | 25–35% | The headline case |
| PNG screenshot | 40–70% | Often dramatic |
| PNG with transparency | 30–60% | WebP keeps the alpha channel |
| Small flat icon | 0% or worse | Container overhead dominates — keep the PNG |
| Existing WebP | Nothing to gain | Re-encoding only loses quality |
The tool flags files that grew rather than quietly handing you a worse version. For a tiny logo or a flat icon, PNG frequently wins, and there is no shame in shipping a mix.
Resizing beats quality settings
The single most common waste in a bundled app is a photograph at 4000 pixels wide displayed in a 400-pixel-wide card. No quality setting recovers that: you are shipping 100 times the pixels anyone will see.
Decide the largest size an image is ever displayed at, double it for high-density screens, and resize to that. A hero image at 1920px and cards at 800px covers almost every phone. Doing that first, then converting to WebP, routinely takes megabytes off an app — far more than moving the quality slider ever will.
Choosing a quality setting
82 is a good default and the reason it is preselected. Below about 70, compression artifacts become visible on gradients and skin tones. Above 95, file size climbs steeply for differences you cannot see on a phone screen. If an image contains fine text or sharp diagrams, push to 90 and check it; for photographs, 80–85 is almost always indistinguishable from the original.
Where to use the result
For a bundled app, replace the images in your project folder and update the references. If you also serve the same site on the web, keep a fallback for anything that must work in very old browsers:
<picture> <source srcset="hero.webp" type="image/webp"> <img src="hero.jpg" alt="…"> </picture>
Inside an Android WebView you do not need the fallback — every Android version that runs a modern WebView decodes WebP natively — so a bundled app can use WebP everywhere and drop the JPEG entirely.
What happens to your files
Encoding uses the browser's own WebP encoder through a canvas, which means two things worth knowing. Everything stays on your machine — useful for unreleased artwork. And metadata does not survive: EXIF, colour profiles and copyright tags are stripped by the canvas. For app assets that is usually welcome, since it removes camera and location data you did not intend to ship. For photography where authorship metadata matters, convert with a tool that preserves it.
Once converted, run the folder through the size calculator to see what the app will actually weigh.