Image Optimization (Android)
AndroidImages stored as PNG or JPEG that would be significantly smaller in WebP format. PNG-to-WebP conversion typically saves 26% lossless or 25-34% lossy vs JPEG.
Images and drawable resources are frequently the second-largest contributor to APK size after native libraries. WebP offers superior compression over JPEG and PNG while maintaining visual quality, supported since Android 4.2.1 (API 17) for lossy and lossless with alpha. AVIF provides even better compression using AV1 encoding, supported since Android 12 (API 31). Choosing the right format per asset type and aggressively optimizing existing images can yield significant size savings.
Why this happens
Unoptimized PNGs: PNG files often contain unnecessary metadata, full alpha channels on opaque images, and unoptimized compression tables.
JPEG/PNG used where WebP is better: Many projects still default to legacy formats despite WebP offering 25-34% better compression.
Multi-density raster assets: Providing PNG/JPEG variants at ldpi/mdpi/hdpi/xhdpi/xxhdpi/xxxhdpi multiplies storage 5-6x for each image.
Large embedded photos: Hero images, onboarding screens, and marketing assets stored as unoptimized bitmaps at full resolution.
Unused alpha channels: PNGs saved with transparency (32-bit RGBA) when the image is fully opaque (24-bit RGB would suffice) waste 25% of the per-pixel storage.
Size impact
Image format conversion is one of the highest-ROI optimizations with minimal effort.
WebP lossless vs PNG
26% smaller on average
WebP lossy vs JPEG
25-34% smaller at equivalent quality
WebP lossy with alpha vs PNG
3x smaller
PNG indexed color (256 colors)
75% reduction per pixel
How we detect it
Scans the res/ directory of the APK for PNG and JPEG files, sorted by size. Android Studio's "Convert to WebP" tool shows estimated savings before conversion. Lint inspections ConvertToWebp and IconMissingDensityFolder help identify conversion candidates.
How to fix
1
Convert PNG/JPEG to WebP in Android Studio
Right-click image files or folders > "Convert to WebP". Set lossy encoding quality to 75% as a starting point. Skip 9-patch files as they do not support WebP.
2
Disable PNG crunching when using WebP
Avoid double-processing by disabling aapt PNG optimization when images are already optimized.
build.gradle.kts
android {
buildTypes {
release {
isCrunchPngs = false
}
}
}3
Use AVIF for Android 12+ targets
Provide AVIF with a WebP fallback using resource qualifiers for maximum compression on newer devices.
Resource qualifiers
// res/drawable-v31/hero_image.avif (AVIF for API 31+)
// res/drawable/hero_image.webp (WebP fallback)4
Optimize remaining PNGs
For PNGs that must remain as PNG (9-patch files), use lossless compression tools like pngquant or zopflipng to reduce file size.
# Lossy PNG optimization (60-80% quality)
pngquant --quality=65-80 --output output.png input.png
# Aggressive lossless compression
zopflipng --iterations=15 input.png output.png5
Reuse drawable resources with tinting
Instead of shipping separate colored icons, use a single icon and apply tints at runtime to reduce the number of drawable files.
Important: 9-patch images cannot be converted to WebP. AVIF decoding in Android 12 and 13 has known bugs (transparent background issues, decoding glitches) and is more reliable from Android 14+. Always visually verify lossy WebP/AVIF output, as artifacts are more visible on gradients and text overlays. Strip EXIF and GPS metadata from JPEGs before inclusion.
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