Chapter Compression
Atahon can compress downloaded manga pages from their original format to WebP, significantly reducing storage usage while maintaining visual quality. Compression is applied during the download process.
How It Works
When compression is enabled (the default), the download worker processes each page through the extension bridge’s native downloadPage method with two additional parameters:
- Quality — WebP quality level (1–100)
- Max Width — Maximum pixel width for the image
The native Kotlin layer handles the actual image decoding, resizing, and re-encoding to WebP format. This happens on the native side for performance — no JavaScript image processing is involved.
Without Compression
- Pages are saved as
.jpgfiles at their original resolution and quality - No resizing or re-encoding is applied
- File sizes depend entirely on the source
With Compression (Default)
- Pages are saved as
.webpfiles - Quality is controlled by 3 settings: Low, Medium and High
- Width is capped at 1.5x your screen width — large enough for pinch-to-zoom but avoids storing unnecessarily huge images
- The original aspect ratio is always preserved
Settings
Configure compression in More > Settings > Downloads:
Compress Downloads Toggle
- On (default): Pages are converted to WebP with the quality and size limits below
- Off: Pages are saved as-is from the source (typically JPEG)
Image Quality
Controls the WebP quality level. Three options are available:
| Option | Quality | File Size | Visual Quality |
|---|---|---|---|
| Low | 65 | Smallest | Good — slight softening on detailed art |
| Medium (default) | 80 | ~40-60% smaller than original | Excellent — indistinguishable for most manga |
| High | 90 | ~20-35% smaller than original | Near-lossless for most content |
Medium (80) is the best quality-to-size ratio for most manga. Use High if you read detailed color illustrations and storage isn’t a concern.
Max Width Calculation
The maximum width is calculated as:
maxWidth = Math.round(screenWidth * 1.5)For a typical phone with a 1080px-wide screen, this means:
- Max width = 1620px
- Images wider than this are downscaled (maintaining aspect ratio)
- Images narrower than this are left untouched
This provides enough resolution for comfortable pinch-to-zoom while avoiding multi-megabyte images from high-resolution sources.
Storage Impact
The actual storage savings depend on the source, but here are typical results:
| Scenario | Original | Compressed (Q80) | Savings |
|---|---|---|---|
| Standard manga chapter (20 pages) | ~15-25 MB | ~6-12 MB | ~50-60% |
| Webtoon chapter (long strips) | ~20-40 MB | ~8-18 MB | ~55-65% |
| Full-color manga (20 pages) | ~25-40 MB | ~12-20 MB | ~45-55% |
Over a library of hundreds of chapters, this adds up to gigabytes of saved storage.
Compression Metadata
Each downloaded chapter’s pages.json file records whether compression was applied:
{
"chapterId": 42,
"pageCount": 20,
"isCompressed": true,
"quality": 80,
"pages": [
{ "index": 0, "filename": "0.webp" },
{ "index": 1, "filename": "1.webp" }
]
}This metadata allows the reader to correctly identify the file format and provides transparency about what quality level was used.
Compression is applied at download time, not retroactively. If you change the quality setting, it only affects future downloads. Already-downloaded chapters keep their original compression settings.
Recommendations
- Storage-constrained devices: Use Low (65) for maximum savings
- Balanced (most users): Keep the default Medium (80) — best quality-to-size ratio
- Quality-focused: Use High (90) if storage isn’t a concern
- Archival: Disable compression entirely to preserve original source quality