Complete documentation for the Baseline JPEG Converter
This tool converts images in EPUB files to baseline JPEG format, optimized for e-ink readers like XTEink X4, Kindle, and Kobo devices. It runs entirely in your browser — no files are uploaded to any server.
• Convert PNG, GIF, WebP, BMP to baseline JPEG
• Smart scaling to 480×800 — dramatically reduces file size
• Grayscale conversion for e-ink displays
• Rotate & split wide images for vertical screens
• Fix SVG covers and metadata issues
• Batch processing multiple EPUBs
Controls the compression level for output images. Higher values mean better quality but larger files.
| Preset | Value | Best For |
|---|---|---|
| Low | 60% | Smallest files, text-heavy books |
| Medium | 75% | Good balance for most content |
| High | 85% | Recommended default, sharp images |
| Max | 95% | Best quality, manga/art with fine detail |
For e-ink displays, 85% is usually indistinguishable from higher values while saving significant space.
Converts all images to grayscale. Recommended for e-ink readers which display in grayscale anyway — reduces file size without visible quality loss.
For manga, comics, and light novels with horizontal spread images that don't fit on vertical e-reader screens.
Each selected image can have its own processing mode:
When an image is split into multiple parts, overlap ensures you don't miss content at the seams.
15% — Safe default, ensures nothing is missed
10% — Good balance, less redundancy
5% — Minimal overlap, best for simple content
In Advanced Mode, all images from your EPUB are displayed in a thumbnail grid for selection.
| Indicator | Meaning |
|---|---|
| Green ✓ badge | Image is selected for processing |
| Grayed out with ✓ | Image fits in 480×800 — no rotation/split needed |
| Disabled ┃┃ button | Image width ≤480px — vertical split not applicable |
The converter automatically detects and fixes common EPUB issues:
<svg><image xlink:href="..."> wrappers that some e-readers can't display.<meta name="cover"> entry.dtb:uid in NCX file with OPF dc:identifier.All images are automatically scaled to fit within the target screen dimensions. This is one of the most impactful optimizations — large source images (often 2000×3000px or more) are reduced to fit 480×800, dramatically reducing file size and improving e-reader responsiveness.
• Images larger than 480×800 are scaled down (aspect ratio preserved)
• Images that already fit are left untouched
• Typical reduction: 70-90% smaller file size
• Result: Faster page turns, less memory usage on e-reader
E-ink displays refresh slowly. Smaller images mean faster rendering, smoother page turns, and longer battery life. A 3000×4000px PNG scaled to 480×800 JPEG can go from 5MB to under 50KB.
| Setting | Value | Notes |
|---|---|---|
| Max Width | 480px | XTEink X4 screen width |
| Max Height | 800px | XTEink X4 screen height |
These values are optimized for XTEink X4 (480×800 @ 220 PPI). For other devices, the code can be modified.
Drop multiple EPUB files at once to convert them all with the same settings.
• Individual progress tracking per file
• Combined statistics (total saved, conversion count)
• Download all converted files as a single ZIP
• Failed files are reported but don't stop the batch
In Advanced Mode, click the 📥 Export button in the log section to save a text file with:
• Timestamp for each operation
• Per-image conversion details (dimensions, sizes, compression ratio)
• Split image details (part names, dimensions)
• Final summary statistics
Use Select Landscape to auto-select spreads, then apply ↻ CW mode with 15% overlap.
Most illustrations are already portrait. Enable grayscale and use 85% quality — no rotation needed.
Use 60% quality + grayscale. Good for text-heavy books where image quality is less critical.