EPUB Render Modes

Duet normally tries to render EPUBs with the full Duet renderer. Some EPUBs contain complex publisher styling, tables, or image rules that can use too much memory for the reader. Render modes let you keep reading those books by asking Duet to simplify the layout work for that book.

Render mode is saved per book. Changing it for one EPUB does not change the default behavior for your other books.

Which Mode Should I Use?

Mode	Best for	What it keeps	What it simplifies
Duet Default	Most books	Full Duet styling, detailed CSS, table layout, image sizing, publisher spacing, Bionic Reading, Guide Dots	Nothing by default
Balanced	Books where Duet has fallen back automatically, or books you want to start in a lighter mode	Publisher spacing, image sizing, decorations, Bionic Reading, Guide Dots	Complex CSS lookups and table layout
Light	Books where Balanced is still too heavy, or books you want to start in the safest mode	Text content, hidden-content rules, basic formatting, Bionic Reading, Guide Dots	Complex CSS lookups, table layout, publisher spacing, image sizing, and decorative separators
Safe Mode	Final automatic fallback for books that still run out of memory in Light	Text content, hidden-content rules, basic formatting	Light-mode simplifications plus embedded styles, Bionic Reading, and Guide Dots

Most users can leave books on Duet Default. If a book runs out of memory while building a section, Duet will automatically try Balanced and then Light. Manual mode changes are mainly for choosing a lighter mode before opening a known-problem book, or for changing the saved mode after Duet has already fallen back.

Duet Default

Duet Default is the normal renderer.

It tries to preserve the book’s layout and publisher styling as much as Duet supports, including:

• CSS rules that depend on surrounding elements
• Tables rendered as tables when possible
• Publisher margins, padding, and paragraph indents
• Publisher image sizing
• Horizontal rules and other visual separators
• Publisher page number markers, if enabled
• Bionic Reading and Guide Dots, if enabled

Use this unless a specific book is causing memory errors, very slow indexing, or rendering problems.

Balanced

Balanced keeps most publisher styling, but avoids the most expensive layout work.

It keeps:

• Publisher margins, padding, and paragraph indents
• Publisher image sizing
• Horizontal rules and other visual separators
• Publisher page number markers, if enabled
• display: none hidden-content rules
• Bionic Reading and Guide Dots, if enabled

It simplifies:

• Complex CSS rules that depend on surrounding elements
• Tables, which are flattened into readable text blocks

Use Balanced when Duet has already fallen back to it, or when you want a known-problem book to start with lighter rendering immediately. The page may not match the publisher layout exactly, but it should still keep more of the book’s visual styling than Light.

Light

Light is the safest mode for difficult EPUBs.

It keeps:

• Text content
• Basic bold, italic, underline, superscript, and subscript handling
• display: none hidden-content rules, so intentionally hidden content stays hidden
• Bionic Reading and Guide Dots, if enabled

It simplifies or removes:

• Complex CSS rules that depend on surrounding elements
• Tables, which are flattened into readable text blocks
• Publisher margins, padding, and paragraph indents
• Publisher image sizing
• Horizontal rules and decorative separators
• Publisher page number markers

Use Light when Duet has already fallen back to it, or when you want a known-problem book to start in the safest mode immediately. Light may look less like the publisher’s original layout, but it gives Duet the best chance of rendering the book on limited memory.

Safe Mode

Safe Mode is an automatic final fallback, not a selectable render mode.

If Duet cannot build a section in Light because memory is still too tight, it tries Safe Mode once. Safe Mode uses Light rendering and also turns off:

• Embedded styles
• Bionic Reading
• Guide Dots

When Safe Mode succeeds, Duet saves those settings for that book. The reader briefly shows Safe Mode over the current page. Your other books keep their own reader settings.

Automatic Fallback

If a book starts in Duet Default and a section runs out of memory while building, Duet automatically retries in this order:

1. Duet Default
2. Balanced
3. Light
4. Safe Mode

If the book starts in Balanced, Duet can fall back to Light and then Safe Mode. If the book starts in Light, Duet can still try Safe Mode.

When a fallback succeeds, Duet saves that successful mode for the book. The next time you open the same book, it starts in the saved mode.

When a book opens in Balanced or Light, the reader briefly shows Balanced Mode or Light Mode over the current page. The message disappears automatically and does not change page layout, margins, or reading position.

If Safe Mode also cannot open the book, long-press the book in File Browser or Recent Books and choose Reset Book Reader Settings. This clears only that book’s reader settings, including a saved Safe Mode or render-mode override. It preserves reading progress, bookmarks, clippings, and reading stats.

Changing A Book’s Render Mode

You can change a book’s render mode before opening it. This is optional because Duet already falls back automatically, but it is useful when you know a book is difficult and want it to start in a specific mode:

• Long-press an EPUB in File Browser
• Long-press an EPUB in Recent Books
• Choose EPUB Render Mode

You can also change it while reading:

1. Open the reader menu.
2. Choose Book Options.
3. Choose EPUB Render Mode.

Changing render mode rebuilds the affected book layout cache. Your reading progress, bookmarks, clippings, reading stats, Bionic Reading setting, and Guide Dots setting are preserved.