85 lines
2.7 KiB
Markdown
85 lines
2.7 KiB
Markdown
# pdf-slim
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Losslessly shrink a PDF. The output renders pixel-for-pixel identically to the
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input; any candidate that doesn't is discarded.
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## How it works
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`pdf-slim` builds several smaller candidates and keeps the smallest one that
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passes verification. The input file is never modified.
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1. **Structural** — `qpdf` object-stream generation and maximum-level flate
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recompression. Always render-safe; a modest win.
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2. **mutool-subset** — `mutool clean` garbage-collects, deduplicates, deflates,
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and natively subsets fonts.
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3. **font-resubset** — for any TrueType `FontFile2` stream still over a size
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threshold (the "Word embedded the whole font" case), the font is re-subset
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with `pyftsubset` against the document's actual character set. Glyph IDs are
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retained (`--retain-gids`) so CID / Identity-H instances sharing the file
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stay valid. The stream is spliced back, lengths are fixed with `fix-qdf`, and
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the result is recompressed.
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Every candidate is verified by rendering each page of both the original and the
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candidate at the same DPI and requiring byte-identical pixels. The smallest
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verified candidate wins. If nothing wins by more than 1%, the input is copied
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through unchanged, so repeated runs are stable.
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## Usage
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```
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pdf-slim input.pdf [output.pdf] [--dpi 200] [--min-font-bytes 150000]
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```
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- `input.pdf` — the PDF to shrink.
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- `output.pdf` — optional; defaults to `<input>-slim.pdf`. Refuses to overwrite
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the input.
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- `--dpi` — verification render resolution (default `200`).
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- `--min-font-bytes` — re-subset embedded TrueType fonts larger than this
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(default `150000`).
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### Example
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```
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[ phanes@forge.silogroup.lan ] << ~/Downloads >>
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[- du -sh 2026-06-08*
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28K 2026-06-08.docx
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1.8M 2026-06-08.pdf
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[ phanes@forge.silogroup.lan ] << ~/Downloads >>
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[- pdf-slim 2026-06-08.pdf 2026-06-08-small.pdf
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input: 2026-06-08.pdf (1,852,511 bytes)
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method: font-resubset (pixel-identical at 200 dpi)
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output: 2026-06-08-small.pdf (192,810 bytes, -89.6%)
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[ phanes@forge.silogroup.lan ] << ~/Downloads >>
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[- du -sh 2026-06-08*
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28K 2026-06-08.docx
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1.8M 2026-06-08.pdf
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192K 2026-06-08-small.pdf
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```
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## Requirements
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The following tools must be on `PATH`:
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- `mutool` (MuPDF)
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- `qpdf` (provides `qpdf` and `fix-qdf`)
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- `pyftsubset` (fontTools)
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- `python3`
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## Ownership
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Owned by SILO GROUP — [www.silogroup.org](https://www.silogroup.org).
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## License
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Copyright (C) 2026 SILO GROUP (www.silogroup.org).
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This program is free software: you can redistribute it and/or modify it under
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the terms of the GNU Affero General Public License as published by the Free
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Software Foundation, either version 3 of the License, or (at your option) any
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later version. See [LICENSE](LICENSE) for the full text.
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