48 lines
1.7 KiB
Markdown
48 lines
1.7 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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## 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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