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feat(compress): add advanced compression parameters and better optimization levels (#4703)

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# Description of Changes

This PR reworks the compression endpoints, to be more consistent and
apply better compression on higher levels. Some improvement on lower is
also expected.

### Overview:
- Added new global flags: --recompress-flate --compress-streams=y
--object-streams=generate
- Added --decode-level=generalized, so that if the original PDF was
poorly compressed then, it can re-compress it better
- Added --stream-data=compress for better compression of vector/text
parts
- Now conditional: --preserve-unreferenced kept only for safe levels ≤3
- Added --optimize-images --jpeg-quality 35–75 depending on level (this
brings significant drop in file size, compared to earlier.)
- Added QPDF_ZOPFLI for level ≥8 which is better algorithm for
compressing JPEG. Comes with approx 5% gain per JPEG on PDFs. See here
for details:
https://qpdf.readthedocs.io/en/stable/cli.html#zopfli-compression-algorithm
- level 9, Ghostscript uses strongest downsampling (72/72/150) and CMYK
-> RGB

### Images:
- Scale factor now ramps 1 -> 9: 0.98, 0.95, 0.88, 0.78, 0.68, 0.58,
0.48, 0.38, 0.28.
- JPEG quality ramps 1 -> 9: 0.92, 0.88, 0.85, 0.80, 0.72, 0.65, 0.55,
0.45, 0.35.

### Results:
<img width="1491" height="731" alt="create-ms_pdf_sizes"
src="https://github.com/user-attachments/assets/43ed2ce2-7524-4c03-8689-96a6cb68d046"
/>

<img width="1481" height="731" alt="img-doc_pdf_sizes"
src="https://github.com/user-attachments/assets/3a217c33-3551-44ac-b499-8283cb36cf5d"
/>

<img width="1470" height="731" alt="lorem-ipsum_pdf_sizes"
src="https://github.com/user-attachments/assets/12a6bc07-1d4b-4648-a66e-ba22d21a1202"
/>
<img width="1482" height="731" alt="pdf-dev-example_pdf_sizes"
src="https://github.com/user-attachments/assets/00632d91-f7b9-4310-a283-f0fca9c922d5"
/>
<img width="1470" height="731" alt="sample-1_pdf_sizes"
src="https://github.com/user-attachments/assets/317a26c2-dd1a-4d63-a578-279b14fd9f37"
/>

Sample files used:


[image-doc.pdf](https://github.com/user-attachments/files/22984417/image-doc.pdf)

[lorem-ipsum.pdf](https://github.com/user-attachments/files/22984418/lorem-ipsum.pdf)
[Create Microsoft Word Document
Templates.pdf](https://github.com/user-attachments/files/22984419/Create.Microsoft.Word.Document.Templates.pdf)

[sample-1.pdf](https://github.com/user-attachments/files/22984420/sample-1.pdf)

### But is it better than the old? (On level 9)
#### Old vs new:
- image-doc: 1.0 MB vs 454 KB
- create-word: 426 KB vs 247 KB
- lorem-ipsum: 44.7 KB vs 44.4


Most of changes are focused on images, so more images = better gains.
Even on lorem-ipsum text PDF (with no images) there still some gains but
not significant.

(so, it is better)

Closes: #4442
Closes: #4720


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---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>
This commit is contained in:
Balázs Szücs
2025-10-30 19:13:11 +01:00
committed by GitHub
parent 9197c24606
commit 83922c4131
1 changed files with 542 additions and 234 deletions
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