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MozJPEG

github.com

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Spec score 8.2 #32 of 85 in Image Compression Software

What it is

MozJPEG is a free, open-source library project that improves JPEG compression efficiency to produce smaller files and higher visual quality. It is intended for graphics programs and image-processing tools, and programs using the libjpeg API can integrate it without MozJPEG-specific integration code. It is compatible with the JPEG standard and the vast majority of deployed JPEG decoders. When converting other formats to JPEG, it uses trellis quantization to target the quality-to-file-size ratio. Its progressive encoding with jpegrescan optimization can losslessly reduce the size of a JPEG when used with jpegtran. The project’s improvements can be disabled at runtime, returning it to libjpeg-turbo behavior. The repository includes a demo cjpeg command-line tool, which is not intended for serious use. Build instructions cover Unix-like systems, macOS, Linux, and Windows with Visual C++ or MinGW. The GitHub repository identifies version 4.1.1 on its latest release page. MozJPEG points users to libjpeg-turbo documentation for additional build help; its repository does not state security certifications or compliance claims.

Spec sheet

Purpose
MozJPEG improves JPEG compression efficiency to achieve smaller files and higher visual quality.Read 7 Oct 2026 · github.com
Free plan
YesRead 20 Sep 2026 · github.com
Security
The repository page does not state security certifications or compliance claims.Read 7 Oct 2026 · github.com
Support
The project points users to libjpeg-turbo documentation for additional build help.Read 7 Oct 2026 · github.com
API access
YesRead 20 Sep 2026 · github.com
Build platforms
The build instructions describe Unix-like systems, macOS, Linux, Windows with Visual C++, and Windows with MinGW.Read 7 Oct 2026 · github.com
Command-line tool
The repository includes a demo cjpeg command-line tool, which the project says is not intended for serious use.Read 7 Oct 2026 · github.com
Compatibility
It is compatible with the JPEG standard and the vast majority of deployed JPEG decoders.Read 7 Oct 2026 · github.com
Compression modes
bothRead 20 Sep 2026 · github.com
Distribution
The GitHub repository provides a latest release page, which identifies version 4.1.1 as the latest release.Read 7 Oct 2026 · github.com
Integration
Programs using the libjpeg API can integrate MozJPEG without writing MozJPEG-specific integration code.Read 7 Oct 2026 · github.com
Library use
The project is intended as a library for graphics programs and image processing tools.Read 7 Oct 2026 · github.com
Metadata controls
YesRead 20 Sep 2026 · github.com
Progressive encoding
Progressive encoding with jpegrescan optimization can losslessly reduce the size of any JPEG when applied with jpegtran.Read 7 Oct 2026 · github.com
Runtime behavior
MozJPEG improvements can be disabled at runtime, in which case it behaves exactly like libjpeg-turbo.Read 7 Oct 2026 · github.com
Supported formats
PPM,PGM,BMP,GIF,TargaRead 20 Sep 2026 · github.com
Trellis quantization
Trellis quantization is used when converting other formats to JPEG to maximize the quality-to-file-size ratio.Read 7 Oct 2026 · github.com

Plans and prices

MozJPEG Free Open-source JPEG encoder library; demo cjpeg tool Read 7 Oct 2026 · github.com

Every MozJPEG plan and price →

Strong points and limits

Strong points

  • Free, open-source JPEG compression library.
  • Can integrate through the libjpeg API without MozJPEG-specific code.
  • Progressive encoding can losslessly reduce JPEG size with jpegtran.
  • Build instructions cover macOS, Linux, and Windows.

Limits

  • Demo cjpeg command-line tool is not intended for serious use.
  • No security certifications or compliance claims are stated.
  • Additional build help points to libjpeg-turbo documentation.

Who it suits

MozJPEG suits developers building graphics programs or image-processing tools that use the libjpeg API. It may also suit teams seeking JPEG compression improvements while retaining compatibility with deployed JPEG decoders.

Verdict

MozJPEG is a library for integrating JPEG compression improvements into graphics and image-processing software. Its decoder compatibility and runtime fallback are useful considerations, while the included command-line tool is explicitly only a demo.

Where Specifiction places it

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