How to use the command 'oxipng' (with examples)

Oxipng is a powerful command-line tool designed to optimize PNG files by losslessly reducing their file sizes. Utilized primarily by web developers and graphic designers, Oxipng compresses images to improve website loading times or decrease space usage without compromising quality. Through its various options, the tool provides flexibility in how images are compressed, achieving optimal results tailored to specific needs.

Use case 1: Compress a PNG file (overwrites the file by default)

Code:

oxipng path/to/file.png

Motivation:
The primary motivation for this use case is to quickly and easily reduce the file size of a PNG image without needing to keep the original copy. This approach is beneficial when storage space is at a premium and you have a backup or certainty that no mistakes will affect critical files.

Explanation:
The command oxipng path/to/file.png consists of the tool name oxipng, followed by the path to the PNG file you want to compress. Without additional options, Oxipng processes the specified image, overwriting the original to achieve maximum compression while preserving visual quality.

Example output:
After running this command, the specified file will be compressed, usually resulting in a smaller file size with the same .png extension as before. You might see a message indicating the percentage of size reduction.

Use case 2: Compress a PNG file and save the output to a new file

Code:

oxipng --out path/to/output.png path/to/file.png

Motivation:
This use case is ideal when you want to keep the original image unaffected by the compression process, ensuring you have both the uncompressed and the compressed versions available. It is particularly useful when you need to compare the quality of both versions or when performing experiments with file optimization.

Explanation:
The command oxipng --out path/to/output.png path/to/file.png includes the option --out which specifies the path where the optimized file will be saved. path/to/output.png indicates the new file’s location and name, while path/to/file.png is the original file that will undergo optimization.

Example output:
The command creates a new file at the specified output path, which is a compressed version of the original. The original file remains unchanged, and the file size of the new PNG will typically be reduced.

Use case 3: Compress all PNG files in the current directory using multiple threads

Code:

oxipng "*.png"

Motivation:
Optimizing multiple images at once saves time, especially when dealing with numerous files such as in a web project. Using multi-threading can significantly speed up this process by distributing the workload across multiple processor cores.

Explanation:
In the command oxipng "*.png", the asterisk * is a wildcard that represents any sequence of characters, which means the tool will apply to all files ending with .png in the current directory. Oxipng uses multiple threads by default, improving the processing speed on multi-core systems.

Example output:
Each PNG file in the directory is processed and overwritten with its optimized version. The terminal output will include processing details, like the original and new file sizes for each image.

Use case 4: Compress a file with a set optimization level

Code:

oxipng --opt 0|1|2|3|4|5|6|max path/to/file.png

Motivation:
Different situations require varying levels of optimization, from the fastest processing with minimal compression to slower processing with maximum compression. Selecting an appropriate optimization level allows users to balance speed and results as per their specific needs.

Explanation:
In the command oxipng --opt 0|1|2|3|4|5|6|max path/to/file.png, --opt specifies the optimization level ranging from 0 (fastest, least compression) to max (slowest, highest compression). path/to/file.png is the path to the file being optimized.

Example output:
The file is processed according to the specified optimization level. You will see the final file size and compression ratio, which will vary with the level chosen.

Use case 5: Set the PNG interlacing type

Code:

oxipng --interlace 0|1|keep path/to/file.png

Motivation:
Interlacing affects how images are rendered on slower internet connections; for example, Adam7 interlacing allows images to be loaded in a series of passes for better perceived performance. Adjusting the interlacing can also influence file size.

Explanation:
The command oxipng --interlace 0|1|keep path/to/file.png includes --interlace, which allows you to set the interlacing type. 0 removes interlacing, 1 applies Adam7 interlacing, and keep retains the existing interlacing setting. path/to/file.png is the file being processed.

Example output:
The output file maintains or changes its interlacing based on the option specified, potentially affecting how quickly or smoothly images render in user interfaces.

Use case 6: Perform additional optimization on images with an alpha channel

Code:

oxipng --alpha path/to/file.png

Motivation:
Images with alpha (transparency) channels may benefit from specific optimizations to further reduce file size because transparency often introduces additional data. This tool helps manage such images more effectively.

Explanation:
The command oxipng --alpha path/to/file.png uses the --alpha flag to signal Oxipng to apply optimizations targeting the alpha channel. path/to/file.png represents the file that will undergo alpha-specific processing.

Example output:
The compressed file maintains its transparency but with enhanced compression that specifically optimizes the alpha data, resulting in a smaller file size without quality loss.

Use case 7: Use the much slower but stronger Zopfli compressor with max optimization

Code:

oxipng --zopfli --opt max path/to/file.png

Motivation:
For scenarios where achieving the absolute smallest file size is critical, such as when optimizing images for mobile platforms or restricted bandwidth environments, using Zopfli with maximum optimization yields superior results despite increased processing time.

Explanation:
In oxipng --zopfli --opt max path/to/file.png, --zopfli instructs Oxipng to use the Zopfli compression algorithm, known for its high compression rates, albeit slower performance. --opt max is used to ensure the highest level of compression, with path/to/file.png as the target file.

Example output:
The output file is notably smaller compared to regular optimization at the expense of longer processing time, providing considerable file size reduction.

Use case 8: Strip all non-critical metadata chunks

Code:

oxipng --strip all path/to/file.png

Motivation:
Stripping metadata can further reduce file size and remove potentially sensitive information embedded in images, such as creation dates or software details, which might be unnecessary for end-use scenarios.

Explanation:
The command oxipng --strip all path/to/file.png leverages the --strip option to remove non-critical metadata chunks, with all indicating that all such data should be stripped. path/to/file.png is the file that will have its metadata removed.

Example output:
The result is a PNG image that is smaller and devoid of any extraneous metadata, potentially enhancing privacy and reducing file bloat.

Conclusion:

Oxipng proves to be a versatile and vital tool in PNG optimization, allowing users to choose from a range of options to balance performance, file size, and quality. Through these practical use cases, one can utilize Oxipng to handle various image optimization tasks effectively, ensuring images are web-optimized, storage-friendly, or tailored to specific output requirements.