How does the file compression work?

The technology behind Neuxpower's File Compressors (NXPowerLite and WeCompress) is best described as "File Optimization". It reduces the file size of image-heavy files by eliminating excess baggage and converting embedded images to the most appropriate file format and resolution.

Optimized files remain in their original format, and will be visually and functionally the same as the original. They don't need to be decompressed or rehydrated, and there's no need for special viewing software - so they can be opened and edited by anybody. File optimization is predominantly "lossy" by design, and below is a list of examples of how it reduces the size of each file type:

PDF (including all sub-sets)

PDF files are most often scanned physical documents or documents that have been created entirely digitally often referred to as 'native' or 'born digital' PDFs. 

Scanned PDF

Scanners often capture document pages as high resolution images without compression. So even documents that appear to be just text can often be entirely images. By reducing the resolution of these images and choosing an efficient image encoding these files can be dramatically reduced.

Native PDF

PDF files generated from an electronic source - such as a Word document, a computer generated report, or spreadsheet data - will usually be formed of a combination of text and images. For this type of file the compressor ignores the text and focuses on resizing and choosing the best format for the embedded images.

Techniques used to optimize PDF file size include:

• Convert inserted images to the most efficient file format
• Adjust the JPEG quality of images
• Resize inserted images to the most appropriate size
• Subset or remove embedded fonts
• Remove private application data

PowerPoint

PowerPoint presentations often contain lots of content that can be compressed; from oversized images to hidden data in embedded charts. The compressor will selectively optimize each of these elements within the files to create leaner, smaller presentations.

Techniques used to optimize PowerPoint file size include:

• Convert inserted images to the most efficient file format
• Adjust the JPEG quality of images
• Resize inserted images to the most appropriate size
• Remove cropped areas of inserted images
• Flatten embedded objects and charts
• Remove unnecessary metadata
• Remove “fast save” information 

To optimize PowerPoint files with more precision you can use a specialised tool like Slidewise, which is designed to make it easy to find size issues in your presentations. You can use it to reduce file size with precision, so that only the content that you want to reduce is changed.

Word

Microsoft Word files contain lots of content that can be optimized; from oversized images and old fast save information to hidden data in embedded objects. The compressor optimizes each of these elements within the files to create leaner, smaller documents.

Techniques used to optimize Word file size include:

• Convert inserted images to the most efficient file format
• Adjust the JPEG quality of images
• Resize inserted images to the most appropriate size
• Remove cropped areas of inserted images
• Convert metafiles
• Flatten embedded objects and charts
• Remove Word 2007 and earlier compatibility
• Remove unnecessary metadata
• Remove “fast save” information 

Excel

Microsoft Excel files can contain a broad range of content that can secretly drive up the file size; from Images to PivotTable Cache and even invisible Excess Cell Formatting. The compressor optimizes each of these elements within the spreadsheets to create leaner, smaller Workbooks.

Techniques used to optimize Excel file size include:

• Convert inserted images to the most efficient file format
• Adjust the JPEG quality of images
• Resize inserted images to the most appropriate size
• Clean excess cell formatting
• Flatten embedded objects and charts
• Reduce the color depth of PNG images

JPEG

Most JPEG images are produced by digital cameras, which are optimized to preserve as much information as possible in order to allow the image to be edited and post-processed. Most of this information is not visually detectable and unnecessarily increases the size of the file. The compressor decodes and re-encode JPEGs using more efficient settings, and it optimizes the Huffman coding and Chroma subsampling used. This can substantially reduce the file size without reducing the image resolution and without changing the perceptual quality of the image.

PNG

To reduce the size of PNG files the compressor reduces the number of colours in a PNG image, which allows it to convert the 24-bit PNG to a much smaller, more efficient 8-bit indexed color image. The file size reduction can often be as much as 60-80% smaller than equivalent 24/32-bit PNG files, and it preserves full alpha transparency. Generated images are compatible with all web browsers and operating systems.

TIFF

Many TIFF files are stored uncompressed despite having a number of lossless compression methods available. This results in much larger file sizes, with the only benefit being slightly faster opening times. The compressor can shrink uncompressed TIFF images by applying lossless LZW compression. For multi-page TIFF files it will apply lossless LZW compression to uncompressed pages.

Please note: Any of the above files found in a Zip file can be extracted and replaced with smaller versions as described above. Once processed all the files will be re-compressed leaving a file that looks like the original Zip just smaller.

Tools mentioned in this article

NXPowerLite Desktop: Our desktop file compressor

WeCompress: Our online file compressor for files up to 50 MB

Slidewise: PowerPoint add-in to make precision file size edits easier

Frequently Asked Questions