PDF Compression: Profiles & Benefits
Optimizing PDFs is like sending your documents to the gym for a workout. We're talking about turning those flabby, oversized files into lean, mean, document machines.
Many developers long for compressed PDF files to simplify their workflows, but the choices and trade-offs that are necessary to make when compressing files should be driven by the intended use of the data within those files. That’s why we designed the Optimizer APIs in the Adobe PDF Library to be configured with these trade-offs in mind.
Datalogics tested the compression capabilities of PDF Optimizer in a comparison with various free and commercially available optimization tools, and we found that the results achieved by different compression tools for the same PDF files varied substantially. We also saw that smaller wasn’t always better, as some compression decisions can permanently alter the usefulness of a file for a particular use case.
Read Exploring the Diverse Use Cases for Compressing PDFs
But let’s take a step back and ask: why do we compress PDF files in the first place and what are the benefits of compressing PDFs?
First, PDF files intended to be delivered to mobile devices will provide a better user experience if they are highly compressed. Mobile devices often depend on cellular networks and device responsiveness for downloads, and page turns can be substantially improved with better file compression. Mobile devices also have low-resolution RGB screens, so converting high-resolution CMYK images to lower-resolution RGB images can make a lot of sense for this scenario.
Secondly, Cloud services charge for upload and download bandwidth as well as monthly fees for storage space used. These fees may seem trivial at first glance, but when redundant content might be archived for a decade or more, the Cloud storage costs become relevant. Smaller files mean less storage space is needed, which means lower costs for you.
Lastly, in the commercial print space PDF files are often created by merging multiple individual files, and this can create print files that are bloated with multiple subsets of the same fonts or duplicate copies of images. Optimizing such files to remove duplicate resources can dramatically improve print performance without impacting the print quality.
What happens when a PDF File is compressed?
There are two types of compression activities, lossless and lossy compression. Lossless compression involves removing duplicate resources, such as fonts and images, and utilizing image and text compression algorithms that retain all of the original data. Lossy compression can involve downsampling high-resolution images or converting color spaces from spaces like the 4 channel CMYK to the 3 channel RGB, which does not cover the same gamut of colors.
Lossy vs Lossless PDF Compression
Lossy and lossless compression are two methods used to reduce the file size of digital content, including PDF files. Here are some of the differences between lossy and lossless PDF compression:
Lossy Compression:
Lossy compression reduces the file size by eliminating some data and information that it deems less essential. This results in a smaller file size but comes at the cost of losing some of the PDF details. In the context of PDF files, lossy compression usually involves reducing the quality of images within the document or using algorithms that discard certain details. For example, reducing the resolution of images or compressing them with a lossy image compression format like JPEG.
Advantages of Lossy PDF Compression:
- Has higher compression ratios, leading to significantly smaller file sizes.
- Good for scenarios where a slight loss in quality is acceptable, such as in images with high levels of detail or color variations.
Disadvantages of Lossy PDF Compression:
- Loss of some data and details, which could be noticeable, especially in high-quality images.
- Not recommended for documents where maintaining the highest possible quality is critical, such as in medical imaging or professional photography.
Lossless Compression:
Lossless compression reduces file size without sacrificing any data or quality. The compressed file, when decompressed, is an exact replica of the original without any loss of information. In the case of PDF files, lossless compression might involve techniques like Run-Length Encoding (RLE), Huffman coding, or the Lempel-Ziv-Welch (LZW) algorithm. These methods identify and eliminate redundancy in the data without discarding any details.
Advantages of Lossless PDF Compression:
- Maintains the original quality of the content without any loss at all.
- Good for scenarios where preserving the highest quality is essential, such as in legal or archival documents.
Disadvantages of Lossless PDF Compression:
- Generally achieves lower compression ratios compared to lossy compression.
- May not result in as significant file size reduction as lossy compression, especially for documents with a large amount of complex graphical content.
Datalogics offers 3 standard profiles for compression:
Low – Preserves the quality of the file while still reducing the file size. Smaller file, same great PDF.
Medium – Balances between stripping out all unnecessary content (High) while still maintaining an acceptable level of quality.
High – Simply makes the file as small as possible.
The ‘Low’ and ‘Medium’ profiles are designed to provide lossless compression, and our ‘High’ profile achieves greater compression via our recommended lossy compression configurations. Each profile can be modified to provide more aggressive lossy compression options, like color space conversion, more aggressive image downsampling, and removal of content or dictionaries that are superfluous for specific use cases.
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