Whether online or offline large file sizes can create a barrier to digital distribution. This (small) document aims to give a few tips on how to reduce sizes while maintaining reasonable quality. Software solutions given here are for use with Windows PCs utilising free and open source software where possible. I have included some links to free online tutorials. The tutorials look useful and providers may have other useful content which I have not checked out. Think before you shrink
- Releasing control? – Your aim in distributing content is to have it used, and often to have it shared by users. To some extent once it is released you lose control, anyone can copy or adapt what you release. How easy do you want to make that? What permissions do you want to give? What restrictions do you want to maintain? Do you want to draw people back to a particular website for updates and additional material? Are there risks to anyone in sharing material?
- Ensure you have appropriate rights – permission to download a file for your own use does not mean automatic permission to share or to modify the file. Hopefully the files will contain copyright or contact details for requesting permission for use. In the case of files that carry a Creative Commons license the terms and conditions for sharing are clearly specified by the choice of license – see https://creativecommons.org/licenses/ .
- Include appropriate metadata – In many cases it is good practice to include details of who created a product and where it can be accessed plus details of copyright and creation/modification date. Sometimes this is included in metadata along with the file (accessed by a right click on the file in Windows Explorer, then a left click on ‘Properties’) which may or may not be copied when decreasing file sizes. Copyright isn’t just about stopping people copying material but can be about ensuring people know what permissions users are given.
- Don’t share more than you intend – In addition to data and information you wish to share you may want to be careful not to share information that could be sensitive or easily misinterpreted. This might include names or photos of people linking them to particular organisations, or embedded information about where a photo was taken. (e.g. in MS Windows you can Check what metadata is associated with a file by a right click on the file in Windows Explorer and then a left click on ‘Properties’ – where you can add or delete metadata under the various tabs.)
- Keep high quality originals and info – Know where graphics, audio and video came from.
- Use batch conversion but check quality – One resize may not fit all. Tools that allow you to perform the same process on multiple files make life easier but may still leave some files larger than they need to be while compressing others to a point where they lose too much quality. Look at what results you get and be prepared to adjust a few.
- Provide links to higher quality distribution files – Small sizes aid distribution, better quality often comes with higher sizes.
Audio CD quality audio can easily occupy 192kbps (kilobytes per second) or larger. For spoken audio it is often possible to compress this to 48kbps or less for an MP3 file. A tutorial by Bill Myers on audio compressing using Audacity at https://www.youtube.com/watch?v=zxBXYSwn5w0 , demonstrates converting a 65Mb wav file a 2Mb mp3 and also adding useful metadata. Batch conversion of files can be done using http://sourceforge.net/projects/lamexp/ If posting to the web you can also use a range of audio sharing services such as https://soundcloud.com/ or http://mixlr.com/. Audio content can also be shared as part of a youtube video with a few simple slides to accompany the audio (this adds to the content makes it more likely to be shared with others and might not increase the file size being streamed by as much as you’d expect)
Video It’s six years since I last uploaded anything to Vimeo and i don’t put much on YouTube either, so I’m not up on all the latest features (stay tuned for an update to this file) but these two sites can do amazing things with any videos you want to share widely. They will sort out all the streaming and file size issues for you and make it easy for you to add captions or have clickable links in the videos themselves. Vimeo gives you the option of whether you want people to be able to download your video or not and let the user decide what quality they want according to the size of screen and quality they want (not surprisingly low quality videos for viewing on phones are smaller than HD quality for big TVs).
Graphics Modern cameras take photos at incredible detail but while a 5000kb photo may allow for cropping and an image that will look sharp on a HD TV screen. It will often still look good reduced to 50-200kb for a powerpoint or web site. An explanation image optimization works can be found at https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/image-optimization. Ultimately however the size depends on the format and the level of detail included in the images. Photo managemet software such as Google’s picasa allows for exporting images reducing the size in terms of number of pixels and the image quality. Other free programs for image optimization include http://www.irfanview.com/ (multiple formats and options) and https://pngquant.org/ (png format). PNG format is best for scalable vector graphics or photos that also include transparent areas. Gif works will graphics with few colours and allows for transparency and for animated graphics. JPG format is best for most photos.
Large file sizes are often caused by embedded graphics. Reducing the number or size of graphics will often drastically reduce file sizes. In Word you can compress pictures from the format menu. Both Word and Powerpoint give an option to compress the pictures when saving(you may want to keep a copy with higher quality images than you use in distribution). It might not be necessary to modify all images in a large document, merely identify and optimize the largest images. Sometimes graphics have been cropped within word but still contain the full picture. Saving a copy of the file as a web page (Save as > Other formats > web page) will create a copy of embedded content in a separate folder.
As with word documents lots of the file size may be due to graphics (see above), but may also be due to embedded audio and video. You may opt for compressing audio and video or simply linking to it online.
Sometimes graphics have been cropped within word but still contain the full picture.
Simply clicking on any picture in the document will bring up the Format menu and allow you to select a Compress Pictures option. You can choose to compress all pictures to the same level or change them individually. It may be worth keeping the original document with larger resolution images and saving copies optimised for print, web or email. At lowest quality text within any images will probably be blurred.
Saving a copy of the file as a web page (Save as > Other formats > web page) will create a copy of embedded content in a separate folder and allow you to look at individual file sizes.
Excel Aside from embedded graphics or lots of data the most common reason for extremely large excel files is inadvertently including empty rows and columns.
PDFs, Zipped files, Apps More on these in a future update to this post.