Making sense of different file formats can be difficult, especially if you have no prior graphic design knowledge. However, you should know the basics, especially when working with a graphic designer for your book cover or interior formatting. Becoming familiar with the alphabet soup of file formats will make for easier client-designer communications, so it’s a good idea to brush up on the lingo. Let’s take a closer look at some commonly used file formats:
EPS
If your project involves illustrations, you’ll probably come across the EPS file format, which is great for printing line art, from technical drawings in a book to high-resolution banners and large signs. EPS stands for Encapsulated Postscript and is a format commonly associated with Adobe Illustrator or CorelDRAW files for vector graphics, which are lines and shapes defined by mathematical calculations. Vector graphics are scaleable and therefore have the same image quality at any size.
AI
AI is the native Adobe Illustrator file format that is vector-based, similar to the EPS format. While it is a proprietary format, AI has more flexiblity and capability than EPS, although EPS is an open format that can be used with a variety of applications.
JPG
JPG is a compression format for raster graphics, which are images made up of pixels, rather than the lines and curves of vector graphics. With JPG, you lose some image quality, because the format compresses the data when saving the image. The tradeoff is smaller file size, so images load or transfer faster, which makes it a popular choice for websites and email graphics.
TIFF
Unlike JPGs, TIFF files use lossless compression, which means they don’t lose quality when compressed. Consequently, they’re the best option for high-resolution images, but their file size can be large, so they are best used for print projects, rather than online graphics that need to load quickly.
PNG
PNGs are often compared to the GIF file format, as they were created to be its better alternative in regards to compression and colors. A PNG file has another distinct advantage: it can be saved with a transparent background, which is ideal for layering images.
PSD
PSD is the native Adobe Photoshop format, which allows for the existence of multiple layers. For example, a book cover designer will often work with modifying layers in a PSD while developing the design concept, then merge those layers and save the cover art as a smaller, more manageable JPG or TIFF image for the author.
INDD
INDD is the extension for documents created with Adobe InDesign, which is a professional-grade page layout application commonly used for multi-page documents such as brochures, magazines and books. INDD files contain all the content, formatting, styles and linked images for a particular publication. Your book designer will likely use InDesign to both create your print book and generate your ebook.
IDML
IDML files are an interchange format for InDesign files represented in XML. The primary use for IDML is to be able to move between different (older) versions of InDesign.
Ebook Formats: EPUB, MOBI, DOCX, PDF
When it comes to ebook formatting, the files you’ll see supported on readers most often are EPUB and MOBI. There are slight differences between the two: MOBI is XHTML-based with JavaScript capabilities and is vendor-specific (Kindle), while EPUB is XML-based and vendor-independent.
DOCX is the Microsoft Word file format used for conversion into other ebook formats. It’s great for editing and as a starting point for ebook conversion of an all-text book but is not a widely supported format on e-readers and does not offer the design flexibility of InDesign for page layout.
Finally, PDF, which stands for Portable Document Format, allows a document to be viewed without the application used to create the document. Because it works across platforms, i.e. Windows or Mac, PDF is a highly portable and extremely versatile format. It is not an ebook format in the standard reflowable sense, but a digital representation of a particular page layout or publication.
Hopefully this overview gives you some basic knowledge about common file formats in the graphic design and book production world, so you can communicate more effectively with your designers and formatters. At the least, you now have some cool acronyms to toss into casual conversation at your next cocktail party or happy hour gathering.
