Now that we’ve defined the various characteristics of digital images, we can examine formats. We’ll outline the basic structures of file formats and their specifications. After that, we can look at specific file formats and see what kind of object each supports.
Purpose-driven
Formats are developed to support a particular application, media type or process. To evaluate the suitability of a particular format, it’s useful to list the various classes of function that the format supports. Here are the most common options.
Capture
Some formats are specifically designed to facilitate image capture. The JPEG format was originally designed as a standardized format for digital cameras. Raw image formats are designed to serve the specific engineering needs of camera manufacturers. This may include special features and capabilities which are unique to a particular camera brand or model. .
Edit
Optimizing images presents a series of challenges that are very different from the ones posed by capture. This can include the need to merge multiple images, to work on selected areas in an image, and/or replace pixels. Most importantly, formats for editing need to allow for reversible changes. TIFF and PSD formats have become the formats of choice for this kind of work because of their flexibility to include all kinds of components in the file. And DNG has become the most capable raw file editing format because of the components that it supports. HEIF is potentially ushering in a new era of edit formats.
Delivery
Traditionally, file delivery puts a premium on predictable rendering through unambiguous color and tonal reproduction. This is usually coupled with either an emphasis on quality or on small file size. For traditional photos, a JPEG file is often the right choice for delivery if it is made with the proper level of compression. In cases where a 16-bit file is required, a TIFF is a better delivery format. PNG is optimised for colors, hard edges and transparency, which makes it great for images with text or logos. For dimensional images or inherently connected images, you’ll need one of the more modern formats.
Archive
When building an archive, it’s usually desirable to save the highest quality image in a standardized format. This can help ensure that the file renders properly and is accessible long into the future. TIFF is commonly understood to be the gold standard for conventional images, but a lossless JPEG or JPEG2000 can be just as good for 8-bit files. DNG offers archive functionality for raw images that is unmatched by any other format, including the ability to automatically check file integrity. And HEIF allows for storage of multimedia and dimensional objects that may be impossible with any other format.
Connectivity
Some formats offer functions that enhance cloud connectivity in important ways. DNG supports editable proxy images that allow for distributed editing of raw images. And the HEIF format includes the ability to wrap application-specific proxies into a single file.
In the next post, we will examine what goes into the creation of a file format.