Photographic Image Quality:
Recording format
Digital cameras today offer the user a wide range of choices for recording the sensor contents onto the memory card. In all fairness, the out-of-the-box setting of this function is often the best one for many applications. But to take full advantage of the camera, a photographer should understand all of the options and consciously set the one that is best for the intended use of the images.
▸ One important consideration in doing this is to realize that many of the recording choices are designed to save space on the memory card and the time that it takes to actually transfer the information to the card. Saving memory space is no longer relevant! Large capacity, cheap memory cards are the norm, and space on the computer for long-term storage is almost free. On the other hand, recording time might be relevant, but only if the camera is being used for large bursts of high-speed continuous shooting such as action sports.
▸ The opposite consideration is to retain the maximum amount of information available in the sensor when it is recorded. Many of the recording choices for image dimensions or quality will irretrievably damage the image without clearly announcing this fact to the user.
▸ Setting the recording format is done somewhere on the camera's menu system, for which there is no standard between manufacturers or even within a single manufacturer's camera lines. Frequently there will be two menus called something like “quality” and “size”—we'll discuss the options under the two actual file structures that are used: JPEG and RAW.
▸ If you are using your phone or one of the compact "point-and-shoot" cameras, you won't have a choice of format: the image will be saved as a JPEG. You might have a choice of compression level, though—so read on.
JPEG
The JPEG file structure was developed almost as soon as computers were able to display graphics. (“JPEG” is pronounced “jay-peg” and stands for the name of the group that designed it.) It is now a universal standard for images on the Internet, and can be displayed by virtually any device anywhere. To produce it, the camera uses a software technique called a “compression algorithm” to reduce file size. The important thing to know about this is that when the file gets smaller, some data and quality will be lost and the process cannot be reversed.
▸ Why you would want to use JPEG: as just stated, it's universal. It's also the default format for most digital cameras, so users don't have to do anything to select it. It requires no computer processing other than what the camera provides, so you can immediately email your images to friends, post them on social media, copy them to your computer like any other file and look at them instantly. In some cameras, this is the only format that is offered.
▸ Why you might not want to use JPEG: even the highest quality compressed file, although it retains very good quality, will never be as capable of computer manipulation and production of large fine prints as a RAW file.
▸ JPEG quality: part of the standard is that JPEG files can be made larger or smaller by selecting how much compression to apply. Less-compressed files retain more information and thus quality; more-compressed files of course save space and upload time (if that's relevant to a particular use of the file). Camera menus might use adjectives such as “normal” and “fine” or offer the user a scale from 1–10, 10 being the highest quality. Always select the highest possible; you can make it smaller later.
▸ Aspect ratio: a sensor is built with a specific aspect ratio—for FF and APS-C sensors this is 3:2; for micro four-thirds and many compact cameras it is 4:3. The camera's recording menu might offer other choices, for example 16:9 for display on a TV screen. Always use the built-in ratio—the others just throw away pixels at the top & bottom or sides of the sensor!
▸ Picture size: you will often see a choice—perhaps small, medium, and large—for the recorded image. Always choose large! This time, pixels are thrown away everywhere (at worst, one of every two).
▸ Special effects or styles: many cameras offer a selection of effects that can be applied to the recorded image, such as “vivid,” “film grain,” “black-and-white,” and so on. The marketing department is at work again! All of these can be done much better with post-processing software without losing the original image. (These are not the same as “scene” selections that affect the camera's automatic exposure choices.) Since the effects are done by the camera's own computer chip, they affect only JPEG images, not RAW.
RAW
A RAW file literally contains the complete raw data, pixel-by-pixel, that was recorded in the camera's sensor. Unfortunately, there is no standardized “RAW” file structure—each manufacturer's system is unique, each with a different filename extension. (Examples include .cr2, .arw, .rw2, and so on.)
▸ Cameras that offer RAW recording come with software that reads their own file structure into the computer and converts it to other, more common, formats. Professional-level image processing programs read RAW files from all major manufacturers and are constantly updated to handle the latest ones.
▸ Why you would want to use RAW: to preserve the maximum possible image data, especially for making large display and fine art prints. Post-processing of RAW files allows for much more adjustment of exposure, color, and other qualities of the image than is possible in JPEG format. This is how professionals achieve the highest quality and greatest control over their work.
▸ Why you might not want to use RAW: if your images will only be used on the Internet or in small prints, the extra data and control is probably not needed. Or if you simply don't have access to post-processing capability, you might not want to bother with RAW except to retain the possibility of using it in the future.
▸ How to compromise: record both RAW and a (possibly small) JPEG. At the cost of more space on the memory card and slower recording time, you get the best of both worlds—immediate online use and all the flexibility and processing power you can apply to the image as time permits.