JPEG and RAW Files

JPEG

This popular format is used by the majority of digital cameras, it was developed by the Joint Photographic Expert Group hence the name JPEG.

An image from a six megapixel camera produces a file around 16mb but with JPEG compression this can be reduced to 1˝mb. The format can reduce file sizes up to 20 times, this is why it's widely used by cameras, computers and websites.

To achieve this compression JPEGs go through a series of processes that reduce the size of the file by eliminating excess or redundant information. Because JPEGs don't keep all the information it's referred to as a "lossy" format. Whenever a JPEG file is resaved some of the image quality is lost, so if an image is saved a number of times this deterioration will be noticeable.

One advantage of JPEG is that when they are saved you can choose the amount of compression required. Cameras usually have a choice of different degrees of compression such as: fine - highest quality/largest file, normal - lower quality/smaller file.

For a JPEG image to be displayed it must be decoded, the opposite of the encoding that took place when it was saved to the memory card in the camera. Unfortunately because some of the information was disposed of it will not match the original exactly. At high quality settings it will be virtually impossible to notice the difference.
 
    

The photographs above show a high quality JPEG image on the left compared to a the same image saved at a low quality setting. The photo on the right is suffering from blocky artefacts which are degrading the definition.
Despite the widespread use of JPEG a new format has been available for some time called JPEG 2000. Even this version of JPEG is to be superseded by JPEG XR, both these recent formats aim to address the shortcomings of the original JPEG format.            
                                                                                                                  
RAW

DSLR and many prosumer cameras give you the option to save your photos in RAW format. This format produces files that have a minimal amount of processing, they are 12 or 14 bit instead of the 8 bit with JPEG, this means that the image captured will have a wider range of tones with extra detail in highlights and shadows. It also offers the ability to change white balance, correct exposure, contrast, saturation, to a far greater extent than is possible with JPEG.

  
Adobe Camera Raw program
Instead of these alterations taking place in the camera the majority of the processing is carried out on the computer giving an extensive amount of control. It can't work miracles so if a picture has a major fault such as camera shake the fact that it's a RAW file won't help.

Every camera produces its own version of the RAW format so software has to be used to convert it into a usable file. Normally the camera manufacturer will supply a raw conversion program, some are comprehensive others are not. There are a number of specialized RAW programs such as Aperture, Bibble Pro, Capture One, Elements, Lightroom and Photoshop.

Shooting in RAW has disadvantages, the files produced are far larger than jpegs so the camera will shoot at a slower speed which may be a drawback if you are photographing sport or wildlife. The fact that RAW files have to be converted adds an extra stage to the process of producing photographs.
Choosing JPEG or RAW

Should you be saving your photographs in JPEG or RAW? Check your camera, many only save in JPEG so there's no decision to make. To keep image quality high as possible always save your images on the finest JPEG setting. The exception to this is when you know the image is going to be emailed, used on ebay or a website, so the photograph is only going to be viewed on the computer screen and a small file size is important.

Digital SLRs normally include an option to save RAW + JPEG file of any photograph you take. This means that you can take advantage of both formats in one go, the difference between saving a RAW file and RAW + JPEG is just a few less shots on the memory card.

There are many times when the type of photography you are doing will help you decide which file type to use. For football or motor racing being able to shoot at a fast continuous speed is an advantage which suggests the use of JPEGs. With landscape, wedding photography the highest quality is required so RAW may be used.

If your camera can save in RAW and you're not already using it, should you be? Try it out on your camera, take a number of shots in RAW then take the same subjects in JPEG. Compare the two images to see if you can see any difference, then you can decide if shooting RAW is of benefit to you.