All digital cameras record images in JPEG format and JPEG is the only file format that can be viewed in all viewing devices and edited by all image editors. For this reason, JPEG is known as the universal file format.


All digital cameras record images in JPEG format and JPEG is the only file format that can be viewed in all viewing devices and edited by all image editors. For this reason, JPEG is known as the universal file format.

When an image is captured in JPEG format, the image processor in the camera converts the raw image data into Red, Green and Blue (RGB) pixel values (a process known as demosaicing). It then applies white balance, saturation, sharpening and other adjustments according to pre-determined formulae. These settings are effectively locked into the image file.

The camera’s microprocessor then compresses the image to reduce the amount of storage space it occupies. And this is the main downside of the JPEG format: image data is lost during this process. The more the image is compressed (by adjusting the Quality setting), the more information is discarded. This ‘lost’ data can never be recovered.
The actual size of a JPEG file depends on the complexity of the subject that has been photographed. Shots containing large areas of blue sky can tolerate a higher degree of compression so they can be two to three times smaller than pictures of detailed subjects – even though they might have originally been the same size as uncompressed files.

One of the advantages of the JPEG format is that the degree of compression is easily adjustable. Almost all digital cameras provide at least two compression levels in the image ‘Quality’ setting; typically designated ‘Fine’ and ‘Normal’. The image ‘Size’ setting has nothing to do with the JPEG format. It simply determines the size of the pixel array that makes up the image. It, too, is adjustable in most cameras.

All digital SLR cameras and some Advanced digicams provide photographers with the ability to shoot raw files. (These files are often presented as ‘RAW’ although these files are simply the raw image data that comes from the camera’s sensor.) The difference between JPEGs and raw files is that JPEGs are processed in the camera whereas raw files have to be processed on your computer.

Having to convert your images from raw to an editable format (JPEG or TIFF) adds an extra step to your workflow. If this is irksome to you, you’re probably better off shooting JPEGs – especially if you don’t print your shots any larger than A4 size. However, if you want to get the most from your digital camera, shooting raw files is the best option.

When you shoot raw files, all of the information recorded by each photosite is used by the camera’s image processor to create the digital image. Nothing is discarded, even when the image processor compresses the raw file to make it smaller. The compression is ‘lossless’ which means all of the image data is retained – and usable by the photographer for subsequent editing.

Unfortunately, raw files are usually proprietary. Not only is Canon’s format different from Nikon’s, Olympus’s and Sony’s and everyone else’s, but raw formats may also vary from model to model within a manufacturer’s range. Before you can edit raw files they must be converted into an editable format – normally JPEG or TIFF (Tagged Image File Format). This requires special software, which is normally supplied with the camera.

The capabilities of this software vary widely between different manufacturers. Some manufacturers provide a wider range of adjustments than others and some have more intuitive user interfaces. Some include basic editing software, while others don’t.

A good raw file converter will allow you to correct errors in exposure, adjust brightness levels to ensure both highlights and shadows contain detail, remove colour casts and, generally, make your digital photograph look as much like the original scene you photographed without losing any of the fine tonal nuances that make the difference between an excellent digital picture and a poor one.

Shooting raw files allows you to take control of the white balance, saturation, sharpening and contrast adjustments during the conversion process. And, because it is done on your own computer, you have much more processing power at your fingertips than the camera can possibly provide.
This is an excerpt from Mastering Digital Photography Pocket Guide 2nd Edition.
Click here for more details on this and other titles in the Pocket Guide series.


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