RAW

Vincent Bockaert, 123di.com

Unlike JPEG and TIFF, RAW is not an abbreviation but literally means "raw" as in "unprocessed". A RAW file contains the original image information as it comes off the sensor before in-camera processing so you can do that processing afterwards on your PC with special software.

The RAW Storage and Information Advantages

In the Color Filter Array topic, we explained that each pixel in a conventional sensor only captures one color. This data is typically 10 or 12 bits per pixel, with 12 bits per pixel currently being most common. This data can be stored as a RAW file. Alternatively, the camera's internal image processing engine can interpolate the raw data to determine the three color channels to output a 24 bit JPEG or TIFF image.
RAW (10 or 12 bit)
Red Channel (8 bit) Green Channel (8 bit) Blue Channel (8 bit) JPEG or TIFF (24 bit)

Even though the TIFF file only retains 8 bits/channel of information, it will take up twice the storage space because it has three 8 bit color channels versus one 12 bit RAW channel. JPEG addresses this issue by compression, at the cost of image quality. So RAW offers the best of both worlds as it preserves the original color bit depth and image quality and saves storage space compared to TIFF. Some cameras offer nearly lossless compressed RAW.

The Flexibility of RAW

In addition, many of the camera settings which were applied to the raw data can be undone when using the RAW processing software. For instance, sharpening, white balance, levels and color adjustments can be undone and recalculated based on the raw data. Also, because RAW has 12 bits of available data, you are able to extract shadow and highlight detail which would have been lost in the 8 bits/channel JPEG or TIFF format.

Disadvantages of RAW

The only drawback is that RAW formats differ between camera manufacturers, and even between cameras, so dedicated software provided by the manufacturer has to be used. Furthermore, opening and processing RAW files is much slower than JPEG or TIFF files. To address this issue, some cameras are offering the option to shoot in RAW and JPEG at the same time. As cameras become faster and memory cards cheaper, this option has no longer performance or storage issues. It allows you to organize and edit your images in a faster way with regular software using the JPEGs. But you retain the option to process in RAW those critical images or images with problems (e.g. white balance or lost shadow and highlight detail). Another trend is that third party image editing and viewing software packages are becoming RAW compatible with most popular camera brands and models. An example is Adobe Photoshop CS. However, as stated in my Photoshop CS review, the way Photoshop processes RAW files can be different from the way the camera manufacturer's software does it and not all settings may be recognized.

This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
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