RAW File Format

A Raw file is…

• not an image file per se (it will require special software to view, though this software is easy to get).
• typically a proprietary format (with the exception of Adobe’s DNG format that isn’t widely used yet).
• at least 8 bits per color – red, green, and blue (12-bits per X,Y location), though most DSLRs record 12-bit color (36-bits per location).
• uncompressed (an 8 megapixel camera will produce a 8 MB Raw file).
• the complete (lossless) data from the camera’s sensor.
• higher in dynamic range (ability to display highlights and shadows).
• lower in contrast (flatter, washed out looking).
• not as sharp.
• not suitable for printing directly from the camera or without post processing.
• read only (all changes are saved in an XMP “sidecar” file or to a JPEG or other image format).
• sometimes admissable in a court as evidence (as opposed to a changeable image format).
• waiting to be processed by your computer.

A camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor.


Raw image files are sometimes called digital negatives, as they fulfill the same role as negatives in film photography: that is, the negative is not directly usable as an image, but has all of the information needed to create an image. Likewise, the process of converting a raw image file into a viewable format is sometimes called developing a raw image, by analogy with the film development process used to convert photographic film into viewable prints.

Shooting in JPEG

When you shoot in JPEG the camera’s internal software will take the information off the sensor and quickly process it before saving it. Some color is lost as is some of the resolution.


The major actor in this case is the Discrete Cosine Transforamtion (or DCT) which divides the image into blocks (usually 8×8 pixels) and determines what can be “safely” thrown away because it is less perceivable. And when the image is put back together a row of 24 pixels that had 24 different tones might now only have 4 or 5. That information is forever lost without the raw data from the sensor recorded in a Raw file.


The quality of a JPEG taken with a DSLR will still be far better than the same shot taken with a top-of-the-line point-n-shoot camera that is as old as your DSLR. You’ll actually be able to shoot more shots using JPEG than Raw because the slowest part of the whole process is actually saving the file to your memory card – so the larger Raws take longer to save.