RAW Files

A Basic Outline and Guide to Understanding and Using 'Camera RAW'

Clive R. Haynes FRPS

Introduction and Overview

The introduction and development of RAW files marks a considerable step forward in the development of digital camera technology and image fidelity.

Why Shoot in RAW?
One distinct advantage in using RAW is the high degree of control that one retains over the captured image.
Having made the decision about ISO, aperture and shutter speed combination other 'in-camera variables' at the time of shooting remain under our control.
Once having captured a scene in RAW one has the ability to virtually revisit the scene and make changes to the camera settings, these include:

Exposure Compensation
White Balance
Colour Control
Tonal Response
Lens Aberration
Noise Reduction

A 'Super Negative'
Changes made at the RAW editing stage retain quality as they are not 'destructive' to pixels. Once the image is opened within Photoshop, the original RAW file itself remains available for further editing if required. By using RAW one retains a 'super-negative'.

What about JPEG and TIFF?
When shooting in JPEG the camera processor makes decisions based upon the amount of 'compression' required for the image. The image looses data during this process and thus fidelity is eroded.
TIFF files are very much larger than JPEG, the processing isn't 'lossy' but the image captured remains 'as is' without the advantages of adjustment and editing as to be found in RAW.

8 bit and 16 bit
Most 'serious' camera's capture a 12 bits per pixel per channel. Unfortunately JPEG has a limit of 8 bits per channel - so a JPEG discards around one third of the data - hardly good news for image fidelity!
An 8 bit image will present 256 levels of greyscale (and this translates for colour into 8 bits per channel - Red, Green & Blue - to give 24 bit total - hence '24 bit colour').

Shooting in (RAW) - 16 bit presents some 32,000 levels of greyscale - a considerable improvement!
Images shot in 16 bit are therefore smoother and their integrity is greatly retained during adjustment and editing.

Is there a downside to RAW?
The downside is confined to the time it takes to write the image to the camera memory, though this is speeding up almost daily and the consequent amount of file space the image occupies (larger than JPEG but smaller than TIFF).

If shooting speed is important as opposed to quality, then choose JPEG - you'll certainly get your pictures - it's a matter of 'horses for courses'.

What do I do?
I shoot RAW as a matter of standard routine, swapping to JPEG only when necessary. You never know when you're going to need to squeeze that extra amount of image quality out of a seemingly ordinary shot.

For a deeper understanding and appreciation of all RAW can offer plus extensive options for the associated RAW Browser in 'CS' I recommend this book:
'Camera RAW with Adobe Photoshop by Bruce Fraser
Published by: Real World
ISBN: 0-321-27878-X

The following pages take you through the main areas of Camera RAW operation. Click the link below.

Know - How Contents
Camera RAW 'Home Page'


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