Apple Aperture Digital Photography Fundamentals - Manual (Page 21)

Chapter 1 How Digital Cameras Capture Images 21
Understanding RAW, JPEG, and TIFF
It’s important to understand the differences between image file types. RAW, JPEG, and
TIFF file types are described below.
RAW
A camera’s RAW file is an uninterpreted, bit-for-bit digital image recorded by the
camera when the image is captured. Along with the pixels in the image, the RAW file
also contains data about how the image was shot, such as the time of day, the
exposure settings, and the camera and lens type. This information is also known as
metadata . RAW refers to the state of the image file before it has been converted to a
common format, such as JPEG or TIFF. Because most photography applications
previously could not process RAW files, RAW files had to be converted before they
could be used in image processing software.
Why Shoot RAW Files?
There are many reasons to capture images as RAW files rather than JPEG files.
However, it’s important to note that RAW image files require additional work to
achieve the color balance you’re looking for, whereas JPEG files are color-balanced by
the camera for you. JPEG files are also smaller than RAW image files, requiring less
storage space.
The advantages to shooting RAW files are:
 Increased bit depth allows for more color-correction “head room.” The JPEG format is
limited to 8 bits per color channel. RAW images store 16 bits per channel, with
12 to 14 bits per channel of color information. Although it may sound confusing, this
means you can do significantly more color correction without degrading the image
or introducing color noise. (For more information about bit depth, see “
Learning
About Bit Depth ” on page 38.)
 After the RAW file is decoded, you work with the most accurate and basic data
about an image.
 You control the white balance, color interpolation, and gamma correction aspects
of the image during post-production rather than when shooting.
 The image file isn’t compressed, as JPEG files are, which means that no image data
is lost.
 Most cameras are capable of and do shoot color outside the gamut range of JPEG
(both Adobe RGB 1998 and sRGB), which means color clipping occurs when you
shoot JPEG files. RAW files preserve the camera’s original image gamut, allowing
Aperture to make image adjustments that take advantage of the full range of
captured colors.
 RAW files give you control of noise reduction (luminance and color separation) and
sharpening after capture. JPEG noise reduction and sharpening are permanently
applied to the image according to the settings on the camera.