exposure
Accessing a broader dynamic range by using camera RAW
The histogram displayed on the back of a digital camera may not accurately refl ect the precise
range of tones that is being captured when the photographer elects to shoot in the camera RAW
format. Most cameras provide information that is geared to the photographer capturing in the
JPEG or TIFF format only. A photographer may therefore underestimate the dynamic range that is
capable of being recorded by their camera. Instead of capturing a dynamic range of approximately
fi ve stops the RAW format may be capable of capturing images with a dynamic range that exceeds
7 or 8 stops when using a DSLR camera. The precise dynamic range will vary on the type of
sensor being used as the smaller sensors fi tted to the prosumer digicams do not enjoy the same
dynamic range as the APS and full-frame sensors fi tted to the DSLR cameras.
In the example above the highlights of the distant clouds were fl ashing when the image was reviewed
in the camera (a common option on many digital cameras for indicating when overexposure has
occurred). The histogram associated with the fi le clearly indicated that the highlights were being
clipped. When the fi le was opened in camera RAW the exposure slider was moved to a value of
−0.50 and usable detail (level 245) was returned to this area of the image. The brightness slider
was raised to compensate for the negative exposure value. If the exposure had been lowered in
camera the dark top that the boy is wearing would have required rescuing instead of the highlights.
Most photographers fi nd that it is preferable to rescue the highlights rather than the shadows
(see the chapter ‘Camera RAW’) although due care must be taken not to allow the highlights to
become completely overexposed. Taking two spot meter readings will enable the experienced
photographer to ascertain the subject brightness range and assess whether this is compatible with
the dynamic range of the sensor they are using.