Apple Aperture Digital Photography Fundamentals User Manual
Page 19
Chapter 1
How Digital Cameras Capture Images
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CMOS
CMOS sensors are capable of recording the entire image provided by the light-sensitive
elements in parallel (essentially all at once), resulting in a higher rate of data transfer to
the storage device. Additional circuitry is added to each individual element to convert
the voltage information to digital data. A tiny colored microlens is fitted on each
element to increase its ability to interpret the color of light. Advances have been made
in recent years in the sensitivity and speed of CMOS sensors, making them the most
common type of digital image sensor found in professional DSLRs.
Megapixels
A camera’s resolution capability is measured in megapixels. This measurement is based
on the number of millions of pixels of image information that can be captured by the
light-sensitive elements on the digital image sensor. Thus, a 15 megapixel camera is
capable of capturing 15 million pixels of information.
ISO
Traditionally, the International Standards Organization (ISO) has provided a benchmark
rating of the relative sensitivity of film. The higher the ISO rating, the more light-
sensitive a particular film is. Higher ISO films require less light to record an image. The
ISO rating has been redefined for digital cameras, indicating the image sensor’s
sensitivity to light. Most DSLRs have ISO settings from 100 to 3200 ISO.
Unfortunately, at higher ISO settings (400 ISO and above), some cameras have difficulty
maintaining consistent exposure for every single pixel in the image. To increase the
sensitivity of the digital image sensor in these situations, the camera amplifies the
voltage received from each image sensor element prior to converting the signal to a
digital value. As the voltage signals from each element are amplified, so are anomalies
within solid dark colors. This results in sporadic pixels with incorrect bright color values,
also known as digital noise. For more information on digital noise, see “
Bayer RGB pattern on CMOS sensor
Voltage values for each element
are created simultaneously.