Scientific Forum
Special Topic
The Digital Darkroom, Part 2:
Digital Photography Basics
Gregory M. Galdino, MD; Paul N. Manson, MD; and Craig A. Vander Kolk, MD
We summarize here the second part of a 3-part series on the digital darkroom. In
this part, we review the basics of digital photography, including (1) the variables in
image capture, processing, and storage that affect picture quality and (2) the various types of digital cameras currently available. The full text of the complete series,
including expanded illustrative material and complete bibliographic documentation,
is now available on our journal Web site at http://www.mosby.com/aesthetic. Please
see page 476 for instructions on how to access Aesthetic Surgery Journal Online and
view the entire series.
D
igital photography is gaining popularity as a replacement for standard 35-mm
photography in plastic surgery, offering such benefits as an overall reduction in
costs, the ability to easily archive and retrieve images, flexibility in communication, enhanced patient education, and computer simulation.1-7 Most photographic principles related to standardization for medical photography, such as those pertaining to
lighting and patient positioning, also apply to digital photography.8-17 However, the
technology of digital photography differs significantly from that of conventional photography; a digital camera is more akin to a scanner or video camera than to a standard
35-mm camera. The user must understand the basics of digital cameras and image capture to take reproducible, standardized photographs while reaping the benefits of this
new technology.
Image Capture
The keystone of digital photography is the image sensor. The most widely used sensor is
the charged-coupled device (CCD), an electronic chip composed of individual lightsensitive electrodes, each of which represents a pixel (picture element) in the final image.18
Light travels through the lens and strikes the electrodes, causing an electronic signal to
be created; the strength of this signal is proportional to the amount of light striking each
electrode. The signal is converted into digital form by a digital converter, processed by
the camera’s microprocessor, and displayed as a color image. Because the CCD is not
sensitive to color, only a black-and-white image is created. However, by placing individual color filters over each electrode, corresponding to red, green, and blue light, the
processor is able to add color to the final image.18,19 Most cameras available today capture 24-bit color (16.7 million colors) and provide image resolutions ranging from 1.5 to
3.5 million pixels, even though the human eye cannot delineate nearly that many colors.
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From the Johns Hopkins Hospital,
Baltimore, MD.
Accepted for publication July 7,
2000.
Reprint requests: Gregory M.
Galdino, MD, Division of Plastic
Surgery, Johns Hopkins Hospital,
8130A McElderry, Baltimore, MD
21234.
Copyright © 2000 by The American
Society for Aesthetic Plastic
Surgery, Inc.
1084-0761/2000/$12.00 + 0
70/1/111557
doi:10.1067/maj.2000.111557
Scientific Forum
Variables directly affecting
image quality
Variables that directly affect the overall
quality of the final digital image
include lens quality (focus, zoom, and
macro capability), viewfinder type,
image sensor, resolution, compression,
and image processing quality.20
Lenses
As in 35-mm photography, the better
the quality of the lens, the better the
picture quality. In some professional
digital cameras, standard 35-mm
autofocus lenses can be mounted on a
digital camera body, allowing interchangeability of existing lenses.
Focus
A digital camera can have fixed-focus
(nonadjustable), autofocus, or manual
focus capability. Fixed-focus cameras
are not recommended for medical
photography. Some digital cameras
offer both autofocus and manual
focus modes, which are usually selected by means of a switch on the camera lens or body. Except for some
newer professional models, such as
the Nikon D1 (Nikon Corporation,
Tokyo, Japan), the focusing mechanism in a digital camera is often slower than that in a standard 35-mm
single-lens reflex (SLR) camera. As in
Figure 1. This digital photograph illustrates the macro capabilities of digital cameras without
35-mm photography, the focusing
the need for additional attachments to the camera. It was taken with the Nikon 950 Coolpix
on macro mode through use of the on-camera flash and softbox lighting. The inset shows the
mechanism looks for contrast and verflower icon commonly used to indicate the macro mode.
tical lines to adjust the focus sharply.
Thus, focusing on the eye for a facial
digital zoom.18,20 Digital zoom often results in poorer
shot or the nipple/areola for a breast shot usually
quality magnification; in addition, the resolution (see
ensures a sharp picture; the subject is then adjusted in
below) is always reduced, because only a portion of the
the frame after focusing. Focusing on areas lacking conCCD is used.18,20 Zoom functions used in medical photrast and lines, such as the cheek or abdomen, can result
tography should rely on optical zoom, not digital zoom.
in out-of-focus pictures.
However, digital zoom is useful for checking the clarity
Zoom
of the image once it is captured.
Magnification of the subject that is performed optically
through the lens is called optical zoom. Magnification
Macro mode
that is controlled digitally, by allocating a smaller portion
Macro capabilities differ between digital cameras. Some
of the CCD to scene capture and then interpolating (addcameras can photograph a subject as close as 6 in withing) extra pixels to reach the final zoom desired, is called
out a macro mode. Other cameras offer a specific macro
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dependent on the size of the sensor. For this reason,
manufacturers often give focal length in terms of 35-mm
equivalency when reporting the zoom capabilities of the
lens. (For example, a 60-mm digital macro lens may be
equivalent to a 90-mm standard 35-mm lens.18) In general, digital cameras require more light than 35-mm cameras.22 Sensor sensitivity is expressed in terms of effective
ISO rating. Most cameras have an effective ISO rating
between 50 and 200 ISO. Adjustable ISO settings allow
photography in lower light conditions but introduce
noise (lessen image quality) at higher ISO settings.
Resolution
Figure 2. Macro images taken with the Nikon 950 Coolpix illustrate
parallax error using the parallax viewfinder. This error is maximized in
images taken close to the subject. A, The view through the viewfinder.
B, The resulting image. To avoid this error, the LCD display should be
used to frame subjects at close distances when one is using a camera
equipped with a parallax viewfinder.
mode (often indicated by a flower symbol or icon) or
super macro mode in which the camera can focus from
0.8 to 20 in, depending on the camera (Figure 1).
Viewfinder
The optical viewfinder is typically one of the following
two types: (1) parallax (rangefinder), seen in many pointand-shoot 35-mm cameras, and (2) through-the-lens, or
SLR. Parallax viewfinders may exhibit parallel distortion
(inaccuracies in subject/lens relationship). This is more
noticeable the closer the camera is to the subject; it disappears or becomes less noticeable at greater distances from
the subject (Figure 2).18
Image sensors
CCDs are generally smaller than film and thus have
different focal lengths. The focal length of the lens is
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Understanding resolution is paramount to understanding
digital photography. The best way to approach resolution is to determine what the image will be used for. For
example, when one is photographing patients, it is
rarely, if ever, necessary to enlarge the image to 8 × 10
in for printing; usually, images measuring 5 × 7 in or
even smaller are sufficient. Most cameras with total
resolutions of 1.5 to 2.7 million pixels capture sufficient
resolution to print excellent 5 × 7-in and 8 × 10-in
photographic-quality prints. If the images are going to
be displayed only on a monitor, an even lower resolution
is sufficient, because most monitors display a maximum
of 72 pixels per inch (PPI) at 640 × 480 or 600 × 800
resolution.21 A general rule of thumb is to always shoot
at a slightly higher resolution than you think is necessary
(according to what the image will be used for).21 Photographing at low resolutions (less than 1.5 million pixels)
can result in low-quality images. File size should be
adjusted with compression (discussed below) instead of
resolution if the resolution setting falls between 1.5 and
2.7 million pixels.
Compression
Most digital cameras capture on one of two file formats:
(1) TIFF (Tagged Image File Format) and (2) JPEG (Joint
Photographic Expert Group). The TIFF format retains all
of the information in the original image and is thus too
large to be used efficiently for patient medical photography. The JPEG format uses a mathematical algorithm to
compress image file size. The compression ratios most
commonly used in this format produce too little image
quality loss to be detected by the human eye.22 Degradation in image quality is noticeable with large compression ratios and repeated resaving of the image in JPEG
format by means of image editing software.22 Compression is usually indicated on the camera as the quality setting—super, high, normal, or low.
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Figure 3. A, An image taken with the Sony DSC-D700. B, The same image taken with the Olympus 600-L. Both images
were taken under identical lighting conditions and color balanced with an 18% gray card (eliminating color shift). This
example shows how digital pictures differ from one camera to the next on the basis of the different image sensors and
processors used in the cameras.
Image processing
Metering
Because different manufacturers use different sensors and
processors to capture and process the image, all digital
cameras are not equal. This is especially evident with
regard to dynamic range—the camera’s ability to capture
detail in the lightest and darkest portions of a photograph
(Figure 3). Different cameras capture the same image differently. To maintain consistency in preoperative and postoperative photographs, the same digital camera should be
used for both.
Most light meters are programmed to expose the photograph for 18% gray (reflecting 18% of the light hitting
it).18 The matrix metering setting (multisegment; portions
of the entire frame contribute to the meter reading) is the
most useful and accommodating setting. It should be
used at all times, except when there is very bright light in
a portion of the photograph (eg, in the operating room)
or a very bright or very dark backdrop, in which case
spot metering may be more useful to avoid inaccurate
exposure.
Variables indirectly affecting image quality
Depth of field
Lighting
Most of the principles of conventional photography that
have to do with lighting setup apply to digital photography. There are several publications illustrating proper
setup.1,3-6, 9,10 Digital photography may use an external
flash via a “hot shoe” connection, the on-camera flash, or
existing light (depending on the lighting conditions) to
allow proper exposure. Because the performance of most
digital cameras decrease as the amount of light decreases,
adequate lighting is essential for good-quality digital photographs (Figure 4).18,22
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In digital photography, as in 35-mm photography,
depth of field is dependent on the focal length of the
lens and the size of the CCD.18 Many digital cameras
have f-stops only in the range of f/2.2 to f/11; thus, the
depth of field is not as adjustable as it is in conventional
35-mm photography.
Color temperature
The term color temperature refers to the inherent color of
the light (in degrees Kelvin): the lower the temperature,
the warmer (slightly reddish) the light; the higher the
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A
B
Figure 4. A, A picture taken in low light conditions. B, A photograph of the same subject taken in adequate lighting
conditions. Note the loss of image detail in the image captured under low light; most professional lite digital cameras
perform best in high light (low ISO) situations. These images were taken with the Olympus 600-L through use of softbox only (A) and softbox with additional photoflood lighting (B) only (no flash).
temperature, the colder (slightly bluish) the light.22 Inas-
Camera Performance
much as digital cameras do not use film, the sensor records
Factors that can improve the performance, enhance the
efficiency, and maximize use of the digital camera include
power, storage capacity, and image transfer capability.
these color temperature casts in the image. Thus, the
color cast can be compensated for by using the white balance control, specific for color temperatures, such as
incandescent and flash. However, for the many conditions in medical photography that involve mixed lighting,
the auto white balance setting should be used.
Output
Monitors, liquid crystal display (LCD) projectors, and
television sets can all be used to view digital images.
Because each source might have different methods of displaying color, have different sets of directions according
to which it instructs the device on how to display color,
and be adjustable with regard to brightness, contrast, and
color, digital images may appear slightly different on dif-
Power
The source of power for the camera has a profound
impact on the length of time the camera can be used, the
maximum number of pictures that can be taken continuously, and the use of the flash and LCD. Digital cameras
are generally powered by one of the following types of
batteries: standard alkaline (usually AA), nickel cadmium,
nickel metal hydride, and lithium ion. The best source of
power is rechargeable batteries, specifically lithium ion or
nickel metal hydride, which lose their charge faster than
disposables but can frequently be reused more than 100
times.18
ferent devices. Software is available to help calibrate the
Storage
monitor display to what is printed or to standardize the
Although digital cameras are “filmless,” they do use a
type of film known as a memory card. Removable
display between computers.
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memory (also known as flash RAM) from digital cameras
generally costs $1 to 5 per MB and comes in 4 standard
formats: Smart Media, Compact Flash, PC Cards, and
Memory Stick.18 An adapter may be required to transfer
images to the computer by means of a card reader or laptop via PCMCIA card slots. A good rule of thumb is to
have a card large enough (32 to 48 MB) that frequent
downloads, which limit picture-taking, can be avoided.
Regularly downloading images into a database can help
you keep track of patient records and information in an
efficient manner.
Image transfer
Image transfer affects digital camera performance and
can have an impact on efficiency. Serial port connections
are generally too slow for a busy practice and are being
replaced by USB connections, which are more than 100
times faster. Removable memory generally requires an
adapter to input the images directly into the computer or
into a card reader. The fastest transfer is accomplished
with an IEEE-1394 (FireWire [Apple Computer, Inc.,
Cupertino, CA], iLink [Sony Corporation, Tokyo, Japan])
connector; these are starting to appear on several newer
camera models.
Choosing a Camera
Our experience has been that the Nikon 950 Coolpix, the
Nikon 990, and the Nikon D1 have macro capabilities
far superior to those of other cameras in their price
range. Nikon, Olympus, Minolta, and Sony have developed cameras targeted for higher-end uses; Fuji and
Canon have also released SLR digital cameras. The only
reasonably priced true SLR digital cameras are the Sony
DSC-D700/770 (Sony Corporation, Tokyo, Japan), the
Olympus 2500 (Olympus Optical Co., Ltd., Tokyo,
Japan), the Nikon D1, and the recently released SLRs
from Fuji and Canon. However, a smaller camera with
the LCD back, such as the Nikon 950/990, is advantageous for intraoperative photography and is the most
portable.
High-end SLR cameras like the Nikon D1 range in price
from $4000 to $5000 and will probably not be available
for less than $2000 in the next few years. These cameras
capture outstanding image quality and are completely
customizable. Most permit the use of interchangeable
lenses. Prices for most of the other higher-end cameras
suitable for photography in plastic surgery range from
$500 to $1500. For those who would like to try digital
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photography without spending a lot of money, the Nikon
950 Coolpix is a good choice; it is available for less than
$600. ■
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