DOI:10.2214/AJR.06.0715
AJR 2007; 188:W96-W97
© American Roentgen Ray Society
Simple Method to Eliminate Camera Reflections in Digital Photographs of Single-Emulsion Films
Gowthaman Gunabushanam and
Sanjay Sharma
All India Institute of Medical Sciences New Delhi, India
WEB—This is a Web exclusive article.
Often, there is a need to digitize film-based images—that is, convert
images on film into an electronic format—for making presentations or for
submission to a journal [1].
The process of digitalization is best done with a dedicated film scanner
[2]. However, because a scanner
may not be readily available, radiologists often photograph films using a
digital camera. A frequently encountered problem when photographing films is
that a reflection of the camera or a light source is formed on the image.
Eliminating these camera reflections can be difficult because image quality is
best when the camera is held at right angles to the film, with the region of
interest in the center of the frame.
Some solutions to get around the camera reflection problem include covering
the front of the camera with a nonreflective material (e.g., black paper) so
that the reflection is less noticeable on the digital image, positioning the
camera at a slight angle to the film so that the camera reflection is
projected outside the frame or region of interest, and increasing the
camera-film distance and then zooming-in to the region of interest (authors'
personal observations). These maneuvers are rather cumbersome and also lead to
decreased quality of the final image.
We describe a simple and effective method to eliminate camera reflections
when photographing single-emulsion films. Single-emulsion films have only one
side coated with light-sensitive chemicals
[3,
4]. The coated side is
nonreflective, whereas the uncoated side is glossy and fairly reflective. When
any single-emulsion film, for example, a mammogram, is placed on the viewbox,
the right way to read it is to have the glossy, reflective side facing the
viewer. If it is photographed this way, the camera reflection becomes
conspicuous (Fig. 1A).
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Fig. 1A —Digital photographs of mammogram show usefulness of described
method. Digital photograph of mammogram film taken with uncoated, glossy side
facing camera. Note reflection of digital camera (arrow) on
image.
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The method for eliminating reflections consists of photographing the film
after flipping it on the viewbox so that the coated, or nonreflective, side
faces the camera. The digital photograph thus obtained is a mirror image of
the actual film (Fig. 1B). This
digital mirror image is then corrected on the computer by horizontally
flipping it back, using the flip function available in most commercially
available software. For instance, in Adobe Photoshop 6.0 (Adobe Systems), this
is done by selecting the Rotate Canvas option on the Image tab. The Flip
Horizontal option is chosen on the sidebar. This flips the image horizontally
around the vertical axis. The new image thus saved has a conventional
configuration with the elimination of the camera reflection
(Fig. 1C).
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Fig. 1B —Digital photographs of mammogram show usefulness of described
method. Digital photograph of same mammogram film as A but taken with
coated, nonreflective side facing camera. Digital mirror image of original is
obtained, and, unlike in A, there is no camera reflection.
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Fig. 1C —Digital photographs of mammogram show usefulness of described
method. Same image file as B but after applying horizontal flip
function using software program. Right-left laterality is restored to
conventional state as it appears to radiologist interpreting mammogram. This
image is now identical to A except camera reflection has been
eliminated.
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To eliminate camera reflection, this method makes use of a unique property
of single-emulsion films—the difference in reflectivity of the two
surfaces. Although mammograms have been used in the example provided, the
method is equally applicable for use with all single-emulsion films including
duplicating film, light-exposed or video-imaging film, and spot films. It may
also be useful in photographing single-emulsion laser-printed films such as
LI-HM DL, LI-FM DL (Fuji Medical Systems), and Ektascan-IR/IRC (Eastman Kodak
Company).
Although the described method is not a substitute for a film digitizer
system, it does provide a simple means to eliminate camera reflections when
photographing single-emulsion films. An added advantage is that this method
can be used in combination with other methods that already may be in use.
References
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AJR 2005;184:1353
-1355[Abstract/Free Full Text]
- Curry TS, Dowdey JE, Murry RC. Physical characteristics of X-ray
film and film processing. In: Curry TS, Dowdey JE, Murry RC.Christensen's physics of diagnostic radiology, 4th ed.
Media, PA: Lea and Febiger, 1990:137
-147
- Bushberg JT, Seibert JA, Leidholdt EM, Boone JM. Screen-film
radiography. In: Bushberg JT, Seibert JA, Leidholdt EM, Boone JM.The essential physics of medical imaging, 2nd ed.
Philadelphia, PA: Lippincott Williams & Wilkins, 2002:145
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