Research of depth of field (DOF) for capsule endoscope is important for the reason that the shapes of the
object plane of the intestine or the stomach are curve surfaces of "<" shape or "c" shape. The depth of field is
dependent on following factors: focal length, circle of confusion, aperture, and subject distance. The first
three factors are improved for wide view angle in prior paper and determined by the chosen sensor, and it is
not going against depth of field. Last factor, subject distance, is the more freedom to enlarge the depth of field.
However, depth of field is the range between near depth of field limit and far depth of field limit that are
acceptably sharp. The fraction of the depth of field behind the focus is always large then the one in front of
the focus distance. The depth of field does change with object distance, and it is increasing as object distance
is increasing. But the object distance of the design for capsule endoscope is short. The object distance setting
in front of the dorm is more efficient to use the depth of field than the one setting at the dome top. Therefore
there is an appropriate design of object distance to make depth of field be used efficiently to inspect curve
surface of intestine and stomach. The more vision information of inspect digestive system is get and is
compared easily to diagnose patients' condition under wide and efficient range of depth of field.
Recently, color reproduction stages are developed greatly, such as liquid-crystal displays, LCD TV, LCD
projectors, DLP projectors, and etc. Wide-color-gamut displays are distinguishing feature of many display
manufacturers. Many researches about multi-primary color displays are proposed, but there are still some
problems which are not solved. This study proposed a novel multi-primary projection display system using
two projectors. One of the two projectors is modified by changing two dichroic mirrors inside. The modified
projector is combined with the other to a new six-primary color display. This study applies equal-luminance
boundary theorem to construct gamut volume and evaluates the merit between gamut volume and brightness.
By this method, the cut-off wavelength of dichroic mirrors can be found out. In the past, to align the images
of the two projectors is pre-distorted to compensate the trapezoidal distortion. This study proposes to
eliminate trapezoidal distortion by using the offset of the projector. This study directly changes dichroic
mirrors to maintain the brightness and contrast, and solves lower brightness and contrast resulted from adding
filters before. Additionally, this study uses a reflection mirror to twist projection path and also constructs a
stage to align projection images more accurately.
Use of the capsule endoscope to inspect the digestive system, and in particular the intestine, for pathological change has recently been a great breakthrough in medical engineering. Some problems, however, need to be overcome. The field of view is not wide enough, and the image quality is not good enough. These drawbacks cause unclear and ambiguous digestive disease examinations by medical professionals. In order to solve these problems, the paper proposes a novel design for miniature lenses with a wide-angle field of view and good imaging quality. The lenses employed in the capsule endoscope would consist of a plastic aspheric lens and a glass lens, in a capsule 9.8 mm (W)×9.8 mm (L)×10.7 mm (H), associated with white LED light sources and a 256×256 CMOS array sensor of 10-µm pixel size. Experimental results prove that the lens field of view can be made as large as 86 deg, and the modulation transfer function for field of view 0 deg can be made 78.2% at 50-lp/mm spatial frequency and 53.3% at 100 lp/mm. Tolerance analysis shows that our design is feasible for manufacture, and consistent with the finished prototype.
Developing the luminous system in a capsule endoscope, it is difficult to obtain an uniform illumination[1] on the
observed object because of several reasons: the light pattern of LED is sensitively depend on the driving current, location
and projective angles; the optical path of LED light source is not parallel to the optical axis of the nearby imaging lenses;
the strong reflection from the inner surface of the dome may saturate the CMOS sensors; the object plane of the
observed intestine is not flat. Those reasons induce the over-blooming and deep-dark contrast in a picture and distort the
original image strongly. The purpose of the article is to construct a photometric model to analyze the LED projection
light pattern, and, furthermore, design a novel multiple LEDs luminous system for obtaining an uniform-brightness
image. Several key parameters resulting as illumination uniformity has been taken under the model consideration and
proven by experimental results. Those parameters include LED light pattern accuracy, choosing LED position relative to
the imaging optical axis, LED numbers, arrangement, and the inner curvature of the dome. The novel structure improves
the uniformity from 41% to 71% and reduces the light energy loss under 2%. The progress will help medical
professionals to diagnose diseases and give treatment precisely based on the vivid image.
Distortion exists in the present capsule endoscope image resulting from the confined space and the wide-angle
requirement [8]. Based on the previous two lens works, the optimal design had obtained that the field of view was about
86 degrees , and MTF was about 18% at 100 lp/mm, but distortion would go to -26%. It's difficult to add another lens on
the 7mm optical path between the dome and imaging lenses for improving distortion. In order to overcome this problem,
we intend to design the optical dome as another optical lens. The original dome is transparent and has an equal thickness,
namely without refracting light almost. Our objective in this paper is to design the inner curvature of the dome and
associate two aspheric imaging lenses in front of the CMOS sensors to advance the distortion with maintaining field of
view and MTF under the same capsule volume. Furthermore, the paper proposes the real object plane of intestine is
nearly a curved surface rather than an ideal flat surface. Taking those reasons under consideration, we design three
imaging lenses with curved object plane and obtain the field of view is about 86 degrees , MTF is about 26% at 100
lp/mm, and the distortion improve to -7.5%. Adding the dome lens is not only to enhance the image quality, but also to
maintain the tiny volume requirement.
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