Optical system and method for composing color images from...

Television – Camera – system and detail – Optics

Reexamination Certificate

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C348S079000

Reexamination Certificate

active

06590612

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to image processing systems for microscopes or other optical systems and, more particularly, to image processing systems which compose color images from low-cost optical systems using multiple wavelength illumination.
BACKGROUND OF THE INVENTION
Traditional high performance wide-field microscopes
10
as shown in
FIG. 1
, achieve a high resolution color image of a specimen (object)
16
with a wide field of view of the object information
18
. Also, by means of a beam splitter
24
, the image
22
,
26
,
30
is fed simultaneously to both a video camera
32
and to an eyepiece
28
. The focusing
48
,
52
is often performed using a manual focus controller
46
. However, autofocus controllers
42
which use the digital image context or additional optics can also be employed to send focusing commands
44
through a selector
50
to control the focusing mechanism
54
.
With such microscopes, a user can look: (1) through the eyepiece
28
; (2) at a video monitor
40
connected to the camera
32
; or (3) at a computer monitor
70
connected through a frame grabber
62
and an image processor
66
to the camera
32
. However, looking through an eyepiece strains the eyes, neck, and shoulders of the user. In addition, when two or more persons wish to view an image simultaneously, viewing the image through a monitor
40
,
70
is clearly superior. Therefore, a high quality image on a monitor screen is preferable. Further, a computer
60
, in addition to grabbing, storing, processing and presenting images, can use the output
34
from a camera
32
for image analysis.
However, the complexity and cost of such traditional high performance wide-field microscope systems is considerable. For example, such traditional microscopes provide illumination
14
using a white light source
12
such as a filament bulb. Such bulbs are not energy efficient. In addition, the color temperature of the bulb, which affects the color balance in the image, changes as the bulb ages.
Another costly requirement of traditional microscopes is that to get a good quality electronic image, one usually employs a relatively expensive three-chip RGB (red, green, blue) camera
32
. Such a camera has internal prisms and filters to separate colors, one color for each of three black and white sensors. However, maintaining the relative positions and orientations of the prisms, filters and sensors during the lifetime of the camera is complex.
Also, for traditional microscopes, the most complex component is the objective (lens)
20
between the bulb
12
and the camera
32
. Since the bulb provides white light, a traditional objective
20
is usually color compensated to supply an image for an eyepiece. In other words, the objective
20
has to produce reasonably sharp images
22
for the whole spectrum of interest at the same time. This spectrum is typically the entire visible spectrum.
To achieve the requirements for a microscope, the color compensated wide field objective
20
of a traditional microscope
10
is a compromise to achieve: (1) color compensation; (2) wide field of view; (3) magnification of 50-100 times; and (4) a numerical aperture which typically is 0.9 for a dry (air immersion) objective and 1.3 for an oil immersion objective.
To provide the compromise for a variety of conditions, traditional microscope systems are often equipped with a number of different objectives, for example, to adapt to the thickness of an optional glass cover slip or to provide overview images using a low magnifying objective. Such different objectives require the individual lens elements to be aligned with tight tolerances.
Also, even with the best possible objectives for visual light, some details of the image remain just beyond visibility. Therefore, a common image processing step is ‘image sharpening’ of captured images
64
performed by an image processor
66
. For example, by amplifying the higher spatial frequencies in an image, small details and edges become enhanced in the sharpened image
68
. Selection of such frequency dependent amplification for the sharpening filter can be optimized if the characteristics of the objective are known. However, the objective characteristics are wavelength dependent, and therefore, ideally, each wavelength should have a respective sharpening filter.
Unfortunately, such separate sharpening filters are difficult to achieve with an RGB camera because each color component of the camera responds to light with a spectrum width of typically +/−50 nanometers which causes overlap between the colors. Thus, for example, the green component may respond to light with wavelengths extending from approximately 500 to 600 nanometers. Accordingly, once a sensor of the camera
32
has been exposed to white light, each wavelength's contribution to the blurring of the image caused by the objective can not be determined and therefore the characteristics for a sharpening filter optimized for a wavelength can not be determined. Thus, a sharpening filter for such a system can only be a compromise.
Accordingly, traditional microscopes fail to provide a low cost system having a computer which generates high performance digital microscope images without filament bulbs and three-chip cameras. Such traditional microscopes also fail to permit the use of a simple objective which is suitable for wavelength tailored image sharpening filters.
SUMMARY OF THE INVENTION
This invention provides a novel design for a low-cost system for digital image microscopy. The system has a performance comparable to that of a much more expensive traditional microscope. Also, the invention can be used to improve the performance of an existing microscope system.
One object of the invention is to generate high quality microscope images on a computer screen to obviate any need of the user to look through the eyepiece. Accordingly, the invention does not provide a direct optical path from the specimen to a user's eyes, but instead lets the images pass through a camera and an image processing computer.
Another object of the invention is to provide an optical system having: (1) an objective which receives electromagnetic radiation from an object, modifies the electromagnetic radiation, and emits the modified electromagnetic radiation as an image of the object; (2) a focusing mechanism which controls the movement of the objective along at least one path to modify the image; (3) one or more cameras which detect separate images for each of a plurality of frequency bands of the modified electromagnetic radiation of the image emitted by the objective; and (4) an automatic focus controller which, in accordance with the detected images: (a) provides control parameters to the focusing mechanism; and (b) determines for each of the frequency bands, an optimal image which corresponds to an optimal focus of the objective for that frequency band. The images can be detected/captured at different times. Also, the camera can be one or more black and white cameras.
A further object of the invention is to provide an automatic focus controller having: (1) a filter calculator for receiving the detected images as image signals and for generating filtered image signals such that noise components of the image signals have been reduced, the noise components being reduced by increasing energy contributions from parts of the image signals which contribute a relatively larger proportion to image components than the noise components and by decreasing energy contributions from other parts of the image signals which contribute a relatively larger portion to the noise components than to the image components; (2) an energy calculator for receiving the filtered image signals and determining energy levels of the filtered image signals; and (3) a control calculator for receiving the energy levels and for generating the control parameters in accordance with the energy levels.
An additional object of the invention is to provide a registration controller which aligns a plurality of optimal images. This registra

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