Patent Grant
8564668
Thermal imagers are used for observation in low light conditions. They are typically sensitive to wavelength ranges that are outside the visible, in the infrared. This includes the near infrared and far infrared. Common applications include military and law enforcement for sighting weapons.
The thermal imagers include a thermal detector chip that detects light in the infrared wavelengths. The detected thermal video images are then displayed to the user on a visible-light video display.
Today, common video thermal detector chips have resolutions of, for example, 320 by 240 pixels. These are relatively low resolution devices compared with more common visible light detection chips, since visible light detector chips have the advantage of being applicable to consumer applications and thus capitalize on those large industries. Moreover, because the photons in thermal applications have lower energy, larger pixels are often required in thermal detector chips, which consequently lowers the total number of pixels per unit area of detector substrate.
On the other hand, visible video displays tend to be higher resolution. A common display resolution is 640 by 480 pixels (VGA). Such displays are often based on liquid crystal (LCD) or organic light emitting diode (OLED) technologies, enabling low power compact devices.
Thermal imagers will use up-sampling to address the resolution disparity between the thermal detector chips and the video displays. The output of each pixel in the lower resolution thermal detector chip is typically replicated into the surrounding, corresponding pixels in the video display. This allows the lower resolution thermal image detected by the thermal detector chips to be expanded into the higher resolution video displays so that the thermal images are displayed on the full scale of the video display.
Often, the thermal imagers will function in dual roles. The same thermal imaging system may sometimes be used in a hand-held mode where the user views the thermal images on the video display directly through the output aperture of the thermal imager and then later attached to a weapon and possibly optically mated with a telescopic scope of that weapon. In these latter applications, possibly only a portion of output of the video display is imaged through the telescopic sight of the weapon. As a result, there is a loss of information since the pixels from the thermal video detector have been upsampled to fill the larger visible video display, but only a portion of that display is visible through the telescopic sight. This suboptimally uses the information from the thermal video detector.
In general, according to one aspect, the present invention concerns a thermal imager. This thermal imager comprises a thermal video detector for detecting thermal video images and generating a video signal representing those thermal video images. Often, imaging optics are used for imaging light onto the thermal video detector. A display mode selector is also provided for enabling selection between different video display modes. A video controller then scales the video signal in response to the display mode of the selector for display on a visible video display. In the typical application, the display mode selector is operated by a user to select between a hand-held mode or mode in which the imager is used with a non-magnifying gun weapon sight, on one hand, and a mode for use with a magnifying telescopic sight of a weapon, on the other.
In the current embodiment, the resolution of the thermal video detector is less than the video resolution of the visible video display. Specifically, in the current example, the resolution of the thermal video detector is one quarter of the display resolution of the visible video display. Then, the video display selector enables user selection between a small video display mode in which the thermal video images are only displayed in a portion of the visible video display and a full scale display mode in which the video images are displayed in the entire or substantially the entirety of the video display.
In general, according to another aspect, the invention features a thermal image display method. This method comprises imaging light onto a thermal detector and detecting thermal video images with the thermal video detector. A thermal video signal representing the thermal video images is then detected. Also, the system receives selection of a display resolution mode. The video signal is then scaled in response to the selected video display mode. And the scaled thermal video images are then displayed on a visible video display.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:
Generally, the thermal imager 100 comprises an input aperture 112. This is typically covered with glass or other transmissive material. In some applications, the input glass aperture is optically coated to attenuate light outside the wavelength operating range of the thermal imager 100 such that the infrared light passes through the aperture into the imager but the visible is reflected or absorbed.
The incoming light 50 in some examples passes through a refractive element 114 or further filtering elements. The light is then collected by a primary mirror 116 and directed to a secondary mirror 118 in a Cassegrain configuration, in one example. The light 50 from the secondary mirror 118 in a typical configuration passes through a central aperture 115 of the primary mirror 116 and is detected by a thermal video detector 120. As described previously, the thermal video detector 120 tends to be a lower resolution device. In the current example, the resolution of the thermal video detector 120 is 320 by 240 pixels.
The thermal video detector 120 generates a video signal representing the thermal video images 150 produced by the light 50. This is provided to a video controller 122, which generates drive signals and video signals for a visible video display 124. In typical configurations, the visible video display is an LCD or OLED based display device.
The visible video images 152 generated by the visible video display 124 are typically imaged by visible light optics 128 at infinity. The visible light thermal video images then pass through the output aperture 130.
In a common application, the thermal imager 100 is used in a hand-held mode or open sight mode where the user's eye 54 directly views the visible thermal video images that are generated by the visible video display 124.
Returning to
The operation of the mode selector 126 and video controller 122 is illustrated with respect to
In more detail,
In the full scale mode, the thermal video images 150 detected by the thermal video detector 120 are displayed in the entirety of the field of the visible video display 124. As described, in the implementation, this actually requires pixel upsampling by the video controller 122 to compensate for the lower resolution display of the thermal video detector 120 (320 by 240 pixels) with respect to the resolution of the visible video display 124 (640 by 480 pixels). Specifically, each pixel of the thermal video detector 120 is replicated by the controller 122 into four pixels of the video display 124. In this mode, the user has the benefit of using the full scale FS of the visible video display 124. This mode is also used with telescopic sights 64 where the input aperture 66 is the same size or substantially the same size as the output aperture 130 of the thermal imager 100.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20110074823 A1 | Mar 2011 | US |
