Patent Application
20140160337
1. Field
The present disclosure relates generally to video camera systems, and more particularly, to viewfinders used in camera systems.
2. Background
Camera viewfinders enable a camera operator to control certain aspects of images captured by cameras including, for example, image content, focus, etc. In video cameras, the viewfinder displays video captured by the camera in a small display screen that may have a diagonal measurement of between 2 inches and 9 inches. Cathode ray tube (CRT) technology has been long used for viewfinders in studio-quality camera systems but CRT systems may not be readily adaptable to high definition applications. These conventional systems often employ monochrome CRT displays for use in viewfinders.
Most conventional broadcast cameras do not have an auto focus system and an operator must use a viewfinder with sufficient resolution to be able to manually focus a picture captured by the camera. High resolution cameras typically use a viewfinder that has a high resolution monochrome CRT display with a dimension of about 2 inches. However, availability of such CRT displays is limited and many replacement display technologies suffer from lower resolution and/or poor dynamic response.
In an aspect of the disclosure, a viewfinder may be constructed using a projection system contained within the viewfinder housing. The projection system enables the viewfinder to offer a selectable display resolution and configurable aspect ratio.
In an aspect of the disclosure, a viewfinder comprises a light source, one or more imaging panels that produce an optical output representative of an image using light received from the light source, a screen that displays the image. A housing encloses the light source, the one or more imaging panels and the screen. The housing may be adapted to receive an eyepiece used to view the image displayed on the screen. The eyepiece may be used to magnify the image.
In an aspect of the invention, the optical output of the imaging panels may be produced from a video signal provided by the camera. The screen may be rectangular and typically has a diagonal dimension that is nine inches or less. In some embodiments, the screen has a diagonal dimension of two inches or less.
In an aspect of the disclosure, the screen has a resolution sufficient to display standard definition images and/or high definition images. In one example, the screen has a resolution that is selectable between 800×480 pixels and 1280×800 pixels. Images may have various resolutions and be in various formats. An example format is Wide Extended Graphics Array (WXGA). An example resolution is 1280×800 pixels. However, one of ordinary skill in the art will appreciate that different resolutions and/or different formats may be implemented without deviating from the scope of the claims.
In an aspect of the disclosure, the screen has a front side and a rear side, and the screen receives the optical output on the rear side of the screen, while the image is viewable on the front side of the screen through the eyepiece. The screen may be constructed from a particulate material such that the screen is characterized by a granularity at its surface and/or within its interior. The resolution of the screen may be determined by the granularity. The screen may be constructed from a fibrous material, and the resolution of the screen is determined by fiber width. The screen may comprise a polytetrafluoroethylene (PTFE) foil.
In an aspect of the disclosure, the image is viewable as a reflection from the screen and the resolution of the screen is determined by a texture of a surface of the screen. The texture of the surface of the screen may be derived from one or more of a chemical treatment of the surface, an embossing of the surface, and an etching of the surface.
In an aspect of the disclosure, the light source produces white light, and a plurality of color filters provides a different colored light to each of the one or more imaging panels. In some embodiments, the light source sequentially produces light having different wavelengths, and the one or more imaging panels comprises a single panel that is sequentially illuminated with the different light.
In an aspect of the disclosure, the one or more imaging panels comprise a digital micromirror device (DMD). In an aspect of the disclosure, the one or more imaging panels comprise a liquid crystal display panel.
In an aspect of the disclosure, one or more optical elements are configured to provide a desired optical path length between the imaging panel and the screen. The optical elements may include reflective and/or refractive elements.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
Certain aspects of video production systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawing by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.
By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, image processors, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionalities described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a non-transitory computer-readable medium. A computer-readable medium may include, by way of example, non-transitory storage such as a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., compact disk (CD), digital versatile disk (DVD)), a smart card, a flash memory device (e.g., card, stick, key drive), random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), a register, a removable disk, as well as a carrier wave, a transmission line, and any other suitable medium for storing or transmitting software. The computer-readable medium may be resident in the processing system, external to the processing system, or distributed across multiple entities including the processing system. Computer-readable medium may be embodied in a computer-program product. By way of example, a computer-program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.
Certain embodiments of the described invention provide an adaptable viewfinder that may be used to display video images having a broad range of formats and/or resolutions. A projection system may be provided within the viewfinder. The projection system may comprise a screen having a diagonal size that can be less than 2 inches. The projection system may be used as a replacement and/or upgrade for cathode ray tube (CRT) viewfinder displays. The projection system may provide various resolutions, and may support both black and white, and color displays.
Viewfinder 104 may include a decoder 140 that receives video from camera 102 and provides image data for display using display system 142. In one example, decoder 140 and display system 142 communicate through shared memory. In another example, display system 142 may receive a formatted and/or encoded video stream. The viewfinder 104 may provide images in color. An example of such a color viewfinder is a 2.7″ quarter high definition (QHD) liquid crystal display (LCD) color panel.
A video processing system of the viewfinder 104 may include a scalar. The scalar may convert incoming video signals into a particular format and/or resolution. The video signal may be received from the camera 102. The video signal may be converted to a resolution corresponding to a compact pico projector engine. For example, the scalar may convert video signals to a Wide Extended Graphics Array (WXGA) format with a resolution of 1280×800 pixels. The scalar may also convert the video signals to other format types and/or resolutions. One of ordinary skill in the art will appreciate that different resolutions and/or different formats may be implemented without deviating from the scope of the claims.
Lens system 106 may be controlled to provide a desired optical configuration of lenses, which configuration may specify, for example, a depth of field setting, a numerical aperture, and a focal length.
In rear-projection mode 200, an image is projected toward one side of screen 204 and viewed by an observer 206 from the other side of screen 204. In some embodiments, the observer 206 views the image through an eyepiece, which may magnify or otherwise adjust or correct the viewed image. Rear-projection screen 204 is typically constructed from a translucent material that passes light with some amount of scattering caused by diffuse reflection within the translucent material, or at one or more surfaces of the screen 204. A transmission factor and the amount of scattering may be determined by the size of particulates (i.e. granularity) in the translucent material, strand sizes of fibers in the translucent material and/or a weave 304 or other patterns 300 within or upon the surfaces of the translucent material (see
The projection screen material is typically configured to scatter light such that an image focused on the projection screen 204 or 224 may be viewed from different angles. Pattern 300 illustrates an idealized pattern of particles that may be used for a back-projection screen 204. The lighter spots 310 represent areas of translucency that are approximately the size of one pixel in an image and that act as a point source of light representative of the pixel. Pattern 300 may also represent an idealized front-projection screen 224, where the lighter spots 310 represent highly reflective areas.
In some embodiments, texture on the surface of projection screen material may be created using a fibrous material that may have a generally woven structure 304. In some embodiments, a textured surface of projection screen material may be derived from particles from which the projection screen material is constructed and/or which may be embedded in the surface of projection screen material. In some embodiments, surface of projection screen material may be textured by chemical treatment, or by embossing and/or by etching. In one example, a white colored PTFE foil used for projection screen has a thickness of approximately 100 μm. PTFE foil may comprise a textured surface and be manufactured with suitable properties to act as a rear projection screen. These properties may include porosity, pore size, density and other characteristics.
In some embodiments, near-ideal diffuse reflection of light, characterized by omnidirectional scattering of light, may be accomplished by controlling the grain size, weave, particle size and other attributes of the screen material. The translucent material may be selected based on a plurality of additional properties that may include the transmission factor of the screen, which can affect brightness. The use of translucent materials with high diffusion properties may result in lower transmission factors and may necessitate the use of higher-powered light sources.
In front-projection mode 220, an image may be projected on the same side 228 of the screen 224 that is viewed by a camera operator or other observer 226. Front projection systems may use a screen 224 that is constructed from high reflectivity materials. Screen 224 may have a surface texture that is selected and controlled to provide a desired resolution. For example, the surface 228 of screen 224 may comprise a roughened or pitted surface that has peaks, valleys, pits and other discontinuities 306, 308 that serve to diffusively reflect incident light. The size and frequency of occurrence of the discontinuities may determine the resolution of screen 224 and, as a consequence, of the viewfinder.
A cross-section view of a screen 320 is also shown for illustrative purposes in
Projection screen 204 or 224 may be constructed using a material that has a textured surface, a porosity and/or a structure comprising fine particles, where the texture of the surface, pores and/or fine define a dimension that may be less than the dimension of a single pixel in the displayed image. In some embodiments, the texture of the surface, pores and/or fine define a dimension that may be close in magnitude to the dimension of a single pixel in the displayed image.
Imaging system 202 or 222 may receive images for projection from one or more of an image processor 122, encoder 124 and an outside video feed. Images may be produced by a camera 102, a video production system, a video recorder, and so on. The image projected on the screen may be viewed along a direct line of sight or along an optical path that includes one or more of a lens system, a mirror and a prism. The displayed image may have one of a plurality of aspect ratios, and may be provided in either black and white or color.
Rear-projection screen 204 may be constructed using a material selected for its diffusion properties. Diffusive materials permit light to pass through the material with limited absorption, but with significant scattering. Scattering may result from repeated scattering events which change the direction of the path of photons (see
Projection systems may exhibit uneven light distribution resulting in an effect that may be referred to as a hot spot. Hot spots may occur when a reflection or other diffused image of a light source or lens, particularly for front-projection systems. Hot spots may occur in rear projection systems because light dispersion from the projection screen 308 may be dependent on the angle of light rays from the projection optics 306, and because the limited light path length of the compact projection system 302 may create a considerable range of angles of light rays.
A hotspot may be observable in a rear projection display screen 204. Hot spots occur when the screen material is thin or lightly diffusive. The hotspot is a diffused image of the light source. Hotspots may be suppressed by eliminating a straight line of sight through the screen 204 to the light source (relative to the optical path). In one example, the screen 204 may be deployed at an angle to the light path. Image generation processors and software may be adapted to remove the keystone distortion that would otherwise arise from the angled display screen 204. Hotspots may be avoided by tilting the angle of viewing, by orientation of an eyepiece, for example. Hotspots may be avoided by coating one or more surfaces of lenses, mirrors and prisms. Keystone correction resulting from tilting the projection screen 204 may be performed either optically, or by processing the video signal provided to the image panel 204.
In certain embodiments, the screen material for a rear-projection screen 204 may be selected or configured to achieve a reflection coefficient that reduces or eliminates glare arising from reflected stray light or invading light that may leak through a housing of the viewfinder 104 and/or a projection display system. In some embodiments, a light absorbing layer may be applied to the screen to prevent ambient light from reflecting from the viewed, front side of the screen. In some embodiments, the housing can be sealed to prevent stray light from entering the viewfinder.
Projection system 402 typically comprises a compact optical engine that includes imaging panel 404, projection lens 406 that produces an image for projection on screen 408 or 444. Additional optical elements 422, 424, 432, 434, and 442, including one or more refractive and/or reflective elements, may be configured to provide a pre-focused and aligned optical output such that the optical engine can be quickly installed within viewfinder 204 with relatively minor adjustment to obtain a focused image on projection screen 408 or 444. In some embodiments, a compact optical engine may also comprise projection screen 408 or 444. In some embodiments, an optical engine may be configurable for use with projection screens 408, 444 of various dimensions. For example, projection screen 408 or 444 may have a diagonal dimension of approximately 2 inches. Projection screen 408 or 444 may have larger diagonal dimensions of 7 inches, 9 inches, etc., or a smaller diagonal dimension, as desired or as determined by the specification and requirements of viewfinder 104.
In one configuration 400, a projection system 402 has a relatively simple light path between projection optics 406 and back-projection screen 408. Projection optics 406 typically comprise a plurality of lenses that receives light from imaging panel 404 and that provides a focused image in a plane coincident with back-projection screen 408, and with a desired depth of focus that can maintain a focused image under normal operating conditions. For example, variations in temperature may cause expansion or contraction of certain viewfinder components 204, thereby causing increased or reduced light paths.
Configurations 420 and 430 illustrate projection systems 402 that employ reflective elements 422, 424, 432 and 434 to increase the path length between imaging panel 404 and projection screen 408. One or more of reflective elements 422, 424, 432 and 434 may comprise convex or concave mirrors, prisms and so on. Additional optical elements may be deployed along the light path between imaging panel 404 and projection screen 408 to focus, defocus, combine and/or deflect light.
Configuration 440 illustrates a projection system 402 that includes one or more reflective elements 442 for directing light from imaging panel 404 onto front-projection screen 444. Projection screen 444 may exhibit lower attenuation than rear project screens 444 and may simplify construction of projection system. The reflective elements 442 may comprise any combination of convex or concave mirrors, prisms, etc.
In the embodiment illustrated at 500, a digital light processor (DLP™) 502 is used to generate a projection image. A DLP™ device can create an image using a matrix of microscopically-small mirrors fabricated on a semiconductor integrated circuit (IC), and the DLP™ device may be referred to as DMD 502. The micromirrors are typically actuated using electrostatic forces to switch the mirror between an on (reflecting) and off (nonreflecting) position. Each mirror of DMD 502 represents a pixel in the projected image. In the on state, light incident onto the mirror is reflected into the lens making the pixel appear bright on the screen. In the off state, the light is directed away from the lens and is internally absorbed, thereby causing the pixel to appear dark. Although, the DMD 502 operates primarily as a digital device, individual mirrors can be pulsed to provide a grayscale effect between on and off positions. In one example, a DMD 502 having a maximum switching frequency of approximately 66 KHz may support 256 gray levels.
A light source 506 provides the light selectively reflected by the micromirrors of DMD 502. To project a color image, three DMDs 502 may be used to generate red, blue and green components of the complete image using color filters to provide colored light to each of the three DMDs 502. Alternatively, a single DMD 502 may receive a multiplexed image, with a sequence of image portions being used to selectively reflect a current color of light provided by light source 506. Optical element 504 may be deployed along the light path, and may include elements for combining three or more colored image portions.
In the embodiment illustrated at 520, an image for projection is generated using one or more LCD panels 508. Light source 506 directs a light through LCD panel 508, which forms a mask representative of the image to be displayed. Three LCD panels 508 may be used to generate red, blue and green components of the complete color image using color filters to provide colored light to each of the three LCD panels 508. Alternatively, a single LCD panel 508 may receive multiplexed portions of the color image, each portion being used to selectively pass a color portion of the complete image. Light source 506 may comprise filters to produce the colored light. Optical element 504 may be deployed along the light path, and may include elements for combining three or more colored image portions.
To obtain a color display, multiple panels 502 or 508 may be used, each providing a different color of the final image. Typically, three colors are combined to obtain a color image, the colors comprising red, green and blue. One or more dichroic filters or mirrors may be used to combine the images. A dichroic filter may comprise a thin-film filter, or interference filter which exhibits very accurate color filtering and selectively passes light of a small range of wavelengths (i.e. colors) while reflecting the other colors. A dichroic mirror or reflector may reflect a small range of wavelengths. In some embodiments, LEDs are used as a light source 506. LED color dichroics may be used to merge the separate color light derived from LED light sources into a single beam. LED color dichroics are specifically optimized for random polarized light emitted from LEDs, providing high transmission and reflection in the respective wavelength ranges of the LED colors. The three-colored light may then be homogenized using fly's eye homogenizers or other homogenizing optics. Homogenizers are used to spread light in order to obtain an evenly illuminated surface at the DMD 502 or LCD panel 508.
Some embodiments use a single DMD 502 or LCD panel 508, illuminated with different wavelength light in a repeating sequence to obtain an image. This field-sequential-color (FSC) approach involves the display in quick successions of three sub-pictures or fields, which are typically the red, blue and green primary colors.
Other technologies can be used to generate images. In one example, an image generation is accomplished using a liquid crystal on silicon (LCoS) panel. In another example, an organic light-emitting diode (OLED) may be used, whereby a light-emitting diode (LED) is coated with an emissive electroluminescent layer formed from an organic compound which emits light in response to an electric current. These and other devices may be used to generate projection images.
Certain embodiments of the invention provide a viewfinder comprising a low cost display system, with high brightness and a much wider color spectrum than can be obtained with direct view LCD panels.
The processor 604 is responsible for managing the bus 602 and general processing, including the execution of software stored on the computer-readable medium 606. The software, when executed by the processor 604, causes the processing system 664 to perform the various functions described infra for any particular apparatus. The computer-readable medium 606 may also be used for storing data that is manipulated by the processor 604 when executing software.
By way of example and without limitation, the aspects of the present disclosure illustrated in
The viewfinder 104 may comprise a light source 506, and one or more imaging panels 502 or 508 that receive light from the light source and produces an optical output representative of an image. The image may be derived from a video signal received from the camera 102. The light source 506 and one or more imaging panels 502 or 508 are typically deployed within the housing 402.
The light source 506 may produce white light whereby a plurality of color filters provide a different colored light to each of the one or more imaging panels 502 or 508. The light source 506 may produce a sequential series of light wavelengths for provision to a single panel 502 or 506. In one example, the light source 506 comprises a plurality of differently colored LEDs. In some embodiments, the imaging panels comprise a DMD 502. In some embodiments, the imaging panels comprise an LCD panel 508.
A screen 408 or 444 may be deployed to display the image produced by the one or more imaging panels 502. The light source 506 and screen 408 or 444 are typically deployed within the housing 402. The screen 408 or 444 can be rectangular and typically has a diagonal dimension of nine inches or less. In some embodiments screen 408 or 444 has a diagonal dimension of two inches or less. Characteristics of the screen 408 or 444 deployed within the viewfinder 104 are selected to provide a desired resolution. For example, the screen 408 or 444 may be used to display standard definition images having an aspect ratio of 4:3, or high definition images having another aspect ratio, such as 16:19, with 800×480 pixels or 960×540 pixels.
The screen 408 or 444 has front and rear sides and, in some embodiments, screen 408 receives light from the imaging panels 502 or 508 at the rear of screen 408 or 444, while the image is viewable through the eyepiece 450 or objective lens 410 on the front side of screen 408 or 444. In such embodiments, screen 408 or 444 may be constructed from a granular material, whereby the resolution of screen 408 or 444 is determined by the size of particles and/or granularity of the material. The screen 408 or 444 may be constructed from a fibrous material, and the resolution of the screen 408 or 444 may be determined by fiber width and/or tightness of weave. In some embodiments, screen 408 or 444 comprises a PTFE foil.
In some embodiments, the image is viewed as a reflection from screen 408 or 444 and resolution of the screen 408 or 444 may then be determined by a texture of a surface of the screen 408 or 444. The texture of the surface of the screen 408 or 444 may derived from one or more of a chemical treatment of the surface, an embossing of the surface, and an etching of the surface.
In some embodiments, one or more optical elements 422, 412, 414 and 416 may be arranged and configured to provide a desired optical path length between the imaging panel 502 or 508 and the screen 408 or 444. Optical elements may comprise one or more refractive and/or reflective elements such as a lens, a mirror, a prism a collimator, etc. The optical elements may be complex elements including multiple individual components.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
This application claims the benefit of and right of priority to U.S. Provisional Application Serial No. 61/675,273, filed on Jul. 24, 2012, which is expressly incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61675273 | Jul 2012 | US |
