# Patent

## Title
Active video projection screen coordinating grayscale values of screen with color pixels projected onto screen

## Abstract

Instead of a monochromatic projection screen, an active projection screen is provided which varies reflectance and gray level (black to white) in synchronization with the content being shown. Groups of multiple screen pixels, which are smaller than each projected pixel from the projector, are assigned to each respective larger projection pixel.

## Background
TECHNICAL FIELD
The application relates generally to video projection screens.
BACKGROUND
Television designers have gone to great lengths to control the backlight level even going so far as to provide per pixel backlight control for liquid crystal display (LCD) televisions. At the same time, the amount of light emitted by the television has increased dynamically. Coupling this large increase in both contrast and brightness with moving to ten bits per color component (over the eight bits previously used) creates what is termed “High Dynamic Range” content.
Because of the monochromatic nature of projection screens, it has been difficult to realize HDR content through a projector system.
SUMMARY
As understood herein, the refresh rate for e-ink projection systems has become nearly comparable to video displays. In an embodiment, a projection screen has a large array (or set of arrays) of e-ink paper. The pixel size on the screen coming from the projector is larger than the size of an individual element of e-ink. For example, a thirty foot wide screen showing a 4K ultra high definition (UHD) can receive projected pixels roughly one tenth of an inch wide. Depending on the curvature of the movie screen and the projection lenses, the size of the pixels will vary slightly across the screen and there may be a slight alignment distortion. Understanding that the pixel size from the projector is larger than the e-ink element size in the screen, an area is established that can display a smooth range of grayscale values that go from pure black to pure white. By having multiple e-ink elements (each either being black or white), gray scale levels can be established using, e.g., stippling techniques. Also, because each individual e-ink element of the projection screen can be individually addressed, the reflective areas of the screen can be aligned per pixel to locations of the pixels sent from the projector.
In an embodiment, the e-ink elements on the active projection screen can be aligned/calibrated to projected pixels using a grid projected onto the screen from the projector. The purpose of using a grid system to align the pixels with the projection system is to calibrate the screen and define which pixel on the screen is assigned with the corresponding pixels from the projection system.
Consequently, areas of the content meant to appear bright will be very bright and area of the content meant to be dark will be very dark with a smooth, continuous gradation between the two. Furthermore, given that some movie projection systems are running at rates much higher than current e-ink might allow, the e-ink based projection screen may be operated at thirty Hz while the projector can be operated at 60 Hz (or higher).
Accordingly, an apparatus includes at least one computer memory that is not a transitory signal and that includes instructions executable by at least one processor to establish, for at least some pixels of at least some frames of a color video file, respective grayscale values. The instructions are executable to, using each one of at least some of the grayscale values, establish plural screen pixel control values. Each screen pixel control value defines whether an associated screen pixel is to be configured to present a white appearance or a black appearance. Thus, each of at least some pixels in the color video file is associated with plural screen pixel control values. The instructions are also executable to arrange the grayscale values and/or the screen pixel control values in a grayscale file in synchronization with the frames of the color video file from whence the grayscale values were derived. Furthermore, the instructions are executable to render the color video file accessible for projection onto an active screen, and to render the grayscale file accessible to the active screen for control of screen pixels in the active screen responsive to the screen pixel control values.
In some embodiments, the screen pixel control values for each grayscale value are established using a stippling-like technique. The grayscale file and color video file both can be sourced from a single source. Or, the color video file can be sent from a first source to a projector for projection onto the active screen, and the grayscale file can be sent from a second source to the active screen.
In example implementations, the grayscale values are established using luminance information in the color video file. The instructions may be executable for establishing, for all pixels of at least some frames of the color video file, respective grayscale values, and using each one of all of the grayscale values to establish plural screen pixel control values. The active screen can be an e-ink screen.
In another aspect, an apparatus includes at least one computer memory that is not a transitory signal and that includes instructions executable by at least one processor to associate respective groups of plural screen pixels in an active screen with respective individual color pixels from a projector to be projected onto the active screen, and in synchronization with projection of the color pixels onto the active screen, to control the respective plural screen pixels of each of at least some of the respective individual color pixels to establish a demanded grayscale on the active screen.
In examples of this latter aspect, the instructions can be executable to establish, for at least some pixels of at least some frames of a color video file, respective grayscale values, and using each one of at least some of the grayscale values, establish plural screen pixel control values. Each screen pixel control value defines whether an associated screen pixel is to be configured to present a white appearance or a black appearance, such that each of at least some pixels in the color video file is associated with plural screen pixel control values. The instructions may be further executable to arrange the grayscale values and/or the screen pixel control values in a grayscale file in synchronization with the frames of the color video file from whence the grayscale values were derived. Moreover, the example instructions can be executable to render the color video file accessible for projection onto the active screen, and to render the grayscale file accessible to the active screen for control of screen pixels in the active screen responsive to the screen pixel control values.
In further examples, the screen pixel control values for each grayscale value can be established using a stippling-like technique. The grayscale values can be established using luminance information in the color video file.
Example instructions may be executable to associate the respective groups of plural screen pixels in the active screen with the respective individual color pixels by projecting at least one column and/or row of color pixels onto the screen, and activating at least plural columns and/or rows of screen pixels. These instructions may be further executable to, based on at least one image of the at least one column and/or row of color pixels projected onto the screen over activated columns and/or rows of screen pixels, associate respective groups of plural screen pixels with the respective individual color pixels. The instructions can be executable to align at least one edge of at least one frame of color pixels with at least one corresponding edge of the active screen.
In another aspect, a method includes associating plural screen pixels with respective individual pixels to be projected. The method also includes projecting the pixels to be projected onto an active screen associated with the screen pixels to produce a demanded color image, and controlling the screen pixels to produce a demanded grayscale background derived from the respective pixels to be projected.
The details of the present application, both as to its structure and operation, can best be understood in reference to the accompanying drawings, to which like reference numerals refer to like parts, and in which:



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an example system including an example in accordance with present principles;
FIG. 2 is a schematic view of the projection screen showing larger projected pixels superimposed on groups of smaller screen pixels to illustrate that each projected pixel is associated with a respective group of screen pixels;
FIG. 3 is a schematic view of the projection screen illustrating an example alignment initialization process, in which one or more edges of the projected pixel footprint are aligned with respective edges of the screen;
FIG. 4 is a schematic view of the projection screen illustrating an example alignment process, in which a mapping of the association of the screen pixels to projected pixels is generated; and
FIG. 5 is a flow chart of example logic.



DETAILED DESCRIPTION
This disclosure relates generally to computer ecosystems including aspects of consumer electronics (CE) device networks such as projector systems. A system herein may include server and client components, connected over a network such that data may be exchanged between the client and server components. The client components may include one or more computing devices including video projectors and projector screens, portable televisions (e.g. smart TVs, Internet-enabled TVs), portable computers such as laptops and tablet computers, and other mobile devices including smart phones and additional examples discussed below. These client devices may operate with a variety of operating environments. For example, some of the client computers may employ, as examples, operating systems from Microsoft, or a Unix operating system, or operating systems produced by Apple Computer or Google. These operating environments may be used to execute one or more browsing programs, such as a browser made by Microsoft or Google or Mozilla or other browser program that can access web applications hosted by the Internet servers discussed below.
Servers and/or gateways may include one or more processors executing instructions that configure the servers to receive and transmit data over a network such as the Internet. Or, a client and server can be connected over a local intranet or a virtual private network. A server or controller may be instantiated by a game console such as a Sony Playstation (trademarked), a personal computer, etc.
Information may be exchanged over a network between the clients and servers. To this end and for security, servers and/or clients can include firewalls, load balancers, temporary storages, and proxies, and other network infrastructure for reliability and security. One or more servers may form an apparatus that implement methods of providing a secure community such as an online social website to network members.
As used herein, instructions refer to computer-implemented steps for processing information in the system. Instructions can he implemented in software, firmware or hardware and include any type of programmed step undertaken by components of the system.
A processor may be any conventional general purpose single- or multi-chip processor that can execute logic by means of various lines such as address lines, data lines, and control lines and registers and shift registers.
Software modules described by way of the flow charts and user interfaces herein can include various sub-routines, procedures, etc. Without limiting the disclosure, logic stated to be executed by a particular module can be redistributed to other software modules and/or combined together in a single module and/or made available in shareable library.
Present principles described herein can be implemented as hardware, software, firmware, or combinations thereof; hence, illustrative components, blocks, modules, circuits, and steps are set forth in terms of their functionality.
Further to what has been alluded to above, logical blocks, modules, and circuits described below can be implemented or performed with one or more general purpose processors, a digital signal processor (DSP), a field programmable gate array (FPGA) or other programmable logic device such as an application specific integrated circuit (ASIC), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be implemented by a controller or state machine or a combination of computing devices.
The functions and methods described below, when implemented in software, can be written in an appropriate language such as but not limited to C# or C++, and can be stored on or transmitted through a computer-readable storage medium such as a random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), compact disk read-only memory (CD-ROM) or other optical disk storage such as digital versatile disc (DVD), magnetic disk storage or other magnetic storage devices including removable thumb drives, etc. A connection may establish a computer-readable medium. Such connections can include, as examples, hard-wired cables including fiber optics and coaxial wires and digital subscriber line (DSL) and twisted pair wires. Such connections may include wireless communication connections including infrared and radio.
Components included in one embodiment can be used in other embodiments in any appropriate combination. For example, any of the various components described herein and/or depicted in the Figures may be combined, interchanged or excluded from other embodiments.
“A system having at least one of A, B, and C” (likewise “a system having at least one of A, B, or C” and “a system having at least one of A, B, C”) includes systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.
Now specifically referring to FIG. 1, an example ecosystem 10 is shown, which may include one or more of the example devices mentioned above and described further below in accordance with present principles. The first of the example devices included in the system 10 is a projection screen assembly 12. The projection screen assembly 12 can be established by some or all of the components shown in FIG. 1. The projection screen assembly 12 includes an active display or screen in that it contains addressable screen elements that establish screen pixels and that can be controlled to establish grayscale values as demanded by a video file to be shortly disclosed.
For example, the projection screen assembly 12 can include one or more e-ink type screens or displays 14 that may be implemented by one or more e-ink arrays. An e-ink array may be made of small polyethylene spheres (for instance, between seventy five and one hundred micrometers in diameter). Each sphere may be made of negatively charged black plastic on one side and positively charged white plastic on the other. The spheres can be embedded in a transparent silicone sheet, with each sphere suspended in a bubble of oil so that it can rotate freely. The polarity of the voltage applied to each pair of electrodes then determines whether the white or black side is face-up, thus giving the pixel a white or black appearance. Other e-ink technology may use polyvinylidene fluoride (PVDF) as the material for spheres. Other e-ink technologies includes electrophoretic with titanium dioxide particles approximately one micrometer in diameter dispersed in a hydrocarbon oil, Microencapsulated Electrophoretic Displays, electrowetting, electrofluidic, and interferomatic modulator displays that can create various colors using interference of reflected light, bistable displays such as flexible plastic electrophoretic displays, cholesteric liquid crystal displays, nemoptic displays made of nematic materials organic transistors embedded into flexible substrates, electrochromic displays, etc.
Other active screen technology that may be used include “meta materials”, chemical-based active screens, and screens with pixels established by carbon nanotubes.
The projection screen assembly 12 may include one or more speakers 16 for outputting audio in accordance with present principles, and at least one input device 18 such as e.g. an audio receiver/microphone or key pad or control keys for e.g. entering commands to at least one screen processor 20. The example screen assembly 12 may also include one or more network interfaces 22 for communication over at least one network 24 such as the Internet, an WAN, an LAN, etc. under control of the one or more processors 20. Thus, the interface 22 may be, without limitation, a Wi-Fi transceiver, which is an example of a wireless computer network interface, such as but not limited to a mesh network transceiver, or it may be a Bluetooth or wireless telephony transceiver. It is to be understood that the processor 20 controls the screen assembly 12 to undertake present principles, including the other elements of the screen assembly 12 described herein such as e.g. controlling the display 14 to present images thereon and receiving input therefrom. Furthermore, note the network interface 22 may be, e.g., a wired or wireless modem or router, other appropriate interface such as, e.g., a wireless telephony transceiver, or Wi-Fi transceiver as mentioned above, etc.
In addition to the foregoing, the screen assembly 12 may also include one or more input ports 26 such as, e.g., a high definition multimedia interface (HDMI) port or a USB port to physically connect (e.g. using a wired connection) to another CE device and/or headphone port to connect headphones to the screen assembly 12 for presentation of audio from the screen assembly 12 to a user through the headphones. For example, the input port 26 (and/or network interface 22) may be connected via wire or wirelessly via the network 24 to a cable or satellite or other audio video source 28 with associated source processor 28A and source computer memory 28B. Thus, the source may be, e.g., a separate or integrated set top box, or a satellite receiver. Or, the source 28 may be a game console or personal computer or laptop computer or disk player. Yet again, the source 28 and/or the color video source discussed below may be cloud servers on the Internet, and may include and perform “cloud” functions such that the devices of the system 10 may access a “cloud” environment via the server 28 in example embodiments. Or, the server 28 may be implemented by a game console or other computer in the same room as the other devices shown in FIG. 1 or nearby.
In any case, the video source 28 controls the reflectance of the video shown on the screen assembly 12 by the below-described projector by inputting grayscale values to the active pixels of the screen assembly 12. The video source 28 may be a separate video source as shown which receives full color video and derives a grayscale rendering thereof according to principles discussed below, in which case the source 28 is tailored to source a separate piece of grayscale content to maximize the usage of the reflectance properties of the screen assembly 12. Such a source 28 may be separate from the screen assembly 12 as shown or it may be incorporated into the screen assembly 12 in some implementations.
Or the source 28 may be the same as the color video source mentioned below, in which case the color video source may include a color video file for projection onto the screen assembly 12 and a corresponding grayscale video file that is sent to the screen assembly 12 to control the active elements in the screen assembly 12.
The screen assembly 12 may further include one or more computer memories 30 such as disk-based or solid state storage that are not transitory signals, in some cases embodied in the chassis of the screen as standalone devices or as a personal video recording device (PVR) or video disk player either internal or external to the chassis of the AVDD for playing back AV programs or as removable memory media.
Still referring to FIG. 1, in addition to the AVDD 12, the system 10 may include one or more other device types. When the system 10 is a home network, communication between components may be according to the digital living network alliance (DLNA) protocol. Or, the projector and screen can be used in a public movie theater.
In one example, a front projector 32 may be used to project demanded images onto the front of the display 14. The example projector 32 may include one or more network interfaces 34 for communication over the network 24 under control of one or more projector processors 36. Thus, the interface 34 may be, without limitation, a Wi-Fi transceiver, which is an example of a wireless computer network interface, including mesh network interfaces, or a Bluetooth transceiver, or a wireless telephony transceiver.
It is to be understood that the projector processor 36 controls the projector 32 to undertake present principles. In this regard, the projector processor 36 may receive signals representing demanded color images from a color video source 38 which may be the same as or different from the video source 28 described previously and which may be established by any one or more of the source types described previously. When separate grayscale and color sources are used, as opposed to separate grayscale and color video files on the same source, the sources 28, 38 may communicate with each other, e.g., via a wired communication path or via the network 24 as shown.
The projector processor 36 controls a lamp assembly 40 to project color light onto the screen assembly 12. The lamp assembly may be a laser lamp assembly or other type of color illuminator assembly. The projector may further include one or more computer memories 42 such as disk-based or solid state storage.
FIG. 2 illustrates that each of at least some and more typically all of the full color projection pixels 200 that are projected onto the screen 14 by the projector 32 is superimposed on a respective group of multiple smaller screen pixels 202. The screen pixels 202 are the active addressable elements of the active screen, e.g., e-ink globes. Thus, the projected pixels 200 that establish the color video images are larger than the active pixels 202 within the screen 14. In the example shown, four screen pixels 202 are correlated to a single projected pixel 200, although different numbers of screen pixels 202 may be correlated to the projected pixels 200. Note that depending on screen curvature and other factors as discussed below, while each projected pixel 200 typically overlaps multiple screen pixels 202, the number of screen pixels 202 assigned to a first projected pixel 200 may not be the same as the number of screen pixels 202 assigned to a second protected pixel 200.
In the example shown, the projected pixels 202 are illustrated as rectilinear areas that border each other across the entirety of the screen 14. In implementation the shape of each projected pixel 202 may not be precisely rectilinear owing to bleed over of light caused by reflection and other effects including lens structure on the projector 32, but present principles understand that such bleed over between adjacent projected pixels 200 is minimized owing to the grayscale control afforded by control of the screen pixels 202 described below. Also, in implementation the footprint of the combined projected pixels 200 that establish the color video image may not be exactly coterminous with, and may be smaller than, the entire active area of the screen 14, in which case FIG. 2 illustrates only the region of the active portion of the screen 14 onto which the color image is projected.
FIG. 3 illustrates an example alignment initialization process of a calibration process for assigning groups of screen pixels to individual projected pixels. In some implementations, the edges of the projected image from the projector 32 are first aligned with edges of the active area of the screen 14. In the example shown, a left-most column 300 of projected pixels 200 can be projected onto the screen 14. A calibration camera 302 may capture the image of the column 300. The calibration camera 302 can be controlled by a processor 304.
Based on the image from the calibration camera 302, the optics of the projector 32 and/or the direction in which the projector 32 is pointed and/or the distance at which the projector 32 is from the screen 14 can be modified to align the left-most column 300 with the left edge 306 of the active portion of the screen 14 as shown, with the left edge being made more visibly manifest by causing the left-most one, two, or three columns of screen pixels 202 to be all white. The projector 32 may be moved left or right by hand by a person observing the image of the column 300 and/or the column 300 itself as it appears on the screen. Or, the processor 304 may receive the image of the column 300 and control a motor 308 (such as a servo or stepper motor or other appropriate apparatus) to move the optics and/or housing of the projector 32 to align the column 300 with the left edge 306.
Note that in some implementations, the left most column 300 may not be aligned with the left edge 306 of the active portion of the screen but rather with a column of screen pixels 202 that is inboard of the left edge and thereafter regarded as a virtual left edge by the system.
It may also be desirable to align the projector 32 with the top edge 310 of the screen 14, with the top edge being made more visibly manifest if desired by causing the top-most one, two, or three rows of screen pixels 202 to be all white. In the example shown, a top-most row 312 of projected pixels 200 can be projected onto the screen 14. The calibration camera 302 may capture the image of the row 312.
Based on the image from the calibration camera 302, the optics of the projector 32 and/or the direction in which the projector 32 is pointed and/or the distance at which the projector 32 is from the screen 14 can be modified to align the top-most row 312 with the top edge 310 of the active portion of the screen 14 as shown. The projector 32 may be moved hand by a person observing the image of the row 312 and/or looking at the row 312 itself as it appears on the screen. Or, the processor 304 may receive the image of the row 312 and control the motor 308 to move the optics and/or housing of the projector 32 to align the row 312 with the top edge 310.
Note that in some implementations, the top most column 312 may not be aligned with the top edge 310 of the active portion of the screen but rather with a column of screen pixels 202 that is below the top edge and thereafter regarded as a virtual top edge by the system. Note further that the edges 306, 310 may alternatively be the physical edges of the screen if desired, when the physical edges are not coterminous with the edges of the active portion of the screen.
If desired, once the left and top rows of projected are aligned with the left and top edges as described, the right and bottom projected pixel column/row may be aligned with the respective edges of the screen according to the algorithm above by, e.g., expanding or shrinking the footprint of the projected image using, e.g., the optics of the projector or by other means. Or, once the first two edges are aligned, the remaining two edges of the projected image may be projected onto the screen with the underlying screen pixels thus being designated as the virtual right and bottom edge of the screen for calibration purposes.
Present principles recognize that rows and columns of screen pixels 202 may not be precisely linear. For example, the screen 14 may be deliberately configured to be mildly concave, and/or local artifacts might exist to introduce non-linearity. Accordingly, FIG. 4 illustrates that once the projector 32 is aligned with the physical or virtual edges of the screen 14, groups of screen pixels 202 may be associated with respective projected pixels 200 so that when color video is projected onto the screen by means of the projected pixels 200, the grayscale of the respective screen area onto which each projected pixel is directed is established by the screen pixels associated with that projected pixel according to disclosure below, even in the presence of non-linearities.
For illustration purposes, FIG. 4 assumes that each projected pixel 200 encompasses an on-screen area in which three columns and two rows of screen pixels 302 are present. Thus, each of at least some, and in most cases all, of the projected pixels 200 is associated with plural (e.g., six) screen pixels 202. As shown, a column of projected pixels 200 may be projected onto the screen 14. It is to be understood that the process of FIG. 4 can start with the left-most column, working right. Rows may also be aligned according to the algorithm described herein, top to bottom. Or, a grid of projected pixels may be projected onto the screen, combining column alignment and row alignment in a consolidated process.
For simplicity of disclosure, a single column 400 of projected pixels 2001-2007 is shown and screen assignment discussed for the pixels in that column. FIG. 4 shows five columns 202A, 202B, 202C, 202D, 202E of screen pixels with the three left-most columns 202A-C initially being assigned to the column 400 of projected pixels. Candidate columns of screen pixels may be “illuminated” for calibration purposes by, e.g., causing the pixels in the candidate columns all to assume the white configuration.
FIG. 4 illustrates that the columns 202A-E are not linear, with the left-most column 202A moving out of the projected column 400 and the fourth column 200D moving into the projected column 400 beginning at the third projected pixel 2003. The screen pixel columns shift back right by one pixel beginning at the sixth projected pixel 2006. The alignment set up in FIG. 4 may be imaged by the calibration cameras shown in FIG. 3, for example, with the calibration image being sent to one or more of the above-described processors for image analysis to note the above-described non-linearity of the seen pixel columns.
In the example shown, the first, second, sixth, and seventh projected pixels 2001, 2002, 2006, 2007 would be associated with screen pixels in the respective row of the respective projected pixel from the first through third columns 202A, 202B, 202C of screen pixels based on, e.g., imaging the presence of those screen pixels within the respective projected pixels, with screen pixels in other candidate columns not being, associated with these respective projected pixels. In contrast, the third, fourth, and fifth projected pixels 2003, 2004, 2005 would be associated with screen pixels in the respective row of the respective projected pixel from the second through fourth columns 202B, 202C, 202D of screen pixels. The process may continue using successive columns and then rows (or using a grid as mentioned above) of projected pixels to associate respective groups of screen pixels 202 with each respective one or at least some and preferably all projected pixels 200 while accounting for possible non-linearities in the screen 14.
Now referring to FIG. 5, the overall logic of example implementations may be seen. At block 500 screen pixel groups are associated with each individual projected pixel according to the algorithms described above. Thus, each one of some or all of the color pixels in a color video file to be projected is associated with a respective plurality of screen pixels.
The grayscale value to be established by the screen pixels associated with a particular color pixel to be projected are then derived as follow. At block 502, for a color video file to be projected onto the screen 14, the logic moves to block 504 to derive a grayscale file from the color video file. The grayscale file may be derived on a pixel-by-pixel basis.
Any appropriate method may be used for deriving a grayscale file from a color file such that the grayscale values in the grayscale file are synchronized with the color values in the color file using, e.g., timing information carried over from the color file into the grayscale file.
As examples, a grayscale value can be derived as follows for each color pixel to be projected.
In systems in which luminance is directly indicated in the pixel data, that luminance may be used as the grayscale value.
When the pixel data indicates only color values for red, green, and blue (RGB), the corresponding grayscale value to be inserted into the grayscale file can use weighted sums calculated from the RGB values, if desired after the gamma compression function has been removed first via gamma expansion.
In some embodiments, gamma expansion may be defined as:

C_\mathrm{linear}= \begin{cases}\frac{C_\mathrm{srgb}}{12.92}, & C_\mathrm{srgb}\le0.04045\\ \left(\frac{C_\mathrm{srgb}+0.005}{1.055}\right)^{2.4}, & C_\mathrm{srgb}>0.04045\end{cases}

where Csrgb represents any of the three gamma-compressed sRGB primaries (Rsrgb, Gsrgb, and Bsrgb, each in range [0,1]) and Clinear is the corresponding linear-intensity value (R, G, and B, also in range [0,1]).
Then, luminance can be calculated as a weighted sum of the three linear-intensity values. The sRGB color space is defined in terms of the CIE 1931 linear luminance Y, which is given by

Y=0.2126 R+0.7152 G+0.0722 B   [5]

The coefficients represent the measured intensity perception of typical trichromat humans, depending on the primaries being used; in particular, human vision is most sensitive to green and least sensitive to blue. To encode grayscale intensity in linear RGB, each of the three primaries can be set to equal the calculated linear luminance Y (replacing R,G,B by Y,Y,Y to get this linear grayscale). Linear luminance typically needs to be gamma compressed to get back to a conventional non-linear representation.
In contrast, for images in color spaces such as Y′UV and its relatives, which are used in standard color TV and video systems such as PAL, SECAM, and NTSC, a nonlinear luma component (Y′) can be calculated directly from gamma-compressed primary intensities as a weighted sum, which can be calculated quickly without the gamma expansion and compression used in colorimetric grayscale calculations. In the Y′UV and Y′IQ models used by PAL and NTSC, the grayscale component can be computed as

Y′=0.299 R′+0.587 G′+0.114 B′

where the prime distinguishes these gamma-compressed values from the linear R, G, B, and Y discussed above.
Yet again, for the ITU-R BT.709 standard used for HDTV developed by the ATSC, the grayscale value “Y′” can be calculated as:

Y′0.2126 R′+0.7152 G′+0.0722 B′. 

Although these are numerically the same coefficients used in sRGB above, the effect is different because they are being applied directly to gamma-compressed values.
Recall that each color pixel to be projected is associated with plural screen pixels. Accordingly, once a single grayscale value is established for each color pixel to be projected, the process then uses that grayscale value to establish screen pixel control data defining the configuration of each of the plural screen pixels associated with the respective color pixel to be projected. Thus, each grayscale value may be expanded into “N” screen pixel control values to establish, for each screen pixel in the group of “N” screen pixels associated with the color pixel to be projected from whence the grayscale value was derived, whether that screen pixel is to be controlled to be white or black.
In one embodiment, this is done using stippling or stippling-like techniques, in which for lighter grayscale values, more of the screen pixels are caused to present a white appearance, and for darker grayscale values, more of the screen pixels are caused to present as black appearance, sometimes using randomly-selected pixels from among the group of screen pixels.
As additional illustrative examples of stippling-like techniques, halftoning or dithering may be used to configure the plural screen pixels associated with the respective color pixel to be projected to establish the derived grayscale value. Example non-limiting details of such techniques may be found in, e.g., Martin et al., “Scale-Dependent and Example-Based Stippling”, Computers & Graphics, 35(1):160-174 (2011) and Salomon, “The Computer Graphics Manual” (Springer-Verlag London, Ltd., 2011), both of which are incorporated herein by reference.
Note that the grayscale file may contain either one or both of the grayscale values corresponding to a single color pixel to be projected.
In cases in which the refresh rate of the color video is faster than the refresh rate afforded by the active screen, each grayscale value may be an average of multiple color video values for the associated color pixel to be projected during a single cycle of screen refresh to which the grayscale value applies. For example, if the screen is refreshed 30 times per second and the color video is refreshed 60 times per second, each grayscale value may be the average of the two grayscale values derived from the two color pixels to be projected during the single screen refresh period. Or, each grayscale value may be a selected one of the multiple color video values for the associated color pixel to be projected during a single cycle of screen refresh to which the grayscale value applies.
While a 4K screen is mentioned above, it is to be understood that other screen resolutions are encompassed by present principles. For example, individual pixels can be increased on the screen for 8K or higher projection systems or combined to a visually equivalent e-ink contrast grid that allows for larger grayscale areas or blocks. This could happen, for instance, when a 4K projection is presented on a very large screen. The combination of the screen size and the projection resolution influences the size of the matching grayscale contrast areas or blocks of e-ink on the screen. Moreover, the e-ink areas can be adjusted for pixel aspect ratios of different sizes, such as square versus rectangular. The e-ink pixel area shape and size can be tailored to how the color video to be projected is shot, e.g., either as DV or intended for film.
The above methods may be implemented as software instructions executed by a processor, including suitably configured application specific integrated circuits (ASIC) or field programmable gate array (FPGA) modules, or any other convenient manner as would be appreciated by those skilled in those art. Where employed, the software instructions may be embodied in a device such as a CD Rom or Flash drive or any of the above non-limiting examples of computer memories that are not transitory signals. The software code instructions may alternatively be embodied in a transitory arrangement such as a radio or optical signal, or via a download over the internet.
It will be appreciated that whilst present principals have been described with reference to some example embodiments, these are not intended to be limiting, and that various alternative arrangements may be used to implement the subject matter claimed herein.

## Claims

1. Apparatus comprising:
at least one computer memory that is not a transitory signal and that comprises instructions executable by at least one processor to:
establish, for at least some pixels of at least some frames of a color video file, respective grayscale values;
using each one of at least some of the grayscale values, establish plural screen pixel control values, each screen pixel control value defining whether an associated screen pixel is to be configured to present a white appearance or a black appearance, such that each of at least some pixels in the color video file is associated with plural of the screen pixel control values;
arrange the grayscale values and/or the screen pixel control values in a grayscale file in synchronization with the frames of the color video file from whence the grayscale values were derived;
render the color video file accessible for projection onto an active screen; and
render the grayscale file accessible to the active screen for control of screen pixels in the active screen responsive to the screen pixel control values.

2. The apparatus of claim 1, comprising the at least one processor.

3. The apparatus of claim 1, wherein the screen pixel control values for each grayscale value are established using a stippling-like technique.

4. The apparatus of claim 1, wherein the grayscale file and color video file are both sourced from a single source.

5. The apparatus of claim 1, wherein the color video file is sent from a first source to a projector for projection onto the active screen, and the grayscale file is sent from a second source to the active screen.

6. The apparatus of claim 1, wherein the grayscale values are established using luminance information in the color video file.

7. The apparatus of claim 1, wherein the instructions are executable for establishing, for all pixels of at least some frames of the color video file, respective grayscale values, and using each one of all of the grayscale values to establish plural screen pixel control values.

8. The apparatus of claim 1, wherein the active screen is an e-ink screen.

9. Apparatus comprising:
at least one computer memory that is not a transitory signal and that comprises instructions executable by at least one processor to:
associate respective groups of plural screen pixels in an active screen with respective individual color pixels from a projector to be projected onto the active screen; and
in synchronization with projection of the color pixels onto the active screen, control the respective plural screen pixels associated with at least some of the respective color pixels to establish a demanded grayscale on the active screen such that the grayscale values of pixels of the active screen are synchronized with projection of color pixels onto the active screen.

10. The apparatus of claim 9, wherein the instructions are executable to:
establish, for at least some pixels of at least some frames of a color video file, respective grayscale values;
using each one of at least some of the grayscale values, establish plural screen pixel control values, each screen pixel control value defining whether an associated screen pixel is to be configured to present a white appearance or a black appearance, such that each of at least some pixels in the color video file is associated with plural of the screen pixel control values.

11. The apparatus of claim 10, wherein the instructions are executable to:
arrange the grayscale values and/or the screen pixel control values in a grayscale file in synchronization with the frames of the color video file from whence the grayscale values were derived.

12. The apparatus of claim 11, wherein the instructions are executable to:
render the color video file accessible for projection onto the active screen; and
render the grayscale file accessible to the active screen for control of screen pixels in the active screen responsive to the screen pixel control values.

13. The apparatus of claim 9, comprising the at least one processor.

14. The apparatus of claim 10, wherein the screen pixel control values for each grayscale value are established using a stippling-like technique.

15. The apparatus of claim 10, wherein the grayscale values are established using luminance information in the color video file.

16. The apparatus of claim 9, wherein the instructions are executable to:
associate the respective groups of plural screen pixels in the active screen with the respective individual color pixels by:
projecting at least one column and/or row of color pixels onto the screen; and
activating at least plural columns and/or rows of screen pixels.

17. The apparatus of claim 16, wherein the instructions are executable to:
based on at least one image of the at least one column and/or row of color pixels projected onto the screen over activated columns and/or rows of screen pixels, associating respective groups of plural screen pixels with the respective individual color pixels.

18. The apparatus of claim 9, wherein the instructions are executable to align at least one edge of at least one frame of color pixels with at least one corresponding edge of the active screen.

19. A method comprising:
associating plural screen pixels with respective individual pixels to be projected;
projecting the pixels to be projected onto an active screen associated with the screen pixels to produce a demanded color image; and
controlling the screen pixels to produce a demanded grayscale background derived from the respective pixels to be projected such that grayscale values of screen pixels of the active screen are coordinated with projection of color pixels onto the active screen.

20. The method of claim 19, comprising:
arranging grayscale values and/or screen pixel control values in a grayscale file in synchronization with frames of a color video file from whence the grayscale values were derived, the color video file including values representing the individual pixels to be projected.