WO2017180347A1

WO2017180347A1 - High resolution and dynamic range persistence of vision display

Info

Publication number: WO2017180347A1
Application number: PCT/US2017/025761
Authority: WO
Inventors: Nick LEINDECKER
Original assignee: Electricks Llc
Priority date: 2016-04-11
Filing date: 2017-04-03
Publication date: 2017-10-19

Abstract

A persistence of vision (POV) display and method for display of images consisting of at least an 8-bit (256 grayscale values) or 24bit color quality using an LED array having only an on/off (1-bit) control. The display modulates each light emitting element over several very short duration periods to produce an effective 256 perceived grayscale levels, realized with e.g. 12 bit depth hardware grayscale, where the sum of the short duration periods are perceived as a single light intensity to the human eye.

Description

HIGH RESOLUTION AND DYNAMIC RANGE PERSISTENCE OF VISION DISPLAY

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to display devices that produce an image based on the visual effect known as persistence of vision (POV).

Description of the State of the Art

[0002] Persistence of Vision (POV) displays utilize the relatively long integration time constant of the human eye's response to light. Practically, this slow integrated response results in the persistence of a latent image for some time after a light source has been turned off, or has moved to a new location. One example of POV is a light tethered to a string. Holding the opposite end of the string, the light is swung through a circular path. Above a certain speed the swinging light appears to the human eye as a continuous circle of light, rather than a point light traveling through a circular path. The appearance of the circular light is due to the POV effect. A device that can be used to produce the POV effect will be generally referred to here as a POV display (or device).

[0003] Persistence of vision displays are well known, examples of which are found in US5406300, US2003/0080924, WO2000/17483, and US2009/0021510. These known POV displays sometimes use strips of light-emitting diodes (LEDs) where a linear array of LEDs is swept through space to produce a two dimensional latent image.

[0004] The known POV displays offer only a relatively low-spatial resolution and color depth when the light source of the display is moved through space, or rely on expensive and sophisticated hardware to achieve higher resolution and color depth. A higher-quality image generation might be possible with the known designs, but would require the use of increasingly sophisticated and relatively more costly electronics, e.g., application specific LED driver integrated circuits with on-chip memory and/or switching for each of the LEDs that make up the linear array. What is needed is a POV display that can produce high-spatial resolution and high color depth without the need for expensive electronics to load and display the image, e.g., a photograph, message, artwork, etc. SUMMARY OF THE INVENTION

[0005] What is disclosed is a POV display that offers high spatial resolution and high color depth (dynamic range). The POV display may be made at a low hardware cost and complexity, which gives it broader appeal to consumers because it is less expensive to make. The hardware according to one embodiment includes an electronic display controller driving a persistence of vision display element. In the preferred embodiment, the display element is a linear array of 'full color' (Red Green Blue) light emitting diodes.

[0006] It is an object of the present invention to provide a high resolution full color display, suitable for reproduction of photographs or other detailed visual objects, which is visually satisfactory when operated at about an 'arm's length' from the viewer. That is, the high spatial resolution offered by the POV display according to the invention is visually perceptible (in high resolution) when the light source passes through a plane that is at about an arm's length distance from the eyes of the observer, e.g., distance from the eyes of the person who is moving the display through space to the image he or she sees, due to the POV effect. An "arm's length distance" may be 1 - 2 feet, 2 - 6 feet, 2 - 3 feet.

[0007] In respect to the existing POV display designs, the requirements of a high performance display suitable for photographs, etc. at close distances, or at arm's length, poses certain challenges. If the sweep rate of the light emitters in the POV display is too slow, the latent image may not perceived as a complete image, but as a moving band of light, or something in between, for instance, a moving partial image, with significant brightness variation from one side to the other. A 'good' persistence of vision display thus requires a sufficiently high sweep rate for an attractive presentation to the human eye.

[0008] According to one embodiment, the requirement for a high spatial resolution and deep color depth POV display is provided by utilizing a pixel size, or pitch of less than 3mm. In other embodiments higher resolution is provided by reducing this pitch to 1 .5 mm or less. In either case - < 3 mm or <= 1 .5 mm - the pitch is sufficiently fine to enable the desired degree of spatial resolution for detailed images being displayed through the POV effect. The respective terms "pixel size" or "pitch" refer to both the arc-length or distance the light emitter travels through space for each image line of the image ("motion sweep" direction, FIG. 2) for producing the POV effect, and the physical spacing of the LED pixels in the linearly arrayed display. The limited rate at which the POV display system can completely display a new image line limits the spatial resolution in the "motion sweep" direction.

[0009] Thus, in order to produce a high spatial resolution image, formed at a relatively high sweep rate, the desired brightness or 'grayscale' value of each pixel in the resultant POV image must be conveyed and displayed in a short interval, for example < 300 microseconds, in order for each POV 'pixel' to occupy less than 1 .5mm in extent along the sweep axis, or motion sweep direction (FIG. 2). If pixel values are not updated quickly, then either the mechanical sweep of the display must be proportionally slower, resulting in an unsatisfactory POV display, or the color depth per pixel must be reduced. It is therefore necessary to enable a device that can rapidly update pixel values in the array. Thus, in order to provide high resolution, the desired light level of the pixel must displayed in the short time interval before the rapid sweep of the display causes stretching of the pixel and impairs resolution along the direction of the sweeping motion. For a 5000 mm/sec sweep rate and 1 .5 mm pitch, which provides a satisfactory POV image at arm's length, the desired brightness or 'grayscale' value is updated every 1 .5/5000 seconds, or the refresh rate for each pixel is 300 microseconds.

[0010] In addition to high spatial resolution, high grayscale or color depth is necessary at each pixel for high quality display of photographs, etc. High color depth requires the ability to drive the perceived pixel brightness to a sufficient number of linearly spaced. In a typical 8-bit (or 24-bit color) image, such as a standard 24-bit color bitmap image, it is necessary to represent 256 levels. In practice, even more levels are required at the display in order to accommodate gamma correction, such that the desired 256 output levels are approximately even spaced in actual perceived brightness when displayed.

[0011] Producing deep color images thus requires a high display bit depth, which when coupled with the high mechanical sweep rate of the display requires a high bit rate to keep LED drivers supplied with fresh pixel data during each pixel display interval, or in accordance with the line refresh rate, which is proportional to the sweep rate and number of lines in the image. [0012] Known are LED display driver integrated circuits that are capable of accepting high bit depth grayscale data and providing a corresponding range of light intensities. However, it is desirable instead, for purposes of making a less expensive and more versatile display device, to utilize a low cost LED drive with direct (or current controlled) binary output, where the LED is either on or off. The invention provides this type of POV display.

[0013] Accordingly, in one respect a high spatial resolution and high color depth POV display is provided that utilizes driven LEDs that have only two values: on and off. The LED on/off state is modulated over a short time interval by the display controller and low cost binary (on/off) LED drivers to produce a range of grayscale or intensity values. Thus, in one respect, the invention is a POV display capable of providing more than a single brightness level using a very low cost on/off LED driver.

[0014] It is common in the prior art to produce 1 -bit (pixel is on or off) or few bit (8 color, 16 color) POV displays using low cost hardware. However, the low color depth is generally unsatisfactory for display of photographic or other detailed visual information. With this in mind, according to another aspect of the invention, there is a LED drive/ brightness encoding technique/method suitable for reproducing high resolution, high color depth ( '16 million' color /full 24-bit) photographic images at arm's length using low cost hardware. A particular hardware implementation of this technique/method is also disclosed.

INCORPORATION BY REFERENCE

[0015] All publications and patent applications mentioned in the present specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. To the extent there are any inconsistent usages of words and/or phrases between an incorporated publication or patent and the present specification, these words and/or phrases will have a meaning that is consistent with the manner in which they are used in the present specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a side-view schematic image of a persistence of vision (POV) display device according to the disclosure.

[0017] FIG. 2 illustrates an image produced by the POV display of FIG. 1 when an array of LED elements are swept through space at a sweep rate.

[0018] FIG. 3 is diagram illustrating one example of how LED on/off values are modulated to produce a range of grayscale values for each pixel of each line of the image produced in FIG. 2. An image line is sub-divided into sublines and time- encoded according to a first method of displaying an image using the POV device of FIG. 1 .

[0019] FIG. 4 depicts a process for loading and storing images as image lines and sublines into memory for direct access.

[0020] FIG.5 is a flow diagram depicting the first method, or a second or third method for displaying a stored image from the POV device, when the device is moved in one direction (leftward) and an opposite direction (rightward).

[0021] FIG. 6 is a general, schematic representation of the electrical components and connections among these components for loading and displaying an image according to the first, second or third method for display.

[0022] FIG.7 is another embodiment of components arranged to load and display an image according to the first, second or third methods for display.

DETAILED DESCRIPTION

[0023] In the description like reference numbers appearing in the drawings and description designate corresponding or like elements among the different views.

[0024] Referring to FIGS. 1 - 2 there is depicted a side view schematic of one example of a hand-held persistence of vision (POV) device 10 and a display

(encoded image) generated when this device is swept through space according to the disclosure. The device 10 includes a handle end 10b and a display end 10a. A user, gripping the handle end 10b, selects a pre-stored image that he or she wishes to display using the selector buttons 22. The pre-stored image may be stored in flash memory 18 and received over a Bluetooth^(R) communication link using an on-board receiver 24. Alternatively, the image may be received via a USB or serial port 20 which can also serve as a connection for charging the device 10.

[0025] The image to be displayed is represented by a series of image lines arranged to be displayed in a predetermined order by the device 10. An image line is displayed using a linear array of light emitting devices, e.g., light emitting diodes (LEDs) 12, arranged along the display end 10a. Also provided in the display end 10a are driver integrated circuits (ICs) 1 1 for controlling the LEDs 12. According to one embodiment there are 16 LEDs for each driver IC 1 1 . The LEDs 12 have only an on and off state. The light intensity emitted from an individual LED is not controllable via an integrated circuit provided with the LED or in the drivers. There is only an on and off state for an LED. The "on" current level of the LED driver may be globally set or dynamically adjusted, but affects the current of all "on" LEDs equally.

[0026] After selecting the image for display, the user sweeps the device 10 through space in a motion sweep direction (FIG. 2). A microprocessor 16 senses this motion through input received from an on-board accelerometer 14. When this motion is sensed the microcontroller or microprocessor 16 causes the LEDs to generate successive image lines in correspondence with where the LEDs are located from a starting position, or by a detected velocity or change in position of the LEDs. In FIG. 2 there are a k number of such image lines generated in correspondence with a detected sweep rate, i.e., the rate at which the user is sweeping the device 10 through space.

[0027] Referring to FIG. 2, as the display end 10a moves through the sweep area, "k" image lines are generated in a predetermined order to produce, through the POV effect, the stored image ("encoded image") for the user or nearby observer, at an arm's length or further away from the observer or user. Each image line is made up of "J" pixels. Each pixel corresponds to an LED in the array, or 3 LEDs for red- blue-green channels. Each of the LEDs have only an on or off value.

[0028] As discussed earlier, it is desirable to produce high color and/or grayscale depth images while using the lowest cost electronics. To achieve this outcome at each pixel in the image line, while utilizing the most basic shift register LED current driver ICs, which provide only on/off (1 -bit) control of the LED output (for example, Texas Instruments SN74HC595, TLC5928), a display time for each image line is divided into sub-intervals or sublines, which may be related in time length by powers of two. The light emitted from each LED (or each of three LEDs for RGB color), for each of the k image lines, thus is produced from a summed series of these shorter duration sublines consisting of on/off LED positions (variable or constant duration). The sum of these shorter length sublines equal the grayscale value for the j^th pixel of the k^th image line of the image.

[0029] The total length of time of any subline is too brief for the human eye to discern from other sublines. The human eye can only see, at best, a single image line that is the summed intensities of the sublines. The result: image lines may be produced with high color depth and spatial resolution using LEDs that provide only on/off (1 -bit) control.

[0030] A first method for encoding and displaying a series sublines containing binary values (bits) for the LED driver in accordance with the foregoing will now be explained in more detail with reference to FIG. 3.

A. Time Encoding: Method 1)

[0031] Referring to FIG. 3 there is a schematic representation of an image, represented by K sequentially arranged image lines, each of which being made up of

J pixels where each pixel corresponds to a light emitting element of an array of light emitting elements of the POV devices, e.g., an array of LEDs 12. For a color image each line may correspond to three separate lines for red-green-blue. For each pixel of each image line there are N sublines, where a value sent to the driver IC for the jth light emitting element by the microprocessor is either on or off. The duration of on or off for each subline may be constant, or it may vary. The duration of a subline may be given by EQ. 1 a: t x 2', i = 0 ... (N-1 ) sec, t is constant (EQ. 1 a)

[0032] The value of the constant t may be a minimum on / off time for the LED. For example, t may be 20 nanoseconds (nsec), or 40 nsec, 80 nsec, 160 nsec, 320 nsec or 25.6 usee. EQ. 1 a is illustrated graphically in FIG. 3. The pixel value for the jth pixel, of the kth image line, or PG,k) resulting from the sum of subline binary values having respective durations given by EQ. 1A, is given by EQ. 1 b:

PG,k) =∑b(i,j,k) x 2ⁱ, i = 0 ... (N-1 )) (EQ. 1 b)

[0033] Where b(i,j,k) has a value of either 0 or 1 . Thus, according to the process, the pixel value P(j,k), which is known from the image data, is not sent to the LED drivers. Instead, each of the much shorter duration sublines, derived from the value of P(j,k), are consequently sent to the LED drivers where the sum of these N binary values, or∑ b(i,j,k) x 2', over the duration given by EQ. 1 a produces the same intensity (as far as perceptible to the human eye) as an LED and driver capable of producing light corresponding to a range of grayscale values. In the preferred embodiment up to 256 grayscale values may be represented by this process using only an LED and driver having a single (1 -bit) on/off level. The total time duration of the sublines (EQ. 1 a) may be adjusted to be appropriate for the desired pitch, e.g., 3 mm, or 1.5 mm for the image line and mechanical sweep rate.

[0034] Thus, in this way, a cumulative on-time (and cumulative, effective pixel brightness P(j,k)) may be achieved, where N represents the 'cumulative on time' for a particular LED generating light for pixel PG,k) of the kth image line. A numerical example follows.

[0035] Referring to EQ. 1 b, the binary code for a pixel with brightness value of 71 13' may be represented as 1 101 1 1 100 1001 , where each position from right to left corresponds to the presence (1 )/"ON" or absence (0)/OFF" of these values: 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1 , respectively, in the summed total. The binary encoding of 71 13' therefore is 4096-Ί " 2048-Ί " 1024-"0" 512-Ί " 256-Ί " 128-Ί " 64-Ί " 32-"0" 16-"0" 8-"1 " 4-"0" 2-"0" 1 -"1 " (for a sum of 71 13). The binary encoded brightness scheme displays 71 13 by ensuring that the pixel is high (on) for the shortest (base) time sub-interval; low (off) for the second shortest time subinterval; low for the next time sub interval; high for the next (which is 8 times longer than the base time subinterval); low for the next (16); low for the next (32); high for the next (64); high for the next (128); high for the next (256); high for the next (512); low for the next (1024); and high for the next two (both 2048 and 4096). In total, by switching the LED on or off for each of these fixed 13 binary-power of two related time sub-intervals, a cumulative 'on-time' (and cumulative brightness) of any value 0-8191 may be created for PG,k)- In this example, the cumulative on time or brightness level of PG,k) = 71 13 is illustrated.

[0036] It will be appreciated that the above binary-encoding scheme of total on- time at each LED over the sublines, as disclosed above, is advantageous because it minimizes the number of data shift clock cycles required to achieve a given grayscale bit depth. Moreover, it will be apparent, as alluded to earlier, that the total On time' of a particular pixel during a complete line display interval is linearly related to the integrated light output of that pixel. However, due to the non-linear response of the human eye, a display 'gamma' factor is implemented where the typically 8-bit (256 level) grayscale levels of an original image are non-linearly mapped to a desired effective 'display brightness' level. This is necessary to create a displayed image in which the human eye perceives equal-brightness steps of the original image as equal-brightness steps in the LED POV display.

[0037] The foregoing binary encoding of LED pixel brightness admits fast, low- overhead display of high color-depth image lines when POV is waved by hand closer than about 70cm (arm's length). As explained earlier, such a POV display requires high pixel spatial density in both X and Y dimensions, and consequently numerous small pixels, and high line display rates. The high line-rate ^* color-depth product possible with the encoding technique discussed in connection with FIG. 3 allows for the display of photograph-like images at about an arm's length using the persistence of vision effect.

[0038] In a presently preferred embodiment, it is preferred to keep the cumulative on time, i.e., the value given by EQ. 1 a, for each line to less than 300usec

(<100usec) to ensure high spatial resolution in the swept direction at typical manually sweep rates of about 2 - 5 m/sec corresponding to a < 1.5 mm horizontal pixel dimension.

[0039] With a 20 nsec minimum on time, presently preferred, it is possible to have up to 14-bit color depth, which is more than sufficient to represent an 8-bit image with allowance for gamma correction appropriate to an LED display and human eye. Gamma correction (where the input intended brightness is mapped to a displayed brightness with an exponential function) is necessary to compensate for the non- linear response of the human eye, such that linear brightness steps in the original image appear as approximately linear brightness steps in the perceived persistence of vision image.

[0040] Gamma correction will be familiar to those of ordinary skill in the visual arts. It is relevant here in that 8 different sublines / time sub-intervals (as may naively have been expected from the 8-bit (256) levels in a typical color bitmap) are insufficient to achieve a satisfactory display (POV or otherwise) of 8-bit data - in fact, a gamma correction which uses 12 bits or more is typically used. This imposes even more stringent requirements on how quickly the line image data must be updated.

[0041] According to another aspect of invention, the image data processing for efficient and streamlined feeding of pixel values to the LED drivers, image data received by the device 10 is pre-calculated and stored to the display's memory in a format which allows on/off data for display during each time interval of each image line to be shifted from the display memory to the LED drivers with only the

application of a number (384 for 128 RGB pixels) of shift clock pulses corresponding to the number of pixels to be displayed in the image line. The on/off data is subsequently latched to the on/off LED current drivers and output is displayed for the designated power of two time interval. This method of storage and display enables the microcontroller to manage the display intervals with zero or very low processing overhead, allowing optimal use of the display intervals for active display.

[0042] Referring to FIG. 4 there is a process for storing an image received on the POV device 10 into memory for direct display by the LED array 12 according to Method 1 (time encoding). The image is selected from a memory location on the device, or may be downloaded directly using the Bluetooth radio, through USB port or a serial connection (FIG. 1 ). The image is loaded and stored in a temporary buffer. The image is then stored as a series of image lines, which are stored as a sequence of N sublines that make up an image line. When the image is selected for display the sublines are sent out sequentially, directly from memory, to the LED drivers. The sublines may be read out back to front or front to back, depending on whether the display 10 is being swept from left to right or right to left. B. LED Drive Current Encoding: Method 2)

[0043] According to a second method for encoding and displaying an image line as a series of sublines the LED drive current is encoded, rather than using a time encoding as in method 1 . The second method also increases the effective bit depth using single (1 -bit) on/off type LEDs and drivers, but replaces the binary encoded pixel on-time subintervals (EQS. 1 a - 1 b) with binary encoded LED drive current values for the sublines across all LED driver ICs. As in the first method there may be N sublines with a total duration of the sublines corresponding to the desired pitch for the image line. The image line division into sublines may include time-encoding as in the first method, or each subline may have a constant duration in time.

[0044] For example, for the first subline the global LED driver IC 'on' current value is set to some minimum value, perhaps 250 micro-Amperes (uA), and the display data held for the prescribed time interval. In the second display sub-interval, the driver 'on' current value is set to 2x the previous value (500 uA) and the new display data held for the prescribed time interval) and so on with current increasing as powers of two. A gamma correction function, (or look-up table value) is again applied to the initial image data to determine the appropriate pixel intensity value for display, such that an approximate linearity of the perceived output is maintained.

C. Hybrid: Method 3)

[0045] According to a third method there is a hybrid combination of Method 1 )

(time encoding) and Method 2) (current encoding). This combination is particularly useful for further reducing the required LED-on time (which enables faster line update rates) while preserving good linearity and color rendition at low brightness levels. In the hybrid method, global LED drive current is increased for the several highest brightness intervals, rather than a further increase of the display time.

[0046] Referring to FIG. 5 there is a shown a flow diagram depicting the steps for displaying an image stored in the above manner. Depending on how the display 10 is being swept the loop through the image lines counts from the max_lines down to zero, or from 0 to the maxjines.

Hardware:

[0047] FIGS. 6, 7 and 8 are schematic illustrations of the components and connections among those components for the POV display 10 from FIG. 1. [0048] FIG. 6 shows a general layout. Referring to this figure, the image is received over the wireless interface and stored in memory, which is provided as part of the image controller. Selector buttons are provided to select the images to display from stored memory. The device may be powered through a USB connection. A battery is provided and battery management for supplying energy to power the POV device. The image controller processes the image data for display (according to one of the first, second or third methods) and stores the processed image to memory (SRAM, flash, DRAM, etc.) in a format optimized for delivery to the LED array. Each line is stored in memory as N sublines consisting of on/off bits for each pixel-bit in the line. N may be thought of as a bit-depth for each pixel of each image line. For an image line consisting of 128 RGB pixels, each sub line is 384 (128^*3[rgb]) bits long.

[0049] For example, when using the first method, the first sub-line holds on/off data for each pixel corresponding to the shortest / least bright display interval. The second sub-line holds the on/off data corresponding to the next power of 2 brightness display interval and so on. The sublines are concatenated (appended to each other, one after another in sequential locations) in memory such that they may be accessed one directly after the other in a sequential read operation with zero overhead. This read-in and processing step is shown in the flow diagram of FIG. 4.

[0050] Display of an image is initiated and the LED current drive enabled when the device is powered on and the image controller receives signals from the accelerometer indicating that the device is being swept.

[0051] The LED array may have N 16-output shift register current source LED drivers. The LED drivers are cascaded to form one (or more) longer shift registers. An example of a shift register LED driver suitable for use is made by Texas

Instruments (TLC59281 ) However, even simpler parallel output shift register ICs such as SN74HCT595 may be used. At the beginning of a line display period, the pre-processed image data is shifted out of memory directly into the display shift registers of the LED array. This data is received by the LED drivers over a "data" serial interface between the controller and LED drivers.

[0052] The data corresponding to on/off states for the first (least significant bit) time interval are latched (transferred to the output driver stages) of the LED array by a latch signal sent using the latch control line. The bit data is then output to the LEDs by driving the output enable control line to enable the output drivers for a time period corresponding to the least significant time interval. During display, data

corresponding to the on/off states for the second time interval is shifted into the display drivers according to the state of the data in the control line at each received clock pulse. At the end of the first display interval, the new data (for second display interval) is latched to the display drivers and output to the LEDs for a time period corresponding to the second least significant time interval, and so on until all on/off time sublines have been displayed. The process then repeats for the next line, until the entire image has been displayed

[0053] The LED driver ICs have 'data input', 'clock', 'latch', and 'output enable' control lines. In this case, the 'clock' is a series of pulses used to shift serial data down the cascaded shift registers. The 'clock' in this case has no bearing to the 'on time' of the LEDs. Rather, it is the 'output enable' control line which enables the LED drivers for the appropriate time period.

[0054] The logic level on the data input line is sampled at each rising edge of the clock signal 384 clock pulses, with 384 rising (and falling) edges loading the cascaded shift registers in the LED drivers with a full complement of on/off data. A rising edge on the latch line then moves this on-off data from the shift register stages to the output drivers. Finally, asserting the /output enable (logic low) turns on output drivers that have 'on' data, causing those connected LEDs to light.

[0055] In the second (current encoded) method, all is as above except that instead of the controller/microprocessor controlling the time for which 'output enable' is held logic high (causing LEDs which have been set to 'on' to light up for the prescribed time). The controller instead adjusts the drive current set point so that when the LEDs are switched on (for whatever time interval, perhaps now equally spaced, and shorter) they are switched on at a deliberately selected current level instead of a fixed current level as in the time encoded method.

[0056] FIGS. 6 and 7 show alternative arrangements of the device components. Comparing FIG. 6 and FIG. 7, the memory component is shown in two positions, either in communication exclusively with or within the microcontroller, or residing on a common data path bus (for instance, SPI). In addition to a microcontroller, examples of suitable controllers include field-programmable gate array (FPGA), digital signal processor or controller (DSP/DSC) or an application specific integrated circuit (ASIC).

[0057] In FIG. 7, placing the memory (serial SPI SRAM or FLASH) directly in communication with the LED display hardware allows the microprocessor to cause data to be transferred directly from the memory to the LED display shift registers by applying only clock pulses. This results in faster / lower overhead for this potentially time consuming transfer.

[0058] FIG. 6 is another workable and perhaps more conventional arrangement, but one which we do not exclude. Reasonably low overhead transfer may be achieved using the 'DMA' (direct memory access) in the microprocessor to move data from the memory directly to the microprocessor outputs connected to the LED display hardware.

[0059] According to another embodiment the device includes a gyroscopic sensor (gryo), which provides information about the rotation of the device. In the case of a hand-waved device, signals from a gyro can be useful because the gyro quantifies the amount and rate of arc (rather than linear translation, as in the case of an accelerometer) the device experiences. This measure is useful because it can be used to compensate for any spatial distortion of the displayed image (compression at the low pixels near handle and expansion at the high pixels near tip) that arises in proportion to the arc. One would pre-distort the image data, such that when displayed, it appears nearer to rectilinear.

[0060] In addition, the gyro is a direct rotation rate measuring device - and because there is nearly always some amount of arc present in the hand-waved motion, the arc/rotation rate is an effective proxy for the instantaneous velocity of the device. Rather than integrate or otherwise interpret the output of the accelerometer, direct readout of the gyro gives information useful for adjusting the line display rate to achieve an image with the intended aspect ratio (e.g., avoiding unduly

compressed display in the horizontal or sweep direction at low sweep rates, and not unduly 'stretched' at high sweep rates) [0061] A gyroscope may be incorporated into the display 10 in the same manner as the accelerometer, and its signals received and processed in the same manner as the accelerometer. In many cases, manufacturers integrate both an accelerometer and a gyro in the same integrated circuit / package, which is one of the embodiments contemplated.

[0062] A gyro can provide more complete information (e.g., degree of rotation arc) about the user's movement of the device. This enables a more sophisticated response to user behavior. In addition, for the possible use case of spinning the device (as on the end of a string, or by a motorized hub) it provides rate information, which would be difficult to infer/extract from accelerometer data.

[0063] The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

[0064] These modifications can be made to the invention in light of the above detailed description. The terms used in claims should not be construed to limit the invention to the specific embodiments disclosed in the specification.

Claims

WHAT IS CLAIMED IS:

1 . A method for displaying an image, comprising

using a hand-held POV display comprising a controller and an array of light emitting elements;

receiving image data on the POV display;

parsing the image data into image lines, each of the image lines comprising a plurality of pixel values for each one of the light emitting elements;

further parsing each of the image lines into a plurality of sublines,

wherein

a subline comprises, for each of the light emitting elements, an input binary value corresponding to the one of the light emitting elements being either on or off, and

such that a summation of the input binary values for each light emitting element equals the pixel value of the image line; and

upon sweeping the POV display through space, generating a first of the image lines by sending the input binary values for each of the plurality of sublines corresponding to the first of the image lines to the respective light emitting elements.

2. The method of Claim 1 , wherein the image data comprises a photograph, the method further including displaying the photograph by repeating the sending the binary values from each of the plurality of sublines to the respective light emitting elements until all image lines of the image are displayed.

3. The method of Claim 1 , wherein the subline further comprises a constant or non-constant duration of time for which binary values are latched to the respective light emitting elements, such that an "on" period of time for one of the light emitting elements may be shorter or longer for a first binary value or .

4. The method of Claim 3, wherein there are N sublines for the first of the image lines and the sum of the durations of the N sublines for one of the light emitting elements is according to EQ. 1 :

∑ (t x 2", i = 0 ... (N-1 )) sec, t is constant (EQ. 1 )

5. The method of Claim 3, wherein the pixel value P(j, k) for a jth pixel of a kth image line from the image data is equal to

∑ b(i) x 2 \ = 0 ... (N-1 )), where b(i) is 0 or 1 .

6. The method of Claim 3, wherein N is between 8 and 16 and t is less than 1000 nanoseconds.

7. The method of Claim 4, wherein N is 12 and t is 20 nanoseconds.

8. The method of Claim 3, further including the step of varying the global drive current value applied to the light emitting devices during each of the sublines to thereby increase or decrease an intensity of light generated by the light emitting element.

9. The method of Claim 1 , wherein each image line comprises three image lines, each pixel of which is a RGB grayscale value.

10. The method of Claim 1 , where the light emitting elements are light emitting diodes (LEDs) having drivers for configuring the LED between only one of two states: on or off.

1 1 . The method of Claim 1 , wherein the duration of each of the sublines is constant.

12. The method of Claim 1 , further including the step of varying a drive current on-value for each of the light emitting devices over the sublines to thereby increase or decrease an intensity of light generated by the light emitting element.

13. An apparatus comprising a memory having stored therein image data, a processor, an array of light emitting elements, and computer implemented logic stored on non-volatile memory, which when executed by the processor performs the following steps: parse the image data into image lines, each of the image lines comprising a plurality of pixel values for each one of the light emitting elements;

further parse each of the image lines into a plurality of sublines,

wherein

such that a summation of the input binary values for each light emitting element equals the pixel value of the image line;

whereupon receiving an input signal for displaying the image data using the light emitting array, the processor further generates a first of the image lines by sending the input binary values for each of the plurality of sublines corresponding to the first of the image lines to the respective light emitting elements.

14. The apparatus of Claim 13, wherein the sublines have an effective bit depth of 12 to produce a gamma corrected effective grayscale range of 256 for each image line.

15. A method for displaying an image, comprising

receiving image data on the POV display;

further parsing each of the image lines into a plurality of sublines,

wherein

a subline comprises, for each of the light emitting elements, a bit, and an associated duration of time for which the bit value is latched to a driver for the light emitting device, such that a total duration of time for the sublines is equal to an image line duration; and

upon sweeping the POV display through space at a sweep rate, generating a first of the image lines by sending the input binary values for each of the plurality of sublines corresponding to the first of the image lines to the respective light emitting elements, wherein a pitch for the image line is equal to the sweep rate multiplied by the image line duration.

16. The method of Claim 15, wherein the pitch is less than or equal to 3 mm.

17. The method of Claim 15, wherein the pitch is less than or equal to 1 .5 mm.

18. The method of Claim 1 or 15, wherein the sweeping of the POV display through space is detected by one or both of an accelerometer and a gyroscopic sensor.

19. The method of Claim 13, wherein the input signal for displaying the image data using the light emitting array is received from one or both of an accelerometer and a gyroscopic sensor.