HK1216689B - Multi-half-tone imaging and dual modulation projection/dual modulation laser projection - Google Patents

Description

Multi-halftone imaging and dual-modulation projection/dual-modulation laser projection

Copyright Notice

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

Technical Field

The present invention relates to display devices and, more particularly, to dual-modulation projectors (including laser projectors) and the creation of halftone images in a pre-modulator of a projector.

Background Art

Dual-modulation projectors and displays include display devices (eg, Whitehead US7403332 and Daly US7064740) and projectors (eg, Sayag US7002533).

Summary of the Invention

The inventors have recognized a need for improved halftoning of premodulator images. The present invention allows the use of smaller halftone tiles on the first modulator of a dual-modulation projection system. The technique uses multiple halftones per frame in the premodulator, synchronized with the modified bit sequence in the primary modulator, to effectively increase the number of levels provided by a given tile size in the halftone modulator. This solves the problem of reduced contrast ratio at low brightness levels associated with small tile sizes and allows the use of smaller PSFs, which reduces halo artifacts in the projected image. Halftoning can also be used to improve the projection of color or polarization-separated 3D imagery.

Each part of the apparatus and method can be conveniently implemented by programming on a general-purpose computer or networked computer, and the results can be displayed on an output device connected to any general-purpose computer or networked computer, or sent to a remote device for output or display. In addition, any component of the present invention represented in a computer program, data sequence and/or control signal can be implemented as an electronic signal broadcast (or transmitted) at any frequency in any medium, including but not limited to wireless broadcast and transmission on copper wire, fiber optic cable and coaxial cable, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and many of its attendant advantages will be more readily obtained as they become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

FIG1 is an illustration of the effect of the number of discrete premodulation levels on local contrast;

FIG2 is an illustration of the improved results obtained when the halftone image is distributed across four subframes;

FIG3 is an illustration of an example PSF and a corrected PSF; and

FIG4 is a diagram of an example bit sequence.

DETAILED DESCRIPTION

Current dual-modulation POC EDR projectors use a single halftone image per frame on the premodulator. A small PSF is desirable to limit halo size on small luminance features and achieve high local contrast. The first non-zero premodulation level is achieved by superimposing fields of PSFs to achieve a relatively flat light field. For a given (small) PSF size, the spacing of the halftone non-zero pixels must be smaller than the PSF, and small enough to achieve such a flat field. This limits the percentage of pixels that must be non-zero to a specific level, and thus determines the first non-zero average level and the number of discrete linear premodulation levels. For example, a PSF that must be repeated on a 5x5 grid would require turning on 1 in 25 premodulator pixels, resulting in a minimum 1/25 non-zero level and 25 discrete premodulation levels.

An image from the described system can have a contrast ratio (CR) of approximately 25X that of the primary modulator; if the initial CR of the primary modulator is 1800, the final image might have a CR of 45,000:1. This assumes that 1 in 25 pixels is always on. Because the pre-modulation DMD is capable of a CR >1800:1, black levels can be much better than 1/45,000 of peak white with the pre-modulation pixels off; however, turning off all pre-modulation pixels can have adverse effects. These effects appear in images at low brightness levels, even with some pixels on. For example, some image features vary with spatial frequencies that exceed those representable by the pre-modulation light field. For these image features, the pre-modulation light field will be constant, unmodulated. The level of the pre-modulation light field will be determined by the local maximum of the image feature. The primary DMD must reduce the pre-modulation light field to produce all levels of the local image feature. Depending on the first non-zero pre-modulation level, the primary DMD may not have enough contrast to produce the lowest level, thereby limiting the local contrast of that image feature sufficiently to affect its appearance. This is particularly critical around the area where the last pixel on the pre-tuned patch is turned off. In this area, the local contrast drops to around 20. These problems can be addressed by increasing the PSF and patch size, but this will increase the halo size and may also produce visible artifacts.

Figure 1 helps illustrate these issues. The blue line (starting on the horizontal axis between 10E-6 and 10E-5) represents the best contrast ratio that can be achieved in this particular auditorium with an ideal infinite contrast ratio 100 nit projector. This limitation occurs because the room has a dark level of 0.0005 nits, measured at the screen. This comes from the ambient room light in the room reaching the screen and reflecting from the screen to the viewer. The red line (starting on the horizontal axis between 10E-4 and 10E-3) represents a single-modulation projector. The projector has an 1800:1 contrast ratio (both simultaneously and sequentially). As the peak level of the local image becomes darker with this projector, the contrast ratio in the local image decreases proportionally because the dark level is constant. This is normal and expected behavior.

The light green line (the thinner line) shows the possible contrast ratio when using a dual-modulation projector with high spatial frequency components (where the pre-tuning is locally constant). As the projected image becomes locally darker just outside peak white, the contrast ratio curve exactly matches the previous case. However, when the level reaches (in this example) approximately 24/25 of peak white, the pre-tuning can change its value from 25/25 to 24/25 pixels open, and the primary modulator can use its full range again.

Thus, for this lower brightness level, we still have a full 1800:1 local contrast ratio. For the situation just before the preset changes its value (to 23/25), the local contrast ratio can be reduced to 24/25*1800. This situation continues with each change in preset, where after each change, the possible CR is reset back to 1800. For example, when 2 pixels are active, the CR drops to 144 (2/25*1800). When only a single pixel is active, the preset cannot be changed until the leakage light through the premodulation is high enough to achieve the desired output level (fully open) using the primary modulator alone. In the illustrative example, this level is 1/1800 of the peak output. There is a large gap between the lowest modulation level achieved with a halftone at 1/25 and 1/1800, and in this zone, the preset must be maintained at the 1/25 level. The primary modulator is the single modulator used for this block, and the contrast ratio drops to a level of approximately 1/25 before the preset halftone can be set to zero. This level is significantly lower than what would be achieved with an ideal projector in this room (approximately 4 times lower than the blue line).

Effect of the number of discrete preset levels on the available local contrast.

The graph shows the image contrast at a local maximum in the image when the pre-modulation is constant and unmodulated.

Pre-adjusted CR = 1800. Primary CR = 1800. Black CR = 200000.

One object of the present invention is to reduce the effects of these artifacts by increasing the number of levels in the premodulator, but without increasing the tile size or PSF size. The concept is relatively simple: use more than a single halftone image per frame. In the previous description, a 5x5 tile was examined. The following description uses a 5x5 tile, but uses 4 subframe halftones per frame. In this example, for each tile, on an individual pixel basis, the pixel can take on a sequence of 5 values, which are 0, 1, 2, 3, or 4 subframes (0, 1/4 frame, 1/2 frame, 3/4 frame, or 1 frame). This allows the 5x5 tile to express 100 positive values (and 0), rather than the initial 25 values (and 0).

If a DMD (TI Digital Mirror Device) is used for the primary modulator, the bit sequence will need to be modified for the modulation chip. DMDs use a form of pulse-width modulation to modulate light; therefore, the light must be constant throughout the entire frame period. Changing the pre-adjusted halftone (four times) during the frame will produce non-constant light and interfere with the PWM results.

Normally, a DMD is used with a single sequence per frame to obtain 16 bits per pixel modulation. It is proposed to modify the bit sequence so that the higher order bits are spread across the frame period; therefore, they are repeated multiple times. For example, if the top 14 bits (out of 16) are repeated, this will allow a pattern in which the top 14 bits are repeated 4 times. The less significant bits will remain unaffected (spread across the entire frame period). This type of repeat ordering has been described in the literature and is used to reduce motion artifacts with DMD-based projection systems. US5986640 describes a similar technique. The halftone image on the pre-modulator will be synchronized with the repeating sequence in the primary modulator so that both modulators will change to the new sequence at the same time.

FIG. 2 shows the improved results obtained when the halftone image is distributed across four sub-frames as described above.

Effect of the number of discrete preset levels on the available local contrast.

The graph shows the image contrast at a local maximum in the image when the pre-modulation is constant and unmodulated.

Pre-adjusted CR = 1800. Primary CR = 1800. Black CR = 200000.

For this case, the lowest contrast ratio from the projector is approximately equal to what can be achieved with an ideal projector in that room.This technique reduces the undesirable contrast ratio reduction without increasing the tile size and corresponding PSF size.

The method of the present invention is implemented in a cinema projector having a laser light source illuminating a premodulator, wherein the laser light source is configured to emit at least two sets of light wavelengths, each set comprising red, green, and blue wavelengths, wherein at least one of the same color wavelengths in different sets is separated to achieve a minimum bandwidth necessary for off-axis viewing without crosstalk through the passband of viewing glasses during normal and off-axis viewing as encountered in standard cinema theaters or theater presentations as part of theme park rides. wherein off-axis viewing is one of approximately 20 degrees, no greater than 20 degrees, and a maximum angle normally encountered in presentations.

In describing the preferred embodiment of the present invention shown in the accompanying drawings, specific terms are used for clarity. However, the present invention is not intended to be limited to the specific terms so selected, and it should be understood that each specific element includes all technical equivalents that operate in a similar manner. In addition, the inventors are aware that newly developed technologies that are not currently known may also replace the described parts and still do not depart from the scope of the present invention. All other described items including but not limited to modulators, frames, subframes, etc. should also be considered under any and all available equivalents.

Those skilled in the art will appreciate that portions of the present invention may be conveniently implemented using a conventional general purpose or special purpose digital computer or microprocessor programmed according to the teachings of the present disclosure.

Those skilled in the art of software will appreciate that a skilled programmer can readily prepare appropriate software coding based on the teachings of this disclosure. Based on this disclosure, those skilled in the art will readily appreciate that the present invention can also be implemented by preparing dedicated integrated circuits or by interconnecting an appropriate network of conventional component circuits.

The present invention includes a computer program product, which is a storage medium (media) having stored thereon/instructions that can be used to control or cause a computer to perform any of the processes of the present invention. The storage medium can include, but is not limited to, any type of disk, including a floppy disk, a minidisc (MD), an optical disk, a DVD, a CD-ROM, a CD or DVD RW+/-, a microdrive, and a magneto-optical disk, a ROM, a RAM, an EPROM, an EEPROM, a DRAM, a VRAM, a flash memory device (including a flash card, a memory stick), a magnetic or optical card, a SIM card, a MEMS, a nanosystem (including a molecular memory IC), a RAID device, remote data storage/archiving/warehousing, or any type of medium or device suitable for storing instructions and/or data.

The present invention includes software stored on any computer-readable medium (media) for controlling the hardware of a general-purpose/special-purpose computer or microprocessor and for enabling the computer or microprocessor to utilize the results of the present invention to interact with a human user or other mechanism. The software may include, but is not limited to, device drivers, operating systems, and user applications. Ultimately, the computer-readable medium also includes software for performing the present invention, as described above.

Included in the programming (software) of a general/special purpose computer or microprocessor are software modules for implementing the teachings of the present invention, including but not limited to preparing a halftone image corresponding to the image data, dividing the frame, synchronizing the bit sequence and applying it to the DMD, and displaying, storing or communicating the results of the processing according to the present invention.

The present invention can suitably include, comprise or basically include the key element (each part or feature) and equivalent thereof of the present invention described herein.In addition, can put into practice the present invention disclosed schematically here when lacking any key element, no matter whether specifically disclose here.Obviously, according to above teaching, a large number of modifications and variations of the present invention are possible.Therefore, it should be understood that within the scope of the appended claims, can put into practice the present invention differently from the specifically described here.

Claims (4)

1. A method for creating a halftone image in a premodulator of a dual-modulation projection system, comprising the following steps: The premodulator is illuminated by a light source from a dual-modulation projection system; During a frame time period, multiple subframe halftone images are excited or displayed on the premodulator, wherein the frame time period includes multiple subframe time intervals, and each of the subframe halftone images is displayed in its respective subframe time interval; and In synchronization with the display of a subframe halftone image on the premodulator, an image is excited or displayed on the primary modulator of the dual-modulation projection system during the frame time interval, wherein the subframe time interval is synchronized with the frame time interval of the primary modulator, thereby increasing the number of levels in the premodulator without increasing the point spread function (PSF) size. 2. The method of claim 1, wherein the light source is modulated locally or globally. 3. The method of claim 1, wherein the light source is configured to emit at least two sets of light wavelengths, each set comprising red, green, and blue wavelengths, wherein at least one of the same color wavelengths in different sets is separated to achieve the minimum bandwidth necessary for off-axis viewing without crosstalk through the passband of the viewing glasses encountered in theme parks or standard cinema screenings as part of a theme park tour, during both normal and off-axis viewing. 4. The method of claim 3, wherein the off-axis viewing is one of approximately 20 degrees, no more than 20 degrees, and the maximum angle normally encountered during projection.