News Column

"Method for Crosstalk Correction for 3d Projection" in Patent Application Approval Process

September 4, 2014

By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Redmann, William Gibbens (Glendale, CA); Huber, Mark J. (Burbank, CA); Harmsen, Jed (Los Angeles, CA), filed on October 3, 2012, was made available online on August 21, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to Thomson Licensing.

The following quote was obtained by the news editors from the background information supplied by the inventors: "The increasing popularity of 3D films is made possible by the ease of use of 3D digital cinema projection systems. However, the rate of rollout of those systems is not adequate to keep up with demand, and is further a very expensive approach to obtaining 3D. Earlier 3D film systems were besieged by difficulties, including mis-configuration, low brightness, and discoloration of the picture, but are considerably less expensive than the digital cinema approach. It is therefore desirable to provide a high-quality film-based 3D presentation that has a quality sufficient to attract audiences to the same degree that digital cinema 3D does by improving the image separation, color, and brightness to compete with, if not exceed, that of the digital cinema presentations.

"Prior single-projector 3D film systems use a dual lens to simultaneously project left- and right-eye images laid out above and below each other on the same strip of film (also referred to as an 'over-and-under' lens, in which an upper lens projects an image for one eye, and a lower lens projects an image for the other eye). These left- and right-eye images are separately encoded (e.g., by distinct polarization or chromatic filters) and projected together onto a screen and are viewed by an audience wearing filter glasses that act as decoders, such that the audience's left eye sees primarily the projected left-eye images, and the right eye sees primarily the projected right-eye images.

"However, imperfection in one or more components in the projection and viewing system, e.g., encoding and decoding filters, projection screen, can result in a certain amount of light for projecting right-eye images becoming visible to the audience's left eye, and vice versa (e.g., a linear polarizing filter in a vertical orientation can pass some horizontally polarized light, or a screen may depolarize a small fraction of light scattering from it), resulting in crosstalk. 'Crosstalk' can generally be used to refer to the phenomenon or behavior of light leakage in a stereoscopic projection system, resulting in a projected image being visible to the wrong eye.

"The binocular disparities that are characteristic of stereoscopic imagery put objects to be viewed by the left- and right-eyes at horizontally different locations on the screen (and the degree of horizontal separation determines the perception of distance). The effect of crosstalk, when combined with a binocular, disparity, is that each eye sees a bright image of an object in the correct location on the screen, and a dim image (or dimmer than the other image) of the same object at a slightly offset position, resulting in a visual 'echo' or 'ghost' of the bright image.

"The projected left- and right-eye images from these prior art 'over-and-under' projection systems also exhibit a differential keystoning effect, in which the two images have different geometric distortions. This is because if the projector is located higher than the horizontal centerline of the screen, the upper lens (typically corresponding to the right-eye image), is higher above the bottom of the screen than is the lower lens (corresponding to the left-eye image) and so has a greater throw to the bottom of the screen, resulting in the right-eye image near the bottom of the screen undergoing a greater magnification than the left-eye image. Similarly, the left-eye image (projected through the lower lens) undergoes a greater magnification at the top of the screen than does the right-eye image.

"These keystone errors detract from the 3D presentation, since in the configuration described, the differential keystoning produces two detrimental effects:

"First, in the top-left region of the screen, the greater-magnified left-eye image appears more to the left than the lesser-magnified right-eye image. This corresponds in 3D to objects in the image being farther away. The opposite takes place in the top-right region, where the greater-magnified left-eye image appears more to the right and, since the audience's eyes are more converged as a result, the objects there appear nearer. For similar reasons, the bottom-left region of the screen displays objects closer than desired, and the bottom-right region displays objects farther away than desired. The overall depth distortion is rather potato-chip-like, or saddle shaped, with one pair of opposite corners seeming to be farther away, and the other pair seeming nearer.

"Second, differential keystoning causes a vertical misalignment between the left- and right-eye images near the top and bottom of the screen, which can cause fatigue when viewed for a long time.

"The presence of differential keystoning further modifies the positions of the crosstalking images, beyond merely the binocular disparity. Not only is the combined effect distracting to audiences, but it can also cause eye-strain, and detracts from the 3D presentation.

"In present-day stereoscopic digital projection systems, pixels of a projected left-eye image are precisely aligned with pixels of a projected right-eye image because both projected images are being formed on the same digital imager, which is time-domain multiplexed between the left- and right-eye images at a rate sufficiently fast as to minimize the perception of flicker. Crosstalk contribution from a first image to a second image can be compensated for by reducing the luminance of a pixel in the second image by the expected crosstalk from the same pixel in the first image. It is also known that this crosstalk correction can vary chromatically, e.g., to correct a situation in which the projector's blue primary exhibits a different amount of crosstalk than green or red, or spatially, e.g., to correct a situation in which the center of the screen exhibits less crosstalk than the edges.

"For example, a technique for crosstalk compensation in digital projection systems is taught in US published patent application US2007/0188602 by Cowan, which subtracts from the image for one eye a fraction of the image for the other eye, where the fraction corresponds to the expected crosstalk. This works in digital cinema (and video) because these systems do not exhibit differential keystone distortion, and the left- and right-eye images overlay each other precisely.

"However, for stereoscopic film-based or digital projection systems such as a dual-projector system (two separate projectors for projecting left- and right-images, respectively) or single-projector dual lens system, a different approach has to be used for crosstalk compensation to take into account of differential distortions between the two images of a stereoscopic pair."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "Various aspects of the present invention relate to at least one method for characterizing crosstalks associated with a projection system for stereoscopic projection, and for producing a film or digital image file with crosstalk compensation based on crosstalks determined using the method.

"One embodiment of the present invention provides a method for producing one of a crosstalk-compensated stereoscopic film or digital image data for use with a projection system. The method includes: (a) projecting a first image of a stereoscopic test image pair on a screen and measuring brightness at one or more locations on the screen; (b) projecting a second image of the stereoscopic test image pair on the screen and measuring brightness at one or more locations on the screen; for each pixel of the stereoscopic test image pair, determining a crosstalk related to the projection system based at least on the brightness measurements from steps (a) and (b); and (d) producing at least one of the stereoscopic film or digital image data, each with pixel adjustments based at least on the system-related crosstalk at each pixel of the stereoscopic test image pair.


"The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

"FIG. 1 is a drawing of a stereoscopic film projection system using a dual (over-and-under) lens projector;

"FIG. 2 illustrates the projection of left- and right-eye images projected with the stereoscopic film projection system of FIG. 1;

"FIG. 3 is a 3D graph showing the gradient of illumination relative to the opening in aperture plate;

"FIG. 4 is a 2D graph showing an example of differential brightness: the differing profiles of the brightness of the right- and left-eye image illumination along the vertical centerline of screen;

"FIG. 5 is a 2D graph of the variation in crosstalk along the vertical centerline of the screen, resulting from the differential brightness shown in FIG. 4;

"FIG. 6 shows a spatial relationship between a pixel from a first image of a stereoscopic pair and proximate pixels from a second image of the stereoscopic pair that may contribute to crosstalk at the pixel of the first image when projected;

"FIG. 7 illustrates a process for compensating for crosstalk at each pixel based on the leakage of a projection system and brightness measurements;

"FIG. 8 illustrates a process for compensating for crosstalk at each pixel based on brightness measurements;

"FIG. 9 illustrates a process for compensating for crosstalk based on brightness measurements;

"FIG. 10 illustrates various luminance parameters associated with a projected stereoscopic image pair; and

"FIG. 11 illustrates a digital stereoscopic projector system suitable for use with the present invention.

"To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale, and one or more features may be expanded or reduced for clarity."

URL and more information on this patent application, see: Redmann, William Gibbens; Huber, Mark J.; Harmsen, Jed. Method for Crosstalk Correction for 3d Projection. Filed October 3, 2012 and posted August 21, 2014. Patent URL:

Keywords for this news article include: Thomson Licensing.

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Source: Politics & Government Week

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