JP2006510931A - Color non-uniformity correction method and apparatus with optical and electronic LCD panel compensation - Google Patents

Abstract

A method and apparatus for correcting image non-uniformity in a projection system includes correcting image non-uniformity of a liquid crystal display and correcting optical non-uniformity of an optical system using optical correction. Have.

Description

  The present invention relates generally to video processing for color displays, and more particularly to a method and apparatus for providing color non-uniformity correction in color displays having liquid crystal (LC) color displays.

  Color displays are used in various electronic devices. These electronic devices include monitors for personal computers, televisions and other video displays. These displays can be direct view cathode ray tube devices or projection devices.

  One type of projection device is based on the optical properties of liquid crystals such as nematic liquid crystals. These projection devices may have a liquid crystal layer disposed on top of the semiconductor transistor array. Often, such an array is one of the complementary metal-oxide-semiconductor (CMOS) used to selectively generate an electric field in a liquid crystal layer. Their electric field changes the polarization angle of the liquid crystal material molecules that allow the modulation of light across the material. The light can be reflected by a reflective element or can be projected onto a screen. In either case, the modulated light is projected onto the screen by optical elements that form a video image. In the case of reflection, the projection device is called a LCOS (Liquid Crystal On Semiconductor) projection display.

Some factors that affect the image quality of the display are resolution, brightness, contrast and color depth. The resolution is the number of pixels displayed on the screen. Often, the resolution is expressed in a specific pixel size (eg, 800x600 for many computer monitors). In this example, the monitor has 800 pixels in the horizontal direction and 600 pixels in the vertical direction. Of course, the larger the number of pixels for a given display area, the smaller the area of each pixel and the greater the resolution.

The color depth defines how many colors can be displayed on the screen. In one wave, the color depth is expressed in binary logic (bits). Each of the three primary colors (red, blue, green) used in a color display has a number representing the color depth or a number of shades of a particular color that can be displayed. The number of colors is typically expressed in binary exponential notation (eg, 2 ⁸ (referred to as 8-bit video) for 256 shades of each of the three primary colors). As can be easily understood, the greater the number of color bits, the greater the number of shades and the greater the color depth. Of course, the higher the color depth, the better the display quality.

  While resolution, brightness, contrast and color depth can be selected for a particular desired image quality, certain factors can reduce image quality. For example, differences in both optical path characteristics and imager (LC panel) characteristics in an LCOS projection device adversely affect the quality of the projected image.

  What is needed is a correction method and apparatus that overcomes certain drawbacks of known correction schemes such as video clipping.

  In an exemplary embodiment of the invention, the method includes correcting image non-uniformity of the liquid crystal display and correcting optical non-uniformity of the optical system using optical correction.

  In another exemplary embodiment of the present invention, an apparatus for correcting image non-uniformity includes an electronic correction device for correcting image non-uniformity of a liquid crystal display and an optical non-uniformity of an optical projection system. And an optical device for correction.

  The present invention can be more fully understood from the following detailed description with reference to the accompanying drawings. It should be noted that the various features are not necessarily drawn to scale. In practice, the dimensions are arbitrarily scaled for ease of explanation.

  In the following detailed description, for purposes of explanation, exemplary embodiments that disclose specific details are set forth in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art understands by understanding the advantages of the present disclosure that the invention may be practiced in other embodiments that depart from the specific details disclosed below. Would be able to. Further, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of the present invention.

  Briefly, the present invention relates to a method and apparatus for providing real-time color non-uniformity correction in an LCD projection system by correcting for image non-uniformity in both LCD and optical systems. Corrections for LCD panel non-uniformity are electronically affected by bilinear interpolation that does not require all storage of correction data for all pixels of all colors in memory. The correction of the optical image non-uniformity of the projection system has an optical element that reduces the brightness level in the region above the desired brightness. Advantageously, video signal clipping and its adverse effects are substantially prevented by the exemplary embodiment.

  FIG. 1 shows an LCD device 100 according to an exemplary embodiment. The LCD 101 is connected to the electronic correction device 102. The electronic correction device provides electronic correction of video non-uniformity due to LCD panel non-uniformity. Video input 107 is coupled to electronic correction device 102. The output of the electronic correction device 102 is output to the LCD driver 108 connected to the LCD 101 as shown in the figure. Electronic correction is illustratively affected by the bilinear interpolation correction technique described in more detail below. The electronic corrector 102 has the necessary elements to influence the calculation of correction data (eg, an interpolator) and to control the LCD to change the video level of each pixel as needed.

  The output 105 from the LCD enters an optical element 103 whose optical element is illustratively a non-uniform distribution of an optically inverse projection system. For example, the optical element can be the negative of the screen that results when the applied video level is uniform gray due to the absence of the LCD 101 in the system. In this way, the light 105 passes through the optical element 103 and is emitted as light 106 incident on the screen.

  As will become more apparent as the description of the present invention continues, correcting the image non-uniformity using the electronic corrector 102 and using the optical element to reduce the image non-uniformity of the optical system. By correcting, the correction level is improved and the image quality on the image screen 104 is improved. However, clipping of the video signal is substantially prevented.

  In general, the electronic correction device 102 provides electronic color non-uniformity correction through video correction. To achieve this correction, the luminance distribution for each pixel in the video level number is evaluated individually for each optical path. As will be appreciated, if not all pixels are evaluated for storage in memory. More precisely, a limited number of pixels located at points of the grid that are spaced relative to each other by a predetermined number of pixels in both the vertical and horizontal directions are evaluated. In the evaluation, the difference between the actual luminance and the nominal luminance is calculated for a specific video level and stored as a correction factor.

  In order to provide high quality correction for the video signal, color correction data is obtained for various color levels. In the exemplary embodiment, four correction data are stored in the memory device in a manner that is readily available for calculation. These data are used for bilinear (or other two-dimensional) interpolation at a specific video level of a grid (segment) of a specific region having a specific number of pixels. In order to achieve color correction in the layer screen, a plurality of color correction data representing different positions of the display are stored for real-time interpolation.

  FIG. 2 is a principle diagram for a bilinear interpolation scheme according to an exemplary embodiment of the present invention. Interpolation block 201 has four measured and stored correction factors (202, 203, 204 and 204) at points representing points on the image screen. The correction factor for any interpolation point (eg, interpolated point 205) in the map of correction data 200 is Michael, entitled “Color Non-Uniformity Correction Method and Apparatus” filed on June 24, 2002. This is exemplarily determined by the electronic correction device 102 according to the technique described in US Patent Application Publication No. 10 / 179,319 by Bhatmustsky. The description of the present invention is partially substituted by using the disclosure of this application.

  Note that the relationship between the light and the electronic video signal from the LCD is not linear. Therefore, any error in the applied video level will result in further errors due to this non-linearity. In order to achieve sufficient correction of the video signal, it is necessary to have a plurality of sets of correction data (several maps of correction data obtained at a preset video level individually for each color) . In order to correct the video signal, the level of the video data is added to the interpolated correction. Theoretically, there can be multiple maps on the map 200 (corresponding to other video levels for which correction data has been measured), and the coefficient to be interpolated is the video level currently being processed. Depending on the real-time and further inter-interpolation between those maps in real time.

  While the described technique for correcting the image according to the non-linear relationship between the image signal and the light projected on the screen is definitely useful, the technique is very useful for various levels and colors of the image. Requires many data points. Further, the correction process can provide a large margin for video correction in the displayed LCD display system. Eventually, when the video level is high and correction or compensation is certain, this leads to clipping of the video signal. As can be appreciated, when the sum of video correction and video level is greater than a specific video level, the video signal is clipped and proper correction is not achieved. This degrades the overall video quality. For example, consider a 255 level video. If the video level of a particular pixel is 190 and the correction factor is determined to be 100, the maximum video level 255 is exceeded by applying this level for correction. As a result of the video signal being clipped, there are harmonics in the signal that are manifested as undesirable artifacts in the image display. However, in accordance with an exemplary embodiment of the present invention, the amount of electronic correction required by the electronic correction device 200 is reduced because a portion of the correction is addressed by the optical element 103, which means that electronic This means a reduction in the level of dynamic correction and a reduction in clipping in video processing.

  As noted above, in order to address the video signal clipping problem, according to an exemplary embodiment of the present invention, the dependent electronic correction amount is limited to prevent video signal clipping. Because of this, some of the compensation that needs to achieve a higher level of correction, which results in clipping in all electronic correction methods, is influenced by the electronic correction device, while the maintained part is the optical element 103 is required to be used. Therefore, color non-uniformity is corrected by a combination of an electronic correction device that controls the LCD panel and an optical element that provides optical correction. Thus, by eliminating the need for electronic correction devices to correct image non-uniformities by both the LCD panel and the optical system, image clipping is prevented and overall correction capability is improved.

The optical element 103 is usefully opposite to the image screen 104, which is typically derived from a grayscale image without the use of an LCD in an optical system, although changes are certainly possible. Illustratively, three separate inverse images (ie, one for each video color) are used. Alternatively, one inverse image can be used to compensate for overall luminance non-uniformity using the remaining corrections electronically required by the electronic correction device 102.
In many applications of the exemplary embodiment, the optical element 103 can be a photographic negative. However, it should be noted that the optical element 103 can be manufactured by image processing techniques including digital photographic techniques and other digital imaging techniques. Finally, optical element 103 can be a color negative (reverse image) of the image screen, but three black and white negatives can be used in the three primary color portions.

  By way of example, the optical element 103 can be manufactured by installing a mirror instead of an LCD panel in a projection system in which an LCD is used. The optical element can be adjusted to suit a particular projection system, or multiple negatives for a given type of projection system can be produced by its production version. In the former case, the image quality is good. The latter case is advantageous when mass production capability is required. Regardless of the degree of correction achieved by the optical element 103, the remaining correction is achieved using the techniques described above and the electronic correction device 102.

  Compensation for non-uniformity for an optical system with the exemplary optical element 103 is accomplished as follows. The output from the LCD is projected onto an image screen with video correction that is evident in the light intensity at each pixel of the image screen. As noted above, this can lead to improvements in compensation that exceed video level limits. Alternatively, the light intensity may be too small due to insufficient correction in the above interpolation method. However, by capturing the inverse (negative) of the image screen in the optical element, each pixel is adjusted to a specific correction. That is, pixels that are too bright due to overcorrection are adjusted by the corresponding 'darker' parts of the optical element, while pixels that are undercorrected so that the intensity level is too low in the image screen Adjusted by the area of the optical element that is low level optically opposite, the corresponding pixel gets higher intensity on the screen.

  Note that in any of the above cases, optical element 103 also corrects the color intensity of each pixel (eg, optical element 103 is the inverse of a color negative or screen image). It is further noted that high quality correction cannot be achieved with the optical element alone, as nonlinear image compensation cannot be provided. That is, the optical element 103 corrects all levels in the same manner. However, in combination with the electronic correction device 102, the optical element provides appropriate image correction.

  The correction technique and apparatus of the exemplary embodiment is advantageous for various reasons. For example, electronic correction / compensation does not need to correct errors in the optical system, thus reducing the required range of video correction. This reduces the problem of clipping of the corrected video signal. Furthermore, since the range of video correction is reduced, the accuracy of the correction calculation is improved. Other advantages of the exemplary embodiment are realized in manufacturing. The combination of optical correction and electronic correction results in a lower correction level for such systems and a substantially higher correction margin compared to known systems. This can solve even more difficult LCD problems, leading to a significant increase in LCD panel yield.

  Finally, the exemplary embodiments described above are achieved for an LCD having image non-uniformity introduced strictly electronically and optical non-uniformity introduced strictly by optical elements. While this can be done, it should be noted that this is not essential. For this reason, some of the optical non-uniformity can actually be compensated electronically by the above method. For example, in a mass production setting where a mass produced optical element is produced for a kind of projection system, the calibration of each LCD device can be realized by electronically performing some optical correction. is there.

  As described above for the present invention, it will be apparent to those skilled in the art that it can be ascertained in many ways that it also has the advantages of the present disclosure. Such variations are not to be regarded as a departure from the scope and spirit of the present invention, and as will be apparent to those skilled in the art, such modifications are subject to the scope of claims and legal It is intended to be included within the scope of equivalence.

1 is a diagram illustrating an image correction apparatus according to an exemplary embodiment of the present invention. FIG. 6 illustrates bilinear interpolation of correction data according to an exemplary embodiment of the present invention.

Claims (19)

A method for correcting image non-uniformity in a projection system comprising:
Correcting image non-uniformity of the liquid crystal display; and correcting optical non-uniformity of the optical system of the projection system using optical compensation;
A method characterized by comprising:   The method of claim 1, wherein the step of correcting for optical non-uniformity comprises a step of providing an optical element in a light path in front of an image screen.   3. A method according to claim 2, wherein the optical element is an inverse image of the light projected on the image screen.   4. A method according to claim 3, wherein the inverse image is photographic negative.   2. The method according to claim 1, wherein the step of correcting the video non-uniformity includes a procedure for electronic correction of the video signal.   2. The method of claim 1, wherein the step of correcting for optical non-uniformity comprises a procedure for optical correction of an optical signal.   6. A method according to claim 5, wherein clipping of the video signal is substantially prevented by the method.   2. The method according to claim 1, wherein the step of correcting the image non-uniformity includes a step of interpolating a plurality of correction data so as to determine a correction coefficient.   4. The method of claim 3, wherein the reverse image further comprises a plurality of photographic negatives.   4. The method of claim 3, wherein the inverse image comprises a digital photographic negative. An apparatus for correcting a video signal in a projection system comprising:
An electronic corrector for correcting image non-uniformity of the liquid crystal display; and an optical element for correcting optical non-uniformity of the projection system;
A device characterized by comprising:   12. The apparatus according to claim 11, wherein the electronic corrector comprises an interpolator that determines a plurality of correction factors.   13. The apparatus of claim 12, wherein the optical element is a reverse image of an image screen of the projection system.   13. The apparatus according to claim 12, wherein the electronic corrector corrects the video non-uniformity by correcting a video signal having a subset of the correction coefficients.   The apparatus of claim 14, wherein clipping of the video signal is substantially prevented.   14. The apparatus of claim 13, wherein the reverse image comprises at least one photographic negative of light projected on the screen.   12. The apparatus of claim 11, wherein the optical element has a negative image of light projected onto an image screen for each of the three primary colors.   14. The apparatus of claim 13, wherein the photographic negative is a digital negative.   13. The apparatus according to claim 12, wherein the interpolator is a bilinear interpolator.

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