Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3179—Video signal processing therefor
  • H04N9/3185—Geometric adjustment, e.g. keystone or convergence
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/74—Projection arrangements for image reproduction, e.g. using eidophor
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3129—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] scanning a light beam on the display screen

Definitions

• the invention relates to a method for compensating geometric image errors in video images with a plurality of lines, each of which has a plurality of pixels, the image errors to be compensated for influencing the length of the lines and the i-th
• Line in the case of uncompensated geometric image errors on a projection surface begins at a location X a i and ends at a location x « .
• the invention relates to a device for displaying video images on a projection surface, in which pixels are illuminated sequentially in several lines and geometric image errors are compensated according to the method, these image errors to be compensated for
• Influence the length of the lines and the i-th line begins with an uncompensated geometric image error on a projection surface at a location X a i and ends at a location x » .
• the invention relates to a device for displaying video images on a projection surface, in which the display on the latter takes place at an oblique position.
• Such geometric image errors can occur, for example, when a slide is projected at an angle.
• a mirror is provided according to WO 97/03380, with which the image is projected onto the rear wall of a projection surface.
• the mirror inclination relative to the projection surface is designed to compensate for trapezoidal distortions so that approximately the same light paths result in all image areas from the projector to the projection surface.
• mirrors are also used in order to avoid the trapezoidal distortions caused by oblique projection, as in the case of the aforementioned
• Compensate projection with overhead projector requires very large mirrors when projecting large images. It would therefore take up a lot of space and, so that the mirrors do not obscure the view of the projection surface, is essentially restricted to rear projections.
• the object of the invention is to provide a compensation method for image errors of the type mentioned and an apparatus for carrying out this method, in which, however, information loss due to missing pixels is reduced at large angles.
• the object is achieved by a method mentioned at the outset, in which an essentially parallel light beam for sequential illumination of the pixels of the video image is deflected line and image onto the projection surface, a light beam for the pixel at any location to which the light beam is deflected, intensity modulated at this location according to the pixel information of the undistorted video image, a size determining the beginning of the line of the compensated image by Xg d ⁇ Max (Xai) and a size determining the end of the line of the compensated image by Xe d ⁇ Min (X e j ) are determined with X ed > X a and the light beam for each line is deflected such that all pixels of line i are sequentially within the range [Xad; Xe] can be displayed on the projection surface.
• values are in a special device for compensating for
• the lack of an inclined projection lacks a source that can be modulated in intensity to emit a substantially parallel light beam for sequential illumination of pixels of the video image, a deflection device for scanning the light beam in lines and images and a control device that does both the intensity modulation for the light beam and its deflection according to one Function controls that by a calculated
• Equalization of the image, at least with respect to the inclination, is provided.
• Rasterize an image This means you are not tied to the matrix of an image.
• This technique has the advantage that the image is always sharp regardless of the distance and even without special optics. The sharpness is practically only limited by the diameter of the light beam. As a result, an image can be distorted with suitable control even without loss of resolution in such a way that, for example, a distortion which is expressed in a line length change is compensated for.
• the image content is recalculated and both the line density and the pixel density in the newly calculated image are shown so distorted that the distortion caused by the projection is a
• Equalization of the video image causes. This means that video images can be displayed with virtually any accuracy. The accuracy of the calculation and the display will of course be much higher for CAD applications than for a television picture, since the eye cannot resolve so well. However, the principle is the same. Later exemplary embodiments provide even more details about the calculation of the distorted images, which are then displayed rectified
• this calculation does not necessarily have to be carried out anew for each video image. It is sufficient, for example, to store the video images distorted in order to correct the distortion on a video tape and then to simply read them out from the video tape in later displays of the video image. Furthermore, the calculations are not only limited to the oblique projection. Other optical influences, such as the deflection behavior of the deflection device, can also be taken into account when recalculating the image. The later exemplary embodiments also provide detailed information on this.
• N pixels are stored sequentially in a memory and the light beam at the beginning of each line i is blanked out during a time interval for rastering the length (X a - ai), then the information intended for intensity modulation for the N pixels within a time interval for rastering the Length (X ed - a d) is read from the memory and the light bundle is intensity-modulated within this time interval with respect to this read-out information and the light bundle is blanked out for the rest of the time interval T for rastering one line after the end of the sequential illumination of the N pixels on the projection surface becomes.
• a preferred further development of the invention provides that a fixed time interval T is specified for all lines and the control device intensity-modulates according to a function by means of which the light beam at the beginning of each line start of a line i during a time interval for rastering the length (X ad -Xai ) is blanked out, then the information intended for intensity modulation for the N image points is read out from the memory within a time interval for rastering the length (Xe -X ad ), the source is intensity-modulated with this information and the light beam is readjusted
• a time control instead of a possible control with different line deflection functions for rasterizing different lines is provided for controlling the compensation.
• an inner area in which the image is displayed is selected from the locations on the projection surface which are accessible through the line deflection and image deflection, that is to say via the extreme values Xgj given by the line grid of line i and the x » .
• This type of selection leads to the determination of two variables X ad and X e , which describe the starting location and the ending location of the lines of the displayed image on the projection surface. The position of these quantities is better illustrated below with the aid of figures.
• Pixels are occupied and the light paths for bundles of light that illuminate these pixels are traced back to the deflection device, where the connection between the deflection angle or raster time for imaging each pixel then inevitably results.
• the intensity of the light beam for each pixel is controlled in inverse proportion to its illumination time.
• the intensities in continuously working sources are corrected according to different raster and thus lighting times.
• an attenuator can be provided in particular for the device. Attenuation is to be aimed for instead of amplification because this can ensure that the power limits of the lasers mentioned as examples for generating the light beams are not exceeded.
• This control with regard to the correct pixel intensity can be carried out in different ways
• the proportional control is carried out after reading the information from the memory. This saves information depth in the memory, since otherwise the necessary increased dynamics of the information due to the scaling with regard to the illumination time, the required word length of the
• the deflection device for the image-based deflection is actuated in a manner deviating from a constant change in the deflection angle with a function on the basis of which the line spacings of adjacent lines differ from one another by a maximum of 30% and in particular less than 10%.
• the specified limits of 10% or 30% are sufficient to ensure that any remaining line spacing is no longer noticed at a suitable distance.
• the specified tolerances also allow image deflection by means of image mirrors which, due to the mechanical movement and the associated inertia, cannot necessarily follow the specified function for compensating the line spacing for all lines of the deflection.
• control function is determined, for example, geometrically so that the for
• the area of the projection surface available on the video image is evenly covered with pixels and the light beams possible due to the arrangement for illuminating pixels are traced back to the deflection device in order to determine the relationship between the deflection angle and the line.
• the deflection can also depend on the position of the respective pixel of the line, so that at least a linear portion of the line deflection in the image deflection and / or vice versa can be mixed in or the image information can then no longer be read line-by-pixel from an image memory, but its addresses can also be read out from the image memory
• Read addresses are formed. Other methods for this are described in more detail below on the basis of the exemplary embodiments.
• the light beam is rastered line by line with a function in which the video information V (x) of the line i for the image information at each location x with respect to video information V iT (x) of an undistorted image by a maximum of an amount of
• the deflection device is controlled with respect to the line deflection, deviating from a constant change in the deflection angle, in which the video information Vj (x) of the line i for the image information at each location x with respect to video information Vrr (x) of an undistorted one
• the pixel density can strongly depend on the line and the position of the respective pixel in the line.
• the light spot of the essentially parallel light beam on the projection surface will be larger or smaller depending on the pixel to be illuminated.
• the diameter of the light beam will generally be selected so that even with the most unfavorable image point locations with regard to the resolution that can be achieved, suitably large image points can still be displayed.
• the resolution could be increased here. For this increase in resolution are
• the analog video signal is thus sampled with a correspondingly higher resolution before being stored and is then available for display in smaller time intervals with an increased resolution.
• control device also stores the information required for dark pixels in the memory for the before and after the time interval for rastering the length (X e ⁇ r X ad ) and the entire line information thus generated in the memory during the time T can be fed to the deflection device.
• the deflection device for reading out from the memory can always be operated in the same way.
• the preparation of the data for the pixels which are blanked according to the invention by storing corresponding information in the memory generates the entire line to be rasterized in one memory line. As will also be better understood below with reference to the exemplary embodiments, this has important features
• the image is recalculated before the video image is displayed with regard to the deflections and the spatial assignment of the pixels in order to display an undistorted image.
• a laser video device can be arranged at a greater angle to the projection surface than in the prior art, when the video image is projected onto a wall
• a first assembly which has the deflection device and at least one socket for insertion for an optical fiber and within which the light introduced into the socket is guided for deflection into the deflection device, a separate one
• Module which has the control device and the intensity-modulable source and at least one socket for inserting an optical fiber and within which the light of the intensity-modulable source is guided into this socket, at least one optical fiber for coupling the first module to the second module via the respective sockets and a fastening device for the first assembly, with which the first assembly can be arranged at an angle to the projection surface, the compensation being designed to compensate for the distortion given by the image at this angle.
• Modulation control containing assembly is only a small, light projection head to be attached as the first assembly on the example of the ceiling of the room, which is easily possible for the average user with little manual knowledge. In this regard, it should be noted that this should be as easy as hanging a lamp, for which the average consumer does not use an electrician, but does it himself.
• the essential electronic devices, both the laser and the modulators, are arranged in a second assembly, which can also contain operating elements.
• the second assembly can be arranged on the floor or on a shelf, for example.
• Optical information is used to transfer the image information between the two modules.
• a socket for the insertion of the optical fiber is provided in the separate modules.
• This socket also facilitates the installation of a video system divided into two modules.
• the second assembly consisting of lasers, modulators and other control devices can also be easily decoupled due to this configuration if it is to be dispatched for maintenance purposes and repairs.
• fastening means for the first assembly the projection head on the ceiling, the wall or the floor of a room and fastening means for a screen are provided as a projection surface on the wall of the room.
• Video devices for example video projection devices that are to be used in a conference hotel in different rooms, can then only be attached to the ceiling in each room and the second module can only be connected in the room due to the simple connection with the optical fiber which the video projection device is to be used.
• a minimum of laser equipment is sufficient for various conference purposes, which greatly reduces the cost of equipping them with such laser projectors.
• Assembly are combined in a housing and this housing has fastening means for fastening to a wall, a ceiling or a floor of a room.
• Projection surface is provided, on the edge, in particular at the upper edge, of a holding device is provided, on which the first assembly is attached off-center from the projection surface, so that the video image is displayed at an angle.
• first assembly is firmly connected to the projection surface, and the entire projection surface with the first assembly and possibly also the second assembly can be moved from room to room.
• the costs for a large number of first assemblies, each for a room, are also saved in this way.
• a video projection device which in particular includes the invention and its further developments, essentially consists of an electronic control unit, an input module, a control circuit for the pixel and line screening and a device for image calculation. Furthermore, the images are to be written continuously, so that a brightness and color modulated collinear light source should be provided
• the deflection system for displaying video images should be biaxial.
• the biaxial deflection system can consist, for example, of a wobble mirror or a line mirror and an image mirror or one or more non-mechanical deflectors or a combination of different deflectors.
• the magnification optics should be corrected without distortion according to the tangent condition and the origin of the beam deflection should be real or apparent in the deflection system, so that the deflection occurs practically from a point in space.
• the projection surface required for displaying the image can be designed for rear projection or front projection.
• control circuit for the pixel and line screening should have a geometry-optimized pixel grid function both in the line and in the image direction depending on the parameters of the deflection system, an inclination in two angular directions and the surface shape of the projection surface calculate.
• these optimized raster functions are used to recalculate the image on the basis of the incoming video data.
• the invention and the further development include both method and device features for correcting line spacings.
• this can be used to correct the tangent error in the image direction and different line spacing in the case of an oblique projection.
• the line length is scaled. This also includes corrections to the pincushion for a two-axis grid and a correction of the line length due to an oblique projection.
• it is provided to correct the pixel spacings within each line so that the image distortion due to the tangent error in the line direction and an oblique projection can be corrected by differently adjustable pixel spacings between two adjacent pixels.
• Video information on the rastered pixels of an image can be determined so that by recalculating the image taking into account the distortion effect of the Projection surface and the distortion effect, which results from the position of the projector to the projection surface, a largely distortion-free image is obtained. Therefore, as can be seen in particular from later exemplary embodiments, an oblique projection in the row direction can also be easily corrected. This oblique projection in the line direction is reduced to an oblique projection in the image direction.
• the line spacings, the line lengths and the pixel spacings are first corrected and then the pixels are completely recalculated in accordance with the corrected locking geometry.
• Show applications can be useful if special optical effects that attract the attention of the audience are to be created.
• the image equalization and image distortion according to the invention is possible with comparatively little technical effort. Some of the corrections specified later are made exclusively by computer program steps in electronic units, some of which already belong to known projection systems. The additional effort for additional units is negligible. However, no intervention in the optical channel is necessary, which is a decisive advantage over known systems in which, for example to avoid pixel loss, the pixel matrix of the LCD matrix could be chosen to be correspondingly distorted.
• an image can be used within wide limits according to the distortion effect of the imaging system, position and direction of the imaging system to the projection surface and the distortion effect of the
• Projection system are predistorted to the projection surface of the projection screen. Even on a, for example, irregularly shaped projection screen can then largely undistorted image.
• the basis is that the distortion effect of the projection on the projection surface can be determined and the projection system is able to use these determined results to specifically change the image built up in lines by means of pixels.
• a further system advantage of a video projector which works with screened collinear light beams is that there is no need to have a predefined relationship between the video data at the input of the projection system and the R-G-B image data at the electronic output of the system.
• the R-G-B light beams are so modulated in brightness, color and direction that a largely sharp undistorted image or a sharp, deliberately distorted image can be displayed on an almost arbitrarily shaped projection surface. Limits are only set by the
• Degree of inclination or curvature of the projection screen is set, since at an angle between the incident light rays and the normal to the projection surface of greater than about 45 °, reflection and scattering conditions occur which do not allow high-quality image display on conventional projection screens.
• the invention can be developed further by recording the information for the correction of the line length within an image and the correction of the pixel spacings within a line in the storage medium and, after reading out the video information, transferring it directly from the storage medium to the projection system.
• the storage medium can be a video tape, for example.
• Control signal for the line spacing in the example for the deflection of the image mirror
• a control signal for the pixel spacing in the example for the modulation of the pixel frequency, from the video data stream. Since this embodiment will always be specific applications, there is no problem that additional control signals have to be impressed on a video information which is per se standardized.
• an assembly of the video projection system namely the projection head, is moved in space during the image projection.
• This movement information can also be contained on the storage medium. This ensures that the image display is corrected for the position of the projector that it is currently occupying in relation to the projection surface.
• Figure 1 shows an embodiment of a device according to the invention
• Figure 2 shows an application of the device of Fig. 1 for
• Figure 3 is a schematic representation for an oblique projection
• FIG. 4 shows a schematic illustration as in FIG. 3, but with geometric errors in two directions;
• Figure 5 is a schematic representation of so-called pillow distortions;
• FIG. 6 shows another distortion due to an oblique projection
• FIG. 7 shows a projection onto a curved projection surface
• Figure 8 is an illustration of a projection into a curved one
• Figure 9 shows a digital circuit for generating clock pulses
• FIG. 10 shows a circuit similar to that in FIG. 9, but implemented as an analog circuit
• Figure 11 is a schematic representation of a projection under a
• FIG. 12 shows a schematic illustration with a different inclination of the projection head to the projection surface
• Figure 13 is a schematic representation to explain a
• Figure 14 is a schematic representation for explaining a
• FIG. 15 shows a control circuit for a deflecting mirror designed as a tilting mirror
• FIG. 16 shows a graphical representation for the dependence of the deflection angles j of an image mirror for different lines i;
• Figure 17 is a graphical representation for the angle of deflection
• Figure 18 is a graphical representation of the deflection angle
• FIG. 19 shows a graphical representation as in FIG. 18, but with projection at an angle ⁇ other than zero;
• Figure 20 shows a circuit arrangement for scaling the
• FIG. 21 shows a circuit arrangement for optimizing the geometry of a
• Figure 22 shows another circuit arrangement for scaling
• FIG. 23 shows a circuit arrangement for optimizing the geometry with equalization of the pixel spacings and real-time image calculation.
• a device 100 is shown schematically in FIG. 1, by means of which the essential method features can also be explained.
• the module 10 receives a video signal (VIDEO in) via an input, which is to be displayed on a projection surface 101 as a video image in front or rear projection.
• this projection surface 101 was designed as a screen in a frame with feet, to which rollers were attached, with which the entire device from
• Fig. 1 moved and could be transported to other rooms, for example.
• the projection of the video image takes place from a projection head 14, which represents a first assembly which, in the exemplary embodiment from FIG. 1, was arranged on an arm fastened to the frame.
• the arm could be folded in to transport the device 1 so that the entire device could also be moved through narrow doors.
• the assembly 10 was also attached to the frame.
• the assembly 10 is connected to the projection head 14 via an electrical cable connection 9 and an optical fiber 5.
• the image is displayed in the device shown in FIG. 1 in the following way:
• the light sources 1 shown in the assembly 10 emit continuous light, which is modulated in intensity by means of modulators 2 in accordance with the "VIDEO in" signal with respect to the color and brightness of the pixel to be written.
• the light beams emerging from the modulators 2 are then combined by a beam combination 3, in the exemplary embodiment a system of dichroic mirrors, so that all light beams coming from the light sources 1 are combined in a common light beam for illuminating the pixels composing the video image.
• This common light beam is then via a coupling optics
• the socket 7 in the projection head 14 is aligned so that the light emerging from the optical fiber 5 falls into a decoupling optics 6, through which the light beam is parallelized again and in a deflection device consisting of the line mirror 11 and image mirror 12 exists, is initiated.
• the line mirror 11 was a polygon mirror, which only allows fixed times T for each line, while the image mirror 12 was designed as a tilting mirror.
• a line-like deflection is carried out by the line mirror 11 and a picture-like deflection is carried out with the image mirror 12.
• Both mirrors and the modulation in the assembly 10 result in a picture structure similar to that in normal television, but instead of light one or more electron beams are intensity-modulated and deflected in order to represent different pixels on the projection surface with respect to line and picture.
• the projection head 14 has a magnifying lens 13 for magnifying the
• the factor K is referred to below as the enlargement factor.
• optical axis of the structure in the projection head is also referred to in FIG. 1 as "OA".
• the "VIDEO in” signal is processed by the electronic control device 8 both for the deflection and for the intensity modulation.
• the following are used in detail: an input module 16 and a control circuit 18 for pixel screening and line screening, which essentially uses the synchronization signals in the video signal in order to guide the line mirror 11 and the image mirror 12 synchronously with the modulation.
• an image memory was specifically provided for storing the image.
• Line mirror 11 and image mirror 12 synchronized a clock generator with which the corresponding pixel information was read from the image memory.
• a device for image calculation 17 was also used, with the respective correct pixels for the geometric equalization or the dark keys mentioned at the beginning. Details of this device 17 are described in more detail below.
• Fig. 2 shows an embodiment in perspective, in which the aforementioned angle ⁇ is set to zero, the device being primarily set up for stationary operation.
• the projection head 14 is arranged on a ceiling 104 of a room.
• the projection of an image 103 takes place at an inclination angle ⁇ on a wall 105, which has the optical properties of a projection surface 101.
• the scattering of the light in a large solid angle required for projection surfaces was achieved by applying a suitable color with a suitable one
• the assembly 10 arranged laterally on a wall on the floor also contains the operating elements. This arrangement can also be changed in the case of very small lasers or lasers of low weight, so that the lasers and the electronics also work on the
• Ceiling are in a common housing with the assembly 10 and then the entire device 100 is attached to the ceiling.
• the device 100 is then controlled, for example, via a remote control. Both possibilities are identified in FIG. 2 by the broken line between the assembly 10 and the assembly with the alternative reference numerals 14 and 100.
• the quantities a and b are shown in FIG. 2, which are still to be used for later formula-based calculations.
• the size a is the distance of the projection head 14 from the projection surface 101 and b the image width shown.
• Inclination angle ⁇ of -15 ° is provided. With these dimensions, a distortion-free image with an image height of 1.5 m and an image width of 2.7 m was possible.
• the distance between the top edge of the picture and the ceiling was 15 cm. With standard room sizes, such a system can fill almost the entire wall with picture content.
• FIG. 3 shows how a rectangular image would generally appear when projected onto a projection surface 101 if the projector were arranged centrally at the top of the projection surface 8 at an angle ⁇ to the projection surface 101.
• the upper picture edge which is designated in FIG. 3 with the reference numeral 20, would be significantly shortened compared to the lower picture edge 21, the vertical side boundaries 22 of the rectangular picture, however, would run obliquely between these edges, so that the trapezoid shown in FIG. 3 would result.
• pixel resolution depends on a matrix, be it the LCD matrix of the state of the art mentioned at the beginning or a shadow mask of an electron beam tube required for displaying color images.
• lines for compensating for the distortion can only be shortened with a loss of information in one line.
• the light beam for illuminating image points can be directed to any desired location on the projection surface 101 due to the property of this image generation system. This is possible because this technique does not rely on a fixed pixel grid.
• the compensation that is possible as a result will be explained in more detail below with reference to FIG. 3.
• Pixel indicated with X e o The last, the nth line starts at X and ends at the point X s. In between, an i-th line is designated by way of example with the starting point X a and Xg.
• a rectangular piece 103 which extends from a size X e to a size X ad , is now cut out of the entire possible trapezoidal grid area, as is illustrated in FIG. 3. This becomes compensation each line only rastered from the value X a to a value Xe.
• the displayed values x ad and X ed were selected as extreme values.
• X ad can be chosen a little larger and X ed a little smaller; what is important for the selection is that X ed is smaller than the minimum of x « and x ad is larger than that
• Xgj is maximum, where X e must be greater than X ad .
• the line screening in the projection head 14 is carried out with a uniform line time T, whereby in the period in which the light beam between the points X a i and Xg d on the
• Projection area 101 would hit, is blanked, while in the range from x ad to X ed the entire line content is projected onto the projection area 101 in the correct position, while for the rest of the time, when X ed to Xj e is rasterized, it is blanked again.
• the video signal provides the pixel information of each line at the same time intervals in accordance with the current video standards, it is expedient for synchronization of the video signal to provide a memory into which this pixel information is first written and then read out synchronously and pixel-by-pixel for rasterization between the locations X ad and X ed becomes.
• continuously operating lasers in particular gas lasers, were used.
• the different speed of writing pixels was taken into account by scaling the brightness with regard to the lighting times of the pixel, as already described in the introduction.
• the diameter of the light bundle which is largest at the edge 21, is chosen in the example of FIG. 3 in such a way that the image resolution required by the video standard to be displayed is achieved there.
• Light beam possible resolution is higher.
• This can be used advantageously by designing the memory for the pixels in line 20 for a larger number of pixels than is required by the video standard.
• the line information for the additional pixels then required can be interpolated using an algorithm for increasing the resolution. This does not necessarily result in an increase in information, since the entire information in one line is also limited by the bandwidth of the video signal. For this reason, it is generally also sufficient to sample the analog video signal introduced on line "VIDEO in" in FIG. 1 with a frequency higher than the pixel frequency of the video standard. The sampling of the analog signal then results automatically
• a projection button 14 arranged perpendicularly and centrally to the projection surface 101 results in a symmetrical trapezoid for the image distortion. If, on the other hand, the projection device is arranged, as in FIG. 1, at the top right corner of the projection surface 101 ⁇ ⁇ O, the trapezoid is no longer symmetrical, but the shape shown in FIG. 4 results. This can also be equalized with the method according to the invention, but with the aid of additional steps, as will be explained later.
• Line correction can be remedied, as in the embodiment of FIG. 4, in which both the angle ⁇ and the angle ⁇ are different from zero.
• FIGS. 3 to 6 each indicate ellipses which are intended to clarify the exit pupil AP for the exit of the light bundles, here of laser beams.
• the reference numerals 102 and 103 are also used.
• the reference numeral 102 means the uncorrected, recorded image, 103 the method-corrected image and 101 the projection surface.
• FIGS. 7 and 8 show the projection onto the outside of a projection surface
• FIG. 8 shows an example for the inside of the projection surface
• FIG. 8 shows a geometry as is common in planetariums and flight simulators.
• the previous reference numerals with the indicated areas are also entered here with the same meaning.
• the two figures are self-evident and it is expressly referred to the content of the figures in this regard in particular.
• the projection head 14 is explained in more detail for a better understanding of the technology.
• the light parallelized by the decoupling optics is thrown onto the respective facet of the line mirror 11 located in front of it, which facet is more uniform
• An image mirror 12 is provided for the image deflection, which is designed as a tilting mirror and is moved back and forth at the image frequency.
• the light beam emanating from the image mirror 12 falls into a magnifying optic 13, which is an afocal lens system, so that it is parallel to the
• Magnifying optics 13 entering light bundles can emerge again as a parallel light bundle.
• This afocal lens system is compensated according to the tangent condition.
• the value of this constant was 3.5.
• control signals for the rotating mirror 11 and the pivoting mirror 12 and also the power supply for these deflection devices were transmitted via the cable connection 9.
• the video information of a line is first stored in a memory, which is then read out synchronously with the display, depending on the distortion to the uniform pixel density.
• the reading can be effected by circuits which always output a clock signal at an output 25 when a new pixel is written on the projection surface 101, that is, when the color or brightness for a new pixel to be displayed is from the memory for modulating the Light beam should be read out.
• FIG. 9 shows a digital circuit for generating the clock signal on the output 25, while FIG. 10 shows an analog circuit that can be used for this.
• a memory 26 is provided for the control according to FIG. 9, which is a RAM in cases in which the compensation is to be changeable for different situations. This can be useful, for example, when the projection head 14 is arranged differently from the projection surface 8. The required information is then stored depending on the conditions that arise in the application. In examples, such as the framed projection surface 101 with a projection head 14 on one arm, in which the geometry is always fixed due to the constant position of the projection head 14 relative to the projection surface 8, this memory can also be a ROM.
• This memory is addressed once by a binary word (line which specifies which line i is currently being mapped. Further address lines, for example for the lower ones Bit values of the addresses of the memory are addressed by the output of a counter 27, which in principle counts up which pixel of line i was mapped at the respective time.
• ROM or the freely programmable storage in RAM a binary word that indicates at which point in time, calculated from the beginning of a line, the next pixel should be written.
• the digital word represents the time in units of the period of a frequency f which is fed on a line 28 into the circuit according to FIG. 9. This frequency f should be a multiple of the pixel frequency in order to maintain the most accurate possible position of the light beam for a distortion correction.
• the time elapsing during the writing of a line is determined by counting the periods of the frequency f with a counter 29.
• the time applied digitally by the memory 26 to the data output 27 is compared by means of a digital comparator 30 with the elapsed time counted in the counter 29.
• a clock pulse is applied to the output line 25, which is used to read the next pixel information from the image memory at the given line information.
• this clock pulse is fed to the input of the counter 27, the digital output value of which is then increased by one, after which the digital time value for the next pixel is read out from the memory 26.
• the digital value for the counter reading which is also used for addressing the image memory for reading out the
• Information content of a pixel is used.
• the counters 27 and 29 are further reset via a signal 32, which is given at the beginning of each line, so that a defined state is set for each new line.
• this line synchronization signal on line 32 is used to set the first pixel in the memory for storing the video information as well as the last pixel to "black", in order to ensure that the light beam in the areas Xgj to X ad and X e to X e i is always blanked.
• the frequency f on the line 28 should, as already mentioned above, be a multiple of the line frequency of the
• Pixel frequency is not always complied with at very high pixel frequencies.
• an analog control according to FIG. 10 is preferred, which does not depend on the digital representation accuracy of the time.
• the time is predetermined by a function generator 33, which generates a sawtooth at an analog output, which begins at the point in time at which the light beam is directed onto the projection surface 101 at the location X a i.
• the slope of the sawtooth is controlled via input 34 in proportion to 1 / (XerXai).
• the output of the function generator 33 leads to an input of an analog comparator 34, the other input 35 of which is connected to the output of an integrator 36. At the beginning of each line, the output of the comparator 36 is clamped to zero via a line 40.
• the first pixel and the last pixel of the memory for the line information are supplied with the information “black” for blanking out the light beam.
• a line for reading out the pixel information of the line stored in the memory thus arises on line 25, the speed of the reading being controlled by the different line lengths given by the distortion on the basis of the information added via control line 39.
• Sawtooth shape show different waveform. This is made possible, for example, by one on the control line 39 depending on digital signals Sawtooth adds higher harmonics as a fundamental vibration according to the desired phase and amplitude.
• the line spacings can also differ markedly from one another. If this error is hardly recognizable even at small angles ⁇ or ⁇ , it is advisable to make a correction for large angles of inclination and high-resolution systems such as those for CAD applications.
• the projection angle ⁇ is the angle between the projection axis, i.e. the optical axis OA of the deflection system, and the normal on the projection surface 101, referred to as the horizontal H.
• the reference point of the angle is the origin of the beam deflection, i.e. the exit pupil AP in this system with magnification optics 13.
• the angular limits are 0 °, (horizontal) to less than +/- 90 °, a negative angle meaning that the projection direction in the embodiment of FIG. 2 is oriented on the bottom.
• a positive angle means that the projection device is aligned on the ceiling side.
• the magnifying optics 13 and the image mirror 12 are arranged with respect to one another such that their entrance pupil EP lies in the vicinity of the image mirror 12 in the origin of the beam deflection.
• the beginning of the image (1st line) is defined in such a way that the lines are written from top to bottom when viewed in the direction of light, which corresponds to standard television standards. All information applies to both a front projection and a rear projection on a projection surface 101.
• the exit pupil AP relates to the angle-increasing projection optics 13. This is the deflection point of the light bundles after passing through the magnification optics 13. Without the magnification optics 13, this spatially fixed deflection point can lie on a beam-deflecting mirror by the point of incidence of a laser beam.
• the size a is the distance between the exit pupil AP and the projection surface
• the distance a is normalized to 1 and the equations given later can, however, be used for dimension-related quantities by appropriate multiplication for the design of various devices.
• the size h is the height of the image
• the size e is the distance on the projection surface between the optical axis OA and the horizontal H, measured on the projection surface 101;
• the angle ⁇ is the optically effective total deflection angle of the image mirror 12; - The angles ⁇ , denote the deflection angle of the image mirror 12 based on the
• the size s is the distance of the first line (picture beginning) from the horizontal H on the projection surface 101;
• the sizes Sj are the distances of the rows i from the horizontal H; - the angles y, - denote the projection angles between the straight lines
• angles ⁇ j are the projection angles between the straight line
• the calculations given here can be simulated electronically in a circuit arrangement according to FIG. 15.
• the angle ß is the optically effective total deflection angle of the line mirror 11.
• the angle ratio of the previously considered angle ⁇ and the angle ß considered here is determined by the design properties (mechanical / optical) of the line mirror 11 and the image mirror 12 and the aspect ratio width b Height h of the image, which was 4: 3 in the exemplary embodiment according to FIG. 1;
• angles ⁇ are the deflection angles of the line mirror for each line i (line opening angle);
• the sizes Lj denote the lengths of the rows i and have an amount of X de -X d i,
• the sizes a are the projection distances of each line i, measured from the exit pupil AP to the respective center of the line;
• the correction factor for the cushion distortion is set to c; -
• the quantities f are correction factors for the line length due to the vertical
• One system advantage is that the angle enlargement K of the projection optics 13 has no influence on this correction factor.
• the correction factor f is the ratio of the projection distance of line i with oblique projection to the projection distance of line i without oblique projection.
• the correction factor for the electronic correction of the line length is further determined according to:
• the line opening angle ß x of each line can be calculated from this:
• the factor R serves as a scaling variable for the described scaling of the line length Lj in the transformation according to the inventive method XeiiX a i ⁇ X ad ; i.
• the line deflection angle ⁇ is a fixed quantity, which is determined by the geometry of the facets of the Line level is specified and the time interval T for each line is also determined via the rotational speed.
• the setting of the line length ie the determination of the beginning of the line X ad and the end of the line X ed , is made by assigning the brightness and color modulation of the
• Pixels for the position of the facet surface of the polygon mirror (line mirror). A corresponding complete control circuit will be explained later.
• the projection angle ⁇ is the
• the angular limits are 0 ° - no inclination - and +/- 90 °, a negative angle meaning that the projection head 14 is inclined towards the beginning of the line. Accordingly, a positive angle means that the projection head 14 is inclined towards the end of the line.
• Projection screen is a rear projection screen and the lines are written from left to right as viewed by the viewer.
• the magnifying optics 13 and the line mirror 11 are arranged with respect to one another such that the entrance pupil EP of the projection optics in the origin of the beam deflection in the
• the beginning of the line is defined in such a way that the lines are written from left to right by the viewer, which corresponds to usual television standards.
• the sizes ß y , - are the deflection angle of the line mirror for each pixel y of a line i in relation to the projection axis OA of the deflection system 14 and the deflection point of the line mirror for the respective line i;
• the size g denotes the distance on the projection surface between the projection axis and the vertical V to the exit pupil on the projection surface;
• the sizes a y ⁇ are projection distances of each pixel of each line i, measured from the exit pupil AP to the respective center of the line;
• angles yi are the projection angles between the straight line
• angles ⁇ y , - are the projection angles between the straight line
• Exit pupil AP to the vertical V on the projection surface, calculated from the pixel distance t yi of each pixel y in each line i:
• This function ß yj f (i, y, ⁇ , ⁇ , K) (see also the graphical representations in FIGS . 5, 18 and 19) is directly impressed on a control voltage of the line level if a deflection device is used whose deflection angle position is within a range Line could be set by an electrical quantity with sufficiently high dynamics.
• the pixel spacing can, however, also be determined by a temporal modulation of the pixel frequency can be set, as has already been described above.
• All brightness and color values of a pixel must be assigned to the angular positions of the deflection system, which in the example correspond to a rectangle (image area 103) that is actually different from that of the deflection device (line mirror and
• Image area is completely covered.
• the line spacing of an image the line length and the pixel spacing within the lines are optimized for the respective projection conditions according to the calculations shown under A, B and / or C and for this geometrically optimized pixel grid in the line direction and image direction for each pixel that can now be displayed from the existing RGB video data is calculated a new video information.
• Methods for processing a video image are known, for example, from DE 195 17 357 C1.
• the method described here can be used in an equivalent manner in order to reduce image distortions on a curved projection surface in accordance with FIGS. 7 and 8.
• the distortion effect of the projection surface is known and that it is incorporated as a data record into the video information or entered into the electronics of the projection device.
• ROM or RAM The transformation from the distorted to the rectified image can be carried out by means of ROM or RAM, as has already been illustrated with reference to FIG. 9.
• the memory values of ROM or RAM are calculated according to the equations above.
• the exit pupil AP is offset from the center of the image both by the angle ⁇ horizontally and by the angle ⁇ vertically.
• the frame shown with a broken line shows the distortion of an uncorrected image 102.
• the solid frame shows the distortion of an uncorrected image 102.
• the solid frame shows the area in which pixels are intensity and color modulated and brought to the display by the deflection device and produce a largely undistorted image 103.
• the dotted lines here show the course of the rastered lines, and it can be seen that a simple line spacing correction in accordance with section A, a scaling of the line length in accordance with section B and a pixel spacing architecture in accordance with section C are not sufficient.
• Figure 7 shows the situation using the example of a front projection onto a concave
• Projection screen 101 which is, for example, the backscattering envelope of a balloon.
• the projector 100 delivers a distorted image 102.
• an image display is possible up to a critical angle, which is formed by the tangents that are applied to a curved surface from the projection center. Because of the decreasing angle from the projection center, the angle that hits the projection screen
• Light rays increase the distortion of the image with increasing distance from the projection center. This distortion can be counteracted by correcting the line spacing and recalculating the screened pixels of the undistorted image 103, taking into account the distortion effect of the projection surface in accordance with the calculation specified in sections A, B, C and D.
• the exit pupil AP is horizontally offset by the angle ⁇ relative to the center of the image to be displayed.
• the frame shown with a broken line shows the distortion of an uncorrected image 102.
• the solid frame shows the area in which pixels are intensity and color modulated, brought to the display by the deflection system and produce a largely undistorted image 103.
• the exit pupil AP is vertically offset from the center of the image by the angle ⁇ .
• the frame shown with a broken line shows the distortion of an uncorrected image 102.
• the solid frame shows the area in which pixels are intensity and color modulated, brought to the display by the deflection system and produce a largely undistorted image 103.
• the dotted lines here show the course of the rastered lines, and it can be seen that a simple line spacing correction according to section A, a scaling of the line length according to section B and a pixel spacing correction according to section C are not sufficient.
• the video information (brightness and color) of each pixel for a low-distortion image display must be recalculated in accordance with step D and assigned to the geometrically optimally corrected pixels to be displayed within the respective lines.
• FIG. 8 shows the conditions using the example of a front projection on a convex projection screen 101, which is, for example, the scattering inner surface of a dome, as is used in a planetarium.
• the projector 100 delivers a distorted image 102.
• undistorted images could only be displayed if the The projector is at the center of a convex projection surface and is rasterized in polar coordinates.
• image distortion occurs. This distortion can be counteracted by correcting the line spacing and recalculating the screened image points of the undistorted image 103, taking into account the distortion effect of the projection surface in accordance with the equations given in sections A, B, C and D.
• the image is now rotated by 90 °, and a correct image is created again, but the image width only corresponds to the original image height.
• the original image is obtained by adapting the number of lines to the number of pixels of a line and adapting the image size by means of zoom optics, with the difference, however, that the information that was originally screened in the line deflection direction is now screened in the image deflection direction and vice versa.
• This procedure is particularly expedient for a projection device which is at an incline with the angle ⁇ ⁇ O to the projection wall, as is shown by way of example in FIG. 14.
• An oblique projection with a slope according to FIG. 6 can thus be attributed to an oblique projection with an inclination according to FIG.
• the pixel information is stored, for example, line by line in a RAM and read out column by column perpendicular to the line direction or vice versa. Then the memory space in the RAM should be dimensioned such that the information for the pixels to be darkened can also be stored in the respective line intervals for the distances (X a ,; X a ) and (X ed ; Xei). With this type of storage, special electronics no longer have to be used for blanking, since then for the pixels for writing the intervals ⁇ ; X ad ) and (x ⁇ ; X e i) dark values are stored. The memory information is then simply read out sequentially.
• FIG. 15 shows a control circuit for generating a deflection angle function for a tilting mirror, as was used as an image mirror 12 in the exemplary embodiment from FIG. 1. Then the calculated deflection angle function is the control variable.
• Control voltage U G for the image mirror is read out from the function memory 71 and fed to a D / A converter 73.
• the generation of the deflection function for the image mirror is synchronized and clocked with the aid of a clock and synchronizing signal generator 76 via the synchronizing signals of the video image to be output.
• the task of the microcontroller 75 is the basic initialization and programming of the programmable function generator 70 as well as the provision and loading of the corrected deflection function via the data controller 74 into the function memory 71.
• a change of parameters or the deflection function for the programmable function generator can be done via the I 2 C -Bus take place from a higher-level facility.
• the parameter for the family of curves is the number i.
• the deflection angle ⁇ yj is shown here again as a function of the pixel number y.
• the parameter for the family of curves is the line number i.
• the arrows drawn in black in FIGS. 18 and 19 indicate the grid sequence.
• FIG. 20 shows a functional circuit diagram of an electronic device for scaling 80 real-time video data with the possibility of dynamic scaling in the row direction.
• the spatial or temporal distribution of the pixels in a line and the video information of each pixel are calculated in real time and related to the raster area of the line mirror 12 which is optimized for the respective geometry of the image display.
• the deflection device delivers a synchronization signal "DEF-Clock" for the output of the pixel data (asynchronous control).
• the R-G-B scaler 81 receives the video input data "R.G.B in”, “H.V SYNC in” via the buffer memory 82. "H, V BLK in”. "PCLK out” fed to the video source.
• input data for the scaler 81 are the correction values Rj which are related to the line opening angle ⁇ j.
• the correction values Syj for the pixel spacing are calculated from the deflection angle function ß y , the line mirror.
• the video data are converted via the buffer memory 83 with the aid of the output controller 85 into an output video data stream “R, G, B out” which is related to the screened pixels of a line and the lines of an image.
• the buffer memory is referred to here as a FIFO (First in - First out).
• FIFO First in - First out
• an image memory for an overall video image is to be provided, which in this example is operated like a FIFO.
• this image memory is then read out column by column when it has been written line by line or vice versa.
• the data and the program of the scaler 81 are applied for dynamic scaling. This is done synchronously on request from the scaler 81.
• the data controller 86 with parameter RAM 87 can also be constructed similarly to the circuit of FIG. 9.
• the microcontroller 75 has only the task of carrying out the basic initialization and of programming all electronic components in accordance with the respective application requirements.
• the microcontroller further provides the dynamic scaling parameters for the parameter RAM 87 via the data controller 86. With fixed projection conditions, these values are read from a ROM. With different angles ⁇ and ⁇ these angles can be entered in an EEPROM. The microcontroller then reads these values for the initialization and calculates the values for a RAM for scaling according to the given equations.
• Parameters for the electronic device for horizontal scaling 80 can also be changed via the rc bus from a higher-level device via the microcontroller 75.
• FIG. 21 shows a block diagram for a circuit for correcting image errors in a video projection with a writing light bundle in real time, in which recalculation of the image is also taken into account, with the functions and shown in FIGS. 11, 12, 13 and 14 in particular the calculation methods shown are taken into account.
• the circuit shown in FIG. 21 enables the extensive correction of image errors in real time, as can occur, for example, when projecting video images onto arbitrarily curved surfaces and / or at any projection angle.
• the device for dynamic scaling 80 By means of the device for dynamic scaling 80, a dynamic scaling of the pixels in the line direction (i-direction) is first carried out, and after a 90 ° rotation of the image in a device for image rotation 90, the pixels are scaled in the image direction (y-direction) in one device 80 ' realized. Then another 90 ° rotation takes place by means of a further device for image rotation 90 ' .
• These devices 80, 80 ' form the
• the video data "R, G, B out” are then fed to the modulators 2 of the light source 10 which can be modulated in brightness and color, the temporal sequence of the pixels being controlled by the signal PCLK generated by the signal "DEF-Clock".
• the time sequence for line and image deflection is controlled by the signals U G (t).
• Each of the devices 80 and 80 ' is essentially a circuit according to FIG. 20, the assemblies necessary for the control, clock generator 76 and microprocessor 75, expediently being implemented only once for the overall system.
• the line length is set in the device for dynamic scaling 80 in the line direction by means of the signal “H BLK”, the signal distribution of which is influenced by the values R, ( ⁇ ,), which also contain the angle deflection function ⁇ yi (S yi ) are.
• the image height is set in the device for dynamic scaling 80 ' in the image direction by means of the signal "V BLK", the signal profile of which is influenced by the values of the deflection angle a.
• the programmable control circuits 70 and 70 ' essentially correspond to that
• control circuits 70 1 and 70 ' together form the control circuit 17 shown in FIG. 1 for pixel and line screening, but the deflection device in both directions must be carried out quickly enough by a control signal.
• miniaturized tilting mirrors or acousto-optical deflectors are suitable for quick distractions.
• an optimized raster geometry is generated in the control circuit for the pixel raster and line raster 17, while in the device for image calculation 17 a new image with optimized resolution for the optimized raster geometry is calculated based on the incoming video information becomes.
• the device 17 can be further simplified if the last 90 ° rotation is not carried out electronically, but simply by rotating the image, i. H. Swap the scan direction by turning the deflection mirror.
• the 22 also shows a programmable modulation circuit 60 with a voltage-controlled oscillator 61 for a suitable frequency modulation of the signal PCLK.
• the programmable modulation circuit 60 realizes a correction of picture errors by controlling the modulation of the picture elements within each line. In particular, the following errors can be corrected:
• Oscillator 61 are synchronized at the beginning of each line.
• the microcomputer 75 generates the voltage proportional to the values of the correction factors S yi . These are stored in a temporary function memory 71 and fed to the voltage-controlled oscillator 61 as required via a control and synchronization circuit 72 and a subsequent D / A converter 73.
• 23 essentially corresponds to a circuit arrangement as described in FIG. 21, but with the circuit from FIG. 22.
• the image mirror 12, a tilting mirror, is also driven here with the voltage U G (t).
• the voltage-controlled oscillator 60 used in the example of FIG. 23 is expediently provided in the clock generator 76.
• the reading of the pixels is timed by means of this circuit via the signal "PCLK out” generated with the aid of the signal "DEF-Clock” and thus the assignment of the pixels to the respective position of the facet of the line mirror, here a polygon mirror, is determined.
• the modulation of the pixels is time-compressed or delayed due to the control, so that the pixels are written sequentially despite the constant deflection speed of the line mirror with corrected intervals.
• Deflection system 11, 12 an optimized raster geometry is only generated for the image deflection (image mirror 12) in the control circuit for the pixel raster and line raster 17.
• the line deflection (line mirror 11) is controlled with a constant signal "H SYNC out".
• the geometry of the line is optimized in the microcomputer 75, which makes the correction values S yi available to the voltage-controlled oscillator 60.
• Correction values Rj control the effective line length via the scaler 80.
• a new image with optimized resolution for the optimized raster geometry is calculated on the basis of the incoming video information, and the "R, G, B out" data are calculated in one by the
• Pixel intervals are output in a sequence determined in time.

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• Engineering & Computer Science (AREA)
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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Geometry (AREA)
• Transforming Electric Information Into Light Information (AREA)
• Projection Apparatus (AREA)
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• 1997
  • 1997-08-27 DE DE19737374A patent/DE19737374C2/de not_active Expired - Fee Related
• 1998
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