WO2004052022A1

WO2004052022A1 - Brightness control of a projection appliance

Info

Publication number: WO2004052022A1
Application number: PCT/EP2003/013628
Authority: WO
Inventors: Harald Lang
Original assignee: Barco Control Rooms Gmbh; Dambach, Soeren
Priority date: 2002-12-04
Filing date: 2003-12-03
Publication date: 2004-06-17
Also published as: DE10256505A1

Abstract

The aim of the invention is to regulate the brightness of a projection appliance (1), especially a rear projection appliance (1) of a projecting screen, such that it is neutral in terms of colour, contrast and light homogeneity, the image production preferably being based on the time-sequential mixture of primary colours using a colour wheel (6). To this end, an intensity reducer, for example, in the form of an adjustable diaphragm disk (22) with a slit-shaped diaphragm having a variable width, is arranged directly adjacent to the focal plane (20) of the condenser (4) of the illumination unit (2) or the focal plane of a focussing lamp reflector.

Description

Brightness control of a projection apparatus

The invention relates to the brightness control in projection apparatus. Projection devices are used to project an image onto a projection screen. The invention is directed to projection apparatuses which have an image generator for displaying the image on a reduced scale, an illumination unit with condenser optics and / or a focusing lamp reflector (for example in an elliptical or more complex form) for illuminating the image generator, and a projection device comprising a projection lens to magnify the image displayed by the imager on the projection screen, a spatial light mixing device to compensate for local differences in the brightness distribution and a variable intensity attenuator

Regulating the luminous flux, which is arranged in the beam path between the lamp of the lighting unit and the imager, include. As a rule, the image generator and / or the projection device for adjusting the position of the projected image on the projection screen is fastened in or on the projection apparatus in a position that can be adjusted with adjustment elements.

A distinction is made between reflected light and rear projection devices. A difference between reflected light projectors and rear projection systems consists in the fact that mostly further optical elements such as deflecting mirrors and projection screens are contained in rear projection apparatuses, which are not used in reflected light projectors.

Both incident light and rear projection devices are used to display an image on a large-scale projection screen. The imaging device can be a transmitted light imaging device, that is to say an imaging device that is transmissively illuminated by an illuminating device for illuminating the imaging device, or a reflecting imaging device that is illuminated by the illuminating device. According to the prior art, for example, transmitted-light liquid-crystal imaging devices or reflective liquid-crystal imaging devices or DMDs (Trademark of Texas Instruments Inc., digital micromirror device) are used.

An illumination unit for illuminating the image generator or for illuminating the transmitted light image generator generally comprises a light source, a reflector and one or more condenser lenses for illuminating the image generator. Furthermore, additional light mixing devices, for example for optimally illuminating a rectangular image format, can be provided. It is also possible to dispense with the condenser optics when using a focusing, for example elliptical, lamp reflector. The projection device or the lighting unit is either integrated into the projection apparatus or attached to it. A projection apparatus is thus a closed, complete unit for displaying an image, a screen for viewing the image being integrated in a rear projection apparatus. Rear projection modules in particular are widely used in cases where a complex image, for example consisting of various video or computer images, is to be displayed over a large area. Widespread areas of application for such rear projection apparatus are screens which are viewed by several people at the same time. Large screen rear projection is particularly widespread in modern control room technology.

If the image displayed is to exceed a certain size and complexity given the quality requirements, this is no longer possible with a single rear projection module. In such cases, the image is composed of partial images, each of which is displayed by a rear projection module. In this case, the image displayed by a rear projection module is a partial image of the overall image of the screen displayed by all rear projection modules.

According to the state of the art it is possible to have a large one

Number of rear projection modules in a modular structure of a projection screen and / or stack one above the other in order to display a large image composed of many individual partial images. The number of rear projection modules that are put together to form a projection screen is up to 150 or more.

Further details on rear projection modules can be found in document EP 0 756 720 B1, to which reference is hereby made.

To achieve homogeneous or homogenized illumination, it is advantageous if the projection apparatus has a spatial light mixing device for compensating differences in brightness distribution. A spatial light mixing device, which extends in the direction of propagation of the light, in particular a light mixing rod, is preferably used here. Light mixing rods are known in the prior art. Known embodiments include, for example, hollow mixing bars (see, for example, US Pat. No. 5,625,738) and full mixing bars (see, for example, DE 10103099 AI).

The homogenization effect of a light mixing rod, also known as the degree of integration, depends on the ratio of the length to the cross section for a given angular distribution of the lighting. The larger this ratio, the higher the degree of integration. In the case of lighting with an aperture number f in the range from 1 to 1.5, the ratio for a conventional light mixing rod is approximately 5 to 10 with a length of 50 mm. A highly integrating mixing stick is about twice the length, i.e. a ratio of 10 to 20. As the ratio increases, the average number of reflections inside the light mixing rod increases, resulting in higher reflection losses and thus a lower light output. For this reason and because of the practically available space for installing the light mixing rod, the degree of integration that can be achieved in practice is limited.

In many cases, high demands are placed on projection devices, in particular on projection screens constructed modularly from a plurality of projection devices. There is a particular problem in achieving and maintaining a certain and uniform brightness of the image or images, which can only be inadequately achieved due to the following technical causes according to the prior art: The lamps used in the different projection devices, which are high-power lamps in many applications, have different basic brightness. This requires a complex adjustment of the individual projection devices in order to achieve a uniform display on a screen.

The luminous flux of the lamps which can be used for the projection apparatus changes over the life of the lamps. This aging process is also dependent on the lamp. This requires repeated brightness adjustment of the projection apparatus.

Manufacturing tolerances of the other optical components also lead to fluctuations in the light flow on the projection surface, which necessitates a brightness adjustment of the projection apparatus.

According to the state of the art, various complex methods are used to solve these high technical requirements, but they do not completely solve the problems mentioned:

The lamps are selected to a high degree in order to overcome minimal manufacturing tolerances that cannot be exceeded. This is associated _t-consuming and costly.

A brightness adjustment is carried out during the installation of a projection apparatus or a screen and / or at fixed service intervals. The brightness distribution is measured on the screen. This is complex and cost-intensive, requires trained personnel and requires an interruption of ongoing operations. Image quality may deteriorate between service intervals. Taking into account the average change in luminous flux during the operating period based on experience. However, the deviation of individual lamps from an average time-dependent change in luminous flux is so great that they lead to visible image artifacts without individual correction.

A determination of the luminous flux by measuring the lamp power by means of electrical measurement of the lamp current and lamp voltage. However, only a small proportion of the available lamp drivers allow such an electrical measurement, and the electrical power of the lamps is not fully correlated with the resulting light flux from the projector.

A manual entry of a time-dependent luminous flux change to be taken into account by the user. However, this requires appropriate training of the user and the activation of special image content, which disrupts continuous operation.

A regulation of the lamp power to stabilize the optical power of the projector. Such regulation of the lamp power means that the lamp would be operated with varying electrical power. This results in an undesirable change in the color tone and a shortening of the lamp life in the commonly used high-performance discharge lamps, which has a disadvantageous effect, in particular for continuous use in picture walls.

Electronic compensation by modifying the image content. However, this is accompanied by a disadvantageous reduction in the contrast and, moreover, no compensation for differences in brightness in the case of dark image content is possible.

A variable intensity attenuator in the form of an aperture diaphragm is used to regulate the luminous flux. turns, which is arranged in the beam path of the illumination optics or the projection optics. However, it has been shown that this changes the primary colors and the contrast. In addition, the homogeneity of the illumination is deteriorated.

A video projector is known from document DE 198 19 245 C1, in which two deflecting mirrors are arranged between the light source and the image generator and a rod-shaped light mixing device is arranged between the deflecting mirrors.

A device for setting or regulating the light flow of the light emitted by the light source onto the entry surface of the light mixing rod or onto the image generator is not provided in the known device.

An endoscope is known from document DE 35 86 855 T2, in which light is coupled into an optical fiber by means of a condenser system, an iris diaphragm which can be variably adjusted being arranged in the focal point of the condenser system. However, the iris diaphragm does not perform the function of a variable intensity attenuator, since the light intensity is regulated via the lamp power by means of a light source driver stage, but has only the purpose of cutting off stray light. If the iris diaphragm were used as a variably adjustable light attenuator to regulate the luminous flux and cut the light flux, the fact that an optical fiber is made up of a fiber bundle would result in specific disadvantages which are similar to the above-mentioned disadvantages of an aperture diaphragm: a changed object contrast and a deterioration in the homogeneity of the illumination. Taking this prior art into account, the invention is based on the object of carrying out a satisfactory solution for the brightness control in the above-mentioned projection apparatus. This object is achieved according to the invention by a projection apparatus with the features of the attached independent device claim or by a method with the features of the attached independent method claim. Preferred refinements and developments of the invention result from the dependent claims and the following description with associated drawings.

A projection apparatus according to the invention for projecting an image on a projection screen thus comprises an image generator for displaying the image on a reduced scale, an illumination unit with condenser optics and / or a lamp with a focusing reflector for illuminating the image generator, a projection device comprising a projection lens for magnifying the image of the image displayed on the projection screen by the image generator, a spatial light mixing device for compensating for local differences in the brightness distribution and a variable intensity attenuator for regulating the luminous flux, which is arranged in the beam path between the lamp of the illumination unit and the image generator, and it points out according to the invention the special feature that the intensity attenuator is arranged in the immediate vicinity of the focal plane of the condenser optics or the focal plane of the focusing lamp reflector of the lighting unit.

A method according to the invention for regulating the brightness of the projected image of a projection apparatus for projecting the image onto a projection screen comprising an image generator for displaying the image in one reduced scale, an illumination unit with condenser optics and / or a focusing lamp reflector for illuminating the image generator, a projection device comprising a projection lens for magnifying imaging of the image represented by the image generator on the projection screen, a spatial light mixing device for compensating for local differences in the brightness distribution and A variable intensity attenuator for regulating the luminous flux, which is arranged in the beam path between the lamp of the lighting unit and the imaging device, has the special feature that the luminous flux is regulated by means of an intensity attenuator which is in the immediate vicinity of the focal plane of the condenser optics of the illuminating unit or the focal plane of a focusing lamp reflector is arranged.

By means of the invention, reliable regulation of the brightness of the projected image that takes individual tolerances and aging processes into account is possible in a relatively simple manner, without this being accompanied by a significant loss of contrast or a change in the color temperature.

Particular practical advantages of the invention result from the fact that the brightness control can be carried out continuously, so that a control loop with continuous control is made possible. It is also advantageous that no additional measuring devices or deployments by trained personnel are required because the adjustment can take place automatically during operation. For this reason, no disruption or interruption of the ongoing operation is required, and also when using lighting devices with a double lamp module to ensure the interruption free operation in the event of lamp failure. By switching to the second lamp, the adjustment is possible immediately.

The invention thus achieves goals which the professional community has long sought. In order to be able to achieve particularly good results, the following measures are preferably used individually or in combination with one another.

According to an additional advantageous feature, it is proposed for projection apparatuses of common size and design that the intensity attenuator is less than 12 mm, preferably less than 6 mm, from the focal plane of the condenser of the lighting unit or the focal plane of a focusing lamp reflector.

It can advantageously be provided that the light entry surface of the spatial light mixing device is arranged in or in the immediate vicinity of the focal plane of the condenser optics of the lighting unit or the focal plane of a focusing lamp reflector.

The intensity attenuator can be designed in various ways. An advantageous embodiment can consist in that the intensity attenuator has one or more light-reducing elements, which are distributed over the cross-section of the beam path and attenuate, absorb or reflect the light. The distribution of the light-reducing elements can be regular or irregular to avoid interference or image artifacts. One possible embodiment of such an intensity attenuator comprises a transparent pane, for example a glass pane, which has a structured coating with the light-reducing elements.

In other embodiments, the intensity attenuation can also be designed as an intensity diaphragm that cuts the beam path, for example in the form of a continuously adjustable aperture diaphragm in the form of an iris diaphragm known from the prior art. Another advantageous embodiment can consist in the fact that the intensity diaphragm has a diaphragm body, for example a disk, in which several diaphragm openings of different sizes are formed next to one another. In this case, the intensity can be adjusted in the discrete steps corresponding to the diaphragm openings.

A preferred embodiment of an intensity diaphragm is that it is designed as a continuously or stepped tapering slot or gap in a diaphragm body, for example a carriage or a disk.

The intensity attenuator advantageously comprises an aperture drive with which the intensity attenuator or the degree of intensity attenuation can be set. The diaphragm drive can be designed, for example, to rotate or shift the intensity attenuator in order to increase or decrease the luminous flux by changing the position of the intensity attenuator.

A practically particularly advantageous embodiment of an intensity attenuator consists in a rotatable disk, in particular a circular disk. If the decrease in intensity is due to a continuously or graduated tapering slit or gap in the Disc is realized, this advantageously extends in the direction of rotation of the disc. The intensity can then be changed by turning the disc.

The arrangement according to the invention of an intensity attenuator in the immediate vicinity of the focal plane of the condenser optics of the lighting unit or the focal plane of a focusing lamp reflector can be used particularly advantageously in projection apparatuses in which the imager can be controlled pixel by pixel and the projection apparatus to implement the time-sequential additive color mixing a color filter that is variable over time - hereinafter referred to as dynamic color filter - for the generation of primary colors. The imager is preferably a digital micromirror device (DMD). A preferred embodiment of a dynamic color filter is a rotating color wheel. According to a particularly advantageous feature, it is provided that the distance between the intensity attenuator and the light entry surface of the dynamic color filter is less than 12 mm, preferably less than 6 mm.

Many commercially available projectors, such as video projectors, use separate channels for each of the three primary colors. Such a system requires an imager and optical paths for each primary color, which must converge on the screen with pixel accuracy. Novel projection apparatuses use only one image generator based on the time-sequential additive color mixture, the entire image being broken down into three single-color partial images with respect to the primary colors red, green and blue. The imager is sequentially illuminated with the primary colors. The image data to be displayed are sent to the image generator in accordance with the color just reaching the image generator. The eye combines the colored partial images into a single full-color image. The eye also combines successive video images and video partial images into a full motion image.

Such a system requires a device for sequentially illuminating the imager with primary colors. The simplest way to set up a dynamic color filter suitable for this is a rotating color wheel, which is used to filter out the desired color from the white spectrum of a lighting unit.

Color wheels of this type for changing the color of the light coupled out from the projection lamp are generally produced from dichroic filters. Due to the manufacturing process, however, the filters have deviations in their spectral filter characteristics, which are reflected in the fact that the edge positions of the filters differ. As a result, there are differences in the perception of the primary colors and the mixed colors.

The image generators currently used in connection with time-sequential image generation are so-called digital micromirror devices, which are described, for example, in US Pat. No. 5,079,544. They comprise an arrangement of small movable mirrors for deflecting a light beam either towards the projection lens (on) or away from the projection lens (off). A gray scale can be achieved by quickly switching the pixels represented by the mirrors on and off. The use of DMDs for digitizing light is also known as DLP (Digital Light Processing). A DLP projection system comprises a light source, optical elements, color filters, digital control and formatting, a DMD and a projection lens. A digital micromirror device (DMD) is preferably used as the imager in time-sequential additive color mixing. However, other imaging devices, for example those mentioned at the beginning, can also be used within the scope of the invention.

The dynamic color filter for the time-sequential generation of primary colors is advantageously a color wheel. Other corresponding ones currently or future available

However, devices can also be used within the scope of the invention.

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the figures. Special features described therein can be used individually or in combination with one another to create preferred embodiments of the invention. Show it:

Fig. 1 is a schematic representation of components of a projection apparatus according to the prior art

Technology with open cover,

2 shows the projection apparatus of FIG. 1 with the diaphragm still closed,

3 the influence of the dimming in FIG. 2 on the filter characteristic of a color wheel,

4 shows two adjacent projection apparatuses of a screen,

5 shows the image brightness of the projection apparatus from FIG. 4 without brightness correction, FIG. 6 shows the brightness of the projection apparatus from FIG

FIG. 4 with brightness correction according to the prior art, 7 test points in the beam path of the illumination optics,

8 angular distributions at test points outside the focal plane of the condenser optics, FIG. 9 angular distributions at test points in the focal plane of the condenser optics,

10 integral angle distributions and the effect of an aperture outside the focal plane of the condenser optics, FIG. 11 integral angle distributions and the effect of an aperture in the focal plane of the condenser optics,

FIG. 12 shows a detail of a projection apparatus according to the invention, FIG. 13 shows a top view of an inventive one

Intensity attenuator in the form of a slotted circular disk from FIGS. 12 and

14 shows a detail of a projection apparatus according to the invention with a control device.

1 shows the optical components of a projection apparatus 1 according to the prior art. It comprises an illumination unit 2 with a lamp 3 as the light source, preferably a discharge lamp, and condenser optics 4. A dynamic color filter 5 in the form of a color wheel 6 and a spatial light mixing device 7 in the form of a beam in the direction of propagation follow in the beam path of the light-extending light mixing rod 8. The light emerging at the light mixing rod 8 is imaged on an imaging device 11 by means of imaging optics 9, which is also referred to as relay optics. The image generated by the image generator 11 is magnified on a projection screen (not shown) by means of a projection lens 12 of a projection device, ie projects the image generated by the image generator 11 in transmission or reflection onto a projection screen not shown. In a preferred application of the invention, the projection apparatus 1 is a rear projection apparatus and the image projected by the projection objective 12 is a partial image of an image wall containing a plurality of projection apparatuses or rear projection apparatuses.

The projected image is constructed using the time-sequential mixture of successive monochrome partial images in the primary colors red, green and blue. The sequence can also contain a fourth partial image in black and white, which is mixed in to increase the image brightness. The sequence of the partial images follows at a sufficiently high speed that the eye cannot follow the color change and a physiological color mixture takes place.

The color wheel 6 is used to generate the primary colors red, green and blue from the white light of the lamp 3 for illuminating the image generator 11. ₍ Imager 11 is preferably a DMD. With appropriate synchronization, imager 11 can generate the monochrome partial images that are assembled by the eye of the viewer of the projected image.

The light from the lamp 3 is focused on the entry of the light mixing rod 8 by means of the condenser optics 4. The rotating color wheel 6 has segments of different colors in the primary colors which, depending on the rotational position of the color wheel 6, contain the spectral components of the lamp 3. speaking to the color filter currently in the beam path. The light mixing rod 8 ensures homogenization of the illumination, and the imaging optics 9 represent the light distribution at the output of the light mixing rod 8 on the imager 11. The color wheel 6 is arranged in the vicinity of the input or the output of the light mixing rod 8.

The basic brightness of the projected image, i.e. the brightness of an image with fully white image content depends on the luminance at the location of the imager 11. Because of the problems mentioned at the outset, it is therefore desirable to control the luminance at the location of the imager 11.

In the prior art, the light flow is controlled by stopping down. Different aperture diaphragms, which are equivalent to one another, come into consideration, namely a diaphragm 13 in the projection objective 12, a diaphragm 14 in the imaging optics 9 or a diaphragm 15 in front of the condenser optics 4. FIG 13 or an equivalent aperture 14 or 15 reduced.

Within the scope of the invention it was recognized that such a dimming according to the prior art is disadvantageous for the following reasons:

The primary colors generated by the color wheel 6 would change. This is due to the fact that the filter characteristics of the filters used, which are mostly dielectric layers, have a clear dependence on the angle of incidence. For this reason, an effective resulting filter curve results for a specific distribution of the incident light as a function of the angle of incidence. If the angular distribution of the light is changed, as is done by stopping down a beam, a changed effective filter curve results, so that the color of the projected image changes. FIG. 3 illustrates how the effective integral transmission T changes as a function of the wavelength λ of the color wheel 6 when the angle distribution of the incident light changes by dimming according to FIGS. 1 and 2. The degree of homogenization of the illumination of the projected image achieved by the light mixing rod 8 depends approximately on the number of reflections in its interior. If the angular distribution is restricted when dimming according to FIG. 2, this results in a lower average number of reflections in the light rod 8. This causes the homogeneity of the image brightness to deteriorate.

The light-dark contrast or the on-off contrast in most imaging devices 11, especially in DMDs, depends on the angular distribution of the incident light. The use of state-of-the-art aperture diaphragms therefore leads to an undesirable change in contrast.

The problems described above are problematic in particular in the case of picture walls in which several projection apparatus are used in parallel and the matrix arrangement of the individual pictures gives an overall picture, because the very sensitive eye of a viewer shows differences in brightness, color and contrast at the transition point from one picture to the next Perceives the image clearly, even if the corresponding variations are not noticeable when looking at just one image. 4 shows two adjacent projection apparatuses la and lb of a screen 16 with projection screens 17a and 17b. They are both controlled by the same data source 18. To simplify the following consideration, this data source is only intended to be the

States "white", i.e. in a 24-bit representation (R, G, B) = (255, 255, 255) and "black", i.e. Generate (R, G, B) = (0, 0, 0) for the entire image area.

The different optical efficiencies of the two projection devices la and lb, which e.g. based on tolerances of the lamps or optical components used, lead to a different image brightness H on the two projection screens 17a and 17b in the uncorrected state. The contrast of the two projection apparatuses la and lb, i.e. H (white) / H (black) is, however, since it is mainly determined by the imager 11 used, an almost constant size for the two projection apparatuses la and lb. The result of this is that the "black" state is also differently bright for the two projection apparatuses la and lb. 5 illustrates the above explanations without correction of the image brightness H.

According to the prior art _ι it is known to align in addition to a basic setting of the brightness H by means of an above-described aperture stop 13, 14 or 15, the image brightness H by a modification of the detailing data from the data source les 18th FIG. 4 illustrates how the image data stream from the data source 18 to the projection apparatuses la and lb is individually adapted by a multiplier stage Xla and Xlb in a simple model. In the example illustrated in FIG. 5, in which the second projection apparatus 1b has a greater brightness than the first projection tion apparatus la, the darker first projection apparatus la would receive an unchanged data stream, ie Xla is set to 100%. In contrast, the second projection apparatus 1b receives a weakened data stream, ie Xlb is set to less than 100%. Through a suitable choice of Xlb it can be achieved in this way that the image brightness H of the first projection apparatus la for white is equal to the image brightness H of the second projection apparatus lb for white, ie H (la, white) = H (lb, white). This is illustrated in Figure 6.

6, however, it can also be seen that the brightness of the "black" state remains unaffected by this type of image data correction, since the data stream for black (0, 0, 0) cannot be further attenuated by a multiplier. The result of this is that projected images or projection apparatuses la and lb which are matched in this way also produce more distinctive images the darker the image content. The only way to achieve an improvement here is to add an additive constant (k, k, k) to the image data stream on projector la. In the example described above, the image brightness H of the first projection apparatus la would therefore have to be "black", i.e. H (la, black) are increased and at the same time the multiplication constant Xla is readjusted. However, this is not only associated with considerable additional effort to achieve a brightness correction, but also reduces the effective contrast of the screen 16 and does not fully utilize the specific contrast properties of an imaging device 11.

The above-described disadvantages of setting and correcting the brightness of projection apparatuses according to the prior art are overcome by the invention Removed the arrangement of an intensity attenuator in the immediate vicinity of the focal plane of the condenser optics of the lighting unit. The mode of operation of the invention is explained in more detail in FIGS. 7 to 11.

FIG. 7 shows an illumination unit 2 with a lamp 3 and condenser optics 4. The envelope 19 in the focal plane 20 of the condenser optics 4 and the light mixing rod 8 are also shown. Six test points TP1, TP2, TP3, TP4, TP5 and TP6 are shown, of which the test points TP1, TP2 and TP3 lie in a plane that is distant from the focal plane 20, and the test points TP4, TP5 and TP6 in the focal plane lie. FIGS. 8 and 9 show the distribution P of the light as a function of the angle θ at the six test points, where θ denotes the amount of the angle between the optical axis 21 and the direction of the individual light beams.

8 shows the angular distributions for the test points TP1, TP2 and TP3 outside the focal plane 20. One recognizes that the. Angle distribution P changes depending on the location of the test point under consideration, ie depending on the distance from the optical axis 21. If a diaphragm is used in the area of the test points TP1, TP2 and TP3, a change in the diaphragm opening leads to a change in the integral, resulting angular distribution, since the areas distant from the optical axis contribute more or less strongly. This change in integral angular distribution is shown in FIG. A comparable effect results for diaphragms 13, 14 or 15 (see FIG. 1). As explained above, the change in the angular distribution leads to a change in the color. Within the scope of the invention it was recognized that these disadvantages can be avoided if the diaphragm is instead arranged in the area of the focal plane 20 of the condenser optics 4. FIG. 9 shows an angular distribution at the test points TP4, TP5 and TP6. It can be seen that the distributions are identical or almost identical, except in terms of absolute scaling. Therefore, as shown in FIG. 11, the integral angular distribution does not change or changes only insignificantly if an aperture is used in the focal plane 20. This knowledge according to the invention creates the precondition for the fact that the contrast, the color and the illumination homogeneity do not change or do not change significantly when the aperture is dimmed.

In the arrangement according to the invention of a variable intensity attenuator for regulating the luminous flux in the immediate vicinity of the focal plane 20, any intensity attenuator of any design can be used without disadvantages, which reduces the amount of light, regardless of whether the amount of useful light is cut, for example, by an arbitrarily shaped aperture or any elements that are arranged homogeneously or inhomogeneously over the cross section of the beam path are reduced, light-cutting or light-attenuating elements.

On the basis of the considerations made in relation to FIG. 7, it can be seen that the advantages according to the invention can be achieved not only by changing the intensity by means of an intensity diaphragm which cuts the beam path and having an aperture, but also by an intensity attenuator which is one or more across the cross-section of the Beam path arranged arranged light-reducing elements that the light weaken, absorb or reflect. With such an intensity attenuator, which can be designed, for example, as a structured coated transparent pane, in particular as a glass pane, not only are attenuated when the intensity is reduced, as is the case with a diaphragm, the beams lying away from the optical axis 21, but also further 19 light rays lying within the envelope.

FIGS. 12 and 13 illustrate a preferred embodiment of an intensity attenuator according to the invention in the form of an intensity diaphragm, which is designed as a diaphragm disk 22 with a continuously tapering slit as a diaphragm opening 23, the slit extending in the direction of rotation of the disk, so that by rotating the diaphragm disk 22 the effective aperture 23 effective in the beam path is changed.

In addition to the diaphragm disk 22 with the diaphragm drive 24, the color wheel 6 with the color wheel drive 25 is shown in FIG. As explained above, the color wheel 6 could also be arranged on the light exit side of the light mixing rod 8.

Since the focal plane 20 should lie in the light entry surface 26 of the light mixing rod 8 in order to achieve the highest possible coupling efficiency of the light generated by the lighting unit 2 into the light mixing rod 8, there is a mechanical conflict: the light entry surface 26 of the light mixing rod 8 , the color wheel 6 and the intensity attenuator, that is, in the exemplary embodiment shown, the diaphragm disk 22 should be positioned at the same location if possible. A compromise solution can therefore be found in practice. The advantages according to the invention are achieved with common sizes of project tion apparatus 1, lighting units 2, lamps 3 and light mixing rods 8 achieved if one or more of the following conditions are met:

The distance A between the intensity attenuator (aperture disk 22) and the focal plane 20 of the condenser optics 4 of the illumination unit 2 is less than 12 mm, preferably less than 6 mm.

The light entry surface 26 of the spatial light mixing device (light mixing rod 8) is arranged in the focal plane 20 or in the immediate vicinity of the focal plane 20 of the condenser optics 4 of the lighting unit 2, i.e. the distance B is less than 10 mm.

The distance C between the intensity attenuator (aperture plate 22) and the light entry surface of the dynamic color filter (color wheel 6) is less than 12 mm, preferably less than 6 mm.

The light entry surface 26 of the spatial light mixing device (light mixing rod 8) should be arranged as precisely as possible in the focal plane 20 of the condenser optics 4 of the lighting unit 2 or the focal plane of the focusing lamp reflector, if possible at a distance of less than 6 mm.

The problem of the spatially sealed arrangement of the light entry surface 26 of the light mixing rod 8, the color wheel 6 and a variable diaphragm is solved by an aperture plate 22 according to FIG. 13 with an aperture opening 23 in the form of an aperture slit with a variable width. The circular aperture disk 22 is positioned as close as possible to the color wheel 6 and on the same axis. The circular shape with a diameter that corresponds to the diameter of the color wheel 6 suppresses acoustic disturbing noises that could arise as a result of the high speed of the color wheel 6 (approx. 10,000 rpm). The effective tive aperture can be adjusted by rotating the circular aperture disc 22 and thus regulate the light flow at the output of the light mixing rod 8.

FIG. 14 shows an exemplary embodiment of a projection apparatus 1 with a control device for adjusting the aperture in the aperture disk 22. It comprises an internal illumination sensor 27 for measuring the brightness of the luminous flux generated by the illumination unit 2 for illuminating the image generator 11 and a control device by means of which the Brightness of the projected image is controlled by controlling the variably adjustable diaphragm disk 22 as a function of the signal from the illumination sensor 27. The sensor 27 has the one emerging from the light mixing rod 8

Amount of light after. The signal from the sensor 27 is thus proportional to the amount of light that would be measurable on the screen if an exclusively white image were projected. The signal from the sensor 27 is thus a measure of the basic brightness of the projection apparatus 1.

This signal is converted in the control device, which includes a data evaluation 28 and a motor control 29, with any predetermined target values into an actuating signal for the diaphragm drive 24, which rotates the diaphragm disk 22 into the desired position by means of the servomotor 30. As a result of the rotary movement, the effective aperture width changes, so that the amount of light is regulated.

In the case of a screen, the setpoint value for the brightness of the projection apparatus can also be determined by comparison with the neighboring modules. For example, the maximum achievable brightness of all modules can be determined with the cover fully open. As a setpoint then the lowest sensor signal of all measured modules is used.

The sensor does not necessarily have to be an internal sensor. It is also possible to adapt the basic image brightness to the ambient brightness, which is measured by an external sensor. The aperture setting could also be selected in accordance with the current image data stream. This would increase the contrast between light and dark image content.

Accordingly, further advantageous configurations can be as follows: - The projection apparatus 1 comprises an ambient sensor for measuring the brightness of the ambient light and a regulating device, by means of which the brightness of the projected image is regulated by controlling the variably adjustable intensity attenuator as a function of the signal from the ambient sensor.

The projection apparatus comprises an image sensor for determining the brightness value of the image content of the projected image or a corresponding analysis device of the data stream and a control device by means of which the brightness of the projected image is regulated by controlling the variably adjustable intensity attenuator as a function of the image content.

The projection apparatus comprises a control device by means of which the brightness as a function of the

Brightness of the neighboring projection apparatus is regulated.

The advantages of the invention include the following: The image brightness can be regulated in a wide range of more than 50%.

The overall contrast does not change. This is an important prerequisite for the adjustment of several projection devices on one screen.

The homogeneity of the illumination does not change. Any electronic corrections can be applied unchanged for all aperture positions. - The color does not change because the primary colors are not distorted when the color is mixed sequentially.

The operating conditions of the lamp do not have to be adjusted. - In picture walls, the. Brightness of neighboring modules can be adjusted to each other.

The brightness of a projection apparatus can be adapted to the ambient brightness, which is particularly advantageous in control rooms for ergonomic reasons.

The contrast dependent on the image content can be increased by regulating the current image content. Dark scenes can be darkened further, bright scenes remain at full brightness. - A particular advantage of the invention is that by means of a control device, the projected image can be regulated while the projection apparatus is in operation, that is to say independently of the image content, without interruption or interference with ongoing operation, without a test image having to be projected and a measurement of the light is only required on the lighting side of the imaging device. LIST OF REFERENCE NUMBERS

1 projection apparatus la first projection apparatus lb second projection apparatus

2 lighting unit 3 lamp

4 condenser optics

5 Dynamic color filter

6 color wheel

7 spatial light mixing device 8 light mixing rod

9 imaging optics 10

11 imagers

12 projection lens 13 aperture in 12

14 aperture in 9

15 aperture in 4

16 projection screen

17a projection screen to la 17b projection screen to lb

18 Data source

19 envelope 20 focal plane

21 optical axis 22 aperture disc

23 aperture

24 aperture drive

25 color wheel drive

26 light entry surface to 8 27 lighting sensor 28 Data evaluation

29 Motor control 30 servomotor

A distance 20/22 B distance 20/26

C distance 22/6

H image brightness

P distribution

T Transmission TPl first test point

TP2 second test point

TP3 third test point

TP4 fourth test point

TP5 fifth test point TP6 sixth test point

Xla multiplier level to la

Xlb multiplier level to lb λ wavelength θ angle

Claims

Expectations

1. Projection apparatus (1) for projecting an image onto a projection screen, comprising an image generator (11) for displaying the image on a reduced scale, an illumination unit (2) with condenser optics (4) and / or a focusing lamp reflector for illuminating the image generator (11), a projection device comprising a projection lens (12) for magnifying imaging of the image represented by the image generator (11) on the projection screen, a spatial light mixing device (7). to compensate for local differences in the brightness distribution and a variable intensity attenuator for regulating the luminous flux which is arranged in the beam path between the lamp (3) of the lighting unit (2) and the imager (11), characterized in that the intensity attenuator is in the immediate vicinity the focal plane (20) of the condenser optics (4) of the lighting unit (2) or the focal plane of a focusing lamp reflector.

Projection apparatus (1) according to one of the preceding claims, characterized in that the intensity attenuator is less than 12 mm, preferably less than 6 mm from the focal plane (20) of the condenser optics (4) of the lighting unit (2) or the focal plane of a focusing lamp reflector.

3. Projection apparatus (1) according to one of the preceding claims, characterized in that the light entry surface (26). spatial light mixing device (7) is arranged in or in the immediate vicinity of the focal plane (20) of the condenser optics (4) of the lighting unit (2) or the focal plane of a focusing lamp reflector.

4. Projection apparatus (1) according to one of the preceding claims, characterized in that the spatial light mixing device (7) is a device which extends in the direction of propagation of the light, in particular a light mixing rod (8).

5. Projection apparatus (1) according to one of the preceding claims, characterized in that the intensity attenuator is designed as an intensity diaphragm which cuts the beam path.

6. Projection apparatus (1) according to claim 5, characterized in that the intensity diaphragm is designed as a continuously adjustable aperture, pupil or iris diaphragm.

7. Projection apparatus (1) according to claim 5, characterized in that the intensity diaphragm has a diaphragm body in which several diaphragm openings of different sizes are formed side by side.

8. Projection apparatus (1) according to claim 5, characterized in that the diaphragm opening (23) of the intensity diaphragm is designed as a continuously or stepped tapering slot or gap in a diaphragm body.

9. Projection apparatus (1) according to one of the preceding claims, characterized in that the intensity attenuator has one or more light-reducing elements which are arranged over the cross section of the beam path and which attenuate, absorb or reflect the light.

10. Projection apparatus (1) according to the preceding claim, characterized in that the intensity attenuator is designed as a structured coated transparent pane, in particular as a glass pane.

11. Projection apparatus (1) according to one of the preceding claims, characterized in that it has an aperture drive (24) for adjusting the intensity attenuator.

12. Projection apparatus (1) after the previous one

Claim, characterized in that the diaphragm drive (24) is designed to rotate or shift the intensity attenuator.

13. Projection apparatus (1) according to one of the preceding claims, characterized in that the intensity attenuator is designed as a rotatable disc (22), in particular as a circular disc.

14. Projection apparatus (1) according to claims 8 and 13, characterized in that the diaphragm opening (23) extends in the direction of rotation of the disc (22).

15. Projection apparatus (1) according to one of the preceding claims, characterized in that it comprises an illumination sensor (27) for measuring the brightness of the luminous flux generated by the illumination unit (2) for illuminating the image generator (11) and a control device by means of which the Brightness of the projected image is controlled by controlling the variably adjustable intensity attenuator as a function of the signal from the lighting sensor (27).

16. Projection apparatus (1) according to one of the preceding claims, characterized in that it comprises an ambient sensor for measuring the brightness of the ambient light and a control device by means of which the brightness of the projected image by controlling the variably adjustable intensity attenuator as a function of the signal of the environmental sensor is regulated.

17. Projection apparatus (1) according to one of the preceding claims, characterized in that it comprises an image sensor for determining the brightness value of the image content of the projected image or a corresponding analysis device of the data stream and a control device by means of which the brightness of the projected image is controlled of the variably adjustable intensity attenuator is regulated as a function of the image content.

18. Projection apparatus (1) according to one of the preceding claims, characterized in that it comprises a regulating device by means of which the brightness is regulated as a function of the brightness of an adjacent projection apparatus.

19. Projection apparatus (1) according to one of claims 15 to 18, characterized in that the projected image can be regulated by means of the control device while the projection apparatus is in operation.

20. Projection apparatus (1) according to one of the preceding claims, characterized in that the image generator

(11) can be controlled pixel by pixel and the projection apparatus comprises a dynamic color filter (5) for time-sequential mixing of primary colors.

21. Projection apparatus (1) according to the preceding claim, characterized in that the image generator (11) is a digital micromirror device (DMD).

22. Projection apparatus (1) according to claim 20, characterized in that the dynamic color filter (5) is a rotating color wheel (6).

23. Projection apparatus (1) according to claim 20, characterized in that the distance (C) between the. Intensity attenuator and the light entry surface of the dynamic color filter (5) is less than 12 mm, preferably less than 6 mm.

24. Projection apparatus (1) according to one of the preceding claims, characterized in that the lighting unit (2) comprises a ^ discharge lamp.

25. Projection apparatus (1) according to one of the preceding claims, characterized in that it is a rear projection apparatus.

26. Screen (16) containing several projection apparatus

(I) according to one of the preceding claims.

27. A method for regulating the brightness of the projected image of a projection apparatus (1) for projecting the image onto a projection screen, comprising an image generator (11) for displaying the image on a reduced scale, an illumination unit (2) with condenser optics (4) and / or a focusing lamp reflector for illuminating the image generator (11), a projection device (12) comprising a projection objective (12) for enlarged imaging of the image represented by the image generator (11) on the projection screen, a spatial light mixing device (7) for compensating for local differences in the brightness distribution and a variable intensity attenuator for regulating the luminous flux in the beam path between the lamp (3) of the lighting unit (2) and the imager

(II) is arranged, characterized in that the luminous flux is regulated by means of an intensity attenuator which is arranged in the immediate vicinity of the focal plane (20) of the condenser optics (4) of the lighting unit (2) or the focal plane of a focusing lamp reflector.

8. The method according to claim 27, characterized in that it comprises a feature of a projection apparatus (1) according to one of claims 2 to 25.