DE10256505A1 - Brightness control of a projection apparatus - Google Patents

Abstract

For the color, contrast and light homogeneity-neutral regulation of the brightness of a projection apparatus (1), in particular a rear projection apparatus of an image wall, the image generation preferably based on the time-sequential mixing of primary colors with a color wheel (6), an intensity attenuator is proposed, for example in the form of an adjustable diaphragm disk (22) with a slit-shaped diaphragm of variable width, 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.

Description

The invention relates to brightness control Projectors. Projection devices are used for projecting of an image on a projection screen. The invention aims on projection apparatus that use an image generator of the picture on a reduced scale, a lighting unit with condenser optics or a focusing lamp reflector (e.g. in elliptical or more complex form) to illuminate the Imager, a projection device comprising a projection lens for enlarged imaging 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 for Regulate the luminous flux in the beam path between the lamp the lighting unit and the imager are arranged. As a rule, the imager and / or the projection device to adjust the position of the projected image on the projection screen in a position adjustable with adjustment elements in or on attached to the projector.

One differentiates between incident light and rear projection apparatus. A difference between reflected light projectors and rear projection systems is that in Rear projection devices mostly other optical elements such as deflecting mirrors and projection screens are included that are not used in reflected light projectors.

Both reflected light and rear projection devices are used to display an image on a large-scale projection screen. The The imager can be a transmitted light imager, that is an imager, the transmissive of an illuminating device for illuminating of the imaging device is illuminated, or a reflecting imaging device, which is illuminated by the lighting device. According to the state In the art, for example, transmitted light liquid crystal imaging devices or also reflective liquid crystal imagers or DMDs (Trademark of Texas Instruments Inc., Digital Micromirror-Device) used.

A lighting unit for illuminating the Imager or transillumination of the transmitted light imager includes in the Usually a light source, a reflector and one or more condenser lenses to illuminate the imaging device. Furthermore, additional light mixing devices, for example to optimally illuminate a rectangular image format, be provided. Also can be used on the condenser optics a focusing, e.g. elliptical lamp reflector omitted become. The projection device or the lighting unit is either integrated in the projector or on it stated. A projection device is thus a closed, complete unit for displaying an image, a screen for in a rear projection apparatus Viewing the picture is integrated.

Rear projection modules in particular find one wide application in cases in which a complex picture, for example consisting of different Video or computer images to be displayed on a large scale. Common uses for such Rear projection apparatus are screens, that are viewed by several people at the same time. In particular Large screen rear projection is widespread in modern control room technology.

If the image displayed with given quality requirements exceed a certain size and complexity this is no longer possible with a single rear projection module. In such make the image is made up of partial images, each from a rear projection module displayed, composed. Each from a rear projection module In this case, the displayed image is a partial image of that of all rear projection modules together displayed overall picture of the screen.

According to the state of the art it is possible one size Number of rear projection modules string together in a modular structure of a projection screen and / or on top of each other to be stacked in order to create a composite from many individual drawing files big screen display. The number of rear projection modules, which are put together to form a projection screen is up to 150 or more.

Further details on rear projection modules are in the 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 comprises a spatial light mixing device for compensating for local differences in the 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 rods (see, for example US 5,625,738 ) and full mixing sticks (see e.g. DE 10103099 A1 ).

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 illumination with an f number 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 rod has about twice the length, ie a ratio of 10 to 20. Since the Ver ratio increases the average number of reflections inside the light mixing rod, this results in higher reflection losses and thus a lower light output. For this reason and because of the practically available space for the installation of 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-performance 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, different, 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 complex and involves high costs.
- 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.
- The consideration of the average change in the luminous flux based on empirical values during the operating period. 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 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 change in luminous flux 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's lifespan in the commonly used high-power 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 is used in the form of an aperture diaphragm for regulating the luminous flux, which is arranged in the beam path of the lighting 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.

The invention is based on this Prior art based the task of a satisfactory solution for the Brightness control with the above-mentioned projection apparatus. This The object is achieved by a projector with the features of the attached independent device claim or by a method with the features of the attached independent method claim solved. Preferred configurations and developments of the invention result themselves from the dependent claims and the following description with accompanying drawings.

A projection apparatus according to the invention for projecting an image onto a projection screen thus comprises an image generator for displaying the image on a reduced scale, an illumination unit with condenser optics 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 one Imager displayed image 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 imager, and according to the invention it has the special feature that the intensity attenuator 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 is arranged.

An inventive method for controlling the Brightness of the projected image of a projector for Projecting the image onto a projection screen comprising a Imager for displaying the image on a reduced scale, one Illumination unit with a condenser optics or a focusing Lamp reflector for illuminating the imaging device, a projection lens comprehensive projection device for magnifying the image of the Imager displayed image on the projection screen, a spatial Light mixing device to compensate for local differences in the Brightness distribution and a variable intensity attenuator for Regulate the luminous flux in the beam path between the lamp the lighting unit and the imager is arranged the peculiarity that the Luminous flux is regulated by means of an intensity attenuator, which in in close proximity to the focal plane of the condenser optics of the lighting unit or the Focal plane of a focusing lamp reflector is arranged.

By means of the invention is a reliable, individual Regulation of the tolerances and aging processes Brightness of the projected image is possible in a relatively simple manner without a noticeable loss of contrast or a change in color temperature accompanied.

Special practical advantages of the Invention result from the fact that the brightness control is continuous carried out can be so that a control loop is made possible with continuous control. It is also advantageous that no additional Measuring devices or Calls trained personnel are required because the comparison is automatic can take place during operation. For this reason, there is none disorder or interruption of ongoing operations required, and also when using lighting devices with a double lamp module to guarantee uninterrupted operation in the event of a lamp failure By switching to the second lamp, the adjustment is possible immediately.

With the invention thus become goals achieved, which the professional community has long sought. In order to achieve particularly good results, the subsequent measures used individually or in combination.

According to an additional advantageous feature is for Projection devices more common Size and type suggested that the Intensity attenuator less than 12 mm, preferably less than 6 mm from the focal plane of the condenser the lighting unit or the focal plane of a focusing Lamp reflector is removed.

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

The intensity attenuator can be different Be trained. An advantageous embodiment can consist in that the Intensity attenuator one or more, about the cross section of the beam path arranged light-reducing Has elements that weaken, absorb or reflect the light. The distribution of the light-reducing elements can be regular or be irregular to avoid interference or image artifacts. A possible embodiment of such an intensity attenuator includes one transparent pane, for example a pane of glass, the one structured coating with light-reducing elements having.

In other embodiments, the intensity attenuator can also be designed as an intensity diaphragm that cuts the beam path, for example in the form of a known from the prior art continuously adjustable aperture diaphragm in the form of an iris diaphragm. Another advantageous embodiment can be that the intensity aperture an aperture body, for example, has a disc in which several different size apertures are formed side by side. In this case, the intensity is in the aperture corresponding discrete levels adjustable.

A preferred embodiment an intensity diaphragm is that they as a continuously or gradually tapering slot or gap in an aperture body, for example, a slide or a disc is formed.

The intensity attenuator advantageously comprises one Aperture drive with which the intensity attenuator or the degree of intensity attenuation is set can be. The aperture drive can be used, for example, to turn or Shifting the intensity attenuator be formed to by a change of location of the intensity attenuator Increase or increase the luminous flux to reduce.

A practically particularly advantageous embodiment of an intensity attenuator consists in a rotatable disk, in particular a circular disk. If the attenuation of intensity is reali ized by a continuously or gradually tapering slit or gap in the disc Siert, 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 in close proximity to the focal plane of the condenser optics of the lighting unit or the The focal plane of a focusing lamp reflector is particularly advantageous can be used in projection apparatus in which the image generator is pixel by pixel is controllable and the projection apparatus for realizing the time sequential additive color mixing a time-variable color filter - hereinafter dynamic Called color filter - for Generation primary Contains colors. The imager is preferably a digital micromirror device (DMD). A preferred embodiment a dynamic color filter is a rotating color wheel. To A particularly advantageous feature is that the distance between the intensity attenuator and the light entry surface of the dynamic color filter less than 12 mm, preferably less than 6 mm.

Many commercially available Projection apparatus, for example video projection devices, use separate channels for every of the three primary colors. Such a system requires for any primary color an imager and optical lines that pixel-perfect on the screen have to converge. new Projection devices use only an imaging device based on the time sequential len additive color mixing, the whole picture in three single-color drawing images with respect to the basic colors red, green and blue is disassembled. The imager is sequential with the primary colors illuminated. The image data to be displayed are correspondingly of the color just reaching the imager to the imager. The eye adds the colored drawing files together into a single full-color picture. The eye adds also successive video images and partial video images a full motion picture together.

Such a system requires one Device for sequentially illuminating the imager with primary colors. The easiest way to set up a suitable dynamic color filter is a rotating color wheel that serves to select the color you want out of the white Filter spectrum of a lighting unit.

Such color wheels to change the color of the Projection lamp decoupled light are generally out dichroic filters. The filters, however, are due to the manufacturing process Deviations in their spectral filter characteristics, which can express that the Differentiate the edge positions of the filters. As a result, there are differences in the perception of the primary colors as well as 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 the patent US 5,079,544 are described. They include 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 includes a light source, optical elements, color filters, digital control and formatting, a DMD and a projection lens.

As an imager at the time sequential additive color mixing is preferred a digital micromirror device (DMD) used. But there are also others, for example at the beginning Imager used in the context of the invention.

The dynamic color filter for time sequential Generation of primary colors is advantageously a color wheel. Other corresponding ones currently or future available Facilities can however, can also be used within the scope of the invention.

The invention is described below of an embodiment shown in the figures. In this special features described can used individually or in combination with each other to preferred To create embodiments of the invention. Show it:

1 1 shows a schematic illustration of components of a projection apparatus according to the prior art with the diaphragm open,

2 the projector of 1 with another closed aperture,

3 the influence of the dimming in 2 on the filter characteristics of a color wheel,

4 two adjacent projection apparatuses on a screen,

5 the image brightness of the projection apparatus from 4 without brightness correction,

6 the brightness of the projectors from 4 with state-of-the-art brightness correction,

7 Test points in the beam path of the lighting optics,

8th Angular distributions at test points outside the focal plane of the condenser optics,

9 Angular distributions at test points in the focal plane of the condenser optics,

10 integral angular distributions and the effect of an aperture outside the focal plane of the condenser optics,

11 integral angular distributions and the effect of an aperture in the focal plane of the condenser optics,

12 a detail of a fiction moderate projection apparatus,

13 a plan of an intensity attenuator according to the invention in the form of a slotted circular disc of 12 and

14 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 state of the art. It includes a lighting unit 2 with a lamp 3 as a light source, preferably a discharge lamp, and condenser optics 4 , A dynamic color filter follows in the beam path 5 in the form of a color wheel 6 and a spatial light mixing device 7 in the form of a light mixing rod B extending in the direction of propagation of the light on the light mixing rod 8th emerging light is by means of imaging optics 9 , which is also referred to as relay optics, to an imaging device 11 displayed.

That from the imager 11 generated image is by means of a projection lens 12 a projection device enlarged on a projection screen, not shown, so projects from the imager 11 Image generated in transmission or reflection on a projection screen, not shown. In a preferred application of the invention, the projection apparatus 1 a rear projection apparatus, and that from the projection lens 12 projected image is a partial image of an image wall containing a plurality of projection apparatus or rear projection apparatus.

The projected image is created using the process of time sequential mixture of successive monochrome drawing files in the primary colors red, green and blue built up. The sequence can also contain a fourth partial image in black and white, that for increase is mixed into the image brightness. The sequence of the drawing files follows at a sufficiently high speed so that the eye cannot follow the color change and a physiological color mixture takes place.

The color wheel 6 serves from the white light of the lamp 3 the primary colors red, green and blue for illuminating the imaging device 11 to create. The imager 11 is preferably a DMD. With appropriate synchronization, the imager can 11 which produce monochrome partial images that are assembled by the eye of the viewer of the projected image.

The light of the lamp 3 by means of the condenser optics 4 on the entry of the light mixing stick 8th focused. The rotating color wheel 6 has different colored segments in the primary colors, depending on the position of the color wheel 6 the spectral components of the lamp 3 transmit according to the color filter currently in the beam path. The light mixing stick 8th ensures homogenization of the illumination, and the imaging optics 9 forms the light distribution at the exit of the light mixing rod 8th on the imager 11 from. The color wheel 6 is near the input or output of the light mixing rod 8th arranged.

The basic brightness of the projected image, ie the brightness of an image with completely white image content, depends on the luminance at the location of the imager 11 from. Because of the problems mentioned above, it is therefore desirable to have the luminance at the location of the imaging device 11 to regulate.

In the prior art, the light flow is controlled by stopping down. Different aperture diaphragms that are equivalent to one another come into consideration here, namely one diaphragm 13 in the projection lens 12 , an aperture 14 in the imaging optics 9 or an aperture 15 in front of the condenser optics 4 , In 2 is shown how the light flux when closing the diaphragm 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 one through the color wheel 6 generated primary colors 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. In 3 illustrates how the effective integral transmission T is a function of the wavelength λ of the color wheel 6 when changing the angular distribution of the incident light by dimming according to the 1 and 2 changed.
- The one from the light mixing stick 8th achieved degree of homogenization of the illumination of the projected image depends approximately on the number of reflections in its interior. If when stopping down 2 the angular distribution is restricted, this results in a lower average number of reflections in the light mixing rod B. This reduces the homogeneity of the image brightness.
- The light-dark contrast or the on-off contrast depends on most imaging devices 11 , especially with DMDs, on the angular distribution of the incident light. The use of aperture diaphragms according to the prior art therefore leads to an undesirable change in contrast.

The problems described above are problematic, in particular in the case of projection walls, in which a plurality of projection apparatuses are used in parallel and the matrix arrangement of the individual images gives an overall image, because the very sensitive eye of a viewer has brightness, color and con perceives differences in contrast at the transition point from one image to the adjacent image clearly, even if corresponding variations in the observation of only one image are not noticeable.

In 4 are two adjacent projection devices 1a and 1b a screen 16 with projection screens 17a and 17b shown. They are both from the same data source 18 driven. To simplify the following consideration, this data source is only intended to state "white", ie in a 24-bit representation (R, G, B) _ (255, 255, 255) and "black", ie (R, G, B ) = (0, 0, 0) for the entire image area.

The different optical efficiencies of the two projection devices 1a and 1b For example, which are based on tolerances of the lamps or optical components used, lead to a different image brightness H on the two projection screens in the uncorrected state 17a and 17b , The contrast of the two projection devices 1a and 1b , ie H (white) / H (black), however, since it is mainly from the imager used 11 is determined, an almost constant size for the two projection apparatus 1a and 1b , This has the consequence that the state "black" for both projection devices 1a and 1b is differently bright. The 5 illustrates the above explanations without correction of the image brightness H.

It is known from the prior art, apart from a basic setting of the image brightness H by means of an aperture diaphragm described above 13 . 14 or 15 the image brightness H also by modifying the data signal from the data source 18 equalize. In 4 is illustrated as in a simple model of the image data stream from the data source 18 advise to the projection apparatus 1a and 1b is individually adjusted by a multiplier stage X1a and X1b. In the in 5 illustrated example in which the second projector 1b greater brightness than the first projector 1a would have the darker first projector 1a receive an unchanged data stream, ie X1a is set to 100%. The second projector 1b on the other hand receives a weakened data stream, ie X1b is set to less than 100%. Through a suitable choice of X1b it can be achieved in this way that the image brightness H of the first projection apparatus 1a for white, the image brightness H of the second projection apparatus is the same 1b for white, ie H ( 1a , white) = H ( 1b , White). This is in 6 illustrated.

In 6 But 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 weakened by a multiplier. The result of this is that projected images or projection apparatuses which have been balanced in this way are also 1a and 1b the darker the image content, the more distinctive the images. The only way to improve this is to send the image data stream to the projector 1a add an additive constant (k, k, k). In the example described above, the image brightness H of the first projection apparatus would have to be 1a for the state "black", ie H (1a, black) are increased and at the same time the multiplication constant X1a is readjusted. However, this is not only associated with a considerable additional effort to achieve a brightness correction, but also reduces the effective contrast of the screen 16 and uses the specific contrast properties of an imaging device 11 not fully out.

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

In 7 is a lighting unit 2 with lamp 3 and condenser optics 4 shown. Furthermore, the envelope 19 in the focal plane 20 the condenser optics 4 and the light mixing stick 8th 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 from the focal plane 20 is removed, and the test points TP4, TP5 and TP6 lie in the focal plane. In the 8th and 9 the distribution P of the light is shown as a function of the angle θ at the six test points, where θ is the amount of the angle between the optical axis 21 and the direction of the individual light rays.

In 8th are the angular distributions for the test points TP1, TP2 and TP3 outside the focal plane 20 shown. It can be seen that the angular distribution P depends on the location of the test point under consideration, ie depending on the distance from the optical axis 21 changes. 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 removed from the optical axis contribute more or less strongly. This change in the integral angular distribution is in 10 shown. For panels 13 . 14 or 15 (please refer 1 ) there is a comparable effect. As explained above, the change in the angular distribution leads to a change in the color.

In the context of the invention, it was recognized that these disadvantages can be avoided if instead the diaphragm in the focal plane 20 the condenser optics 4 is arranged. In 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. Of half changes as in 11 is shown, the integral angular distribution is not, or only insignificantly, when in the focal plane 20 an aperture is used. 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.

Based on the 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 that cuts the beam path with an aperture, but also by an intensity attenuator that has one or more light-reducing elements that are distributed over the cross section of the beam path. that weaken, absorb or reflect the light. Such an intensity attenuator, which can be designed, for example, as a structured coated transparent pane, in particular as a glass pane, not only reduces the intensity, as is the case with a diaphragm, which is distant from the optical axis 21 lying rays weakened, but also further within the envelope 19 lying rays of light.

The 12 and 13 illustrate a preferred embodiment of an intensity attenuator according to the invention in the form of an intensity diaphragm, which acts as an aperture disk 22 with a continuously tapering slot as the aperture 23 is formed, wherein the slot extends in the direction of rotation of the disc, so that by rotating the aperture disc 22 the effective aperture opening effective in the beam path 23 is changed.

In 12 is next to the aperture disc 22 with the aperture drive 24 also the color wheel 6 with the color wheel drive 25 shown. As explained above, the color wheel 6 also on the light exit side of the light mixing rod 8th be arranged.

Since to achieve the highest possible coupling efficiency of the lighting unit 2 generated light in the light mixing rod 8th the focal plane 20 in the light entry area 26 of the light mixing stick 8th there should be a mechanical conflict: the light entry surface 26 of the light mixing stick 8th , the color wheel 6 and the intensity attenuator, ie the diaphragm disk in the illustrated embodiment 22 should be positioned in the same place if possible. A compromise solution can therefore be found in practice. The advantages according to the invention are in common sizes of projection apparatus 1 , Lighting units 2 , Lamps 3 and light mixing sticks 8th achieved if one or more of the following conditions are met:
- The distance A between the intensity attenuator (aperture disk 22 ) and the focal level 20 the condenser optics 4 the lighting unit 2 is less than 12 mm, preferably less than 6 mm.
- The light entry area 26 the spatial light mixing device (light mixing rod 8th ) is in the focal plane 20 or in the immediate vicinity of the focal plane 20 the condenser optics 4 the lighting unit 2 arranged, ie the distance B is less than 10 mm.
- The distance C between the intensity attenuator (aperture disc 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 area 26 the spatial light mixing device (light mixing rod 8th ) should be as close as possible to the focal plane 20 the condenser optics 4 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 dense arrangement of light entry surface 26 of the light mixing stick 8th , the color wheel 6 and a variable aperture is through an aperture disc 22 according to 13 with an aperture 23 solved in the form of an aperture slit with variable width. The circular aperture disc 22 becomes as close as possible to the color wheel 6 and positioned on the same axis. Due to the circular shape with a diameter that corresponds to the diameter of the color wheel 6 corresponds to acoustic noise due to the high speed of the color wheel 6 (approx. 10,000 rpm) could be suppressed. The effective aperture can be adjusted by rotating the circular aperture disc 22 adjust and thus the light flow at the output of the light mixing rod 8th regulate.

The 14 shows an embodiment of a projection apparatus 1 with a control device for adjusting the aperture in the aperture disc 22 , It includes a projector-internal lighting sensor 27 for measuring the brightness of the from the lighting unit 2 for illuminating the imaging device 11 generate luminous flux and a control device, by means of which the brightness of the projected image by controlling the variably adjustable aperture plate 22 depending on the signal from the lighting sensor 27 is regulated. The sensor 27 shows the from the light mixing stick 8th emerging light quantity after. The signal from the sensor 27 is therefore 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 therefore a measure of the basic brightness of the projection apparatus 1 ,

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

The setpoint for the brightness of the project Onsapparatates can also be determined in the case of a screen by comparison with the neighboring modules. For example, the maximum achievable brightness of all modules can be determined when the cover is fully open. The lowest sensor signal of all measured modules is then used as the setpoint.

The sensor does not necessarily have to be an internal sensor his. It is also possible the basic image brightness to the ambient brightness by an external sensor is measured to adapt. The aperture setting could also be used can be selected according to the current image data stream. In this way would an increase in the contrast between light and dark image content let it be realized.

Accordingly, further advantageous designs can be as follows:
- The projector 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, as well as a control device by means of which the brightness of the projected image is regulated by controlling the variably adjustable intensity attenuator depending on the image content.
- The projection apparatus comprises a control device by means of which the brightness is controlled as a function of the brightness of the adjacent projection apparatus. 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.
- The brightness of neighboring modules can be adjusted to each other in picture walls.
- 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.

1

projector

1a

first projector

1b

second projector

2

lighting unit

3

lamp

4

condenser

5

dynamic color filter

6

Color wheel

7

spatial Light mixing device

8th

Light mixing rod

9

imaging optics

10

11

imager

12

projection lens

13

Aperture in 12

14

Aperture in 9

15

Aperture in 4

16

screen

17a

Projection screen too 1a

17b

Projection screen too 1b

18

Data Source

19

envelope

20

focal plane

21

optical axis

22

aperture disc

23

aperture

24

diaphragm drive

25

Farbradantrieb

26

Light entry area too 8th

27

illumination sensor

28

data analysis

29

motor Controller

30

servomotor

A

distance 20/22

B

distance 20/26

C

distance 6.22

H

brightness

P

distribution

T

transmission

TP1

first test point

TP2

second test point

TP3

third test point

TP4

fourth test point

TP5

fifth test point

TP6

sixth test point

x1a

Multiplier level too 1a

X 1b

Multiplier level too 1b

λ

wavelength

θ

angle

Claims (28)

Projector ( 1 ) for projecting an image onto a projection screen, comprising an image generator ( 11 ) to display the image on a reduced scale, a lighting unit ( 2 ) with condenser optics ( 4 ) or a focusing lamp reflector to illuminate the imaging device ( 11 ), a projection lens ( 12 ) comprehensive projection device for enlarged imaging of the image from the image generator ( 11 ) displayed image on the projection screen, a spatial light mixing device ( 7 ) to compensate for local differences in the brightness distribution and a variable intensity attenuator to regulate the luminous flux in the beam path between the lamp ( 3 ) of the lighting unit ( 2 ) and the imager ( 11 ) is arranged, characterized in that the intensity attenuator is 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 is arranged. Projector ( 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 is removed. Projector ( 1 ) according to one of the preceding claims, characterized in that the light entry surface ( 26 ) the spatial light mixing device ( 7 ) 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 is arranged. Projector ( 1 ) according to one of the preceding claims, characterized in that the spatial light mixing device ( 7 ) a device extending in the direction of propagation of the light, in particular a light mixing rod ( 8th ) is. Projector ( 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. Projector ( 1 ) according to claim 5, characterized in that the intensity diaphragm is designed as a continuously adjustable aperture, pupil or iris diaphragm. Projector ( 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. Projector ( 1 ) according to claim 5, characterized in that the aperture ( 23 ) the intensity diaphragm as a continuous or stepped tapering slot or gap is formed in a diaphragm body. Projector ( 1 ) according to one of the preceding claims, characterized in that the intensity attenuator has one or more light-reducing elements which are distributed over the cross section of the beam path and which weaken, absorb or reflect the light. Projector ( 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. Projector ( 1 ) according to one of the preceding claims, characterized in that it has a diaphragm drive ( 24 ) for setting the intensity attenuator. Projector ( 1 ) according to the preceding claim, characterized in that the diaphragm drive ( 24 ) is designed to rotate or shift the intensity attenuator. Projector ( 1 ) according to one of the preceding claims, characterized in that the intensity attenuator as a rotatable disc ( 22 ), in particular as a circular disc. Projector ( 1 ) according to claims 8 and 13, characterized in that the diaphragm opening ( 23 ) in the direction of rotation of the disc ( 22 ) is designed to extend. Projector ( 1 ) according to one of the preceding claims, characterized in that it comprises an illumination sensor ( 27 ) for measuring the brightness of the lighting unit ( 2 ) for illuminating the imaging device ( 11 ) generated luminous flux 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 from the illumination sensor ( 27 ) is regulated. Projector ( 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 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. Projector ( 1 ) according to one of the preceding claims, characterized in that it has an image sensor for determining the brightness value of the image content de s. 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 by controlling the variably adjustable intensity attenuator as a function of the image content. Projector ( 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. Projector ( 1 ) according to one of Claims 15 to 18, characterized in that the projected image can be regulated by means of the regulating device while the projection apparatus is in operation. Projector ( 1 ) according to one of the preceding claims, characterized in that the image generator ( 11 ) can be controlled pixel by pixel and the projection device is a dynamic color filter ( 5 ) for the time-sequential mixing of primary colors. Projector ( 1 ) according to the preceding claim, characterized in that the image generator ( 11 ) is a digital micromirror device (DMD). Projector ( 1 ) according to claim 20, characterized in that the dynamic color filter ( 5 ) a rotating color wheel ( 6 ) is. Projector ( 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. Projector ( 1 ) according to one of the preceding claims, characterized in that the lighting unit ( 2 ) comprises a discharge lamp. Projector ( 1 ) according to one of the preceding claims, characterized in that it is a rear projection apparatus. Screen ( 16 ), containing several projection devices ( 1 ) according to one of the preceding claims. 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 ) to display the picture in egg a reduced scale, a lighting unit ( 2 ) with condenser optics ( 4 ) or a focusing lamp reflector to illuminate the imaging device ( 11 ), a projection lens ( 12 ) comprehensive projection device for enlarged imaging of the image from the image generator ( 11 ) displayed image on the projection screen, a spatial light mixing device ( 7 ) to compensate for local differences in the brightness distribution and a variable intensity attenuator to regulate the luminous flux in the beam path between the lamp ( 3 ) of the lighting unit ( 2 ) and the imager ( 11 ) is arranged, characterized in that the luminous flux is regulated by means of an intensity attenuator which is 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 is arranged. A method according to claim 27, characterized in that it is a feature of a projection apparatus ( 1 ) according to any one of claims 2 to 25.