Exemplary aspects of the present invention relate to image display control methods, image display control apparatus, and image display control programs adapted to display a large-screen image and/or high-resolution image by arranging plural image projection units and projecting partial images from the projection units.
The size of a display provided by a related art single display unit and the resolution of the display have limitations. Related art methods and apparatus for arranging and using plural image display control units to achieve a large screen exceeding the limitation or a display of high resolution exceeding the limitation are available. At this time, a method of how to make unnoticeable the boundaries between the displays provided by the individual display units to provide one natural display as a whole is a problem to be addressed and/or solved.
Related art methods of making unnoticeable the boundaries are roughly classified into two major categories: combining method and overlapping method. The feature of the composite method is that any point on the whole displayed image is displayed by any one display unit. The feature of the overlapping method is that regions capable of being displayed by the individual display units are made to overlap with each other and that a display on such overlapping regions is superimposingly provided by the plural display units.
One example of the composite method is a method using a mechanical combination. This method includes mechanically bonding together flat-panel display units (e.g., liquid crystal display units) themselves at their edges. This has the advantage that once the units have been bonded, the state is maintained stably. However, it is difficult to create a display device having bondable edges.
Another composite method uses image projection units. Images projected by image projection units are apparently combined on the surface of the display. This makes it unnecessary to bond together display units themselves and hence the apparatus has a relatively large number of degrees of freedom. However, the composite state produces error due to mechanical or electrical aging of the apparatus because mechanical bonding is not used. Furthermore, the errors greatly affect the display quality. It is difficult to maintain good state of display.
One example of the overlapping method is a method of using plural image projection units. A part of an image projected from one image projection unit is superimposed on a part of an image projected from the other image projection unit.
In particular, one output is gradually reduced in an overlapping region while the other output is gradually increased at the same time. Thus, boundary regions are connected smoothly. This overlapped state produces error due to mechanical or electrical aging of the apparatus in the same way as the composite method. However, in the overlapping method, error affects the quality of display to a lesser extent than in the composite method. However, it is difficult to control the display in the overlapping region.
These are described in further detail below with reference to the drawings.
FIG. 21 is a schematic of a related art composite method using plural (four, in this example) image projection units (such as projectors) PJ1, PJ2, PJ3, and PJ4. As shown in this FIG. 21, the image projection units PJ1, PJ2, PJ3, and PJ4 are arranged such that their respective display regions A1, A2, A3, and A4 can be displayed without overlap or gap. However, the display provided by each of the image projection units PJ1, PJ2, PJ3, and PJ4 easily deforms into an irregular quadrilateral having no right angles due to slight installation error or aging. Therefore, it is difficult to precisely arrange their display regions A1, A2, A3, and A4 in this way and to maintain the arrangement.
FIG. 22 is a schematic of a case in which the four image projection units PJ1, PJ2, PJ3, and PJ4 display the individually displayable display regions A1, A2, A3, and A4 such that there are overlapping regions Z in parts of the regions A1-A4. In this related art method, a display can be provided either by the composite method or by the composite method.
FIGS. 23A-23D show a method of providing a display by the composite method of FIG. 22. To simplify the explanation, only the three image projection units PJ1, PJ2, and PJ3 are taken into account. Also, only processing on one line is herein considered. It is assumed that the three image projection units PJ1, PJ2, and PJ3 already know what regions of the displayable display regions of the image projection units overlap with each other.
Specific related art methods for knowing the overlapping regions include methods described, for example, in JP-A-H8-294073 and JP-A-2002-238064, respectively. The method described in JP-A-H8-294073 permits the user to have a clear view of both ends of each overlapping region. The method lets the user indicate the overlapping regions, whereby the method knows them. The method described in JP-A-2002-238064 knows overlapping regions using an entry made by a camera.
FIGS. 23A-23C indicate the values of weights about displays provided by the three image projection units PJ1, PJ2, and PJ3 on some line. As shown in the figure, each weight has two values, “1” and “0”. They can be quite easily implemented in software or by a circuit. Here, the weight “1” means the output value itself is responsive to some input. Also, the weight “0” means a black output. P1, P3, P4, and P6 in the figure indicate the end points of the overlapping regions. P2 and P5 indicate image division positions to carry out a composition in this example. One specific example of implementation of the method of FIG. 23 is described in JP-A-2002-277958. The sum of these weights is a constant value of“1” over the whole display region as shown in FIG. 23D.
FIGS. 24A-24D show the image projection unit PJ2 located in the center of FIGS. 23A-23D has shifted ΔX in the direction of the arrow X. At this time, summation of the weights of the displays shown in FIGS. 24A-24C, respectively, produces portions of weight 0 (i.e., black portions that provide no display) and portions of weight 2 (i.e., very bright portions because of superimposition of displays) as shown in FIG. 24D. These can be quite easily discerned visually. The quality of display deteriorates greatly.
FIGS. 23A-23D and 24A-24D assume only processing on same line. Where a two-dimensional way of thinking is introduced, more difficult circumstances will exist.
FIGS. 25A-25C illustrate this. As shown in FIG. 25A, a case in which display regions A1 and A2 of two image projection units PJ1 and PJ2 overlap with each other at an angle is disclosed. It is assumed that the display region A1 of the image projection unit (referred to as the image projection unit PJ1) displaying the left side of FIGS. 25A-25C is a region in gray color of FIG. 25A and that the display region A2 of the image projection unit (referred to as the image projection unit PJ2) displaying the right side of FIGS. 25A-25C is a region in gray color of FIG. 25B.
As shown in FIG. 25C, the display regions A1 and A2 of the both image projection units PJ1 and PJ2 overlap with each other, producing a portion (portion al in gray color) of excessive brightness. Also, a portion (black portion a2) that is displayed by none of the image projection units PJ1 and PJ2 exists. This is a phenomenon that cannot be avoided in the case where the minimum unit of display of the image projection units has a finite size and the displays of image projection units overlap at an angle.
FIGS. 26A-26D show a method of achieving a display provided by the overlapping method. FIGS. 26A-26C show the values of weights on some line of the displays provided by the three image projection units PJ1, PJ2, and PJ3.
As shown in FIGS. 26A-26D, one weight gradually decreases in the overlapping region, while the other increases gradually. Summation of the weights produces a constant value over the whole display region as shown in FIG. 26D.
FIGS. 27A-27D show a circumstance in which the image projection unit PJ2 located in the center of FIG. 26 has produced a positional deviation in the same way as in FIGS. 24A-24D. At this time, summation of the weights of the displays shown in FIGS. 24A-24C produces unevenness as shown in FIG. 27D. This indicates that deterioration of the display quality due to a positional deviation is smaller, as can be seen by comparison with FIGS. 24A-24D showing an example of the composite method. That is, concave portions of the weights are displayed slightly darkly. Conversely, convex portions are displayed slightly brightly. This indicates the superiority of the overlapping method over the composite method in which black and bright lines are noticed clearly as to positional deviation of image projection units.
However, it is not so straightforward to connect images in the overlapping regions smoothly, because a nonlinear relation exists between the input to each image projection unit and the display output (output brightness) due to gamma correction to adjust the nonlinear characteristics of the human perception.
FIG. 28 is a schematic of the aforementioned nonlinear relation between the input and output. In particular, the human perception has logarithmic characteristics. Where a proportional relation is created between the input and the output brightness, it follows that variations in the output brightness are felt to be greater at small inputs while variations in the output brightness are felt to be smaller at large inputs. As a result, as shown in FIG. 29, it is not felt that twice of the value of the output brightness when the input value is 127, for example, is a value close to the output brightness when the input value is 255. Therefore, in a normal display device, the correspondence between the input and output brightness is often set to a function inverse to a function as shown in FIG. 28 such that the value of the brightness perceived by a human approaches the input value. Specifically, the function of FIG. 28 is upwardly convex. As a function inverse to this function of FIG. 28, a downwardly convex relation is often set.
The effects of the nonlinearity are particularly shown in FIGS. 30A and 30B. As shown in FIG. 30A, it is assumed that an input value to be displayed (i.e., output value) is constant. In this case, if the sum of input values to the respective image projection units in the overlapping region is made constant, the sum of the output values decreases in the overlapping region as shown in FIG. 30B, for the following reason. As described previously, a downwardly convex nonlinear relation exists between the input value and output value as an inverse function to the function of FIG. 28.
FIGS. 31A and 31B illustrate a method of correcting this and making constant the output value over the overlapping region. To make constant the output value as shown in FIG. 31B, it is necessary to gradually nonlinearly increase or reduce the input to each image projection unit in the overlapping region as shown in FIG. 31A. The nonlinearity depends on the function shown in FIG. 28. The function varies depending on the value of the gamma adjustment or the nonlinearity of other component. Furthermore, the nonlinearity changes depending on user's change of settings or varies due to aging characteristics. Accordingly, in order to control the sum of the output values to a desired value, it is necessary to perform nonlinear processing including many parameters.