Screen of projection display

Abstract: A longitudinal-stripe lenticular lens screen (14) and a transverse-stripe lenticular lens screen (23) are superposed, and a light diffusing agent (21) is mixed only in the longitudinal-stripe lenticular lens screen. Consequently, the light transmittance is high although the angle of view can be three-dimensionally widened by the two lenticular lens screens. In addition, since scan lines of an image are blurred by two diffusion planes, Moiré effects become inconspicuous.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a screen for use in a projection display which displays an image by projecting it onto a screen. Description of the Prior Art As shown in Fig. 1, a projection display enlarges an image displayed on, e.g., a cathode-ray tube 11 and projects the enlarged image onto a screen 13 by using a projection lens 12. Such projection displays are divided into two categories, a front type (reflection type) and a rear type (transmission type), according to the type of the screen 13. The screen 13 of the rear type projection display is, as shown in Fig. 2, generally constituted by a longitudinal-stripe lenticular lens screen 14, in which lenticular lenses extend in the longitudinal direction, and a Fresnel lens screen 15. Note that a mirror 16 is arranged betweeen the projection lens 12 and the screen 13 to bend an optical path, thereby decreasing the dimensions of the projection display. The Fresnel lens screen 15 causes light 17 of a projected image to be incident perpendicularly to the lenticular lens screen 14. The lenticular lens screen 14 refracts the incident light 17 and thereby diffuses the light 17 emerged from it. In a conventional screen of a projection display, as shown in Figs. 3A and 3B, a light diffusing agent 21 is mixed in the lenticular lens screen 14 in order to increase the diffusion angle of the light 17. Note that, in order to prevent a decrease in contrast caused by reflection of external light, a black surface 22 which consists of black stripes is formed on the exit surface of the lenticular lens screen 14 except for the positions of the lenticular lenses. In a conventional screen of a projection display of the above sort, however, although a practically satisfactory angle of view can be obtained in the horizontal direction with the aid of the lenticular lens screen 14, the angle of view in the vertical direction is narrow since only the effect of the light diffusing agent 21 is useful in this direction. When the angle of view in the vertical direction is narrow, a screen which is bright when a viewer watches it while sitting in a chair or on a floor is dark if, for example, he or she watches it while lying on a floor, and so no high-quality images can be displayed in that case. To widen the angle of view in the vertical direction, therefore, the amount of the light diffusing agent 21 to be mixed in the lenticular lens screen 14 may be increased, or, as shown in Fig. 4, a transverse-stripe lenticular lens screen 23 may be superposed on the longitudinal-stripe lenticular lens screen 14. The use of the two lenticular lens screens 14 and 23, however, increases the manufacturing cost. For this reason, as shown in Figs. 5A to 5C, it has been attempted to use a single microlens screen 24 in which a plurality of microlenses are arranged into a matrix-like pattern in place of the two lenticular lens screens 14 and 23. If, however, the amount of the light diffusing agent 21 to be mixed in the lenticular lens screen 14 is increased, reflection of incident light is increased to decrease the light transmittance, and this decreases the brightness and contrast of an image. In addition, if the transverse-stripe lenticular lens screen 23 is additionally formed and the light diffusing agent 21 is mixed in both of the two lenticular lens screens 14 and 23, the light transmittance decreases to decrease the brightness and contrast of an image. If, in contrast, the light diffusing agent 21 is mixed in neither the lenticular lens screen 14 nor 23, Moiré effects become conspicuous between the lenticular lenses of the transverse-stripe lenticular lens screen 23 and scan lines of an image. Therefore, none of the above conventional examples can display high-quality images. Figs. 6 to 8 illustrate a three-tube rear projection display and a conventional example of a screen used in this display. In this display, cathode-ray tubes 31, 32 and 33 for displaying red, green and blue images are arranged horizontally, and projection lenses 41 to 43 project light components 34 to 36 which are modulated by their respective colors. The screen is constituted by a Fresnel lens screen 44 and a lenticular lens screen 45. Note that no mirror is shown in these drawings. The Fresnel lens screen 44 causes the light components 34 to 36, which are projected by the projection lenses 41 to 43, to be incident perpendicularly to lenses 45a on the incident side of the lenticular lens screen 45. The lenticular lens screen 45 synthesizes the incident light components 34 to 36 to form a color image and also widens the light components 34 to 36 of a displayed image, which emerge from lenses 45b on the exit side, in the horizontal direction rather than in the vertical direction. Since the cathode-ray tubes 31, 32 and 33 for displaying red, green and blue images are arranged at different positions, angles at which the light components 34 to 36 modulated by their respective colors are incident on the lenticular lens screen 45 also differ from one another. Consequently, as shown in Fig. 7, images of the light components 34 to 36 are formed at different positions on the surface of each lens 45b on the exit side. Between the individual lenses 45b, on the other hand, a black nonreflecting portion, i.e., a black surface, which is called black stripes 46, is formed into longitudinal stripes in order to absorb external light and to thereby increase the contrast of a displayed image with respect to the external light. In this conventional example, the black stripes 46 project in the exit direction of the light components 34 to 36 farther than the lenses 45b. In this conventional example as described above, if the screen is viewed obliquely, as shown in Fig. 8, all of the light components 34 to 36 of the respective colors shown in Fig. 7 can be seen in a region in which an angle defined between the normal to the lenticular lens screen 45 and the viewing direction of an eye is small (angle =  2 ). In this conventional example, however, the black stripes 46 project in the exit direction farther than the lenses 45b as described above. Therefore, in a region in which the angle defined between the normal to the lenticular lens screen 45 and the viewing direction of an eye is large (angle =  1 ) it is impossible to see the light components 34 to 36 emerged from the skirt of the lens 45b since they are eclipsed by the black stripe 46. This gives rise to a phenomenon called color shift or color shading in which, even if an image of the same color is displayed on the entire surface of the screen, the color of the image changes depending on the angle at which a viewer watches the screen. Therefore, the conventional example shown in Figs. 6 to 8 cannot display high-quality images. EP 0 433 403 further discloses a screen which consists of two sections each comprising a sheet having a flat rear surface and a front surface with an array of cylindrical lenses. Only one array of cylindrical lenses is inclined to the horizontal whereas the other is horizontal. Besides, the provision of two sections having flat rear surfaces facing each other reduces the quality. The light transmittance is reduced and the brightness and contrast of the image are affected. SUMMARY OF THE INVENTION The invention overcomes the drawbacks of the prior art by providing a screen and an image source producing images to be displayed on the screen that are built up from scan lines, the screen comprising first and second lenticular lens screens superposed such that the extending directions of respective lenticular lenses are different, characterized in that the extending direction of said lenticular lenses of said first lenticular lens screen is inclined with respect to the direction of scan lines of an image to be displayed, and the extending direction of said lenticular lenses of said second lenticular lens screen is either perpendicular to or inclined with respect to the direction of the scan lines. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic side view showing a projection display to which the present invention is applicable; Fig. 2 is a perspective view showing the first conventional example of the present invention; Figs. 3A and 3B show the problem of the first conventional example, in which Fig. 3A is a vertical side view and Fig. 3B is a horizontal side view; Fig. 4 is a perspective view showing the second conventional example; Figs. 5A to 5C show the third conventional example, in which Fig. 5A is a front view, Fig. 5B is a rear view, and Fig. 5C is a side view; Fig. 6 is a schematic side view showing a projection display using the fourth conventional example; Fig. 7 is an enlarged side view showing the main part of the fourth conventional example; Fig. 8 is a side view for explaining the problem of the fourth conventional example; Figs. 9A and 9B show an embodiment, not according to the present invention, in which Fig. 9A is a vertical side view and Fig. 9B is a horizontal side view; Fig. 10A is a vertical side view showing another embodiment, not according to the present invention, and Fig. 10B is a vertical side view for explaining the problem to be solved by this embodiment; Fig. 11 is a perspective view showing the embodiment of the present invention; Figs. 12A and 12B are rear views of a lenticular lens screen for explaining this embodiment; Fig. 13 is a front view showing the another embodiment, not according to the present invention. Fig. 14 is a side view showing the another embodiment, not according to the present invention; and Fig. 15 is a side view showing the another embodiment, not according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present invention will be described below with reference to Figs. 11,12A and 12B. Note that the same reference numerals as in the conventional examples shown in Figs. 1 to 7 denote the same parts in this embodiment. An embodiment, not according to the present invention will be described first. In this first embodiment, as shown in Fig. 4, a transverse-stripe lenticular lens screen 23 is superposed on a longitudinal-stripe lenticular lens screen 14. This embodiment has essentially the same arrangement as that of the conventional example illustrated in Fig. 4 except that a light diffusing agent 21 is not mixed in at least one of the two lenticular lens screens 14 and 23. In the embodiment with this arrangement, although the angle of view can be widened three-dimensionally by the two lenticular lens screens 14 and 23, reflection of incident light is little and therefore the light transmittance is high compared to a structure in which the light diffusing agent 21 is mixed in both the lenticular lens screens 14 and 23. Consequently, the brightness and contrast of an image are high, and this makes it possible to display high-quality images. Figs. 9A and 9B show another embodiment, not according to the present invention. In this embodiment, like in the above embodiment, a transverse-stripe lenticular lens screen 23 is superposed on a longitudinal-stripe lenticular lens screen 14. This embodiment has essentially the same arrangement as that of the conventional example illustrated in Fig. 4 except that a light diffusing agent 21 is mixed in only the lenticular lens screen 14, i.e., is not mixed in the lenticular lens screen 23. In this embodiment, like in the above embodiment, although it is possible to widen the angle of view by the use of the two lenticular lens screens 14 and 23, the light transmittance is high since the light diffusing agent 21 is mixed only in the lenticular lens screen 14. In addition, as is apparent from Fig. 9A showing the vertical side surfaces of the lenticular lens screens 14 and 23, two diffusion planes 25 and 26 are formed in the vertical direction by lenticular lenses on the exit side of the lenticular lens screen 23 and by the light diffusing agent 21 mixed in the lenticular lens screen 14, and a spacing d is present between these diffusion planes 25 and 26. This spacing d allows the lenticular lens screens 14 and 23 to serve as an optical low-pass filter in the vertical direction. Consequently, scan lines of an image are blurred, and this makes Moiré effects inconspicuous between the lenticular lenses of the transverse-stripe lenticular lens screen 23 and the scan lines of an image. This optical low-pass filter, however, has no influence on resolution in the horizontal direction. Therefore, this embodiment can realize a three-dimensional angle of view and a high-quality image at the same time. Fig. 10A shows another embodiment, not according to the present invention. This embodiment has essentially the same arrangement as that of the above embodiment shown in Figs. 9A and 9B except that, in contrast to that embodiment, a longitudinal-stripe lenticular lens screen 14 in which a light diffusing agent 21 is mixed is located on the incident side of light 17, and a transverse-stripe lenticular lens screen 23 in which no light diffusing agent 21 is mixed is located on the exit side of the light 17. If the light diffusing agent 21 is also mixed in the lenticular lens screen 23 positioned on the exit side of the light 17, not only the light 17 of an image but external light 27 are diffused by the light diffusing agent 21, as shown in Fig. 10B, and this lowers the contrast of an image. In this embodiment, however, the light diffusing agent 21 is mixed only in the lenticular lens screen 14 arranged on the incident side of the light 17. Therefore, as can be seen from Fig. 10A, the external light 27 diffused by this light diffusing agent 21 is absorbed by a black surface 22 of the lenticular lens screen 23. Consequently, this embodiment can further increase the contrast of an image and achieve a fairly high image quality. Figs. 11, 12A and 12B illustrate the embodiment of the present invention. This embodiment has, as shown in Fig. 11, essentially the same arrangement as that of the conventional example shown in Fig. 4 except that a longitudinal-stripe lenticular lens screen 14 and a transverse-stripe lenticular lens screen 23 are rotated 45º with respect to the direction of scan lines of an image while the stripe directions of the two lenticular lens screens 14 and 23 are perpendicular to each other. In this embodiment with the above arrangement, if the pitch between stripes of the lenticular lens screens 14 and 23 is P 1 , as shown in Fig. 12A, a pitch P2 between the stripes in the vertical direction of an image is narrow, P 1 /2 ½ , as shown in Fig. 12B. For this reason, the frequency of Moiré between the lenticular lenses and the scan lines of an image in this embodiment is higher than that in the conventional example shown in Fig. 4, and this makes Moiré effects inconspicuous. In this embodiment, both the longitudinal-stripe lenticular lens screen 14 and the transverse-stripe lenticular lens screen 23 are rotated 45º with respect to the direction of scan lines of an image. However, it is also possible to rotate the transverse-stripe lenticular lens screen 23 alone. Another embodiment, not according to the present invention will be described below. This embodiment has essentially the same arrangement as that of the conventional example illustrated in Figs. 5A to 5C except that a microlens screen having a plurality of microlenses arranged into a matrix pattern is rotated with respect to the direction of scan lines of an image, like in Fig. 12B. This embodiment can also achieve an effect similar to that of the above fourth embodiment according to the invention. Fig. 13 shows another embodiment, not according to the present invention. This embodiment has essentially the same arrangement as that of the conventional example illustrated in Figs. 5A to 5C except that, as shown in Fig. 13, a plurality of microlenses are arranged in a direction perpendicular to the direction of scan lines of an image, and the microlenses in adjacent arrays in the direction of scan lines are offset by a half of the pitch between these microlenses. In this embodiment, assuming that the pitch between microlenses in one array is P1, an essential pitch P2 in the vertical direction of an image is P 1 /2 which is further narrower than those of the previous embodiment and the embodiment according to the invention. This further raises the frequency of Moiré between the microlens arrays and the scan lines. For this reason, Moiré effects in this embodiment are more inconspicuous than those in the previous embodiment and the embodiment according to the invention. Fig. 14 shows a lenticular lens screen 45 according to another embodiment. not according to the present invention which is applied to a screen of a three-tube rear projection display. Fig. 14 corresponds to Fig. 8 illustrating one of the above conventional examples. This embodiment has essentially the same arrangement as that of the conventional example shown in Figs. 6 to 8 except that the whole body of each lens 45b on the exit side of the lenticular lens screen 45 projects in the exit direction of light farther than black stripes 46. In this lenticular lens screen 45 of this embodiment, the pitch between lenses 45a on the light incident side is 0.78 mm, and the width of each lens 45b on the light exit side is 0.35 to 6.45 mm. In this embodiment with the above arrangement, as is apparent from Fig. 14, even if the screen is viewed obliquely, light components emerged from the lenses 45b can be seen without being eclipsed by the black stripes 46 not only in a region in which the angle defined between the normal to the lenticular lens screen 45 and the viewing direction of an eye is small (angle =  2 ) but also in a region in which this angle is large (angle =  1 ). For this reason, this embodiment causes little color shift and color shading, making display of high-quality images possible. Fig. 15 shows a lenticular lens screen 45 according to another embodiment not according to the present invention, and corresponds to Fig. 14 illustrating the above embodiment. This last embodiment has essentially the same arrangement as that of the above embodiment except that the skirts of lenses 45b on the exit side of the lenticular lens screen 45 are positioned closer to the light incident side than black stripes 46, but the apexes of the lenses 45b project in the light exit direction farther than the black stripes 46. In this last embodiment with the above arrangement, as can be seen from Fig. 15, even if the screen is viewed obliquely, the amount of light components eclipsed by the black stripes is smaller than that in the conventional example shown in Figs. 6 to 8. Therefore, this embodiment causes less color shift and color shading than in that conventional example, and this makes it possible to display high-quality images.

Claims: A projection system comprising a screen and an image source producing images to be displayed on the screen that are built up from scan lines, the screen comprising first and second lenticular lens screens (14, 23) superposed such that the extending directions of respective lenticular lenses are different, the extending direction of said lenticular lenses of said first lenticular lens screen (14) being inclined with respect to the direction of scan lines of an image to be displayed, characterized in that the extending direction of said lenticular lenses of said second lenticular lens screen (23) is either perpendicular to or inclined with respect to the direction of the scan lines.

Inventors: HANABUSA TAKAOMI, TAKEUCHI HIROMITSU, TAKUMA HIROKAZU, HANABUSA, TAKAOMI, TAKEUCHI, HIROMITSU, TAKUMA, HIROKAZU, HANABUSA, TAKAOMI, C/O SONY CORPORATION, TAKEUCHI, HIROMITSU, C/O SONY CORPORATION, TAKUMA, HIROKAZU, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: H04N9
IPC codes: H04N9, G03B21, H04N5