新背投屏幕如何改進廣泛的垂直視角-日本理工dissertation  Invited Paper: Rear Projection Screen with Improved Wider Vertical

Viewing Angle

Tsuyoshi Kashiwagi, Kei Kato, Daijiro Kodama, Futoshi Oosawa, and Michihisa Ide

Display Components Operations, Dai Nippon Printing Co., Ltd.

73-1, Obara, Nutanishi-cho, Mihara-shi, Hiroshima-ken 729-0473, Japan

摘要 Abstract

We developed a new rear projection screen compriseding of two total internal reflecting prism sheets laminated to each other in a 90 degree angle. 這種屏幕的優點是不僅具有更廣泛的垂直視野角，而且改進黑電平，顏色溫度的均勻性，減少閃爍性，并減少重影圖像。The advantages of this screen are not only wider vertical viewing angle, but improved black level, the uniformity of color temperature, reduced scintillation, and reduced ghost images.  http://ukthesis.org/dissertation_writing/Engineering/

介紹 1. Introduction

More and more large-screen displays are appearing in the market these days. Displays include liquid crystal displays, plasma displays, rear projection displays, and so on. These displays have advantages and disadvantages within each other. Regarding prices, rear projection displays are lower than other displays. 目前的投影顯示器有一個寬的水平的視角，但他們比其他顯示器具有更窄的垂直視角，圖像不能被從頂部或底部觀察。On the other hand, current projection displays have a wide horizontal viewing angle but they have a narrower vertical viewing angle than other displays, and the images cannot be seen when viewed from either the top or bottom.

我們開發了一個新的投影屏包括兩個內部反射棱鏡片90度彼此層疊度，提高了垂直視角。We developed a new projection screen comprised of two total internal reflecting prism sheets laminated to each other in 90 degrees, which improved the vertical viewing angle. Below is the report of this new projection screen.

新背投的結構 2. Structure of New Rear Projection

Screen

A rear projection screen comprises of a first sheet layer with a Fresnel lens on the projection side and a second layer formed with a horizontal lenticular lens with a substrate diffuser on the observation side. 到目前為止，增加擴散器已被用來拓寬更廣泛的垂直可視角度，但即使如此，它未能能達到足夠的視角。So far, increased diffusers have been used to broaden the wider vertical viewing angle, but even then it was not possible to achieve an adequate viewing angle. On the other hand, if the two lenticular lens sheets are not laminated in a 90 degree angle, there is a loss of the surface-reflection of light. If the two sheets are laminated, the laminated lenticular lens has no effect on the light and there would be a refractive index surface.#p#分頁標題#e#

A structure of new rear projection screen is shown in Figure1. By laminating two total internal reflecting prism sheets made up of numerous strung pedestal prisms in a 90 degree angle, light is diffused not only on a horizontal direction but in a vertical direction as well, so the newly developed screen manages to achieve an expansion of the wider vertical viewing angle that was not possible with existing technologies.

Figure 1: Structure of New Rear Projection Screen

3. Results

3.1 Optical Performances

3.1.1 Gain Distributions

We measured the luminance in foot-Lamberts with the screen (ft-l) and then replaced the screen with a foot- candle probe in the position of the mechanical center of the screen (ft-cd). The gain is computed by following formula:

Gain = ft-l/ft-cd × π

Vertical gain distributions of three type screens (TYPE1,

TYPE2, and Current-type) are shown in Figure 2, and horizontal

gain distributions of that one are shown in Figure 3.

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- 60 - 40 - 20 0 20 40 60

Angle(Degrees)

Gain

TYPE1

TYPE2

Current

Figure 2: Vertical Gain Curve

Holizontal Gain

 

- 60 - 40 - 20 0 20 40 60

Angle(Degrees)

Gain

TYPE1

TYPE2

Current

Figure 3: Horizontal Gain Curve

TYPE1 TYPE2 Current

PG 1.7 2.6 4.2

αv（°

） 30 14 9

βv（°

） 40 22 13

αh（°

） 39 39 37

βh（°

） 46 46 45

Table 1: Peak Gain, and Viewing Angle

Vertical and horizontal luminance distribution is measured, and α v , and α h is the 1/2 angle between the screen’s gain that falls to 1/2 of the peak gain, and β v, and β h is the 1/3 angle between the screen’s gain that falls to 1/3 of the peak gain. Peak gain, α v, β v, α h and β h of three type screens are shown in Table 1.

TYPE2 has 1.5 times wider vertical viewing angle than the

current-type, and TYPE1 has 3 times wider vertical viewing angle than the current-type, while the horizontal viewing angle is almost equal to the current type. Since the screens don’t enhance the light, PG is down. However if the power of the light source is up, there is no problem and the screen with wider viewing angle in all directions is achieved.

3.1.2 Improved Black Level

We measured the black luminance of three type screens by using a luminance meter in a bright room of 250lx and 500lx. The results are shown in Table 2, 3, and 4.#p#分頁標題#e#

TYPE1 TYPE2 Current

250lx Luminance 2.1 2.9 5.1

500lx (cd/m2) 3.1 4.1 7.9

Table 2: Black Level (Front side)

TYPE1 TYPE2 Current

250lx Luminance 0.9 1.3 2.1

500lx (cd/m2) 1.5 1.9 3.5

Table 3: Black Level (45 degrees of horizontal side)

TYPE1 TYPE2 Current

250lx Luminance 1.5 2.2 3.2

500lx (cd/m2) 2.5 3.5 6.0

Table 4: Black Level (15 degrees of upper side)

The black level of both TYPE1 and TYPE2 screens was under half than the current screen type in all directions. Since the current type does not have vertical black stripes, it cannot reduce the reflecting light of illumination from the Fresnel lens. However, TYPE1 and TYPE2 screens with vertical black stripes can reduce the reflecting light of illumination from Fresnel lens.

3.1.3 Uniformity of Color Temperature

We then measured the uniformity of color temperature by using a photometer and colorimeter. The size of these screens was 50 inches, and these screens were put on a TV. The measuring distance equipment was two meters (the length of three times as long as horizontal length) away from the center of screen, and we measured the uniformity of color temperature. The results are

shown Table 5.

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50.4 / T. Kashiwagi

TYPE1 TYPE2 Current

Difference of Color Temp 4000K 6000K 10000K

Table 5: Difference of Color Temperature

(Front side)

TYPE1 TYPE2 Current

Difference of Color Temp 10000K 10000K >10000K

Table 6: Difference of Color Temperature

(45 degrees of horizontal side)

TYPE1 TYPE2 Current

Difference of Color Temp 2000K 4000K >10000K

Table 7: Difference of Color Temperature

(15 degrees of upper side)

The differences of color temperature from maximum to minimum for both TYPE1 and TYPE2 screens were better than of the current type.

3.1.4 Reduced Scintillation

We measured the scintillation of the screens through the CCD luminance meter. If we can observe the screen to have strong scintillation, the luminance difference of CCD is high. These screens were set on a TV, the measuring tool equipment was 1 meter away from the center of screen, and the size of measuring area was 40mm×60mm. We calculated the average of each pixel’’ s luminance (Ave） and the standard deviation of each pixel’ ’ s luminance ( σ ) , and （ σ /Ave ） × 100 for standardization. The results are shown in Figure4 and Table 8.

TYPE1

TYPE2

Current

Figure 4: Enlarged Pictures of Screens#p#分頁標題#e#

TYPE1 TYPE2 Current

Ave(cd/m2) 135.3 237.4 425.3

σ(cd/m2) 6.1 10.6 23.9

σ/Ave×100 4.5 4.5 5.6

Table 8: Evaluation of Scintillation

The scintillation of both TYPE1 and TYPE2 screens were lower than the current type.

3.1.5 Reduced Ghost Images

We took a photograph of the ghost images of screens through the CCD camera. The results are shown in Figure5.

 

Current TYPE1

Figure 5: Ghost Images

We can see thatthe reduced the ghost images are reduced of in the new type screen.

3.2 Other Features

3.2.1 Glass-Substrate Screen

We also developed TYPE1 and TYPE2 screens with a glass base with AR film.由于屏幕與更廣泛的垂直視角增加，表面的平坦性和鋒利度看起來像類似高畫質等離子顯示器電視。 As the screen with a wider vertical viewing angle increased, the flatness of the surface and the sharpness looked like similar to plasma display televisions with high image quality.

3.2.2 One-piece Screen

The depth of projection display television is thinner than before1). Thus, Wwe developed most suitablea screens with flatscreen type projection display screen for such trends. The structure of a one-piece screen is a unified Fresnel lens and two total-reflecting prism sheets laminated in a 90 degree angle based on a glass-substrate. It has been possible to eliminate imagedistortion and achieve high-definition images because of the uniformity of all components.

結論 4. Conclusion

As demonstrated by the above-mentioned, it is clear that 我們的新屏幕提供了最好的圖像質量和改進的缺陷傳統的背投屏幕。背投市場顯示預計在未來得到很大的擴展。our new

screen provides the best image quality and improves the defects of conventional rear projection screens. The market for rearprojection

displays is expected to expand greatly in the future.

6. References

[3][1]S. Shikama et al., SID Symposium Digest 33, 1250 (2002)

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