GB1595610A - Colour video projection apparatus - Google Patents
Colour video projection apparatus Download PDFInfo
- Publication number
- GB1595610A GB1595610A GB1743978A GB1743978A GB1595610A GB 1595610 A GB1595610 A GB 1595610A GB 1743978 A GB1743978 A GB 1743978A GB 1743978 A GB1743978 A GB 1743978A GB 1595610 A GB1595610 A GB 1595610A
- Authority
- GB
- United Kingdom
- Prior art keywords
- viewing screen
- images
- cathode ray
- image
- blue
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/12—Picture reproducers
- H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Video Image Reproduction Devices For Color Tv Systems (AREA)
- Projection Apparatus (AREA)
- Transforming Electric Information Into Light Information (AREA)
Description
(54) COLOUR VIDEO PROJECTION APPARATUS
(71) We, SONY CORPORATION, a corporation organised and existing under the laws of Japan, of 7-35 Kitashinagawa6, Shinagawa-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to colour video projection apparatus.
A known colour video projection apparatus is arranged as shown in Figures 1 and 2 of the accompanying drawings, A cathode ray tube 1 for providing a red video image and a cathode ray tube 2 for providing a green video image face a screen 4, while a cathode ray tube 3 for providing a blue video image is arranged with the axis of the cathode ray tube 3 vertical. Light from the red image of the cathode ray tube I is transmitted through a semi-reflecting mirror 5 and is refracted by a lens 6 to form an image on the screen 4. Light from the green image of the cathode ray tube 2 is refracted by a lens 7 to form an image on the screen 3, and light from the blue image of the cathode ray tube 3 is reflected by the semi-reflecting mirror 5 and is refracted by the lens 6 so as also to form an image on the screen 4. The three images are superimposed in register and hence form a colour image.
In this apparatus, the optical axis 8 of the lens 6 and the optical axis 9 of the lens 7 intersect with the normal 10 to the screen 4 at the centre of the screen 4 at an angle w as shown in Figure 1. Moreover, the optical axis 8 of the lens 6 and the optical axis 9 of the lens 7 are symmetrical with each other relative to the normal 10. This means that the red image on the screen 4 is deformed into the shape of a trapezium as shown in
Figure 3A. On the other hand, the green image on the screen 4 is deformed as shown in Figure 3B. The blue image on the screen is deformed as shown in Figure 3A, because the blue image is projected through the lens 6. When these projected images are superimposed to form the colour image, the respective individual colour images do not coincide with each other exactly, particularly at the sides of the screen 4. In particular the red and green images do not coincide with each other and the blue and green images do not coincide with each other, although the red and blue images do coincide with each other.
To overcome this problem, the cathode ray tubes 1, 2 and 3 can be provided with correcting means which cause deformations opposite to those occurring in projection, so as to caflcel these latter deformations.
However, this adds substantially to the expense and moreover it is difficult to produce the required deformations accurately.
According to the present invention there is provided a colour video projection apparatus comprising:
a viewing screen whereon a plurality of
projected images can be superimposed
in register;
a plurality of cathode ray tubes screens
for providing said images;
a plurality of focussing means to project
images from said cathode ray tube
screens into said viewing screen in
register to form a superimposed image;
the optical axes of said plurality of
focussing means being substantially
parallel to each other, and the central
axis of at least one of said cathode ray
tube screens being so deflected from
the corresponding one of said optical
axes of said focussing means to make
the projected images coincide with
each other on said viewing screen: and
intercepting means disposed partly to
intercept the light emitted by at least
one of said cathode ray tube screens so
as to compensate for unevenness of
distribution of brightness in said
projected images.
The invention will now be described by way of example with reference to the accompanying drawings, in which:
Figures 1 to 3 have been referred to above in relation to the known projection apparatus:
Figure 4 is a plan view of the basic arrangement of a colour video projection apparatus according to the invention;
Figure 5 is a perspective view of part of the arrangement of Figure 4;
Figures 6A and 6B illustrate projected red and green images on a viewing screen;
Figure 7 is a view of superimposed images;
Figure 8 is a graph showing the distribution of the brightnesses of red and green projected images across the width of a viewing screen;
Figure 9 is a plan view of an embodiment of colour video projection apparatus according to the invention; and
Figure 10 is a graph showing the distribution of the brightnesses of red and green projected images across the width of a viewing screen with the apparatus of Figure 9;
The arrangement shown in Figures 4 and 5 comprises a cathode ray tube 11 which forms a red video image and a cathode ray tube 12 which forms a green video image, the cathode ray tubes 11 and 12 being arranged so that the screens thereof face a viewing screen 14 on which the projected images are superimposed in register. A cathode ray tube 13 which forms a blue video image is arranged so that the axis of the cathode ray tube 13 is vertical. Light
from the red image on the cathode ray tube
11 is transmitted through a semi-reflecting
mirror 15 and is refracted by a lens 16, to
produce a red image on the viewing screen
14. Light from the cathode ray tube 12 is
refracted by a lens 17 and projected on the viewing screen 14. Finally, light from the cathode ray tube 13 is reflected by the semireflecting mirror 15 and refracted by the lens 16 to form a blue image on the viewing screen 14. The three projected colour images are superimposed in register on the viewing screen 14 so as to form a colour image.
In this arrangement the optical axis 18 of the lens 16 and the optical axis 19 of the lens
17 are parallel to a normal 20 to the viewing screen 14, the normal 20 passing through the centre of the viewing screen 14. The optical axes 18 and 19 are symmetrical to each other relative to the normal 20, and the axes
18 and 19 are displaced from the normal by predetermined equal distances d.
In this way, the projected images are
prevented from having trapezoidal
deformation at least in the vertical direction
of the viewing screen 14, because the optical axes 18 and 19 of the lenses 16 and 17 are parallel to the normal 20. That is to say, the red projected image 21 has the rectangular shape shown in Figure 6A, and the blue projected image has the same shape, while the green projected image 22 has the rectangular shape shown in Figure 6B, when the lenses 16 and 17 arranged with the optical axes 18 and 19 are horizontal.
Therefore the respective images coincide with each other in the vertical direction of the viewing screen 14, when the images are superimposed in register to form the colour image. There is in particular no loss of registration in the vertical direction of the viewing screen 14.
In fact, however, the red projected image 21 and the green projected image 22 do not coincide with each other in the horizontal direction on the viewing screen 14, there being a mis-registration by a distance 2d as shown in Figure 7. This is because the optical axis 18 of the lens 16 is separated from the optical axis 19 of the lens 17 by the distance 2d. The blue projected image is coincident with the red projected image 21 on the viewing screen 14.
To remove this horizontal shift, the cathode ray tubes 11, 12 and 13 are deflected relative to the lenses 16 and 17.
More particularly, the central axes 23 and 24 of the cathode ray tubes 11 and 12 are arranged to be parallel to but deflected outside of the optical axes 18 and 19 of the lens 16 and 17 by equal distances e as shown in Figure 4. The central axis of the cathode ray tube 13 is also deflected to the right of the optical axis 18 of the lens 16 by the distance e, so that the central light beam from the blue image on the cathode ray tube 13 coincides with the central light beam of the red image when the blue light beam is reflected by the semi-reflecting mirror 15.
In this way both the horizontal and the vertical shift between the respective images is removed, so that the red, green and blue images are superimposed in precise register on the viewing screen 14.
The light beams emitted from the centres of the screens of the cathode ray tubes 11, 12 and 13 must be focussed on the centre of the viewing screen 14 by the lenses 16 and 17. In particular, the light beams emitted from the centres of the screens of the cathode ray tubes 11, 12 and 13 and passing through the centres of the lenses 16 and 17 must impinge on the centre of the viewing screen 14 without having been refracted by the lenses 16 and 17. Therefore the relation between d and e is as given by the following equation:
e/d=a/b (1) where a is the distance between the front surfaces of the cathode ray tubes 11, 12 and 13 and the lenses 16 and 17, and b is the distance between the lenses 16 and 17 and the surface of the viewing screen 14 as shown in Figure 4. Moreover, as is well known, the relation between a and b is given by the following equation:
Va+l/b=l/f (2) where f is the focal length of the lenses 16 and 17. Accordingly, the relation between d and e is given by the following equations:
e/d=f/(b-f) (3) or
e/d=(a-f)/f (4)
While the arrangement described
overcomes the problem of obtaining
accurate registration of the images on the
viewing screen, there is a residual problem
the solution to which will be described with
reference to Figures 8 and 9.
As described above, vertical optical
deformation of the superimposed images is
overcome by arranging the lenses 16 and 17
with the optical axes 18 and 19 parallel to
and deflected from the normal 20 to the
viewing screen 14. Additionally, correction
of the horizontal shift between images is
overcome by arranging the cathode ray
tubes 11, 12 and 13 such that the central
axes of the cathode ray tubes 11, 12 and 13
are deflected from the optical axes 18 and
19 of the lens 16 and 17, a consequence of these arrangements is, however, that the distribution of the brightnesses of the
images across the width of the viewing screen 14 is asymmetrical relative to the
centre of the viewing screen 14, because the optical axes 18 and 19 are deflected from the normal 20.
That is, the distributions of the brightnesses of the red image and the blue image projected by the lens 16 are as shown
by the curve 25 in Figure 8, and the distribution of the brightness of the green image projected by the lens 17 is as shown by the curve 26 in Figure 9. The width of the viewing screen 14 is L. It will be seen from
Figure 8 that the red and blue colour are emphasised on the righthand side of the viewing screen 14 and the blue colour is emphasised on the lefthand side of the viewing screen 14.
To overcome this problem the embodiment shown in Figure 9 includes an intercepting plate 27 in front of the lenses 16 and 17. The intercepting plate 27 partly intercepts the red and blue light beams with the righthand sides of the intercepting plate 27 and also partly intercepts the blue light beam with the lefthand side of the intercepting plate 27. With this arrangement, the distributions of the brightnesses of the red and blue image across the width of the viewing screen 14 can be made almost symmetrical relative to the centre of the viewing screen 14, as shown by the line 28 in Figure 10.
Moreover, the distribution of the brightness of the green image across the width of the viewing screen 14 can also be made almost symmetrical relative to the centre of the viewing screen 14, as shown by the line 29 in
Figure 10. In this way a uniform colour tone can be obtained right across the viewing screen 14 when the red, green and blue images are superimposed in register using the apparatus of Figure 9. Alternatively, a pair of intercepting plates 30 arranged between the lenses 16 and 17 and the viewing screen 14 may be used to intercept the light beams, this being shown by broken lines in Figure 9. In this modification, the righthand intercepting plate 30 intercepts the red and blue light, and the lefthand intercepting plate 30 partly intercepts the green light beam.
WHAT WE CLAIM IS:
1. A colour video projection apparatus comprising:
a viewing screen whereon a plurality of
projected images can be superimposed
in register;
a plurality of cathode ray tubes screens
for providing said images;
a plurality of focussing means to project
images from said cathode ray tube
screens onto said viewing screen in
register to form a superimposed image;
the optical axes of said plurality of
focussing means being substantially
parallel to each other, and the central
axis of at least one of said cathode ray
tube screens being so deflected from
the corresponding one of said optical
axes of said focussing means to make
the projected images coincide with
each other on said viewing screen; and
intercepting means disposed partly to
intercept the light emitted by at least
one of said cathode ray tube screens so
as to compensate for unevenness of
distribution of brightness in said
projected images.
2. Apparatus according to claim 1 comprising three cathode ray tubes respectively providing said plurality of cathode ray tubes screens which respectively provide red, green and blue video images, and wherein said plurality of focussing means comprises two lenses, the light beam of a first video image being transmitted through a semi-reflecting mirror and refracted by said first lens, the light beam of a second video image being
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (5)
- **WARNING** start of CLMS field may overlap end of DESC **.13 and the lenses 16 and 17, and b is the distance between the lenses 16 and 17 and the surface of the viewing screen 14 as shown in Figure 4. Moreover, as is well known, the relation between a and b is given by the following equation: Va+l/b=l/f (2) where f is the focal length of the lenses 16 and 17. Accordingly, the relation between d and e is given by the following equations: e/d=f/(b-f) (3) or e/d=(a-f)/f (4) While the arrangement described overcomes the problem of obtaining accurate registration of the images on the viewing screen, there is a residual problem the solution to which will be described with reference to Figures 8 and 9.As described above, vertical optical deformation of the superimposed images is overcome by arranging the lenses 16 and 17 with the optical axes 18 and 19 parallel to and deflected from the normal 20 to the viewing screen 14. Additionally, correction of the horizontal shift between images is overcome by arranging the cathode ray tubes 11, 12 and 13 such that the central axes of the cathode ray tubes 11, 12 and 13 are deflected from the optical axes 18 and19 of the lens 16 and 17, a consequence of these arrangements is, however, that the distribution of the brightnesses of the images across the width of the viewing screen 14 is asymmetrical relative to the centre of the viewing screen 14, because the optical axes 18 and 19 are deflected from the normal 20.That is, the distributions of the brightnesses of the red image and the blue image projected by the lens 16 are as shown by the curve 25 in Figure 8, and the distribution of the brightness of the green image projected by the lens 17 is as shown by the curve 26 in Figure 9. The width of the viewing screen 14 is L. It will be seen from Figure 8 that the red and blue colour are emphasised on the righthand side of the viewing screen 14 and the blue colour is emphasised on the lefthand side of the viewing screen 14.To overcome this problem the embodiment shown in Figure 9 includes an intercepting plate 27 in front of the lenses 16 and 17. The intercepting plate 27 partly intercepts the red and blue light beams with the righthand sides of the intercepting plate 27 and also partly intercepts the blue light beam with the lefthand side of the intercepting plate 27. With this arrangement, the distributions of the brightnesses of the red and blue image across the width of the viewing screen 14 can be made almost symmetrical relative to the centre of the viewing screen 14, as shown by the line 28 in Figure 10.Moreover, the distribution of the brightness of the green image across the width of the viewing screen 14 can also be made almost symmetrical relative to the centre of the viewing screen 14, as shown by the line 29 in Figure 10. In this way a uniform colour tone can be obtained right across the viewing screen 14 when the red, green and blue images are superimposed in register using the apparatus of Figure 9. Alternatively, a pair of intercepting plates 30 arranged between the lenses 16 and 17 and the viewing screen 14 may be used to intercept the light beams, this being shown by broken lines in Figure 9. In this modification, the righthand intercepting plate 30 intercepts the red and blue light, and the lefthand intercepting plate 30 partly intercepts the green light beam.WHAT WE CLAIM IS: 1. A colour video projection apparatus comprising: a viewing screen whereon a plurality of projected images can be superimposed in register; a plurality of cathode ray tubes screens for providing said images; a plurality of focussing means to project images from said cathode ray tube screens onto said viewing screen in register to form a superimposed image; the optical axes of said plurality of focussing means being substantially parallel to each other, and the central axis of at least one of said cathode ray tube screens being so deflected from the corresponding one of said optical axes of said focussing means to make the projected images coincide with each other on said viewing screen; and intercepting means disposed partly to intercept the light emitted by at least one of said cathode ray tube screens so as to compensate for unevenness of distribution of brightness in said projected images.
- 2. Apparatus according to claim 1 comprising three cathode ray tubes respectively providing said plurality of cathode ray tubes screens which respectively provide red, green and blue video images, and wherein said plurality of focussing means comprises two lenses, the light beam of a first video image being transmitted through a semi-reflecting mirror and refracted by said first lens, the light beam of a second video image beingrefracted by said second lens and the light beam of a third video image being reflected by said semi-reflecting mirror and refracted by said first lens.
- 3. Apparatus according to claim 2 wherein said intercepting means comprises a plate disposed so that one end region of said plate partly intercepts light from said first and third video images and another end region of said plate partly intercepts light from said second video image.
- 4. Apparatus according to claim 3 wherein said intercepting means comprises a first plate disposed partly to intercept light from said first and third video images and a second plate disposed partly to intercept light from said second video image.
- 5. A colour video projection apparatus substantially as hereinbefore described with reference to Figures 4 to 10 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5288377A JPS53138326A (en) | 1977-05-09 | 1977-05-09 | Projector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1595610A true GB1595610A (en) | 1981-08-12 |
Family
ID=12927269
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1743978A Expired GB1595610A (en) | 1977-05-09 | 1978-05-03 | Colour video projection apparatus |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS53138326A (en) |
| AU (1) | AU525507B2 (en) |
| CA (1) | CA1099547A (en) |
| DE (1) | DE2820175A1 (en) |
| FR (1) | FR2390870A1 (en) |
| GB (1) | GB1595610A (en) |
| NL (1) | NL7804924A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57162588A (en) * | 1981-03-30 | 1982-10-06 | Masaharu Nishiyama | Stereoscopic x-ray television device |
| JPS62160437A (en) * | 1986-01-08 | 1987-07-16 | Kawasaki Heavy Ind Ltd | Superposing method for projection image |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1235344A (en) * | 1968-12-10 | 1971-06-09 | Harries Electronic Corp | Improvements relating to optical correction systems |
| JPS604635B2 (en) * | 1975-03-12 | 1985-02-05 | ソニー株式会社 | color projector |
| JPS5271944A (en) * | 1975-12-11 | 1977-06-15 | Sanyo Electric Co Ltd | Projection-type color tv unit |
-
1977
- 1977-05-09 JP JP5288377A patent/JPS53138326A/en active Pending
-
1978
- 1978-05-02 AU AU35670/78A patent/AU525507B2/en not_active Expired
- 1978-05-03 GB GB1743978A patent/GB1595610A/en not_active Expired
- 1978-05-04 CA CA302,615A patent/CA1099547A/en not_active Expired
- 1978-05-08 NL NL7804924A patent/NL7804924A/en not_active Application Discontinuation
- 1978-05-09 DE DE19782820175 patent/DE2820175A1/en active Granted
- 1978-05-09 FR FR7813721A patent/FR2390870A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| AU3567078A (en) | 1979-11-08 |
| JPS53138326A (en) | 1978-12-02 |
| CA1099547A (en) | 1981-04-21 |
| DE2820175C2 (en) | 1987-12-03 |
| AU525507B2 (en) | 1982-11-11 |
| DE2820175A1 (en) | 1978-11-23 |
| FR2390870B1 (en) | 1983-11-18 |
| FR2390870A1 (en) | 1978-12-08 |
| NL7804924A (en) | 1978-11-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19940503 |