GB2092330A - Improvements in and relating to colour photography - Google Patents

Abstract

A photographic recording and reproducing device has near the projection lens 1 a filter comprising a plurality of triplets of strips 2,2', etc. in each of the primary colours. A screen of cylindrical lenses 4 project images of the filter strips onto a film 3. The image of each triplet 2 formed by each cylindrical lens coincides with the image of an adjacent triplet formed by an adjacent lens. The projection lens can be stopped down in steps without producing a colour cast by including complete triplets of filter strips. <IMAGE>

Description

SPECIFICATION Improvements in and relating to colour photography The invention relates to the photographic recording and reproduction of colour pictures using a strip filter divided into different coloured strips and a film provided with a lenticular screen of cylindrical lenses extending parallel to the strips of the filter.

In previously proposed devices for lenticular screen photography the size of the strip filter in relation to the focal length of the image-forming lense determines the light sensitivity of the system.

Stopping down is possible only in one dimension, by reducing the length of a rectangular aperture stop in the direction of the length of the filter strips.

Although this achieves one of the aims of stopping down, to decrease the exposure, the depth of field is increased only in one dimension. Furthermore, using this method the microscopic images of the strip filter on the image support, which images carry the colour information, are likewise reduced in one dimension which may result in an inadmissible strain on the resolving power of the photographic layer and thus in the appearance of graininess, this ultimately reducing the reliability of the strip filter image.

It is an object of the invention to provide a device in which variable stopping down is possible without the quality of the strip filter images being appreciably decreased, and without the cost being unduly increased.

The invention provides a device for the photographic recording and/or reproduction of colour pictures, comprising means for projecting an image onto or from an image plane and a strip filter so disposed in substantially the plane of an aperture stop of the projection ray path that when a film having arranged on it a suitable lenticular screen is positioned in the image plane the lenses of the lenticular screen form images of the strip filter in the image plane, the strip filter comprising a repeating pattern of parallel filter strips, each repeat of the pattern comprising one strip in each of a plurality of colours.

The invention also provides a device for the photographic recording and/or reproduction of colour pictures according to the lenticular screen principle, comprising a strip filter that is assigned to the object and is divided in the form of steps into a plurality of filter strip triplets each consisting of one red, one green and one blue strip arranged in the aperture stop of the lens; and having arranged on the film on the side facing the lens a screen of cylindrical lenses extending parallel to the strips of the colour filter; the focal length of each cylindrical lens and the object distance from the strip filter to the lenticular screen being such that the area behind each individual cylindrical lens is filled by the image of a central filter strip triplet of the strip filter.

By means of the invention it is possible, using simple optical means, to increase exposure without elaborate and expensive constructions, without visibly reducing the optical resolution that can be achieved and without a change in colour occurring. It is possible with purely optical means of signal processing or optical means in co-operation with electronic means, to obtain isotropic stopping down that is independent of the direction of the ray path without, or almost without, reducing redundancy.

An optical system constructed in accordance with the invention will now be described by way of example only with reference to Fig. 3 of the accompanying drawings, in which: Figure 1 shows schematically one previously proposed form of optical recording system; Figure 2 shows schematically one previously proposed form of optical reproduction system; and Figure 3 shows one form of optical system according to the invention.

In one previously proposed optical recording system, shown schematically in Fig. 1, a single colour filter strip triplet 2 is arranged in the diaphragm aperature of the image-forming lens 1. The size of the strip filter 2 in relation to the focal length of the lens 1 determines the light sensitivity of the recording system. On the surface of a film 3 having a photographic layer there is a cylindrical lenticular screen 4 which is preferably imprinted into the film base in such a manner that each cylindrical lens of the cylindrical lenticular screen is assigned an image point which is filled exactly by an image of the filter unit, so that image contains three colour separation for each image point.

Stopping down is possible only in the direction of the length of the filter strips by reducing the length of a rectangular aperture stop. although this achieves one of the aims of stopping down. to reduce the exposure, the depth of field is increased only in one dimension. Furthermore, using this method, the microscopic images of the strip filter on the image support, which images carry the colour information, are likewise reduced in one dimension which may result in an inadmissible strain on the resolving power of the photographic layer and this in the occurrence of graininess, because untimately the redundancy of the strip filter image is reduced.

The corresponding optical reproduction system, shown schematically in Fig. 2, uses substantially the same components as the recording system, but in the reverse order. An image located on the film 3 is illuminated with a light source 5 and projected by means of a lens 1 via the cylindrical lenticular screen 4.

According to the invention, instead of a single colour filter strip triplet 2 there are arranged substantially in the plane of the aperture stop of the lens a plurality of colour strip filter triplets and the imageforming geometry of the cylindrical lenticular screen and the film is so arranged that the image of a single strip filter triplet from this plurality of filter triplets produced by one cylindrical lens exactly and precisely fills the area in the photograhic layer corresponding to the extent of an individual cylindrical lens.

A strip filter and cylindrical lens configuration for a variable aperture is shown in Fig. 3. The plurality of colour strip filter triplets is indicated by the central triplet 2 (zero th triplet) and one further triplet 2' (the first triplet on the left as seen in Fig. 3). An adjustable aperture is defined in part by a slide element 6 which is shown by dashed lines in the setting for the smallest aperture opening which is the width of exactly one colour strip filter triplet. The aperture may be square or otherwise rectangular; if required it may instead be circular.

As shown in Figure 3, the image of the central (zero th) strip filter triplet 2 formed by the ith cylindrical lens lies directly behind the ith cylindrical lens. The image of the first triplet on the levt formed by the (i + 1 )th cylindrical lens is superimposed on the image of the central triplet formed by the ith cylindrical lens. For the sake of clarity the other lateral images that occur and their super impositions are not shown in Figure 3.

Using such an arrangement of a plurality of colour filter strip triplets 2 in the aperture of the imageforming lens 1, it is possible to obtain isotropic stopping down, giving the same action in ali directions, without, or almost without, reducing the redundancy in the image.

The image-forming geometry of the cylindrical lenticular screen and the film is, as stated above, so arranged that, because of the said plurality of triplets, the image of each strip filter exactly fills the area of one individual cylindrical lens.

If the recording lens is stopped down with the aid of a (square) aperture diaphragm to such an extent that the image of only the central strip filter unit is formed on the photographic layer, the the entire arrangement is exactly equivalent to that used in conventional lenticular screen photography with a corresponding fixed aperture. If the square aperture opening is enlarged symmetrically about the optical axis in such a manner that light now passes also through the adjacent strip filter triplets, each cylindrical lens forms an image of these units to either side of the optical axis in the regions of the cylindrical lenses that are adjacent to the left and the right (as seen in Figure 3) of it.

As a result, there is no impairment of the optical image of the object on the photographic layer but only an increase in the exposure caused by the superimposition of in each case two images of strip filter triplets per image point. The increase in the exposure corresponds to that obtained on enlargement of the aperture.

In a recording system of the most simple type it is possible with the measure described above to obtain the following series off-stops with light passing through an odd integral number of filter triplets in each case: 16 - 5.33 - 3.20 - 2.29 - 1.78.

It is clearthatthe spacing of the stops is very great at the start of the series. It is therefore preferable so to construct the device that three filter triplets are used even in the case of the smallest aperture. A more advantageous division is then obtained starting, for example, fill: 11 - 6.60 - 4.71 - 3.67 - 3.00 A more uniform division may be obtained if a rectangular aperture with sides in the ratio of 1 to is used instead of a square aperture at some settings. This ratio of 1 :is chosen because in the case of a square aperture the reduction in the depth of field in the direction of the diagonals of the square compared with the depth of field in the direction of the sides of the square is negligible, and the length of a diagonal of a square is Wtimes the length of a side of the same square.On that basis the following range off-stops can be obtained, again starting with three triplets: 11 - 7.85 - 4.73 - 3.09 - 2.51 If greater expenditure of resources is permitted then it is possible to obtain any desired aperture setting, even a circular aperture stop being possible if the colour imbalance that then occurs is corrected.

For this purpose, the aperture setting chosen is preferabley recorded by means of a code exposed onto the film. On reproduction by suitable, advantageously electronic, reproduction means, the necessary signal corrections are automatically carried out in response to this code, so that the picture appears again in the correct colours. Since the corrections correspond to simple colour filtering operations, they may be carried out in the optical copy of the lenticuiar screen image. Matrixing is generally unnecessary.

Claims (21)

1. A device for the photograhic recording and/or reproduction of colour pictures, comprising means for projecting an image onto or from an image plane and a strip filter so disposed in substantially the plane of an aperature stop of the projcetion ray path that when a film having arranged on zit a suitable lenticular screen is positioned in the image plane the lenses of the lenticular screen form images of the strip filter in the image plane, the strip filter comprising a repeating pattern of parallel filter strips, each repeat of the pattern comprising one strip in each of a plurality of colours.

2. A device as claimed in claim 1, wherein each repeat of the said pattern comprises three strips, one in each of the additive primary colours.

3. A device as claimed in claim 1 or claim 2, wherein the said aperture stop is adjustable to vary the number of strips of the strip filter through which projection rays can pass.

4. A device as claimed in claim 3, wherein the aperture of the aperture stop is rectangular, with edges parallel and perpendicular to the filter strips.

5. A device as claimed in claim 4, wherein the aperture stop is movable between a plurality of stable positions at each of which equal numbers of filter strips of each colour appear in the aperture.

6. A recording device as claimed in any one of claims 3 to 5, which comprises means for exposing onto a film in the image plane an indication of the aperture setting.

7. A reproducing device as claimed in any one of claims 1 to 6, which comprises means for detecting and indication exposed onto a film of the aperture setting at which an image was exposed onto that film.

8. A reproducing device as claimed in claim 7 which comprises means for automatically making colour corrections during reproduction of an image in response to the said indication of the aperture setting.

9. A device as claimed in claim 1 and substantially as hereinbefore described with reference to, and as shown in, Figure 3 of the accompaying drawings.

10. A device as claimed in any one of claims 1 to 9, further comprising a lenticular screen of cylindrical lenses on the side of the image plane towards the lens, each cylindrical lens extending parallel to the filter strips and forming an image of the filter strips in the image plane.

11. A device as claimed in claim 10, wherein when more than one repeat of the pattern is projected onto the image plane an image of one repeat formed by one cylindrical lens is coincident with an image of an adjacent repeat formed by an adjacent cylindrical lens.

12. A device as claimed in claim 10 or claim 11, wherein the lenticular screen is formed in the surface of a photographic film in the image plane.

13. A device for the photographic recording and/or reproduction of colour pictures according to the lenticular screen principle, comprising a strip filter that is assigned to the object and is divided in the form of steps into a plurality of filter strip triplets each consisting of one red, one green and one blue strip arranged in the aperture stop of the lens; and having arranged on the film on the side facing the lens a screen of cylindrical lenses extending parallel to the strips of the colour filter; the focal length of each cylindrical lens and the object distance from the strip filter to the lenticular screen being such that the area behind each individual cylindrical lens is filled by the image of a central filter strip triplet of the strip filter.

14. A device as claimed in claim 13, wherein when the aperture stop opened images of the filter strip triplets adjacent to the central triplet are formed by each cylindrical lens in the areas behind the adjacent cylindrical lenses.

15. A device as claimed in claim 14, wherein the strip filter comprises 11 triplets, and the aperture stop is arranged to be set at a plurality of discrete settings corresponding substantially to the fnumbers 11, 7.9, 4.7, 3.1, and 2.5 wherein the numbers of strip triplets exposed are 3, 5, 7, 9 and 11, respectively, and in each case the aperture is square or is rectangular with lengths of sides substantially in the ratio V.

16. A device as claimed in any one of claims 13 to 15, comprising means arranged to register the aperture setting of the device by exposing corresponding features onto the film.

17. A device as claimed in claim 16, comprising means for exposing clearly assigned code features the film to register the different aperture settings and means for reading out those features on reproduction of the film and, by means of derived control signals, automatically carrying out corresponding colour corrections.

18. A device as claimed in claim 17, wherein the colour correction is controlled by means of optical filters.

19. A device as claimed in claim 17 wherein the colour correction is controlled by electrical or electronic means for influencing the control signals.

20. A device as claimed in any one of claims 16 to 19, wherein the aperture stop is circular.

21. A device as claimed in any one of claims 13to 19, wherein the aperture stop is rectangular.