GB2198608A - Image transmitter - Google Patents

Description

-I- 1 1 2198608 IMAGE TRANSMITTER The present invention relates to image

transmitters of the type which include a projecting lens from which the image which is to be sent directly or via a mirror system is projected onto a scanning device which is provided to scan the projected image to generate an electrical transmission signal which is modulated in synchronism with the scanning and in accordance with the degree of brightness of different portions of the image.

In long distance transmission of images using sequential scanning in an image transmitter, scanning is is at present 0 fte n done by having the image material projected onto the scanning device; the image material is thus not used directly, such as in the form of a paper-copy. During scanning, the image is projected through a lens, which is preferably positioned so that its optical axis is aligned perpendicular to the image plane and extends from the centre of the image.

If the scanning device contains reflective surfaces which are parallel to the image plane, reflections from them will fall on the lens and will thereafter be re-reflected to the scanning - device so that phantom images are produced'during scanning. Such reflective surfaces can be found on members such as a row scanner, which extends in the transverse direction of the projected image in order to scan it line by line. When transmitting colour images, colour filters must be placed in front of the scanning device directly opposite the lens. These colour filters are in the shape of planar plates and they tend to cause reflections, especially from very bright image portions.

An object of the present invention is to provide an arrangement which eliminates the re-reflection of reflections in order to prevent phantom images from arising.

In accordance with the present invention, there is provided an image transmitter of the type which includes a projecting lens from which an image which is to be sent directly or via a mirror system is projected onto a scanning device which is provided to scan the projected image to generate an electrical transmission signal which is modulated in synchronism with the scanning and in accordance with the degree of brightness of different portions of the image, wherein those elements in the scanning device which have surfaces which tend to lead to reflections, are placed at an angle in relation to the image plane of the projected image so that reflections from said surfaces do not strike the front surface of the lens and can therefore not be re-reflected by it but are rather deflected to the side of it. The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: 20 Fig.1 is a simplified perspective view of an image transmitter; Figs. 2 and 3 show first and second examples of the scanning device in the transmitter, both examples being shown on an enlarged scale; and 25 Fig.4 shows schematically the light beam path in the image transmitter. The invention is described with reference to an image transmitter which is adapted for the transmission of colour images. 30 According to Fig.1, on and in a casing 1, the image transmitter includes an illumination device 2, a picture holder 3, a mirror 5, a lens 6, a scanning device 7 having an image window 8 and a row scanner 9, as well as a motor 10, a supporting beam 11, on which the mirror 5, the lens 6 and the scanning device 7 are mounted, together with a mirror 12, which is pivotable by means of a hinge 13. In addition to the 1) illumination device 2, on the outside of the casing, a projection window 14, a keyboard 15, an electronic unit 16-and an electronic display 17 are provided.

The illumination device 2 can be raised and under it is a circularopening 18 into which a circular socket 20 on the picture holder 3, see Fig.2, can be inserted. Furthermore, the film holder 3 has a picture window 21 which, when the socket of the film holder is in the opening 18, is located in the light beam path from the illumination device 2 when it is in its lowered position. The light beam passes downwards to the mirror 5 which deflects it through the lens 6 and onwards to the scanning device 7 where, however, as is shown in Fig.1, the beam may be deflected to the projection window 14 by raising the mirror 12.

When using the image transmitter, a picture, which is in the picture holder 3, is projected by means of light from the-illumination device 2 via the mirror 5 and the lens 6 into the image window 8 of the scanning device 7, where it is scanned a number of times determined by the colour separation, by means of the row scanner 9. in order to create an electric signal. This signal may be sent to a receiver or may be used in some other way for the purpose of image reproduction. 25 The scanning device 7 shown in Fig.1 is shown-on an enlarged scale and in more detail in Fig.2. The figure shows a first, simple embodiment. The row scanner 9 comprises a longitudinally extending body which is movable along guide rods 20 by means of the motor 10. Both the motor 10 and the guide rods 20 are supported in a frame 21 with an opening 22 in which the row scanner 9 can move and which substantially corresponds to the image plane. The image which is to be scanned consists of a projection within the opening 22 of the actual film image 4 in the picture holder 3. As has been explained above, the projection is made using light from the illumination device 2, along a light beam path via the mirror 5 and through the lens 6. The image is thus projected in such a way that its focal plane lies in the opening 22 and is level with a row-scanning element on the row scanner 9. This row-scanning member consists of a row of light-sensitive elements 23 which, by means of electronic control, can be caused to generate electrical signals sequentially, so that one line of the image is scanned. As the row scanner moves on the guide rods 20, line after line of the image is scanned until it has been scanned entirely. This results in a modulated electrical signal which represents all of the picture elements of the picture, the resolution of which is determined by the size and graduation of the light-sensitive elements along the row scanner 9 and the rate at which it moves In relation to the scanning rate along the row scanner, that is to say, the line density.

The light-sensitive elements 23 consist of photo sensors which, under the influence of light, generate electric current, the strength of which is proportional to the strength of the illumination. These lightsensitive elements are constructed in such a way that they have a front surface of high reflectivity which therefore causes the front surface 25 of the row scanner to tend to reflect incident light from the lens. If the front surface 25 were directly opposite the lens, this light would be reflected to the front surface of the lens and from there, in a secondary reflection, back to the light-sensitive elements, so that a phantom image could arise during registration.

In the present arrangement, this is eliminated by mounting the front surface 25 of the row scanner 9 at an angle to the projection plane of the image. In an apparatus of the type shown in Fig.1, an angle of approximately 10' has been found suitable.

-7 v li When'transmitting a colour image, one must separate it into different colours using colour filters and scan it sequentially, colour by colour. In order not to distort colour perception when viewing the image in the picture window 14 via the mirror 12, it is preferable to place the colour filters adjacent to the scanning device 7. In the present arrangement, each of the colour filters consists of a narrow plate 34, which is mounted in front of the row scanner 9.

When the colour filter plates 34 have all been mounted on the row scanner they will follow along with it-during scanning. Each colour filter plate need have only the same width as the width of the light-sensitive elements 23 of the row scanner, that is, only the width of one line. For reasons of handling it is, however, advisable to provide the plate witha somewhat greater width. which facilitates handling so that the mounting precision need not be so great. The length must of course be equal to.the length of the row of light- sensitive elements.

The necessary colour filters may be combined in a switching device. -One possibility is to utilize a colour filter plate with several regions, each of which displays one of the predetermined colours. By manoeuvering the plate into different positions, the different regions may be placed in front of the row of light-sensitive elements.

As is shown in Fig.3, the scanning device 7 for colour image transmission (the same reference numerals are used in Fig.3 as in Figs. 1 and 2 for common parts) has a row scanner 9 which is moveable along its guide rods 20. There is, however, a second guide device 30 in front of the row scanner 9 that is, on the side from which the bundle of light beams from the projection device falls. The guide device 30, by means of a slide 31, supports a plate 32, which is parallel to the light-sensitive elements of the row scanner 9. The plate 32 supports a number of colour filters 34, mounted in openings 33 through it. Seven colour filters are shown here. The minimum number for attaining the desired colour separation is three. In this case, the device has been made more universal by providing three filters for separation of positive images and three for negative images, and one opening 33 is reserved for the creation of a black/white signal. This is intended for black and white pictures and for the black print of four-colour printing.

Additionally, the device includesa drive for the slide 31 so that it can be moved back and forth along the guide device 30. The latter suitably includes a is screw 35 which meshes with the threading of a nut (not shown) on the slide 31 and which is driven by means of a second motor 36, which is included in the drive.

The drives for moving the row scanner 9 along the guide rods 20 and the colour separation slides 31, together with the filters 34, along the guide device 30, are arranged for a specific, co-ordinated drive sequence. This is achieved by rotational control of the motors 10 and 36. As is well known, electrical motors, often of the stepper motor type, are at present available which can be driven so as to follow a complicated rotational pattern, usually under the control of computer equipment. Such a motor is used in the present scanning device, and at least for the embodiment now under discussion, must be provided for coordinated control of the two slide devices. The manner in which this is accomplished is known to one skilled in the art and need not be described in detail herein.

Fig. 4 shows schematically, in what corresponds to a view from above, the internal parts of the image n 11 -7transmitter, as shown in Fig. 1, namely, the lens 6 and the scanning device 7. The scanning device is illustrated in Fig. 4 in its simpler form in accordance wih Fig. 2. The reference numeral 38 designates the light beam path through the lens 6 towards the scanning device 7. It will be understood from the figure that reflections return towards the lens if light strikes the reflecting surfaces which are parallel to the image plane or surfaces which are positioned at a small angle relative to this plane. The light which is reflected towards the front surface of the lens will in turn be reflected back towards the scanning device as a secondary reflection. It is this which gives rise to the said phantom images, and the risk of phantom images is is especially great when there is large contrast between different image.portions, whereby very bright portions can lead to discernible phantom images in dark portions.

The manner inwhich phantom images are avoided by means of the invention is shown in Fig. 4. It is achieved by positioning the front surface 25 of the row scanner 9, as has been mentioned earlier, at an angle in such a way that the reflection, which is shown as the broken lines 39 in Fig. 4, is directed sideways at such an angle that no reflection can ever fall on the lens. When filters ate used, the holder 32 may also be arranged with the portions which secure the filter plates in a zig-zag pattern, as is shown clearly in Fig. 3. In this manner, each filter plate will be angularly positioned.

Thus, the surfaces which are opposite one another in the light beam path and which are reflective are positioned at such an angle in relation to each other - that no reflections can pass back and forth between them. Since the best placement of the projection lens -8is directly in front of the image plane, with the optical axis normal to the plane, it is unavoidable that the front surface of the lens will constitute such a reflective surface. Opposite this surface is the scanning device, which will move in the image plane. Other reflective surfaces are also found on the scanning device which are impossible or difficult to avoid. The row scanner is thus reflective in the region of the light-sensitive elements. As has been made clear, the invention may also be applied for such reflective surfaces as colour filters.- . 0 0 4 1 9, t.

151 -9CLADIS 1. An image transmitter of the type which includes a projecting lens from which an image which is to be sent directly or via a mirror system is projected onto a scanning device which is provided to scan the projected image to generate an electrical transmission signal which is modulated in synchronism with the scanning and in accordance with the degree of brightness of different portions of the image, wherein those elements in the scanning device which have surfaces which tend to lead to reflections, are placed at an angle in relation to the image plane of the projected image so that reflections from said surfaces do not strike the front surface of the 1jens and can therefore not be re-reflected by it but are rather deflected to the side of it.

2. An image transmitter as claimed in claim 1, wherein the scanning device includes a row scanner of the type having light-sensitive elements with a reflective front surface.

3. An image transmitter as claimed in claim 1 or 2, wherein one or several colour filters for colour separation of the image in conjunction with transmission are positioned between the scanning device and the lens, such that the front surface of the or each said filter is arranged at an angle to the image plane of the projected image.

4. An image transmitter substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

........................ 0....... 0..................... 0 Published 1988 Pt The Patent Office, State House, 66/71 High Holborn, London WCIR 4TP. Further copies raay be obtained from The Patent office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87. Sales Brancri, br. zaary uray, ui%p-u-,