IMAGING APPARATUS

Abstract: Imaging apparatus, particularly for use in colour scan­ ning apparatus, comprises a converging lens (2) for receiving light rays from an illuminated object (1). Image multiplying means (4) is arranged to receive light rays from the converging lens (2), to separate the light rays into at least two subsidiary light beams, and to guide the subsidiary light beams towards respective image planes (8) at each of which an image (7,9) of the object is focussed by the converging lens (2). At least one detector array (10,11) is positioned at each image plane to detect a respective subsidiary portion of each image, the arrangement being such that the subsidiary portions together form a continuous portion of the image.

Description: CROSFIELD ELECTRONICS LIMITED IMAGING APPARATUS The invention relates to apparatus for detecting an area of information such as a line or area of picture information. Photo-detector arrays are commonly used in imaging systems for imaging a line or area of picture information. One of their limitations, however, is that the number of picture elements available within the image field is normally limited by the number of detector elements. Linear charge coupled device (CCD) arrays with 3456 elements in a straight line are currently available. However, any detector array is mounted in a block which has a finite portion at each end beyond the ends of the detectors and it is therefore impossible to position a number of detector arrays end to end without losing the ability to sense that part of the image falling between each detector array. Longer detector arrays have been made but these suffer from problems of temperature stability and manufacturing cost. The extent of the problem can be appreciated when it is considered that in a high resolution imaging system it is typically necessary to have a line of 10,000 picture elements, and this would require the use of several linear arrays end to end. One attempt at solving this problem is to arrange the arrays on either side of an optima.1 beam splitter as for example illustrated in US-A-4,005,285. Unfortunately, the optical performance requirements of the beam splitter make the system very expensive both in development and production. It is a high risk approach which is likely to suffer problems with spectral matching of the two beams, ghost images, polarisation, and alignment. An alternative arrangement (Sprague and Turner, Optical Engineering Vol. 20, No. 6) suggests a matrix of small apertures superimposed onto an area array. For full effectiveness this method requires a custom made chip which is costly, In accordance with the present invention, imaging apparatus comprises an imaging system for receiving light rays from an illuminated object; image multiplying means arranged to receive light rays from the imaging system, to separate the light rays into at least two subsidiary light beams, and to guide the subsidiary light beams towards respective image planes at each of which an image of the object is focused by the imaging means; and at least one detector array positioned at each image plane to detect a respective subsidiary portion of each image, the arrangement being such that the subsidiary portions together form a continuous portion of the image. The essential difference between this invention and conventional beam splitting arrangements is that each image is formed by different light rays originating from the object rather than from common light rays which have been split. The apparatus in accordance with the invention thus has several advantages over the known beam splitter arrangement. For example, scratches on the image multiplying means cause less "noised on the detector arrays compared with scratches on the beam splitters since the scratches will only affect one or some of the images and not be common to all the images. Other advantages are that there are no longer problems with spectral matching, polarisation, or ghost images. Normally, the area of information will comprise a line of information in which case the detector arrays will be linear arrays. Other non-linear areas could, however, be detected. As will be appreciated, by providing a number of images of the area of information, the detector arrays can effectively be optically abutted without physically coming into contact with each other. Typically, one detector array will be positioned at each image plane although for large images, more than one detector array could be positioned at one or more of the image planes. Preferably, a single imaging means such as a convex lens is used. Preferably, the image multiplying means is positioned at the pupil of the imaging system so that the image multiplying means effectively splits the pupil of the imaging system. To determine the position of the pupil of a lens, a variable aperture is positioned at the lens and the pupil forms the aperture when the aperture is so positioned that variation in its size causes lightening or darkening of an image without affecting the boundary of the image. Two examples of apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a first example; Figures 2A and 2B are views taken on the lines A-A and B-B on Figure 1 respectively; and, Figure 3 illustrates a second example. Figure 1 illustrates an illuminated original, which may be a picture or other information, 1 which is positioned in the object plane of a converging lens 2. In colour scanning apparatus the original will comprise a transparency mounted on a transparent cylinder 1' shown partly in phantom. Such apparatus could be our Crosfield Magnascan 645. An area 3 of the original 1 which is to be scanned has a width indicated by PQ and a length extending into the paper. Light beams from a source (not shown) pass through the area 3 and are received by the imaging lens 2 which transmits the light beams to a glass plate 4 positioned at the pupil of the lens 2. The glass plate 4 comprises a lower portion 5, as seen in the drawing, having parallel sides and an upper portion 6 having a wedge shape. The glass plate 4 effectively splits the pupil of the lens 2 so that two subsidiary light beams are generated. Light transmitted through the parallel sided portion 5 of the glass plate 4 forms a first image 7 in an image plane 8 while light transmitted through the wedge shaped portion 6 of the glass plate 4 forms a second image 9 also in the image plane 8 but spaced from the first image 7. A first linear detector array 10 of photo-detector elements such as CCDs, is positioned to sense a subsidiary portion of the first image 7 while a second detector array 11 is positioned to detect a different subsidiary portion of the second image 9. The arrangement of the detector arrays 10, 11 and the images 7, 9 can be seen more clearly in Figure 2. Figure 2A illustrates the area 3 of the original 1 which is to be scanned. Figure 2B illustrates the first and second images 7, 9 which are formed by the lens 2 and the glass plate 4 in the image plane 8. The detector array 10 comprises a support block 12 on which are mounted CCD photo-detector elements 13. Typically each array 10 will comprise 3456 elements 13. It will be seen that the support block 12 extends beyond the ends of the photo-detector elements 13. The detector array 10 is positioned so that the right hand subsidiary portion, as seen in the drawing, of the first image 7 is detected by the array of elements 13. The second detector array 11 comprises a support block 14 on which is mounted an array of CCD photo-detector elements 15. Again, it will be seen that the support block 14 extends beyond either end of the elements 15. The detector array 11 is positioned to detect the left-hand subsidiary portion, as seen in the drawing, of the second image 9. As can be seen in Figure 2B, the two arrays of elements 13, 15 are aligned so that effectively a continuous portion of the area 3 is detected. Thus it can be seen that the left-hand end of the elements 13 optically abuts the right-hand end of the elements 15. Figure 3 illustrates a second example, the left-hand portion of which is similar to that of Figure 1 and so the same reference numerals have been used. Instead of the glass plate 4 of the Figure 1 example, a pair of mirrors 16, 17 are positioned immediately behind the lens 2 and at the pupil of the lens to reflect the light beams in upward and downward directions, as seen in the drawing. The mirror 16 causes the formation of a first image 18 in an image plane 19, while the mirror 17 causes the formation of a second image 20 in an image plane 21. The first detector array 10 is positioned to detect a portion of the first image 18, while the second detector array 11 is positioned to detect a portion of the second image 20. The relationship between the detected portions of the first and second images 18, 20 is similar to that described with reference to the images 7, 9 in the previous example. In each of these cases, where the apparatus is incorporated into colour scanning apparatus, the cylinder 1' will be gradually rotated so that the original 1 will move in a downward direction, as seen in the drawings. This then enables successive lines of the original to be scanned, the lengths of the line corresponding to the total length of the elements 13, 15. The converging lens 2, the splitting arrangement 4 or 16, 17 and the detector arrays 10, 11 will be incorporated into a conventional analyse head of the colour scanning apparatus and the outputs from the detectors 10, 11 will be fed to conventional processing electronics such as described in European Patent Specification No. 0090596.

Claims: CLAIMS 1. Imaging apparatus comprising an imaging system (2) for receiving light rays from an illuminated object (3); image multiplying means (4; 16,17) arranged to receive light rays from the imaging system, to separate the light rays into at least two subsidiary light beams, and to guide the subsidiary light beams towards respective image planes (8;19,21) at each of which an image (7,9;18,20) of the object is focused by the imaging means; and at least one detector array (10,11) positioned at each image plane to detect a respective subsidiary portion of each image, the arrangement being such that the subsidiary portions together form a continuous portion of the image. 2. Imaging apparatus according to claim 1, wherein the detector arrays comprise linear arrays (10,11). 3. Imaging apparatus according to claim 1 or claim 2, wherein the detector arrays comprise CCD arrays (10,11). 4. Imaging apparatus according to any of the preceding claims, wherein the image multiplying means (4; 16, 17) is positioned at the pupil of the imaging system (2). 5. Imaging apparatus according to any of the preceding claims, wherein the image multiplying means (4) comprises a first portion (6) for refracting incident light rays and a second portion (5) through which incident light rays pass substantially unrefracted. 6. Imaging apparatus according to claim 5, wherein the image multiplying means comprises a glass plate (4) having a wedge shaped portion (6) for refracting incident light rays and an integral parallel sided portion (5) through which incident light rays pass substantially unrefracted. 7. Imaging apparatus according to any of claims 1 to 4, wherein the image multiplying means comprises a pair of outwardly facing plane mirrors (16,17) angled towards one another and facing towards the imaging system (2). 8. Imaging apparatus according to any of the preceding claims, wherein at least some of the image planes (8) are coplanar, the corresponding images (7,9) being focussed at different positions in the image plane. 9. Colour scanning apparatus comprising imaging apparatus in accordance with any of the preceding claims.

Inventors: AUGHTON, JOHN EDWARD
Applicants: CROSFIELD ELECTRONICS LIMITED
Application year: 1984
Main classification: G02B27
IPC codes: G02B27, H04N1