A METHOD OF ALIGNING IMAGES TO BE SCANNED AND A SCANNING APPARATUS FOR SUCH ALIGNMENT

Abstract: The invention relates to a method of aligning at least two images, where each image (2) has at least one associated alignment area or mark (3a, 3b) positioned at a given position in relation to the image. The method of aligning comprises identifying the position of at least one alignment mark or area associated with each image, scanning a first image and at least one alignment area or mark of the first image, scanning a second image and at least one alignment area or mark of the second image, determining the displacement of each of the alignment area(s) or mark(s) of the second image in relation to the alignment area(s) or mark(s) of the first image, and cancelling out at least partly the determined displacement(s) of the alignment area(s) or mark(s) of the second image.

Description: A METHOD OF ALIGNING IMAGES TO BE SCANNED AND A SCANNING APPARATUS FOR SUCH ALIGNMENT The present invention relates to a method of aligning at least two images to be scanned and a scanning apparatus for such alignment, where each image has at least one associated alignment area or mark positioned at a given position in relation to the image. Alignment of this type is predominantly performed in order to superpose e.g. a number of colour separations, which are typically screened, of an original image or integrating these separations with text in the graphic industry. In the art, separating the colours of a colour original into e.g. the well-known CMYK or YCMB (Yellow, Cyan, Magenta, Black) colour separations is performed using a computer and suitable software. This separation is performed in order to be able to reproduce the original in e.g. a printing process using the base colours of the colour separation. In order to be able to precisely position these e.g. four individual and separate representations of the image, the separation also provides alignment or registering marks precisely positioned in relation to the actual image. Depending on the apparatus producing the colour separations, these alignment or registering marks may be crosses in the film material representing the separations, or the marks may be holes, indentations or notches therein. In the situation where holes, notches or indentations are provided, these are used in order to precisely position the separations in e.g. the printing machine. In the other situation where the marks are crosses or other types of marks or where selected image areas are used for alignment, this positioning in the printing machine may be more difficult. The same problem may be seen when e.g. desiring to scan the separations to electronically superpose these, as the separa- tions should be positioned very precisely on the scanner. At present, this positioning of the images is performed by fixing the images on e.g. sheets of transparent film or job- sheets having registering holes for engagement with register¬ ing pins -on the scanner, in positions where all separations are superposed when positioned on the scanner. Typically, the positioning error should be less than 5/100 mm, whereby this work is quite time consuming. This positioning or aligning of the separations may be carried out based on the alignment marks, but it is also possible to select corresponding image areas of each colour separation and use these selected areas as alignment or registering areas. An object of the present invention is to provide a solution to this problem of aligning images to be subsequently scanned. Thus, a first aspect of the invention is to provide a method of aligning at least two images to be scanned, each image being associated with at least one corresponding alignment area or mark positioned at a given position in relation to the image, which images when scanned are arranged on a sub¬ stantially planar surface of a scanning apparatus for digitizing images. The method according to this aspect of the invention comprises identifying the approximate position of at least one corresponding alignment area or mark associated with each of the images, a first scanning process comprising scanning at least part of the at least one alignment area or mark of the first image, a second scanning process comprising scanning at least part of the at least one alignment area or mark of the second image, determining the displacement (s) of each of the at least one alignment area(s) or mark(s) of the second image in relation to the at least one alignment area(s) or mark(s) of the first image, and cancelling out at least partly the determined displace¬ ment(s) of alignment area(s) or mark(s) of the second image. Here is should be understood that by an alignment area or mark according to the present invention is meant a graphical area or element having a two dimensional structure, which can be unambiguously identified in order to be used for aligning. In accordance with the present invention it is preferred that the alignment process is an integral part of the image scan¬ ning process or processes in which digitized forms of the images are obtained. Thus, it is preferred that the first scanning process comprises scanning the first image in order to obtain a digitized form of the first image, said scanning of the first image preferably being performed after or before scanning of the alignment area(s) or mark(s) of the first image. It is furthermore preferred that the at least partly cancelling out of the determined displacements is followed by a third scanning process comprising scanning the second image in order to obtain a digitized form of the second image. In order to scan an image or an alignment area or mark, it is preferred that the image or alignment area or mark is moved along a substantially linear path during scanning. The scan¬ ning process may be performed by using a scanner head which also or as an alternative can be moved along a substantially linear path during scanning. Preferably, the movement of the image and/or the movement of scanning head defines a direc¬ tion of scanning. Typically, a scanning head may comprise one or more CCD- elements, and it is preferred that the direction of scanning is defined as being substantially perpendicular to a direc¬ tion defined by the longitudinal extension of the CCD-element when arranged in the scanner head. In one embodiment of the invention the scanning is performed by scanning the alignment area(s) or mark(s) and/or images in bands or stripes. In this embodiment it is preferred that the scanning head is moved in the direction of scanning, while the image may be moved in a direction parallel to the direc¬ tion of scanning. Before a scanning of the second image is performed it is preferred to at least partly cancel out the determined dis¬ placement^) of alignment area(s) or mark(s). Such at least partly cancelling out of displacement(s) may be carried out by adjusting the position of the second image, which adjust¬ ment may be performed by a controlled movement of the image. The image may be moved so as to at least partly cancel out determined displacemen (s) of alignment area(s) or mark(s) in a direction substantially parallel and/or substantially perpendicular to the direction of scanning. The position of the image to be scanned may also be adjusted relatively to the position of the scanner head by a con¬ trolled movement of the scanner head. The scanner head may be moved so as to at least partly cancel out determined dis¬ placement (s) of alignment area(s) or mark(s) in a direction substantially parallel and/or substantially perpendicular to the direction of scanning. The at least partly cancelling out of the determined dis¬ placement (s) of alignment area(s) or mark(s) may also or alternatively be performed by controlling the scanning of the second image. Here, the starting point of the scanning of the second image may be selected based on the determined dis¬ placement^) of alignment area(s) or mark(s). Thus, the scanning of the second image may be controlled so as to have a starting point having a displacement in relation to a corresponding starting point of the scanning of the first image, said displacement being substantially equal to the remaining part of the determined displacement (s) of alignment area(s) or mark(s) in a direction substantially parallel to the direction of scanning. In a preferred embodiment of the invention, the images and their associated alignment areas or marks are present on at least one film or job-sheet, which film(s) or job-sheet (s) when the alignment areas or marks and/or images are scanned is/are mounted on the substantially planar surface of the scanning apparatus. It is furthermore preferred that each image and its associated alignment area(s) or mark(s) is/are present on a separate film or job-sheet. It should be understood that the identified area(s) or mark(s) of each image which are selected for alignment can be part of the image itself, but they may also be positioned outside an area covered by the image. The present invention also relates to a second aspect which provides a method of aligning at least two images to be scanned, each image being associated with at least one corre¬ sponding alignment mark positioned at a given position in relation to the image, each image being present on a film, which films when scanned is/are mounted on a substantially planar surface of a scanning apparatus having a scanning head which is moved along a substantially linear path during scanning, said method comprising scanning at least part of a film comprising a first image and the at least one corresponding alignment mark(s) , determining the positio (s) of the at least one alignment mark(s) of the first image, scanning at least part of a film comprising a second image and the at least one corresponding alignment mark(s) , determining the displacement (s) of the position(s) of each of the at least one alignment mark(s) of the second image in relation to the determined position(s) of the at least one alignment mark(s) of the first image, and cancelling out or removing at least partly the determined displacement (s) of position(s) of alignment mark(s) in a direction substantially perpendicular to the direction of movement of the scanner head by adjusting, on the basis of the determined displacement (s) , the position of the film carrying the second image in relation to the position of the first image. Here is should be understood that when at least partly cancelling out displacements in a direction substantially perpendicular to the direction of movement of the scanner head, such cancelling may also comprise an at least partly cancellation of displacements in a direction parallel to the direction of movement of the scanner head. This may for example be the situation when at least partly cancelling out displacements by performing a rotation of the film comprising the second image around an axis substantially perpendicular to the planar surface. Before a scanning of the second image can be performed it is preferred to cancelling out or removing at least partly a remaining displacement of the determined displacement (s) of position(s) of alignment mark(s) in a direction substantially parallel to the direction of movement of the scanner head. It is further preferred that this at least partly cancelling is performed by controlling the position of the scanning head when scanning the second image. However, the scanning head may also be moved in order to at least partly cancel out such a displacement before the scanning of the second image is started. It is also preferred that the adjustment of the position of the film carrying the second image in a direction substan¬ tially perpendicular to the direction of movement of the scanner head comprises a movement of the planar surface of the scanning apparatus in a direction substantially perpen¬ dicular to the direction of movement of the scanner head. Here it is to be noted that if only one alignment area or mark is associated with each image to be scanned, the second image to be scanned may be rotated in relation to the posi- tion of the first image, even when any displacement between their respective alignment areas or marks has been corrected for. Thus, it is preferred to have at least two alignment areas or marks associated with each image to be scanned, with the associated alignment areas or marks positioned at given positio (s) in relation to the image. The at least partly cancelling out of determined displacement(s) may comprise a rotation of the second image around an axis perpendicular to the planar surface. The rotation of the image is preferably being performed by rotating the planar surface of the scan¬ ning apparatus. The angle of rotation of the image or the planer surface may be in the range from -1° to +1, preferably in the range from -0.4° to +0.4°. However, the invention is not restricted to these ranges of rotation as the invention would also work with any greater range of angle of rotation, for example from -10° to +10°. In a preferred embodiment of the present invention, the rotation and/or movement of the image or planar surface is controlled by electronic means, for example by means of a computer or a microcontroller. Similarly, it is preferred that adjustment performed by moving the scanner head is also controlled by such electronic means. Thus, it is preferred that the determined displacement (s) are stored electroni- cally. The adjustment of the position of the second image or the film carrying the second image may thus be controlled by electronic controlling means based on the stored determined displacement (s) . Similarly, the position of the scanner head when starting an image scanning of the second image may be controlled by electronic controlling means based on the stored determined displacement (s) . It should be understood that according to a method of the invention, identifying the alignment area(s) or mark(s) of the first image or determining of the position of the align¬ ment area(s) or mark(s) of the first image may be done manu¬ ally by a system operator by use of position digitizing means or based on scanned data representing a preview of the first image and associated alignment area(s) or mark(s) . However, when subsequently having scanned alignment area(s) or mark(s) of a second image, the displacement(s) of the alignment mark(s) of the second image may be determined automatically by calculations performed by use of electronic calculation means, for example a computer or a microcontrol¬ ler, based on scanning data representing the alignment area(s) or mark(s) of the first image and the alignment area(s) or mark(s) of the second image. An example of such an automatic determination routine is given in Example 1. It is also to be understood that the method described above also can be used when aligning any higher number of images, when each such image has to be aligned to a first image after identification of the alignment area(s) or mark(s) of the first image or after determination of the position of the alignment area(s) or mark(s) of the first image. Thus, it is preferred that three or four images are to be aligned and subsequently scanned, where each such image preferably repre¬ sents a colour separation of a colour image. A third object of the invention is to provide a scanning apparatus for aligning subsequently scanned images, each image being associated with at least one corresponding align¬ ment mark(s) positioned at a given position in relation to the image, the images being present on at least one film, where the apparatus comprises a substantially planar surface on which the film(s) is/are mounted during scanning, a scanning head which is adapted to be moved along a substantially linear path and at a substantially constant distance from the surface during scanning of a film or image, and rotating means for rotating the substantially planar surface at an angle. It is preferred that this scanning apparatus further com¬ prises means for moving the scanning head along the linear path, means for moving the substantially planar surface in a direction substantially perpendicular to the direction of movement of the scanner head, electronic calculation means for determining position(s) and/or displacement(s) of positions of alignment mark(s) during or after scanning of alignment mark(s), electronic storage means for storing the determined position(s) and/or displacement(s) of positions of alignment mark(s) , first electronic control means for controlling the move¬ ment of the scanning head, second electronic control means for controlling the movement of the substantially planar surface in the direction substantially perpendicular to the direction of movement of the scanner head, and third electronic control means for controlling the angle of rotation of the substantially planar surface. A fourth aspect of the invention provides for a scanning apparatus for aligning subsequently scanned images, each image being associated with at least one corresponding align¬ ment mark positioned at a given position in relation to the image, the images being present on at least one film, where the apparatus comprises a substantially planar surface on which the film(s) is/are mounted during scanning, a scanning head which is adapted to be moved along a substantially linear path and at a substantially constant distance from the surface during scanning of a film or image, means for moving the scanning head along the linear path, means for moving the substantially planar surface in a direction substantially perpendicular to the direction of movement of the scanner head, electronic calculation means for determining position(s) and/or displacement (s) of positions of alignment mark(s) during or after scanning of alignment mark(s), electronic storage means for storing the determined position(s) and/or displacement (s) of positions of alignment mark(s) , first electronic control means for controlling the move¬ ment of the scanning head, and second electronic control means for controlling the movement of the substantially planar surface in the direction substantially perpendicular to the direction of movement of the scanner head. Preferably, this apparatus further com¬ prises rotating means for rotating the substantially planar surface at an angle, and third electronic control means for controlling the angle of rotation of the substantially planar surface. It is preferred that the third electronic control means is adapted to control the angel of rotation of the substantially planar surface, so as to for subsequently scanned images at least partly cancel out relative displacements of the images, said control being based on the determined position(s) and/or displacement(s) of positions of alignment mark(s). Prefer¬ ably, the third electronic control means is adapted to con- trol the rotating means so as to rotate the substantially planar surface before scanning of an image. It is furthermore preferred that the second electronic con¬ trol means is adapted to control the movement of the substan- tially planar surface so as to for subsequently scanned images at least partly cancel out relative displacements of the images in a direction substantially perpendicular to the direction of movement of the scanner head, said control being based on the determined position(s) and/or displacement (s) of positions of alignment mark(s). Similarly, it is preferred that the first electronic control means is adapted to control the movement of the scanner head so as to for subsequently scanned images at least partly cancel out relative displacements of the images in a direc- tion substantially parallel to the direction of movement of the scanner head, said control being based on the determined position(s) and/or displacement(s) of positions of alignment mark(s) . The invention furthermore relates to a fifth aspect which provides for a scanning apparatus for digitizing images and aligning subsequently scanned images, each image being asso¬ ciated with at least one corresponding alignment area or mark positioned at a given position in relation to the image, said apparatus comprising a substantially planar surface on which the images are arranged during scanning, a scanning head which is adapted to scan the images and the associated alignment area(s) or mark(s), electronic calculation means adapted to determine dis- placement (s) of corresponding scanned alignment area(s) or mark(s) associated with a first and a second image, respecti¬ vely, of two images to be subsequently scanned, elec¬ tronic storage means for storing the determined displace¬ ment^) of alignment area(s) or mark(s), and first electronic control means for controlling the scan¬ ning of the images by use of the scanner head so as to at least partly cancel out determined displacemen (s) of align¬ ment area(s) or mark(s) . In a preferred embodiment of the scanning apparatus according to the fifth aspect of the invention the apparatus further comprises means for moving the substantially planar surface and/or the scanning head along a substantially linear path during scanning, and second electronic control means for controlling the movement of the substantially planar surface and/or the movement of the scanning head, so as to further at least partly cancel out determined displacement (s) of align¬ ment area(s) or mark(s) . It is also or alternatively pre¬ ferred that the scanning apparatus according to the fifth embodiment of the invention comprises rotating means for rotating the substantially planar surface at an angle, and third electronic control means for controlling the angle of rotation of the substantially planar surface, so as to fur¬ ther at least partly cancel out determined displacement (s) of alignment area(s) or mark(s). In a preferred embodiment of the scanning apparatus according to the invention, the rotation means is adapted to rotate the substantially planar surface at an angle in the range of -1° to +1°, preferably in the range of -0.4° to +0.4°. It is furthermore preferred that the first electronic control means is adapted to cancel out at least partly determined displacement(s) of alignment area(s) or mark(s) by control¬ ling the scanning of the second image or any subsequent images to be scanned. Similarly, it is preferred that the second electronic control means is adapted to at least partly cancel out determined displacement (s) of alignment area(s) or mark(s) by controlling the movement of the substantially planar surface or the movement of the scanner head. 13 In order to determine the displacement (s) of alignment area(s) or mark(s), it is preferred that the electronic calculation means is adapted to perform an auto correlation of scanning data representing alignment areas or marks of images to be subsequently scanned. In a preferred embodiment the scanning apparatus is a flat bed scanner. It is also preferred that the scanning head comprises at least one CAD-element. Other aspects of the invention appear from the claims. The invention can be more fully understood from the following detailed examples when taken in conjunction with the accom¬ panying drawings, in which: Fig. 1 shows a film having one image and its associated alignment marks, Fig. 2 shows a film having 4 images with associated alignment marks, and Fig. 3 shows a schematic drawing of a scanning apparatus according to a preferred embodiment of the invention. EXAMPLE 1 In the following, the process and apparatus of the invention will be described by way of an example, where a number of colour separations of a colour image is to be superpositioned in order to generate the original image. In the present example, the individual separations or images are positioned individually, each on its own transparent film, which may be adhered to a job-sheet preferably having registering holes for precise positioning on the scanner. The separations themselves have no registering holes - only alignment or registering areas or marks. In the present example the alignment areas or marks can be marks such as crossed lines provided during printing or plotting of the colour separations of the original image. This is illustrated in Fig. 1 which show an image 2 presented on a film 1. The film 1 also bears alignment marks 3a, 3b, 3c and 3d associated with the image 2. The alignment marks are positioned at given positions in relation to the image 2, which may represent one colour separation; for the other separations of the colour image the alignment marks should be placed in the same position in relation to the image. In Fig. 1 is shown 4 alignment marks, however images having l, 2, 3 or any convenient number of alignment marks can be scanned according to the invention. The manual method of superpositioning these separations is precisely positioning the films of images on the job-sheets so that the registering marks of the films when positioned on the scanner are positioned as close as possible to the same position. Typically, a positioning precision of 5/100 mm is required. Thus, this positioning operation is time consuming. After positioning of the images, these images are scanned and processed in order to superpose these and regenerate the original image in a page layout. In the present example each film carrying an image and asso¬ ciated alignment marks is adhered to a job-sheet having registering holes for positioning of the job-sheet on the scanner. Each image should preferably be adhered at the same position in relation to the registering holes of the job- sheet, thereby ensuring that the alignment marks of images to be subsequently scanned are within the alignment area to be scanned. This can be obtained by identifying the alignment marks of each corresponding image and having these substan¬ tially aligned when adhering the image carrying films to the job-sheets. However, the precision required in this operation is of the order of 1 mm and thus several orders of magnitude smaller than the precision required for fully manually align¬ ing the images. According to the present example, the separations are scanned one at the time and subsequently processed as described below. Before scanning of an image, areas comprising alignment marks of the first image to be scanned are identified, which iden- tification is presently performed by, on the film carrying the first image to be scanned, positioning a digitizer at the position or close to the position of each of the marks to be used for the alignment so as to approximately defining the positions of these alignment marks. The areas corresponding to the alignment marks of the images to be subsequently scanned are identified or approximately defined through the identification of the alignment marks of the first image. In the following, two alignment marks are used. First, the identified two alignment marks of the first image are scanned followed by a scan- of the first image. Hereafter, the second film is placed on the scanner with its alignment marks appro¬ ximately arranged at positions corresponding to the positions of the alignment marks of the first image during scanning of this first image. Now, the second film is at least partly scanned, the scanning comprising the area including the alignment marks, and from the scanned data the displacements of the second image in relation to the first image is determined as described in the below procedure. After determination of the displacement of the second image this displacement is adjusted for as described below, and a full scan of the second image is performed. The above mentioned steps of aligning and scanning of the second image are preferably followed when aligning and scan¬ ning subsequent images. The separations may be scanned with a resolution of 250 lines/cm. In this situation, the presently used area scanned in order to identify the alignment mark will correspond to 5,12 x 5,12 mm 2 , resulting in an image size of 128x128 pixels in 8 bits pixels. Naturally, other resolutions may be used depending on the resolution obtainable by the scanner used. In this preferred embodiment, a given precision when defining the areas of the alignment marks is required in order to ensure that the alignment marks of the subsequent images are within the scanned area of approx. 5x5 mm 2 . However, the precision required in this operation is several orders of magnitude smaller than the precision required for fully manually aligning the images. Each of these smaller scanned images is Fourier transformed using 50% zero filling in order to avoid edge effects. The image is high pass filtered by using a box filter having a size of 10x10 values on the transformed image, now consti¬ tuted by 256x256 values. During the filtering all values within a box of size 10x10 values around the zero frequency values are set to zero; the frequencies outside this box remain unchanged. Determining the displacement of an alignment mark of a subse¬ quent image compared to the corresponding alignment mark of the first scanned image is performed by: a) scanning on the subsequent film the area identified on the first film, b) subjecting the scanned area of the first film to the above procedure, c) subjecting the scanned area of the subsequent film to the above procedure, and d) complex conjugating the Fourier transformed image corre¬ sponding to the second film and multiplying the two trans¬ formed images. The multiplied Fourier spectre is inversely Fourier trans¬ formed and the highest value in the resulting image is found by simply checking all values in the 256x256 cross correlated image. The above procedure is similar to a cross correlation between high pass filtered versions of the two scanned small areas. From this cross correlated image, the following procedure will determine the displacement between the alignment marks. If only a small precision of the determination of the dis¬ placement between the marks is required, the position of the pixel in the cross correlated image having the largest value will be used to determine this displacement. However, if a better precision is desired, one can assume that the scanned image contains no abrupt shifts and that it, consequently, may be interpolated by e.g. a low-order poly¬ nomial in order to better identify the actual position of the peak. This assumption is typically valid for this type of data. In the presently preferred operation, the pixel values of the eight pixels closest to the highest-value-pixel are compared, and that of those pixels having the highest value is iden¬ tified (the highes -value-neighbour) . Subsequently, it is assumed that the actual peak value is positioned in the area between four neighbouring pixels defining a square and comprising the highest-value-pixel and the highes -value-neighbour. Therefore, the 4x4 pixels symmetrically positioned around the four-pixel square comprising the highest-value-pixel and the highest-value-neighbour are fitted by a 2D Lagrange poly¬ nomial of third order. This, in effect, corresponds to low pass filtering the image. From this Lagrange polynomial, the position of the highest value may be determined with a precision of +/- a half pixel at 1000 lines/cm. This should be compared to the precision obtainable if no interpolation is used, i. e. corresponding to the resolution of the scanning which is typically 250 lines/cm. The displacement of the mark of the subsequent image compared to that of the firstly scanned image may be found as the difference of positions from the position of the maximum value and the centre of the correlated image using the reso- lution of the scanned image. From the determined displacements of the alignment marks of the two images, the subsequent image may be moved so as to cancel out or remove at least part of this displacement. Subsequent to this displacement, the subsequent image is scanned in a controlled manner taking into account a dis¬ placement, if any, in the direction of movement of the scan¬ ner head. If only one alignment or registering mark is scanned corre¬ sponding to each image, a translation of the subsequent images may be performed. If more than one alignment mark is used, also a rotation of the subsequent images may be per¬ formed in order to more precisely adapt the positioning of the subsequent images to that of the first image. Presently, the actual displacement of the image is provided on the flat bed of the scanner - preferably an ESKOSCAN 2024 manufactured by ESKOFOT A/S, Denmark, - by actually translat¬ ing and/or rotating the flat bed. As this displacement may be performed quite precisely, the resulting displacement of the images may easily obtain a final resolution where the align¬ ment marks of all e.g. four separations of a colour image are positioned within 0.05 mm. This precision may only be obtained manually with great difficulty. The ESKOSKAN 2024 scanner scans an image by scanning the image in bands or stripes of max. 1 cm and by moving the flat bed of the scanner so as to scan a new band. Thus, the flat bed is moved in a direction perpendicular to the direction of movement of the scanner head. The additional rotation of the flat bed of the scanner com¬ pared to normal scanning is preferably performed using a step motor. Thus, using the above-mentioned preferred scanner, the dis¬ placement of a subsequent image compared to that of the first image is removed by first rotating the flat bed in accordance with the determined angular difference - if any. As the preferred rotation is preferably performed around a center positioned at a corner of the flat bed and, thus, not necessarily close to the image, the rotation will not only rotate the image, but also translate this slightly. Consequently, this translation should be taken into account when determining the movement of the flat bed and when deter¬ mining the displacement of the starting point of the subse¬ quent image scanning. At present, the step motor rotating the flat bed of the scanner is able to rotate the flat bed a total of ±0.4°, which gives a certain limit to the original positioning error of the image on the flat bed which can be compensated for. However, it will be possible to provide a scanner having a larger possible rotation of the flat bed, such for example as ±1° or ±10°. The above procedure is not sensitive to the actual position of the identifying pointer in relation to the alignment mark. The final result of the operation performed on the data representing the scanned alignment marks of the two corre¬ sponding images, is the position in which the probability is the largest for the information of the two images to overlap, whereby it, naturally, will be best if the mark is totally inside the area, as this generates the results with the highest reliability. Even if a smaller part of the mark is in the area, the procedure will result in an approximately correct determined displacement. In addition, the method is insensitive to the actual align¬ ment mark used. Substantially all types of alignment marks may be used, as, as mentioned above, this statistical method merely provides information relating to the position where the information of the two images has the highest possibility of over1apping. Fig. 3 shows a schematic drawing of a scanning apparatus according to the invention. In Fig. 3 a film 1 having an image 2 with associated alignment marks 3a, 3b is to be aligned for subsequently image scanning of the image 2. The film 1 is mounted or adhered to a substantially planar sur¬ face 12, preferably by using vacuum. The film or image is scanned by a scanning head 13 comprising a camera 14, where the scanning head 13 during scanning is moved along a sub- stantially linear path in the direction indicated by an arrow C following guiding rails 16a, 16b. The camera 14 of the scanning head 13 comprises a CCD element, with the longitudi¬ nal extension of the CCD element substantially perpendicular to the direction of movement of the scanner head 13. The planar surface 12 can be rotated around an axis perpen¬ dicular to the planar surface 12 by an angle A in order to align the image to be scanned, and the planar surface 12 can be moved in a direction which is substantially perpendicular to the direction of movement of the scanning head 13 as indicated by an arrow B following guiding rails 15a, 15b. In a preferred embodiment the image to be aligned is firstly rotated an angle by rotating the planar surface 12 in order to adjust for any errors of rotation between the position of the image to be scanned and the position of the first scanned image. Hence, any remaining errors in the direction of B is substantially cancelled by moving the planar surface 12 in the direction of B. For any remaining errors in the direction of C, the scanning head can be moved so as to substantially cancel out such errors. This is preferably done when scanning the image by selecting the starting point of the scanning of the image so as to take into account any such difference between the position of the first image and the position of the image to be scanned. However, the scanning head may also be moved to the determined starting point without being part of the actual scanning process. In the below Example 2, four images with associated alignment marks are presented of the same job-sheet. EXAMPLE 2 In the following is described an example referring to the situation where more than one image with associated alignment marks are positioned on the same job-sheet. This is illu¬ strated on Fig. 2 which shows a job-sheet 4 having four films 13, 14, 15 and 16 with respective images 5, 7, 9 and 11 and associated alignment marks 6a, 6b, 8a, 8b, 10a, 10b and 12a, 12b. In the example of Fig. 2 each image has two associated alignment marks being positioned a given positions in rela¬ tion to the image. In this example the four films are adhered to the job-sheet by a coarse manual alignment so that the four images are positioned approximately parallel to each other. Thus, if the positions of the two alignment marks 6a, 6b of image 5 are known, it is sufficient to know the position of alignment mark 8a in order to determine the position of alignment mark 8b of image 7. Once the films have been adhered to the job-sheet, areas comprising a first corresponding alignment mark of each image are identified, which identification is performed by, on the film carrying the images to be scanned, positioning a digitizer at the position or close to the position of each of the first marks to be used for the alignment so as to approx¬ imately defining the positions of these first alignment marks. For the first image to be scanned the area to be scanned around the second alignment mark is also defined in this way. Having identified the areas to be scanned of the first align¬ ment marks of the four images and the area to be scanned of the second alignment marks of the first images, the areas to be scanned of the second alignment marks of the remaining three images to be subsequently scanned can be determined. In the following scanning process, the areas of the two alignment marks of the first image are scanned, followed by a scanning of the first image. Then the areas of the two align¬ ment marks of the second image are scanned, followed by a determination of displacements of the alignment marks of the second image, an adjustment of the position of the second image, followed by a scanning of the second image. Having scanned the alignment marks of the second image, the procedure of Example 1 is repeated for each pair of marks in order to determine the displacements of the alignment marks of the second image, and hence, the displacement of the second image in relation to the first image. The adjustment of the position of the second image may be performed by, based on the determined displacements, rotating the planar surface of the scanning apparatus on which the job-sheet is arranged and/or by moving the planar surface in a direction substantially perpendicular to a direction of movement of the scanner head. This adjustment is done to partly cancel out the determined displacements, while the remaining determined displacements are cancelled out by controlling or moving the position of the scanner head when scanning the second image. The scanning procedure for the third and fourth images to be scanned follows the scanning procedure of image two. Natural¬ ly, this procedure may be performed for any number of images positioned on the same job-sheet.

Claims: CLAIMS 1. A method of aligning at least two images to be scanned, each image being associated with at least one corresponding alignment area or mark positioned at a given position in relation to the image, which images when scanned are arranged on a substantially planar surface of a scanning apparatus for digitizing images, said method comprising identifying the approximate position of at least one corresponding alignment area or mark associated with each of the images, a first scanning process comprising scanning at least part of the at least one alignment area or mark of the first image, a second scanning process comprising scanning at least part of the at least one alignment area or mark of the second image, determining the displacement (s) of each of the at least one alignment area(s) or mark(s) of the second image in relation to the at least one alignment area(s) or mark(s) of the first image, and cancelling out at least partly the determined displace¬ ment(s) of alignment area(s) or mark(s) of the second image. 2. A method according to claim 1, wherein the first scanning process comprises scanning the first image, said scanning of the first image preferably being performed after or before scanning of the alignment area(s) or mark(s) of the first image, and/or the at least partly cancelling out of the determined displacements is followed by a third scanning process comprising scanning the second image. 3. A method according to claim 2, wherein the image is moved along a substantially linear path during scanning, and/or wherein the scanner comprises a scanning head which is moved along a substantially linear path during scanning, said movement of the image and/or the scanning head preferably defining a direction of scanning. 4. A method according to any of claims 1-3, wherein the scanning is performed by scanning the alignment area(s) or mark(s) and/or images in bands or stripes. 5. A method according to claim 3 or 4, wherein the scanning head or the images being scanned is/are moved in a controlled movement so as to at least partly cancel out determined displacement (s) of alignment area(s) or mark(s) in a direc¬ tion substantially perpendicular to the direction of scan¬ ning. 6. A method according to any of the preceding claims, wherein the images and their associated alignment areas or marks are present on at least one film or job-sheet, which film(s) or job-sheet(s) when the alignment areas or marks and/or images are scanned is/are mounted on the substantially planar sur- face of the scanning apparatus. 7. A method according to claim 6, wherein each image and its associated alignment area(s) or mark(s) is/are present on a separate film or job-sheet. 8. A method according to any of the preceding claims, com- prising cancelling out at least partly the determined dis¬ placement(s) of alignment area(s) or mark(s) by controlling the scanning of the second image, and/or by adjusting the position of the second image. 9. A method according to claim 3, wherein the determined displacement(s) is/are at least partly cancelled out in a direction substantially parallel to the direction of the movement of the scanning head and/or the movement of the images. 10. A method according to any of the preceding claims, where- in the identified alignment area(s) or mark(s) of each image is/are part of the image itself. 11. A method according to any of the claims 1-10, wherein the identified alignment area(s) or mark(s) of each image is/are positioned outside an area covered by the image. 12. A method according to any of the preceding claims, where- in each image has at least two associated alignment areas or marks positioned at given positio (s) in relation to the image, and wherein the at least partly cancelling out of determined displacemen (s) comprises a rotation of the second image around an axis perpendicular to the planar surface, said rotation of the image preferably being performed by rotating the planar surface of the scanning apparatus. 13. A method according to claim 12, wherein the angle of rotation of the image is in the range from -1° to +1, prefer¬ ably in the range from -0.4° to +0.4°. 14. A method according to claim 4, wherein the scanning of the second image is controlled so as to have a starting point having a displacement in relation to a corresponding starting point of the scanning of the first image, said displacement being substantially equal to the remaining part of the deter- mined displacement(s) of alignment area(s) or mark(s) in a direction substantially parallel to the direction of the bands of scanning. 15. A method of aligning at least two images to be scanned, each image being associated with at least one corresponding alignment mark positioned at a given position in relation to the image, each image being present on a film, which films when scanned are mounted on a substantially planar surface of a scanning apparatus having a scanning head which is moved along a substantially linear path during scanning, said method comprising scanning at least part of a film comprising a first image and the at least one corresponding alignment mark(s) , determining the position(s) of the at least one alignment mark(s) of the first image, 27 scanning at least part of a film comprising a second image and the at least one corresponding alignment mark(s), determining the displacement (s) of the position(s) of each of the at least one alignment mark(s) of the second image in relation to the determined position(s) of the at least one alignment mark(s) of the first image, and cancelling out or removing at least partly the determined displacement(s) of position(s) of alignment mark(s) in a direction substantially perpendicular to the direction of movement of the scanner head by adjusting, on the basis of the determined displacemen (s) , the position of the film carrying the second image in relation to the position of the first image. 16. A method according to claim 15, further comprising cancelling out or removing at least partly a remaining dis¬ placement of the determined displacement(s) of position(s) of alignment mark(s) in a direction substantially parallel to the direction of movement of the scanner head, said at least partly cancelling being performed by controlling the scanning of the second image. 17. A method according to claim 15, wherein the adjustment of the position of the film carrying the second image in a direction substantially perpendicular to the direction of movement of the scanner head is performed by moving the planar surface of the scanning apparatus in a direction substantially perpendicular to the direction of movement of the scanner head. 18. A method according to any of claims 15-17, wherein each image has at least two associated alignment marks positioned at given position(s) in relation to the image, and wherein the adjustment of the position of the film carrying the second image comprises a rotation of the film around an axis perpendicular to the planar surface, said rotation of the film preferably being performed by rotating the planar sur- face of the scanning apparatus. 19. A method according to claim 18, wherein the angle of rotation of the film is in the range from -1° to +1, prefer¬ ably in the range from -0.4° to +0.4°. 20. A method according to claim 16, wherein the scanning of the second image is controlled so as to have a starting point having a displacement in relation to a corresponding starting point of the scanning of the first image, said displacement being substantially equal to the remaining displacement of the determined displacement(s) of position(s) of alignment mark(s) in the direction substantially parallel to the direc¬ tion of movement of the scanner head. 21. A method according to any of the preceding claims, where¬ in the determined displacement (s) are stored electronically. 22. A method according to claim 21, wherein the at least partly cancelling out of determined displacement (s) is con¬ trolled by electronic controlling means based on the stored determined displacement (s) . 23. A method according to claims 8 and 21 or 16 and 21, wherein the image scanning is controlled by electronic con- trolling means based on the stored determined displace¬ ment(s) . 24. A method according to any of the preceding claims, where¬ in the identification or determining of position(s) of the at least one alignment area(s) or mark(s) of the first image is performed manually by a system operator by use of position digitizing means or based on scanned data representing a preview of the first image and associated alignment area(s) or mark(s) . 25. A method according to any of the preceding claims, where- in the displacement (s) of each of the at least one alignment area(s) or mark(s) of the second image is/are determined by calculations performed by use of electronic calculation means based on scanning data representing the at least one align¬ ment area(s) or mark(s) of the first image and the at least one alignment area(s) or mark(s) of the second image. 26. A method according to claim 25, wherein the calculations performed comprise an auto correlation of the scanned data representing the at least one alignment area(s) or mark(s) of the first image and the scanning data representing the at least one alignment area(s) or mark(s) of the second image. 27. A method according to any of the preceding claims, where- in at least three or at least four images are to be aligned and subsequently scanned, said images preferably representing colour separations of a colour image. 28. A method according to any of the claims 6-27, wherein the film is transparent and is placed between the scanning head and a source of illumination. 29. A method according to any of the claims 6-27, wherein the film is non-transparent and both the scanning head and a source of illumination are placed on the same side of the film. 30. A method according to any of the preceding claims, where¬ in the scanning apparatus is a flat bed scanner and the scanning head preferably comprises at least one CCD-element. 31. A scanning apparatus for aligning subsequently scanned images, each image being associated with at least one corre- sponding alignment mark(s) positioned at a given position in relation to the image, the images being present on at least one film, said apparatus comprising a substantially planar surface on which the film(s) is/are mounted during scanning, a scanning head which is adapted to be moved along a substantially linear path and at a substantially constant distance from the surface during scanning of a film or image, and rotating means for rotating the substantially planar surface at an angle. 32. A scanning apparatus according to claim 31, further comprising means for moving the scanning head along the linear path, means for moving the substantially planar surface in a direction substantially perpendicular to the direction of movement of the scanner head, electronic calculation means for determining position(s) and/or displacemen (s) of positions of alignment mark(s) during or after scanning of alignment mark(s), electronic storage means for storing the determined position(s) and/or displacement (s) of positions of alignment mark(s) , first electronic control means for controlling the move¬ ment of the scanning head, second electronic control means for controlling the movement of the substantially planar surface in the direction substantially perpendicular to the direction of movement of the scanner head, and third electronic control means for controlling the angle of rotation of the substantially planar surface. 33. A scanning apparatus for aligning subsequently scanned images, each image being associated with at least one corre¬ sponding alignment mark positioned at a given position in relation to the image, the images being present on at least one film, said apparatus comprising a substantially planar surface on which the film(s) is/are mounted during scanning, a scanning head which is adapted to be moved along a substantially linear path and at a substantially constant distance from the surface during scanning of a film or image, means for moving the scanning head along the linear path, means for moving the substantially planar surface in a direction substantially perpendicular to the direction of movement of the scanner head, electronic calculation means for determining position(s) and/or displacement (s) of positions of alignment mark(s) during or after scanning of alignment mark(s), electronic storage means for storing the determined position(s) and/or displacement (s) of positions of alignment mark(s) , first electronic control means for controlling the move¬ ment of the scanning head, and second electronic control means for controlling the movement of the substantially planar surface in the direction substantially perpendicular to the direction of movement of the scanner head. 34. A scanning apparatus according to claim 33, further comprising rotating means for rotating the substantially planar surface at an angle, and third electronic control means for controlling the angle of rotation of the substantially planar surface. 35. A scanning apparatus for digitizing images and aligning subsequently scanned images, each image being associated with at least one corresponding alignment area or mark positioned at a given position in relation to the image, said apparatus comprising a substantially planar surface on which the images are arranged during scanning, a scanning head which is adapted to scan the images and the associated alignment area(s) or mark(s), electronic calculation means adapted to determine dis¬ placement(s) of corresponding scanned alignment area(s) or mark(s) associated with a first and a second image, respecti¬ vely, of two images to be subsequently scanned, electronic storage means for storing the determined displacement (s) of alignment area(s) or mark(s), and first electronic control means for controlling the scan¬ ning of the images by use of the scanner head so as to at least partly cancel out determined displacement (s) of align¬ ment area(s) or mark(s). 36. A scanning apparatus according to claim 35, further comprising means for moving the substantially planar surface and/or the scanning head along a substantially linear path during scanning, and second electronic control means for controlling the movement of the substantially planar surface and/or the movement of the scanning head, so as to further at least partly cancel out determined displacement(s) of alignment area(s) or mark(s) . 37. A scanning apparatus according to claim 35 or 36, further comprising rotating means for rotating the substantially planar surface at an angle, third electronic control means for controlling the angle of rotation of the substantially planar surface, so as to further at least partly cancel out determined displacement(s) of alignment area(s) or mark(s). 38. A scanning apparatus according to claim 32 or 34, wherein the third electronic control means is adapted to control the angel of rotation of the substantially planar surface, so as to for subsequently scanned images at least partly cancel out determined displacement (s) of alignment area(s) or mark(s). 39. A scanning apparatus according to claim 37 or 38, wherein the third electronic control means is adapted to control the rotating means so as to rotate the substantially planar surface before scanning of an image. 40. A scanning apparatus according to claim 31 or 34 or any of claims 37-39, wherein the rotation means is adapted to rotate the substantially planar surface at an angle in the range of -1° to +1°, preferably in the range of -0.4° to +0.4°. 41. A scanning apparatus according to any of the claims 32 or 34-40, wherein the first electronic control means is adapted to cancel out at least partly determined displacement (s) of alignment area(s) or mark(s) by controlling the scanning of the second image or any subsequent images to be scanned. 42. A scanning apparatus according to any of the claims 32 or 34-40, wherein the second electronic control means is adapted to at least partly cancel out determined displacement (s) of alignment area(s) or mark(s) by controlling the movement of the substantially planar surface or the movement of the scanner head. 43. A scanning apparatus according to any of the claims 32 or 34-42, wherein the electronic calculation means is adapted to perform an auto correlation of scanning data representing alignment areas or marks of images to be subsequently scanned. 44. A scanning apparatus according to any of the claims 31- 43. wherein the scanning apparatus is a flat bed scanner. 45. A scanning apparatus according to any of the claims 31-44 wherein the scanning head comprises at least one CCD-element.

Inventors: DYBDAL NIELS, ELL SOEREN CHRISTIAN, HEDEGAARD CHRISTEN, HEMMINGSEN HANS, JENSEN KIM SKOVGAARD, MOSELUND KJELD, DYBDAL, NIELS, ELL, SOEREN, CHRISTIAN, HEDEGAARD, CHRISTEN, HEMMINGSEN, HANS, JENSEN, KIM, SKOVGAARD, MOSELUND, KJELD
Applicants: DYBDAL NIELS, ELL SOEREN CHRISTIAN, ESKOFOT DIGITAL GRAPHIC SYSTEM, HEDEGAARD CHRISTEN, HEMMINGSEN HANS, JENSEN KIM SKOVGAARD, MOSELUND KJELD, DYBDAL, NIELS, ELL, SOEREN, CHRISTIAN, ESKOFOT DIGITAL GRAPHIC SYSTEMS APS, HEDEGAARD, CHRISTEN, HEMMINGSEN, HANS, JENSEN, KIM, SKOVGAARD, MOSELUND, KJELD
Application year: 1996
Main classification: G03F9
IPC codes: G03F9, G06T1, H04N1