METHOD OF AND DEVICE FOR CODING AND DECODING AN IMAGE OF AN OBJECT BY MEANS OF PENETRATING RADIATION

Abstract: A method of and a device for the coding and decoding of an object by means of point-shaped radiation sources. The point sources are subdivided in groups which successively irradiate the object. Two sources distributions can be derived from the groups of radiation sources (a negative radiation intensity is assigned to at least one group), the sum of the autocorrelation functions thereof having the value "0" outside the origin. The coded images generated by means of the various groups are recorded (and also their negatives). Combinations of a coded image and a negative are decoded via point holograms or lens matrices, thus forming a subimage. The sum of all subimages forms an object image which is free of artefacts.

Description: "Method of and device for coding and decoding ax_ image of an object by means of penetrating radiation". The invention relates to a method of coding and decoding an image of an object by means of radiation which is emitted by point sources and which irradiates the object in different directions in order to form shadow 5 images of the object which are superposed on a recording medium, the coded image thus formed being decoded by convolution of the superposed shadow images with a function which is determined by the point' source distribution used for irradiating the object. 10 The invention furthermore relates to a device for coding and decoding an image of an object by means of penetrating radiation, said device comprising for the coding of an image of an object a two-dimensional dis¬ tribution of point sources and a two-dimensional image 15 recording medium which are situated in two parallel planes at a distance from each other in order to form superposition Images of the object, said device comprising for the decoding of the superposition images means for convoluting the recorded superposition images with at 20 least a part of an image point function which is defined by the point source distribution, and means for summing the convoluted superposition images. It is known that objects can be coded by irradiat¬ ing the object from different positions by means of X- 25 rays or other incoherent radiation and by recording the shadow images on a recording medium. Thus, a super¬ position image is obtained in which the information con¬ cerning the object is not directly accessible. The object or a layer object can be made visible again only during 30 a second phase, i.e. the decoding of the superposition image. A method and a device of the described kind are known from German Patent Application NO. P 25.35. 08.9 The decoding by means of the known specific arrays of the recording sources using incoherent or also coherent point distributions produces artefacts which prevent the signal-to-noise ratio from exceeding a given threshold. The invention has for its object to provide a method of and a device for the coding and decoding of images of the described kind in which the object is decoded without disturbing artefacts. To this end, a method in accordance with the in— vention is characterized in that the point sources are arranged according to a regular matrix, at least three different groups of point sources being used to form a corresponding number of superposition images in succession a combination of groups forming a first source distributio function and a further combination of groups forming a second source distribution function, the sum of the auto¬ correlation functions of said source distribution function having the value zero except in one point (origin), after which the different superposition images, or combinations with the negatives thereof, are convoluted with image poin functions of the groups of sources in order to obtain convoluted images which are summed in order to obtain a decoded image. The combinations of groups which produce a first and a second source distribution function having the said property (the sum of the autocorrelation functions is zero with the exception of a value in one point (the origin) ) are referred to as complementary combinations or complementary source distribution functions. In the case of self-radiating objects, the array of radiation sources is effectively replaced by a cor¬ responding array of diaphragms with holes wherethrough the radiation emitted by the object passes and is incident on a recording medium. The method can be used for two- dimensional as well as three-dimensional objects. In the case of three-dimensional objects, the reconstruction of the individual layers can be continuously performed by changing the scale of all superposition images on the recording means. OMP /_. WIP The artefact-free decoding of a layer may be understood to mean that the radiation sources, are sub¬ divided into groups of each time positive sources (recording on a positive film) and negative sources (recording on a negative film) , so that the sum of the autocorrelation of the distributions in the origin has a high value, corres¬ ponding to the sum n of all sources, and that no secondary points occur in the sum of the autocorrelations of the two point source distributions. The decoded image is produced exactly with a mean intensity which is proportional to the value of the autocorrelation sum in the origin. It is to be noted that one—dimensional complementary codes have the arithπietical property that the sum of their autocorrelation consists of a maximum without''-secondary points (see IRE Transactions on Information Theory, Vol. ~ , pages 82-87. 1961, M.J.E. Golay) . The invention, however, is based on the use of complementary two-dimensional point codes, the two coherent codes being different and complementary in a sense that the sum of their autocorrelation has the previously described properties. A device in .accordance with the invention is characterized in that for the coding the device comprises means for the sequential activation of the point sources in at least three and at the most four different groups in order to obtain at least three coded images, a first number of groups of point sources forming a first distribution function and a second number of groups forming a second distribution function, the sum of the autocorrelations of said distribution functions having the value zero except in one point (origin), for the decoding the device com¬ prising means for convoluting, either sequentially or simultaneously, the coded images with an image point function associated with the coded images, each of which is determined by a different group of point; sources. The decoding of the object can be performed by means of a computer, by analog electronic or by optical methods. The optical decoding can also be realized by means of a four-channel optical system, as will be described O PI hereinafter. The invention will be described in detail herein¬ after with reference to the accompanying diagrammatic d awin . Figure 1a) shows complementary point codes of the order 4, Fig. 1b) the autocorrelation of the two codes "and their sum, Figures 2.a_ and 1_ show a complementary code of the order .6 and diferent distributions of the points in 4 groups, respectively, Figure shows complementary codes of the order n, n having the value 1, 2, 4, 8 and 16, Figure 4 shows the combination of codes of lower order in order to form codes of higher order, Figure 5 shows complementary codes of the order n, n having the value 3/2 , 5 and 10, Figures 6a.—d show radiation source distributions according to the complementary codes of the order n, n having the value 3/2, 5 . 10 and 20, with code rotation and overlapping combination, Figure 6_e shows a slanted radiation source dis¬ tribution, Figure ~ shows an arrangement for forming coded images, Figure 8 shows an arrangement for decoding the coded images obtained by means of the arrangement shown i Figure ~ , Figure 9 shows a part of the optical system of th arrangement shown in Figure 8, Figure 10 shows an electro-optical device for the coding and the immediate decoding of a layer of τhe objec and Figure 11 is a detailed view of a part of the arrangement shown in Figure 10. Figure 1 illustrates the principle on the basis o a pair of complementary point distributions (codes A, B with points + and -). An object 0 is recorded once by mea of a point distribution with the code A, so that a coded ■ -5- image 0' of the object 0 is formed according to the cor¬ relation 0' A = 0 x A ( 1 ) means "convolution". The object 0 is recorded a second time with the point source distribution B, so that the coded image: 0' B = 0 x B (2) is formed. Each of these two coded images is then subjected to a correlation with the point image distribution function A and B, respectively, resulting in 0" A = 0 x A:©A (3) 0" B = 0 x B ©B (4) " When the images 0" and 0" thus obtained are added, the following is obtained 0" = 0" A + 0" B = 0 x (A ( ) A + B @ B) (5) Figure 1b shows the autocorrelations of the point source distributions A and B and the sum of both autocorrelations. The distributions A and B are chosen so that the sum of their autocorrelation has a value only in the origin M, so arithmetically it is a £ -function, so that the equation (5) can be rewritten as: 0" = 0 x £ - 0 (6) Formule (6) demonstrates that the object has been faithfully reconstructed. Figure 2 shows an example of the- coding of the ob¬ ject, a recording being made, for example, on X-ray film by means of X-rays. The complementary point source distributions are of the order 16 in Figure 2a and can be subdivided into four groups in a different manner before the recording. The distributions chosen by way of example are shown in Figure 2b. The distribution P.. is based on the fact that each time the code point distributions A and B are separately subdivided, that is to say four recordings of the object 0 are made, each time with the point source distribution g-i . goj h and h ; g D and h„ being "negative" sources. OMPI This means that the shadow images formed by means of g_. and h are subtracted from the shadow images formed by means of g- and h.. , respectively. Coded images according t (l) and (2) are then obtained 0 « A = 0 x βl - 0 x g 2 = 0^ - 0^ (7) in which X-ray tubes which are simultaneously flashed. Decoding Is realized by the correlation according to (3) and (4) °" = -° ~ ~ ° - ® ( *1 - *2> + ( - °h > © ^ - °fc, ) ®*1 ÷ < <> *,, * ° βl ) © ^ + ( \ - ° 2 ) ® h 1 + ( °h_- ® ^ (9) The four additions of the equation (9) can be realized, for example, in four optical channels, as will be described hereinafter. However, from the coded image 0 , 0 , 0, , 0, negatives also have to be made and henc S- g " ■ - h 2 the combinations O - 0 , 0 - 0 , 0, - 0, . 0, - 0 S , S 2 S 2 δ 1 " . ~ - ~ ~Z ~ - he combinations are convolute with the point distribu¬ tions ~ - , , 1 , h p , respectively, and are subsequently summed. Instead of using the distribution P.. during the recordings, it is alternatively possible to use the dis¬ tribution P 2 shown in Figure 2b. This distribution offers the advantage that it is disjunct, which means that each radiation source is used only once for the formation of coded images. The reconstruction of the object is again realized in four channels, because the distributions A and B can be composed from the distributions t_ , t_, s_, s~« Moreover, on the basis of the distribution ~ - of Figure 2b, three recordings may also suffice if the complementary code pair has the property which only means that the source positions of the two codes A and B correspond exactly. It follows from (lθ) that: -7- = g 1 + g - h. ( 1 1 ) so that 0 - 0 + 0 - 0 ( 12 ) 2 δ 1 g 2 1 Insertion of ( l 2 ) in ( 9 ) produces 0" = (0 - 0 ) © g + (0 - 0 ) © g- + s . s 2 ~2 fe 1 { z - - " -,-_ ■ ® h ι + ( ° gl + °. 2 - 2 - ® ~ - ( 13 ) so that only the three recordings O , O and O, are required. Four channels are still required for the re¬ construction. The number of channels for the reconstruction can also be reduced to three, because it also follows from (lθ) that g 2 = h η + h 2 - g 1 " 0*0 and insertion of (14) in (13) results in -, (2.0 g2 - 2.0 ) ® 2 where only three recordings are made and only three channels are required for the reconstruction. In addition to*- the described possibility -, there are other possibilities of reducing the number of recordings and or channels for the reconstruction to three by way of (lθ). For example, the possibility can be chosen where in total the smallest number of sources is used for all exposures together. This is technically advantageous and it also means a lower radiation load for a patient to be irradiated. The order of the complementary codes indicates how many X-ray tubes in a point source distribution are used for forming coded images of the object. The described method of coding and decoding is applicable to flat, two- dimensional objects. The layers of an arbitrary three- dimensional object can be decoded by changing the scale of the coded images as described in German Offen- legungsschrift 25.35.408.9 (= PH 75-122c). In order to find the complementary codes, the in athematical rules for forming the complementary codes OMPI _. IPO ^ are described hereinafter. I. Properties of complementary codes. Some definitions. If A is a code, -A or the inverse code of A indicates the code where each +1 is changed into a -1 and vice versa. Two codes A and B are called disjunct if no position of a source of A corresponds to a position of a source of B. The sum of two disjunct codes A and B is denoted as A + B and is defined as the code produced by combination of A and B. Each source in A + B, therefore, was already a source in A or B where it had the same value +1 or -1. The sum of two codes A and -B is also indicated as the differe ce of A and B and is written as A - B. Using these definitions, the following definitions can be demonstrated by simple algebra: Rule: When A and B are complementary codes, the following codes are also complementary: 1 ) B and A. 2) A and-B. 3) A and any translation of B. 4) A and the rotation of B through 180 . 5) Rotations of A and B through the same angle. 6) Mirror-images of A and B with respect to the same axis. 7) Stretchings of A and B in the same direction and by the same factor (also ζ_ 1. i.e. a compression) 8) Identical slanting of A and B. 9) A + B and A - B, if A and B are disjunct. A large number of further rules can be deduced from these rules by the successive execution of some of said operations, utilizing the above rules 1 to 9. II. Formation of complementary codes. Using a pair of complementary codes, new complementary codes having the same source numbers can be obtained by way of the rules 1 to 8. Using the rule 9. complementary code pairs having an increasingly larger number of sources can be step-wise obtained. The formation process is in general as follows: OM a) Take an already known pair of complementary codes (for example from the one-dimensional, see Figure 3)« b) Apply one of the rules 1 to 8 (also several times). c) Apply rule 9. d) Terminate the formation process with the newly obtained pair or continue at b). An important combination is that of b) and c) which implies the combination of B with A and -B with A, con¬ sisting of rule 3 and 9, (generalization of the one- dimensional combination which converts a pair of comple¬ mentary codes A, B, each of which comprises n sources, into a new pair of complementary codes, each of which ■ comprises 2n sources). A further possibility is the interleaving of A and B and of A and -B by way of the rule 3 (+ possibly twice the rule 7) and 9. III. Concrete codes. Two-dimensional complementary codes can be obtained in accordance with the combination of rules (under II) as follows: Use is made of the codes A and B, each of which consists of only one source +1. First a horizontal com¬ bination of B with A and -B and A is performed, the codes thus produced being renamed A and B. Subsequently, a similar vertical combination is performed, followed by a horizontal combination etc. Thus, for each integer n a pair of complementary codes of the order 2 is obtained and for each even n even source distributions which exactly form a square having the length and the width 2 ' . The first five pairs of complementary codes obtained according to this rule are shown in Figure ~ . IV. Invariability of complementary codes. The codes given in III and in Figure ~ represent; only some examples for complementary pairs. Obviously, as is indicat¬ ed sub II, complementary codes can also be derived from the rules given sub I in many other ways, notably by- rotation, mirror-imaging stretching and slanting of the cod¬ es given in Figure 3« The codes given therein, whose order is an odd OMPI V-- WIPO power of 2 ( ', 8, ...) have a rectangular shape instead o a square shape, the length of said rectangle being twice its width. However, using the general formation rule stated sub. II, codes with a distribution in an approxima- tely square area can also be indicated for these orders. To this end, it is ensured by rotation through (rule ) and stretching by the factor 2 (rule 7) that two complementary codes occupy exactly the black fields of an (imaginary) checkerboard. Translation in the horizo tal direction by one field to the left (rule 3) ensures that the first code occupies the black fields of the checkerboard and the second code occupies the white fields Subsequently, the two codes are interleaved in accordance with rule 9 » as described sub II. When the codes used as a basis define a source distribution in a square area, such a distribution will also be defined by the codes produced by interleaving (in any case, the square is rotated through 4 )• In figure 4 this principle for converting the described com¬ plementary code pair of the order 16 into a code pair of the order 32, which defines a source distribution in an almost square area, has been shown. Using the same combination principle previously used for forming the complementary codes of the orders 1, 2, 4, 8, 16, new complementary code pairs can also be obtained, starting also with a different complementary pair of codes, and the positioning of the radiation source for the image coding can be defined accordingly. Hereinafter it is shown, by way of example, how from the pair of codes + + - and + . + determined directly as a complementary pair and one of which has the order 3 said the other has the order 2, a series of complementary code pairs of the orders 5, 10,... are built up. The combination is not always performed alternately vertically and horizontally, but such that always a source distribution in a square area is defined as well as possible. OMP V WIIP The Figures 6a. - d show radiation source dis¬ tributions for codes of the order 3/2, 5 . 10, 20, utilizing the combination rule 1 ) (Figure 6b) , the rotation rule 4) (Figure 6c_) , and overlapping combinations (Figure 6d) being-'used. Figure 6_e shows a regular matrix structure of equilateral triangles obtained by slanting through 30° to the left. The arrangement shown in Figure 7 comprises four X-ray sources Q 1 to Q. which are arranged in one plane and which can be connected to a power supply + via diodes D and switches S_. to S^. When the switches S_ to Sr are operated, part of the sources Q 1 to L irradiate an ob¬ ject 0, so that shadow images of the object 0 are formed on a positive film . and a negative film F p . For the sake of clarity, these shadow images are not shown. The two films F, and F~ are arranged parallel to the plane in which the sources Q. are arranged. The arrangement shown in Figure 7 corresponds to the radiation (point) source distribution shown in Figure 1. The radiation sources to be activated via the switches S.. and S 2 form a code B. The radiation sources to be activated via the switches S_, and S form a.code A. When the switch S is closed for a brief 4period of time T, the object 0 is irradiated by the sources - , 2 and ζ . As described with reference to Figure 2, the coded images 0 and -O are recorded on the films F_ and F_. After replacement of the films F- and F_, the switch S„ is closed for the same period of the switches S_ and S ^ respectively. The coded images 0 , -O , ... 0, and -0. , ob- 1 g 1 2 2 tained by means of the arrangement described with reference to Figure 7, are decoded by means of an arrangement which will be described with reference to Figure 8. The arrangement shown comprises four optical channels, each of which is irradiated by one of four parallel beams of monochromatic light. The four light O PI l , WWIIPPOO _Λ beams can be obtained, for example, by the splitting of a laser beam LA by means of semitransparent and fully refle ive mirrors (see Figure 9)« Each processing channel com¬ prises a first lens system L1 for forming a wide light be from the narrow laser beam in order to illuminate the coded images 0 to -0. . The light beams modulated by th S 1 2 coded images are projeered on point holograms H, G via zoom lenses Z. Behind the point holograms H.. , H-, G_. , G_ there is arranged a projection screen S on which four light beams from the point holograms form a decoded image. The decoded image is an image of section of the object 0 (see Figure 7) » said section being situated parallel to the plane in which the sources Q-, to Q sere situated. As will be clear from the formula (9)j in the firs channel the decoded (positive) image 0 and the negative the third channel there are situated the coded image 0, , the negative of the image O, and behind the zoom lens the point hologram H... Obviously 2, in the fourth channel there are situated the coded image 0, and the negative of 0, which are decoded via the point 2hologram H p . The coded 1 images 0 to O Ή and the negatives thereof are pair-wise slid on a frame TO which is arrsnged on a rigid support 1 which may be a slide frame holder. Similarly, there is provided a second frame 3 in which a (photo)sensitive film can be inserted for the recording of a decoded image. The lens system L1 and the point holograms G.. , H_ , G ≥ and H 2 are each secured in a stationary frame 7 and 5 . respectively, and require only one optical alignment operation, together with the zoom lenses Z which are mounted in a frame 9 which is displaceable parallel to the optical axis (direction indicated by arrows 11 ) of each channel for reasons yet to be described. The arrangement briefly described above can be constructed by means of OMP ■r lP conventional optical meεins such as mirrors, lenses, lens holders, and other customarily used parts. Figure 9 is more detailed view of two optical channels of the arrangement of Figure 8. A laser XA is used to form a monochromatic light beam which is split into two parallel light beams by the mirrors S.. and Sp... Each beam in its turn is split into two further parallel beams, so that four parallel light beams are formed due to the use of the mirrors Sp- and Sp_ and the semitrans— parent mirrors S 2 and S_. The light beam is converted in each optical channel by a lens system 4 into a wide beam of light which illuminates the entire coded image (for example, 0 and -O ). Instead of the large lens of the s 1 E 2 lens system LI , use can alternatively be made of a frosted glass plate, the distance between the frosted glass plate and the coded images being as small as possible. The light transmitted by the coded image is converted, via a zoom ens system Z, into an intermediate image A. , 2 , A„, j , which is decoded via the imaging lens 2 and the hologram r & The decoded image obtained via a channel is a sub-image which forms a complete (decoded) image S in conjunction with the three sub-images obtained via the further optical channels. Instead of using the imaging lens and the hologram (the point hologram or the multi¬ plication hologram is the image point function of the group of sources with which the coded positive image arranged in the optical channel is formed), use can be made of a matrix of lenses, the position of the lenses in the matrix being determined by the image point function (the positions of the X-ray sources used for the recording) . It is to be noted that an arrangement for the decoding of coded images which comprises only two optical channels is already known from the German Of enlegungsschrift P 25.35.408.9. Figure 10 shows a device for the coding of images and the decoding of coded images. The device comprises a holder 13 in which there are arranged a number of X-ray sources, an image intensifier 15. two decoding sections which are coupled to the exit window 21 via a fully reflective mirror 17 and a semi ransparent mirror 19, each of said decoding sections comprising a lens matrix 23, 25, a diaphragm 27, 29, an image pick-up tube 31, 33, 5 a differential amplifier 35, and an image display device 37 in the form of a television monitor. The X-ray tubes arranged in the holder 13 are subdivided into three sub—groups, each of which can be connected to the power supply voltage + via an associated 10 switch S , S^ς, S-_. The sub-division into three subgroups is realized on the basis of the rule described with reference to Figure 2b (?-). The switches S_, Sg, S_ are sequentially closed and opened, so that the coded images 0 , 0 and 0, of an object are projected onto the S r 9 g 2 . entrance screen 39 of the image intensifier 15 sequentiall with the subgroups. The image received by the image in— .tensifier is displayed on the entrance screen 21 introduce and intensified form. Via the semitransparent mirror 19, the coded image O , 0 or 0 Ή , is projected onto a _ S-j So J~ ι rotating diaphragm 27. The diaphragm 27 leaves given parts of the lens matrix uncovered, as will be described herein¬ after, so that the coded images 0 , O and 0, are de- g 1 e 2 1 coded with the image point functions g_ , h p , an h_ , respectively. The decoded images are picked-up by the 25 image pick-up tube 3 • The decoding of the images O , 0 and 0, _> -I S_ X-J with the correct image point function g- - p and h 1 is realized as follows. Each of the diaphragms 27 and 29 comprises three sectors. Each sector comprises slots 6θ 30 which enable the passage of the light to given lenses of the lens matrix in a given position of the diaphragm. The cooperation between the switches S_, S,-, S,_, the diaphragm 27, 29 and the shape of the diaphragms will be described, by way of example, with reference to the source arrangemen 35 shown in Figure 7. As can be seen in formule (15), an image of a section of an object is obtained by a sum of three correlations. The formula 15 can be rewritten as: When the object is exposed by means of the sources Q.. , _ 2 and Q (subgroup with the image point function g- ) during a first exposure operation, the coded image 0 (appearing on the exit window 21 of the image intensifier 15 . i decoded with the function g- via the semitransparent mirror 19, the diaphragm 27 and the lens matrix 23. To this end, the diaphragm 27 comprises slits in a sector (see Figures 11a. and b) which leave 'the location of the lenses in the matrix free during a third of the revolution of the diaphragm 27. Via the semitransparent mirror 19, the mirror 17, the diaphragm 29 and the lens matrix 25, the coded image O is also decoded with the function h-, (see Figures 11a and b). The decoded images are picked-up by means of the pick-up tubes 31 and 33 and are converted into an electric signal. The two electric signals thus obtained are applied to a differential amplifier 35, the output signal of which is applied to the monitor 37, so that the difference between the two signals: 2. (o (aT) g- - 0 ( ) ..) is displayed on the exit screen 41. For a second exposure of the object, the sources 1 , Q 2 and Q„ are used . The coded image O, obtained via the image intensifier 15 is processed in the same way as the previously coded image O . The diaphragm 27 and 29, δ 1 however, have been rotated one third of a revolution further, so that the function h... via the di h 27 d ith th f ti h via diaphragm 29. The decoded images are applied to the monitor via the pick-up tubes 31, 33 and the differential amplifier circuit 35 (the applied signal: 2.(θ, (x) h... - < _, © • _ ) • For a third exposure of the object, only a single source Q. is used. Like the two previously coded images 0 and 0, , the coded image 0 is decoded via the lens -_ • -, --- S_ OMPI Λ, WIPO Λ matrices 23 and 25 and the diaphragms 27 and 29. The diaphragms are rotated a third of a revolution further again with respect to their position during the second exposure, so that now the coded image 0 is decoded, via S_ the diaphragm 27, with the function g- and the coded image O is decoded with the function h„ via the diaphragm 29. Th2e decoded images are applied to the monitor 37 via the pick-up tubes and the dif erential amplifier circuit 3 The applied signal 2.(θ g (x) - - 0_ (x) h,,) (= 2.(θ g 0 h p - O ( g ) has changed its sign, because the source Q used is a "positive" source, whilst according to the calculation a "negative" source has to be used (which actually does not exist). The third exposure is followed again by an exposur by means of the first group of X-ray sources Q_. , 2 and Q for which the diaphragms 27 and 29 are rotated one third of a revolution further, i.e. back to their starting posit ion. After the repeat of the first exposure, the second an the third irradiation are repeated etc. If the image frequency (exposure frequency) is hig enough, the successive images on the monitor screen will b observed as one image due to the inertia of the human eye. The use of an image screen with some after glow will also stimulate the "summing" of the successive images. In order to synchronize the (continuous) rotation of the diaphragms with the exposure of the object and the reading of the pick-up tubes, near a diaphragm 2 there is arranged an optical detector 43 which per second supplies a number of pulses which are a measure for the (rotary) position of the diaphragms which are driven together (not shown). The pulse divider 45, being used as a counter, counts the number of pulses and supplies a pulse when a given position is reached. Via the control logic 49, where the pulse is applied, a switch S , S^- or S-, is briefly closed for a next exposure. The pulse is also applied to a deflection signal generator 47 in order to synchronize the reading of the two image pick-up tubes 31 and 33 and the display of the images read with the speed of evolution of the diaphragms. DInstead of using synchronously rotating diaphragms, use can also be made of stationary diaphragms, in which case electromechanical shutters are used for blocking the passage of light to a lens of the lens matrix or not. The opening and closing of the shutters should then be synchronized, like the opening and closing of the switches S , S,-, S~, for the successive exposures by means of the deflection signals (for example, for the moni- tor). Via a semitransparent mirror 51, the coded images successively formed on the exit screen 21 can be recorded by means of a film camera 53, ~ film image being made of each object image. To this end, the film camera 53 is coupled to the pulse divider 45 for the required synchronization pulse. A film thus exposed can be introduced into the decoding array again (after development) by projecting the film against the rear of the mirror 51 as indicated by an arrow 55« As a result, a moving object can be studied, without it being necessary to expos___ this object each time to X-rays again. Furthermore, between the mirrors 23 and 25 and the diaphragms 27 and 29 two coupled zoom lenses can be arranged (denoted by arrows 57 and 57') in order to enable reconstruction of more than one layer of the object, as shown in Figure 9. For the sake of clarity , the zoom lenses are not shown in the Figure. The diaphragms used in the device shown in Figure 10 are shown in the Figures 11a. and b. Each diaphragm 27, 2 is formed by a round disc, for example, of aluminium which is divided into three sectors, in which some slits 60 which are shaped as an arc of a circle are provided. The slits 60 in each sector allow the passage of the light originating from the exit window of the image intensifier to some of the lenses in the matrix 23, 25 arranged behind the diaphragm (diagrammatically shown). Thus, during rotation of the diaphragms 27, 29, the coded image is decoded with a function which is determined by the sector of the disc which is situated in front of the lens matrix. As appears from the foregoing description, the diaphragm 27 should comprise three sectors which produce the functio g- , 1 and g. in conjunction with the lens matrix.23. The diaphragm 29 should comprise three sectors which produce the functions h... , h 2 and h 1 in conjunction with the lens matrix 25. The edge of the disc is provided with slits 61 (only a few are shown) which produc ' pulses in conjunction with an optical sensor (Figure 1θ).

Claims: - WHAT IS CLAIMED IS: 1. A method of coding and decoding an image of an ob¬ ject by means of radiation which is emitted by point sources and which irradiates the object in different directions in order to form shadow images of the object which are super- 5 posed on a recording medium, the coded image thus formed being decoded by convolution of the superposed shadow images with a function which is determined by the point source distribution used for irradiating the object, characterized in that the point sources are arranged accord- ID ing to a regular matrix, at least three different groups of point sources being used to form a corresponding number of superposition images in succession, a combination of groups forming a first source distribution function and a further combination of groups forming a second source 15 distribution function, the sum of the autocorrelation functions of said source distribution functions having the value zero except in one point (origin) , after which the different superposition images, or combinations with the negatives thereof, are convoluted with image point 20 functions of the groups of sources in order to obtain convoluted images which are summed in order to obtain a decoded image. 2. A method as claimed in Claim 1 , characterized in that the radiation sources for forming coded images are 25 used in four disjunct groups (t-, t„, s_, s ? ) which are successively activated, it being possible to compose the two distribution functions from said groups, a coded image formed by means of the first group of sources (t..) being used as a positive in the first as well in the second 30 distribution function, a coded image formed by means of the second group of sources (tp) being used as a negative in the first as well as in the second distribution function, a coded image formed by means of the third group of sources _fR_-_ξ OMPI , W W vv II iPPrOO _. / (s-) being used as a positive in the first distribution function and as a negative in the second distribution function, a coded image formed by means of the fourth group of sources (s 2 ) being used as a negative in the first distribution function and as a positive in the second distribution function, after which a sum of the positives of the coded images formed by means of the first and the third group of sources (t- , s..) and the negatives of the coded images formed by means of the second and the fourth group of sources (t 2 , s 2 ) is convoluted with the image point function of the first group of sources t_ , thus pro¬ ducing a first sub-image, a sum of the negative and the positive of the images coded by means of the first and the second, respectively group of sources (t.., t 2 ), being convoluted with the image point function of the second group of sources (t ), thus forming a second sub-image, a sum of the positive and the negative of the images coded with the third and the fourth, respectively, group of sources (s-, s„) being convoluted with the image point function of the third group of sources (s,), thus forming a third sub—image, a sum of the negative and the positive of the images coded with the third and the fourth, respectively group of sources (s-, s_) being convoluted with the image point function of the fourth group of sources (s 2 ), thus forming a fourth sub-image, the sum of the four sub-images forming a decoded image. 3« A method as claimed in Claim 1, characterized in that during the coding of the object with two complementa distribution functionsof sources, each distribution functi comprises all sources which are subdivided into different groups (g- , g 2 and h... , 2 ) for each distribution function, the object being coded by irradiation by two groups (_-"- ] » S o ) °-? a first distribution function and by only one group (h... ) of the second distribution function in order to obtain a positive as well as a negative of three images sequentially coded with the groups. 4. A method as claimed in Claim 3, characterized in that during the decoding _—=τ= -^U £ OMP a. a first sum of a positive and a negative of the images coded by means of first and the second group (g , p )jrespectively of sources associated with the first distribution function is convoluted with the image point function of the first group ( g. ) of sources in order to obtain a first sub-image, b. a negative of the first sum is convoluted with the image point function of the second group ( s_ ) °f sources in order to obtain a second sub-image, c. a second sum of two times a positive of the image coded by means of the group (h 1 ) of sources associat¬ ed with the second distribution function and of the negatives of the images coded by means of the groups of the sources (g 1 , g 2 ) associated with the first distribution function is convoluted with the image point function of the third group (h- ) in order to obtain a third sub-image, d. a negative of the second sum is convoluted with an image point function which is determined by the differen¬ ce between the image point function of all sources and the image point function of the third group of sources (h ) in order to obtain a fourth sub-image, the sum of the four sub-images producing a decoded image. 5« A method as claimed in Claim 3, characterized in that during the decoding a. the sum of a positive and a negative of the images coded by means of a first group ( g . ) and a second group ( g o ) °f sources, respectively, which form the first distribution function is convoluted with the image point function of the first group (g. ) in order to obtain a first sub—image. b. the sum of a positive and a negative of the images coded by means of the third group (h 1 ) and the first group (g , respectively, of sources being convoluted with the image point function of the third group in order to obtain a second sub-Image, c. the sum of a positive and a negative -of the images coded by means of the second group (g ) and the / \ 2 third group {ii- ) , respectively, of sources is convoluted O PI with an image point function which is determined by the difference between the image point function of all sources and the image point function of the third group of sources (h 1 ) in order to obtain a third sub—image, the sum of the 5 three sub—images forming a decoded image. 6. A method as claimed in Claim 3 - characterized in that sequentially during the decoding a. an image coded by means of a first group (g..) of sources associated with the first distribution function 10 is convoluted simultaneously and separately with the image point function of the first group (g 1 ) and with the image point function of a third group (h.- ) of sources associated with the second distribution function, in order to obtain a first and a second, respectively, sub—image, ^5 said second sub—image being subtracted from the first sub- image in .order to obtain a first difference image, b. an image coded by means of the third group (it. ) of sources Is simultaneously and separately convoluted with the image point functions of the third and the fourth 20 respectively group (h., ) , (h 2 ) of sources associated with the second distribution function in order to obtain a thir and a fourth sub-image, respectively, said fourth -sub- image being subtracted from the third sub-image in order t obtain a second difference image, 25 c. an image coded by means of the second group ( o of sources of the first distribution function Is simul¬ taneously and separately convoluted with the image point functions of the first and the fourth group (g..), (h p ) of sources, respectively, associated with the first and the 30 second distribution function, respectively, in order to obtain a fifth and a sixth sub-image, said sixth sub-Image being subtracted from the fifth sub-image in order to ob¬ tain a third difference image, after which the decoded image is obtained by the summing of the three difference 5 images. 7. A device for coding and decoding an image of an object by means of penetrating radiation, said device comp i -ising for the coding of an image of an object a two- OMP - - dimensional point source distribution and a two—dimensionaJL_„ recording medium which are arranged in two parallel planes at a distancefrom each other in order to form superposition images of the object, said device comprising for he decod- ing of the superposition images means for the convoluting of the recorded superposition images with at least a part of an image point function which is defined by the point source distribution, and means for summing the convoluted superposition images, characterized in that the device for the coding comprises, means for the sequential activation of the point sources in at least three and at the most four different groups in order to obtain at least three coded images, a first number of groups of point sources forming a first distribution function and a second number of groups forming a second distribution function, the sum of the autocorrelation of said. distribution functions having the value zero with the exception of the value in one point (origin), the device for the decoding comprising means for convoluting, either sequentially or simultaneously, the coded images with an image point function associated with the coded images, each of said functions being determined by different groups of point sources. 8. A device as claimed in Claim ~ , characterized in that the means for the decoding of the coded images com¬ prise at least three parallel operating processing channels, each channel comprising means for creating a two—dimensional, flat diffusely radiating light source, a holder which is arranged in front of the light source and which serves to accommodate at least one coded image, a lens and a holder for accommodating a point hologram of the point source distribution associated with the coded image, said means for the decoding furthermore comprising a projection screen on which a sub-image originating from each channel and generated via the point hologram is projected. 9. A device as claimed in Claim 6, characterized in that the means for "the decoding of the coded images com¬ prise at least three parallel operating processing channels, each channel comprising means for creating a two-dimensional flat diffuse radiation radiating light source, a holder which is arranged in front of the light source and which serves to accommodate at least one coded image and a holde for accommodating a matrix of lenses, the position of whic in the matrix is determined by the positions of the point source distribution associated with the decoded image, sai means for the decoding furthermore comprising a projection screen on which a sub-image originating from each channel and generated via the lens matrix is projected. 10. A device as claimed in Claim 7, characterized in that the means for the decoding comprise a two-dimensional radiation detector for forming, on the output thereof, a luminescent coded image, a semitransparent mirror and a fully reflective mirror which are coupled to the detector in order to obtain two identical, luminescent coded images two assemblies of a matrix of lenses and a variable diaphragm for the separate optical convolution of the two luminescent images with the image point function associate with the images, two image pick-up devices, on a target of which the convoluted images are projected for the electronic scanning of these images, a differential stage which comprises two inputs whereto two outputs of the imag pick-up devices are coupled in order to determine a dif¬ ference between the two convoluted images, and a display/ recording device for displaying the difference, the posit¬ ions of the lenses in the matrix being determined by the positions of the point sources in the point source dis¬ tribution, sequential activation of three groups of point sources being possible, for which each variable diaphragm is in three different conditions, each condition being determined by the activated group of point sources.

Inventors: PASEDACH K, WEISS H
Applicants: PASEDACH K, PHILIPS NV, PHILIPS PATENTVERWALTUNG, WEISS H, PHILIPS PATENTVERWALTUNG GMBH
Application year: 1980
Main classification: A61B6
IPC codes: A61B6, G01N23, G01T1, G02B5, G02B27, G03H1, G03H5