Image fusion using acquisition technique

Abstract

A first radiographic image of a manufactured object is captured in a digital radiographic (DR) detector using a low energy exposure level less than a saturation level of the DR detector. A second radiographic image of the manufactured object is captured using a high exposure level greater than the known saturation level of the DR detector. The captured first and second radiographic images of the manufactured object are combined to form a final image.

Description

IMAGE FUSION USING ACQUISITION TECHNIQUEBACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to a radiographic imaging system and method that may be used for nondestructive testing (NDT) applications. In particular, to a method of capturing and combining radiographic images during nondestructive testing.

[0002] When thick metallic parts such as steel castings are tested using an x-ray imaging system, the testing procedure imposes a challenge to the imaging system. First, a high kV (kilovolts) and high exposure level mAs (milli-amp- seconds) are needed to penetrate thick areas of the casting in order to generate a high enough signal level on the radiographic image receptor, or digital radiographic (DR) detector, for visualization and examination by an inspector. The nonuniform casting thickness may result in overly excessive x-ray beam penetration through thinner regions of the casting which then impacts the detector, as well as the directly exposed regions of the detector's imaging area if the casting does not entirely cover the DR detector's image receptor. The imaging receptor may become saturated, which causes artifacts in subsequent image acquisitions, and, in addition, may obscure a current image for inspection.

[0003] There is a need to balance the requirement of high x-ray exposure energies for penetrating the thick region(s) of a metal casting and low x-ray exposure energies for clearly imaging the thinner regions, and to avoid detector saturation while achieving a good image signal-to-noise ratio (SNR). Image frame averaging and / or accumulation has been used in practice to mitigate these issues. In one example, an amount of x-ray energy for each exposure (hereafter designated En), or each image frame, is captured in a DR detector such that the maximum x-ray energy level (hereafter designated Emax) that is captured is less than the detector's known saturation level (hereafter designated Esat). A number of image frames are captured (hereafter designated N), then averaged ((Ei + . . . EN)-? N) to create a new averaged image that has improved SNR because the averaging is equivalent to using a much higher exposure level. In another example, the multiple captured image frames N may be summed together (Ei + . . . EN) to create a new image with improved SNR. The SNR of this new image may improve by a factor of the square root of N (N‘ / 2).

[0004] The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE INVENTION

[0005] A first radiographic image of a manufactured object is captured in a digital radiographic (DR) detector using a low energy exposure level less than a saturation level of the DR detector. A second radiographic image of the manufactured object is captured using a high exposure level greater than the known saturation level of the DR detector. The captured first and second radiographic images of the manufactured object are combined, for example by adding, to form a final image. An advantage that may be realized in the practice of some disclosed embodiments is that any saturation region in the captured second image does not appear in the final image.

[0006] In one embodiment, a first radiographic image of a manufactured object is captured using an x-ray source set at a low exposure level. A second radiographic image of the manufactured object is captured using the x-ray source set at a high exposure level higher than the low exposure level. The first and and second captured radiographic images of the manufactured object are combined to form a final image.

[0007] In one embodiment, a first set of radiographic images of a manufactured object is captured using a DR detector having a known saturation level and an x-ray source set at a first exposure energy level that will not cause pixels in the DR detector to become saturated. A second set of radiographic images of the manufactured object is captured using the DR detector and the x-raysource set at a second exposure level at least twice the first exposure energy level. The captured first and second sets of radiographic images of the manufactured object are combined to form a final image.

[0008] The summary descriptions above are not meant to describe individual separate embodiments whose elements are not interchangeable. In fact, many of the elements described as related to a particular embodiment can be used together with, and possibly interchanged with, elements of other described embodiments. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

[0009] This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings below are intended to be drawn neither to any precise scale with respect to relative size, angular relationship, relative position, ortiming relationship, nor to any combinational relationship with respect to interchangeability, substitution, or representation of a required implementation., emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which:

[0011] FIG. 1 is a schematic perspective view of an exemplary digital x- ray imaging system;

[0012] FIG. 2 is a schematic diagram of a two dimensional imaging pixel array in a DR detector;

[0013] FIG. 3 is a perspective diagram of an exemplary DR detector;

[0014] FIG. 4 is a cross section diagram of an exemplary DR detector;

[0015] FIGS. 5A-5D each illustrate a series of radiographic images of one object, with an underexposed image of the object, having a higher noise level, on the left; an overexposed image of the object, saturated in the areas that have less thickness, in the center; and a fused or combined image of the object, using the left and center images to increase the dynamic range of the combined image in terms of material thickness discrimination, on the right; and

[0016] FIG. 6 displays another example of different levels of x-ray energy exposure showing a fused, underexposed, and an overexposed image, left-to-right, respectively.DETAILED DESCRIPTION OF THE INVENTION

[0017] FIG. 1 is a perspective view of a digital radiographic (DR) imaging system 10 that may include a generally curved or planar DR detector 40 (shown in a planar embodiment and without a housing for clarity of description), an x-ray source 14 configured to generate radiographic energy (x-ray radiation), and a control station that includes a digital monitor, or electronic display, 26, configuredto display images 24 captured by the DR detector 40, and a processing system 34 for controlling operation of the (DR) imaging system 10, according to one embodiment. The DR detector 40 may include a two dimensional array 12 of detector cells 22 (imaging pixels or photosensors), arranged in electronically addressable rows and columns. The DR detector 40 may be positioned to receive x-rays 16 passing through an object 18, such as a metal, manufactured component, during a radiographic testing procedure, emitted by the x-ray source 14. As shown in FIG. 1, the radiographic imaging system 10 may use an x-ray source 14 that emits collimated x-rays 16, e.g., an x-ray beam, selectively aimed at and passing through the preselected manufactured object 18 such that the emitted x- rays 16 fall on an imaging region, i.e., imaging pixel array 12, of the DR detector 40. The x-ray beam 16 may be attenuated by varying degrees along its plurality of rays according to the structure, e.g., varying thickness, of the metal object 18, which attenuated x-rays are detected by the array 12 of imaging pixels 22. The curved or planar DR detector 40 may be positioned, as much as possible, in a perpendicular relation to a central ray of the plurality of rays 16 emitted by the x- ray source 14. In a curved array embodiment, the source 14 may be centrally positioned such that a larger percentage, or all, of the imaging pixels 22 are positioned perpendicular to incoming x-rays from the centrally positioned source 14. The array 12 of individual imaging pixels 22 may be electronically addressed (scanned) by their position according to column and row. As used herein, the terms "column" and "row" refer to the vertical and horizontal arrangement of the photosensor cells 22 and, for clarity of description, it will be assumed that the rows extend horizontally, and the columns extend vertically. However, the orientation of the columns and rows is arbitrary and does not limit the scope of any embodiments disclosed herein. Each individual imaging pixel 22 may be scanned by readout circuitry 28, 30, described herein, to determine a stored voltage level generated therein by an incoming x-ray beam energy level. The voltage level stored in each imaging pixel 22 may be read out by the circuitry 28, 30, and stored electronically as a digitized numerical value. As is well known, an A / D converter may be used to convert the stored voltage level in each pixel 22 into a digital value. A higher numerical value may be understood to represent agreater amount of x-ray energy absorbed by an individual imaging pixel 22 during an imaging procedure of an object 18.

[0018] In one exemplary embodiment, the rows in the array of imaging pixels 12 may be scanned one or more at a time by electronic scanning circuit 28 so that the exposure data from the array 12 may be transmitted to electronic readout circuit 30. Each imaging pixel 22 may independently store a charge, or voltage, proportional to an intensity, or energy level, of the attenuated radiographic radiation, or x-rays, received and absorbed in the pixel 22. Thus, each imaging pixel, when read out by circuits 28, 30, provides information defining a pixel of a radiographic image 24, e.g. a brightness level or an amount of energy absorbed by the pixel 22, that may be digitally decoded by read out circuit 30, such as using an A / D / converter, and transmitted to be displayed by the digital monitor 26 for viewing by a user. An electronic bias circuit 32 may be electrically connected to the two-dimensional detector array 12 to provide a bias voltage to each of the imaging pixels 22.

[0019] Each of the bias circuit 32, the scanning circuit 28, and the read-out circuit 30, may communicate with control processing unit 34 over a connected cable 33 (wired), or the DR detector 40 and the control processing unit 34 may be equipped with a wireless transmitter and receiver to transmit radiographic image data wirelessly 35 to the control processing unit 34. The control processing unit 34 may include a processor and electronic memory (not shown) to control operations of the radiographic imaging system 10 as described herein, including control of circuits 28, 30, and 32, for example, by use of programmed instructions, and to store and process image data. The control processing unit 34 may also be used to control activation of the x-ray source 14 during a radiographic exposure, controlling an x-ray tube electric current magnitude (mAs), and thus the fluence of x-rays in x-ray beam 16, and / or the x-ray tube voltage (kVp), and thus the energy level of the x-rays in x-ray beam 16. A portion or all of the control processing unit 34 functions may reside in the detector 40 in an on-board processing system 36 which may include a processor and electronic memory to control operations of the DR detector 40 as described herein, including control of circuits 28, 30, and32, by use of programmed instructions, and to store and process image data similar to the functions of standalone control processing system 34. The image processing system may perform image acquisition and image disposition functions as described herein. The image processing system 36 may control image transmission and image processing and image correction on board the detector 40. Alternatively, control processing unit 34 may receive raw image data from the detector 40 and process the image data and store it, or it may store raw unprocessed image data in local memory, or in remotely accessible memory.

[0020] With regard to a direct detection embodiment of DR detector 40, the imaging pixels 22 may each include a sensing element sensitive to x-rays, i.e., it absorbs x-rays and generates an amount of charge carriers, voltage, in proportion to a magnitude of the absorbed x-ray energy. A switching element may be configured to be selectively activated to read out the charge level of a corresponding imaging pixel 22. With regard to an indirect detection embodiment of DR detector 40, imaging pixels 22 may each include a sensing element sensitive to light rays in the visible spectrum, i.e. it absorbs light rays and generates an amount of charge carriers in proportion to a magnitude of the absorbed light energy, and a switching element that is selectively activated to read the charge level of the corresponding sensing element. A scintillator, or wavelength converter, may be disposed over the imaging pixel array 12 to convert incident x-ray radiographic energy to visible light energy. Thus, in the embodiments disclosed herein, it should be noted that the DR detector 40 (or DR detector 300 in FIG. 3 or DR detector 400 in FIG. 4) may include an indirect or direct type of DR detector.

[0021] Examples of sensing elements used in sensing array 12 include various types of photoelectric conversion devices (e.g., photosensors) such as photodiodes (P-N or PIN diodes), photo-capacitors (MIS), photo-transistors or photoconductors. Examples of switching elements used for signal read-out include a-Si TFTs, oxide TFTs, MOS transistors, bipolar transistors and other p-n junction components.

[0022] FIG. 2 is a schematic diagram 240 of a portion of a two- dimensional array 12 for a DR detector 40. The array of photosensor cells 212, whose operation may be consistent with the photosensor array 12 described above, may include a number of hydrogenated amorphous silicon (a-Si:H) n-i-p photodiodes 270 and thin film transistors (TFTs) 271 formed as field effect transistors ( FETs) each having gate (G), source (S), and drain (D) terminals. In embodiments of DR detector 40 disclosed herein, such as a multilayer DR detector (400 of FIG. 4), the two-dimensional array of photosensor cells 12 may be formed in a device layer that abuts adjacent layers of the DR detector structure, which adjacent layers may include a rigid glass layer or a flexible polyimide layer or a layer including carbon fiber without any adjacent rigid layers. A plurality of gate driver circuits 228 may be electrically connected to a plurality of gate lines 283 which control a voltage applied to the gates of TFTs 271, a plurality of readout circuits 230 may be electrically connected to data lines 284, and a plurality of bias lines 285 may be electrically connected to a bias line bus or a variable bias reference voltage line 232 which controls a voltage applied to the photodiodes 270. Charge amplifiers 286 may be electrically connected to the data lines 284 to receive signals therefrom. Outputs from the charge amplifiers 286 may be electrically connected to a multiplexer 287, such as an analog multiplexer, then to an analog-to-digital converter (ADC) 288, or they may be directly connected to the ADC, to stream out the digital radiographic image data at desired rates. In one embodiment, the schematic diagram of FIG. 2 may represent a portion of a DR detector 40 such as an a-Si:H based indirect flat panel, curved panel, or flexible panel imager.

[0023] Incident x-rays, or x-ray photons, 16 are converted to optical photons, or light rays, by a scintillator, which light rays are subsequently converted to electron-hole pairs, or charges, upon impacting the a-Si:H n-i-p photodiodes 270. In one embodiment, an exemplary detector cell 222, which may be equivalently referred to herein as a pixel, may include a photodiode 270 having its anode electrically connected to a bias line 285 and its cathode electrically connected to the drain (D) of TFT 271. The bias reference voltage line 232 cancontrol a bias voltage of the photodiodes 270 at each of the detector cells 222. The charge capacity of each of the photodiodes 270 is a function of its bias voltage and its capacitance. In general, a reverse bias voltage, e.g., a negative voltage, may be applied to the bias lines 285 to create an electric field (and hence a depletion region) across the pn junction of each of the photodiodes 270 to enhance its collection efficiency for the charges generated by incident light rays. The image signal represented by the array of photosensor cells 212 may be integrated by the photodiodes while their associated TFTs 271 are held in a nonconducting (off) state, for example, by maintaining the gate lines 283 at a negative voltage via the gate driver circuits 228. The photosensor cell array 212 may be read out by sequentially switching rows of the TFTs 271 to a conducting (on) state by means of the gate driver circuits 228. When a row of the pixels 22 is switched to a conducting state, for example by applying a positive voltage to the corresponding gate line 283, collected charge from the photodiode in those pixels may be transferred along data lines 284 and integrated by the external charge amplifier circuits 286. The row may then be switched back to a non-conducting state, and the process is repeated for each row until the entire array of photosensor cells 212 has been read out. The integrated signal outputs are transferred from the external charge amplifiers 286 to an analog-to-digital converter (ADC) 288 using a parallel-to-serial converter, such as multiplexer 287, which together comprise read-out circuit 230.

[0024] This digital image information may be subsequently processed by processing system 34 to yield a digital image 24 which may then be digitally stored and immediately displayed on monitor 26, or it may be displayed at a later time by accessing the digital electronic memory containing the stored image. The flat panel DR detector 40 having an imaging array 212 as described with reference to FIG. 2 is capable of both single-shot (e.g., static, radiographic) and continuous (e.g., fluoroscopic) image acquisition.

[0025] FIG. 3 shows a perspective view of an exemplary prior art generally rectangular, planar, portable wireless DR detector 300 according to one embodiment of DR detector 40 disclosed herein. The DR detector 300 mayinclude a flexible substrate to allow the DR detector to capture radiographic images in a curved orientation, such as positioning the DR detector 300 around a portion of a pipe. The flexible substrate may be fabricated in a permanent curved orientation, or it may remain flexible throughout its life to provide an adjustable curvature in two or three dimensions, as desired. The DR detector 300 may include a similarly flexible housing portion 314 that surrounds a multilayer structure comprising a flexible photosensor array portion 22 of the DR detector 300. The housing portion 314 of the DR detector 300 may include a continuous, rigid or flexible, x-ray opaque material or, as used synonymously herein, a radioopaque material, surrounding an interior volume of the DR detector 300. The housing portion 314 may include four flexible edges 318, extending between the top side 321 and the bottom side 322, and arranged substantially orthogonally in relation to the top and bottom sides 321, 322. The bottom side 322 may be continuous with the four edges and disposed opposite the top side 321 of the DR detector 300. The top side 321 comprises a top cover 312 attached to the housing portion 314 which, together with the housing portion 314, substantially encloses the multilayer structure in the interior volume of the DR detector 300. The top cover 312 may be attached to the housing 314 to form a seal therebetween and be made of a material that passes x-rays 16 without significant attenuation thereof, i.e., an x-ray transmissive material or, as used synonymously herein, a radiolucent material, such as a carbon fiber plastic, polymeric, or other plastic based material.

[0026] With reference to FIG. 4, there is illustrated in schematic form an exemplary cross-section view along section 4-4 of the exemplary embodiment of the DR detector 300 (FIG. 3). For spatial reference purposes, one major surface of the DR detector 400 may be referred to as the top side 451 and a second major surface may be referred to as the bottom side 452, as used herein. The multilayer structure may be disposed within the interior volume 450 enclosed by the housing 314 and top cover 312 and may include a flexible curved or planar scintillator layer 404 over a curved or planar the two-dimensional imaging sensor array 12 shown schematically as the device layer 402. The scintillator layer 404 may be directly under (e.g., directly connected to) the substantially planar top cover 312,and the imaging array 402 may be directly under the scintillator 404. Alternatively, a flexible layer 406 may be positioned between the scintillator layer 404 and the top cover 312 as part of the multilayer structure to allow adjustable curvature of the multilayer structure and / or to provide shock absorption. The flexible layer 406 may be selected to provide an amount of flexible support for both the top cover 312 and the scintillator 404 and may comprise a foam rubber type of material. The layers just described comprising the multilayer structure each may generally be formed in a rectangular shape and defined by edges arranged orthogonally and disposed in parallel with an interior side of the edges 318 of the housing 314, as described in reference to FIG. 3.

[0027] A substrate layer 420 may be disposed under the imaging array 402, such as a rigid glass layer, in one embodiment, or flexible substrate comprising polyimide or carbon fiber upon which the array of photosensors 402 may be formed to allow adjustable curvature of the array and may comprise another layer of the multilayer structure. Under the substrate layer 420 a radioopaque shield layer 418 may be used as an x-ray blocking layer to help prevent scattering of x-rays passing through the substrate layer 420 as well as to block x- rays reflected from other surfaces in the interior volume 450. Readout electronics, including the scanning circuit 28, the read-out circuit 30, the bias circuit 32, and processing system 36 (all of FIG. 1) may be formed adjacent the imaging array 402 or, as shown, may be disposed below frame support member 416 in the form of integrated circuits (ICs) electrically connected to printed circuit boards 424, 425. The imaging array 402 may be electrically connected to the readout electronics 424 (ICs) over a flexible connector 428 which may comprise a plurality of flexible, sealed conductors known as chip-on-film (COF) connectors.

[0028] X-ray flux may pass through the radiolucent top panel cover 312, in the direction represented by an exemplary x-ray beam 16, and impinge upon scintillator 404 where stimulation by the high-energy x-rays 16, or photons, causes the scintillator 404 to emit lower energy photons as visible light rays which are then received in the photosensors of imaging array 402. The frame support member 416 may connect the multilayer structure to the housing 314 and mayfurther operate as a shock absorber by disposing elastic pads (not shown) between the frame support beams 422 and the housing 314. Fasteners 410 may be used to attach the top cover 312 to the housing 314 and create a seal therebetween in the region 430 where they come into contact. In one embodiment, an external bumper 412 may be attached along the edges 318 of the DR detector 400 to provide additional shock-absorption.

[0029] With respect to the radiographic images of manufactured steel castings shown in FIGS. 5A-5D, proper sensitivity (SNR) for each image can be more easily achieved in areas of the manufactured object that have less thickness. As shown in each of FIGS. 5A-5D, the images on the left are underexposed and so have a higher noise level, while the images in the center are overexposed and therefore are saturated in the areas of the manufactured objects that have less thickness. The images on the right are fused, or combined, using the left and center images, in order to increase the dynamic range of the combined image in terms of material thickness discrimination. FIG. 6 shows a combined image of a metal casting on the left, which is a combination of the same metal casting image in the middle, which is underexposed, and on the right, which is overexposed. In one embodiment, combining the images may include adding together the images.

[0030] When a desirable minimum SNR threshold has to be satisfied to ensure the quality of a radiographic inspection image, it is desirable to provide the operator a recommended exposure technique setting. For example, an exposure level per frame (En), in units of mAs, and a minimum number of frames (Nmin) may be specified. This can be determined through the acquisition of a scout image. A scout image is a preliminary exposure image that serves as a sample image of a metal casting under inspection. Usually, the exposure energy level is controlled such that the detector's imaging pixels do not become saturated, i.e., the exposure energy level is kept below the saturation energy level (< Esat). The operator can then select two or more regions of interest (ROI) for SNR (or, interchangeably, CNR: contrast-to-noise ratio) calculation. Using a monitor to display the scout image, the scout image may be windowed and leveled (adjust contrast and brightness), or image processed under control of a system operator.A cursor utility may be used by the operator, e.g., placing two or more rectangular cursors on the displayed scout image of a metal object corresponding to two or more ROIs within the scout image. The operator selected image areas are stored in the image processing system to perform calculations as described herein.

[0031] In one example, the number of images frames (M) that are needed to achieve the desired SNR may be determined using the following formula:M = (SNRmin / SNR)2where SNRmin is the desired SNR determined by the radiographer, SNR = (mean pixel intensity) -? (standard deviation of the pixel intensity) — both factors with respect to the ROI, and M is rounded up to the nearest positive integer.

[0032] In another example, assuming that each captured image frame will have used the same exposure technique setting as the scout image, SNR may be determined by calculating the signal difference between two of the operator selected ROIs in the image, divided by the noise level from either one of the two selected regions or the average noise level from either one of the two selected regions. To determine the signal difference, an average pixel intensity for each of the operator selected ROIs is calculated by averaging the signal intensity for all of the pixels in each ROI, then the calculated averages are subtracted. In one embodiment, a sixteen bit digital radiographic detector may output a value between 0 and 65535 for each pixel in the ROI. The noise level for each ROI may be determined by calculating a standard deviation of the pixel intensity of all of the pixels in the ROI or by calculating their average pixel intensity, for example, or using another preferred measure of centrality.

[0033] A graphical user interface (GUI) may be provided with an x-ray imaging system for an operator that uses the operator's selected calculation method to automatically calculate the number of frames needed, automatically sets the system acquisition energy levels and automatically captures the calculated number of image frames at the determined energy levels. Frame averaging and / or accumulation is not without limitations. For example, when a current imagesignal level is below the known noise floor (Emin) of the DR detector it is likely that no matter how many frames are exposed and averaged, and / or accumulated at the current signal level, the combined image signal of all the exposed images would not be sufficient to reach a minimum SNR for the combined image. One way to address this issue is to increase the exposure power level (mAs) such that the x-ray energy signal received by the DR detector is greater than the DR detector's noise floor (Emin). This can create a problematic situation wherein the DR detector's image receptor becomes saturated. To overcome this problem, the operator may acquire two sets of images. The first set, which may be frame averaged and / or accumulated using multiple images, may also consist of a single image frame. The first set is captured at a lower exposure level, below the DR detector's known saturation level (Emax), without saturating the DR detector's image receptor, i.e., the DR detector's imaging pixels. Depending on the DR detector being used, it may be known that the DR detector becomes saturated at 90% of its maximum pixel intensity 65535 (Emax = 58982). The second set, which, similar to the first set, can be frame averaged and / or accumulated or simply can be a single image frame, is captured at a very high exposure level (by 2X or more than the exposure used for the first set) which may cause saturation of the DR detector's imaging pixels. The images captured from the higher exposure level (second set) are then combined with the images captured at the lower exposure (first set) having pixels that are not saturated, which creates a final image for the operator to review and inspect.In one example, for the image pixels that are not saturated in both the lower exposure levels (first set) and higher exposure levels (second set) images, a scale factor (sf) may be calculated based on the ratio of the pixel values in these two images. The scale factor represents the ratio of the actual exposure applied to the low and high exposure images, e.g., 0.5. Each pixel value in the final image (vf) where the pixel values are not saturated in neither the low exposure (vl) and the high exposure (vh) may be calculated as: vf = (vl + vh) / (1 + sf). The pixel values in the final image (vf) where the pixel values are saturated in the higher exposure image may be set as vf = vl. This procedure may improve workflow byreducing the number of images to review down to one. This blending method may be performed with operator assistance or may be performed by software automatically. Thus, such a method may include the step of capturing one or more radiographic images of a manufactured object using a DR detector having a known saturation level and an x-ray source set at a first exposure energy level that will not cause pixels in the DR detector to become saturated, and a step of capturing one or more radiographic images of the manufactured object using the DR detector and the x-ray source set at a second exposure level at least twice the first exposure energy level. The last step is determining the pixel values of the final image using the formula vf = (vl + vh) / (1 + sf). If multiple images are captured at each of the first and second exposure energy levels, then the image noise level for each of the exposure energy levels may be determined using a preferred measure of centrality, such as an average pixel intensity, before applying the formula to each of the averaged images.

[0034] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “service,” “circuit,” “circuitry,” “module,” and / or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

[0035] Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non- exhaustive list) of the computer readable storage medium would include thefollowing: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by, or in connection with, an instruction execution system, apparatus, or device.

[0036] Program code and / or executable instructions embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0037] Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language and conventional procedural programming languages. The program code may execute entirely on the user's computer (device), partly on the user's computer, as a standalone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (FAN) or a wide area network (WAN), or the connection may be made to a cloud server.

[0038] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or ifthey include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

CLAIMS:

1. A method comprising: capturing a first radiographic image of a manufactured object using a digital radiographic (DR) detector and using an x-ray source set at a low exposure level preselected to be less than a known saturation level of the DR detector; capturing a second radiographic image of the manufactured object using the source set at a high exposure level preselected to be greater than said known saturation level of the DR detector; and combining the captured first and second radiographic images of the manufactured object to form a final image.

2. The method of claim 1, wherein the step of capturing the first radiographic image comprises capturing a preselected number of low exposure radiographic images of the manufactured object, the step of capturing the second radiographic image comprises capturing a preselected number of high exposure radiographic images of the manufactured object, and wherein the step of combining comprises: averaging the preselected number of low exposure radiographic images; averaging the preselected number of high exposure radiographic images; and combining the averaged low exposure radiographic images with the averaged high exposure radiographic images to form the final image.

3. The method of claim 2, further comprising determining the preselected number of low exposure radiographic images using the formula:M = (SNRmin / SNR)2.

4. The method of claim 1 , wherein any saturation region in the captured second image does not appear saturated in the final image5. A method comprising: capturing a first radiographic image of a manufactured object using an x-ray source set at a low exposure level; capturing a second radiographic image of the manufactured object using the x-ray source set at a high exposure level higher than the low exposure level; and combining the captured first radiographic image of the manufactured object and the captured second radiographic image of the manufactured object to form a final image.

6. The method of claim 5, wherein the step of capturing the first radiographic image of the manufactured object comprises capturing a plurality of radiographic images of the manufactured object using the x-ray source set at the low exposure level.

7. The method of claim 6, wherein the step of capturing the second radiographic image of the manufactured object comprises capturing a plurality of radiographic images of the manufactured object using the x-ray source set at the high exposure level.

8. The method of claim 6, wherein the step of combining comprises adding together the plurality of radiographic images of the manufactured object using the x-ray source set at the low exposure level.

9. The method of claim 7, wherein the step of combining comprises adding together the plurality of radiographic images of the manufactured object using the x-ray source set at the low exposure level and adding together the plurality of radiographic images of the manufactured object using the x-ray source set at the high exposure level.

10. The method of claim 6, wherein the step of combining comprises averaging the plurality of radiographic images of the manufactured object using the x-ray source set at the low exposure level.

11. The method of claim 7, wherein the step of combining comprises averaging the plurality of radiographic images of the manufactured object using the x-ray source set at the low exposure level and averaging the plurality of radiographic images of the manufactured object using the x-ray source set at the high exposure level.

12. A method comprising: capturing a first set of radiographic images of a manufactured object using a DR detector having a known saturation level and an x-ray source set at a first exposure energy level that will not cause pixels in the DR detector to become saturated; capturing a second set of radiographic images of the manufactured object using said DR detector and said x-ray source set at a second exposure level at least twice the first exposure energy level; and combining the captured first and second sets of radiographic images of the manufactured object to form a final image.

13. The method of claim 12, further comprising setting the x- ray source at an exposure energy level that will not cause pixels in a selected region of interest in the DR detector to become saturated.

14. The method of claim 13, wherein the step of combining comprises adding together the captured first and second sets of radiographic images of the manufactured object.

15. The method of claim 13, wherein the step of combining comprises averaging pixel values in each of the first and second sets of radiographic images of the manufactured object in the selected region of interestand adding together the averaged pixel value for each of the first and second sets of radiographic images.

Images