WO2003001165A1

WO2003001165A1 - Processing of phase data to select phase visualisation image

Info

Publication number: WO2003001165A1
Application number: PCT/AU2002/000590
Authority: WO
Inventors: Brendan Edward Allman; Mark Leopold Von Bibra; Keith Nugent
Original assignee: Iatia Imaging Pty Ltd
Priority date: 2001-06-26
Filing date: 2002-05-14
Publication date: 2003-01-03

Abstract

Method and apparatus of producing images of an object are disclosed. Phase data relating to an object is obtained by detecting a radiation wavefield and processing data relating to the detected field to produce phase data relating to the object. Various image modalities can then be produced by further processing the phase data to produce a particular phase visualisation modality image relating to the object. Such images include Hoffman modulation contrast images, differential interference contrast images, Zernike phase contrast images, Dark Field contrast images, and Darkground images. The method and apparatus also enables the production of intensity modulated images by obtaining intensity data and modulating the image with that intensity data. Enhancement can be supplied to both the phase data and the intensity data if required.

Description

PROCESSING OF PHASE DATA TO SELECT PHASE VISUALISATIONIMAGE

Field of the Invention

This invention relates to a method and apparatus for imaging an ob ect .

Background of the Invention

Many conventional methods and apparatus are in existence for imaging an object, and in particular, which relate to microscopy.

The most simple form of imaging an object in microscopy is to simply produce an absorption or intensity image by projecting light through the object and viewing the light through an optical system. The light most typically is in the visible spectrum but electromagnetic radiation of other wavelengths such as x-rays may also be utilised. Reference to radiation should also be understood to include electrons.

Other techniques for producing an image of an object include Hoffman Modulation Contrast Microscopy, Differential Contrast Microscopy, Zernike Phase Contrast Microscopy and Dark Field Microscopy. These techniques include the illumination of an object and the detection of the light emanating from the object by an optical system. The image of the object can be viewed by a person looking through the optical system or a record of the image can be obtained by detecting the image with a camera or other recording device.

Depending on the nature of the object, any one or more of these forms of imaging may result in structure within the object or on the object being more readily visible. Thus, any one or more of these techniques may be used in order to reveal structure or surface topography of an object. These forms of microscopy are most commonly used with objects in the form of biological specimens, and light is diffracted, reflected, interfered or refracted by optical discontinuities (such as cell membrane, nucleus, and internal organelles) and light which has been manipulated in this manner enters the objective lens of the optics and can be viewed by a user or recorded by a camera. The image produced includes both phase and intensity information. The phase and intensity information in the image cannot be separated one from the other.

The optical systems used to create images of the abovementioned type can also be relatively complicated and therefore expensive. For example, Darkfield Microscopy requires blocking out of the central light which ordinarily passes through and around a specimen. This allows oblique rays to impinge on the specimen which may be mounted on a microscope slide. The system has a spherically concave top lens which produces light rays which pass through the lens in the form of an inverted hollow cone. Other optical components of the system will include eye-pieces, a high numerical aperture objective lens, an iris diaphram, an oblique hollow light cone, a cardonoid condenser, the concave mirror which is referred to above and an opaque light stop which performs the blocking function mentioned previously.

Typically, the microscope may include a number of optical systems each for producing a separate type of image and most typically the types of images which are discussed above.

Summary of the Invention

The object of the present invention is to enable various modalities of an object to be formed without the need for specialised optics relating to each of the required images . The invention, in a first aspect, may be said to reside in an apparatus for forming an image of an object, including; detecting means for detecting a radiation wavefield from the object; processing means for producing phase data relating to the object from the radiation wavefield detected by the detector; and the processing means being for further processing the phase data relating to the image to produce a phase visualisation modality image relating to the object.

Since the present invention includes processing means to manipulate phase data to produce the required phase visualisation modality, specialised optics to produce these modalities are not required as the modalities are generated in software rather than by optical configurations. Thus, according to this aspect of the invention the only optics which may be required is that which is required to produce the original phase data.

Thus, the same optics can generally be used to provide data which enables various different phase visualisation modalities, such as Hoffman Modulation Contrast images. Differential Interference Contrast images, Zernike Phase Contrast images, Darkfield Contrast images and Darkground images to be produced.

In the preferred embodiment of the invention the phase data relating to the image is generated by quantitative determination of the phase of the radiation wavefield in accordance with the teachings of International patent application no. PCT/AU99/00949 (publication number WO 00/26622) owned by the University of Melbourne. The content of this International application is incorporated into this specification by this reference. The technique disclosed in the International application discloses method and apparatus for solving the transport of intensity equation to enable both phase and intensity data relating to an object to be determined independently. This enables a phase image of an object to be produced which can provide detail, particularly in biological samples, which is not apparent when a conventional intensity or absorption image of the object is viewed.

However, in other embodiments of the invention phase data relating to the radiation wavefield can be determined in other ways such as by interference techniques.

In one embodiment of the invention the phase visualisation modality comprises a differential interference contrast image and the further processing by the processing means including; determining a spatial difference of the phase image data to produce difference data; then performing a shear interference function on the difference data.

In this embodiment the processing means determines the difference by taking the spatial derivative of the phase data in a predetermined direction.

In this embodiment of the invention the processing means performs the shear interference function by taking the sine function of a value including the derivative of the phase data .

In the preferred embodiment of the invention, the sine function is the sine of a preselected combiner prism angle plus π/4 multiplied by the derivative of the phase data.

Preferably the spatial derivative of the phase data is normalised between a value of -1 and 1, and the normalised value of the spatial derivative is used in the taking of the sine function. In this embodiment, the processing means may also be for introducing intensity data relating to the object into the visualisation modality image by multiplying the phase data by intensity data relating to the object.

Preferably the apparatus includes displaying means for displaying the phase visualisation modality image.

In this embodiment of the invention the phase data is specified in wavelengths and after the taking of the derivative of the phase data the derivative data is converted to radians.

Preferably the method further includes normalising the shear interference data and also the intensity image data to a scale between 0 and 1.

In another embodiment of the invention the modality image is a Zernike Phase Contrast image and the processing means is for further processing the phase data by interference between reference data and the phase data to obtain the Zernike Phase Contrast image.

In this embodiment the processor means is for simulating the interference by taking the cosine of the phase data.

This embodiment of the invention may also include the processing means applying a phase enhancement by multiplying the phase data by an enhancement factor to improve visualisation.

This embodiment may also include phase plate excursion data and the processing means is for taking the cosine function of the excursion data to produce first cosine data, adding the excursion data to the phase data and taking the cosine of the added phase image data and excursion data to produce second cosine data, multiplying phase plate absorption data relating to intensity data of the object detected by the detector means to the first cosine data to produce first preliminary data, multiplying the second cosine data by the absorption data to produce second preliminary data, and then adding together the said first and second preliminary data and the cosine of the phase data to provide third preliminary data relating to the modality image, and adding the third preliminary data to the square of the phase plate absorption data to produce the Zernike Phase Contrast image.

In this embodiment of the invention the processing means may also apply inversion and intensity modulation steps to the modality image to provide different contrast effects.

In a third embodiment of the invention which relates to a Darkfield modality image, the processor determines the gradient of the phase data and compares the gradient of the data with predetermined gradient ranges, and dependent on the range in which the gradient of the phase image falls, setting a predetermined "greyscale" shade value between black and white to the phase image so as to produce the Darkfield image.

In this embodiment the processing means may also be for modulating the Darkfield image with intensity data by multiplying the Darkfield image data with the intensity data.

In this embodiment the processing means may also be for determining whether the image will be a bright contrast mode image or a dark contrast mode image.

Thus, the contrast data merely results in the image being ^wa black on white image" or the negative of that image, namely a "white on black image" . In a further embodiment of the invention the phase modality image is a Hoffman Modulation Contrast image and the processing means is for taking the difference between phase data in a predetermined direction, comparing the difference data with predetermined threshold ranges, setting the phase data to particular values depending on the range in which the difference data falls, so as to produce the Hoffman Modulation Contrast image.

Preferably the processor takes the difference of the image data by taking the spatial derivative of the phase image in a predetermined direction.

Preferably the range in which the derivative of the phase data falls is determined by setting predetermined ranges having a range width and a centre position, comparing the predetermined ranges with the spatial derivatives of the phase data and setting the phase data to a particular colour shade between black and white depending upon the range in which the derivative of the phase image data falls.

Preferably the processing means includes five different ranges for the derivative of the phase image data, the first range being for setting the phase data to black level, the second range being for setting the phase data to a "colour" shade between black and gray, a third range being for setting the phase image data to gray, a fourth range for setting the phase image data to a "colour" shade between gray and white, and a fifth range for setting the phase data to white.

This embodiment of the invention may also include modulating the phase data by intensity data to add some intensity information into the image. Preferably the processor determines the shade of the image data between black and gray, and gray and white by applying an error function to the data.

In a still further embodiment of the invention which relates to Darkground images, the processing means is for taking the cosine of the phase data and subtracting the cosine of the phase data from 1 to produce the Darkground image.

Preferably this embodiment includes phase enhancement and the processing means includes user input for inputting a phase enhancement factor and for normalising the phase data between 0 and 1 and for multiplying the enhancement factor by π/2 and subtracting π multiplied by the normalised phase.

Preferably the processing means is also for receiving user input indicating if intensity modulation is required and the processing means normalises intensity data to scale between 0 and 1, and produces the Darkground image by multiplying the normalised intensity data by 1 minus the cosine of the phase data.

The invention may also be said to reside in a method of forming an image of an object, including; detecting a radiation wavefield from the object; producing phase data relating to the image from the radiation wavefield; and processing the phase data relating to the image to produce a phase visualisation modality relating to the image .

In this embodiment the processing step determines the difference by taking the spatial derivative of the phase data in a predetermined direction.

In this embodiment of the invention the processing step performs the shear interference function by taking the sine function of a value including the derivative of the phase data.

In this embodiment, the processing step introduces intensity data relating to the image into the visualisation modality image by multiplying the phase data by intensity data relating to the image.

Preferably the method further includes displaying the phase visualisation modality image.

In another embodiment of the invention the modality image is a Zernike Phase Contrast image and the processing means further processes the phase data by interference between reference data and the phase data to obtain the Zernike Phase Contrast image. In this embodiment the processing step performs the interference step by taking the cosine of the phase data.

This embodiment of the invention may also include applying a phase enhancement by multiplying the phase data by an enhancement factor.

This embodiment may also include providing phase plate excursion data and the processing step takes the cosine function of the excursion data to produce first cosine data, adds the excursion data to the phase data and taking the cosine of the added phase image data and excursion data to produce second cosine data, multiplies phase plate absorption data relating to intensity data of the object detected by the detector means to the first cosine data to produce its preliminary data, multiplies the second cosine data by the absorption data to produce second preliminary data, and then adds together the said first and second preliminary data and the cosine of the phase data to provide third preliminary data relating to the modality image, and adds the third preliminary data to the square of the phase plate absorption data to produce the Zernike Phase Contrast image.

In this embodiment of the invention the processing step may also apply inversion and intensity modulation steps to the modality image to provide different contrast effects.

In a third embodiment of the invention which relates to a Darkfield modality image, the further processing determines the gradient of the phase data and compares the gradient of the data with predetermined gradient ranges, and dependent on the range in which the gradient of the phase image falls, setting a predetermined "colour" shade value between black and white to the phase image so as to produce the Darkfield image. In this embodiment the processing step may also be for modulating the Darkfield image with intensity data by multiplying the Darkfield image data with the intensity data.

In this embodiment the processing step may also be for determining whether the image will be a bright contrast mode image or a dark contrast mode image.

Thus, the contrast data merely results in the image being "a black on white image" or the negative of that image, namely a "white on black image" .

In a further embodiment of the invention the phase modality image is a Hoffman Modulation Contrast image and the processing step takes the difference between phase data in a predetermined direction, compares the difference data with predetermined threshold ranges, sets the phase data to particular values depending on the range in which the difference data falls, so as to produce the Hoffman

Modulation Contrast image.

Preferably the processing step includes five different ranges for the derivative of the phase image data, the first range being for setting the phase data to black level, the second range being for setting the phase data to a colour shade between black and gray, a third range being for setting the phase image data to gray, a fourth range for setting the phase image data, to a "colour" shade between gray and white, and a fifth range for setting the phase data to white.

In a still further embodiment of the invention which relates to Darkground images, the processing step takes the cosine of the phase data and subtracts the cosine of the phase data from 1 to produce the Darkground image.

Preferably this embodiment includes phase enhancement and the processing step includes user input for inputting a phase enhancement factor and for normalising the phase data between 0 and 1 and for multiplying the enhancement factor by π/2 and subtracting π multiplied by the normalised phase.

Preferably the processing step includes user input indicating if intensity modulation is required and the processing step normalises intensity data to scale between 0 and 1, and produces the Darkground image by multiplying the normalised intensity data by 1 minus the cosine of the phase data.

The invention may also be said to reside in an apparatus for forming an image of an object from phase data relating to the object which is produced by detecting a radiation wavefield from the object and processing the detected radiation wavefield to produce the phase data, the apparatus including; processing means for further processing the phase data relating to the image to produce a phase visualisation modality image of the object. This aspect of the invention may also be said to reside in a method of forming an image of an object from phase data relating to the object which is derived by detecting a radiation wavefield from the object and processing the detected radiation wavefield to obtain the phase data, the method including; further processing the phase data relating to the object to produce a phase visualisation modality image relating to the object.

In preferred embodiments the processing means and the processing step includes the features which are described above.

The invention in a further aspect resides in a computer program per se and also to a computer program stored on computer readable storage media for producing an image of an object, the program including; code for processing phase data relating to the object to produce a phase visualisation modality image relating to the object.

Preferably the program further includes code for producing the phase data from an electronically detected radiation wavefield from the object.

Preferably the code also producing intensity data relating to the object.

Preferably the code also includes code for performing the preferred processing steps described above.

In the preferred embodiment of the invention the method and apparatus also provides for the addition of some intensity data to the modality image. Thus, the preferred embodiments may also provide for the processing means to modulate the phase data with intensity data so as to produce a visualisation modality image which does include some intensity data relating to the object.

In one specific embodiment, the intensity data is achieved in accordance with the teachings of the above-mentioned

International application and all of the intensity data is added to the phase data. However, in other embodiments the scale factor of the intensity data could be added to a phase data if desired.

Preferred embodiments of the invention will be described, by way of example, with reference to the accompanying drawings in which;

Figure 1 is a schematic illustration of an arrangement for determination of phase data relating to radiation emanating from an object in which the object is illuminated with plane wave radiation;

Figure 2 is a schematic illustration similar to Figure la but with the object illuminated by point source radiation;

Figure 3 is a schematic drawing illustrating an exempli gratin system according to one embodiment of the invention; Figure 4 is a flowchart describing software operation of one embodiment of the invention which relates to the formation of a differential interference contrast image;

Figure 5 is a flow chart describing software operation according to an embodiment relating to the formation of a Zernike Phase Contrast image;

Figure 6 is a flow chart which is a continuation of the flowchart of Figure 5;

Figure 7 and Figure 8 are flowcharts showing software routines which can be used in the embodiment of Figure 6;

Figure 9 is a flowchart illustrating software operation of an embodiment of the invention for forming Darkfield images;

Figure 10 is a flowchart which continues on from the flowchart of Figure 9; Figure 11 is a flowchart showing software operation of an embodiment of the invention relating to the formation of a Hoffman Modulation Contrast image;

Figure 12 is a continuation of the flowchart of Figure 11; Figure 13 is a flowchart showing a routine used in the flowchart of Figure 12;

Figure 14 shows a flow chart according to a still further embodiment of the invention; and

Figure 15 is a flow chart of an alternative embodiment.

Figures 1, 2 and 3 are drawings taken from the abovementioned International application which illustrate the manner in which phase data, and also intensity data, relating to a wavefield emanating from an object is determined to enable a phase image of the object to be constructed and, if desired, displayed on a monitor. In Figures 1 and 2 an object is illuminated by plane wave radiation 2 or point source radiation 2 to produce reflected beam 3. In the embodiment shown the radiation passes through the object. However, the radiation could be reflected from the object. If the radiation passes through the object then the bulk structure of the object can be imaged. If the radiation is reflected from the object the topography of the object can be imaged.

At each point in space the optical beam possesses two properties: intensity and phase. Intensity is a measure of the amount of energy flowing through each point, while phase gives a measure of the direction of the energy flow. An intensity record of the wave front 3 is determined at two different planes after the radiation passes through the object. The intensity data can be captured by a camera including a charged couple device so that the wavefield is detected and converted to electronic format by the camera. Although in the embodiment shown in Figure 1 and 2 two planes A and B are shown in the most preferred embodiments of the invention an image is captured at three planes namely one which is in focus, one which is slightly defocused on one side of the in focus plane and the other which is slightly defocused on the other side of the in focus plane. These three intensity records provide data which enables the transport of energy equation to be solved so as to produce phase data and intensity data relating to the object in the manner which is described in the aforesaid International application.

In one practical embodiment of the invention the camera 21 which captures the intensity images is mounted on a microscope 20. A stepper motor 22 may be connected to the focus mechanism of the microscope so as to move the optics of the microscope 20 or the camera 21 so as to provide the three images referred above which are taken at three different planes. The camera 21 is connected to a processor 23 which may be in the form of a personal computer as is the stepper motor 22 so that data detected by the camera 21 is supplied to the processor 23 for manipulation in the manner which will be described hereinafter and also in the aforementioned International application. The processor 23 is connected to a monitor for enabling images to be displayed on the monitor. Images can also be retained in electronic format in the processor 23 or printed if desired.

Although in the preferred embodiment intensity records are taken at different planes to provide the two or three intensity records which enable the transport of energy equation to be solved to provide the intensity and phase data, the data could be obtained by taking intensity records at a common plane by using radiation of different wavelengths so as to provide intensity data which will enable the transport of intensity equation to be solved.

Figure 4 shows a flowchart illustrating software operation which enables a differential interference contrast image to be produced from the phase data. Thus, according to the first embodiment of the invention not only can a phase image of the object be obtained which is in accordance with the teachings in the aforementioned International application, the phase data which enables the phase image to be produced can be further processed so as to produce a differential interference contrast image without the need for any additional optics to that which is used to provide the phase interference. Thus, according to this embodiment of the invention and any other embodiments described below, the various phase modality images are produced by software by processing the phase image data rather than by special optics which transmits light from the object to a user or camera to obtain a record of the image.

With reference to Figure 4, at step 401 the phase image data which is obtained in the manner described in the before mentioned International application, or by any other suitable way, is specified in wavelength. The derivative of the phase image data is determined at step 402 in a direction specified by theta which can be input into the processor 23 by a user. Thus, the user is able to identify the angle of which the spatial derivative is taken. Thus, the user can input angle data into the processor or select from a menu of angles so as to produce the spatial derivative in the required direction.

The spatial derivative data is, if necessary, then converted to radians by multiplying by 2π at step 403. At step 403a, the spatial derivative data is normalised between a value of -1 and 1. At step 403b, a combiner prism angle is set by the user. This combiner prism angle is a value which is indicative of the separation of the interfering beams in a conventional DIC optics system. Thus, the software enables the user to select an appropriate combiner angle which may have been used should an optical system have been used to create the DIC image. The sine of the following function is then taken at step 404:

(combiner prism angle + π/4 x spatial derivative value at step 403)

The taking of the sine produces, in effect a shear interference function which is the basis of a differential interference contrast image and which would normally be performed by optics by splitting the light into two paths and recombining the light so that it interferes to produce the shear interference.

The data produced at step 404 is normalised in step 405 between 0 and 1. This step merely normalises the data to a convenient scale consistent with intensity data which can be combined with the phase data as will be described below. Step 404 produces the differential interference contrast image and the image can be displayed on the monitor show in Figure 3 as step 406.

The preferred embodiment of the invention has the advantage that the differential interference contrast image can include only phase data relating to the object without any intensity data. In conventionally formed differential interference contrast images the image includes both phase data and intensity data which cannot be separated one from the other.

If it is desired to include intensity data in the image the processor enables a user input 409 to indicate at step 410 whether intensity modulation of the phase data is also required. If the intensity modulation is not required then the information can be displayed at step 406 as previously described. If intensity modulation is required intensity data 412 which is obtained in the manner described in the aforementioned International application is first normalised to scale between 0 and 1 at step 413 (to match the normalised data at step 405) and the data at step 405 and the data of step 433 is multiplied together at step 414 so that the phase data is modulated by the intensity data. The modulated image can then be displayed at step 406. The amount of modulation can be determined by the user, by the manipulation of the normalisation scale. Thus, any desired amount of intensity modulation can be produced into the image if desired.

Figures 5 to 8 show flowcharts according to a second embodiment of the invention and which describe software for producing a Zernike Phase Contrast image. Once again, phase image data obtained in accordance with the

International application referred to above at step 419 is specified in wavelengths and is converted to radiance by multiplying by 2π at step 420. The processor 23 has the ability to enable a user to input whether phase enhancement is required. Step 421 is therefore a user input such as Yes or No to indicate whether or not enhancement is required. At step 422 the software determines if phase enhancement is required. This step increases the visibility or contrast of the image by stretching the phase data provided by a factor to increase the phase data to a range of -π/2 to π/2. Thus the data is stretched to occupy the full range of -π/2 to π/2. If phase enhancement is required the phase data is normalised at step 423 between -π/2 and π/2 and at step 424 the data is multiplied by a phase enhancement factor 425 which can be selected by the user by an appropriate input or menu selection on the processor 23. If no phase enhancement is required the program moves to step 426. At step 426 the cosine of the phase data or phase enhanced phase data is taken. The taking of the cosine performs an interference function which is indicative or simulates interference between a reference beam and a sample beam in Zernike optics.

At step 427 phase plate excursion data (ie. an angle oc) i added to the phase image data "φ" and the cosine of the added data is determined to produce first cosine data. This enables a user to switch between dark and bright contrast modes by changing the phase plate excursion property. The phase plate excursion property can be controlled by user input 428 into the processor 23 or by selecting from a menu displayed by the processor. The selections are typically π/2 or -π/2 to give either white or black image (dark contrast) or black or white image (bright contrast) . The cosine of the excursion data "<=" is taken at step 429 to give second cosine data, and phase plate absorption "α" at step 430 can also be set by a user which effectively sets the phase plate transmission which will otherwise be specified by the optical transmission in a Zernike phase plate using convention Zernike optics. This phase plate is used in the Zernike optics to achieve the phase offset in the zero order illumination, required for the phase interference condition to be met. The phase plate absorption is multiplied by -1 and by the intensity data to produce first preliminary data. The data obtained at step 426 is multiplied by -1 to provide second preliminary data and the data obtained at step 427 is multiplied by the absorption selected at 430. The first, second and third preliminary data are added together at step 434.

Referring to Figure 6 at step 435 the addition of the first, second and third preliminary data is multiplied by two. The phase plate absorption 430 (which is the same as that referred to in Figure 5) is multiplied by itself at step 436 and the data obtained at steps 435 and 436 are added together at step 437. If different contrast effects are required inversion and intensity modulation steps can be performed at step 438 and then the image can be displayed on the monitor in Figure 7 at step 439.

The inversion and intensity modulation steps are shown in Figures 7 and 8. In these steps intensity modulation 440 can be selected by user input into the processor 23. At step 441 the software determines whether intensity modulation has been selected by the user. If no then step 438 is not preformed and the display of data at 439 simply displays the data provided at step 437. If intensity modulation is required intensity image data 450 which is obtained from the radiation wavefield in the manner described in the aforesaid International application is normalised between 1 and 0 at step 452 as required by the user so that the required amount of intensity modulation can be achieved and the data of step 437 is multiplied by the normalised intensity data in step 453. The intensity modulated image can then be displayed at step 439.

Figure 8 shows a system which simply inverts the image at step 437 (or 438) and simply provides the negative of that image. The requirement for inversion can be provided by the user by appropriate input 455 or by selecting from a menu displayed by the processor or user input into the processor and at step 456 a check is made as to whether inversion is required. If inversion is required step 457 is performed which subtracts the result of the data of steps 437 or 438 from its maximum value to thereby produce a negative image of the data which is obtained at steps 437 and 438.

Figures 9 and 10 show a further embodiment of the invention which describes software for producing a Darkfield image. Once again the phase image data acquired in the manner referred to above is specified in wavelengths at step 460. At step 480 the amplitude of the two dimensional gradient function of the phase data is taken. This in effect provides an indication of the direction of the wavefield. At step 481 the gradient is normalised between 0 and 1. Threshold colour ranges are set by a user or present in the software at steps 482 and 483 by specifying a width or number of ranges between 0 and 1 and also the centre position of each range. For example, a range corresponding to a colour shade of black / gray having a threshold position and a centre position of 0.5 width and a gray / white range may have a centre threshold position of +0.5 width. A number of ranges having different thresholds are provided as shown at 484. At 485 the threshold values are corrected to 0 if less than 0 and one if greater than 1. These threshold values are compared with the normalised data at step 481 by comparison step 486. If the normalised value of the gradient function of step 481 is less than the black gray threshold in step 484, 485 the phase data is set to 0 at step 487. If between black/gray or gray/white thresholds the data is renormalised to scale between black/gray and gray/white thresholds at step 488. If the gradient is greater than the gray/white threshold the data is set to 1 at step 489.

At 490 a user can control the software to provide the required contrast, for example, a black on white image or a white on black image. At step 491 the software determines the user input at 490 to determine whether a black on white image is required or white on black image. If black on white is required the program moves to step 493 in Figure 10. If white on black is required the data is effectively inverted at step 492 and then the program goes to step 493. The inversion step 492, if required, is performed by subtracting the result at steps 487, 488 and 489 from the maximum value. At step 493 the program determines whether intensity modulation which can be set at 496 by user input into the processor, is required. If no the data of step 493 can be displayed at step 497. If yes the intensity image data at 498 is normalised at step 499 so that the desired amount of intensity modulation can be provided and the data produced at steps 487, 488 and 489 is multiplied by the intensity data at step 500 and the image then displayed at step 497.

Steps 487, 488 and 499 provide some fine tuning of the gray scale of the data which is to be displayed. Some of the data at step 487 is regarded as simply black data and the data at step 499 white data. Step 488 determines a gray scale between those extremes by renormalising the relevant data which was scaled at step 481. This provides a smooth translation between black and white so as to produce the Dark Field image.

Figures 11 to 13 show an embodiment relating to the production of Hoffman Modulation Contrast images.

Once again phase data at step 550 is specified in wavelengths and the difference of the phase image data is taken at step 552. Most preferably this difference is performed by taking the spatial derivative in a particular direction which can be specified by user input. At step 553 the data produced by the derivative is normalised between 1 and 0.

As in the earlier embodiment various ranges are set by selecting a range width 554 at a centre position 555. This gives the various ranges with a centre position for each range at step 556. A softening factor 557 can be selected by the user by input into the processor to add or subtract softening from each of the ranges at step 558. This smoothes the transition from black to gray and gray to white. This produces the various ranges at 559 which provide threshold values for the derivative of the phase information and which will be used to assign a gray scale to that data.

With reference to Figure 12 at step 560 the derivative data is compared with the threshold values in step 559. If the derivative data is less than the black/gray lower threshold the image data is set to black level at step 561. If the derivative data is between black/gray lower and black/gray upper thresholds the data at step 562 is renormalised to scale between black/gray lower and black/gray upper by applying a suitable curve function as will be described in detail hereinafter. If the derivative data is between black/gray upper and gray/white lower thresholds the phase data is set to gray level value at step 563. If the derivative is between gray/white lower and gray/white upper thresholds the phase data is renormalised at step 564 between gray/white lower and gray/white upper by the suitable curved function previously mentioned. If the derivative is greater than gray/white upper threshold the phase data is set to white level value at step 565.

As in the earlier embodiments intensity modulation can be selected by the user at 570 and the program at step 571 determines if intensity modulation is required. If so intensity data 572 is normalised in step 573 and the colour shaded data obtained at steps 561 to 565 is multiplied by the selected intensity data in step 574.

The result can then be displayed at step 575. If no intensity modulation is required the data produced at steps 561 to 565 is displayed at step 575.

Figure 13 shows a flowchart relating to software for applying a suitable curve function to the renormalised data of steps 562 and 564. This routine smooth the gray level assigned to the data in this range between the upper and lower values in accordance with a predetermined function so as to provide a smooth transition in gray scale for the data which falls within these ranges. The preferred function is an error function which normalises the data at step 590 and then multiples the result by 2 and subtracts 1 at step 591. The result is then divided by .5 at step 592. A standard error function of that result is then obtained at step 593. The result is then renormalised to scale between an upper limit of the required range 595 and a lower limit of the required 596, at step 597. The program then returns to step 571.

The application of the curve function to the data which falls within the range specified at steps 562 and 564 results in the data approaching the extremes of these threshold levels gradually rather than in a linear fashion. This provides a more genteel contrast between the threshold ends of these values and the black level value, gray level value and white level value at steps

561, 563 and 565.

Figure 14 shows a still further embodiment of the invention which relates to the production of a Darkground image. In this embodiment, phase data which is obtained in the same manner as previously described, and which may originally be expressed in wavelengths, metres or angle, is converted to an angle and provided at step 600. Step 601 requires input from a user to determine whether any phase enhancement of the Darkground image is required. If no phase enhancement is required, the program moves to step 605, which will be described hereinafter. If phase enhancement is required, the program move to step 602 and the phase data obtained at step 600 is normalised to scale between 0 and 1. At step 603, the user determines the amount of phase enhancement which is required and a phase enhancement factor is selected by the user. This could be done by way of a menu or simply by the user inputting a particular value for the phase enhancement factor. The program at step 604 multiplies the enhancement factor selected by the user by π/2 and then subtracts π multiplied by the normalised phase, which is obtained at step 602.

The program then moves to step 605 which requires a user input to indicate whether the user requires any intensity modulation of the Darkground image. If no intensity modulation is required, the program moves to step 606. If phase enhancement was performed in the manner described above, the Darkground image is determined by subtracting the cosine of the function of the phase data which is obtained at step 604 from 1. If no phase enhancement was utilised, the phase data obtained at step 600 is used in the calculation of step 606 so that the Darkground image is determined by subtracting the cosine of the phase data obtained at step 600 from 1.

If the user does require intensity modulation, the data which is presented at step 605 following the phase enhancement, if selected, or the original phase data at step 600 if phase enhancement is not selected, is then used in the subsequent steps shown in Figure 15.

If intensity modulation is required, the intensity data which is obtained in the manner described in the earlier embodiments is provided at step 607 and that data is normalised to scale between 0 and 1 and step 608. The Darkground image is then determined at step 609 by multiplying 1 minus the cosine of the phase data by the normalised intensity value obtained at step 608. The phase data which is used is the phase data which is presented at step 605 and which may be the phase enhancement data obtained at step 604 if phase enhancement is required, or the phase data at step 600 if no phase enhancement is required. Thus, this embodiment of the invention enables the Darkground image to be produced with either phase enhancement and intensity modulation, or both phase enhancement and intensity modulation, or no phase enhancement or intensity modulation.

Figure 15 shows a flow chart of a further embodiment of the invention which relates to the inclusion of intensity data in the image. This embodiment can be used in all the previous embodiments instead of the steps previously described for the inclusion of intensity modulation data.

As shown in Figure 15, the user first makes a decision at step 700 as to whether intensity modulation is required. If the answer is no, then the program simply goes to step 707 where the phase image is displayed without any intensity modulation.

If intensity modulation is required, the program goes to step 701 to provide intensity data obtained in the manner previously described.

At step 702, the user then makes a decision as to whether the intensity modulation is to be enhanced or not enhanced. If no enhancement of the intensity modulation is required, the program moves to step 706 where the phase data is multiplied by the intensity data, and then the intensity modulated image is displayed at step 706.

If enhancement of the intensity modulation is required, the program goes from step 703 which normalises the intensity data to a value between zero and one. An enhancement factor is set by the user at step 704. That intensity data is then multiplied at step 705 with the enhancement factor and at step 706 those values are multiplied with the intensity data to provide the enhanced intensity modulation. The phase image with the intensity modulation is displayed at step 706.

The preferred embodiments of the invention, whilst being described in relation to various well known phase modality images, could also produce phase modality images of different types by appropriate and desired manipulation of the phase data and intensity data. The preferred embodiments have the advantage that the phase data and intensity data can be separated one from the other or recombined by modulating the phase data with the intensity data either completely with the intensity data or by a scaled function of the intensity data so that a certain amount of intensity data can be re-included into the image, all the intensity data can be included in the image or none of the intensity data can be included. These images can be produced without special optics by software manipulation according to the programs illustrated with reference to the flowcharts described above.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

Claims

1. An apparatus for forming an image of an object, including; detecting means for detecting a radiation wavefield from the object; processing means for producing phase data relating to the object from the radiation wavefield detected by the detector; and the processing means being for further processing the phase data relating to the image to produce a phase visualisation modality image relating to the object.

2. The apparatus of claim 1 wherein the phase visualisation modality comprises a differential interference contrast image and the further processing by the processing means including; determining a spatial difference of the phase image data to produce difference data; then performing a shear interference function on the difference data.

3. The apparatus of claim 2 wherein the processing means determines the difference by taking the spatial derivative of the phase data in a predetermined direction.

4. The apparatus of claim 3 wherein the processing means performs the shear interference function by taking the sine function of a value including the derivative of the phase data.

5. The apparatus of claim 4 wherein the sine function is the sine of a preselected combiner prism angle plus π/4 multiplied by the derivative of the phase data.

6. The apparatus of claim 5 wherein the spatial derivative of the phase data is normalised between a value of -1 and 1, and the normalised value of the spatial derivative is used in the taking of the sine function.

7. The apparatus of claim 1 wherein the processing means may also be for introducing intensity data relating to the object into the visualisation modality image by multiplying the phase data by intensity data relating to the object .

8. The apparatus of claim 1 wherein the apparatus includes displaying means for displaying the phase visualisation modality image.

9. The apparatus of claim 1 wherein the phase data is specified in wavelengths and after the taking of the derivative of the phase data the derivative data is converted to radians .

10. The apparatus of claim 3 wherein the processing means normalises the shear interference data to a scale between 0 and 1.

11. The apparatus of claim 1 wherein the modality image is a Zernike Phase Contrast image and the processing means is for further processing the phase data by interference between reference data and the phase data to obtain the Zernike Phase Contrast image.

12. The apparatus of claim 11 wherein the processor means is for simulating the interference by taking the cosine of the phase data.

13. The apparatus of claim 12 wherein the processing means is for applying a phase enhancement by multiplying the phase data by an enhancement factor to improve visualisation.

14. The apparatus of claim 11 including phase plate excursion data and the processing means is for taking the cosine function of the excursion data to produce first cosine data, adding the excursion data to the phase data and taking the cosine of the added phase image data and excursion data to produce second cosine data, multiplying phase plate absorption data relating to intensity data of the object detected by the detector means to the first cosine data to produce first preliminary data, multiplying the second cosine data by the absorption data to produce second preliminary data, and then adding together the said first and second preliminary data and the cosine of the phase data to provide third preliminary data relating to the modality image, and adding the third preliminary data to the square of the phase plate absorption data to produce the Zernike Phase Contrast image.

15. The apparatus of claim 11 wherein the processing means is also apply inversion and intensity modulation steps to the modality image to provide different contrast effects.

16. The apparatus of claim 1 wherein the image is a Darkfield modality image, the processor determines the gradient of the phase data and compares the gradient of the data with predetermined gradient ranges, and dependent on the range in which the gradient of the phase image falls, setting a predetermined "greyscale" shade value between black and white to the phase image so as to produce the Darkfield image.

17. The apparatus of claim 16 wherein the processing means is also for modulating the Darkfield image with intensity data by multiplying the Darkfield image data with the intensity data.

18. The apparatus of claim 16 wherein the processing means may also be for determining whether the image will be a bright contrast mode image or a dark contrast mode image .

19. The apparatus of claim 1 wherein the phase modality image is a Hoffman Modulation Contrast image and the processing means is for taking the difference between phase data in a predetermined direction, comparing the difference data with predetermined threshold ranges, setting the phase data to particular values depending on the range in which the difference data falls, so as to produce the Hoffman Modulation Contrast image.

20. The apparatus of claim 19 wherein the processor takes the difference of the image data by taking the spatial derivative of the phase image in a predetermined direction.

21. The apparatus of claim 20 wherein the range in which the derivative of the phase data falls is determined by setting predetermined ranges having a range width and a centre position, comparing the predetermined ranges with the spatial derivatives of the phase data and setting the phase data to a particular colour shade between black and white depending upon the range in which the derivative of the phase image data falls.

22. The apparatus of claim 19 wherein the processing means includes five different ranges for the derivative of the phase image data, the first range being for setting the phase data to black level, the second range being for setting the phase data to a "colour" shade between black and gray, a third range being for setting the phase image data to gray, a fourth range for setting the phase image data to a "colour" shade between gray and white, and a fifth range for setting the phase data to white.

23. The apparatus of claim 19 wherein the processor is for modulating the phase data by intensity data to add some intensity information into the image.

24. The apparatus of claim 22 wherein the processor determines the shade of the image data between black and gray, and gray and white by applying an error function to the data.

25. The apparatus of claim 1 wherein the image is a Darkground image, the processing means is for taking the cosine of the phase data and subtracting the cosine of the phase data from 1 to produce the Darkground image.

26. The apparatus of claim 25 wherein the processing means includes user input for inputting a phase enhancement factor and for normalising the phase data between 0 and 1 and for multiplying the enhancement factor by π/2 and subtracting π multiplied by the normalised phase .

27. The apparatus of claim 25 wherein the processing means is also for receiving user input indicating if intensity modulation is required and the processing means normalises intensity data to scale between 0 and 1, and produces the Darkground image by multiplying the normalised intensity data by 1 minus the cosine of the phase data.

28. A method of forming an image of an object, including; detecting a radiation wavefield from the object; producing phase data relating to the image from the radiation wavefield; and processing the phase data relating to the image to produce a phase visualisation modality relating to the image .

29. The method of claim 28 wherein the phase visualisation modality comprises a differential interference contrast image and the further processing by the processing means including; determining a spatial difference of the phase image data to produce difference data; then performing a shear interference function on the difference data.

30. The method of claim 29 wherein the processing step determines the difference by taking the spatial derivative of the phase data in a predetermined direction.

31. The method of claim 29 wherein the processing step performs the shear interference function by taking the sine function of a value including the derivative of the phase data.

32. The method of claim 29 wherein the processing step introduces intensity data relating to the image into the visualisation modality image by multiplying the phase data by intensity data relating to the image.

33. The method of claim 29 wherein the method further includes displaying the phase visualisation modality image.

34. The method of claim 30 wherein the phase data is specified in wavelengths and after the taking of the derivative of the phase data the derivative data is converted to radians.

35. The method of claim 34 wherein the method further includes normalising the shear interference data and also the intensity image data to a scale between 0 and 1.

36. The method of claim 28 wherein the modality image is a Zernike Phase Contrast image and the processing means further processes the phase data by interference between reference data and the phase data to obtain the Zernike Phase Contrast image.

37. The method of claim 36 wherein the processing step performs the interference step by taking the cosine of the phase data.

38. The method of claim 36 including applying a phase enhancement by multiplying the phase data by an enhancement factor.

39. The method of claim 36 including providing phase plate excursion data and the processing step takes the cosine function of the excursion data to produce first cosine data, adds the excursion data to the phase data and taking the cosine of the added phase image data and excursion data to produce second cosine data, multiplies phase plate absorption data relating to intensity data of the object detected by the detector means to the first cosine data to produce its preliminary data, multiplies the second cosine data by the absorption data to produce second preliminary data, and then adds together the said first and second preliminary data and the cosine of the phase data to provide third preliminary data relating to the modality image, and adds the third preliminary data to the square of the phase plate absorption data to produce the Zernike Phase Contrast image.

40. The method of claim 36 wherein the processing step may also apply inversion and intensity modulation steps to the modality image to provide different contrast effects.

41. The method of claim 28 wherein the image is a Darkfield modality image, the further processing determines the gradient of the phase data and compares the gradient of the data with predetermined gradient ranges, and dependent on the range in which the gradient of the phase image falls, setting a predetermined "colour" shade value between black and white to the phase image so as to produce the Darkfield image.

42. The method of claim 41 wherein the processing step is for modulating the Darkfield image with intensity data by multiplying the Darkfield image data with the intensity data.

43. The method of claim 42 wherein the processing step is for determining whether the image will be a bright contrast mode image or a dark contrast mode image.

44. The method of claim 28 wherein the phase modality image is a Hoffman Modulation Contrast image and the processing step takes the difference between phase data in a predetermined direction, compares the difference data with predetermined threshold ranges, sets the phase data to particular values depending on the range in which the difference data falls, so as to produce the Hoffman Modulation Contrast image.

45. The method of claim 44 wherein the processor takes the difference of the image data by taking the spatial derivative of the phase image in a predetermined direction.

46. The method of claim 45 wherein the range in which the derivative of the phase data falls is determined by setting predetermined ranges having a range width and a centre position, comparing the predetermined ranges with the spatial derivatives of the phase data and setting the phase data to a particular colour shade between black and white depending upon the range in which the derivative of the phase image data falls.

47. The method of claim 46 wherein the processing step includes five different ranges for the derivative of the phase image data, the first range being for setting the phase data to black level, the second range being for setting the phase data to a colour shade between black and gray, a third range being for setting the phase image data to gray, a fourth range for setting the phase image data, to a "colour" shade between gray and white, and a fifth range for setting the phase data to white.

48. The method of claim 28 wherein the image is a Darkground image, the processing step takes the cosine of the phase data and subtracts the cosine of the phase data from 1 to produce the Darkground image.

49. The method of claim 48 wherein the processing step includes user input for inputting a phase enhancement factor and for normalising the phase data between 0 and 1 and for multiplying the enhancement factor by π/2 and subtracting π multiplied by the normalised phase.

50. The method of claim 49 wherein the processing step includes user input indicating if intensity modulation is required and the processing step normalises intensity data to scale between 0 and 1, and produces the Darkground image by multiplying the normalised intensity data by 1 minus the cosine of the phase data.

51. An apparatus for forming an image of an object from phase data relating to the object which is produced by detecting a radiation wavefield from the object and processing the detected radiation wavefield to produce the phase data, the apparatus including; processing means for further processing the phase data relating to the image to produce a phase visualisation modality image of the object.

52. A method of forming an image of an object from phase data relating to the object which is derived by detecting a radiation wavefield from the object and processing the detected radiation wavefield to obtain the phase data, the method including; further processing the phase data relating to the object to produce a phase visualisation modality image relating to the object.

53. A computer program per se and also to a computer program stored on computer readable storage media for producing an image of an object, the program including; code for processing phase data relating to the object to produce a phase visualisation modality image relating to the object.

54. The program of claim 53 wherein the program further includes code for producing the phase data from an electronically detected radiation wavefield from the object.

55. The program of claim 54 wherein the code is also for producing intensity data relating to the object.