WO2001039104A1 - A method for generating gray scale transfer functions for use in displaying a digital radiogram - Google Patents
A method for generating gray scale transfer functions for use in displaying a digital radiogram Download PDFInfo
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- WO2001039104A1 WO2001039104A1 PCT/US2000/030938 US0030938W WO0139104A1 WO 2001039104 A1 WO2001039104 A1 WO 2001039104A1 US 0030938 W US0030938 W US 0030938W WO 0139104 A1 WO0139104 A1 WO 0139104A1
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- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000012546 transfer Methods 0.000 title claims abstract description 11
- 230000006870 function Effects 0.000 title description 18
- 238000004590 computer program Methods 0.000 claims 2
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- 230000005855 radiation Effects 0.000 description 8
- 238000004422 calculation algorithm Methods 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 238000012545 processing Methods 0.000 description 6
- 230000008859 change Effects 0.000 description 4
- 238000002601 radiography Methods 0.000 description 4
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- 238000013507 mapping Methods 0.000 description 2
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- 208000010392 Bone Fractures Diseases 0.000 description 1
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- 230000035945 sensitivity Effects 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Classifications
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- G06T5/92—
Definitions
- This invention relates to a method for displaying a radiographic image composed of a plurality of digital values, and more particularly to a method for generating a look up table (LUT) representing a desired gray scale transfer (GST) function for displaying a visually enhanced radiogram.
- LUT look up table
- GST gray scale transfer
- a major advantage of digital data detection systems is the wide dynamic range of signal capture.
- Display media such as radiographic film or cathode ray tube (CRT) displays, on the other hand, have a substantially more limited dynamic range.
- a typical digital x-ray capture system can have a useful dynamic detection range of greater than a 1,000: 1.
- the typical currently available display media are generally limited to a dynamic range of less than 100: 1. There is, therefore, need to determine and select the optimal limited range of useful data for diagnostic display, and then properly display such range on the available display medium.
- the method most often used in actual practice for mapping the data derived from the detector is to store a plurality of GST curves representing empirically derived GST shapes in the form of LUTs in a memory , and to select one of the stored GSTs to reproduce a given image. If the desired region of interest in the reproduction proves too dark, or has insufficient contrast, another GST curve is chosen and the output observed again and so on, until an acceptable image is produced.
- Such method is limited by the number of curves stored, and does not allow for continuous changing of the contrast and brightness of the displayed image.
- It is an object of this invention to provide a method for generating on demand a gray scale transfer curve for use in displaying an image comprised of a plurality of digital values representing pixel gray scale levels with a desired contrast and brightness. This is achieved by using a single sigmoid shaped function Y f(X, a, b, c) wherein the function resembles an H&D curve of a photographic film.
- the Y axis represents digital output values to be used in displaying an image, while the X axis represents input digital values representing captured image information.
- a is a number representing boundary conditions for X and Y
- b is a first parameter controlling the location of the curve along the X axis
- c is a second parameter controlling the slope of the curve slope.
- This function is used to derive a Look-Up-Table (LUT) representing a continuous GST curve having the desired contrast and brightness.
- LUT Look-Up-Table
- the above described method permits the derivation of families of GST curves and corresponding LUTs representing different contrasts and brightness, by varying the values of the parameters "b" and "c" .
- Parameter "c” is dependent on the maximum input digital value possible. Experience has shown that in a system where the input values have been normalized and range between 0 and 100, good results are obtained with values for "c” selected between 0.02% and 0.2% of the maximum scale value for X, and preferably between 0.06% and 0.10%. Parameter "b” is given by:
- a Y u * ( l+ b*e Xu ).
- Figure 1 shows a typical H&D curve for a screen-film combination used in traditional radiography.
- Figure 2 shows a family of GST curves obtained through the process of this invention illustrating the change of contrast as a function of parameter "c".
- Figure 3 shows a family of GST curves obtained through the process of this invention illustrating the change in output values and thus brightness levels (or film density if the display medium is film) for a given region of input values as a function of parameter "b".
- Figure 1 shows two typical H&D curves for two hypothetical photographic films used in capturing X-ray radiation. What these curves show are the exposed and developed film density as a result of radiation exposure.
- the Y axis represents the film density and the X axis the logarithm of the exposure. Exposure is the product of the incident radiation intensity times the duration of incidence of the radiation onto the film. The exposure may be the result of irradiating the film with x-rays only or it may be the result of exposing the film through a film intensifying screen combination. Different films have different H&D curves. The slope of the curve at any point indicates the contrast characteristic of the particular film or film screen combination at a given exposure level. The shift of the curve to the right or left relative to the Y axis is related to the reproduced density, (or brightness) of portions of the exposed areas, and is, in photographic film, a function of the film screen system sensitivity.
- Such processing typically includes: (a) determining the exposure range and image densities that carry significant information for diagnostic purposes, (b) compressing the extensive data obtained from the detector usually from 14 bits to 12 or 8 bits and (c) mapping the data through an input - output transformation so that the output data used in displaying the image will display an image of desirable visual characteristics with optimum contrast at optimum brightness, or when the display medium is hard copy such as film, density.
- the data is next mapped onto a gray scale transfer (GST) curve through the use of a look up table (LUT) , and the new values are sent to a display device for image display.
- GST gray scale transfer
- LUT look up table
- the digital values prior to processing through the LUT are referred to hereinafter as the input digital values while the values resulting from the LUT operation on the input values are referred to as the output digital values.
- the digital output values are used to drive a display device which can be a CRT monitor in which case the output values represent brightness levels of the displayed image on the monitor, or the display device may be a hard copy output device with the output being a photosensitive material, in which case the output values represent optical density (gray scale) of the output image.
- a higher output value represents a darker image in CRT displays and a higher density image (darker) image in hard copy display.
- Parameter "c” is related to the scaling of the X-axis, and the maximum possible digital value, i.e. maximum scale value, of the input digital values on the X-axis, X m a ⁇ value - "c" has been found by experience to be preferably between 0.01% and 0.2% of X m x value •
- the input digital values are normalized, that is the X axis value range is between 0 and 100, preferred values for "c” are between 0.01 and 0.20 with the most preferred range being between 0.06 and 0.1.
- "c" values range, i.e. 0.05 to 0.5, and so on. Values outside these ranges may be also be used, however experience has shown that most applications will obtain optimum visual results using values within the given range.
- the boundary conditions depend on the digital input and output value range.
- X u and Y u are the X and Y values representing the upper limits of possible input and output digital values.
- the input and output boundary conditions for X u and Y u are 255 and 255.
- both the input and output values are normalized digital values ranging from 0-100, in which case X u and Y u are equal to 100. In such case,
- Figure 3 shows another family of curves where the parameter "c” controlling contrast is held constant while parameter "b” has been changed. In this case the point of maximum contrast has been shifted progressively to the right along the X-axis, X ma ⁇ co ntr as t being 45, 60 and 75 respectively. Equation (2) yields the following values for "b”: 28.79, 121.51 and 403.
- the result of this curve shift is a change in the output value for a given input value. For example a digital value of 60 will result in an output value of 28, 54 and 82 respectively. A value of 28 will be represented as much brighter than one of 82 in the final image. Depending on the particular portion of the data one wants to emphasize any one of these curves may provide better visual results. For instance if the information sought to be observed is in the range of between 60 and 80 input digital normalized values, then curve III is probably the best suited to display the information since this data range is displayed over a range of 30 to 80 output normalized values. On the other hand if the desired input range is between 30 and 60 in the input axis, curve I is best. The equations are typically used as follows.
- the point of maximum contrast for use as Xmax contrast usually varies between 30 and 80 and is preferably about 45.
- Default parameters have been developed based on experimental results for different types of radiograms, i.e. chest lateral, chest frontal, GI, bone fractures etc. Typical values for parameters were given above in this description.
- the default parameters provide a beginning point from which one may, after observing the displayed image, select parameters and modify the GST to produce a visual appearance best suited to the particular examination needs. For example, if the image appears generally flat, parameter "c" may be increased to provide better contrast. Similarly if a particular region of special interest in the image appears dark, X ma ⁇ contra st and parameter "b" can be altered to shift the GST to the left or to the right changing the brightness of that region.
- the GST may be applied to the input values on the fly, so to speak, by calculating output (Y) values for each input (X) value of the digital image, or a LUT table may be created prior to displaying the image and stored in memory for later use during the image display. In either case there is never a need to store a large number of LUTs representing different GSTs in the system, and to attempt to optimize the visual appearance of the displayed radiogram by selecting one of the stored GSTs.
- This invention provides an infinite number of GSTs any one of which can be rapidly generated and tailored to produce an image with proper contrast, brightness (or density), and generally a visual appearance that simulates accurately the appearance of similar radiograms obtained through traditional radiography using a film screen combination.
- Such program may be embodied in a computer readable medium such as magnetic tape or disc, or in a CD or any other medium usable for programming a computer.
- Programming a computer to solve for values of Y given a function such as equation 1 is well known in the art.
- Such program will be structured to accept input values for "c" and X m a X contrast from a keyboard or other input device, or may retrieve such values from a stored data base containing preselected values for "c" and X mx contrast for different types of radiograms.
- the program will next calculate "b” and "a” by solving equations (2) and (3).
- Values for Y u and X u may be input either by the operator or, preferably be stored in memory in the computer as part of an initialization process.
- the program will use these parameter values to solve equation (1) for each input value. This may be done by providing the program with the ability to receive input values and calculate an output value each time an input value is received, or to pre- calculate all output values for the full range of input, X axis, values and form a LUT which is stored in a memory and used to supply output values for each input value received.
- Such program may be a stand alone program, or, preferably, may be part of a larger program used to process the data received from a radiation detector and to supply such data for display to a display medium.
Abstract
Description
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00978500A EP1236161A4 (en) | 1999-11-24 | 2000-11-10 | A method for generating gray scale transfer functions for use in displaying a digital radiogram |
CA002385631A CA2385631A1 (en) | 1999-11-24 | 2000-11-10 | A method for generating gray scale transfer functions for use in displaying a digital radiogram |
JP2001540696A JP2003515825A (en) | 1999-11-24 | 2000-11-10 | Method of generating a gray scale transfer function for use in displaying digital x-ray images |
Applications Claiming Priority (2)
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US09/449,075 | 1999-11-24 | ||
US09/449,075 US6370265B1 (en) | 1999-11-24 | 1999-11-24 | Method for generating gray scale transfer functions for use in displaying a digital radiogram |
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WO2001039104A1 true WO2001039104A1 (en) | 2001-05-31 |
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PCT/US2000/030938 WO2001039104A1 (en) | 1999-11-24 | 2000-11-10 | A method for generating gray scale transfer functions for use in displaying a digital radiogram |
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US (1) | US6370265B1 (en) |
EP (1) | EP1236161A4 (en) |
JP (1) | JP2003515825A (en) |
CA (1) | CA2385631A1 (en) |
WO (1) | WO2001039104A1 (en) |
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-
2000
- 2000-11-10 EP EP00978500A patent/EP1236161A4/en not_active Withdrawn
- 2000-11-10 JP JP2001540696A patent/JP2003515825A/en active Pending
- 2000-11-10 WO PCT/US2000/030938 patent/WO2001039104A1/en not_active Application Discontinuation
- 2000-11-10 CA CA002385631A patent/CA2385631A1/en not_active Abandoned
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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EP1377029A2 (en) * | 2002-06-24 | 2004-01-02 | Eastman Kodak Company | Enhancing the tonal characteristics of digital images |
EP1377029A3 (en) * | 2002-06-24 | 2005-03-30 | Eastman Kodak Company | Enhancing the tonal characteristics of digital images |
US7113649B2 (en) | 2002-06-24 | 2006-09-26 | Eastman Kodak Company | Enhancing the tonal characteristics of digital images |
EP1626567A3 (en) * | 2004-08-10 | 2008-03-19 | Konica Minolta Medical & Graphic, Inc. | Image processing system and image processing method |
EP1684505A3 (en) * | 2005-01-25 | 2009-03-18 | Sharp Kabushiki Kaisha | Brightness level converting apparatus and method |
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JP2003515825A (en) | 2003-05-07 |
US6370265B1 (en) | 2002-04-09 |
EP1236161A4 (en) | 2005-05-11 |
EP1236161A1 (en) | 2002-09-04 |
CA2385631A1 (en) | 2001-05-31 |
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