ASTM E2007-10(2016)
(Guide)Standard Guide for Computed Radiography
Standard Guide for Computed Radiography
SIGNIFICANCE AND USE
4.1 This guide is intended as a source of tutorial and reference information that can be used during establishment of computed radiography techniques and procedures by qualified CR personnel for specific applications. All materials presented within this guide may not be suited for all levels of computed radiographic personnel.
4.2 This guide is intended to build upon an established basic knowledge of radiographic fundamentals (that is, film systems) as may be found in Guide E94. Similarly, materials presented within this guide are not intended as “all-inclusive” but are intended to address basic CR topics and issues that complement a general knowledge of computed radiography as described in 1.2 and 3.2.28.
4.3 Materials presented within this guide may be useful in the development of end-user training programs designed by qualified CR personnel or activities that perform similar functions. Computed radiography is considered a rapidly advancing inspection technology that will require the user maintain knowledge of the latest CR apparatus and technique innovations. Section 11 of this guide contains technical reference materials that may be useful in further advancement of knowledge associated with computed radiography.
SCOPE
1.1 This guide provides general tutorial information regarding the fundamental and physical principles of computed radiography (CR), definitions and terminology required to understand the basic CR process. An introduction to some of the limitations that are typically encountered during the establishment of techniques and basic image processing methods are also provided. This guide does not provide specific techniques or acceptance criteria for specific end-user inspection applications. Information presented within this guide may be useful in conjunction with those standards of 1.2.
1.2 CR techniques for general inspection applications may be found in Practice E2033. Technical qualification attributes for CR systems may be found in Practice E2445. Criteria for classification of CR system technical performance levels may be found in Practice E2446. Reference Images Standards E2422, E2660, and E2669 contain digital reference acceptance illustrations.
1.3 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Buy Standard
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2007 − 10 (Reapproved 2016)
Standard Guide for
Computed Radiography
This standard is issued under the fixed designation E2007; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ing Classification of Wire Image Quality Indicators (IQI)
Used for Radiology
1.1 This guide provides general tutorial information regard-
E1025 Practice for Design, Manufacture, and Material
ing the fundamental and physical principles of computed
Grouping Classification of Hole-Type Image Quality In-
radiography (CR), definitions and terminology required to
dicators (IQI) Used for Radiology
understand the basic CR process. An introduction to some of
E1316 Terminology for Nondestructive Examinations
the limitations that are typically encountered during the estab-
E1453 Guide for Storage of Magnetic Tape Media that
lishment of techniques and basic image processing methods are
Contains Analog or Digital Radioscopic Data
also provided. This guide does not provide specific techniques
E2002 Practice for Determining Total Image Unsharpness
or acceptance criteria for specific end-user inspection applica-
and Basic Spatial Resolution in Radiography and Radios-
tions. Information presented within this guide may be useful in
copy
conjunction with those standards of 1.2.
E2033 Practice for Computed Radiology (Photostimulable
1.2 CR techniques for general inspection applications may
Luminescence Method)
be found in Practice E2033. Technical qualification attributes
E2339 Practice for Digital Imaging and Communication in
for CR systems may be found in Practice E2445. Criteria for
Nondestructive Evaluation (DICONDE)
classification of CR system technical performance levels may
E2422 Digital Reference Images for Inspection of Alumi-
be found in Practice E2446. Reference Images Standards
num Castings
E2422, E2660, and E2669 contain digital reference acceptance
E2445 Practice for Performance Evaluation and Long-Term
illustrations.
Stability of Computed Radiography Systems
1.3 The values stated in SI units are to be regarded as the E2446 Practice for Manufacturing Characterization of Com-
puted Radiography Systems
standard. The inch-pound units given in parentheses are for
information only. E2660 Digital Reference Images for Investment Steel Cast-
ings for Aerospace Applications
1.4 This standard does not purport to address all of the
E2669 Digital Reference Images for Titanium Castings
safety concerns, if any, associated with its use. It is the
2.2 SMPTE Standard:
responsibility of the user of this standard to establish appro-
RP-133 Specifications for Medical Diagnostic Imaging Test
priate safety and health practices and determine the applica-
Pattern for Television Monitors and Hard-Copy Recording
bility of regulatory limitations prior to use.
Cameras
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 Unless otherwise provided within this guide, terminol-
E94 Guide for Radiographic Examination
ogy is in accordance with Terminology E1316.
E746 Practice for Determining Relative Image Quality Re-
sponse of Industrial Radiographic Imaging Systems
3.2 Definitions:
E747 Practice for Design, Manufacture and Material Group-
3.2.1 aliasing—artifacts that appear in an image when the
spatial frequency of the input is higher than the output is
capable of reproducing. This will often appear as jagged or
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
stepped sections in a line or as moiré patterns.
tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology
(X and Gamma) Method. 3.2.2 basic spatial resolution (SR )—terminology used to
b
Current edition approved July 1, 2016. Published July 2016. Originally approved
describe the smallest degree of visible detail within a digital
in 1999. Last previous edition approved in 2010 as E2007 -10. DOI: 10.1520/
image that is considered the effective pixel size.
E2007-10R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from Society of Motion Picture and Television Engineers (SMPTE),
the ASTM website. 3 Barker Ave, 5th Floor, White Plains, NY 10601.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2007 − 10 (2016)
3.2.2.1 Discussion—The concept of basic spatial resolution 3.2.10 contrast-to-noise ratio (CNR)—quotient of the digi-
involves the ability to separate two distinctly different image tal image contrast (see 3.2.13) and the averaged standard
features from being perceived as a single image feature. When deviation of the linear pixel values.
two identical image features are determined minimally distinct,
3.2.10.1 Discussion—CNR is a measure of image quality
the single image feature is considered the effective pixel size.
that is dependent upon both digital image contrast and signal-
If the physical sizes of the two distinct features are known, for
to-noise ratio (SNR) components. In addition to CNR, a digital
example, widths of two parallel lines or bars with an included
radiograph must also possess adequate sharpness or basic
space equal to one line or bar, then the effective pixel size is
spatial resolution to adequately detect desired features.
considered ⁄2 of their sums. Example: A digital image is
3.2.11 digital driving level (DDL)—terminology used to
determined to resolve five line pairs per mm or a width of line
describe displayed pixel brightness of a digital image on a
equivalent to five distinct lines within a millimetre. The basic
monitor resultant from digital mapping of various gray scale
spatial resolution is determined as 1/ [2 × 5 LP/ mm] or 0.100
levels within specific look-up-table(s).
mm.
3.2.11.1 Discussion— DDL is also known as monitor pixel
3.2.3 binary/digital pixel data—a matrix of binary (0’s, 1’s)
intensity value; thus, may not be the PV of the original digital
values resultant from conversion of PSL from each latent pixel
image.
(on the IP) to proportional (within the bit depth scanned)
3.2.12 digital dynamic range—maximum material thickness
electrical values. Binary digital data value is proportional to the
latitude that renders acceptable levels of specified image
radiation dose received by each pixel.
quality performance within a specified pixel intensity value
3.2.4 bit depth—the number “2” increased by the exponen-
range.
tial power of the analogue-to-digital (A/D) converter resolu-
3.2.12.1 Discussion—Digital dynamic range should not be
tion. Example 1) In a 2-bit image, there are four (2 ) possible
confused with computer file bit depth.
combinations for a pixel: 00, 01, 10 and 11. If “00” represents
3.2.13 digital image contrast—pixel value difference be-
black and “11” represents white, then “01” equals dark gray
tween any two areas of interest within a computed radiograph.
and “10” equals light gray. The bit depth is two, but the number
3.2.13.1 Discussion—digital contrast = PV2 – PV1 where
of gray scales shades that can be represented is 2 or 4.
PV2 is the pixel value of area of interest “2” and PV1 is the
Example 2): A 12-bit A/D converter would have 4096 (2 )
pixel value of area of interest “1” on a computed radiograph.
gray scales shades that can be represented.
Visually displayed image contrast can be altered via digital
3.2.5 blooming or flare—an undesirable condition exhibited
re-mapping (see 3.2.11) or re-assignment of specific gray scale
by some image conversion devices brought about by exceeding
shades to image pixels.
the allowable input brightness for the device, causing the
3.2.14 digital image noise—imaging information within a
image to go into saturation, producing an image of degraded
computed radiograph that is not directly correlated with the
spatial resolution and gray scale rendition.
degree of radiation attenuation by the object or feature being
3.2.6 computed radiographic system—all hardware and
examined and/or insufficient radiation quanta absorbed within
software components necessary to produce a computed radio-
the detector IP.
graph. Essential components of a CR system consisting of: an
3.2.14.1 Discussion—Digital image noise results from ran-
imaging plate, an imaging plate readout scanner, electronic
dom spatial distribution of photons absorbed within the IP and
image display, image storage and retrieval system and interac-
interferes with the visibility of small or faint detail due to
tive support software.
statistical variations of pixel intensity value.
3.2.7 computed radiographic system class—a group of com-
3.2.15 digital image processing—the use of algorithms to
puted radiographic systems characterized with a standard
change original digital image data for the purpose of enhance-
image quality rating. Practice E2446, Table 1, provides such a
ment of some aspect of the image.
classification system.
3.2.15.1 Discussion—Examples include: contrast,
3.2.8 computed radiography—a radiological nondestructive
brightness, pixel density change (digital enlargement), digital
testing method that uses storage phosphor imaging plates
filters, gamma correction and pseudo colors. Some digital
(IP’s), a PSL stimulating light source, PSL capturing optics,
processing operations such as sharpening filters, once saved,
optical-to-electrical conversion devices, analogue-to-digital
permanently change the original binary data matrix (Fig. 1,
data conversion electronics, a computer and software capable
Step 5).
of processing original digital image data and a means for
3.2.16 equivalent penetrameter sensitivity (EPS)—that
electronically displaying or printing resultant image data.
thickness of penetrameter, expressed as a percentage of the
3.2.9 contrast and brightness—an application of digital
section thickness radiographed, in which a 2T hole would be
image processing used to “re-map” displayed gray scale levels
visible under the same radiographic conditions. EPS is calcu-
of an original gray scale data matrix using different reference
lated by: EPS% = 100/ X (√ Th/2), where: h = hole diameter,
lookup tables.
T = step thickness and X= thickness of test object (see E1316,
3.2.9.1 Discussion—This mode of image processing is also
E1025, E747, and Practice E746).
known as “windowing” (contrast adjustment) and “leveling”
(brightness adjustment) or simply “win-level” image process- 3.2.17 gray scale—a term used to describe an image con-
ing. taining shades of gray rather than color. Gray scale is the range
E2007 − 10 (2016)
FIG. 1 Basic Computed Radiography Process
of gray shades assigned to image pixels that result in visually since without this basic conversion (to gray scales) there would
perceived pixel display brightness. be no discernable radiographic image (see Fig. 5-B).
3.2.17.1 Discussion—The number of shades is usually posi-
3.2.21 photostimulable luminescence (PSL)—
tive integer values taken from the bit depth. For example: an
photostimulable luminescence (PSL) is a physical phenom-
8-bit gray scale image has up to 256 total shades of gray from
enon in which a halogenated phosphor compound emits bluish
0 to 255, with 0 representing white image areas and 255
light when excited by a source of red spectrum light.
representing black image areas with 254 shades of gray in
3.2.22 pixel brightness—the luminous (monitor) display
between.
intensity of pixel(s) that can be controlled by means of
3.2.18 image morphing—a potentially degraded CR image
electronic monitor brightness level settings or changes of
resultant from over processing (that is, over driving) an
digital driving level (see 3.2.11).
original CR image.
3.2.23 pixel density—the number of pixels within a digital
3.2.18.1 Discussion—“Morphing” can occur following sev-
image of fixed dimensions (that is, length and width).
eral increments of image processing where each preceding
image was “overwritten” resulting in an image that is notice- 3.2.23.1 Discussion—for digital raster images, the conven-
ably altered from the original. tion is to describe pixel density in terms of the number of
pixel-columns (width) and number of pixel rows (height). An
3.2.19 look up table (LUT)—one or more fields of binary
alternate convention is to describe the total number of pixels in
digital values arbitrarily assigned to a range of reference gray
the image area (typically given as the number of mega pixels),
scale levels (viewed on an electronic display as shades of
which can be calculated by multiplying pixel-columns by
“gray”).
pixel-rows. Another convention includes describing pixel den-
3.2.19.1 Discussion—A LUT is used (applied) to convert
sity per area-unit or per length-unit such as pixels per in./mm.
binary digital pixel data to proportional shades of “gray” that
Resolution (see 7.1.5) of a digital image is related to pixel
define the CR image. LUT’s are key reference files that allow
density.
binary digital pixel data to be viewed with many combinations
of pixel gray scales over the entire range of a digital image (see
3.2.24 pixel value (PV)—a positive integer numerical value
Fig. 5-A).
directly associated with each binary picture data element
(pixel) of an original digital image where gray scale shades
3.2.20 original digital image—a digital gray scale (see
(see 3.2.17) are assigned in linear proportion to radiation
3.2.17) image resultant from application of original binary
exposure dose received by that area.
digital pixel data to a linear look-up table (see 3.2.24 and
3.2.19 prior to any image processing. 3.2.24.1 Discussion—Computed radiography uses gray
3.2.20.1 Discussion—This original gray scale image is usu- scale shades to render visual perceptions of image contrast;
ally considered the beginning of the “computed radiograph”, thus, linear pixel value (PV) is used to measure a specific shade
E2007 − 10 (2016)
of gray that corresponds to the quantity of radiation exposure of definition (that is, distinction) associated with the geometry
absorbed within a particular area of a part. With this of exposure and inherent unsharpness of the CR system (that is,
relationship, a PV of “0” can correspond with “0” radiation inherent or total unsharpness). Guide E94 provides fundamen-
dose (white image area of a negative image view) whereas a tal guidance related to geometrical unsharpness a
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2007 − 10 E2007 − 10 (Reapproved 2016)
Standard Guide for
Computed Radiography
This standard is issued under the fixed designation E2007; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide provides general tutorial information regarding the fundamental and physical principles of computed radiography
(CR), definitions and terminology required to understand the basic CR process. An introduction to some of the limitations that are
typically encountered during the establishment of techniques and basic image processing methods are also provided. This guide
does not provide specific techniques or acceptance criteria for specific end-user inspection applications. Information presented
within this guide may be useful in conjunction with those standards of 1.2.
1.2 CR techniques for general inspection applications may be found in Practice E2033. Technical qualification attributes for CR
systems may be found in Practice E2445. Criteria for classification of CR system technical performance levels may be found in
Practice E2446. Reference Images Standards E2422, E2660, and E2669 contain digital reference acceptance illustrations.
1.3 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for
information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E94 Guide for Radiographic Examination
E746 Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems
E747 Practice for Design, Manufacture and Material Grouping Classification of Wire Image Quality Indicators (IQI) Used for
Radiology
E1025 Practice for Design, Manufacture, and Material Grouping Classification of Hole-Type Image Quality Indicators (IQI)
Used for Radiology
E1316 Terminology for Nondestructive Examinations
E1453 Guide for Storage of Magnetic Tape Media that Contains Analog or Digital Radioscopic Data
E2002 Practice for Determining Total Image Unsharpness and Basic Spatial Resolution in Radiography and Radioscopy
E2033 Practice for Computed Radiology (Photostimulable Luminescence Method)
E2339 Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE)
E2422 Digital Reference Images for Inspection of Aluminum Castings
E2445 Practice for Performance Evaluation and Long-Term Stability of Computed Radiography Systems
E2446 Practice for Manufacturing Characterization of Computed Radiography Systems
E2660 Digital Reference Images for Investment Steel Castings for Aerospace Applications
E2669 Digital Reference Images for Titanium Castings
2.2 SMPTE Standard:
RP-133 Specifications for Medical Diagnostic Imaging Test Pattern for Television Monitors and Hard-Copy Recording
Cameras
This guide is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology (X and
Gamma) Method.
Current edition approved June 1, 2010July 1, 2016. Published July 2010July 2016. Originally approved in 1999. Last previous edition approved in 20082010 as
E2007 - 08.E2007 -10. DOI: 10.1520/E2007-10.10.1520/E2007-10R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from Society of Motion Picture and Television Engineers (SMPTE), 3 Barker Ave, 5th Floor, White Plains, NY 10601.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2007 − 10 (2016)
3. Terminology
3.1 Unless otherwise provided within this guide, terminology is in accordance with Terminology E1316.
3.2 Definitions:
3.2.1 aliasing—artifacts that appear in an image when the spatial frequency of the input is higher than the output is capable of
reproducing. This will often appear as jagged or stepped sections in a line or as moiré patterns.
3.2.2 basic spatial resolution (SR )—terminology used to describe the smallest degree of visible detail within a digital image
b
that is considered the effective pixel size.
3.2.2.1 Discussion—
The concept of basic spatial resolution involves the ability to separate two distinctly different image features from being perceived
as a single image feature. When two identical image features are determined minimally distinct, the single image feature is
considered the effective pixel size. If the physical sizes of the two distinct features are known, for example, widths of two parallel
lines or bars with an included space equal to one line or bar, then the effective pixel size is considered ⁄2 of their sums. Example:
A digital image is determined to resolve five line pairs per mm or a width of line equivalent to five distinct lines within a millimetre.
The basic spatial resolution is determined as 1/ [2 × 5 LP/ mm] or 0.100 mm.
3.2.3 binary/digital pixel data—a matrix of binary (0’s, 1’s) values resultant from conversion of PSL from each latent pixel (on
the IP) to proportional (within the bit depth scanned) electrical values. Binary digital data value is proportional to the radiation dose
received by each pixel.
3.2.4 bit depth—the number “2” increased by the exponential power of the analogue-to-digital (A/D) converter resolution.
Example 1) In a 2-bit image, there are four (2 ) possible combinations for a pixel: 00, 01, 10 and 11. If “00” represents black and
“11” represents white, then “01” equals dark gray and “10” equals light gray. The bit depth is two, but the number of gray scales
2 12
shades that can be represented is 2 or 4. Example 2): A 12-bit A/D converter would have 4096 (2 ) gray scales shades that can
be represented.
3.2.5 blooming or flare—an undesirable condition exhibited by some image conversion devices brought about by exceeding the
allowable input brightness for the device, causing the image to go into saturation, producing an image of degraded spatial
resolution and gray scale rendition.
3.2.6 computed radiographic system—all hardware and software components necessary to produce a computed radiograph.
Essential components of a CR system consisting of: an imaging plate, an imaging plate readout scanner, electronic image display,
image storage and retrieval system and interactive support software.
3.2.7 computed radiographic system class—a group of computed radiographic systems characterized with a standard image
quality rating. Practice E2446, Table 1, provides such a classification system.
3.2.8 computed radiography—a radiological nondestructive testing method that uses storage phosphor imaging plates (IP’s), a
PSL stimulating light source, PSL capturing optics, optical-to-electrical conversion devices, analogue-to-digital data conversion
electronics, a computer and software capable of processing original digital image data and a means for electronically displaying
or printing resultant image data.
3.2.9 contrast and brightness—an application of digital image processing used to “re-map” displayed gray scale levels of an
original gray scale data matrix using different reference lookup tables.
3.2.9.1 Discussion—
This mode of image processing is also known as “windowing” (contrast adjustment) and “leveling” (brightness adjustment) or
simply “win-level” image processing.
3.2.10 contrast-to-noise ratio (CNR)—quotient of the digital image contrast (see 3.2.13) and the averaged standard deviation
of the linear pixel values.
3.2.10.1 Discussion—
CNR is a measure of image quality that is dependent upon both digital image contrast and signal-to-noise ratio (SNR) components.
In addition to CNR, a digital radiograph must also possess adequate sharpness or basic spatial resolution to adequately detect
desired features.
3.2.11 digital driving level (DDL)—terminology used to describe displayed pixel brightness of a digital image on a monitor
resultant from digital mapping of various gray scale levels within specific look-up-table(s).
E2007 − 10 (2016)
FIG. 1 Basic Computed Radiography Process
3.2.11.1 Discussion—
DDL is also known as monitor pixel intensity value; thus, may not be the PV of the original digital image.
3.2.12 digital dynamic range—maximum material thickness latitude that renders acceptable levels of specified image quality
performance within a specified pixel intensity value range.
3.2.12.1 Discussion—
Digital dynamic range should not be confused with computer file bit depth.
3.2.13 digital image contrast—pixel value difference between any two areas of interest within a computed radiograph.
3.2.13.1 Discussion—
digital contrast = PV2 – PV1 where PV2 is the pixel value of area of interest “2” and PV1 is the pixel value of area of interest
“1” on a computed radiograph. Visually displayed image contrast can be altered via digital re-mapping (see 3.2.11) or
re-assignment of specific gray scale shades to image pixels.
3.2.14 digital image noise—imaging information within a computed radiograph that is not directly correlated with the degree
of radiation attenuation by the object or feature being examined and/or insufficient radiation quanta absorbed within the detector
IP.
3.2.14.1 Discussion—
Digital image noise results from random spatial distribution of photons absorbed within the IP and interferes with the visibility of
small or faint detail due to statistical variations of pixel intensity value.
3.2.15 digital image processing—the use of algorithms to change original digital image data for the purpose of enhancement
of some aspect of the image.
3.2.15.1 Discussion—
E2007 − 10 (2016)
Examples include: contrast, brightness, pixel density change (digital enlargement), digital filters, gamma correction and pseudo
colors. Some digital processing operations such as sharpening filters, once saved, permanently change the original binary data
matrix (Fig. 1, Step 5).
3.2.16 equivalent penetrameter sensitivity (EPS)—that thickness of penetrameter, expressed as a percentage of the section
thickness radiographed, in which a 2T hole would be visible under the same radiographic conditions. EPS is calculated by: EPS%
= 100/ X (√ Th/2), where: h = hole diameter, T = step thickness and X= thickness of test object (see E1316, E1025, E747, and
Practice E746).
3.2.17 gray scale—a term used to describe an image containing shades of gray rather than color. Gray scale is the range of gray
shades assigned to image pixels that result in visually perceived pixel display brightness.
3.2.17.1 Discussion—
The number of shades is usually positive integer values taken from the bit depth. For example: an 8-bit gray scale image has up
to 256 total shades of gray from 0 to 255, with 0 representing white image areas and 255 representing black image areas with 254
shades of gray in between.
3.2.18 image morphing—a potentially degraded CR image resultant from over processing (that is, over driving) an original CR
image.
3.2.18.1 Discussion—
“Morphing” can occur following several increments of image processing where each preceding image was “overwritten” resulting
in an image that is noticeably altered from the original.
3.2.19 look up table (LUT)—one or more fields of binary digital values arbitrarily assigned to a range of reference gray scale
levels (viewed on an electronic display as shades of “gray”).
3.2.19.1 Discussion—
A LUT is used (applied) to convert binary digital pixel data to proportional shades of “gray” that define the CR image. LUT’s are
key reference files that allow binary digital pixel data to be viewed with many combinations of pixel gray scales over the entire
range of a digital image (see Fig. 5-A).
3.2.20 original digital image—a digital gray scale (see 3.2.17) image resultant from application of original binary digital pixel
data to a linear look-up table (see 3.2.24 and 3.2.19 prior to any image processing.
3.2.20.1 Discussion—
This original gray scale image is usually considered the beginning of the “computed radiograph”, since without this basic
conversion (to gray scales) there would be no discernable radiographic image (see Fig. 5-B).
3.2.21 photostimulable luminescence (PSL)—photostimulable luminescence (PSL) is a physical phenomenon in which a
halogenated phosphor compound emits bluish light when excited by a source of red spectrum light.
3.2.22 pixel brightness—the luminous (monitor) display intensity of pixel(s) that can be controlled by means of electronic
monitor brightness level settings or changes of digital driving level (see 3.2.11).
3.2.23 pixel density—the number of pixels within a digital image of fixed dimensions (that is, length and width).
3.2.23.1 Discussion—
for digital raster images, the convention is to describe pixel density in terms of the number of pixel-columns (width) and number
of pixel rows (height). An alternate convention is to describe the total number of pixels in the image area (typically given as the
number of mega pixels), which can be calculated by multiplying pixel-columns by pixel-rows. Another convention includes
describing pixel density per area-unit or per length-unit such as pixels per in./mm. Resolution (see 7.1.5) of a digital image is
related to pixel density.
3.2.24 pixel value (PV)—a positive integer numerical value directly associated with each binary picture data element (pixel) of
an original digital image where gray scale shades (see 3.2.17) are assigned in linear proportion to radiation exposure dose received
by that area.
E2007 − 10 (2016)
3.2.24.1 Discussion—
Computed radiography uses gray scale shades to render visual perceptions of image contrast; thus, linear pixel value (PV) is used
to measure a specific shade of gray that corresponds to the quantity of radiation exposure absorbed within a particular area of a
part. With this relationship, a PV o
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.