ASTM E2825-18
(Guide)Standard Guide for Forensic Digital Image Processing
Standard Guide for Forensic Digital Image Processing
SIGNIFICANCE AND USE
4.1 Processed images are used for many purposes by the forensic science community. They can yield information not readily apparent in the original image, which can assist an expert in drawing a conclusion that might not otherwise be reached.
4.2 This guide addresses image processing and related legal considerations in the following three categories:
4.2.1 Image enhancement,
4.2.2 Image restoration, and
4.2.3 Image compression.
SCOPE
1.1 This guide provides digital image processing guidelines to ensure the production of quality forensic imagery for use as evidence in a court of law.
1.2 This guide briefly describes advantages, disadvantages, and potential limitations of each major process.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E2825 − 18
Standard Guide for
1
Forensic Digital Image Processing
This standard is issued under the fixed designation E2825; 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 4. Significance and Use
4.1 Processed images are used for many purposes by the
1.1 This guide provides digital image processing guidelines
forensic science community. They can yield information not
to ensure the production of quality forensic imagery for use as
evidence in a court of law. readily apparent in the original image, which can assist an
expert in drawing a conclusion that might not otherwise be
1.2 This guide briefly describes advantages, disadvantages,
reached.
and potential limitations of each major process.
4.2 This guide addresses image processing and related legal
1.3 This international standard was developed in accor-
considerations in the following three categories:
dance with internationally recognized principles on standard-
4.2.1 Image enhancement,
ization established in the Decision on Principles for the
4.2.2 Image restoration, and
Development of International Standards, Guides and Recom-
4.2.3 Image compression.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
5. Image Enhancement
5.1 Image enhancement is any process intended to improve
2. Referenced Documents
the visual appearance of an image.
2
2.1 ISO/IEC Standard:
5.1.1 Use brightness adjustment when the image is too
ISO/IEC 10918-1:1994 Information technology—Digital
bright or too dark. If the image is made too bright, there is a
compression and coding of continuous-tone still images:
risk of loss of detail in light areas. If the image is made too
Requirements and guidelines (JPEG) (also published as
dark, there is a risk of loss of detail in the dark areas.
CCITT Recommendation T.81 (1992))
5.1.2 Use color processing to modify the color characteris-
tics of objects within an image. This includes color space
3. Summary of Practice
transformations, pseudocoloring, and hue and saturation ad-
3.1 The original image shall be preserved. Any image
justments.
processing should be applied only to a working copy of the
5.1.2.1 Application of these techniques can compromise the
image.
color fidelity of the image.
3.2 Any changes made through image processing shall meet
5.1.3 Use contrast adjustment when the image lacks suffi-
the following criteria:
cient contrast. If the image contrast is increased too much,
3.2.1 Processing steps are documented in a manner suffi-
there is a risk of loss of detail in both light and dark areas.
cient to permit a comparably trained person to understand the
5.1.4 Use cropping to remove that portion of the image that
steps taken, the techniques used, and extract comparable
is outside the area of interest.
information from the image; and
5.1.5 Use dodging and burning to adjust brightness in
3.2.2 The end result is presented as a processed or working
localized areas.
copy of the image.
5.1.6 Use linear filtering techniques (see Fig. 1) to increase
the contrast of small detail in an image. These include
3.3 Avoid the introduction of artifacts that add misleading
sharpening, blur removal, edge enhancement, and deconvolu-
information to the image or the loss of image detail that could
tion. If a low degree of enhancement is used, the image will
lead to an erroneous interpretation.
remain an accurate representation of the scene. If a high degree
of enhancement is used, the image may no longer be an
1
This guide is under the jurisdiction of ASTM Committee E30 on Forensic
accurate representation of the overall scene, though it still may
Sciences and is the direct responsibility of Subcommittee E30.12 on Digital and
be useful as an adjunct for interpretation of small details.
Multimedia Evidence.
Current edition approved March 1, 2018. Published April 2018. Originally
5.1.6.1 Ahigh degree of enhancement can also increase the
approved in 2012. Last previous edition approved in 2012 as E2825. DOI:
visibility of existing noise and artifacts; examples of noise
10.1520/E2825-18.
2 include film grain, snow appearing on a television screen, or
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. random color dots.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E2825 − 18
FIG. 1 This Example Illustrates the Effects of Linear Filtering—Left: Original Image, Middle: Blurred Image, and
...
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: E2825 − 12 E2825 − 18
Standard Guide for
1
Forensic Digital Image Processing
This standard is issued under the fixed designation E2825; 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 digital image processing guidelines to ensure the production of quality forensic imagery for use as
evidence in a court of law.
1.2 This guide briefly describes advantages, disadvantages, and potential limitations of each major process.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ISO/IEC Standard:
ISO/IEC 10918-1:1994 Information technology—Digital compression and coding of continuous-tone still images: Requirements
and guidelines (JPEG) (also published as CCITT Recommendation T.81 (1992))
3
2.2 SWGIT Material:
SWGDE/SWGIT Glossary SWGDE and SWGIT Digital & Multimedia Evidence Glossary, updated June 8, 2012
3. Terminology
3.1 Definitions:
3.1.1 artifact, n—visual/aural aberration in an image, video, or audio recording resulting from a technical or operational
limitation. SWGDE/SWGIT Glossary
3.1.1.1 Discussion—
Examples include speckles in a scanned picture or “blocking” in images compressed using the JPEG standard.
3.1.2 compression, n—process of reducing the size of a data file (see lossy compression and lossless compression).
SWGDE/SWGIT Glossary
3.1.3 grayscale image, n—continuous tone image that has only one component. ISO/IEC 10918-1:1994
3.1.4 grayscale transformation, n—operation that modifies a single channel or component of image data (for example, a single
color).
3.1.5 image, n—imitation or representation of a person or thing, drawn, painted, photographed, and so forth.
SWGDE/SWGIT Glossary
3.1.6 image enhancement, n—any process intended to improve the visual appearance of an image or specific features within an
image. SWGDE/SWGIT Glossary
3.1.7 lossless, adv—descriptive term for encoding and decoding processes and procedures in which the output of the decoding
procedure(s) is identical to the input to the encoding procedure(s). ISO/IEC 10918-1:1994
3.1.8 lossless coding, n—mode of operation that refers to any one of the coding processes defined in this guide in which all of
the procedures are lossless. ISO/IEC 10918-1:1994
1
This guide is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.12 on Digital and Multimedia
Evidence.
Current edition approved May 1, 2012March 1, 2018. Published October 2012April 2018. Originally approved in 2012. Last previous edition approved in 2012 as E2825.
DOI: 10.1520/E2825-12.10.1520/E2825-18.
2
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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E2825 − 18
3.1.9 lossless compression, n—compression in which no data are lost and all data can be retrieved in their original form.
SWGDE/SWGIT Glossary
3.1.10 lossy, adv—descriptive term for encoding and decoding processes that are not lossless. ISO/IEC 10918-1:1994
3.1.11 lossy compression, n—compression in which data are lost and cannot be retrieved in their original form.
SWGDE/SWGIT Glossary
3.1.12 noise, n—variations or disturbances in brightness or color information in an image that do not arise from the scene.
SWGDE/SWGIT Glossary
3.1.12.1 Discussion—
Sources of noise include film grain, electronic variations in the input device sensor and circuitry, and stray electromagnetic fields
in the signal pathway. It frequently refers to visible artifacts in an image.
3.1.13 original image, n—accurate and complete replica of the primary image, irrespective of media.
SWGDE/SWGIT Glossary
3.1.13.1 Discussion—
For film and analog video, the primary image is the original image.
3.1.14 primary image, n—first instance in which an image is recorded onto any media that is a separate, identifiable object.
SWGDE/SW
...
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