ISO 21227-1-2003 Paints and varnishes, Assessment of defects on coated surfaces using optical imaging – Part 1: General guidance

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ISO 21227-1 was developed by Technical Committee ISO/TC 35, Paints and Varnishes, Subcommittee SC 9, Common Test Methods for Paints and varnishes.

ISO 21227-1-2003 Paints and varnishes, Assessment of defects on coated surfaces using optical imaging – Part 1: General guidance

ISO 21227 consists of the following parts under the general heading Paints and Varnishes – Assessment of Defects on coated Surfaces Using optical Imaging:

— Part 1: General guidance

— Part 2: Evaluation procedure for multiple impact lithotriptic test results

— Part 3: Assessment procedures for delamination and corrosion around lines

At the time this part of ISO 21227 was published, Parts 2 and 3 were being prepared.

Traditional ISO testing methods used to assess surface defects and appearance changes typically use graphic standards that depict specific types of surface deterioration and require human visual evaluation. Compared with human visual assessment techniques, the techniques described in the various sections of this standard can produce more objective, accurate, quantitative and repeatable results.

ISO 21227-1-2003 Paints and varnishes, Assessment of defects on coated surfaces using optical imaging – Part 1: General guidance

1 range
This part of ISO 21227 defines and provides guidance for the use of optical imaging systems to quantitatively characterize defects that occur on the surface of coatings after exposure in various test methods (e.g. lithotripsy, weathering or crosscutting tests). One goal of ISO 21227 is to use optical imaging to reproduce the results of existing visual evaluation methods. In addition, optical imaging provides more information that can be used to assess coating defects in more detail.

This part of ISO 21227 contains a general introduction to optical imaging methods and definitions. The performance and accuracy requirements of individual test methods are described in other sections of the standard.

2 Normative references
The following references are required for the use of this document. For dated references, citation-only versions apply. For undated references, the new version of the reference (including any revisions) applies.

CIE publication No. 17.4:1987, International Vocabulary for Lighting /IEC 60050-845:1987, International Vocabulary for Electricians – Lighting

3 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.

3.1 Optical Imaging

A method of acquiring, digitizing, processing, and analyzing images using optical elements and computer systems

3.2 Lighting

Apply light to a scene, object, or its surroundings so that they can be seen

[Source: CIE 17.4:1987 /IEC 60050-845:1987]

3.2.1 Reflection Lighting

Light source and optical sensor are arranged on the same side of the object lighting

3.2.2 Transmission Lighting

Light sources and optical sensors arranged on opposite sides of an object for illumination

3.2.3 Open field lighting

An image acquisition method for detecting light reflected by an object and light scattered by an object by an optical sensor

3.2.4 Dark field lighting

An image acquisition method in which an optical sensor detects only the light scattered by an object

3.2.5 Directional Lighting

Illumination in which light on a working plane or object is primarily incident from a particular direction

[Source: CIE 17.4:1987 /IEC 60050-845:1987]

3.2.6 Diffuse Lighting

Light on a working surface or object does not come primarily from illumination in a particular direction

[Source: CIE 17.4:1987 /IEC 60050-845:1987]

3.3 Terms related to optical sensors

3.3.1 Visual Field

The area on the surface of an object picked up by an optical sensor

3.3.2 Region of Interest

The part of the original image used for image processing and image analysis

3.3.3 Purpose

An optical system, usually consisting of one or more lenses, used to acquire a visual field image

ISO 21227-1-2003 Paints and varnishes, Assessment of defects on coated surfaces using optical imaging – Part 1: General guidance

3.3.4 Object distance

The distance between the first lens of the objective lens and the object provides a clear image

3.3.5 Focal depth

The difference between minimum and maximum object distances

3.4 Image Acquisition

Image capture

The process of creating a two-dimensional raw image of an object

3.4.1 Original image

The digital image taken by the image acquisition system does not require any image processing

3.4.2 Charge-coupled device CCD

A device that uses semiconductor materials as optical sensors

Note 1: CCD chips are subdivided into very fine components, each corresponding to a pixel of the digitized image. CCDS can be arranged in arrays (digital cameras) or rows (line scanners).

3.4.3 Scanner

An image acquisition device using a one-dimensional optical sensor in which CCDS are arranged in a row

Note 1: The image is built by line scanning the surface of the object.

3.4.4 Digitization

The process of converting an analog image to a digital image

Note 1: The image is divided into pixels by a grid, and each pixel is assigned a grayscale level.

3.4.5 pixels

The minimum image forming element to which grayscale is assigned

3.4.6 Resolution

The number of pixels per unit length on an object surface

Note 1: If the resolution in the X and Y directions is different, the two values need to be reported.

3.4.7 Gray level

The shade of gray assigned to the pixel

Note 1: The shadow is usually a positive integer value taken from the gray level.

3.4.8 Gray scale

A series of grays between white and black

Example: The 8-bit gray scale has 28 (= 256) grays. Grey level 0 corresponds to black and grey level 255 (256th) corresponds to white.

3.4.9 Gamma C

The function Y is equal to X, the exponent gamma

X is the input signal;
Y is the output signal;
X and Y range from 0 to 1 (0 for black, 1 for white)
3.4.10 Image Acquisition Card

A device used to convert an analog video signal into a digital raw image

3.5 Image Processing

The software manipulates the original image to prepare it for subsequent image analysis

Note 1: For example, image processing may be used to eliminate errors generated during image acquisition or to reduce image information to the desired extent.

3.5.1 Binary Image

An image in which each pixel is 0 (black) or 1 (white)

3.5.2 Gamma correction

The modification of gamma value can be carried out by software or hardware

3.5.3 Brightness

The average gray of a specified portion of the image

3.5.4 Contrast

The difference between the grayscale of two specified parts of an image

ISO 21227-1-2003 Paints and varnishes, Assessment of defects on coated surfaces using optical imaging – Part 1: General guidance

3.5.5 Shadow correction

Software method for correcting object illumination inhomogeneity

3.5.6 Thresholding

To reduce the number of different gray levels of the image, it is recommended to obtain a binary image

Note 1: To generate a binary image, each pixel in a grayscale image is assigned a grayscale level of 0 or 1, depending on whether the pixel’s grayscale is greater than, less than, or equal to a given constant (the threshold).

3.5.7 Partition

Edge detection

A method for isolating and locating optical edges in a given digital image

3.6 Image Analysis

Reduces image information to a set of application-specific values

3.6.1 Reference Panel

A specified panel that has been evaluated and therefore has a known rating

Note 1: It is used to check the reproducibility and repeatability of parameter Settings.

3.7 Image Evaluation

The process of associating a set of values resulting from image analysis with one or more characteristic values through a classification or rating scheme

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