iso13406-检测重点标准英文版.doc

ISO 13406-2 ISO testing certificate for LCD displays
Quality, not price, is the main point
Europeans, and particularly Germans, are generally said to have a strong affinity for standards, guidelines and regulations. At times they even come in for some teasing because of this. But were would the IT industry be without binding guidelines such as, for example, MPR, TCO, ISO TUV etc., regulating quality and ergonomic standards of CRT monitors for years? So far, LCD was the exception to the standardization trend, since technology was persuasive due to their ergonomic, environmentally friendly qualities. In this way they distinguished themselves from CRT monitors. But now, standardization committees have begun to respond to the pressure from industry, which had recognized that reliable parameters for making quality distinctions were in the interests of industry, and began demanding them. As from Spring , when the ISO standard 13406-2 was adapted for LCD, LCD displays are able to obtain a special ISO testing certificate.

Viewing angle
The image quality of TFT monitors is not consistently good from every perspective. In general, one can say that the quality is better the more one approach a line of sight that is vertical to the monitor surface. You can evaluate the quality of a TFT monitor, inter alias, from the evenness of its brightness, contrast or color when viewing the screen from a range of various viewing angles. These qualities can vary when viewed from various viewing angles, as they relate to the focal point of view.
The ISO 13406-2 standard provides from our classes of viewing angles that represent real-life using situations.
Class I -
This permits several users to view the entire display area at the same time. This applies both for intended viewing distance (between 40 and 60 cm, depending on the size and resolution of the monitor) and for a viewing angle within an 80 cone without any restriction of visual efficiency.
Class II –
Permits a single user to view the entire area of the display. This applies for intended viewing distance (between 40 and 60cm, depending on the size and resolution of the monitor) from every position in front of the screen, in such a way that regularity of information (brightness, contrast, colors) is maintained.
Class III –
Permits a single viewer to view the entire area of the display. This applies for intended viewing distance (between 40 and 60 cm, depending on the size and resolution of the monitor) from one fixed position, in such a way that regularity of information (brightness, contrast, colors) is maintained.
Class IV –
Permits a single user to view the center of the screen. This applies for intended viewing distance (between 40 and 60cm, depending on the size and resolution of the monitor) from one fixed position, in such a way that regularity of information (brightness, contrast, colors) is maintained.

Pixel faults
A 15-inch LCD monitor consists of 1024x 768 pixels, each of which contains three sub pixels. One transistor regulates the color of each sub pixel (one transistor per sub pixel!). If one of these transistors fails, the pixel can either appear permanently black or white or display the wrong color. Due to manufacturing issues, errors can arise on the panels (the actual picture elements) of TFT monitors, Depending on what kind of fault is present, and the image can be distorted to a greater or lesser degree. A blinking pixel, for example, is more of an irritant than a constantly illuminated red one. A cluster of defective pixels in a small area is more apparent than if the faults are distributed over the entire panel.
Depending on how many defects such as these occur in a panel, one can categorize TFT monitors into four pixel fault classes.
No pixel faults –
The pixel matrix is regular. There are no gaps or defective pixels.
Type I malfunction –
A complete pixel is constantly illuminated. The result is a constantly white point.
Tolerance per 1 million pixels:
Class I: 0
Class II: 2
Class III: 5
Class IV: 50
Type II malfunction –
A complete pixel is not illuminated at all. The result is a constantly dark point.
Tolerance per 1 million pixels:
Class I: 0
Class II: 2
Class III: 15
Class IV: 150
Type III malfunction –
One or two sub pixels (red, green or blue) are permanently switched on or off. This results in a pixel in one of the basic colors (red, green, blue, cyan, magenta, yellow) – here cyan. A blinking pixel can also occur.
Tolerance per 1 million pixels:
Class I: 0
Class II: 5
Class III: 50
Class IV: 500

Fault cluster I –
There are several Type I or II malfunctions in a field of 5x5 pixels.
Tolerance per 1 million pixels:
Class I: 0
Class II: 0
Class III: 0
Class IV: 5

Fault cluster II –
There are several Type III malfunctions in a 5x5 pixel area.
Tolerance per 1 million pixels:
Class I: 0
Class II: 2
Class III: 5
Class IV: 50

Cluster definition
1. Cluster is defined as two or more Type III defects within 5*5 pixel matrix.
2. Aim is to minimize number of clusters, when counting defects.
3. Individual Type III defects can be double or triple counted, when counting clusters.

Luminance and brightness distribution
With LCD monitors, luminance of the screen surface is achieved by backlighting. A thin foil covering the entire display background distributes the light of a number of light elements situated at the edges of the display over the entire display area.
Luminance is a measure for the light emitted from the monitor. Because of their backlighting, LCD monitors exhibit luminance of over 200 cd/m2 and thus a greater degree of luminance overall as compared with CRT monitors.
Furthermore, the evenness of brightness distribution is important for the quality of image generation. Irregularities can result in particular from improper or imprecise of the LCD monitor also from lower quality lighting systems.
Since the human eye perceives colors in relation to their brightness, irregularities in the distribution of brightness will also lead to deficiencies in the display of color.

Flicker
Depending on the various methods of image generation, LCD monitors offer a score of advantages as versus CRT monitors. Absolutely flicker-free imaging, with a much more precise focal point than is the case with conventional CRT screens, where flicker is unavoidable because the image has to be constantly refreshed. If the refresh or image repeats rate is less than 85 Hertz, the user will see flicker. LCD does not require any picture repeats of this kind: The pixels change only if something changes in the image itself. A typical LCD backlight operates in the 60 kHz frequency band, i.e. up to 1000 times faster than CRT monitors. This prevents any flicker. Due to their technology, LCD monitors do not flicker at lower picture frequencies either. The lower the picture refresh frequency is set on the graphics card, the better the display will be able to digitalize it, and the more stable and detailed the picture will be.

Font analysis
The characters must be clear and sharp. There must not be any distracting irregularities as regards the characters and surfaces of equal luminance.
Characters must be sufficiently large and have an appropriate character and line pitch. This means: Font matrix must be at least 7 x 9 (with x height) as well as 3 pixels under baseline. Character height of the large characters should be at least 2.9 mm at a viewing distance of 50mm. Character width of the upper case characters should be 70-90% of their height, and should not fall below 50% of the characte4r height. Lower case characters should have at least 70% of the width of upper case characters. The character height should be approximately 70% of that of upper case characters. Even in the low pixel zone, the characters have to be displayed such that there is no danger of mistaking them.

Reflections
The reflection characteristics of an LCD screen are of particular importance in very bright ambient conditions or in the vicinity of multiple light sources, as acceptable display quality is required here as well. The standard provides for three quality classes:
(1) Appropriate for general office conditions without special requirements as to workplace lighting.
(2) Appropriate for most office conditions, with few exceptions.
(3) Appropriate for office conditions with controlled luminance, i.e. the workstation is subject to special lighting requirements.

Contrast
Contrast is the ratio between the individual tones of brightness in the picture. Picture contrast is of crucial importance for the quality of a TFT monitor. This means that –depending on the quality of the monitor and ambient light conditions, the perceptual difference between picture areas which are very dark – even black in the most extreme cases – and very bright ones – even white in the most extreme cases – can be very great or very slight.
Monitors with strong contrast, or where the environment is dark, display more levels of brightness between their extremes than do monitors with weak contrast or where there is bright ambient light. In ideal conditions, good monitors achieve contrast of approximately 1:300.
ISO standard 13406-2 measures the contrast of a monitor under three different ambient conditions: in absolute darkness, under office conditions and under conditions of daylight.
I) Darkroom (<51x)
In absolute darkness, display contrast is at its greatest. The values achieved here are, however, not normally applicable in everyday conditions.
II) Office conditions (293 lx)
Display contrast is already somewhat reduced due to the brighter ambient lighting. This measuring parameter approximates most closely the conditions at a workstation.
III) Daylight (>5000 lx)
In bright daylight outside, display contrast is strongly reduced. The contrast ratio is only a fraction of that observed in the darkroom. This measurement is largely irrelevant to work inside buildings.

ISO 13406 Part 2 – The New Standard for LCD brings Transparency to the Display Market
ISO 13406 Part 2, introduced at the beginning of this year, as part of the TUV ergonomic testing, is the answer of the International Organization of Standardization (ISO) to the increased demand for liquid crystal displays. The new standard deals with ergonomic requirements specific to LCD technology. So far, only ISO 9241 Parts 3, 7, and 8 have set standards for visual display terminals, but they were initially developed for Cathode Ray Tube (CRT) monitors and did not take all of the LCD characteristics into account.
The key quality issues covered by the new standard ISO 13406 Part 2 are therefore:
- Display luminance
- Contrast
- Color reproduction
- Luminance and color uniformity
- Font analysis
- Flicker
- Reflection
- Pixel defects
The above-mentioned properties are evaluated and the results translated into the three categories explained below. These categories are explicitly stated on the ISO certificate issued for the monitor in question

Viewing Angles
One of the characteristics specific to LCD is the fact that the quality of the displayed image depends on the viewing angle. Apart from the display quality, luminance, color reproduction, and contrast have to be taken into consideration. The ISO 13406 Part 2 standard specifies measurement values for ergonomic design and quality requirements in order to evaluate the performance of an LCD monitor from different viewing angles. Classes from I to IV describe the main use for which a monitor has been designed. For example, a class IV monitor is to be used by a single person sitting right in front of the screen. Class I monitors are designed for a number of people viewing from different angles at the same time.

Viewing angle classification provides performance assessment type of application
Class I: For parallel viewing by several users
Class II: Adequate for 1 user (suitable for general office use)
Class III: Limited viewing angle
Class IV: Unacceptable for general use

Reflection
The reflection class of an LCD tells the customer which monitor is best for which office environment and lighting conditions. The new standard divides the tested monitors into 3 performance classes. Class I stands for devices suitable for general office environments and different lighting conditions. The suitability of class II monitors is restricted. These monitors are only suitable for most office environments, since strong changes of light intensity might influence the display quality. Class III monitors should only be used in office environments with controllable lighting conditions that is where the lighting conditions are almost constant.

Contrast ratio measurements:
Dark room
IEC < 5 lx ISO < 3 lx
Office light
Horizontal 500 lx monitor angle 293 lx
Sunlight
> 5000 lx
Quotes from TUEV Rheinland:
“Contrast ratios of 300:1, 350:1, 400:1 are lies”
LCD Monitor manufacturers must specify contrast ratio:
“Xxx: 1 in dark room (5 lx), yyy: 1 in standard office environment (293 lx)”

Pixel Defects

Pixel defects are characteristics of LCD monitors, which are due to technology and production engineering reasons. A 15“ display with the standard resolution of 1024x768 dpi, for example, consists of 2.4 million cells. With such an enormous number it is virtually impossible for each and every cell to function perfectly. There is a high possibility that individual cells are faulty, that is they are constantly turned on or off. The result is constantly bright or dark pixels. By clearly defining pixel defect categories, ISO 13406 Part 2 provides transparency, since it enables customers to compare the product properties guaranteed by the manufacturers. Once a monitor is assigned to a certain pixel defect category, the manufacturer has to make sure that all monitors of the same type meet the corresponding compliance criteria in mass production.
Which defect belongs to which pixel defect category is determined according to the number of pixel defects and the quality of the defect (defect type).
The following table provides an overview of the different classes and types of pixel defects. The number of pixel defects is defined per 1 million pixels.
Pixel defect
Category
Defect type 1
(Constantly bright pixel)
Defect type 2
(Constantly dark pixel)
Defect type 3
(Defect sub pixel, either constantly bright (red, green, blue) or constantly dark)
I
0
0
0
II
2
2
5
III
5
15
50
IV
50
150
500

A constantly bright pixel (defect type 1) is more irritating to the user than a constantly dark one (defect type 2). The least irritating is a defect sub pixel being just dark or shining either red, green, or blue (defect type 3). The number of pixel defects tolerated by the standard depends on the degree of the user’s irritation. Therefore, the number of tol