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SEMI D31-1102 © SEMI 2002 4 seems to be the bou ndary. He re we propose Equation 1 which regressively analyzes the ● i n F i g u r e 1 a s criteria for standardization. 72 . 0 1 97 . 1 33 . 0 +       = S Cjnd … .. …

SEMI D31-1102 © SEMI 2002 3

RELATED INFORMATION 1

EXPERIMENT OUTLINE FOR CALCULATION OF MEASUREMENT

INDEX FOR LUMINANCE MURA IN FPD IMAGE QUALITY INSPECTION

NOTE: This related information is not an official part of SEMI D31. This related information was approved for

publication by full letter ballot procedures on July 19, 2002.

R1-1 Purpose

R1-1.1 It has been reported that under the range of

certain conditions, a basic expression of FPD mura

quality level can be made, using their size and

contrast

[1]

. Here, recreating those experiments, we

verified their reproducibility, conducting the

experiment with a goal of calculating a measurement

index for luminance mura for standardization.

R1-2 Experiment Method

R1-2.1 Experiment Equipment

R1-2.1.1 The experiment utilized a 14.1 inch, 1024 X

768 pixel backlit TFT/LCD. As there was a need to

display low contrast luminance muras, it was reworked

to display 256 gradations in a 43 cd/m

~ 54 cd/m

range. A program capable of displaying rectangular

and round muras as desired was created, and the muras

were displayed in the center of the prepared LCD. The

subjects could freely adjust the luminance of the

displayed luminance muras using a handheld ten-key

pad.

R1-2.2 Experiment Conditions

R1-2.2.1 21 types of muras were used. These were

four round types (diameter:7, 25, 55, 305 pixels) and 17

rectangular types (31×1, 153×1, 240×1, 480×1, 31×2,

153×2, 240×2, 31×3, 153×3, 240×3, 31×16, 69×35,

140×17, 240×10, 1×31, 1×153, 1×240). Observation

conditions were a viewing distance of 500 mm, and

view angle normal to the center of the LCD. The

experiment room was a darkroom, and the background

luminance of the luminance mura was 48 cd/m

R1-2.3 Subjects/Experiment Procedure

R1-2.3.1 The subjects for the experiment were 16

adults, with no eye disease and with near vision

strength (50 cm) of 1.2 or greater for both eyes. Of the

16 subjects, there was an Expert group of 8 (7 male, 1

female, average age 40 years), consisting of engineers

from LCD makers, who regularly conduct mura

inspections and analysis. The remaining 8 subjects (6

males, 2 females, average age 21) were college

students, a Novice group who were conducting

luminance mura evaluation for the first time. Using the

ten-key pad, the subjects adjusted the luminance of

mura, to a point “where mura can just no longer be

detected” (referred to as “jnd”: just noticeable

difference below) and to a “point where mura can

clearly be detected” (referred to as “distinct” below),

recording the contrasts at these times. Muras brighter

than the background and lighter than the background

were both targeted.

R1-3 Experiment Results

R1-3.1 The following matters became clear from the

experiment.

• The larger the area of the mura, the smaller jnd

contrast (C jnd) became. (Muras are more visible

as area becomes larger)

• Muras with a width of one pixel, compared to other

muras, require nearly 1.5 to 2 times the contrast.

(Muras with a width of one pixel are difficult to

detect)

• Comparing the distribution between the subjects,

there was no difference between the Expert and

Novice groups for jnd contrast (C jnd)

• Compared to the Expert group, the Novice group

had a larger distribution for distinct contrast.

R1-3.2 The relation between mura area and jnd

contrast showed the same trend as in past experience

[1]

and the quality of reproducibility was confirmed.

Therefore at this point, for the sake of standardization,

we examined the function for mura area, and tried

linear regression for it with jnd contrast. Figure 1

shows the results. When the horizontal axis is

33.0

(S is mura area in mm

units), and the vertical axis is at

contrast, the bold line shows a strong correlation

coefficient, understood through linear regression.

R1-3.3 This bold line shows the relation between mura

area and contrast at the point where the mura becomes

just not detectable (jnd), and if area is determined, then

jnd contrast (C jnd) can be figured out. In Figure 1, ○

is a mura with a width of one pixel, and ● represents

other muras (not one pixel wide) respectively

representing the averages of the 16 subjects. As noted

above in 2), a mura with a width of one pixel tends to

be slightly different, which is why they were handled

separately. Also considering past experiment results,

when viewing distance is 500mm, the 0.3mm level

SEMI D31-1102 © SEMI 2002 4

seems to be the boundary. Here we propose Equation 1

which regressively analyzes the ● in Figure 1 as

criteria for standardization.

72.0

97.1

33.0













Cjnd

….. Equation 1

R1-3.4 The criteria for standardization, jnd, is

determined by the C jnd straight line, but we also

propose, based on this criteria, quality levels for other

visible muras. Figure 1 shows straight lines made up of

2.0 jnd and 3.0 jnd. × is distinct contrast for the

Expert group, but in cases besides 1-pixel wide muras,

it can be understood to be distributed slightly above the

2.0 jnd straight line.

R1-3.5 This indicates that the straight-line relationship

of Figure 1 is not only jnd level, but also consists of

visible contrast level. Accordingly, with the bold line

jnd as a standard, mura quality level can be expressed

by n in n x jnd. From the experiment results this time,

from 3.0 being a level slightly above distinct, it can be

thought that it is desirable to operate using a range of

levels 1.0 to 3.0.

R1-4 Summary

R1-4.1 A proposal was made regarding the

quantization of FPD luminance mura. The quality level

of a mura can be expressed as a function between mura

area and contrast, using the contrast at the jnd point as

criteria. By using this method, even if mura area,

shape, or contrast is different, we can now calculate

similar quality level jnd.

C jnd = 1.97 (1/f(S) ) + 0.72

= 0.87

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

1/f(S)

Contrast (%)

3.0 jnd

2.0 jnd

1 pixel-width Mura

f(S) = S

0.33

S :unit (mm

)

Figure R1-1

Relation between luminance mura area and jnd contrast (C jnd)

(●: jnd contrast of mura not 1 pixel wide, ○:jnd contrast of mura 1 pixel wide,

×: Distinct contrast of all muras (Average of Expert group only))

Prepared by R. Yoshitake and T. Tamura

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