Source: http://www.docstoc.com/docs/97329543/Method-Of-And-Apparatus-For-Image-Enhancement-Taking-Ambient-Illuminance-Into-Account---Patent-7995851
Timestamp: 2013-12-19 10:04:58
Document Index: 215506592

Matched Legal Cases: ['art.\n12', 'art.\n20', 'Application No. 2005', 'art 110', 'art 120', 'art 130', 'art 140', 'art 150', 'art 160', 'art 110', 'art 110', 'art 114', 'art 116', 'art 120', 'art 120', 'art 120', 'art 122', 'art 130', 'art 140', 'art 130', 'art 140', 'art 150', 'art 110', 'art 120', 'art 150', 'art 150', 'art 154', 'art 156', 'art 158', 'art 160', 'art 150', 'art 120', 'art 160', 'art 110', 'art 114', 'art 116', 'art 124', 'art 120', 'art 120', 'art 122', 'art 150', 'art 154', 'art 156', 'art 158', 'art 158', 'art 158', 'art 158', 'art 160', 'Application No. 2005']

Method Of, And Apparatus For Image Enhancement Taking Ambient Illuminance Into Account - Patent 7995851
United States Patent: 7995851
7,995,851
Method of, and apparatus for image enhancement taking ambient illuminance
A method of and an apparatus for image enhancement taking ambient
illuminance into consideration. The image enhancement method includes
calculating an original-luminance contrast which is a luminance contrast
with respect to an original-luminance of pixels forming an original
image, calculating a fade-luminance by reflecting the variation of
perceived luminance based on an ambient illuminance into the
original-luminance, calculating a defade-luminance by converting the
fade-luminance to maintain the original-luminance contrast, and
calculating a display-luminance by reflecting the variation of perceived
luminance by the ambient illuminance into the defade-luminance. Improving
luminance contrast through adjustment of luminance based on ambient
illuminance, effectively reduces the fade phenomenon.
Lee; Seong-deok (Suwon-si, KR), Kim; Chang-veong (Yongin-si, KR), Lebedev; Dmitry (Moscow, RU), Rozhkova; Galina (Moscow, RU), Bastakov; Vladmir (Moscow, RU), Kwak; Young-Shin (Suwon-si, KR)
11/353,955
10-2005-0013767
382/254  ; 345/11; 345/74.1; 345/75.1; 345/75.2; 345/77; 382/272; 382/274
G06K 9/40&amp;nbsp(20060101); G09G 3/20&amp;nbsp(20060101); G09G 3/22&amp;nbsp(20060101); G09G 3/30&amp;nbsp(20060101); G09G 1/06&amp;nbsp(20060101); G06K 9/38&amp;nbsp(20060101)
Zettel et al.
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2004/0227719
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2005/0180629
Masuno et al.
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Daiku et al.
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1.  An image enhancement method, comprising: calculating an original-luminance contrast which is a luminance contrast between an original-luminance of pixels forming an
original input image;  calculating a fade-luminance by reflecting a variation of perceived luminance based on an ambient illuminance into the original-luminance;  calculating a defade-luminance by using the original-luminance contrast and a fade-average
luminance with respect to the calculated fade-luminance to maintain the original-luminance contrast;  and calculating a display-luminance for displaying an output image by reflecting the variation of luminance as perceived by the ambient illuminance,
into the defade-luminance.
2.  The image enhancement method of claim 1, wherein the calculating of the defade-luminance comprises: calculating the fade-average luminance by using the fade-luminance and the fade-luminance values with respect to neighboring pixels;  adding
the original-luminance contrast and a predetermined weight;  and multiplying the fade-average luminance by a result of the adding, and outputting a result of the multiplying as the defade-luminance.
3.  The image enhancement method of claim 2, wherein the predetermined weight is `1`.
4.  The image enhancement method of claim 2, wherein the calculating of the defade-luminance further comprises: limiting the defade-luminance within a predetermined luminance range.
5.  The image enhancement method of claim 4, wherein: when the defade-luminance is less than a first sum, which is the sum of an ambient luminance corresponding to the ambient illuminance and a predetermined lowest luminance, the limiting of the
defade-luminance comprises changing the defade-luminance to the first sum, and when the defade-luminance exceeds a second sum, which is the sum of the ambient luminance corresponding to the ambient illuminance and a predetermined highest luminance, the
limiting of the defade-luminance comprises changing the defade-luminance to the second sum.
6.  The image enhancement method of claim 1, wherein the calculating of the display-luminance comprises: subtracting the ambient luminance corresponding to the ambient illuminance from the defade-luminance and outputting the result of the
subtracting as the display-luminance.
7.  The image enhancement method of claim 1, wherein the calculating of the original-luminance contrast comprises: calculating an original-average luminance by using the original-luminance and original-luminance values with respect to
neighboring pixels;  calculating an original-luminance difference by subtracting the original-average luminance from the original-luminance;  and dividing the original-luminance difference by the original-average luminance, and outputting the result of
the dividing as the original-luminance contrast.
8.  The image enhancement method of claim 1, wherein the calculating of the fade-luminance comprises: converting the ambient illuminance, as being input, into a corresponding ambient luminance;  adding the ambient luminance and the
original-luminance;  and outputting the result of the adding as the fade-luminance.
9.  The image enhancement method of claim 8, wherein the calculating of the fade-luminance further comprises: inputting a value corresponding to the ambient illuminance.
10.  The image enhancement method of claim 8, wherein the calculating of the fade-luminance further comprises: sensing the ambient illuminance to input the ambient illuminance value.
11.  An image enhancement apparatus, comprising: an original-luminance contrast calculation part calculating an original-luminance contrast which is a luminance contrast between an original-luminance of pixels forming an original input image;  a
fade-luminance calculation part calculating a fade-luminance by reflecting a variation of luminance as perceived based on an ambient illuminance into the original-luminance;  a defade-luminance calculation part calculating a defade-luminance by using the
original-luminance contrast and a fade-average luminance with respect to the fade-luminance, which is calculated by the fade-luminance calculation part, to maintain the original-luminance contrast which is calculated by the original-luminance contrast
calculation part;  and a display-luminance calculation part calculating a display-luminance for displaying an output image by reflecting the variation of luminance as perceived by the ambient illuminance into the defade-luminance calculated by the
defade-luminance calculation part.
12.  The image enhancement apparatus of claim 11, wherein the defade-luminance calculation part comprises: a low pass filter (LPF) calculating the fade-average luminance by using the fade-luminance calculated by the fade-luminance calculation
part and fade-luminance values with respect to neighboring pixels;  an adding part adding the original-luminance contrast calculated by the original-luminance contrast calculation part and a predetermined weight;  and a multiplying part multiplying the
fade-average luminance calculated by the LPF by the result of adding t, and outputting the result of multiplication as the defade-luminance.
13.  The image enhancement apparatus of claim 12, wherein the predetermined weight is `1`.
14.  The image enhancement apparatus of claim 12, wherein the defade-luminance calculation part further comprises a limiting part limiting the defade-luminance within a predetermined luminance range.
15.  The image enhancement apparatus of claim 14, wherein: when the defade-luminance is less than a first sum, which is the sum of ambient luminance corresponding to the ambient illuminance and a predetermined lowest luminance, the limiting part
limits the defade-luminance to the first sum, and when the defade-luminance exceeds a second sum, which is the sum of the ambient luminance corresponding to the ambient illuminance and a predetermined highest luminance, the limiting part limits the
defade-luminance to the second sum.
16.  The image enhancement apparatus of claim 11, wherein the display-luminance calculation part subtracts the ambient luminance corresponding to the ambient illuminance from the defade-luminance, and outputs the result of the subtracting as the
display-luminance.
17.  The image enhancement apparatus of claim 11, wherein the original-luminance contrast calculation part comprises: a low pass filter (LPF) calculating an original-average luminance by using the original-luminance and original-luminance values
with respect to neighboring pixels;  a subtracting part calculating an original-luminance difference by subtracting and the original-average luminance which is calculated by the LPF from the original-luminance;  and a dividing part dividing the
original-luminance difference calculated by the subtracting part, by the original-average luminance calculated by the LPF, and outputting the result of division as the original-luminance contrast.
18.  The image enhancement apparatus of claim 11, wherein the fade-luminance calculation part comprises: a converting part converting the ambient illuminance as being inputted, into a corresponding ambient luminance;  and an adding part adding
the external luminance converted by the converting part, with the original-luminance, and outputting the result of adding as the fade-luminance.
19.  The image enhancement apparatus of claim 18, further comprising: an ambient illuminance sensing part sensing the ambient illuminance of the apparatus and inputs and inputting the ambient illuminance to the converting part.
20.  The image enhancement apparatus of claim 18, further comprising: an ambient illuminance input part operable by a user to input a value corresponding to the ambient illuminance to the converting part.
This application claims the benefit of Korean Patent Application No. 2005-13767, filed Feb.  18, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
Aspects of the present invention relate to a method of and an apparatus for image enhancement.  More particularly, aspects of the present invention relate to a method of and an apparatus for image enhancement which enhances luminance contrast by
luminance adjustment.
When a display device such as a TV, a monitor, or a mobile phone is in a brighter place where ambient illuminance is high, a human eye perceives relatively decreased luminance contrast compared to the image being actually displayed.  The
reduction of luminance contrast leads to a reduction of image clarity.  The reduction of image clarity is called a `fade` phenomenon.
For example, when the luminance contrast of an original image as shown in FIG. 1A reduces to the luminance contrast as shown in FIG. 1B due to high ambient illuminance, the fade phenomenon occurs.  FIGS. 1A and 1B show mean and standard
deviation (std) values.
A conventionally available way to improve the luminance contrast and thus reduce the fade phenomenon, is to simply expand luminance distribution.  However, due to limited range of expansion of the luminance distribution, the fade phenomenon has
not been effectively controlled or compensated.
To overcome the above and/or other problems occurring in the conventional display devices, an aspect of the present invention provides an apparatus for and a method of image enhancement, which reduces a fade phenomenon by enhancing luminance
contrast through adjustment of image luminance based on the ambient illuminance.
The above and/or other aspects are achieved by providing an image enhancement method, comprising calculating an original-luminance contrast which is a luminance contrast with respect to an original-luminance of pixels forming an original image,
calculating a fade-luminance by reflecting a variation of perceived luminance based on an ambient illuminance into the original-luminance, calculating a defade-luminance by converting the fade-luminance to maintain the original-luminance contrast, and
calculating a display-luminance by reflecting the variation of perceived luminance by the ambient illuminance into the defade-luminance.
The calculating of the defade-luminance may comprise calculating a fade-average luminance by using the fade-luminance and the fade-luminance values with respect to neighboring pixels, adding the original-luminance contrast with a predetermined
weight, and multiplying the fade-average luminance by the result of the adding, and outputting the result of multiplication as the defade-luminance.  The predetermined weight may be `1`.
When the defade-luminance is not more than a first sum, which is a sum of ambient luminance corresponding to the ambient illuminance and a predetermined lowest luminance, the he defade-luminance may be limited by changing the defade-luminance to
the first sum, and when the defade-luminance exceeds a second sum, which is a sum of the ambient luminance corresponding to the ambient illuminance and a predetermined highest luminance, the defade-luminance may be limited by changing the
The calculating of the original-luminance contrast may comprise calculating an original-average luminance by using the original-luminance and original-luminance values with respect to neighboring pixels, calculating an original-luminance
difference by subtracting the original-average luminance from the original-luminance, and dividing the original-luminance difference by the original-average luminance, and outputting the result of the dividing as the original-luminance contrast.
The calculating of the fade-luminance may comprise converting the ambient illuminance as being input, into a corresponding ambient luminance, and adding the ambient luminance with the original-luminance, and outputting the result of adding as
the fade-luminance.
The above and or other aspects may also be achieved by providing an image enhancement apparatus, comprising an original-luminance contrast calculation part calculating an original-luminance contrast which is a luminance contrast with respect to
an original-luminance of pixels forming an original image, a fade-luminance calculation part calculating a fade-luminance by reflecting a variation of perceived luminance based on an ambient illuminance into the original-luminance, a defade-luminance
calculation part calculating a defade-luminance by converting the fade-luminance, which is calculated by the fade-luminance calculation part, to maintain the original-luminance contrast which is calculated by the original-luminance contrast calculation
part, and a display-luminance calculation part calculating a display-luminance by reflecting the variation of the perceived luminance by the ambient illuminance into the defade-luminance calculated by the defade-luminance calculation part.
The defade-luminance calculation part may comprises a LPF (Low pass filter) calculating a fade-average luminance by using the fade-luminance calculated by the fade-luminance calculation part and the fade-luminance values with respect to
neighboring pixels, an adding part adding the original-luminance contrast calculated by the original-luminance contrast calculation part with a predetermined weight, and a multiplying part multiplying the fade-average luminance calculated by the LPF by
the result of adding calculated by the adding part, and outputting the result of multiplication as the defade-luminance.  The predetermined weight may be `1`.
When the defade-luminance is not more than a first sum, which is the sum of ambient luminance corresponding to the ambient illuminance with a predetermined lowest luminance, the limiting part may limit the defade-luminance by changing the
defade-luminance to the first sum, and when the defade-luminance exceeds a second sum, which is the sum of the ambient luminance corresponding to the ambient illuminance with a predetermined highest luminance, the limiting part may limit the
defade-luminance by changing the defade-luminance to the second sum.
The original-luminance contrast calculation part may comprise a low pass filter (LPF) calculating an original-average luminance by using the original-luminance and original-luminance values with respect to neighboring pixels, a subtracting part
calculating an original-luminance difference by subtracting the original-average luminance which is calculated by the LPF from the original-luminance, and a dividing part dividing the original-luminance difference calculated by the subtracting part by
the original-average luminance calculated by the LPF, to output the result of division as the original-luminance contrast.
The fade-luminance calculation part may comprise a converting part converting the ambient illuminance as being externally input, into a corresponding ambient luminance, and an adding part adding the external luminance converted by the converting
part, with the original-luminance, to output the result of adding as the fade-luminance.
described below in order to explain the present invention by referring to the figures.  Well known functions or constructions are not described in detail to avoid obscuring the invention in unnecessary detail.
FIG. 2 is a block diagram of an image enhancement apparatus according to an embodiment of the present invention.  The image enhancement apparatus according to the embodiment shown in FIG. 2 enhances luminance contrast by adjusting a luminance of
the image.  In the enhancement of luminance contrast through luminance adjustment, the image enhancement apparatus takes ambient illuminance into account.  Accordingly, a lesser fade phenomenon will occur in the image being displayed even with high
The image enhancement apparatus according to the embodiment shown in FIG. 2 may include an original-luminance contrast calculation part 110, a fade-luminance calculation part 120, an ambient illuminance sensing part 130, an ambient illuminance
input part 140, a defade-luminance calculation part 150 and a display-luminance calculation part 160.
The original-luminance contrast calculation part 110 calculates luminance contrast with respect to original-luminance (C.sub.o(x, y)) (hereinafter called original-luminance contrast), by using original-luminance (Y.sub.o(x, y)) as being input.
The term `original-luminance contrast` refers to the luminance of the pixels forming the original image.  The original-luminance contrast calculation part 110 may include a first low pass filter (LPF) 112, a subtracting part 114 and a dividing part 116.
The fade-luminance calculation part 120 calculates fade-luminance (Y.sub.F(x, y)) by using the original-luminance (Y.sub.o(x, y)) and the ambient illuminance (I.sub.E).  In detail, the fade-luminance calculation part 120 calculates
fade-luminance (Y.sub.F(x, y)) by reflecting a luminance variance, as perceived by the ambient illuminance (I.sub.E), into the original-luminance (Y.sub.o(x, y)).  The fade-luminance calculation part 120 includes a first adding part 122 and a converting
The ambient illuminance sensing part 130 measures the ambient illuminance of the place where the display device is located.  The ambient illuminance input part 140 may operate as an interface through which the ambient illuminance may be input
directly by a user, or indirectly through an external device (not shown).  The image enhancement apparatus may include one or both of the ambient illuminance sensing part 130 and the ambient illuminance input part 140.
The defade luminance calculation part 150 calculates defade-luminance (Y&#39;.sub.DF(x, y)), by using the original-luminance contrast (C.sub.o(x, y)) being output from the original-luminance contrast calculation part 110 and the fade-luminance
(Y.sub.F(x, y)) being output from the fade-luminance calculation part 120.  In detail, the defade-luminance calculation part 150 converts the fade-luminance (Y.sub.F(x, y)) to maintain the original-luminance contrast (C.sub.o(x, y)) so that the
defade-luminance (Y&#39;.sub.DF(x, y)) can be calculated.  The defade-luminance calculation part 150 may include a second LPF 152, a second adding part 154, a multiplying part 156 and a limiting part 158.
The display-luminance calculation part 160 calculates display-luminance (Y.sub.D(x, y)), by using the defade-luminance (Y&#39;.sub.DF(x, y)) being output from the defade-luminance calculation part 150 and ambient luminance (Y.sub.E) being output
from the fade-luminance calculation part 120.  The display-luminance calculation part 160 may calculate the display-luminance (Y.sub.D(x, y)), by reflecting the luminance variation as perceived by the ambient illuminance (I.sub.E) into the
defade-luminance (Y&#39;.sub.DF(x, y)).
A process of enhancing luminance contrast using ambient illuminance-based luminance adjustment by the image enhancement apparatus according to the embodiment of the present invention shown in FIG. 2 will now be described below with reference to
FIGS. 2 and 3.  FIG. 3 is a flowchart explaining a method of image enhancement which takes ambient illuminance into account according to an embodiment of the present invention.
Referring to FIGS. 2 and 3, the first LPF 112 of the original-luminance contrast calculation part 110 calculates original-average luminance (L.sub.o(x, y)), by using the original-luminance (Y.sub.o(x, y)) being input and the original-luminance
of neighboring pixels (S210).  More specifically, the first LPF 112 multiplies the above luminance values by corresponding coefficients, sums the results of the multiplications, and thus calculates the original-average luminance (L.sub.o(x, y)).  The
original-average luminance may be calculated as shown in expression (1):
According to the expression (1), the size of a mask is 5(i=-2,-1,0,+1,+2).times.5(j=-2,-1,0,+1,+2).  Examples of the coefficients (f.sub.LPF(i, j)) of the 5.times.5 mask are shown in Table 1.
TABLE-US-00001 TABLE 1 i = -2 i = -1 i = 0 i = +1 i = +2 J = -2 1/256 4/256 6/256 4/256 1/256 J = -1 4/256 16/256 24/256 16/256 4/256 J = 0 6/256 24/256 36/256 24/256 6/256 J = +1 4/256 16/256 24/256 16/256 4/256 J = +2 1/256 4/256 6/256 4/256
Next, the subtracting part 114 calculates original-luminance difference (D.sub.o(x, y)) by subtracting and the original-average luminance (L.sub.o(x, y)) from the original-luminance (Y.sub.o(x, y)) (S220).  The original-luminance difference
(D.sub.o(x, y)) may be calculated as shown in expression (2): D.sub.o(x,y)=Y.sub.o(x,y)-L.sub.o(x,y) (2)
Next, the dividing part 116 calculates the original-luminance contrast (C.sub.o(x, y)), by dividing the original-luminance difference (D.sub.o(x, y)) by the original-average luminance (L.sub.o(x, y)) (S230).  The original-luminance contrast
(C.sub.o(x, y)) may be calculated as shown in expression (3):
An original image having the original-luminance (Y.sub.o(x, y)) is shown in FIG. 4A.  FIG. 4B shows the image constituted using the original-average luminance (L.sub.o(x, y)).  Additionally, FIG. 4C shows the image being constituted by the
original-luminance differences (D.sub.o(x, y)) and FIG. 4D shows the image being constituted by the original-luminance contrast (C.sub.o(x, y)).
The converting part 124 of the fade-luminance calculation part 120 converts the ambient illuminance (I.sub.E) as input into a corresponding ambient luminance (Y.sub.E) (S240).  The fade-luminance calculation part 120 may perform the conversion
with reference to a pre-stored (I.sub.E)-(Y.sub.E) conversion table.  The ambient luminance (Y.sub.E) and the corresponding ambient illuminance (I.sub.E) are stored in the (I.sub.E)-(Y.sub.E) conversion table in a form of a database.
Next, the first adding part 122 adds the ambient luminance (Y.sub.E) with the original-luminance (Y.sub.F(x, y)), and thus calculates the fade-luminance (Y.sub.o(x, y)) (S250).  The fade-luminance (Y.sub.F(x, y)) may be calculated as shown in
expression (4): Y.sub.F(x,y)=Y.sub.o(x,y)+Y.sub.E (4)
Next, by using the fade-luminance (Y.sub.F(x, y)) as being input to the second LPF 152 of the defade-luminance calculating part 150 and the fade-luminance values with respect to the neighboring pixels, the fade-average luminance (L.sub.F(x, y))
is calculated (S260).  The second LPF 152 may be embodied in the same way as the first LPF 112.
Meanwhile, the second adding part 154 adds the original-luminance contrast (C.sub.o(x, y)) and a predetermined weight (w), and outputs the result of addition (C.sub.o(x, y)+w) (S270).  The weight (w) may be selected from any value and may be set
and/or changed.  The weight (w) may be set to `1`.
The multiplying part 156 calculates the defade-luminance (Y.sub.DF(x, y)), by multiplying the fade-average luminance (L.sub.F(x, y)) by the result of the addition, (C.sub.o(x, y)+w), (S280).  The defade-luminance (Y.sub.DF(x, y)) may be
calculated as shown in expression (5): Y.sub.DF(x, y)=(C.sub.o(x, y)+w).times.L.sub.F(x, y) (5)
When `w=1`, the defade-luminance contrast (C.sub.DF(x,y)), which is the luminance contrast with respect to the defade-luminance (Y.sub.DF(x, y)), becomes identical to the original-luminance contrast (C.sub.o(x,y)), which is the luminance
contrast with respect to the original-luminance (Y.sub.o(x,y)).  More specifically, the defade-luminance contrast (C.sub.DF(x,y)) may be calculated as shown in expression (6):
.function..function..function..function.  ##EQU00003##
When `w=1` is set and the expression 5 is appropriately rearranged, the right side of the expression (6) becomes identical to the original-luminance contrast (C.sub.o(x, y)), and as a result, the defade-luminance contrast (C.sub.DF(x,y)) becomes
identical to the original-luminance contrast (C.sub.o(x, y)) as shown in expression (7).
.function..function..function..function..function.  ##EQU00004##
When the defade-luminance (Y.sub.DF(x, y)) is out of a predetermined range, the limiting part 158 limits the defade-luminance (Y.sub.DF(x, y)) within the predetermined range, to output a final defade-luminance (Y&#39;.sub.DF(x, y)) (S290).
More specifically, when the defade-luminance (Y.sub.DF(x, y)) is smaller than a sum of a predetermined lowest luminance (Y.sub.L) and the ambient luminance (Y.sub.E), (Y.sub.L+Y.sub.E), the limiting part 158 converts the defade-luminance
(Y.sub.DF(x, y)) to (Y.sub.L+Y.sub.E).  When the defade-luminance (Y.sub.DF(x, y)) exceeds the sum of a predetermined highest luminance (Y.sub.H) and the ambient luminance (Y.sub.E), (Y.sub.H+Y.sub.E), the limiting part 158 converts the defade-luminance
(Y.sub.DF(x, y)) to the sum (Y.sub.H+Y.sub.E).  When the defade-luminance (Y.sub.DF(x, y)) is not less than (Y.sub.L+Y.sub.E) and not more than (Y.sub.H+Y.sub.E), the limiting part 158 directly outputs the defade-luminance (Y.sub.DF(x, y)) without
conversion.  Accordingly, Y&#39;.sub.DF(x, y) becomes identical to Y.sub.DF(x, y).  The calculation of the final defade-luminance in the operation 290 may be expressed by (i), (ii) and (iii) as follows: i) If Y.sub.DF(x, y)&amp;lt;(Y.sub.L+Y.sub.E), then
Y&#39;.sub.DF(x, y)=(Y.sub.L+Y.sub.E).  ii) If Y.sub.DF(x, y)&amp;gt;(Y.sub.H+Y.sub.E), then Y&#39;.sub.DF(x, y)=(Y.sub.H+Y.sub.E).  iii) If (Y.sub.L+Y.sub.E).ltoreq.(Y.sub.DF(x,y).ltoreq.(Y.sub.H+Y.sub.E), then Y&#39;.sub.DF(x, y)=Y.sub.DF(x, y).
Next, the display-luminance calculation part 160 calculates display-luminance (Y.sub.D(x, y)), by subtracting the ambient luminance (Y.sub.E) from the final defade-luminance (Y&#39;.sub.DF(x, y)) and (S300).  The display-luminance (Y.sub.D(x, y))
may be calculated as shown in expression 8: Y.sub.D(x,y)=Y&#39;.sub.DF(x,y)-Y.sub.E (8)
The calculated display-luminance (Y.sub.D(x, y)) is used in displaying the image on a screen.  Because the display-luminance (Y.sub.D(x, y)) has enhanced luminance contrast through luminance adjustment based on the ambient illuminance, the image
can be displayed using the display-luminance (Y.sub.D(x, y)) with a reduced fade phenomenon even when ambient illuminance is very high (that is, even when the ambient environment is very bright).
FIG. 5A shows the luminance contrast of the original image, and FIG. 5B shows the fade phenomenon due to reduction of luminance contrast due to high ambient illuminance.  FIG. 5C shows the enhancement of luminance contrast which is obtained by
adjusting the luminance according to aspects of the present invention, reducing the fade phenomenon.  Mean and standard deviation (std) values are as shown in FIGS. 5A, 5B and 5C.
As described above luminance contrast can be enhanced by adjusting luminance in consideration of ambient illuminance, accordingly reducing the fade phenomenon.  As a result, a clearer image can be provided even with high ambient illuminance.
The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention.  The present teaching can be readily applied to other types of apparatuses.  Although a few embodiments of the present
invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and
Method of, and apparatus for image enhancement taking ambient illuminance into account, et al., Seong-deok Lee, Chang-veong Kim, Dmitry Lebedev, Galina Rozhkova, Vladmir Bastakov, Young-Shin Kwak, Application number 11 353-955, Image Analysis, Computer Graphics Processing And Selective Visual Display Systems
S This application claims the benefit of Korean Patent Application No. 2005-13767, filed Feb. 18, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.BACKGROUND OF THE INVENTION 1. Field of the Invention Aspects of the present invention relate to a method of and an apparatus for image enhancement. More particularly, aspects of the present invention relate to a method of and an apparatus for image enhancement which enhances luminance contrast byluminance adjustment. 2. Description of the Related Art When a display device such as a TV, a monitor, or a mobile phone is in a brighter place where ambient illuminance is high, a human eye perceives relatively decreased luminance contrast compared to the image being actually displayed. Thereduction of luminance contrast leads to a reduction of image clarity. The reduction of image clarity is called a `fade` phenomenon. For example, when the luminance contrast of an original image as shown in FIG. 1A reduces to the luminance contrast as shown in FIG. 1B due to high ambient illuminance, the fade phenomenon occurs. FIGS. 1A and 1B show mean and standarddeviation (std) values. In order to provide a clearer image, the fade phenomenon must be appropriately controlled or compensated, such as by improving the luminance contrast of the image being displayed. A conventionally available way to improve the luminance contrast and thus reduce the fade phenomenon, is to simply expand luminance distribution. However, due to limited range of expansion of the luminance distribution, the fade phenomenon hasnot been effectively controlled or compensated.SUMMARY OF THE INVENTION To overcome the above and/or other problems occurring in the conventional display devices, an aspect of the present invention provides an apparatus for and a method of image enhancement, which reduces a fade phenomenon by enhancing luminancecontrast through adjustment of image luminance based on the ambien
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