Digital Camera Patent Abstract
There is disclosed an automatic white-balance correction method
for digital camera, which divides a captured picture into multiple
sampled regions for performing a white-balance correction. The image
data of the captured picture is transformed form RGB format to YCrCb
format. Then, the mean values of Y, Cr, and Cb are calculated for
each sampled region based on the multiple sampled regions. Finally,
Cr and Cb are used as two coordinate axes to define four quadrants,
and the values of Cr and Cb of each sampled region are used to determine
a corresponding quadrant for each sampled region, thereby determining
a correction direction based on the number of sampled regions in
each quadrant. Digital Camera Patent Claims
What is claimed is:
1. An automatic white-balance correction method for digital camera,
which divides a captured picture into multiple sampled regions for
performing a white-balance correction, the method comprising the
steps of: (A) transforming image data of the captured picture form
RGB format to YCrCb format; (B) calculating mean values of Y, Cr,
and Cb for each sampled region based on the multiple sampled regions;
and (C) using Cr and Cb as two coordinate axes to define four quadrants,
and using the values of Cr and Cb of each sampled region to determine
a corresponding quadrant for each sampled region, thereby determining
a correction direction based on the number of sampled regions in
each quadrant.
2. The automatic white-balance correction method for digital camera
as claimed in claim 1, wherein in step (C), if the sampled regions
are substantially distributed in quadrants II and IV, a ratio of
Cr and Cb is adjusted to be 1:1 for correction.
3. The automatic white-balance correction method for digital camera
as claimed in claim 2, wherein when the sampled regions are substantially
distributed in quadrant II, a red gain is decreased and a blue gain
is increased for correction.
4. The automatic white-balance correction method for digital camera
as claimed in claim 2, wherein when the sampled regions are substantially
distributed in quadrant IV, a red gain is increased and a blue gain
is decreased for correction.
5. The automatic white-balance correction method for digital camera
as claimed in claim 1, wherein when the sampled regions are substantially
distributed in quadrant III, red and blue gains are increased simultaneously
for correction.
6. The automatic white-balance correction method for digital camera
as claimed in claim 1, wherein when the sampled regions are substantially
distributed in quadrant I, red and blue gains are decreased simultaneously
for correction.
7. The automatic white-balance correction method for digital camera
as claimed in claim 1, further comprising a step (B') between steps
(B) and (C) for filtering out regions which are too bright or too
dark based on the value of Y of each sampled region.
8. The automatic white-balance correction method for digital camera
as claimed in claim 7, wherein in step (B'), the sampled region
is filtered out if its Y value is outside a range of 64.about.180.
9. The automatic white-balance correction method for digital camera
as claimed in claim 1, wherein the captured picture is divided into
an upper region, a middle region, and a lower region.
10. The automatic white-balance correction method for digital camera
as claimed in claim 9, wherein the upper region is further divided
into left and right regions.
11. The automatic white-balance correction method for digital camera
as claimed in claim 9, wherein the lower region is further divided
into left and right regions.
12. The automatic white-balance correction method for digital camera
as claimed in claim 9, wherein the middle region is further divided
into left, right and center regions, and a subject region in the
center region.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of image color adjustment
and, more particularly, to an automatic white-balance correction
method for digital camera, digital video camera, or PC camera.
2. Description of Related Art
Currently, the automatic white-balance correction method is in
wide spread use in the digital camera, digital video camera or a
PC camera. However, the variation of natural light due to different
time or weather condition and the effect of artificial illumination
may cause errors in color tones as taking pictures by a camera or
video camera. For example, the picture will show yellow color when
the color temperature of light source is low, and blue color when
the color temperature of light source is high. Therefore, the high
color temperature (8500K) of light source from the fluorescent lamps
commonly used in our everyday life will make the color of picture
to be of blue color. Moreover, the specific wavelength of the fluorescent
lamps may also make the color of picture to be of green color. As
such, there is a need to perform an adjustment such that the color
of the captured object is not affected by the circumstance. Such
an adjustment is performed by white-balance correction, which allows
the captured picture to be white-balanced in color. That is, the
color of a white object is always shown to be white under any light
sources.
The white-balance correction of the conventional analog camera
is performed by integrating the red and blue chromatic signals (R-Y
and B-Y) respectively, so as to control the gains of the red and
blue signal, thereby the integral value being approached to the
white-balance point. Therefore, the aforementioned white-balance
correction is easily disturbed by the color of the object to be
captured, and the color of the captured image will deviate from
the origin color of the picture. In the advanced digital camera,
the red and blue signals of objects taken by the photo-sensors are
used to control the gains of red and blue signals for performing
the white-balance correction. However, due to the limitation of
visual angle of sensitivity of the photo-sensors, the performance
of such a white-balance correction is not satisfactory.
Another white-balance correction method for digital camera is performed
by analyzing the image to determine the luminance (Y), blue chrominance
(Cb) and red chrominance (Cr) for the pixels of each region in the
picture, so as to alleviate the color deviation in different color
temperatures. However, such a white-balance correction method only
considers the general variation of color temperature rather than
artificial illumination, for example, the fluorescent lamps, and
thus it can not work well for white-balance correction under fluorescent
lamps. Furthermore, such a conventional method judges the color
temperature according to the variation degree of the neighboring
regions and the concentration of color. It results in less color
loss for the object having a huge color block and a high color concentration.
However, the probability of having a huge color block in a general
environment is quit low and the CCD camera usually has different
sensing features in the center and the peripheral portions. The
huge color blocks with the same color exist very seldom in general
environment. The judgement of color concentration may result in
having no correction for the color block with a high color concentration,
which may be caused by color temperature. Therefore, this adjustment
can be applied to a specific condition, but is not suitable in general
environment to achieve the white-balance correction. Therefore,
there is a need to have a novel white-balance correction method
to mitigate and/or obviate the aforementioned problems.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an automatic
white-balance correction method for digital camera, which utilizes
the variation curve of color temperature as a reference for performing
an adjustment, so as to avoid abnormal correction result, and avoid
being influenced by small color block.
With this object in view, the automatic white-balance correction
method for digital camera in accordance with the present invention
divides a captured picture into multiple sampled regions for performing
a white-balance correction. The method includes the steps of: (A)
transforming image data of the captured picture form RGB format
to YCrCb format; (B) calculating mean values of Y, Cr, and Cb for
each sampled region based on the multiple sampled regions; and (C)
using Cr and Cb as two coordinate axes to define four quadrants,
and using the values of Cr and Cb of each sampled region to determine
a corresponding quadrant for each sampled region, thereby determining
a correction direction based on the number of sampled regions in
each quadrant.
Other objects, advantages, and novel features of the invention
will become more apparent from the following detailed description
when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates multiple sampled regions of the
captured picture in accordance with the automatic white-balance
correction method of the present invention;
FIG. 2 is the flowchart of the automatic white-balance correction
method of the present invention; and
FIG. 3 is a color distribution diagram established by the automatic
white-balance correction method in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is illustrated an automatic white-balance
correction method for digital camera in accordance with a preferred
embodiment of the present invention, wherein the taken picture is
divided, based on the trisection sampling theorem, into an upper
region 11 (sky), a middle region 12 (subject), and a lower region
13 (ground). Due to the fact that a large upper or lower region
may result in a difficulty to determine the left-right relation
as the features are disappeared after being averaged, each of the
upper and lower regions is further equally divided into two region,
thereby producing the regions A3, A4, A7, and A8 as shown in the
figure. Based on the same reason, the middle region 12 is also divided
in such a manner that two regions are located at left and right
sides, respectively, and a subject region is preset in the center
region, thereby defining four regions A1, A2, A5, and A6 as shown
in the figure. As such, the overall sampled picture is divided into
eight regions A1.about.A8.
FIG. 2 is a flowchart of the automatic white-balance correction
method for adjusting the CCD image data captured by the digital
camera, which first transforms the CCD image data from RGB format
to YCrCb format according to the following equation: ##EQU1##
and the transformed data are calculated based on the aforementioned
A1.about.A8 regions to determine the mean values of Y, Cr and Cb
of each region.
If the transformed image data of each sampled region is too bright
or too dark, the color will be suppressed and its value is not required
for the white-balance correction. Therefore, such transformed data
can be filtered out. That is, by evaluating the value of Y for each
sampled region, it is determined whether the condition of Min Y<Y<Max
Y is satisfied, where Y is in the range of 0.about.255, and Min
Y and Max Y are preferred to be 64 and 180, respectively. If the
value of Y is not satisfied the aforementioned condition, the corresponding
sampled region is too dark or too bright, and thus is not required
for white-balance correction.
After filtering, the effective image data of the sampled regions
are obtained for adjusting the ratio of colors to achieve the white-balance.
The adjustment process is based on that fact that the color is changed
from red to blue when the color temperature is changed from low
to high. Thus, the correction is focused on the gains of the red
and blue colors. Although the green color is also varied with the
change of color temperature, its influence is not so obvious and
can be compensated by the red and blue colors. Consequently, only
the red and blue colors are used in the actual color adjustment
process. With reference to FIG. 3, there is shown a color distribution
diagram, wherein the Cr and Cb are used as two coordinate axes to
divide the color relation into four quadrants, and the values of
Cr and Cb of each sampled region are used as coordinate values 31
for being filled into the diagram, so as to determine the corresponding
quadrant for a sampled region, thereby obtaining the color feature
of each sampled region.
From the distribution of each sampled region shown in FIG. 3, it
is able to determine the occupied ratio of each quadrant by statistics,
so as to decide whether the whole picture is deviated in color or
only a part of the picture is deviated in color. If only a part
of the picture is deviated in color, it is possible that such a
color deviation is caused by capturing a color block, instead of
the change of color temperature, and thus there is no need to perform
any color adjustment. When most of the picture is deviated in color,
the color deviation direction can be determined by inspecting the
number of sampled regions in each quadrant, so as to perform a color
correction in an opposite direction.
In general, the sampled regions are mostly distributed in quadrant
II or IV; that is, the color is deviated to red and blue color.
Under such a condition, it is simply to adjust the ratio of Cr and
CB to be 1:1, wherein, when color is deviated to red, the red gain
is decreased and the blue gain is increased, and when color is deviated
to blue, the blue gain is decreased and the red gain is increased.
If most of the picture is distributed in quadrant III, it indicates
that the picture may be taken under the light of fluorescent lamp
and the color is deviated to green. Under this condition, there
are two methods applicable for correction. One is to adjust the
gain of green color, which results in the adjustment of all three
RGB colors, so that it becomes difficult in distinguishing the color,
and the distortion is increased. The other preferable one is to
adjust and increase the gains of red and blue colors simultaneously
to achieve the same effect. Similarly, if most of the picture is
distributed in quadrant I, the gains of read and blue colors are
decreased simultaneously to compensate the deviation.
In view of the foregoing, the automatic white-balance correction
method in accordance with the present invention is able to utilize
the variation curve of color temperature as a reference for performing
an adjustment, so as to avoid abnormal correction result. Furthermore,
the present invention is able to determine whether the color deviation
is caused by the light source or a single color block, so as not
to be influenced by a small color block. Because the illumination
of a light source is comprehensive and it is impossible to have
only one or two regions being influenced, the aforementioned effect
can be achieved.
Although the present invention has been explained in relation to
its preferred embodiment, it is to be understood that many other
possible modifications and variations can be made without departing
from the spirit and scope of the invention as hereinafter claimed.
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