SUMMARY OF THE INVENTION
[0001] To solve the foregoing problems, the present invention employs an optical sensor
accompanied by sensing elements disposed on a display. The optical sensor is calibrated
before leaving a factory so that image self-calibration may be performed by the display
itself without need of any external device and software. The present invention may
be applied on occasions when it is not convenient to set up external devices and may
reduce corrective maintenance cost of displays.
[0002] The primary purpose of the present invention is to provide an image self-calibration
method for LCD displays which employs a front optical sensor disposed on the display
to calibrate the gray scale level and color temperature of the display. The optical
sensor will be pre-calibrated before use to maintain stable and consistent reference
values.
[0003] Further, the foregoing method specifically includes the following steps: (1) set
up a front optical sensor on a display; (2) calibrate the front optical sensor with
a calibration reference device; (3) the front optical sensor calibrates the gamma
value and color temperature of the display.
[0004] The present invention further provides an image self-calibration device for LCD displays
comprising a front optical sensor disposed in front of an LCD display panel and a
calibration reference device disposed in a middle of the LCD display. The calibration
reference device and the display are connected to a computer. The front optical sensor
is employed to calibrate the gray scale level and color temperature of the display.
The calibration reference device is employed to pre-calibrate the front optical sensor.
[0005] The present invention has the following advantages. Image pre-calibration is performed
on the installed optical sensor before it leaves a factory, and the calibrated optical
sensor directly performs gray scale level and color temperature calibration on the
display. The present invention is easy to implement and can effectively inspect and
calibrate images on displays.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006]
FIG. 1 is a schematic view of image calibration performed on a front optical sensor
according to the present invention; and
FIG. 2 is a schematic view of image self-calibration performed by the front optical
sensor itself according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0007] The foregoing purposes of the present invention along with its structure and performance
characteristics are further illustrated in the following description of specific embodiments
in conjunction with the accompanying figures. Please refer to FIGS. 1 and 2.
[0008] The present invention is illustrated in a flow diagram and a schematic flow diagram
including the following three steps.
[0009] Step 1: set up a front optical sensor on a display. A front optical sensor 2 is disposed
in front of an LCD display 1 panel to prevent LCD display panel degradation from causing
luminance attenuation, so that measurement data may be more accurate.
[0010] Step 2: calibrate the front optical sensor, perform the following steps to get measurement
data, and compare the measurement data with those obtained by the calibration reference
device 3. When the difference between the measurement data and the calibration reference
device 3 is smaller than the margin of error, Delta E (2000) < 5, the calibration
is successful.
- A. Set up a colorimeter or a spectrometer in an appropriate position on the display
to serve as a calibration reference device 3;
- B. Connect the display 1 and the calibration reference device 3 to a computer;
- C. Calibrate the luminance of the display 1 to a minimum value within a range of application
and display a completely black test screen. After the luminance becomes stable, the
optical sensor 2 measures Red, Green, and Blue channels and the obtained data is
while the calibration reference device 3 measures the coordinates x and y of chrominance space and luminance (brightness) Y and the obtained data is
- D. Display a test screen 4 on the display 1. The calibration reference device 3 measures
the coordinates x and y of chrominance space and luminance (brightness) Y and stores the measured data. Simultaneously the front optical sensor measures the
Red, Green, and Blue channels and the clear channel and stores the measured data;
Test screen in application: rgb=(255 0 0), rgb=(0 255 0), rgb=(0 0 255)
Three sets of measured data of three test screens obtained by the calibration reference
device 3:
Measured data obtained by the corresponding front optical sensor:
- E. Apply the relation equation of chrominance space and color stimulus, wherein the
x and y in the equation are coordinates of chrominance space and the X, Y, and Z are color stimulus:
Transfer the measured data obtained in steps 3 and 4 by the calibration reference
device 3 into color stimulus and get four sets of color stimulus:
- F. Establish a transfer matrix between the measured data obtained by the front optical
sensor and the color stimulus obtained in step 4. Get a transfer matrix coefficient
and establish a conversion equation:
wherein
is the color stimulus, and
is the measured data obtained by the front optical sensor;
Enter into the conversion equation the measured data obtained by the front optical
sensor and the color stimulus measured and converted by the calibration reference
device 3 at steps 3, 4, and 5 and get the transfer matrix M.
- G. Display other test screens on the display and measure them by the front optical
sensor to obtain measured data. Convert the measured data into x, y, and Y via equations 4, 2, and 1. Compare x, y, and Y with the measured data obtained by the calibration reference device 3. When the difference
between them is smaller than the margin of error, the calibration is successful.
Step 3: the front optical sensor calibrates the display.
[0011]
A. Measure a minimum luminance value Lmin and a maximum luminance value Lmax of the display by the front optical sensor. Calculate the contrast radio C = Lmax / Lmin of the display to confirm that it corresponds to the specifications of DICOM;
B. Calibrate the gamma value by performing the following steps:
- a. Control and calibrate a backlight of the display to an appropriate luminance with
feedback from the front optical sensor. The luminance must be greater than a minimum
luminance as specified in DICOM;
- b. Show a 32-level gray scale test screen on the display, which is measured and recorded
by the front optical sensor to serve as a reference luminance. Also, establish a luminance
characteristic curve;
- c. Based on the requirements of display chip, interpolate the reference luminance
by performing three cubic spline interpolations and get the luminance reference table
required by the display chip. The size of the luminance reference table is n;
- d. Use the target gamma value and gamma value equation 5 to calculate the luminance
value required for each level. Select a nearest corresponding level from the luminance
reference table and enter it into the gamma table.
x = 0,1...n-1; and
- e. Firmware of the display loads the gamma table obtained in step 4 and measures the
gray scale curve again to verify whether the result of the calibration is correct
and complete gamma calibration.
C: Calibrate the color temperature by performing the following steps:
- a. Control and calibrate a backlight of the display to an appropriate luminance with
feedback from the front optical sensor. The luminance must be greater than a minimum
luminance as specified in DICOM;
- b. Show a completely white test screen on the display. The front optical sensor uses
the transfer matrix to measure the coordinates x and y of the current chrominance space and luminance (brightness) Y of the display, and Red, Green, Blue gain values of the display in the temporary
storage. R-Gain is directly proportional to the x in color coordinates (x, y) which corresponds to the color temperature, G-Gain is directly proportional to y, and B-Gain is inversely proportional to x and y. Further, R-Gain, G-Gain, B-Gain and the luminance Y satisfy the following equation: Y=0.299*R Gain+0.587*G Gain+0.114*B Gain. Hence, calibrate the R-Gain, G-Gain, and
B-Gain of the display in the temporary storage to calibrate the color temperature
of the display screen;
- c. Firmware of the display loads the R-Gain, G-Gain, and B-Gain values and measures
the coordinates x and y of the chrominance space and luminance (brightness) Y of the display again to verify whether they fall within a margin of tolerable error
and complete color temperature calibration.
[0012] The present invention performs image pre-calibration on an installed front optical
sensor and uses the front optical sensor to directly calibrate the gray scale level
and color temperature of the display. The present invention is easy to implement and
can effectively inspect and calibrate images on the display.
[0013] The foregoing preferred embodiments of the present invention are illustrated of the
present invention rather than limiting of the present invention. It is intended to
cover various modifications and changes included within the spirit and scope of the
appended claims, the scope of which should be accorded the broadest interpretation
so as to encompass all such modifications and similar structures.
1. A method of image self-calibration for LCD displays, wherein calibration is performed
by a front optical sensor on the display to calibrate the gray scale level and color
temperature of the display; and wherein the front optical sensor requires pre-calibration
before use.
2. The method of image self-calibration for LCD displays as defined in claim 1, wherein
the method specifically includes the following steps:
(1) Set up a front optical sensor on a display;
(2) Calibrate the front optical sensor with a calibration reference device; and
(3) The front optical sensor calibrates the gamma value and color temperature of the
display.
3. The method of image self-calibration for LCD displays as defined in claim 2, wherein
step 2 further includes the following steps:
(21) Set up a calibration reference device in front of the display;
(22) Connect the display and the calibration reference device to a computer;
(23) Display a test screen on the display. The calibration reference device measures
the coordinates x and y of chrominance space and luminance Y and stores the measured data on the computer. The front optical sensor measures the
display and stores the measured data;
(24) Enter the measured data obtained by the calibration reference device in step
(23) into a relation equation of the chrominance space and color stimulus to get color
stimulus;
(25) Establish a transfer matrix between the measured data obtained by the front optical
sensor in step (23) and the color stimulus obtained in step (24) to get a transfer
matrix coefficient;
(26) Display other test screens on the display and measure them by the front optical
sensor to obtain measured data. Convert the measured data into coordinates of chrominance
space and luminance. Compare them with the measured data obtained by the calibration
reference device. When the difference between them is smaller than the margin of error,
Delta E (2000) <5, the calibration is successful.
4. The method of image self-calibration for LCD displays as defined in claim 2, wherein
the calibration reference device is a colorimeter or a spectrometer.
5. The method of image self-calibration for LCD displays as defined in claim 2, wherein
gamma value calibration performed by the front optical sensor includes the following
steps:
(311) Control and calibrate a backlight of the display with feedback from the front
optical sensor, so that its luminance is greater than a minimum luminance as specified
in DICOM;
(312) Show a test screen on the display, which is measured and recorded by the front
optical sensor to serve as a reference luminance. Also, establish a luminance characteristic
curve based on the reference luminance;
(313) Based on the requirements of display chip, interpolate the reference luminance
and get the luminance reference table required by the display chip. The size of the
luminance reference table is n;
(314) Use the target gamma value and gamma value equation, L(x) = L0 + (Ln-1-L0) × (x/n)γ, to calculate the luminance value required for each level.
Select a nearest corresponding level from the luminance reference table and enter
it into the gamma table; and
(315) Firmware of the display loads the gamma table obtained in step (314) and measures
the gray scale curve again to verify whether the result of the calibration is correct
and complete gamma calibration.
6. The method of image self-calibration for LCD displays as defined in claim 5, wherein
the following steps are further included before step (311):
Measure a minimum luminance value Lmin and a maximum luminance value Lmax of the display by the front optical sensor. Calculate the contrast radio C = Lmax l Lmin of the display to confirm that it corresponds to the specifications of DICOM.
7. The method of image self-calibration for LCD displays as defined in claim 5, wherein
in step (313) the reference luminance is interpolated by three cubic spline interpolations.
8. The method of image self-calibration for LCD displays as defined in claim 2, wherein
color temperature calibration performed by the front optical sensor includes the following
steps:
(321) Control and calibrate a backlight of the display with feedback from the front
optical sensor, so that the luminance is greater than a minimum luminance as specified
in DICOM;
(322) Show a test screen on the display. The front optical sensor obtains measured
data and uses a transfer matrix to measure the coordinates of the current chrominance
space and luminance (brightness) of the display. Calibrate the R-Gain, G-Gain, and
B-Gain of the display in the temporary storage to calibrate the color temperature
of the display screen based on a relation between the R-Gain, G-Gain, and B-Gain and
coordinates of chrominance space;
(323) Firmware of the display loads the calibrated R-Gain, G-Gain, and B-Gain values
and measures the coordinates of the chrominance space and luminance of the display
again to verify whether they fall within a margin of tolerable error, Delta E (2000)
<5, and complete color temperature calibration.
9. An image self-calibration device for LCD displays, comprising a front optical sensor
disposed in front of an LCD display panel and a calibration reference device disposed
in a middle of the LCD display. The calibration reference device and the display are
connected to a computer. The front optical sensor is employed to calibrate the gray
scale level and color temperature of the display. The calibration reference device
is employed to pre-calibrate the front optical sensor.
10. The image self-calibration device for LCD displays as defined in claim 9, wherein
the calibration reference device is a colorimeter or a spectrometer.