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Digital Camera Patent Abstract
A method for consistently determining color information of an object
utilizing a high resolution digital image taken with a digital camera.
The object is set in a fixed environmental and lighting condition
and the digital camera is set with certain predetermined fixed settings
to provide consistent and repeatable digital images. The digital
image is taken with a predetermined neutral reference adjacent the
object. A commercially available image editing software is used
to standardize and analyze the color information of the digital
image based on the neutral reference.
Digital Camera Patent Claims
What we claim is:
1. A method of determining color information of an object utilizing
a digital image taken with a digital camera, comprising the steps
of: providing a predetermined fixed environmental and lighting condition
for said object; setting said camera with predetermined fixed settings;
providing a predetermined neutral reference adjacent said object
at a predetermined location; capturing said digital image to include
said object and said neutral reference; providing a commercially
available image editing software capable of standardizing and analyzing
the digital image; standardizing said digital image based on said
neutral reference using said computer program; and analyzing the
color information of said object using said computer program.
2. The method of claim 1 wherein said digital image is a high resolution
digital image.
3. The method of claim 1 wherein said digital camera is a digital
SLR camera.
4. The method of claim 1 wherein said predetermined fixed environmental
and lighting condition comprises the use of a powerful flash with
said camera.
5. The method of claim 1 wherein said predetermined fixed environmental
and lighting condition comprises a predetermined room and predetermined
room illumination.
6. The method of claim 5 wherein said predetermined room having
neutral color walls and ceiling.
7. The method of claim 5 wherein said predetermined room illumination
having no natural sunlight.
8. The method of claim 1 further comprising the steps of aligning
said camera at a predetermined orientation with respect to said
object.
9. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to manual exposure
mode with a fixed aperture.
10. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to aperture priority
exposure mode.
11. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to matrix metering.
12. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to center-weighted
metering.
13. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to a fixed magnification
ratio close to 1:1.
14. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to manual flash mode.
15. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to a fixed white balance.
16. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to a fixed image resolution.
17. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to a fixed file type.
18. The method of claim 1 wherein said predetermined fixed settings
of said camera comprises setting said camera to the lowest ISO value
on said camera.
19. The method of claim 1 wherein said camera comprises a Nikon
D100 camera body, a 105 mm AF Mikro Nikkor lens and a Nikon SB29s
flash without diffuser, and said predetermined fixed settings of
said camera comprises setting said camera to: a. {fraction (1/125)}s
exposure time; b. F36 aperture; c. 1:1.2 magnification ratio; d.
flash white balance e. 0 exposure compensation; f. jpeg file type;
g. center weighted metering; and h. 200 ISO setting.
20. The method of claim 1 wherein said predetermined neutral reference
is a gray card having a reflectance value of 18%.
21. The method of claim 1 wherein said commercially available image
editing software is ADOBE Photoshop.RTM..
22. The method of claim 1 wherein standardizing said digital image
further comprising the steps of eliminating color cast of said digital
image and fine tuning said digital image by adjusting the brightness.
23. The method of claim 1 wherein the color information of said
object is expressed in Lab values.
24. The method of claim 23 wherein the color information of said
object is expressed in RGB values.
25. The method of claim 24 further comprising the step of converting
said RGB values into Lab values.
26. A method of determining color information of a tooth utilizing
a digital image taken with a digital camera, comprising the steps
of: providing a predetermined fixed environmental and lighting condition
for said tooth; setting said camera with predetermined fixed settings;
providing a predetermined neutral reference adjacent said tooth
at a predetermined location; providing a black background behind
said tooth; capturing said digital image to include said object
and said neutral reference; providing a commercially available image
editing software capable of standardizing and analyzing the digital
image; standardizing said digital image based on said neutral reference
using said computer program; and analyzing the color information
of said tooth using said computer program.
Digital Camera Patent Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/549,766 filed Mar. 2, 2004, which
is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of determining
a specific color of any object utilizing a digital camera. In particular,
a simple and cost effective method of determining tooth shade from
a high resolution digital photograph utilizing commercially available
software.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] Not applicable.
REFERENCE TO A "SEQUENCE LISTING"
[0004] Not applicable.
BACKGROUND OF THE INVENTION
[0005] The therapeutic outcome of tooth-bleaching procedures can
be assessed by different methods. Existing methods of tooth shade
analysis include the use of shade guide, colorimeter, spectrophotometer
or digital photography. Shade guide is a set of predetermined color
shade swatches, e.g. Vitapan.RTM.'s shade guide, that allows a dentist/technician
to visually compare different color shade swatches with a patient's
tooth by placing the swatch adjacent the patient's tooth. This type
of tooth shade analysis is disadvantageously subject to many variables
and subjective determinations. It is neither not standardized nor
objective. The results vary depending on the lighting conditions,
background effects, and the dentist's/technician's color visual
acuity, binocular differences, fatigue of the retina, age, medications
taken, etc. The problem with visual analysis is compounded by the
inherent construction of the tooth. Each tooth is made up of the
inner dentin, which is opaque and yellowish and the outer enamel,
which is transparent and bluish. Light reflects and disperses when
it hits the tooth, which causes the tooth to appear both translucent
and opalescent. Translucency results when blue light (short wavelengths)
is dispersed. Opalescency results when red-orange light (longer
wavelengths) is transmitted. Other factors also affect visual tooth
shade analysis: morphology, texture, gloss and color (hue, value,
and chroma) of the tooth. Therefore, visual comparison is highly
inaccurate.
[0006] Colorimeters and spectrophotometers provide more standard
color analysis by using computer aided color selection. The goal
of these devices is to eliminate surrounding and illumination influences
to provide reproducible results that can be documented. A colorimeter
measures light by breaking it down into its red-green-blue (RGB)
components. A color's numeric value is then determined using the
CIE XYZ color space or CIE Lab or CIE Luv values and is visually
interpreted in a color space graph. Limitations of calorimeters
include difficulty to read the monitor, difficulty to analyze lower
teeth and cannot read composite resin material. A spectrophotometer
measures spectral data, i.e. the amount of light energy reflected
from an object at several intervals along the visible spectrum.
These measurements provide a complex data set of reflectance valves
which are visually interpreted in the form of a spectral curve.
Spectrophotometers similarly have their limitations: an expensive
system, can analyze anterior teeth only, difficult to analyze lower
teeth and does not provide clinical pictures for records. Both of
these types of electronic devices are generally expensive, technically
sensitive and do not replace control by the human eye.
[0007] Although prior art digital photography has been used for
tooth shade analysis, its accuracy and repeatability is poor because
the photography fails to take into consideration the important factors
such as light, camera technology and standardizing the procedure.
Some prior art method uses the automatic mode of the photographic
equipment, which results in non-repeatable and non-comparable images
because the lighting condition and the procedure are not otherwise
standardized. For example, an image taken in automatic mode for
bright teeth will ordinarily be too dull and provide "false"
information for analysis. Other prior art method uses a "motorized
zoom lens," which has no influence on the outcome of an image
analysis. Also, determining each red-green-blue (RGB) value of each
tooth pixel sounds impressive, but this is exactly what every CCD
or CMOS chip does, even in low-costs digital cameras and does not
improve the accuracy of the image. Some expensive prior art devices
utilize digital images and proprietary software for analyzing the
images, but fail to consider standardizing the condition and procedure
of collecting the images.
[0008] Therefore, there is a need for a method for consistently
determining color of an object using digital cameras that takes
into consideration light, camera technology, a standardized procedure
and the use of a commercially available standard image editing software
to produce repeatable and comparable images for color analysis.
BRIEF SUMMARY OF THE INVENTION
[0009] The method of the present invention provides a repeatable
and definable process using digital photography from which color
results can be compared.
[0010] The method of the present invention determines the specific
color based on Lab values, which is a color industry standard, from
a high resolution digital photograph or image using commercially
available software. The digital photograph can be taken with any
brand of digital SLR camera and advantageously, facilitates and
lowers the cost of practicing the method of the present invention.
The use of commercially available software to analyze the digital
photographs also advantageously lowers the cost of practicing the
method of the present invention.
[0011] In accordance with the method of the present invention,
the digital photographs are taken under standardized conditions,
including light condition, photographic equipment technology and
settings of the photographic equipment to produce repeatable images.
Although the resulting digital photographs minimize the color cast
in the image, to further eliminate color cast and to adjust image
brightness, a neutral reference point, such as a piece of gray card,
is provided within the digital image. The gray card allows the image
editing software to eliminate any remaining color cast that results
despite standardized conditions and to adjust image brightness.
Color values of the fine tuned image are then determined by the
software and are available for comparison with other images taken
under the same method of the present invention.
[0012] Due to the repeatability of the images using the method
of the present invention, it is useful for assessing the therapeutic
outcome of tooth-bleaching procedures and determining tooth shade
during tooth restorative procedures.
[0013] The method of the present invention is simple, non-invasive,
fast and reliable. The method is useful not only to the dental profession,
but also for other medical and industrial fields, where color is
important.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates the use of a small piece of gray card
together with a black contraster put behind the teeth.
[0015] FIG. 2 is a screenshot of the ADOBE Photoshop.RTM. program
surface.
[0016] FIG. 3 is a screenshot of the ADOBE Photoshop.RTM. illustrating
an image is loaded for analysis.
[0017] FIG. 4 is a screenshot of the ADOBE Photoshop.RTM. illustrating
the Levels menus is opened and the grey eye dropper is selected.
[0018] FIG. 5 is a screenshot of the ADOBE Photoshop.RTM. changing
RGB values to Lab values.
[0019] FIG. 6 is a screenshot of the ADOBE Photoshop.RTM. illustrating
the image brightness is changed to an L-value of 54 (grey card).
[0020] FIG. 7 is a screenshot of the ADOBE Photoshop.RTM. showing
the selection of the tooth to be measured, with reflections excluded.
[0021] FIG. 8 is a screenshot of the ADOBE Photoshop.RTM. illustrating
the metering of the L-value of the selected tooth by the Histogram
function.
[0022] FIG. 9 is a screenshot of the ADOBE Photoshop.RTM. illustrating
the metering of the a-value of the selected tooth by the Histogram
function.
[0023] FIG. 10 is a screenshot of the ADOBE Photoshop.RTM. illustrating
the metering of the L-value of the selected tooth by the Histogram
function.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Although the description below will be directed to tooth
shade analysis, the method of the present invention is useful and
applicable to analyze color of any objects.
[0025] Photography has been used for many years in an attempt to
improve communication between dentists and dental technicians. Until
recently no method was described that allowed dental photographs
alone to replace shade selection by the dentist and/or the dental
technician. Other methods had to be used to assess tooth color shade
and brightness. Nevertheless, a photograph image provides the dental
technician with a lot of information, including tooth morphology,
surface texture, color distribution, luster, and other properties.
[0026] Interest in tooth-bleaching procedures has dramatically
increased in recent years. Today bleaching is considered an integral
part of esthetic dentistry. Initially conventional photographs were
made using 35 mm slide film. Some researchers used slides in combination
with secondary methods such as calorimeters to determine a clinically
observable color change. Recently digital photography has started
to replace conventional photography. Researchers have started to
use digital cameras for the assessment of bleaching methods by generating
a digital image and loading it into image editing software. This
software provides numeric values of image color and brightness.
Film-processing images then can be digitized and analyzed with commercial
software (e.g. Adobe Photoshop.RTM., Adobe Systems Incorporated,
San Jose, Calif.). Although digitizing images taken from conventional
film can be done, the results are less reliable. In additional to
the technical variables such as light and camera technology, other
factors affect images taken with conventional film (e.g. film type,
number of film emulsion, storage conditions, the processing of the
film, etc.). Therefore, in principal, methods using film that is
later digitized cannot be more precise than methods using direct
digital photography of the present invention as conventional methods
add more variables to the process.
[0027] A reliable and repeatable method of determining color of
an object with digital photography requires the use of comparable
images. Many different factors determine whether comparable images
are achievable. For example, photographic equipment, settings of
the photographic equipment, and lighting condition all affect the
resulting digital image brightness and color rendition. Therefore,
a highly standardized photographic procedure is required.
[0028] Photographic Equipment
[0029] Digital cameras can be divided into three groups: amateur,
semiprofessional and professional cameras. In dental photography,
only semiprofessional and professional cameras should be used.
[0030] Although most dentists are satisfied with the results obtained
with semiprofessional cameras, there are limitations. The most important
limitation is that these cameras do not allow perfect image control
since in most cases the liquid crystal display (LCD) screen has
to be used as a viewfinder. As a result, there is no control over
the position of the focusing plane and therefore, the depth of field.
Very often one has to rely on the auto-focus function. Some cameras
have a rather long lag time, which makes focusing difficult. The
lighting of these systems is not variable and cannot be adapted
to the situation. A major disadvantage in this context is that not
all cameras of this group allow manual exposure and flash mode.
[0031] If professional results are expected and to provide better
image control, professional digital SLR cameras are needed. Professional
digital SLR cameras generally allow close-up range, interchangeable
lenses, system flash, storage medium and power supply. It is convenient
for a user of conventional SLR cameras to use digital SLR cameras
because digital SLR cameras are based on conventional bodies such
that interchangeable lenses and flash equipment for conventional
SLR cameras of the same brand can be used for digital photography.
Some examples of professional cameras adapted for use in dental
photography include Nikon D1X.RTM., Nikon D70.RTM., Nikon D100.RTM.,
Fuji FinePix S2 Pro.RTM., Canon EOS 10D.RTM., and 20D.RTM. and Sigma
SD-10.RTM..
[0032] The Nikon D1X.RTM. is a professional camera system that
is based on a professional camera body; it is therefore rather expensive.
It provides 5.5 MP images, 3 fps and has a firewire connection to
a personal computer.
[0033] The Nikon D70.RTM. and D100.RTM. are 6.1 MP cameras based
on the N80 body. Each provides good color rendition and connects
to a personal computer by means of a USB cable.
[0034] The Fuji FinePix S2 Pro.RTM. is a another 6.1 MP (SuperCCD)
camera based on the N80 Nikon body. It uses a firewire connection
to a personal computer. TTL flash metering also works with Nikon
macro flashes.
[0035] The Canon EOS 10D.RTM. and 20D.RTM. are 6.3 MP and 8.3 MP
cameras, respectively, each with a CMOS sensor, ring flash, and
twin flash with a eTTL metering. It works with a personal computer
via a USB connection.
[0036] Sigma SD-10.RTM. is based on the Sigma SA-9.RTM. and contains
a Foveon X3 sensor with a 3.5 MP resolution. Since every photo diode
receives the whole color information, an X3 sensor can be compared
with a conventional charge-coupled device (CCD) or CMOS sensor with
a 7.8 MP image.
[0037] Lighting Condition
[0038] Different factors have influence on the color rendition
and image brightness in digital photography, including lighting
condition.
[0039] "Photography" means "writing/drawing with
light." One of the most important properties of light is its
color temperature (i.e. the color of light radiated by a "black
body," expressed in degrees Kelvin). Unlike our brain, which
adapts to different color temperatures and "sees" a white
sheet of paper always as white, even when lit by a yellowish light
source, a camera sees the color temperature as it is: neutral at
6500.degree. K, yellowish at 2800 to 4000.degree. K, and bluish
at temperatures between 7000 and 9000.degree. K.
[0040] Color temperature of daylight changes depending on the time
of the day, the season, the weather, and the direction a window
is facing. Therefore, daylight affects the color rendition of an
image, causing a certain color cast. This is why color shade selection
in the dental office should not be performed under daylight.
[0041] Room illumination affects color rendition as well. Very
often fluorescent tubes are used that are designed to imitate daylight.
Normally, they have no continuous spectrum and are not perfectly
neutral. The dental operating lamp is another source of color cast.
Often halogen bulbs are used in the lamp, which have a color temperature
between 3000 and 3400.degree. K, causing a yellowish cast. Light
reflected from the clothing of the patient (as well as from that
of the assistant and dentist), the walls, and the ceiling can cause
a weak color cast. Therefore, neutral tones are recommended for
use in the operating room.
[0042] The color temperature of the flash light itself is important.
Powerful flash lights with a short flash duration time tend to be
a little more bluish than are weak flash systems. Inadequate color
temperature depends on the mixture of gases in the tube. The type
of flash is important as well as it determines the lighting angle.
A ring flash with axial light direction causes another color rendition
as a side (point or a twin) flash. The amount of light fired by
a flash and the consequent image brightness depend also on the charge
the flash condensator has. Often the condensator is not recharged
completely, even though the flash-ready LED indicates that the flash
is set to fire again. It is important to wait another three or four
seconds before taking the photo.
[0043] The influence of these factors cannot be avoided completely,
but it can be minimized by the following measures:
[0044] Daylight should be blocked out (room without windows or
at least facing north)
[0045] Neutral colors should be used for the ceiling, walls, and
clothing.
[0046] A powerful flash should be used.
[0047] The aperture should be closed at least to stop 16 or 22.
[0048] The flash condensator should be given time to recharge completely.
[0049] Camera Technology
[0050] Camera technology also has influence on the color rendition
and image brightness in digital photography. The term camera technology
includes the lens, camera alignment and patient position, exposure
mode, and camera sensor, etc.
[0051] Every lens has its own color characteristic, which depends
on the type of glass used for the lens elements and the coating
on their surfaces to prevent flare. As this characteristic does
not change from one exposure to the next and as it has only a very
weak influence, the color characteristic is not really a problem
in this context. Since the lens has an indirect influence on color
rendition, its focal length (working distance), together with the
chosen magnification ratio, determines the working distance and
thereby the lighting angle if a flash system is used that is fixed
to the lens.
[0052] In the context of dental photography, camera alignment is
important even though it is not a technical property of the camera
but involves the handling of the camera. It is important to align
the camera in a repeatable way. The optical axis of the camera should
always be oriented according to the anatomic planes of the patient.
It should be perpendicular to the patient's frontal plane and go
over into the occlusal plane without an angle. Only in this way
can one expect repeatable results concerning the inclination of
the camera in relation to the front teeth. The use of a grid screen
is used to facilitate alignment. A chin rest may also be used to
stabilize the patient's position.
[0053] Modern cameras offer different exposure modes. Besides a
manual exposure mode in which the aperture and exposure time can
be preset manually, normally three automatic modes are available:
aperture priority (the aperture is preselected, and the camera sets
the exposure time automatically), shutter priority (the aperture
is set by the camera after the shutter speed is set), and the program
mode (both parameters are set by the camera). For the present invention,
and in dental photography, the manual and the aperture priority
modes are used. The principal problem with setting exposure modes
is that the camera does not know what brightness an object has,
whether it is very dark, very bright, or has a medium brightness
level. Therefore, the exposure system of the camera always tries
to generate a picture with a medium brightness value, corresponding
with a medium gray tone. Consequently, very bright objects (e.g.
a white cast) are reproduced darker, whereas dark objects are reproduced
brighter. In these cases an exposure compensation has to be used
to adjust the exposure. In the case of a bright object, light has
to be added; if the object is dark, light has to be reduced. Therefore,
an automatic exposure mode cannot be used to obtain reproducible
results regarding tooth brightness.
[0054] To make matters more complicated, the different light meter
characteristics of a camera (i.e. integral, spot, center weighted,
and matrix metering) have an influence on image brightness too.
In dental photography, spot metering system does not produce good
results because the results depends on what is located within the
limited small metering area. Matrix metering system take different
image segments into account individually for light metering and
works well for dental photography. Similarly, center-weighted metering
system works well for dental photography. To obtain reproducible
results for tooth shade analysis, the method of the present invention
requires the exposure metering characteristic used to be consistent,
with the use of manual exposure and flash modes (without TTL flash
metering).
[0055] In a digital camera the image of an object is projected
onto the surface of the sensor. One-layer sensors include CCD, Super
CCD and CMOS. Three-layer sensor includes X3. As these sensors consist
of millions of single photo elements, the image is split into millions
of picture elements (pixels). Brightness is recorded for each single
pixel and then transformed into an electric signal. Color is generated
by internal data processing because photo diodes are colorblind.
For this purpose most digital cameras use color mosaic filters.
The exception is the X3 sensor from Foveon.
[0056] Color rendition and image brightness depend very much on
the type of sensor, the filters that are used for generating color
information, the computer algorithms, the white balance settings.
Resulting images with the automatic white balance setting can differ
based on the lighting condition. Therefore, automatic white balance
setting is to be avoided for the method of the present invention.
To get reproducible results concerning color rendition and image
brightness when using a digital camera, the following is required:
[0057] Work in a consistent surrounding (e.g. same room, same lighting
condition, etc.).
[0058] Use the same equipment (e.g. a digital SLR camera with macro
lens and electronic flash).
[0059] Choose the same magnification ratio (e.g. as close to 1:1
as possible) to avoid any distortion.
[0060] Select a manual exposure (i.e. no automatic exposure mode;
always preset the same aperture based on the same flash system's
light output).
[0061] Select the manual flash mode (no TTL flash metering).
[0062] Select a fixed white balance (no automatic white balance).
[0063] Select the same image resolution (to allow consistency and
reproducibility).
[0064] Select the same file type (TIFF or JPEG with same degree
of image compression to allow consistency and reproducibility).
[0065] Set a low ISO value (e.g. ISO 100 or 125 to attain best
image quality)
[0066] Put a black background 100 behind the teeth 102 to avoid
differences of the semitransparent tooth owing to the tongue position
of the patient, as shown in FIG. 1.
[0067] Use a standardized camera alignment.
[0068] Use the same metering characteristics--either center weighted
or matrix.
[0069] Even if all the above rules are obeyed, there will be differences
causing a color cast and a variability in image brightness. These
are mostly due to a certain technical variability of the camera
system (e.g. aperture opening or flash function). Therefore, a method
must be used that allows the fine tuning of color rendition and
image brightness.
EXAMPLE OF SETTINGS OF PHOTOGRAPHIC EQUIPMENT
[0070] For the Nikon D100(camera body, a 105 mm AF Mikro Nikkor
lens and the Nikon SB29s flash without diffuser, the following settings
is used for the method of the present invention:
[0071] Exposure time: {fraction (1/125)}s
[0072] Aperture: F36
[0073] Magnification ratio: 1:1.2 (once focused, this ratio provides
enough distance between the camera and the teeth to include the
canines)
[0074] White balance: flash
[0075] Exposure compensation: 0
[0076] File format: jpeg
[0077] Metering characteristics: center weighted
[0078] ISO setting: 200 (lowest available for this camera)
[0079] It is important for the practice of the present invention
that the same settings are used when photographs are taken. Therefore,
it is preferred that these settings be fixed.
[0080] Reference Color
[0081] Even with the use of a highly standardized photographic
procedure, other factors remain that affect color and brightness
that cannot be excluded completely. Therefore, a piece of gray card
is used. A gray card is a piece of cardboard or plastic with a surface
that has a reflectance value of 18%. This represents the middle
tone used for exposure determination, half way between pure black
and pure white. It is the same tone of gray for which a camera meter
is calibrated; therefore, a gray card is used for exposure metering.
Also, the gray card is a neutral target, meaning the red, blue,
and green values are equal. The idea behind the use of a gray card
is to put something in the picture that has a known value, in other
words, that we know to be pure gray, and then let the software make
sure that that object is interpreted as grey. Thereby, a color cast
of the whole picture is eliminated. The grey card serves two functions:
(1) to eliminate possible color casts of the digital image caused
by lighting conditions, camera technique, etc.; and (2) to allow
"fine tuning" of the digital image brightness to get repeatable
and comparable photographs. Both of these functions can be performed
using a commercially available standard image editing program.
[0082] As normal gray cards available in the photographic stores,
such as qpcard (available from http://www.qpcard.com), are too big
to include into a 1:1 shot of the present invention, only a small
piece of gray card 101 is used. It can be punched out using an office
hole punch and fixed to the surface of a tooth 103 or to the gum
area 105 adjacent a tooth with a small amount of petrolatum, to
serve as an intraoral reference 101 as shown in FIG. 1. The gray
card 101 can also be placed behind or in front of the tooth 103.
Preferably, images are taken with the intraoral reference 101 at
the same position each time to produce repeatable and comparable
images.
[0083] Software Analysis
[0084] Commercially available standard image editing software such
as ADOBE Photoshop.RTM., from Adobe Systems Incorporated, San Jose,
Calif., can be used to eliminate color casts and fine tune image
brightness before the relevant color values are metered by the same
software to compare photographic results.
[0085] The step-by-step procedure in using ADOBE Photoshop.RTM.
is as follows:
[0086] 1. After starting the program, open the INFORMATION menu
104 in the Photoshop.RTM. WINDOWS menu; this will provide the color
information of each single pixel. See, FIG. 2.
[0087] 2. Use CTRL+O to open the image 106 to be analyzed. See,
FIG. 3.
[0088] 3. To eliminate an overall color cast, open the Levels dialogue
108 by pressing CTRL+L (or Image, then Adjust, then Levels). A histogram
110 and three eye-dropper tools 112 will appear. The middle one
is the gray one (see FIG. 4). Select it and move it over the piece
of gray card in the picture. Click again to eliminate the global
color cast of the image. This can be controlled by checking the
Information panel: the R, G and B values, which would have been
slightly different before, will now have the same value. The Lab
values will have changed as well: a and b will be set to 0; the
L value will not have changed.
[0089] 4. Change the color space from RGB to Lab. This has to be
done for Lab values to be recorded using the histogram of Photoshop.RTM..
Also, it provides the advantage that Lab values can be compared
with the results of electronic devices that use these same values.
If these data are only used for patient information and a comparison
with other data is not planned, this step is not necessary: click
Image, then Mode, then Lab (see FIG. 5).
[0090] 5. To obtain images with a comparable brightness, image
brightness is compared with a medium value. The brightness of an
image is expressed by the L value. By clicking Image then Adjust,
then Brightness/Contrast, the overall image brightness can be changed.
The brightness level is adjusted to an L value of 54, which is a
medium gray value. This sets the brightness of the whole image to
a fixed value, which then can be compared with the brightness of
other images (see FIG. 6).
[0091] 6. The tooth to be measured is selected by using the magnetic
lasso. The selected tooth will be surrounded by a broken line 114
on the monitor. This line 114 indicates that all measurements refer
only to the image content within the line 114 (see FIG. 7). Although
the whole tooth is shown to be selected, a representative area of
the center, cervical or incisal part may be sufficient so long as
the representative area is without opacities or other characteristics
such as reflections.
[0092] 7. Reflections on the tooth surface must be excluded. This
can be done easily by the use of the "magic wand"+ALT
(or masking mode) to go over the reflections, which are then excluded
from analysis with the broken lines 116 (see FIG. 7).
[0093] 8. L, a, and b values of the selected area are metered by
clicking Image, then Histogram (see FIGS. 8-10). The Photoshop.RTM.
histogram 118 gives information about the mean L, a, and b values,
their median, the standard deviation, and the number of pixels that
were taken into account.
[0094] To transform the Photoshop.RTM. Lab values into the Commission
Internationale de l'Eclairage (CIE) Lab values, one has to consider
that the range of these values is different in both systems. In
Photoshop.RTM. the range of the mean L value (L(PM)) is 0 to 255.
The CIE L value ranges from 0 to 100. By converting Photoshop.RTM.'s
Lab values into CIE Lab values, results can be compared with other
color analysis devices. A transformation can be done by using the
following formula:
L=L(PM).times.{fraction (100/255)}
[0095] Different image editing software may have different ranges
of mean L values than Photoshop.RTM.. However, one skilled in the
art can similarly convert the image editing software's Lab values
into the CIE Lab values with a modification of the formula above.
[0096] The a and b values are transformed in the same manner. The
Photoshop.RTM. mean a and b values (a(PM) and b(PM)) range from
0 to 255, and the CIE a and b values range from -120 to +120. The
transformation formulas are as follows:
a=(a(PM)-128).times.{fraction (240/255)}
b=(b(PM)-128).times.{fraction (240/255)}
[0097] With regard to tooth-bleaching procedures, the important
values for assessment are L, the whiteness of a tooth, b, the yellowness,
and a, the redness. After tooth bleaching major changes of the L
and b values can be found, whereas the a values show only minor
differences. The .DELTA.b score (the difference in yellowness before
and after bleaching) has the most perceptual relevance. From a clinical
point of view the .DELTA.E score, which measures the composite color
change and includes the three Lab values, seems to be of minor interest
as it is not indicative of an overall color change of the tooth.
[0098] Although the procedure above is described with respect to
ADOBE Photoshop.RTM., other image-editing software can be used for
the method of the present invention.
[0099] Results Using the Method of the Present Invention
[0100] The method of the present invention provides a simple, fast,
inexpensive and highly accurate tooth shade analysis. Compared with
electronic devices such as spectrophotometers and colorimeters,
using digital photography in accordance with the present invention
to assess tooth color and the outcome of the bleaching procedures
has an additional advantage in that there are numeric data that
can be evaluated as well as an image. The image provides additional
information such as color distribution, transparent areas, morphology
and surface texture. This is critical to achieving an accurate clinical
impression.
[0101] Although certain features of the invention have been illustrated
and described herein, other better modifications and changes will
occur to those skilled in the art. It is, therefore, to be understood
that the appended claims are intended to cover all such modification
and changes that fall within the spirit of the invention. |