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WO2008097622A1 - Estimation automatique d'illuminant et ajustement de la balance des blancs - Google Patents

Estimation automatique d'illuminant et ajustement de la balance des blancs Download PDF

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Publication number
WO2008097622A1
WO2008097622A1 PCT/US2008/001649 US2008001649W WO2008097622A1 WO 2008097622 A1 WO2008097622 A1 WO 2008097622A1 US 2008001649 W US2008001649 W US 2008001649W WO 2008097622 A1 WO2008097622 A1 WO 2008097622A1
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WO
WIPO (PCT)
Prior art keywords
illuminant
input
control system
colors
color
Prior art date
Application number
PCT/US2008/001649
Other languages
English (en)
Inventor
Li Hong
Original Assignee
Nikon Corporation
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Filing date
Publication date
Application filed by Nikon Corporation filed Critical Nikon Corporation
Publication of WO2008097622A1 publication Critical patent/WO2008097622A1/fr

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/90—Dynamic range modification of images or parts thereof
    • G06T5/92—Dynamic range modification of images or parts thereof based on global image properties
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/90—Determination of colour characteristics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/80—Camera processing pipelines; Components thereof
    • H04N23/84—Camera processing pipelines; Components thereof for processing colour signals
    • H04N23/88—Camera processing pipelines; Components thereof for processing colour signals for colour balance, e.g. white-balance circuits or colour temperature control
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/10—Image acquisition modality
    • G06T2207/10024—Color image

Definitions

  • Cameras are commonly used to capture an image of a scene. Most scenes are not illuminated by a 100% pure white illuminant. For example, sunlight at midday is much closer to white than the late afternoon or morning sunlight which includes more yellow. The color of light reflected from an object will vary according to the color of the illuminant that is illuminating the scene. As a result thereof, for example, if the illuminant produces light that includes a lot of yellow, a white object in the scene will not be captured as a white object with a typical film type camera.
  • some digital cameras include a program that first estimates the color of the illuminant, and subsequently adjusts all of the colors in an input image according to the color of the illuminant. This is commonly referred to as white balance correction.
  • white balance correction the digital camera attempts to compensate for variations in the colors in the input image caused by an off-white illuminant, and the actual color of the objects in the scene are more accurately represented in the provided image.
  • existing white balance correction programs have not been able to quickly and accurately estimate the correct illuminant in all situations. As a result thereof, the color correction is not satisfactory in all situations. Further, some white balance correction programs are extremely complex to implement and are computationally expensive.
  • the present invention is directed to an image apparatus for estimating an illuminant of a scene and subsequently providing an adjusted image of a scene.
  • the image apparatus includes a capturing system and a control system.
  • the capturing system captures information for an input image of the scene.
  • the input image is defined by a plurality of input colors.
  • the control system compares at least one of the input colors to an illuminant database that includes an illuminant gamut of observable colors for at least one possible illuminant.
  • the control system determines a separation distance between the at least one input color and a closest observable color for each possible illuminant.
  • a separation distance is assigned to each input color based on how far or close that input color is to the closest observable color for each possible illuminant. For example, a small separation distance can be assigned if the input color is near the closest observable color and a large separation distance can be assigned if the input color is far away from the closest observable color.
  • the illuminant database includes an illuminant gamut of observable colors for a plurality of possible illuminants.
  • the control system determines a separation distance between the at least one input color and a closest observable color for each of the possible illuminants in the illuminant database.
  • control system can evaluate the input colors and obtain a set of non-redundant input colors.
  • the control system determines a separation distance between each of the input colors in the non-redundant set and its respective closest observable color for each of the possible illuminants in the illuminant database.
  • the control system adds each separation distance for each possible illuminant in the illuminant database to determine a total consistency error for each possible illuminant in the illuminant database.
  • the control system can evaluate the total consistency error for each of the possible illuminants and determine which of the possible illuminants has the lowest total consistency error. After determining which of the possible illuminants has the lowest total consistency error, the control system performs color correction on the input image based on which possible illuminant has the lowest total consistency error.
  • the control system accurately estimates the possible illuminant from the illuminant database with relatively simple computations.
  • the control system can apply the correct level of color adjustment to the input image to provide an adjusted image that accurately approaches the true colors in the scene.
  • true colors or "actual colors” shall mean the colors that are present at the scene when the scene is illuminated by a white light, such as standard illuminant D65.
  • the present invention is also directed to one or more methods for estimating an illuminant of a scene and subsequently providing an adjusted image providing an adjusted image of the scene.
  • Figure 1 is a simplified top plan view of a scene and an image apparatus having features of the present invention
  • Figure 2A is a simplified front perspective view of one embodiment of the image apparatus
  • Figure 2B is a simplified rear view of the image apparatus of Figure 2A and an adjusted image of the scene of Figure 1 ;
  • Figure 3A is graph that illustrates a gamut of observable colors for a first possible ill ⁇ minant
  • Figure 3B is graph that illustrates a gamut of observable colors for a second possible illuminant
  • Figure 4 is graph that illustrates input colors for an input image
  • Figure 5A is graph that illustrates both the gamut of observable colors for the first possible illuminant and the input colors for the input image
  • Figure 5B is graph that illustrates both the gamut of observable colors for the second possible illuminant and the input colors for the input image
  • Figure 5C is a chart that includes a non-redundant list of input colors and their respective separation distances for a plurality of possible illuminants
  • Figure 6 is a flowchart that illustrates the operation of the image apparatus; and Figure 7 is a simplified illustration of another embodiment of an image apparatus having features of the present invention.
  • Figure 1 is a simplified top plan illustration of an image apparatus 10 and a scene 12 that is illuminated by an illuminant 14.
  • the image apparatus 10 is designed to (i) capture an input image (illustrated in Figure 4), (ii) evaluate the input image 416 to estimate the illuminant, and (iii) perform white balance adjustment on the input image 416 based on the estimated illuminant to provide an adjusted image 218 (illustrated in Figure 2B).
  • the image apparatus 10 uses an illuminant estimation method that estimates the illuminant with improved accuracy, and the illuminant estimation method can be performed with relative simple calculations and implementation. As a result thereof, the image apparatus 10 is more likely to correctly estimate the illuminant, the image apparatus 10 is more likely to provide the correct color correction, and the adjusted image 218 more accurately approaches the true colors in the scene 12.
  • the type of scene 12 captured by the image apparatus 10 can vary.
  • the scene 12 can include one or more objects 20, e.g. animals, plants, mammals, and/or environments.
  • the scene 12 is illustrated as including three objects 20.
  • the scene 12 can include more than three or less than three objects 20.
  • one of the objects 20 is a wall 2OA
  • one of the objects 20 is a first painting 2OB attached to the wall 2OA
  • one of the objects 20 is a second painting 2OC attached to the wall 2OA.
  • the illuminant 14 is a fluorescent lamp positioned away from the wall 2OA.
  • Non-exclusive examples, of other possible illuminants 14 can include (i) the sun at sunrise with a clear sky, (ii) the sun at sunset with a clear sky, (iii) the sun at midday with a clear sky, (iv) an electronic flash, (v) a flashlight, (vi) the sun with a moderately overcast sky, (vii) the sun with shade or a heavily overcast sky, (viii) an incandescent bulb, or (ix) a candle.
  • the color of light reflected from the objects 20 will vary according to the color temperature of the illuminant 14 that is illuminating the object 20. More specifically, the color of light reflected from the objects 20 depends on two functions, namely the spectrum function (e.g. the characteristics) of the illuminant, and the surface reflectance function of the object 20.
  • the illuminant 14 is positioned outside the scene 12. Alternatively, the illuminant 14 can be part of the scene 12 captured by the image apparatus 10.
  • the image apparatus 10 is water resistant and is adapted to capture images of scenes that are partly or fully in a liquid such as water.
  • the image apparatus 10 can be enclosed by an outer shell (not shown) that surrounds and encloses the image apparatus 10 and that provides a watertight barrier around the image apparatus 10.
  • Figure 2A illustrates a simplified, front perspective view of one, nonexclusive embodiment of the image apparatus 10.
  • the image apparatus 10 is a digital camera, and includes an apparatus frame 222, an optical assembly 224, a capturing system 226 (illustrated as a box in phantom), a power source 228 (illustrated as a box in phantom), a flash system 230, and a control system 232 (illustrated as a box in phantom).
  • the design of these components can be varied to suit the design requirements and type of image apparatus 10.
  • the image apparatus 10 could be designed without one or more of these components.
  • the image apparatus 10 could be designed without the flash system 230.
  • the apparatus frame 222 can be rigid and support at least some of the other components of the image apparatus 10.
  • the apparatus frame 222 includes a generally rectangular shaped hollow body that forms a cavity that receives and retains at least a portion of the capturing system 226.
  • the " apparatus frame 222 can include an aperture 234 and a shutter mechanism 236 that work together to control the amount of light that reaches the capturing system 226.
  • the shutter mechanism 236 can be activated by a shutter button 238.
  • the shutter mechanism 236 can include a pair of blinds (sometimes referred to as "blades") that work in conjunction with each other to allow the light to be focused on the capturing system 226 for a certain amount of time.
  • the shutter mechanism 236 can be all electronic and contain no moving parts.
  • an electronic capturing system 226 can have a capture time controlled electronically to emulate the functionality of the blinds.
  • the optical assembly 224 can include a single lens or a combination of lenses that work in conjunction with each other to focus light onto the capturing system 226.
  • the image apparatus 10 includes an autofocus assembly (not shown) including one or more lens movers that move one or more lenses of the optical assembly 224 in or out until the sharpest possible image of the subject is received by the capturing system 226.
  • the capturing system 226 captures information for the input image 416.
  • the design of the capturing system 226 can vary according to the type of image apparatus 10.
  • the capturing system 226 includes an image sensor 240 (illustrated in phantom), a filter assembly 242 (illustrated in phantom), and a storage system 244 (illustrated in phantom).
  • the image sensor 240 receives the light that passes through the aperture
  • an image sensor 240 for digital cameras is known as a charge coupled device ("CCD").
  • An alternative image sensor 240 that may be employed in digital cameras uses complementary metal oxide semiconductor (“CMOS”) technology.
  • CMOS complementary metal oxide semiconductor
  • the image sensor 240 by itself, produces a grayscale image as it only keeps track of the total intensity of the light that strikes the surface of the image sensor 240. Accordingly, in order to produce a full color image, the filter assembly 242 is necessary to capture the colors of the image.
  • the control system 232 can selectively compensate the colors in the raw input image 416.
  • the storage system 244 stores the various images before the images are ultimately printed out, deleted, transferred or downloaded to an auxiliary compensation system (not shown in Figure 2A), an auxiliary storage system or a printer.
  • the storage system 244 can be fixedly or removable coupled to the apparatus frame 222.
  • suitable storage systems 244 include flash memory, a floppy disk, a hard disk, or a writeable CD or DVD.
  • the power source 228 provides electrical power to the electrical components of the image apparatus 10.
  • the power source 228 can include one or more chemical batteries, either the one time use disposable batteries (such as alkaline, zinc-air), or the multiple use rechargeable batteries (such as nickel-cadmium, nickel-metal-hydride, lead-acid, lithium-ion).
  • the flash system 230 provides a flash of light that can be used to selectively illuminate at least a portion of the scene 12 (illustrated in Figure 1).
  • control system 232 is electrically connected to and controls the operation of the electrical components of the image apparatus 10.
  • the control system 232 can include one or more processors and circuits and the control system 232 can be programmed to perform one or more of the functions described herein.
  • the control system 232 is coupled to the apparatus frame 222 and is positioned within the apparatus frame 222.
  • control system 232 includes software that evaluates the input colors from the input image 416 of the scene and uses an illuminant estimation procedure to estimate the illuminant. Subsequently, the control system 232 adjusts the color of the input image 416 based on the estimated illuminant to provide the adjusted image 218.
  • an illuminant database 245 (illustrated as a box) is stored in the storage system 244 for access by the control system 232 during the illuminant estimation procedure.
  • the illuminant database 245 stores a separate gamut of all observable colors for each of a plurality of possible illuminants.
  • the illuminant database 245 can store a separate gamut of all possible colors for at least approximately 5, 10, 15, 20, 25, 30, 35, 40, 50, or more different possible illuminants.
  • the accuracy of the estimation increases as the number of possible illuminants in the illuminant database is increased.
  • Non-exclusive, specific examples for possible illuminants in the illuminant database 245 can include (i) the gamut of observable colors from a fluorescent light, (ii) the gamut of observable colors from an incandescent light, (iii) the gamut of observable colors from a candlelight, (iv) the gamut of observable colors from the sun at sunrise with a clear sky, (v) the gamut of observable colors from the sun at sun ⁇ et with a clear sky, (vi) the gamut of observable colors from the sun at midday with a clear sky, (vii) the gamut of observable colors from an electronic flash, (viii) the gamut of observable colors from a flashlight, (ix) the gamut of observable colors from the sun with a moderately overcast sky, and/or (x) the gamut of observable colors from the sun with shade or a heavily overcast sky.
  • the image apparatus 10 can include an image display 246 that displays the adjusted image 218 and/or the raw input image. With this design, the user can decide which adjusted images 218 should be stored and which adjusted images 218 should be deleted.
  • the image display 246 is fixedly mounted to the apparatus frame 222 on the back side.
  • the image display 246 can be secured to the apparatus frame 222 with a hinge mounting system (not shown) that enables the display to be pivoted away from the apparatus frame 222.
  • a hinge mounting system (not shown) that enables the display to be pivoted away from the apparatus frame 222.
  • an image display 246 includes an LCD screen.
  • the image display 246 can display other information such as the time of day, and the date.
  • the image apparatus 10 can include one or more control switches 248 electrically connected to the control system 232 that allows the user to control the functions of the image apparatus 10. Additionally, one or more of the control switches 248 can be used to selectively switch the image apparatus 10 to the white balance adjustment mode in which one or more of the adjustment features disclosed herein is activated.
  • Figure 3A is a simplified graph that illustrates a gamut 360A of observable colors (represented as"X”) 362A for a first possible illuminant 364A.
  • Figure 3B is simplified graph that illustrates a gamut 360B of observable colors (represented as "X") 362B for a second possible illuminant 364B.
  • These gamut 360A, 360B can be just two possible examples of the plurality of gamut that are stored in the storage system 244.
  • the gamut 360A, 360B illustrated in Figures 3A and 3B are merely examples that were created to facilitate this discussion and are not the observable colors 362A, 362B for any actual illuminant. Further, depending upon the characteristics of the illuminant 364A, 364B, the gamut 360A, 360B can include greater or fewer observable colors 362A, 362B than those illustrated in Figures 3A and 3B. The number of observable colors 362A, 362B will depend on the sampling rate of the chromaticity space, and also depends on the selection typical object surface reflectance functions.
  • each gamut 364A, 364B in the illuminant database 245 of observable colors is expressed in the chromatic scale.
  • the chromaticity space should generate a relatively large separation among the different possible illuminants.
  • the exact chromatic scale can be selected to achieve the best performance and implementation efficiency of the system.
  • the chromatic scale can be (i) rb (r/g, b/g); (ii) rg (r/b, g/b); (iii) bg (b/r, g/r); (iv) rgb_rb
  • r/r+g+b, b/r+g+b (r/r+g+b, b/r+g+b); (v) rgb_rg (r/r+g+b, g/r+g+b); or (vi) rgb_bg (b/r+g+b, g/r+g+b).
  • the chromaticity space should have uniform sampling for easy data manipulation.
  • a low sampling rate to discretize the chromaticity space can also be desired for lower storage requirement and lower computational load by the control system, in general, chromaticity spaces with better separation among the different illuminants should result in better illuminant estimation accuracy.
  • each gamut 360A, 360B is illustrated in two dimensions.
  • each gamut can be in RGB real scale space and in three dimensions, or 3-d RGB cone space.
  • the performance of the illuminant estimation is strongly dependent on the accuracy of the illuminant gamut 360A, 360B in the illuminant database 245.
  • One way to build the illuminant database 245 includes directly taking pictures for various illuminants and various scenes.
  • Another way to build the illuminant database 245 is to synthesize the observable illuminant colors for each possible illuminant.
  • Yet another way to build the illuminant database 245 includes using captured pictures and synthesized data.
  • the illuminant gamut for each of the plurality of possible illuminants is pre-generated and is transferred to the storage system 244 (illustrated in Figure 2A) of the image apparatus 10 for access by the control system 232.
  • Figure 4 is a simplified graph that illustrates non-redundant input colors 466 (represented as "O") for an input image 418.
  • the control system 232 determines the input color 466 at each pixel of the input image 416, and generates a list of input colors 466.
  • the control system 232 reduces the list of input colors 466 to a non-redundant list 571 (illustrated in Figure 5C) of input colors 466.
  • These non-redundant input colors 466 are illustrated in Figure 4.
  • the input colors 466 illustrated in Figures 4 are merely an example of possible input colors 466 that was created to facilitate this discussion.
  • the input image 416 can include greater or fewer non-redundant input colors 466 and the distribution of these input colors 466 can be different than those illustrated in Figure 4.
  • the number of input colors 466 will depend on the sampling rate of the chromaticity space, and also depends on the selection typical object surface reflectance functions of the objects in the scene.
  • the input colors 466 are expressed in the same chromatic scale as the gamuts 360A, 360B of possible illuminants 364A, 364B.
  • the input colors 466 can be in RGB space and in three dimensions.
  • Figure 5A is a simplified graph that illustrates both the gamut 360A of observable colors (represented as “X”) 362A for the first possible illuminant 364A and the non-redundant input colors 466 (represented as “O") for the input image 416.
  • Figure 5B is simplified graph that illustrates both the gamut 360B of observable colors (represented as "X”) 362B for the second possible illuminant 364B and the non-redundant input colors 464 (represented as "O") for the input image 416.
  • Figures 5A and 5B facilitate the discussion on how the control system 232 (illustrated in Figure 2A) estimates the possible illuminant.
  • the control system 232 uses software that directly computes and determines a consistency matching error and compares each of the non- redundant input colors 466 to the respective closest observable 362A, 362B for each of the possible illuminants 364A, 364B in the illuminant database 245.
  • the control system 232 determines a separation distance 570 between each individual input color 466 and a closest observable color 362A, 362B for each possible illuminant 364A, 364B.
  • a separation distance 570 is assigned to each non-redundant input color 466 based on how far or close the input color 466 is to the closest observable color for 362A, 362B for each possible illuminant 364A, 364B.
  • one of the input colors 466 has been labeled a first input color 466A; one of the input colors 466 has been labeled a second input color 466B; one of the input colors 466 has been labeled a third input color 466C; one of the input colors 466 has been labeled a fourth input color 466D; and one of the input colors 466 has been labeled a fifth input color 466E.
  • the closest observable color 362A to the first input color 466A has been labeled 362AA; the closest observable color 362A to the second input color 466B has been labeled 362AB; the closest observable color 362A to the third input color 466C has been labeled 362AC; the closest observable color 362A to the fourth input color 466D has been labeled 362AD; and the closest observable color 362A to the fifth input color 466E has been labeled 362AE.
  • the closest observable color 362B to the first input color 466A has been labeled 362BA; the closest observable color 362B to the second input color 466B has been labeled 362BB; the closest observable color 362B ' to the third input color 466C has been labeled 362BC; the closest observable color 362B to the fourth input color 466D has been labeled 362BD; and the closest observable color 362B to the fifth input color 466E has been labeled 362BE.
  • the control system 232 has determined (i) a first separation distance 570AA between the input color 466A and its closest observable color 362AA, (ii) a second separation distance 570AB between the input color 466B and its closest observable color 362AB, (Hi) a third separation distance 570AC between the input color 466C and its closest observable color 362AC, (iv) a fourth separation distance 570AD between the input color 466D and its closest observable color 362AD, and (v) a fifth separation distance 570AE between the input color 466A and its closest observable color 362AE.
  • the control system 232 has determined (i) a first separation distance 570BA between the input color 466A and its closest observable- color 362BA, (ii) a second separation distance 570BB between the input color 466B and its closest observable color 362BB, (iii) a third separation distance 570BC between the input color 466C and its closest observable color 362BC, (iv) a fourth separation distance 570BD between the input color 466D and its closest observable color 362BD, and (v) a fifth separation distance 570BE between the input color 466A and its closest observable color 362BE.
  • a small distance can be assigned if the input color is close to an observed color, and a large distance will be assigned if there is no close observed color to the input color.
  • the separation distance 570 can be computed by searching for the minimum chromaticity distance between the input color and the closest observable color.
  • the separation distance 570 for each input color can be scaled based upon the appropriate brightness level of the input color (e.g. the green channel value) to give more weight for brighter colors as they tend to be more reliable than dark colors.
  • the scaling adjustment can be optional arid should be evaluated based on the tradeoff between computational complexity and potential gain in illuminant estimation accuracy.
  • the control system 232 can determine that (i) the first separation distance 570AA is approximately 0 because the input color 466A overlaps the closest observable color 362AA, (ii) the second separation distance 570AB is approximately 5, (iii) the third separation distance 570AC is approximately 4, (iv) the fourth separation distance 570AD is approximately 10, and (v) the fifth separation distance 570AE is approximately 4.5.
  • the control system 232 can determine that (i) the first separation distance 570BA is approximately 0 because the input color 466A overlaps the closest observable color 362BA, (ii) the second separation distance 570BB is approximately 0.5 because the input color 466B is very close to the closest observable color 362BB, (iii) the third separation distance 570BC is approximately 2, (iv) the fourth separation distance 570BD is approximately 2, and (v) the fifth separation distance 570BE is approximately 2.
  • Figure 5C is a chart that includes a matrix of a non-redundant list 571 of input colors and its respective separation distances 570 for a plurality of possible illuminants, including the first possible illuminant 364A and the second possible illuminant 364B.
  • the control system 232 determines the separation distance 570 between each input color of the non-redundant set 571 and its closest observable color for each possible illuminant in the illuminant database.
  • the control system 232 adds each separation distance fcv each possible illuminant in the illuminant database to determine a total consistency error 572 for each possible illuminant in the illuminant database. After totaling the separation distances 570 for each illuminant, the control system 232 determines which of the possible illuminants has the best total consistency error. For example, if a small distance is assigned if the input color is close to an observed color and a large distance is assigned if there is no close observed color to the input color, then the lowest total consistency error 572 is the best.
  • the first possible illuminant 364A has a total consistency error of 198
  • the second possible illuminant 364B has a total consistency error of 120
  • the N possible illuminant has a total consistency error of 15.
  • the N possible illuminant has the lowest and best total consistency error.
  • the control system 232 After determining which of the possible illuminants has the best total consistency error, the control system 232 performs color correction on the input image based on which possible illuminant has the best total consistency error. For example, in Figure 5C, the N possible illuminant has the best total consistency error 572. Thus, the control system 232 performs color correction based on the N possible illuminant.
  • the image apparatus 10 can accurately estimates the possible illuminant of the scene with relatively simple computations. This improves the performance of the image apparatus 10 and reduces the cost to manufacture the control system 232 and the image apparatus.
  • steps can be added to the algorithm to improve the efficiency of the system. For example, there can be some preprocessing methods to sort the observable colors for each possible illuminant. Further, the separation distance between each possible input color and its respective closest observable color for each possible illuminant can be precalculated.
  • Figure 6 is a simplified flow chart that further illustrates one non-exclusive example the operation of the image apparatus. It should be noted that one or more of the steps can be omitted or the order of steps can be switched.
  • the illuminant gamut for the desired possible illuminants are generated and are transferred to the image apparatus 610.
  • the image apparatus is aimed toward the scene 612. Subsequently, the user presses lightly on the shutter button to enable the image apparatus to automatically focus on the object(s) 614. Next, the user presses the shutter button all the way, which resets the image sensor, and expose ⁇ the image sensor to light 616.
  • the ADC measures the charge at each photosite of the image sensor and creates a digital signal that represents the values of the charge at each photosite 618.
  • the control system interpolates the data from the different photosites, with assistance from the filtering component, to create the raw input image 620.
  • the control system extracts the input colors from the input image 622 and generates a non- redundant list of input colors.
  • the control system computes the consistency matching error for the input colors to each of the illuminant gamut in the illuminant database 624.
  • the control system determines the best matching illuminant based on the lowest total consistency error 626.
  • FIG. 7 is a simplified illustration of a combination having features of the present invention, including a camera 710, and a post-processing adjustment system 712.
  • the camera 710 captures the input image (not shown in Figure 7) and the adjustment system 712 estimates the illuminant and performs the appropriate levels of white balance adjustment to the input image.
  • the adjustment system 712 includes a control system with software that (i) evaluates the input image to estimate the illuminant, and (ii) performs white balance adjustment on the input image based on the estimated illuminant.
  • the captured image can be transferred to the adjustment system 712 via an electrical connection line (not shown), a wireless connection, or in another fashion.
  • the camera 710 can include a removable storage system (not shown in Figure 7) that is selectively removed from the camera 710 and inserted into a docking port (not shown) of the adjustment system 712.
  • the design of the adjustment system 712 can be varied.
  • the adjustment system 712 can be a personal computer that includes the appropriate software.
  • the methods of estimating the possible illuminant described above can be used in combination with one or more other prior art automatic white balance algorithms.
  • the consistency matching error method disclosed herein can be used in conjunction with a "gray world” illuminant estimation approach, a "white patch” illuminant estimation approach, or variations thereof.
  • the average surface reflectance is "gray”. Therefore, it simply takes the average colors of the image as the gray color and adjusts the image accordingly.

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  • Facsimile Image Signal Circuits (AREA)

Abstract

L'invention porte sur un appareil d'image (10) permettant d'estimer un illuminant (14) d'une scène (12) et de donner par la suite une image ajustée (218) d'une scène (12). Ledit appareil comprend un système de capture (226) et un système de commande (232). Le système de capture (226) capture des informations pour une image d'entrée (416) de la scène (12). L'image d'entrée (416) comprend une pluralité de couleurs d'entrée (466). Le système de commande (232) compare les couleurs d'entrée (466) à une base de données d'illuminants (245) qui comprend une gamme d'illuminants (360A) ayant des couleurs observables (362A) pour une pluralité d'illuminants possibles (364A). De façon plus précise, le système de commande (232) détermine une distance de séparation (570) entre chaque couleur d'entrée non redondante (466) et la plus proche couleur observable (362A) pour chacun des illuminants possibles (364A). En d'autres termes, une distance de séparation (570) est attribuée à chaque couleur d'entrée (466) sur la base de la distance à laquelle la couleur d'entrée (466) est la couleur observable la plus proche (362A) pour chaque illuminant possible (364A). Ensuite, le système de commande (232) ajoute chaque distance de séparation (570) pour chaque illuminant possible (364A) dans la base de données d'illuminants (245) pour déterminer une erreur de cohérence totale (572) pour chaque illuminant possible (364A). En outre, le système de commande (232) détermine quel est l'illuminant possible (364A) qui a la meilleure erreur de cohérence totale (572). Finalement, après avoir déterminé quel est l'illuminant possible (364A) qui a la meilleure erreur de cohérence totale (572), le système de commande (232) effectue une correction de couleur sur l'image d'entrée (416) sur la base de la détermination de l'illuminant possible (364A) qui a la meilleure erreur de cohérence totale (572).
PCT/US2008/001649 2007-02-08 2008-02-07 Estimation automatique d'illuminant et ajustement de la balance des blancs WO2008097622A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US90041307P 2007-02-08 2007-02-08
US60/900,413 2007-02-08

Publications (1)

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WO2008097622A1 true WO2008097622A1 (fr) 2008-08-14

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030035156A1 (en) * 2001-08-15 2003-02-20 Sony Corporation System and method for efficiently performing a white balance operation
US20050219379A1 (en) * 2004-03-30 2005-10-06 Ge Shi Method and apparatus for automatic white balance
US20060177128A1 (en) * 2005-02-08 2006-08-10 Karthik Raghupathy White balance with zone weighting

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030035156A1 (en) * 2001-08-15 2003-02-20 Sony Corporation System and method for efficiently performing a white balance operation
US20050219379A1 (en) * 2004-03-30 2005-10-06 Ge Shi Method and apparatus for automatic white balance
US20060177128A1 (en) * 2005-02-08 2006-08-10 Karthik Raghupathy White balance with zone weighting

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