# Patent

## Title
Method and system for enhancing portrait images

## Abstract

A retouching method for enhancing an appearance of a face located in a digital image involves acquiring a digital image containing one or more faces and detecting a location of facial feature points in the faces, where the facial feature points include points identifying salient features such as skin, eyes, eyebrows, nose, mouth, and hair. The location of the facial feature points are used to segment the face into different regions such as skin, eyes, eyebrows, nose, mouth, neck and hair regions. Facially relevant characteristics of the different regions are determined and, based on these facially relevant characteristics, an ensemble of enhancement filters are selected, each customized especially for a particular region, and the default parameters for the enhancement filters are selected. The enhancement filters are then executed on the particular regions, thereby producing an enhanced digital image from the digital image.

## Background
FIELD OF THE INVENTION
The present invention relates generally to the field of digital image processing, and in particular to the creation of improved imaging products derived from portrait-type images of human subjects.
BACKGROUND OF THE INVENTION
For centuries, only the wealthy or privileged classes of society could afford to employ the skilled artisans who labored to produce a fine likeness in painting, sculpture, and drawing. In many cases, portraiture served a purpose greater than the simple creation of an acceptable likeness of reality. In subtle or overt ways, the artist's work would interact with the desires and intentions of the subjects. A second category of artistic license involved improvement on reality. Thus, subjects were rendered in such a way as to minimize their physical imperfections and to present the most attractive possible appearance.
In modern society, portraiture is no longer the exclusive domain of the wealthy and powerful. The advent of photography into all levels of society has rendered creation of portrait images to be an ubiquitous part of many of life's major events. Weddings, graduations, birthdays, arrival of a baby—all of these events, and more—are commonly captured with relatively standardized portrait images in western cultures. While the state of technology enables individual amateurs to capture and even enhance images such as these, there still exists a class of professional photographers that provide creation of higher-quality portrait images. Not surprisingly, the goals of the portraitist remain the same as in bygone centuries—to present the subject in the most pleasing possible way. In essence, the subject wants to be seen as they wish they were, not as they really are.
In response to the desire for people to be seen as they wish they are, and not the way they really are, professional photographers resort to retouching the portrait image to give people their preferred appearance. Retouching involves changing a photo image in some way that was not captured or depicted in the original photographic image. One of the goals of retouching a portrait image is to make a person look better by removing temporary imperfections such as blemishes or dark circles under the eyes or permanent imperfections such as moles or wrinkles, while still maintaining the personality of the individual. Removing facial blemishes, moles and scars, softening lines and wrinkles, decreasing bags under the eyes, whitening teeth and the whites of the eyes are examples of retouching performed to improve or enhance the appearance of an individual in a portrait image.
Before the advent of the digital age, retouching of images were performed on either the negative or printed image by modifying the image using dyes to mask or change imperfections in the portrait image. Now that digital image capture devices are routinely available, the preferred method of retouching is done via digital imaging techniques performed on the captured digital images. Digital methods allow enhancements to be performed that were either extremely hard to do or previously impossible to perform on the analogue image. Image editing software such as Adobe Photoshop® can be used to refine portraits by removing blemishes, straightening noses, balancing eyes and applying digital make-up.
Improvements in computer technology and image processing algorithms are enabling new classes of automated and semi-automated image enhancements. Relating to the subject of portrait images, relevant technological developments include face detection and recognition, facial feature detection and masking, face re-posing, and red-eye detection and correction.
In published PCT Patent Application WO 00/76398 A1, “Skin Imaging Analysis Systems and Methods”, Hillebrand et al. disclose a system that can detect skin defects and calculate a skin severity index. This system is aimed towards the cosmetic and skin care market. The system can also simulate improvements to the defected skin areas that would be realized upon the use of a recommended treatment or product that eliminates or hides the skin defect. The skin defects are detected using color information and standard morphing techniques are used to simulate improvements in the defected skin areas.
In published European Patent Application EP 1 030 267 A1, “Method of Correcting Face Image, Makeup Simulation Method, Makeup Method, Makeup Supporting Device and Foundation Transfer Film”, Utsugi describes a method for preparing an ideal post-makeup face through image processing based on a desirable face or a model face. The technique involves making highlighted areas, and the shapes of the eyebrows, the eyelines, and the lip line closer to that of a desirable face or a model face within a range where modification by makeup is possible.
The drawback of such systems, especially for batch portraiture systems as used, e.g., for weddings, graduations, school and sports pictures, birthdays, arrival of a baby, etc., is the intense interaction required with the customer to input preferences and evaluate results. For example, in Utsugi the makeup customer's presence is required to settle on the model face, e.g., selected from the faces of popular talents, actresses or actors, and on the various adjustments made to reach the model face. Moreover, a skilled operator is required to work with the customer to produce an acceptable result.
Even with the advent of digital imaging, therefore, retouching portraits is a craft unto itself and to this day remains more of an art form than a science. In addition, the process of retouching portrait images is a highly manual and time consuming process performed by skilled operators. It therefore would be advantageous to develop a system that uses automated and semi-automated portrait image enhancement methods to enable the facile retouching of portraits. The present invention solves the above mentioned shortcomings of the current art by providing methods and system for automated enhancement of the appearance of the human subjects in images.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a retouching method for enhancing an appearance of a face located in a digital image comprises the steps of: (a) acquiring a digital image containing one or more faces: (b) detecting a location of facial feature points in the one or more faces, said facial feature points including points identifying salient features including one or more of skin, eyes, eyebrows, nose, mouth, and hair; (c) using the location of the facial feature points to segment the face into different regions, said different regions including one or more of skin, eyes, eyebrows, nose, mouth, neck and hair regions; (d) determining one or more facially relevant characteristics of the different regions; (e) based on the determined facially relevant characteristics of the different regions of the face, selecting (1) two or more enhancement filters each customized especially for a particular region and (2) the default parameters for the enhancement filters; and (f) executing the enhancement filters on the particular regions, thereby producing an enhanced digital image from the digital image.
The advantage of the invention is that it efficiently uses automated and semi-automated portrait image enhancements methods to enable the retouching of portraits without requiring skilled operator intervention to make and supervise the retouching corrections. Thus, the highly manual and time consuming processes performed by skilled operators is avoided and the retouching method may be implemented on a batch process.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are diagrams of a system for practicing the invention and a graphical user interface for use with the system, respectively.
FIG. 2A is a flowchart of an embodiment for implementing the invention with an optional degree of user intervention.
FIG. 2B is a flowchart of an automatic embodiment for implementing the invention in a batch mode without user intervention.
FIG. 3 is a flowchart of the facial detection and facial point location steps shown in FIGS. 2A and 2B.
FIG. 4 is a pictorial example showing the location of salient feature points on a detected face.
FIG. 5A is a flowchart of a method for determining a neck region.
FIGS. 5B–5D are pictorial examples that visually illustrate the process of creating the final neck probability map.
FIG. 6 is a diagram of the ensemble of enhancement filters used in the system illustrated in the flowcharts of FIGS. 2A and 2B.
FIG. 7A is a flowchart for a skin texture enhancing filter shown in FIG. 6.
FIG. 7B is a diagram of a pixel neighborhood comprising the valley edge filter kernal used by the skin texture enhancing filter.
FIG. 8 is a flow chart showing a preferred embodiment of selecting and modifying skin features according to the invention.
FIG. 9 is a pictorial example of a pinwheel filter illustrating line segments defined around a defect pixel.
FIGS. 10A and 10B together represent a flow chart illustrating a process utilizing the pinwheel filter of FIG. 9 for estimating corrected values for a defect pixel.
FIG. 11 is a flow chart illustrating a preferred embodiment for calculating new pixel values in the process illustrated in FIG. 10.
FIG. 12 is a flow chart illustrating a process for creating line segments through a feature pixel in the pinwheel filter shown in FIG. 9.
FIG. 13 is a flow chart of a presently preferred embodiment of the skin tone enhancing filter as shown in FIG. 6.
FIG. 14 is a flow chart of a presently preferred embodiment of the calculation of shadow/highlight strength for use in the skin tone enhancing filter shown in FIG. 13.
FIGS. 15A, 15B and 15C are illustrations of several functions showing the effect of different blending coefficients used in the skin enhancing filter shown in FIG. 13.
FIG. 16 is a flow chart of a presently preferred embodiment of the teeth and eye enhancing filters shown in FIG. 6.
FIG. 17 is an illustration of a blending function used in the skin texture enhancing filter.
FIG. 18 is a pictorial example of the control points used in making a shape adjustment of an eye.
FIG. 19 is a flowchart for a presently preferred embodiment of a shape enhancing filter as shown in FIG. 6.



DETAILED DESCRIPTION OF THE INVENTION
Because image processing systems employing facial feature detection and feature enhancement are well known, the present description will be directed in particular to attributes forming part of, or cooperating more directly with, method and system in accordance with the present invention. Attributes not specifically shown or described herein may be selected from those known in the art. In the following description, a preferred embodiment of the present invention would ordinarily be implemented as a software program, although those skilled in the art will readily recognize that the equivalent of such software may also be constructed in hardware. Given the system as described according to the invention in the following materials, software not specifically shown, suggested or described herein that is useful for implementation of the invention is conventional and within the ordinary skill in such arts. As a matter of nomenclature, in the description of the present invention, there is reference to enhancement filters as methods that enhance the visual appearance of a face in a digital image. For example, an eye enhancement filter is a method of enhancing the whiteness and/or iris color of the eye.
If the invention is implemented as a computer program, the program may be stored in conventional computer readable storage medium, which may comprise, for example; magnetic storage media such as a magnetic disk (such as a floppy disk or a hard drive) or magnetic tape; optical storage media such as an optical disc, optical tape, or machine readable bar code; solid state electronic storage devices such as random access memory (RAM), or read only memory (ROM); or any other physical device or medium employed to store a computer program.
FIG. 1A illustrates a system 10 that is useful in practicing the present invention. The system 10 includes a personal computer PC 12 containing a central processing unit (CPU) that can execute a set of predefined steps in carrying out the method of the present invention. A digital storage media 20 is also provided in connection with PC 12 for storing digital images. The digital storage media 20 can include different types of devices, such as RAM, ROM, hard and floppy drives, etc. The digital storage media 20 can also be used to locally store the generated enhanced images. In addition, digital image capture devices such as a scanner 28 and a digital camera 30, which are additional sources of digital images, can also be provided to the computer 12. However, it is to be understood that the digital images may be obtained from any source. A user interacts with the computer 12 via input devices 40, such as a mouse and/or keyboard, and a display monitor 50 that is connected to the computer 12. The system 10 may also contain a device such as a printer 34 for locally outputting the images. Typically, the above components would reside on, in the sense of being directly connected to, the PC 12.
Alternatively, the above components do not have to all reside on the host computer 12 but can reside on a server 62 that can be connected to a client PC 12 via a communication network 70. The server may also contain a central processing unit (CPU) that can execute a set of predefined steps in carrying out the method of the present invention. The server may also be connected to a storage media 65 and one or more printers 60. This can enable images to be remotely acquired, stored and printed via the communication network 70 using the storage media 65 and printer 60 connected to the server 62. The software for carrying out the present invention is typically stored on storage media 20. Alternatively, this software can be downloaded from the server via the communication network 70. The software for carrying out the present invention can be executed either on the client using the CPU contained in the PC 12 or on the server side using the CPU contained in the server 62. The communication network 70 may comprise a private network, such as a local area network (LAN), or a public network, such as the Internet that can be accessed by an individual using an Internet Service Provider (ISP). As is customary in such networks, the remote network service provider may also be accessed by a customer using a retail kiosk or any other appropriate communication device.
FIG. 1B shows an example of Graphic User Interface (GUI) for the software that carries out the present invention; the software runs locally on the system 10 or remotely on the server 62, and produces a GUI screen 78 as shown in FIG. 1B. The user launches the software and downloads an image to be enhanced. When the image is downloaded, the Graphic User Interface screen 78 is displayed on the display 50. An image 80 on the left of the GUI screen 78 is the original downloaded image with the face to be enhanced by the method of the present invention. On the right, an image 82 with the enhanced face is presented. In one embodiment, when the image is downloaded, the user clicks on the eyes of the face 80 to be enhanced. In response, as will be described in detail later, the system automatically finds facial feature points and segments the face into different features (e.g., eyes, eyebrows, etc.) and a neck region. The system sets up default parameters and applies all enhancement filters in a predefined order to the original image.
The resulting image 82 is displayed on the right side of the GUI screen 78. The sliders 90, 92, 94, 96 and 98 allow the user to interactively change parameters of different enhancement filters. The initial positions of the sliders correspond to the default values set up automatically by the system. The main appearance enhancer slider 90 combines all component enhancement sliders. The component sliders include a texture enhancer slider 92, a skin enhancer slider 94, an eye enhancer slider 96 and a teeth enhancer slider 98. The texture enhancement slider 92 controls parameters of the texture enhancement filter. The skin enhancer slider 94 controls parameters of the skin tone enhancement filter. The eye enhancer slider 96 and the teeth enhancer slider 98 control parameters of the eye and teeth whitening filters, respectively. All the enhancement filters are described in detail in the following sections. The minimum and maximum for all sliders are set up to “no enhancement” (e.g., at the left extreme of each slider) and to “maximum enhancement” (e.g., at the right extreme of each slider), respectively.
The user can control the level and look of facial enhancement by using the one global appearance enhancer slider 90 or the separate component sliders 92–98. Whenever the user changes a position of the main appearance enhancer slider 90, the system maps the position of the slider into appropriate parameter values of the enhancement filters and applies all the enhancement filters in the predefined order to the original image. The enhanced image 82 is then displayed on the right side of the GUI screen 78. Whenever the user changes one of the component enhancer sliders 92–98, the system applies all enhancement filters to the original image in the predefined order based on the positions of each component enhancer slider. The enhanced image 82 is then displayed on the right side of the GUI screen 78. Part of the GUI design in the preferred embodiment is the option of modifying facial feature points and a neck region outline. When the user selects that option from the menu “Edit” pulled down from the top bar of the GUI screen 78, the facial feature points and neck region outline points are overlaid on the original image 80 and the user can modify location of the displayed points by using the user input device 40, such as a pointing device. The tool bar 84 contains specific tools the user can use to interact with and modify the displayed images. For example a tool for zooming in and out, a tool for editing feature points, a blending tool to locally blend the original image with the enhanced image, a tool for spatially modifying the results of an enhancement filter, etc.
FIG. 2A is a schematic flowchart illustrating one embodiment of the method of enhancing a portrait image according to the present invention. After initiating the process in step 200, a digital image is acquired by the system and then displayed on the display monitor 50 in an acquisition and display step 205. In the present invention, a digital image refers not only to images obtained from photographs, but to digital images obtained without limitation from any source, for example, from a digital camera, scanning of a hardcopy image, or electronically from another source. In a locate step 210, the individual faces in the image are detected and the location of the facial feature points on each face are identified. The process of locating the faces and their associated feature points can be performed manually by the user, or semi-automatically or automatically using image processing techniques. The locations of the facial feature points are used to identify and segment different regions of the face (such as skin, eyes, nose, mouth, hair, etc.) and the neck region. In a display step 215, the facial feature points are overlaid on the image and displayed on the display monitor 50. Optionally, feature points outlining the neck region are displayed as well. If the facial feature points were determined automatically or semi-automatically, the user at a decision step 220 has an opportunity to decide if the feature points need to be adjusted. If the user decides that the feature points need to be adjusted, at a modify step 225 the user can adjust the facial feature points using the input device 40. Optionally, the user can adjust feature points outlining the neck region as well.
At a default setup step 230 the system uses the location of the facial feature points to identify and segment different regions of the face, such as skin, eyes, nose, mouth, hair, facial hair, etc., and determine the appropriate default parameters for the enhancement filters. In the preferred embodiment the neck region is automatically segmented based on location of facial feature points. The method of segmenting a neck region will be described in detail later. Accordingly, in step 230 the system determines the appropriate default parameters for enhancement filters for the neck region as well. Optionally, at this stage the gender and age of the face can be determined manually or automatically using gender and age classification algorithms. An example of automatic gender classification is described in B. Moghaddam and M. H. Yang, “Gender Classification with Support Vector Machines” in Proc. of 4th IEEE Int'l Conf. On Face & Gesture Recognition, March 2000, which is incorporated herein by reference. Typical algorithms for age classification operate by performing an analysis of a digital image of a subject's face for particular detailed facial features such as facial feature ratios and wrinkle analysis. An automatic age classifier algorithm useful for the practice of the present invention is disclosed in U.S. Pat. No. 5,781,650 to Lobo and Kwon, which is incorporated herein by reference. Gender and age classification can be used to decide on which enhancement filters should be executed along with gender specific parameters. For example, as a default a larger amount of texture and skin enhancement can be applied to female faces than to male faces.
The system then executes the enhancement filters in an execution step 235 using the appropriately chosen parameters. Alternatively, as shown by broken line, the user at a user selection step 240 can decide which enhancement filters should be executed along with the appropriate parameters for the enhancement filters. After the system finishes executing the enhancement filters in the step 235 the enhanced image is displayed in a display 245 on the display monitor 50. At this point the user can decide if the enhanced image is acceptable. If the image is not acceptable, the user can choose either to change the enhancement filters and/or their parameters in the user selection step 240 or adjust the location of the facial feature points in the modify step 225. In one embodiment, the user can choose to sequentially execute different enhancement filters to see the effect a given enhancement filter has on the image. In this embodiment, the user will cycle through steps 240, 235, 245, 250 changing the enhancement filters and parameters until an acceptable result is obtained. If the enhanced image is deemed acceptable in a decision step 250, the user can chose either to locally print in a local print step 255 on the printer 34 or locally archive in a local archive step 260 on storage media 20. Alternatively, if the system is connected to a server 62 via a communication link 70, the user can also choose either to remotely print in a remote print step 265 on the printer 60 or remotely archive in a remote archive step 270 on storage media 65. After the appropriate action has been chosen and completed, the system queries for the presence of a new image (query step 275) and depending on the response, cycles back to the acquire and display step 205 for the next image or ends the process (ending step 280).
FIG. 2B shows an alternative embodiment of enhancing a portrait image according to the present invention that is more conducive for highly automated and efficient production at a commercial photographic establishment. This embodiment describes an automatic batch process for running a large number of images through the portrait enhancement system without the necessity of user intervention. At an acquisition step 282, an image is acquired from a list (computer file) of images that have been selected to be enhanced. At a face detection and location step 284, the faces in the image are automatically detected and the locations of the facial feature points on each face are automatically identified. In an enhancement selection step 286, the system characterizes the face and determines the appropriate ensemble of enhancement filters and default parameters for the enhancement filters. Optionally, at this stage the gender and age of the face can be determined automatically using gender and age classification algorithms (as described hereinbefore).
Alternatively, the age and gender of the faces in the image can be supplied to the system via metadata associated with the image, e.g., the age and gender can be supplied from a customer-supplied photofinishing envelope or by otherwise querying the user. The default filters and parameters can also be supplied as image dependent metadata or as an image independent setting before the process of enhancement is implemented. The system then executes the ensemble of enhancement filters in an enhancement execution step 288 using the appropriately chosen parameters. If there is more than one face in the image, this fact is noted in the face query step 290 and the system iterates through steps 286, 288, and 290 until all faces in the image are enhanced. At a storage step 292 the enhanced image is stored. The process of enhancing the images is continued until all the input images have been enhanced (image query step 294). After all the images have been processed (ending step 296), the enhanced images may be applied to the utilization stages 255–270 shown in FIG. 2A. Optionally, after all the images have been processed (ending step 296), the enhanced images can then be brought into the user interactive system, such as described in FIG. 2A, to be checked and if needed modified before the utilization stage (steps 255–270 in FIG. 2A).
FIG. 3 is a flowchart for the facial detection and point location step 210 of FIGS. 2A and 2B, showing the process of locating the salient facial feature points on the faces present in the image according to the present invention. A face detection module 310 is applied to the digital image to mark the locations and rough sizes of all human faces present in the image, and a facial feature detector 315 locates the salient facial feature points on the detected faces. The face detection step can be performed manually by the user or automatically using one of the numerous face detection methodologies that have been recorded in the academic literature. A preferred automatic face detection method for this application consists of methods described in Henry Schneiderman, A Statistical Model for 3D Object Detection Applied to Faces and Cars, Ph.D. Thesis, Robotics Institute, Carnegie Mellon University, May 2000, which is incorporated herein by reference. Alternatively, if a manual approach is used to detect faces a preferred method is for the user to click on both eyes of one or more of the faces present in the image. The spatial separation of the eyes can be used to estimate the size of the face.
Following detection of one or more faces, the image coordinates and estimated size of each face are in turn provided to the facial feature detector 315, which has the task of locating the salient facial feature points on the detected faces. In the preferred embodiment, an active shape model is used as the facial feature detector. The active shape model is described in A. Lanitis, C. J. Taylor, and T. F. Cootes, “Automatic interpretation and coding of face images using flexible models,” IEEE Trans. on PAMI, Vol. 19, No. 7, pp 743–756, 1997, which is incorporated herein by reference. The detected feature points are used to identify, outline, and segment different regions of the face, such as the facial skin region, eyes, nose, mouth, eyebrows, hair, facial hair, etc., and a neck region. The detected regions are identified by the corresponding binary masks. The binary masks of the regions are then spatially feathered to generate alpha masks. The alpha masks are used in step 235 and 288 to blend the results of the enhancement filter (e.g. texture enhancement filter) with the original image. Feathering binary masks and applying the resulting alpha masks in blending operation ensure smooth transition between regions that have and have not been enhanced. To generate alpha masks the binary masks are feathered by blurring the binary masks with a blurring function where the blur radius is chosen based upon the size of the face. The binary masks are used to determine where to spatially apply the enhancement filters as shown in FIG. 2A and FIG. 2B.
Referring to FIG. 4, there is shown an visual example of the location of salient feature points 420 on a detected face 410. Typically these facial feature points are located either manually or automatically using image processing techniques.
In many images it is critical to apply the skin enhancement filters not only to the face region but also to the neck region. In a presently preferred embodiment, the neck region is determined by combining a modified generic neck shape model with a skin color classifier. The flow chart for the method of determining neck region is shown in FIG. 5A. In a generic mapping step 550, a generic probability map for a neck region is created. A generic neck probability map is based upon a priori knowledge of the shape of the neck. In the preferred embodiment, a generic probability map is created by averaging a sample population of normalized images that represent an anticipated population of images to be enhanced (e.g. portrait type images). The sample images are normalized by scaling each image to the same predefined location of the eyes. In each sample image, a neck region is outlined manually. The final neck probability for each pixel is an average sum of a scoring function equal to 1 if a given pixel is a part of neck region and 0 otherwise for all sample images. A generic neck probability map can be created using heuristic approximation. If a gender of a person in the image is known, a different probability map is used for men and women in the preferred embodiment. Usually, a skin region is more visible in portraits of women than of men. In a scaling step 554, a generic neck probability map is scaled to fit individual feature points of the chin line and the face outline.
In a skin color classification step 556, a neck probability map is created based on color segmentation. A supervised pixel-based color classifier is employed to mark all pixels that are within a specified distance of skin color. The pixel-based color classifier, which is a conditional probability function of pixel color C belonging to skin, is modeled as a Gaussian,




  
    
      
        
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where mean vector μ and the covariance matrix Σ are estimated from the defined skin region. The vector C corresponds to the pixel's red (R), green (G), and blue (B) signal. The above approach is also applicable when C is represented in other color spaces, e.g., CIELAB, YUV, HSV, etc. A subset of the facial skin region is used to determine a conditional skin probability distribution. In a presently preferred embodiment the skin region above the eyes and skin regions where facial hair is detected are excluded from use in estimating the mean vector μ and the covariance matrix Σ in equation EQ. 1. The neck probability is defined according to equation EQ. 1 for all pixels outside the face region and below the chin line, and is equal to 0 otherwise.

In a final map generation step 558, the final probability map is created by combining the scaled generic neck probability map and the skin color based probability map. In the preferred embodiment, two probability maps are arithmetically multiplied. The resulting neck probability map is used as an alpha channel to determine how to blend the results of the enhancement filters with the original image. The binary neck region mask is created by thresholding the final neck probability map. If the probability is greater than 0 for a given pixel, the corresponding mask value is equal to 1 thereby indicating the neck region, otherwise the mask value is equal to 0 thereby indicating a non-neck region. The binary neck region mask is used to determine where to apply the enhancement filters.
FIGS. 5B–5D demonstrate visually the process of creating the final neck probability map. Referring to FIG. 5B, a scaled generic neck probability map is shown. A generic probability map is scaled to match the individual feature points outlining the face. A generic neck probability map is based on a priori knowledge of neck location relative to the outline of the face as described in the previous section. The generic neck probability shown in FIG. 5B is one possible example based on heuristic rules rather than statistical analysis recommended in the previous section. It serves the purpose of demonstrating qualitative characteristics of the process. A central region 570 within the generic mask has high values (e.g. greater than 0.5 and less than or equal to 1) corresponding to the high probability of the neck region. A border region 572 has lower values (e.g. greater than 0 less than 0.5) corresponding to the lower probability of the neck region. The probability of the neck region tapers off to a value of 0 outside the region 572. In general, the probability decreases in a continuous manner from the center of the region 570 to the edges of the region 572 in a horizontal direction and from top to bottom in a vertical direction. The central region of the mask that is right below the chin line has the largest probability associated with it.
An outline 574 of the neck probability map determined by a skin color classifier is shown in FIG. 5C. The skin color based probability is calculated according to the equation EQ. 1 as described in the previous section. The probability values outside the outlined region 574 are equal to 0. The probability values within the region 574 are greater than 0, as defined by equation EQ. 1. The two neck probability maps: the scaled generic neck probability map and the neck probability map based on skin color classification are combined by arithmetic multiplication of the two. The outline of the resulting final neck probability map is shown in FIG. 5D. The central region 576 corresponds to the high probability region 570 cropped by the skin color probability region 574. The region 578 corresponds to the low probability region 572 cropped by the skin color probability region 574.
Once the facial feature points and neck region have been located, an ensemble (i.e., two or more) of appearance enhancement filters can be applied to the face and neck regions in the image. Referring to FIG. 6, several different enhancement filters are shown. In the preferred embodiment, the following enhancement filters are implemented: a skin texture enhancement filter 610, a skin tone enhancement filter 620, a teeth enhancement filter 630, an eye enhancement filter 640, and a facial feature shape enhancement filter 650. All these filters are described in detail in the following sections of the specification. The enhancement filters can be applied in any order. In one embodiment, the user can select any of the enhancement filters in any order he/she wants to apply them to the faces and neck regions in the image. However, in the preferred embodiment, the system sets a default order of applying enhancement filters together with the appropriate parameters.
If the user elects to run default settings, then all enhancement filters are applied in the default order with the default parameters and the enhanced image is displayed on the monitor. The default order of enhancement filters is as follows: the skin texture enhancement filter, the skin tone enhancement filter, the teeth and eye whitening filter (in either order), and the facial feature shape enhancement filter. The enhancement filters are described in the next sections in the same order as the default order of applying filters to the original image.
Texture Enhancing Filter
The task of the skin texture enhancing filter is to smooth the local texture of the skin, remove blemishes, dark spots, etc. and to either remove or lessen the extent and deepness of wrinkles. Referring to FIG. 7A, there is shown a flowchart for a skin texture enhancing filter according to the present invention. In a skin feature generation step 710, the skin features that are within the skin region delineated by the facial feature points are detected. Then the detected skin features are modified in a feature modification step 720. Skin feature map contains features that we wish to modify, such as blemishes, dark spots, wrinkles, etc.
In the prior art, color analysis is used to locate specific skin defects. Also in the prior art, the detection of skin defects is performed by analyzing the histogram of the color signals associated with the pixels contained within a finite 2-dimensional window that is slid over the skin region. A region is considered to contain a skin defect if its associated histogram is found to be bimodal. Since these techniques use color information as part of their primary detection means, it requires that the imaging system be color calibrated and/or the image to be analyzed be correctly color balanced. The efficacy of using color information is enhanced when controlled lighting and/or colored filters are used to capture the images. In addition, accurate color reproduction is needed if the detected defects are going to be further classified as blemishes, brown spots, etc based on the color of the defect.
In photographs, the skin imperfections such as wrinkles, blemishes, etc manifest themselves as (are really just) highlights and shadows in places where they should not be. The skin imperfections thus correspond to local intensity maxima and minima. The highlights correspond to peaks and the shadows correspond to valleys in the luminance image. In a departure from the prior art, and according to a preferred embodiment of the current invention, skin imperfections are detected by applying peak and valley detectors to the luminance image formed from the component RGB signals. Valley/peak detectors are second difference operators. The luminance is defined as a weighted linear combination of the red R, green G, and blue B signals, as follows,

L=k1R+k2G+k3B  (EQ. 2)

where k values represent the weights. A presently preferred choice of weights for generating the luminance image is k1=k2=k3=0.333. Examples of valley/peak operators can be found in D. E. Pearson and J. A. Robinson, “Visual Communication at Very Low Data Rates,” Proceedings of the IEEE, Vol. 73, No. Apr. 4, 1985.

A presently preferred peak/valley operator is a series of four directional operators of the type employed by Pearson et al. A vertical operator V, which is applied to the middle pixel m in the 5×5 neighborhood of pixels shown in FIG. 7B, where the pixel locations are designated a through y, is defined by equation EQ. 3, as follows,

V=f+k+p+j+o+t−2(h+m+r)  (EQ. 3)

This operator is applied at each pixel location in the delineated skin region. Similarly, a horizontal operator H of the form shown in equation EQ. 4 and a pair of right and left diagonal operators DL and DR as shown in equations EQ. 5 and EQ. 6. Respectively, are applied at each pixel location in the delineated skin region, as follows,

H=b+c+d+v+w+x−2(l+m+n)  (EQ. 4)

DR=c+g+k+o+s+w−2(i+m+q)  (EQ. 5)

DL=c+i+o+k+q+w−2(g+m+s)  (EQ. 6)

These operators not only detect valleys/peaks, but they also have a secondary response to the feet/shoulder of edges. Thus they are referred to as valedge/peakedge detectors. Valedge features correspond to positive values of the operator's output whereas peakedge features correspond to negative values. A valley/peak detector that is sensitive only to valleys/peaks is obtained by applying logical conditions to operators. For vertical valleys the logical valley detector correspondence is given by:

if (f+k+p)>(h+m+r) and (j+o+t)>(h+m+r) then V=(f+k+p+j+o+t)−2(h+m+r) else V=0  (EQ. 7)

For vertical peaks the logical peak detector correspondence is given by:

if (f+k+p)<(h+m+r) and (j+o+t)<(h+m+r) then V=(f+k+p+j+o+t)−2(h+m+r) else V=0  (EQ. 8)

Logical detectors for a horizontal and diagonal valleys/peaks have similar form. Both valley/peak and valedge/peakedge operators are effective for generating the skin feature map according to the present invention. From this point on we use the term valley/peak operators to refer both to valley/peak and valedge/peakedge operators.

Prior to applying the oriented valley/peak filters to the image, the effects of noise in the image are suppressed by applying a noise reduction filter. Appropriate noise filters are low pass filters, median filters, and other linear and non-linear filters commonly employed to reduce noise in digital images.
The oriented valley/peak images generated by the operators are thresholded so as to retain only (strong) relevant skin features. For valley feature maps, pixels with values less than a specified threshold Tv are set to zero. For peak feature maps, pixels with values greater than a specified threshold Tp are set to zero. The threshold can be either a fixed global threshold or an adaptive threshold. A presently preferred threshold method is to use an adaptive threshold whose value is given by equation EQ. 9.

T=βLavg  (EQ. 9)

where β is a constant and Lavg is the local average luminance about the pixel. Different values of β can be used for the vertical, horizontal, and diagonal components. The local average luminance Lavg may be the value of the pixel itself or the average luminance of a neighborhood of pixels, for example a 3×3 neighborhood of pixels.

A presently preferred step is to generate a combined skin feature map F by combining the individual oriented feature maps.

F=max {H,V,DR,DL}  (EQ. 10)

Additionally, each pixel in F can be labeled according to which oriented filter it originated from. The oriented label data and/or the individual oriented skin feature maps can be useful in removing features such as wrinkles where features of a particular orientation are preferentially removed.

The task of the skin texture enhancing filter is to smooth the local texture of the skin. The spatial size of the texture that the skin texture enhancing filter smoothes is a function of the size of the face. Thus the spatial size of the valley/peak filters is adaptively determined based upon the size of the face. Specifically, the separation between the eyes is used to determine the size of the valley/peak filter. One generic representation for the vertical valley/peak operator is




  
    
      
        
          V
          ⁡
          
            (
            
              x
              ,
              y
            
            )
          
        
        =
        
          
            
              1
              
                2
                ⁢
                h
              
            
            ⁢
            
              
                ∑
                
                  i
                  =
                  
                    -
                    h
                  
                
                h
              
              ⁢
              
                I
                ⁡
                
                  (
                  
                    
                      x
                      -
                      w
                    
                    ,
                    
                      y
                      +
                      i
                    
                  
                  )
                
              
            
          
          -
          
            2
            ⁢
            
              I
              ⁡
              
                (
                
                  x
                  ,
                  
                    y
                    +
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                )
              
            
          
          +
          
            I
            ⁡
            
              (
              
                
                  x
                  +
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          .
          
            
          
          ⁢
          11
        
        )
      
    
  




where w and h are chosen as a function of the face size. Generic valley/peak detectors for a horizontal and diagonal valleys/peaks have a similar form.

A presently preferred isotropic valley/peak detector is given by subtracting the blurred luminance image Ib from the luminance image I

F(x,y)=I(x,y)−Ib(x,y)  (EQ. 12)

The blurred luminance image can be generated by applying a blur filter such as a Gaussian or a box filter to the luminance image. The output of the valley/peak detector is thresholded as described above to generate peak and valley feature maps. The radius of the blur filter is chosen as a function of the face size (which is an example of a default parameter) and the size of the skin feature that one wishes to detect.

The feature maps are further refined by grouping pixels that are connected to each other via connected component labeling. Connected component labeling scans an image and groups its pixels into components based on pixel connectivity, i.e., all pixels in a connected component are in some way connected with each other. Once all groups have been determined, each pixel is labeled according to the component it was assigned to. Each connected component corresponds to a skin feature. Each skin feature is characterized and classified by its feature-based characteristics such as size, shape, and location in the skin region. The size corresponds to the number of pixels in the component (which is an example of a default parameter). Shape information is useful in delineating wrinkle features from other skin features such as blemishes. In addition the features delineated in the skin feature map can be further classified using the color information associated with the pixels that have been identified as skin features. Once the skin feature maps are generated they are used to select the skin features that are going to be modified in step 720.
Referring to FIG. 8, there is shown a flow chart illustrating a preferred embodiment of selecting and modifying skin features according to the present invention. In a feature selection step 810, features to be modified are selected based on their characteristics. As mentioned above, the feature characteristics correspond to the size, shape, and color and are selected based upon the location of these features in the skin region. In a dilation step 820, the selected skin features are then (adaptively) dilated and then modified in a filtering step 830. The effect of dilation on a skin feature is to enlarge the size of the skin feature. The amount of dilation can be either a fixed amount for all selected skin features or an adaptive amount based upon the characteristics of the skin feature. In a presently preferred embodiment, the skin features are adaptively dilated based upon their size and the size of the face (which is an example of a default parameter). Larger skin features are dilated more than smaller skin features. The process of dilation can be carried out using standard morphological operators.
Optimal skin enhancement is obtained by sequentially modifying skin features by cycling through the steps of 810, 820, and 830 while changing the type of skin feature to be modified, albeit all the desired skin features can be selected and modified in one cycle through the steps 810, 820, and 830. In a presently preferred embodiment the valley skin features are first selected and modified in steps 810–830, and then the residual peak skin features are selected and modified in the second iteration through steps 810–830. In order to preserve the skin texture, only skin features whose sizes are between a specified minimum and a maximum size are modified. Alternatively, in order to preserve the skin texture, only skin features whose sizes are larger than a specified minimum size are modified. In addition, the minimum and maximum size of the skin features to be modified directly scale with the size of the face.
In step 830, a pinwheel filter is applied to each pixel of dilated features. Pixels of dilated features are referred to as feature pixels. All other remaining pixels are referred to as non-feature pixels. In the embodiment of the present invention, feature pixels are defined by a binary mask, where a value of 0 corresponds to feature pixels and a value of 1 corresponds to non-feature pixels. The pinwheel filter interpolates new values of a given feature pixel by using neighboring non-feature pixels aligned in line segments centered at the feature pixel. The pinwheel filter is described in detail in commonly-assigned U.S. Pat. No. 6,104,839 “Method and Apparatus for Correcting Pixel Values in a Digital Image”, which issued Aug. 15, 2000 in the names of David R. Cok et al, and which is incorporated herein by reference. A brief description of the pinwheel filter is included here for clarity and to specify some modifications to the original algorithm as described in the patent by Cok et al. Referring to FIG. 9, the SET of four line segments 930 is graphically demonstrated (vertical V, horizontal H, two diagonal line segments D1 and D2) for the selected feature pixel 940. The four line segments are spaced at 45° degree increments. The dilated features 920 are represented in gray (shaded) color. The line 910 represents a face boundary. Each line segment in the SET is composed of both feature and non-feature pixels on both sides of the pixel 940. The non-feature pixels and feature pixels in the line segment are pixels local to the selected feature pixel 940 in a given direction defined by the line segment. The method of creating the SET of line segments is described in detail later.
Referring to FIGS. 10A and 10B, the method for calculating new values for each feature pixel in the image by applying the pinwheel filter is shown. In step 1004, the number of line segments NL, the maximum number of pixels on one side of the line segment MAX_NP1 and the minimum number of pixels on one side of the line segment MIN_NP1 are set. These parameters will be explained in detail in reference to FIG. 12. The maximum number of pixels on one side of the line segment MAX_NP1 and the minimum number of pixels on one side of the line segment MIN_NP1 are set based on the size of the face (which is an example of a default parameter). The larger the size of the face, the larger the values of MAX_NP1 and MIN_NP1. The dependence of these two parameters upon the size of the face is unique to the present invention compared to the method described by Cok et al. In step 1006, the first feature pixel PSEL is selected. In step 1008, the SET of NL line segments is created through the pixel PSEL. In the preferred embodiment, the number of line segments NL in SET is equal to 4, corresponding to vertical, horizontal and two diagonal line segments.
A method of creating line segments is shown in FIG. 12. In step 1110 of FIG. 12, the first segment is selected, e.g., the vertical line segment (V). In step 1120, the direction of one side of the line segment is selected. This is a direction in which pixels are being added to the line segment starting at pixel PSEL. For each segment, two directions are defined that correspond to two sides of the line segment centered at pixel PSEL. In step 1130, feature pixels are being added to the line segment until a first non-feature pixel is reached along a given direction. In step 1140, the first non-feature pixel is added to the line segment and the neighboring non-feature pixels in a given direction are being added to the line segment until one of the following conditions is met:

    
    
        maximum number of non-feature points on one side MAX_NP1 is reached,
        face boundary or face feature boundary is reached,
        new feature pixel is reached.

The maximum number of non-feature points on one side of the line segment MAX_NP1 is set in step 1004 (FIG. 1A) based on the face size. The line segments must not cross the face boundary or boundaries of the regions excluded from the texture enhancement process (like eye regions, mouth regions, etc.). The above constraining condition for creating valid line segments is unique to the present invention compared to the method described by Cok et al. When adding pixels to one side of the line segment is completed, then the direction is set for the second side of the line segment in step 1160, and the process is repeated for the second side of line segment in steps 1130–1140. When two sides are completed (step 1150), then the next line segment from the SET is selected (step 1180) and the process is repeated in steps 1120–1160. When all NL line segments in SET are created (step 1170) the process is completed (step 1190).

    
    


Referring back to FIG. 10A, after creating the SET of NL line segments in step 1008 as described above, the line segments having less than MIN_NP1 of non-feature points on at least one side are removed from the SET (step 1010). If no remaining valid line segments are left in the SET (step 1014), then pixel values are not changed for the pixel PSEL (step 1052) and a new feature pixel PSEL is selected (step 1046 and 1048) and the process is repeated (starting with step 1008). If the number of remaining valid line segments N in SET is greater than 0 (step 1014), then for each remaining valid line segment a linear fit is calculated (step 1016) for the non-feature pixels in the valid line segment for each channel. In step 1018, mean square fitting error is calculated for each valid line segment for non-feature pixels for each channel based on the linear fit computed in the previous step 1016. In step 1020, total mean square fit error is calculated for each valid line segment as an average of mean square fitting errors for all channels for a given valid line segment according to the following equation.




  
    
      
        
          
            MSE
            n
          
          =
          
            
              
                1
                K
              
              ⁢
              
                
                  ∑
                  
                    k
                    =
                    1
                  
                  K
                
                ⁢
                
                  
                
                ⁢
                
                  
                    MSE
                    
                      n
                      ,
                      k
                    
                  
                  ⁢
                  
                    
                  
                  ⁢
                  where
                  ⁢
                  
                    
                  
                  ⁢
                  n
                
              
            
            =
            1
          
        
        ,
        
          
        
        ⁢
        ...
        ⁢
        
          
        
        ,
        N
      
    
    
      
        (
        
          EQ
          .
          
            
          
          ⁢
          13
        
        )
      
    
  




where K is a number of channels in the image. For black and white images, K is equal to 1. For color images, K is usually equal to 3 (e.g. 3 channels corresponding to R,G,B channels).

In step 1022, values PSELn,k are calculated for pixel PSEL for each valid line segment n for each channel k based on linear fit computed in step 1016. In step 1024, new pixel values PSELk are calculated for each channel k. The final pixel values of the enhanced image are determined by blending new pixel values PSELk for each channel k with the original pixel values according to alpha masks generated in the previous sections. The blending operation insures smooth transition between enhanced and not enhanced regions of the skin. The blending operation in step 1024 and alpha masks are unique to the present invention compared to the method described by Cok et al. In an alternative embodiment the final pixels values PSEL _OUTk of the enhanced image are determined by adaptively blending the new pixels values PSELk with the original pixels values PSEL_INk for each channel k.

PSEL_OUTk=αPSELk+(1−α)PSEL_INk  (EQ. 14)

The blending coefficient α used to blend the new and original pixel values is dependent upon the characteristics of the of the skin feature that the pixel originated from. For example, as shown in FIG. 17, the blending coefficient α can be a function of the size of the skin feature that the pixel originated from. Referring to FIG. 17, for small skin feature size whose size is less than min the original pixels values are not modified. For the skin features whose size are between min and mid the new pixels values are used as the final pixel values. And for large skin features whose size is greater than mid the final pixels values are determined by blending the new and original pixels values. In certain region (e.g. around the eyes) it is sometimes preferable not to entirely remove a skin feature but to modify its harsh appearance. Thus in another embodiment, the blending coefficient α is also dependent upon the location of the skin feature pixel. Different methods of calculating new pixel values PSELk are described later. If the selected feature pixel PSEL is not the last feature pixel (step 1046), then the next feature pixel is selected (step 1048) and the process is repeated starting with step 1008. Otherwise the whole process is completed (step 1050).

In the preferred embodiment where the number of line segments NL is equal to 4, the step of calculating new values PSELk for the selected feature pixel PSEL (step 1024 in FIG. 10) is shown in detail in FIG. 11. The method presented here in FIG. 11 is unique to the present invention compared to the method described by Cok et al. It is assumed there is at least one valid line segment in SET (N>0). Referring to FIG. 11, if number of valid line segments N in SET is equal to 1 (step 1026), then new values PSELk for each channel k are equal to values PSEL1,k calculated for that line segment (step 1028). Otherwise in step 1030, SET of valid line segments is sorted in descending order based on mean square root error value MSEn for each line segment n. As a result of sorting in step 1030, the first valid line segment in SET (n=1) has the highest mean square root error and the last valid line segment (n=N) has the lowest mean square root error in SET. If the number of valid line segments N in SET is equal to 2 (step 1032), then new values PSELk for each channel k are equal to averaged values of PSEL1,k and PSEL2,k (step 1034). Otherwise, if the number of valid line segments N in SET is equal to 3 (step 1036), then new values PSELk for each channel k are equal to values of PSEL2,k calculated for the valid line segment with the mid value of mean square root error (n=2) (step 1038). Otherwise, the number of valid line segments N is equal to 4, and new values PSELk for each channel k are equal to averaged values of PSEL2,k and PSEL3,k (step 1040). The final pixel values of the enhanced image are calculated by blending new pixel values PSELk for each channel k with the original pixel values (step 1024) according to alpha masks generated in the previous sections.
In a second embodiment for calculating new pixel values, new values PSELk for each channel k (step 1024 in FIG. 10) are calculated in the following way. First, weight values Wn,k are calculated for each line segment n for each channel k according to the equation EQ. 15.




  
    
      
        
          
            W
            
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              where
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Next, new values PSELk are calculated for each channel as a weighted sum of PSELn,k values determined for each valid line segment n and for each channel k according to the equation EQ. 16.





  
    
      
        
          PSEL
          k
        
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              ∑
              
                i
                =
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The final pixel values of the enhanced image are calculated by blending new pixel values PSELk for each channel k with the original pixel values according to alpha masks (step 1024) generated in the previous sections. The blending operation and alpha masks are unique to the present invention compared to the method described by Cok et al.

The majority of the skin features that we wish to modify correspond to valley features i.e., a dark area surrounded by a light area. In most instances, skin features are going to be modified regardless of the color information associated with the pixels that have been identified as skin features, albeit there may be instances where an individual may not want a defining facial characteristic such as a beauty mark to be removed from the photograph of the individual. In these instances, the color information associated with the skin feature pixels can be used in determining the type of skin feature that should or should not be removed. An alternative approach is to build a tool into the Graphical User Interface that will allow the operator to undo an undesirable modification (e.g., the removal of a desirable beauty mark). In a preferred embodiment, the user chooses an undo/redo tool from the graphical list of tools 84, and moves the undo/redo tool via pointing device 40 such as a mouse to the location of the skin feature in the original image 80 the user wishes to restore. Clicking on the skin feature in the original image 80, which is displayed on the left, causes the feature to be added back to the enhanced image 82, which is displayed on the right. Clicking again on the restored skin feature in the original image now causes the skin feature to be removed from the enhanced image. Thus, the undo/redo tool works, toggling back and forth, by either removing a skin feature from the enhanced image if it is present in the enhanced image or restores it to the enhanced image if it is not present in the enhanced image. In an alternative embodiment, the texture enhancer slider 92 can be set to no enhancement and the tool 84 can be used to allow the user to choose which skin features to remove.
In another embodiment, the graphical user interface acquires and displays a digital image containing one or more faces. A skin feature map is generated by use of any of the aforementioned techniques to identify and map the skin features; the skin feature map therefore represents the skin features on the one or more faces in the digital image. The pointing device 40 is then used to point to a particular skin feature. In response to a point and click operation of the pointing device, the skin feature map is referenced as to the particular feature and the appropriate enhancement for that feature, provided by an appropriate enhancement filter, is initiated for the skin feature being pointed at.
Skin Tone Enhancement Filter
The task of the skin tone enhancing filter 620 (FIG. 6) is to improve the overall appearance of the skin tone. The skin tone filter evens out unbalanced skin tone and creates a more even colored skin tone. In addition, the skin tone filter is used to modify the color of the skin tone to produce a more desirable skin color representation. This corresponds to modifying both the luminance and chrominance of the skin to match individual and culture preferences of skin tone rendition. Moreover, skin tone problems tend to be on a larger spatial scale than texture. It is important not to even out the skin tone too much because faces without highlights or shadows are flat and tend to be uninteresting.
Referring to FIG. 13, there is shown a flowchart for a presently preferred embodiment of a skin tone enhancing filter according to the present invention. The skin tone-enhancing filter adaptively compresses highlights and shadows by adaptively blending (in a blending step 1240) the input image I(x) with a blurred version Ib(x) of the input image obtained from a blending step 1210, as follows.

O(x)=α(x)Ib(x)+(1−α(x))I(x)  (EQ. 17)

where α(x) is a blending coefficient obtained from a coefficient generation step 1230 and x=(x, y) is the location of a pixel. The blending operation is applied to all the color channels. The blending coefficient is a function of the shadow/highlight SH(x) strength image at x obtained from the shadow/peak generation step 1220, as follows.

α(x)=f[SH(x)]  (EQ. 18)

Referring to FIG. 14, there is shown a presently preferred embodiment of calculating the shadow/highlight strength image according to the present invention. The shadow/highlight strength image from step 1220 is generated by subtracting an average luminance image 1320 from a luminance image 1310. The luminance image is calculated by using equation EQ. 2. The average luminance image can be either a local average luminance image or a global average luminance. A local average luminance image can be generated by applying a blur filter such as a Gaussian or box filter to the luminance image, whereas the global average luminance is calculated by determining the average luminance of the skin within the skin region delineated by the feature points. The shadow/highlight strength is analogous to a valley/peak image when using the local average image to calculate the shadow/highlight image. In a preferred embodiment, the blur radius used to calculate the shadow/highlight map should be larger than the blur radius or extent of the valley/peak detector used in the texture enhancing filter. In either case, the blur radius is dependent upon the size of the face (which is an example of a default parameter).
In its simplest embodiment, the blending coefficient is a constant f[SH(x)]=α(x)=α, which is an example of a default parameter, and is not dependent upon the shadow/highlight strength image as shown in FIG. 15A. The blending functions shown in FIGS. 15B and 15C are useful for toning down highlights and hot spots caused by lights and/or oily skin, while leaving shadow regions unchanged.
The skin tone filter can also be used to modify the color rendition of the skin. In a presently preferred embodiment, the color C of a region such as the skin region can be modified Cmod by shifting the mean and variance of the color distribution of a region as follows

Cmod(x,y)=k(C(x,y)−{overscore (C)})+Cpreferred(x,y)  (EQ.19)

where the vector C(x, y) corresponds to the pixel's red (R), green (G), and blue (B) signal, Cpreferred is the preferred color vector, {overscore (C)} is the current mean color vector, and k is a constant that can vary between 0 and 1. The preferred color Cpreferred (x, y) can vary spatially depending upon the region of the skin to be modified.

A preferred embodiment for lightening or darken the skin region is to modify the contrast of the skin region as follows

Cmod(x,y)=Cγ(x,y)  (EQ.20)

where values of γ less than one correspond to lightening the skin color and values of γ greater than one correspond to darkening the skin color.

An alternative embodiment for lightening the skin region is given by




  
    
      
        
          C
          mod
        
        =
        
          C
          
            1
            -
            
              γ
              ⁡
              
                (
                
                  1
                  -
                  C
                
                )
              
            
          
        
      
    
    
      
        (
        
          EQ
          .
          
            
          
          ⁢
          21
        
        )
      
    
  




and for darkening the skin region is given by





  
    
      
        
          C
          mod
        
        =
        
          1
          -
          
            
              1
              -
              C
            
            
              1
              -
              γC
            
          
        
      
    
    
      
        (
        
          EQ
          .
          
            
          
          ⁢
          22
        
        )
      
    
  




where γ varies between 0 and 1.

The above approach is also applicable when C is represented in other color spaces, e.g., CIELAB, YUV, HSV, etc. In addition, these equation can be applied to all or a subset of the components of C. This is particularly true when C is represented in a color space (e.g., CIELAB) where the components are related to the luminance (L*) and chrominance (a*b*).
Teeth and Eye Enhancing Filter
The task of the teeth and eye enhancing filter(s) 630 and 640 (FIG. 6) is to increase the luminance and whiteness of the teeth and eyes. Referring to FIG. 16, there is shown a flowchart for a presently preferred embodiment of a teeth and eye whitening filter according to the present invention. At an eye/teeth mask generation step 1510, the salient facial feature points 420 (FIG. 4) are used to generate a mask that identifies pixels that correspond to the eye and teeth regions. Using the input image at a valley/peak map generation step 1520, the valley/peak map is generated using Eq. 12 where the radius of the blur is determined by the eye separation (which is an example of a default parameter). At a scaling factor generation step 1530, the valley/peak map and the color information are used to calculate scaling factors (which are examples of default parameters) for the luminance and chrominance values of the pixels within the eye and teeth masks. Then at a pixel modification step 1540, the scaling factors are applied to the luminance and chrominance values of the pixels within eye and teeth regions generating new luminance and chrominance values.
In a presently preferred embodiment, the RGB values for pixels within the mask regions are converted to CIELAB (L*a*b*) space and the luminance and chrominance values are modified as follows,

L*=L*·(1+kP)  (EQ.23)

a*=a*/(1+kP)  (EQ.24)

b*=b*/(1+kP)  (EQ.25)

where k is the aforementioned default parameter and P is the probability that the pixel belongs either to the whites of the eyes or to a tooth. A presently preferred expression for the probability P is as follows,





  
    
      
        P
        =
        
          {
          
            
              
                
                  1
                  -
                  
                    
                    
                      F
                      /
                      β
                    
                    
                  
                
              
              
                
                  
                    if
                    ⁢
                    
                      
                    
                    -
                    β
                  
                  ≤
                  F
                  ≤
                  0
                
              
            
            
              
                0
              
              
                otherwise
              
            
          
        
      
    
    
      
        (
        
          EQ
          .
          
            
          
          ⁢
          26
        
        )
      
    
  




where F is calculated using Eq. 12 with a blur radius chosen as a function of the face size and β is a threshold.

Shape Enhancement Filter

The task of the shape enhancing filter 650 (shown in FIG. 6) is to modify the shape of facial features such as the eyes, nose and mouth. The shapes of the facial feature are enhanced by modifying their shape using standard warping techniques. An example of a warping technique useful for practicing the current invention is given by T. Beier and S. Neely. Feature-Based Image Metamorphosis, Computer Graphics, 26(2): 35–42, New York, N.Y., July, 1992, Proceedings of SIGGRAPH '92, which is incorporated herein by reference.
Referring to FIG. 19, there is shown a flowchart for a presently preferred embodiment of a shape enhancing filter 650 according to the present invention. At a source control point determination step 1910, the source control points 1810 (see FIG. 18) that are used for warping the image are determined by the feature points 420 (see FIG. 4) delineating the facial feature (e.g., eye) to be shape enhanced. In a destination control point determination step 1920, the destination control points 1820 are determined. The location of destination control points 1820 defines the new location of the source control points 1810 in the shape modified image. The destination control points 1820 (D1, D2, D3, and D4) are respectively the new locations of the source control points 1810 (S1, S2, S3, and S4). In a warping step 1930, the source and destination control points are used to warp the image. The location of the destination control points 1820 are defined by the desired change of the facial feature shape. For example, if it is desired to increase the size of the eyes the destination control points 1820 are positioned as shown in FIG. 18.
In a presently preferred embodiment, the parameters of the shape enhancing filter are used to define whether the facial feature shape is increased or decreased by specifying the location of the destination control points 1820. The shape enhancing filter can be incorporated into the GUI screen 78 (see FIG. 1B) through an additional slider control. Moreover, there may be a unique shape enhancing slider for each facial feature. The system maps the position of the slider into appropriate parameter values of the shape enhancement filters. Moving the slider in one direction causes the facial feature to decrease in size while moving the slider in the opposite direction causes the facial feature to increase in size. The default position of the respective slider thus could be a neutral position not effecting any shape enhancement (until the slider is moved one way or the other).
Throughout the foregoing description, certain parameters have been specified as candidates for system default parameters, which, e.g., determine the initial settings of the enhancement filters and the initial settings of the enhancement sliders used in the graphical user interface. These parameters have been selected without limitation as examples of appropriate default parameters and should not be seen as a definitive or limiting set of parameters. It should be clear to one of ordinary skill in this art that many other parameters, including others cited in this description, could be chosen and/or designated as default parameters.
PARTS LIST


    10 system
    12 personal computer (PC)
    20 storage media
    28 scanner
    30 digital camera
    40 input devices
    50 display monitor
    60 printer
    62 server
    65 storage media
    70 communication network
    78 graphical user interface (GUI) screen
    80 original image
    82 enhanced image
    90 appearance enhancer
    92 texture enhancer
    94 skin enhancer
    96 eye enhancer
    98 teeth enhancer
    200 initiation step
    205 acquisition and display step
    210 locate step
    215 display step
    220 decision step
    225 modify step
    230 default setup step
    235 execution step
    240 user selection step
    245 display step
    250 decision step
    255 local print step
    260 local archive step
    265 remote print step
    270 remote archive step
    275 query step
    280 ending step
    282 acquisition step
    284 face detection and location step
    286 enhancement selection step
    288 enhancement execution step
    290 face query step
    292 storage step
    294 image query step
    310 face detection module
    315 facial feature detector
    410 detected face
    420 salient feature points
    550 generic mapping step
    554 scaling step
    556 skin color mapping step
    558 map combination step
    570 central region with generic mask
    572 border region
    574 outline of neck probability map
    576 central region
    610 skin texture enhancement filter
    620 skin tone enhancement filter
    630 teeth enhancement filter
    640 eye enhancement filter
    650 facial feature shape enhancement filter
    710 skin feature generation step
    720 feature modification step
    810 feature selection step
    820 dilation step
    830 filtering step
    910 face boundary
    920 dilated features
    930 line segments
    940 feature pixel
    1002—
    1190 pinwheel filter steps
    1210 blurring step
    1220 shadow/peak generation step
    1230 coefficient generation step
    1240 blending step
    1310 luminance image
    1320 average luminance image
    1330 subtracting step
    1510 eye/teeth mask generating step
    1520 valley/peak map generating step
    1530 scaling factor generation step
    1540 pixel modification step
    1810 source control points
    1820 destination control points
    1910 source control point determination step
    1920 destination control point determination step
    1930 warping step

## Claims

1. A method for enhancing the skin texture of a face appearing in a digital image, said method comprising the steps of:
(a) generating a luminance image from the digital image;
(b) using a valley/peak detector to detect skin features in the luminance image;
(c) classifying the skin features according to their feature-based characteristics;
(d) selecting relevant skin features for modification;
(e) modifying the relevant skin features using an adaptive interpolation procedure, thereby producing a modified image; and
(f) blending the digital image and the modified image to produce an enhanced image.

2. The method as claimed in claim 1 wherein the valley/peak detector used in step (b) has a spatial size that is dependent upon a size of the face.

3. The method as claimed in claim 2 wherein the skin features are classified in step (c) according to at least one of their size, shape, color and location in the skin region.

4. The method as claimed in claim 3 wherein relevant skin features are selected in step (d) based on their size being between a minimum and maximum size, in order to preserve skin texture.

5. The method as claimed in claim 4 wherein the minimum and maximum sizes are scaled to the size of the face.

6. The method as claimed in claim 3 wherein relevant skin features are selected in step (d) based on their size being larger than a specified minimum size, in order to preserve skin texture.

7. The method as claimed in claim 3 wherein the selected skin features from step (d) are adaptively dilated using morphological operators based upon the size of the feature.

8. The method as claimed in claim 1 wherein the step of modifying the relevant skin features in step (e) uses a directional interpolation filter having a pinwheel configuration; representing line segment lengths.

9. The method as claimed in claim 8 wherein a minimum and maximum number of points on a line segment depends upon a size of the face.

10. The method as claimed in claim 8 wherein a minimum and maximum number of points on the line segment depends upon a size of the feature.

11. The method as claimed in claim 8 wherein the line segments do not cross a boundary of a facial region or a boundary of any skin feature not selected for modification in step (d).

12. The method as claimed in claim 8 wherein the line segments do not cross a boundary of any skin feature.

13. The method as claimed in claim 8 wherein processed pixel values for the relevant skin features are obtained by adaptively blending new pixel values obtained from the pinwheel filter with original pixel values from the digital image as a function of a size of the relevant skin feature.

14. The method as claimed in claim 3 wherein the step (f) of blending comprises adaptively blending the digital image and the modified image as a function of the size of a skin feature to produce an enhanced image.

15. The method as claimed in claim 3 wherein the step (f) of blending comprises adaptively blending the digital image and the modified image as a function of the location of a skin feature to produce an enhanced image.

16. The method as claimed in claim 1 wherein step (b) detects valley skin features and peak skin features and step (e) preferentially modifies valley skin features before modifying peak skin features.

17. A computer storage medium having instructions stored therein for causing a computer to perform the method of claim 1.

18. A method for enhancing the skin tone of a face appearing in a digital image, said method comprising the steps of:
(a) generating a blurred version of the digital image;
(b) generating a blending coefficient; and
(c) applying a blending operation to the digital image and its blurred version to generate an enhanced image with improved skin tone, wherein the blending operation uses the blending coefficient to combine the digital image and its blurred version;
wherein the blending coefficient is generated from a shadow/highlight strength image obtained from the digital image, said shadow/highlight strength image having a shadow/highlight strength value for each pixel of said digital image, and wherein the blending operation uses the blending coefficient to adaptively combine the digital image and its blurred version.

19. A method for enhancing the skin tone of a face appearing in a digital image, said method comprising the steps of:
(a) generating a blurred version of the digital image;
(b) generating a blending coefficient; and
(c) applying a blending operation to the digital image and its blurred version to generate an enhanced image with improved skin tone, wherein the blending operation uses the blending coefficient to combine the digital image and its blurred version;
wherein the blending coefficient is generated from a shadow/highlight strength image obtained from the digital image, and wherein the blending operation uses the blending coefficient to adaptively combine the digital image and its blurred version; and
wherein the step (b) of generating a blending coefficient comprises the steps of generating a luminance image from the digital image, generating an average luminance image from the luminance image, and subtracting the average luminance image from the luminance, image to generate a shadow/highlight image.

20. The method as claimed in claim 19 wherein the digital image is a color image having a plurality of color channels and the blending operation is applied to each channel of the color image.

21. A computer storage medium having instructions stored therein for causing a computer to perform the method of claim 19.

22. A method for enhancing the skin texture of a face appearing in a digital image, said method comprising the steps of:
generating a luminance image from the digital image;
using a valley/peak detector to detect a plurality of skin features in said luminance image;
classifying said skin features according to feature-based characteristics;
modifying one or more of said skin features using an adaptive interpolation procedure to produce a modified image; and
blending the digital image and said modified image to produce an enhanced image.

23. The method of claim 22 wherein said valley/peak detector has a spatial size that is dependent upon a size of the face.

24. The method of claim 23 wherein said feature-based characteristics include at least one of size, shape, color and location.

25. The method of claim 24 wherein said one or more skin features each have a size between predetermined minimum and maximum sizes.

26. The method of claim 25 wherein said predetermined minimum and maximum sizes are scaled to the size of the face.

27. The method of claim 24 wherein said one or more skin features are larger than a specified minimum size.

28. The method of claim 24 wherein said modifying further comprises adaptively dilating using morphological operators based upon respective size of said one or more skin features.

29. The method of claim 22 wherein said modifying further comprises using a directional interpolation filter.

30. The method of claim 29 wherein said filter has a pinwheel configuration representing line segment lengths.

31. The method of claim 30 further comprising determining a plurality of facial regions and wherein said pinwheel configuration has line segments that do not cross a boundary between two or more of said facial regions.

32. The method of claim 30 wherein said pinwheel configuration has line segments that do not cross into ones of said plurality of skin features excluded from said modifying.

33. The method of claim 30 wherein said pinwheel configuration has line segments that do not cross into said skin features.

34. The method of claim 33 wherein said blending is adaptive as a function of a size of the respective said modified skin feature.

35. The method of claim 33 wherein said blending is adaptive as a function of a size of the respective said modified skin feature.

36. The method as claimed in claim 22 wherein said using step detects valley skin features and peak skin features and said modifying further comprises modifying said valley skin features then modifying said peak skin features.

37. A computer storage medium having instructions stored therein for causing a computer to perform the method of claim 22.

38. A system for enhancing the skin texture of a face appearing in a digital image, said system comprising:
means for generating a luminance image from the digital image;
means for using a valley/peak detector to detect a plurality of skin features in said luminance image;
means for classifying said skin features according to feature-based characteristics;
means for modifying one or more of said skin features using an adaptive interpolation procedure to produce a modified image; and
means for blending the digital image and said modified image to produce an enhanced image.

39. The system of claim 38 wherein said valley/peak detector has a spatial size that is dependent upon a size of the face.

40. The system of claim 39 wherein said feature-based characteristics include at least one of size, shape, color and location.

41. The system of claim 40 wherein said one or more skin features each have a size between predetermined minimum and maximum sizes.

42. The system of claim 41 wherein said predetermined minimum and maximum sizes are scaled to the size of the face.

43. The system of claim 40 wherein said one or more skin features are larger than a specified minimum size.

44. The system of claim 40 wherein said means for modifying further comprises means for adaptively dilating using morphological operators based upon respective size of said one or more skin features.

45. The system of claim 38 wherein said means for modifying further comprises means for using a directional interpolation filter.

46. The system of claim 45 wherein said filter has a pinwheel configuration representing line segment lengths.

47. The system of claim 46 further comprising means for determining a plurality of facial regions and wherein said pinwheel configuration has line segments that do not cross a boundary between two or more of said facial regions.

48. The system of claim 46 wherein said pinwheel configuration has line segments that do not cross into ones of said plurality of skin features excluded from said modifying.

49. The system of claim 46 wherein said pinwheel configuration has line segments that do not cross into said skin features.

50. The system of claim 49 wherein said blending is adaptive as a function of a size of the respective said modified skin feature.

51. The system of claim 49 wherein said blending is adaptive as a function of a size of the respective said modified skin feature.

52. The system of claim 38 wherein said mean for using detects valley skin features and peak skin features and said means for modifying modifies in the order said valley skin features, and then, said peak skin features.

53. A method for enhancing the skin tone of a face in a digital image, said method comprising the steps of:
generating a blurred version of the digital image;
generating a blending coefficient; and
blending the digital image and said blurred version using said blending coefficient;
said method further comprising:
obtaining a shadow/highlight strength image from the digital image, said shadow/highlight strength image having a shadow/highlight strength value for each pixel of said digital image; and
generating said blending coefficient from said shadow/highlight strength image.

54. A method for enhancing the skin tone of a face in a digital image, said method comprising the steps of:
generating a blurred version of the digital image;
generating a blending coefficient; and
blending the digital image and said blurred version using said blending coefficient;
said method further comprising:
obtaining a shadow/highlight strength image from the digital image; and
generating said blending coefficient from said shadow/highlight strength image;
wherein said obtaining further comprises:
generating a luminance image from the digital image;
generating an average luminance image from said luminance image; and
subtracting said average luminance image from said luminance image to generate said shadow/highlight strength image.

55. The method of claim 54 wherein said blending is adaptive.

56. The method of claim 54 wherein the digital image is a color image having a plurality of color channels and said blending is applied to each channel of the color image.

57. A computer storage medium having instructions stored therein for causing a computer to perform the method of claim 54.

58. A system for enhancing the skin tone of a face in a digital image, said system comprising:
means for generating a blurred version of the digital image;
means for generating a blending coefficient; and
means for blending the digital image and said blurred version using said blending coefficient;

said system further comprising:
means for obtaining a shadow/highlight strength image from the digital image, said shadow/highlight strength image having a shadow/highlight strength value for each pixel of said digital image; and
means for generating said blending coefficient from said shadow/highlight strength image.

59. A system for enhancing the skin tone of a face in a digital image, said system comprising:
means for generating a blurred version of the digital image;
means for generating a blending coefficient; and
means for blending the digital image and said blurred version using said blending coefficient,

further comprising:
means for obtaining a shadow/highlight strength image from the digital image; and
means for generating said blending coefficient from said shadow/highlight strength image:
wherein said means for obtaining further comprises:
means for generating a luminance image from the digital image;
means for generating an average luminance image from said luminance image; and
means for subtracting said average luminance image from said luminance image to generate said shadow/highlight strength image.

60. The system of claim 58 wherein said blending is adaptive.

61. The system of claim 58 wherein the digital image is a color image having a plurality of color channels and said blending is applied to each channel of the color image.