Patent Publication Number: US-9846924-B2

Title: Systems and methods for detection and removal of shadows in an image

Description:
TECHNICAL FIELD 
     The present disclosure relates in general to information handling systems, and more particularly, to video and/or still image capture and removal of shadows from an image. 
     BACKGROUND 
     As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
     Information handling systems include cameras for capturing images, whether videos or still images. Such images may be used in many applications, including teleconferencing applications or simply capturing images for entertainment, documentation, business, or other purposes. 
     In many image capture scenarios, the presence of strong shadows is undesirable and degrades the quality of the image. If such images are taken of written material, such shadows may reduce legibility or readability of content. Such shadows may be present in numerous scenarios, including when subjects are under uneven lighting conditions or when capturing images outdoors in bright sunlight. 
     While some existing techniques may be used to reduce shadowing, such techniques may have shortcomings. For example, exposure levels in high-dynamic range (HDR) may be over-exposed or under-exposed and not set properly in shadow areas. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, one or more disadvantages and problems associated with reduction of shadows in images may be reduced or eliminated. 
     In accordance with embodiments of the present disclosure, an information handling system may include a processor and a non-transitory computer-readable medium embodying a program of instructions. The program of instructions may be configured to, when read and executed by the processor, receive a visible-light image from a visible-light sensor, receive an infrared image from an active infrared sensor, and compare the visible-light image to the infrared image to determine shadow regions of the visible-light image having shadows. 
     In accordance with these and other embodiments of the present disclosure, a method may include receiving a visible-light image from a visible-light sensor, receiving an infrared image from an active infrared sensor, and comparing the visible-light image to the infrared image to determine shadow regions of the visible-light image having shadows. 
     In accordance with these and other embodiments of the present disclosure, an article of manufacture may include a non-transitory computer readable medium and computer-executable instructions carried on the non-transitory computer readable medium, the instructions readable by a processor. The instructions, when read and executed, may cause the processor to receive a visible-light image from a visible-light sensor, receive an infrared image from an active infrared sensor, and compare the visible-light image to the infrared image to determine shadow regions of the visible-light image having shadows. 
     Technical advantages of the present disclosure may be readily apparent to one skilled in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates a block diagram of an example image capture system, in accordance with embodiments of the present disclosure; 
         FIG. 2  illustrates an example camera having multiple sensors, in accordance with embodiments of the present disclosure; 
         FIGS. 3A-3C  illustrate example images captured by sensors of the example camera depicted in  FIG. 2 , in accordance with embodiments of the present disclosure; and 
         FIG. 4  illustrates a flow chart of an example method for detection and removal of shadows in an image, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments and their advantages are best understood by reference to  FIGS. 1-4 , wherein like numbers are used to indicate like and corresponding parts. 
     For the purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, entertainment, or other purposes. For example, an information handling system may be a personal computer, a PDA, a consumer electronic device, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include memory, one or more processing resources such as a central processing unit (CPU) or hardware or software control logic. Additional components of the information handling system may include one or more storage devices, one or more communications ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communication between the various hardware components. 
     For the purposes of this disclosure, computer-readable media may include any instrumentality or aggregation of instrumentalities that may retain data and/or instructions for a period of time. Computer-readable media may include, without limitation, storage media such as a direct access storage device (e.g., a hard disk drive or floppy disk), a sequential access storage device (e.g., a tape disk drive), compact disk, CD-ROM, DVD, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), and/or flash memory; as well as communications media such as wires, optical fibers, microwaves, radio waves, and other electromagnetic and/or optical carriers; and/or any combination of the foregoing. 
     For the purposes of this disclosure, information handling resources may broadly refer to any component system, device or apparatus of an information handling system, including without limitation processors, service processors, basic input/output systems, buses, memories, I/O devices and/or interfaces, storage resources, network interfaces, motherboards, and/or any other components and/or elements of an information handling system. 
       FIG. 1  illustrates a block diagram of an example image capture system comprising an information handling system  102 , in accordance with embodiments of the present disclosure. In certain embodiments, information handling system  102  may comprise a personal computer (e.g., a desktop computer or a portable computer). In these and other embodiments, information handling system  102  may comprise a mobile device (e.g., smart phone, a tablet computing device, a handheld computing device, a personal digital assistant, or any other device that may be readily transported on a person of a user of such mobile device). In these and other embodiments, information handling system  102  may comprise a Voice over Internet Protocol (VoIP) phone (e.g., a purpose-built hardware device that appears much like an ordinary landline telephone). In these and other embodiments, information handling system  102  may comprise a video camera assembly. In these and other embodiments, information handling system  102  may comprise a still camera assembly. 
     As depicted in  FIG. 1 , information handling system  102  may include a processor  103 , a memory  104  communicatively coupled to processor  103 , a storage resource  110  communicatively coupled to processor  103 , and a user interface  114  communicatively coupled to processor  103 . 
     Processor  103  may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data, and may include, without limitation, a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, processor  103  may interpret and/or execute program instructions and/or process data stored in its memory  104 , storage resource  110 , and/or another component of information handling system  102 . 
     Memory  104  may be communicatively coupled to its associated processor  103  and may include any system, device, or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). Memory  104  may include random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), a PCMCIA card, flash memory, magnetic storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to its associated information handling system  102  is turned off. 
     Each storage resource  110  may include a system, device, or apparatus configured to store data. A storage resource  110  may include one or more hard disk drives, magnetic tape libraries, optical disk drives, magneto-optical disk drives, solid state storage drives, compact disk drives, compact disk arrays, disk array controllers, and/or any other systems, apparatuses or devices configured to store data. In certain embodiments, storage resource  110  may include one or more storage enclosures configured to hold and/or power one or more of such devices. In the embodiments represented by  FIG. 1 , storage resource  110  may reside within its associated information handling system  102 . However, in other embodiments, storage resource  110  may reside external to its associated information handling system  102  (e.g., may be coupled to information handling system  102  via a network). 
     As shown in  FIG. 1 , a storage resource  110  may have stored thereon an imaging application  112 . Imaging application  112  may comprise a program of instructions which a processor  103  may read and execute to process images captured by camera  120  to reduce or eliminate undesired shadows from a visible light image captured by a visual light sensor of camera  120 , as described in greater detail below. When executed, active portions of imaging application  112  may be loaded from storage resource  110  into memory  104  for execution by processor  103 . Although imaging application  112  is depicted in  FIG. 1  as being locally stored to a storage resource  110  of an information handling system  102 , in some embodiments, imaging application  112  may be stored externally or remotely from an information handling system  102  and accessible to such information handling system  102  via a network, and loaded by processor  103  from such network (e.g., such imaging application  112  may be a streaming application). 
     User interface  114  may comprise any instrumentality or aggregation of instrumentalities by which a participant subject  122  may interact with information handling system  102 . For example, user interface  114  may permit a user to input data and/or instructions into information handling system  102  (e.g., via a keypad, keyboard, touch screen, microphone, camera, and/or other data input device), and/or otherwise manipulate information handling system  102  and its associated components. User interface  114  may also permit information handling system  102  to communicate data to a participant  122  (e.g., via a display device, speaker, and/or other data output device). As shown in  FIG. 1 , user interface  114  may include one or more of a display  116 , microphone  118 , camera  120 , and speaker  124 . 
     A display  116  may comprise any suitable system, device, or apparatus configured to display human-perceptible graphical data and/or alphanumeric data to a participant  122 . For example, in some embodiments, display  116  may comprise a liquid crystal display. 
     A microphone  118  may comprise any system, device, or apparatus configured to convert sound incident at microphone  118  to an electrical signal that may be processed by processor  103 . In some embodiments, microphone  118  may include a capacitive microphone (e.g., an electrostatic microphone, a condenser microphone, an electret microphone, a microelectromechanical systems (MEMs) microphone, etc.) wherein such sound is converted to an electrical signal using a diaphragm or membrane having an electrical capacitance that varies as based on sonic vibrations received at the diaphragm or membrane. 
     A camera  120  may comprise any system, device, or apparatus configured to record images (moving or still) into one or more electrical signals that may be processed by processor  103 . In some embodiments, camera  120  may comprise a multiple-sensor camera configured to capture multiple types of images, such as multiple-sensor camera  120  depicted in  FIG. 2  and described in greater detail below. In operation, camera  120  may capture images of a subject  122 , which may be a person (including, without limitation, a user of information handling system  102 ), animal, or other object. 
     A speaker  124  may comprise any system, device, or apparatus configured to produce sound in response to electrical audio signal input. In some embodiments, a speaker  124  may comprise a dynamic loudspeaker, which employs a lightweight diaphragm mechanically coupled to a rigid frame via a flexible suspension that constrains a voice coil to move axially through a cylindrical magnetic gap such that when an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver&#39;s magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier. 
     In addition to processor  103 , memory  104 , storage resource  110 , and user interface  114 , information handling system  102  may include one or more other information handling resources. Such an information handling resource may include any component system, device or apparatus of an information handling system, including without limitation, a processor, bus, memory, I/O device and/or interface, storage resource (e.g., hard disk drives), network interface, electro-mechanical device (e.g., fan), display, power supply, and/or any portion thereof. An information handling resource may comprise any suitable package or form factor, including without limitation an integrated circuit package or a printed circuit board having mounted thereon one or more integrated circuits. 
       FIG. 2  illustrates an example camera  120  having multiple sensors, in accordance with embodiments of the present disclosure. As shown in  FIG. 2 , camera  120  may include a visible light sensor  202 , an active infrared sensor  204 , an infrared source  206 , a depth sensor  208 , and a light source  210 . 
     Visible light sensor  202  may comprise any system, device, or apparatus configured to sense electromagnetic energy in the visible spectrum (e.g., from approximately 400 nanometers in wavelength to approximately 700 nanometers in wavelength) and based on the electromagnetic energy sensed, capture a visible-light image having a plurality of pixels representative of the visible spectrum electromagnetic energy sensed relative to each pixel, such as visible-light image  302  depicted in  FIG. 3A . Such visible-light image  302  may be black and white or color. Devices similar to visible light sensor  202  are often simply referred to as “cameras.” 
     Active infrared sensor  204  may comprise any system, device, or apparatus configured to sense electromagnetic energy in the non-visible infrared spectrum (e.g., greater than 700 nanometers in wavelength) and based on the electromagnetic energy sensed, capture an infrared image having a plurality of pixels representative of the infrared spectrum electromagnetic energy sensed relative to each pixel, such as infrared image  304  depicted in  FIG. 3B . As its name implies, active infrared sensor  204  senses infrared energy reflected from a subject  122  originating from an active source  206  of infrared energy. Such infrared source  206  may comprise any system, device, or apparatus located in close proximity to infrared sensor  204  which emits infrared radiation (e.g., an infrared lamp for converting electrical energy into electromagnetic radiation in the infrared spectrum). 
     Depth sensor  208  may comprise any system, device, or apparatus configured to resolve distance based on the known speed of light, measuring a time-of-flight of a light signal between light source  210  and subject  122  for each pixel of the image, and based on the distance sensed, capture a depth image having a plurality of pixels representative of the distance sensed relative to each pixel, such as depth image  306  depicted in  FIG. 3C . Light source  210  may comprise any system, device, or apparatus located in close proximity to depth sensor  208  which emits electromagnetic radiation (e.g., visible light or non-visible radiation). In some embodiments, depth sensor  208  may comprise a time-of-flight camera. In other embodiments, depth sensor  208  may comprise a structured light camera. In yet other embodiments, depth sensor  208  may comprise a stereo camera comprising at least two sensors and an optional light source. 
     Although the foregoing contemplates a separate active infrared sensor  204  and depth sensor  208 , in some embodiments, depth sensor  208  and light source  210  may also be capable of capturing two-dimensional infrared images, thus allowing depth sensor  208  to serve the functionality of infrared sensor  204  as well. 
     In operation, imaging application  112  may receive as inputs a visible-light image  302 , an infrared image  304 , and a depth image  306 , and based thereon, identify potentially unwanted shadows present in the visible-light image  302  (e.g., shadow  308  present in visible-light image  302 ) and characterize such shadows in order to remove or reduce such shadows. In other words, for each visible-light image  302  captured, a corresponding (e.g., substantially contemporaneous) infrared image  304  and a corresponding (e.g., substantially contemporaneous) depth image  306  are also captured. Because active source  206  may have the effect of illuminating subject  122  like a flashlight from the point of view of camera  120 , infrared sensor  204  may not “see” shadows resulting from visible light sources in the environment of subject  122 . Thus, a truly dark material may typically appear dark in both the visible-light image  302  and the corresponding infrared image  304 , and because a shadow may only appear dark in the visible-light image  302 , the visible-light image  302  and its corresponding infrared image  304  may be compared to detect pixel regions in the visible-light image  302  that are dark (e.g., below a pre-determined brightness threshold) but have corresponding pixel regions in the infrared image  304  that are not similarly dark. An example of this approach is described in greater detail with respect to  FIG. 4 , below. 
       FIG. 4  illustrates a flow chart of an example method  400  for detection and removal of shadows in an image, in accordance with embodiments of the present disclosure. According to some embodiments, method  400  may begin at step  402 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of information handling system  102 . As such, the preferred initialization point for method  400  and the order of the steps comprising method  400  may depend on the implementation chosen. 
     At step  402 , imaging application  112  may initialize each value of a data structure referred to herein as a shadow mask to zero. Such shadow mask may include a plurality of values, each value corresponding to a pixel of a visible-light image  302 . 
     At step  404 , imaging application  112  may segment the visible-light image  302  into dark regions and non-dark regions. For example, imaging application  112  may use an image segmentation algorithm and pre-determined thresholds for brightness and/or colors that are considered “dark.” As a result, regions of visible-light image  302 , such as shadow  308 , may be identified as a dark region while the remainder of the visible-light image  302  may be identified as possessing non-dark regions. In some embodiments, imaging application  112  may also use depth image  306  to automatically classify background pixels (e.g., those pixels outside the infrared sensing range of infrared sensor  204  and the depth sensing range of depth sensor  208  corresponding to black pixels of depth image  306  of  FIG. 3C ) as non-dark regions. Such automatic classification of background pixels as being in non-dark regions may reduce required image processing resources in cases in which it would be beneficial to remove shadows in foreground objects, but such shadows can be tolerated in background objects (e.g., portrait shots). 
     At step  406 , imaging application  112  may compare each dark region of the visible-light image  302  to its corresponding region of the infrared image  304 . At step  408 , based on the comparisons, imaging application  112  may determine if each corresponding region of the infrared image  304  is also dark. Such determination may be made according to any standard, such as whether a corresponding region of the infrared image  304  has at least a predetermined number and/or concentration of pixels in the corresponding region of the infrared image  304  that fall below a predetermined brightness threshold for the region to be considered a dark region. For each dark region of visible-light image  302  having a corresponding region of infrared image  304  determined to be dark, method  400  may proceed to step  410 . Otherwise, for each dark region of visible-light image  302  having a corresponding region of infrared image  304  determined to not be dark, method  400  may proceed to step  412 . 
     At step  410 , in response to a dark region of visible-light image  302  having a corresponding region of infrared image  304  determined not to be dark, meaning that such dark region is a shadow region, imaging application  112  may assign each value in the shadow mask for pixels in the shadow region a value corresponding to a depth value associated with such pixel in depth image  306 . Typically, a depth camera may assigns a value of zero to the closest object of an image, and the values increase as the depth of the objects increase. However, in the present disclosure, the depth value assigned in step  410  may employ an inverse of such approach, in which background objects have a depth value of zero, and with increasing values or objects closer to camera  120 . After completion of step  410 , method  400  may end. 
     At step  412 , in response to a dark region of visible-light image  302  having a corresponding region of infrared image  304  determined to be dark, meaning that such dark region is not a shadow region, imaging application  112  may assign each value in the shadow mask for pixels not in a shadow region a value of zero, indicating that such pixels are not in shadow regions. After completion of step  412 , method  400  may end. 
     Although  FIG. 4  discloses a particular number of steps to be taken with respect to method  400 , method  400  may be executed with greater or fewer steps than those depicted in  FIG. 4 . In addition, although  FIG. 4  discloses a certain order of steps to be taken with respect to method  400 , the steps comprising method  400  may be completed in any suitable order. 
     Method  400  may be implemented using one or more information handling systems  102 , components thereof, and/or any other system operable to implement method  400 . In certain embodiments, method  400  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
     After the shadow mask for the visible-light image  302  is created according to method  400 , data of the shadow mask may be processed by imaging application  112  to remove or reduce shadows and render a corrected visible-light image  302  with the shadows removed or reduced. The scope of such shadow reduction based on a shadow mask is outside the scope of this disclosure, although one example technique may involve using the values present in the shadow mask, which are representative of a depth of each pixel in shadow regions, to characterize a surface shape of subjects in the shadow regions in order to edit the visible-light image  302  to reduce or eliminate the appearance of shadows. 
     It is to be understood that the image analysis approaches discussed above are not limited to the embodiments disclosed above. For example, in analyzing visible-light image  302  to determine dark regions, imaging application  112  may in some embodiments process certain channels of a color image (e.g., a luminance channel). As another example, in some embodiments, sensors  202 ,  204 , and  208  may not be positioned in the exact location and may have differences in resolution and other parameters, such that the systems and methods described above may need to account for differences in the corresponding images  302 ,  304 , and  306 . Thus, imaging application  112  may in some embodiments compensate for such differences by adjusting a pixel map to account for offsets between sensors and other sensor parameters. Alternatively, imaging application  112  may use pixel information from infrared image  304  and depth image  306  to detect shadow pixels, and then “grow” to neighboring pixels in the visible-light image  302  that exhibit the same color and/or brightness characteristics as the known shadow pixels. 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. 
     All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.