CN116508326A - Tone mapping method and apparatus, computer usable medium storing software for implementing the method - Google Patents
Tone mapping method and apparatus, computer usable medium storing software for implementing the method Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 50
- 238000013507 mapping Methods 0.000 title claims abstract description 38
- 230000035945 sensitivity Effects 0.000 claims description 9
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- 238000003672 processing method Methods 0.000 abstract 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/90—Dynamic range modification of images or parts thereof
- G06T5/92—Dynamic range modification of images or parts thereof based on global image properties
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/16—Human faces, e.g. facial parts, sketches or expressions
- G06V40/172—Classification, e.g. identification
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/70—Circuitry for compensating brightness variation in the scene
- H04N23/71—Circuitry for evaluating the brightness variation
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10024—Color image
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/20—Special algorithmic details
- G06T2207/20092—Interactive image processing based on input by user
- G06T2207/20104—Interactive definition of region of interest [ROI]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/30—Subject of image; Context of image processing
- G06T2207/30196—Human being; Person
- G06T2207/30201—Face
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Abstract
A method of tone mapping an image according to the present disclosure includes: the image processing method includes acquiring an image, determining whether a photographing condition is a backlight condition, calculating brightness using a camera parameter and selecting a tone curve according to the calculated brightness when the photographing condition is determined not to be the backlight condition, selecting a tone curve suitable for the backlight condition when the photographing condition is determined to be the backlight condition, and performing tone mapping on the image using the selected tone curve.
Description
Technical Field
The present disclosure relates generally to the field of image processing technology, and more particularly, to a method and apparatus for tone mapping an image, and a computer usable medium storing software for implementing the method.
Background
In recent years, color imaging devices have been developed, which are widely used in devices such as mobile phones, digital cameras, and the like. With the advancement of high-speed/large-capacity data communication, a high-speed processor or high color quality is also required.
One of the techniques is a face recognition system for smart phone face unlocking, which uses images to perform tone mapping on original images, so that the success rate of the face recognition system can be effectively improved.
However, under certain conditions, such as backlighting, a suitable image may not be obtained.
According to conventional techniques, a histogram is used to calculate the luminance used to select a tone curve for tone mapping. However, this approach is time consuming and not always effective.
Therefore, it may be difficult to obtain a proper image in a limited time; so that it is impossible to improve the success rate of face unlocking.
Disclosure of Invention
The present disclosure is directed to solving at least one of the above-mentioned technical problems. Accordingly, the present disclosure needs to provide a method and apparatus for tone mapping, and a computer usable medium storing software for causing a computer to implement the method for tone mapping.
According to one aspect of the disclosure, a method for tone mapping may include:
acquiring an image;
judging whether the shooting condition is a backlight condition or not;
when the photographing condition is determined not to be the backlight condition, calculating brightness using the camera parameter, and selecting a tone curve according to the calculated brightness;
when the photographing condition is determined to be a backlight condition, selecting a tone curve suitable for the backlight condition; and
tone mapping is performed on the image using the selected tone curve.
In some embodiments, the method further comprises:
performing face unlocking by using the tone-mapped image, and judging whether the face unlocking is successful or not; and
and displaying a judgment result of face unlocking.
In some embodiments, when determining whether the photographing condition is a backlight condition, the method further includes:
setting a specific region on an image;
calculating a first average luminance inside the specific region and a second average luminance outside the specific region;
determining whether a difference between the first average luminance and the second average luminance is greater than a threshold; and
when the difference is determined to be greater than the threshold value, it is determined that the photographing condition is a backlight condition, and when the difference is determined to be not greater than the threshold value, it is determined that the photographing condition is not a backlight condition.
In some embodiments, the processor can set the region in the following manner: the center position of the specific region is located on a line in the direction of gravity.
In some embodiments, a camera parameter, i.e., F_value, may be included when the photographing condition is determined not to be the backlight condition 2 The brightness is calculated by the following formula of exposure time and ISO sensitivity:
where C is the calibration contrast.
In some embodiments, the image may be a still image or one of a plurality of still images forming a moving image.
According to one aspect of the disclosure, an apparatus for tone mapping may include:
a camera unit configured to acquire an image;
a processor configured to input a current image to determine whether a photographing condition is a backlight condition, calculate brightness using a camera parameter when the photographing condition is determined not to be the backlight condition, and select a tone curve according to the calculated brightness, select a tone curve suitable for the backlight condition when the photographing condition is determined to be the backlight condition, and perform tone mapping on the image;
and a display unit configured to display the tone-mapped image.
In some embodiments, the processor may be further configured to perform face unlocking using the tone mapped image, determine whether the face unlocking was successful, and display the determination of the face unlocking.
In some embodiments, when the processor determines whether the photographing condition is a backlight condition, the processor may be further configured to set a specific region on the image, calculate a first average luminance inside the specific region and a second average luminance outside the specific region to determine whether a difference between the first average luminance and the second average luminance is greater than a threshold, determine that the photographing condition is the backlight condition when the difference is determined to be greater than the threshold, and determine that the photographing condition is not the backlight condition when the difference is determined to be not greater than the threshold.
In some embodiments, the processor can set the region in the following manner: the center position of the region is located on a line in the direction of gravity.
In some embodiments, when the photographing condition is determined not to be the backlight condition, the processor may use a camera parameter including F_value 2 The brightness is calculated by the following formula of exposure time and ISO sensitivity:
where C is the calibration contrast.
In some embodiments, the image may be a still image or one of a plurality of still images forming a moving image.
According to one aspect of the present disclosure, a computer usable medium stores software for causing a computer to implement the above-described method for tone mapping.
Drawings
These and/or other aspects and advantages of the disclosed embodiments will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings, wherein:
fig. 1 is a flowchart showing a method for tone mapping according to a comparative example;
FIG. 2A is an example photograph of an original image in a backlit condition;
fig. 2B is an example photograph of an image obtained by the tone mapping method according to the comparative example;
fig. 3 is a block diagram schematically showing a circuit configuration of an apparatus for tone mapping according to a first embodiment of the present disclosure;
fig. 4 is a flowchart illustrating a method for tone mapping according to a second embodiment of the present disclosure;
fig. 5 is a flowchart illustrating a method for determining whether a photographing condition is a backlight condition according to a second embodiment of the present disclosure;
FIG. 6 is a photograph showing a rectangular area for face unlocking and the direction of gravity;
FIG. 7A is an example photograph of an original image in a backlit condition; and
fig. 7B is an example photograph of an image obtained by the tone mapping method according to the first and second embodiments of the present disclosure.
Detailed Description
Embodiments of the present disclosure will be described in detail, and examples of the embodiments will be illustrated in the accompanying drawings. Throughout the specification, identical or similar elements and elements having identical or similar functions are denoted by identical reference numerals. The embodiments described herein with reference to the drawings are illustrative and are intended to be illustrative of the present disclosure and should not be construed as limiting the present disclosure.
Before explaining a method for tone-mapping an image according to an example of the present disclosure, for comparison, a method according to a comparative example in which a backlight condition is not detected is explained.
The method for tone mapping according to the comparative example includes the following steps shown in fig. 1.
In step S11, the brightness is calculated by camera parameters such as f_value, ISO sensitivity, and/or exposure time.
In step S12, a tone curve is selected according to the calculated luminance.
In step S13, tone mapping is performed using the selected tone curve.
As shown in fig. 2A, in the example of a photograph taken under backlight conditions, the central area is dark and the surrounding areas are much brighter than the central area.
Under such typical backlight conditions, the central area may be too dark to recognize the face; therefore, a proper image cannot be obtained according to the above method.
Even if a backlight condition is detected in a conventional face recognition system, the histogram is used to calculate the brightness, which is time-consuming as described above.
An apparatus for tone mapping an image according to a first example of the present disclosure is as follows.
Referring to fig. 3, an apparatus 10 for performing tone mapping for face unlocking according to a first embodiment of the present disclosure includes a camera unit 11, a processor 12, a display unit 13, and a memory 14.
The camera unit 11 acquires images under various photographing conditions including backlight conditions. The image may be a still image or one of a plurality of still images forming a moving image.
The processor 12 inputs an image from the camera unit 11, determines whether or not a photographing condition is a backlight condition, selects an appropriate tone curve according to the determination, performs tone mapping on the captured original image using the selected tone curve, and performs face unlocking using the tone mapped image.
When the processor 12 determines that the photographing condition is a backlight condition, the processor 12 selects a tone curve suitable for the backlight scene. When the processor 12 determines that the photographing condition is not the backlight condition, the processor 12 calculates brightness using camera parameters such as f_value, ISO sensitivity, and/or exposure time, and selects a tone curve according to the calculated brightness.
When determining whether the photographing condition is a backlight condition, the processor 12 calculates a first average luminance inside a rectangular area in which a face is assumed to exist, calculates a second average luminance outside the rectangular area, determines that the photographing condition is a backlight condition when a difference between the first average luminance and the second average luminance is greater than a threshold value, and determines that the photographing condition is not a backlight condition when the difference is not greater than the threshold value.
The processor 12 also performs tone mapping on the original image using the selected tone curve, performs face unlocking using the tone mapped image, and determines whether face unlocking was successful.
The display unit 13 receives the determination result of the face unlocking from the processor 12, and displays the determination result on the screen thereof.
A method for tone mapping according to a second embodiment of the present disclosure includes the following steps shown in fig. 4.
In step S21, an image is acquired under various conditions including a backlight condition. The image may be a still image or one of a plurality of still images forming a moving image.
In step S22, it is determined whether or not the photographing condition is a backlight condition.
If so, i.e. if the photographing condition is a backlight condition, in step S25, an appropriate tone curve suitable for the backlight scene is selected. If not, i.e., if the photographing condition is not a backlight condition, the brightness is calculated using camera parameters such as f_value, ISO sensitivity, and/or exposure time in step S23. In step S24, a tone curve is selected according to the calculated luminance.
In step S26, tone mapping of the acquired (original) image is performed using the selected tone curve.
In step S27, face unlocking is performed using the tone-mapped image, and it is determined whether face unlocking is successful.
In step S28, the determination result of face unlocking is displayed.
A method for determining whether the photographing condition is a backlight condition is described in detail below with reference to fig. 5.
In step S31, a rectangular area is set on the image acquired in step S21 and displayed on the display unit 13. As shown in fig. 6, the rectangular area 21 is an area where the existence of a face is assumed. The center position of the rectangular area is not precisely the center of the entire image, and the center position should be shifted to some extent on a line in the direction of gravity. The direction of gravity on the image may be determined by the acceleration sensor of the smartphone. For example, the size of the rectangular region may be empirically set to about 1/4 of the width and 1/4 of the height of the entire image.
In step S32, a first average luminance inside the rectangular region and a second average luminance outside the rectangular region are calculated.
In step S33, it is determined whether the difference between the first average luminance and the second average luminance is greater than a threshold value.
As a first example, the threshold is 50, the first average luminance is 10, and the second average luminance is 100.
The difference between the first and second average luminance is 90, and thus the difference is greater than the threshold value, then it is determined that the photographing condition is a backlight condition.
As a second example, the threshold is 50, the first average luminance is 75, and the second average luminance is 100.
The difference between the first average luminance and the second average luminance is 25, and thus the difference is not greater than the threshold value, it is determined that the photographing condition is not the backlight condition.
As described above, in step S33, if the difference between the first average luminance and the second average luminance is greater than the threshold value, the process proceeds to step S34, and it is determined that the photographing condition is the backlight condition. If the difference between the first average luminance and the second average luminance is not greater than the threshold value, the process proceeds to step S35, where it is determined that the photographing condition is not the backlight condition.
Further, if it is determined that the photographing condition is not the backlight condition, it is possible to use, for example, a camera including a camera parameter, i.e., f_value 2 The following formulas of exposure time (exposure time) and ISO sensitivity (ISO sensitivity) calculate Luminance (luminence):
wherein C is the exact contrast.
A computer usable medium according to a third embodiment of the present disclosure stores software for causing a computer or an apparatus having the configuration of the above-described first example of the present disclosure to implement a method for tone mapping and a method of the above-described second example of the present disclosure.
According to the above-described apparatus for tone mapping according to the first embodiment, the method for tone mapping according to the second embodiment, and the medium for tone mapping according to the third embodiment of the present disclosure, even if a photographing condition is a backlight condition, a suitable image can be obtained by tone mapping using a tone curve suitable for the backlight condition, and the success rate of face unlocking can be improved.
Fig. 7A shows an example photograph of an original image under a backlight condition. The interior of the central region where the face is present is much darker than the exterior of that region.
Fig. 7B shows photographs obtained by the above-described first, second and third embodiments of the present disclosure. The inside of the center area where the face exists is brighter than the inside of fig. 7A, and thus it is possible to recognize the face. Therefore, a proper image can be obtained, and the success rate of face unlocking can be improved.
In describing embodiments of the present disclosure, it should be understood that terms such as "central," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "interior," "exterior," "clockwise," and "counterclockwise" should be interpreted as referring to the directions or locations depicted or shown in the drawings at the time of discussion. These related terms are only used to simplify the description of the present disclosure and do not indicate or imply that the devices or elements referred to must have a particular orientation or must be constructed or operated in a particular orientation. Accordingly, these terms should not be construed as limiting the present disclosure.
Furthermore, terms such as "first" and "second" are used herein for descriptive purposes and are not intended to indicate or imply relative importance or significance or the number of technical features indicated. Thus, features defined as "first" and "second" may include one or more of the features. In the specification of the present disclosure, unless otherwise specified, "a plurality" means "two or more than two".
In describing embodiments of the present disclosure, unless otherwise indicated or limited, terms "mounted," "connected," "coupled," and the like are used broadly and may be, for example, fixed, removable, or integral, or may be a mechanical or electrical connection, or may be a direct or indirect connection via an intermediate structure, or may be an internal communication of two elements as would be understood by one of ordinary skill in the art in view of the particular circumstances.
In embodiments of the present disclosure, unless specified or limited otherwise, structures that "on" or "under" a first feature may include embodiments in which the first feature is in direct contact with the second feature, as well as embodiments in which the first feature and the second feature are not in direct contact with each other, but are contacted by additional features formed therebetween. Furthermore, a first feature "on (touching)", "over (not touching) or" over (contactable by) a second feature may include embodiments where the first feature is "on (touching) the second feature," over (not touching) or "over (contactable by) the second feature, orthogonally or obliquely, or simply meaning that the first feature is at a higher elevation than the second feature; while a first feature that is "under", "directly under" or "at the bottom of" a second feature may include embodiments in which the first feature is "under", "directly under" or "at the bottom of" the second feature, either orthogonally or obliquely, or simply meaning that the first feature is at a lower elevation than the second feature.
The above illustration provides various embodiments and examples to implement different structures of the present disclosure. To simplify the present disclosure, certain elements and arrangements are described above. However, these elements and arrangements are merely examples and are not intended to limit the present disclosure. Further, reference numerals and/or drawing letters may be repeated in the various examples of the disclosure. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations. In addition, the present disclosure provides examples of different processes and materials. However, those skilled in the art will appreciate that other processes and/or materials may be used.
Reference throughout this specification to "an embodiment," "some embodiments," "an example embodiment," "an example," "a particular example," or "some examples" means that a particular feature, structure, material, or characteristic associated with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the above-identified phrases in various places throughout this specification are not necessarily all referring to the same embodiment or example of the disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
Any process or method described in the flow diagrams or otherwise described herein can be understood as comprising one or more modules, segments, or portions of code that comprise executable instructions for implementing specific logical functions or steps in the process, and the scope of the preferred embodiments of the present disclosure includes other implementations in which functions can be implemented in an order other than that shown or discussed, including in substantially the same order or in an opposite order, as would be understood by those skilled in the art.
The logic and/or steps described elsewhere herein or shown in a flowchart, for example, a particular sequence of executable instructions for implementing the logic function, may be embodied in any computer readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, including a processor, or other system that can fetch the instructions from the instruction execution system, apparatus, or device that executes the instructions. For the purposes of this description, a "computer-readable medium" can be any apparatus that can be used by or in connection with an instruction execution system, apparatus, or device that can be adapted to contain, store, communicate, propagate, or transport the program. More specific examples of the computer-readable medium include, but are not limited to: an electronic connection (electronic device) with one or more wires, a portable computer housing (magnetic device), a random access memory (random access memory, RAM), a Read Only Memory (ROM), an erasable programmable read only memory (erasable programmable read-only memory, EPROM or flash memory), a fiber optic device, and a portable compact disc read only memory (compact disk read-only memory, CDROM). Furthermore, the computer readable medium may even be paper or other suitable medium upon which the program can be printed, as the paper or other suitable medium may be optically scanned, then compiled, decoded or otherwise processed in a suitable manner, and then stored in a computer memory, for example, when the program is required to be electronically obtained.
It should be understood that each portion of the present disclosure may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the various steps or methods may be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, the steps or methods may be implemented by one or a combination of the following techniques known in the art, similar to another embodiment: discrete logic circuits having logic gates for implementing data signal logic functions, application specific integrated circuits having logic gates in appropriate combinations, programmable gate arrays (programmable gate array, PGA), field programmable gate arrays (field programmable gate array, FPGA), and the like.
Those skilled in the art will appreciate that all or part of the steps in the above described exemplary methods of the present disclosure may be implemented using program command related hardware. The program may be stored in a computer-readable storage medium when run on a computer, the program comprising one or a combination of the steps of the method embodiments of the present disclosure.
Furthermore, each functional unit of embodiments of the present disclosure may be integrated in a processing module, or the units may be physically separated, or two or more units are integrated in a processing module. The integrated module can be implemented in hardware or in the form of a software functional module. When the integrated module is implemented in the form of a software functional module and sold or used as a stand-alone product, the integrated module may be stored in a computer-readable storage medium.
The storage medium may be a read-only memory, a magnetic disk, a CD, or the like.
Although embodiments of the present disclosure have been shown and described, it will be understood by those skilled in the art that these embodiments are illustrative and not to be construed as limiting the present disclosure, and that changes, modifications, substitutions, and alterations may be made to the embodiments without departing from the scope of the disclosure.
Claims (13)
1. A method for tone mapping an image, the method comprising:
acquiring the image;
judging whether the shooting condition is a backlight condition or not;
calculating brightness using a camera parameter when the photographing condition is determined not to be the backlight condition, and selecting a tone curve according to the calculated brightness;
selecting a tone curve suitable for the backlight condition when the photographing condition is determined to be the backlight condition; and
tone mapping is performed on the image using the selected tone curve.
2. The method of claim 1, wherein the method further comprises:
performing face unlocking by using the tone-mapped image, and judging whether the face unlocking is successful or not; and
and displaying a judgment result about the face unlocking.
3. The method according to claim 1 or 2, wherein when determining whether the photographing condition is a backlight condition, the method further comprises:
setting a specific region on the image;
calculating a first average brightness inside the specific area and a second average brightness outside the specific area;
determining whether a difference between the first average luminance and the second average luminance is greater than a threshold; and
when the difference is determined to be greater than the threshold value, it is determined that the photographing condition is the backlight condition, and when the difference is determined to be not greater than the threshold value, it is determined that the photographing condition is not the backlight condition.
4. A method according to claim 3, wherein the specific area is set in the following manner: the center position of the specific area is located on a line in the direction of gravity.
5. The method according to any one of claims 1 to 4, wherein when the photographing condition is determined not to be the backlight condition, a camera parameter including f_value is used 2 The brightness is calculated by the following equation for exposure time and ISO sensitivity:
where C is the calibration contrast.
6. The method of any one of claims 1 to 5, wherein the image is a still image or one of a plurality of still images forming a moving image.
7. An apparatus for tone mapping an image, the apparatus comprising:
a camera unit configured to acquire the image;
a processor configured to input a current image to determine whether a photographing condition is a backlight condition, calculate brightness using a camera parameter and select a tone curve according to the calculated brightness when the photographing condition is determined not to be the backlight condition, and select a tone curve suitable for the backlight condition and perform tone mapping on the image using the selected tone curve when the photographing condition is determined to be the backlight condition; and
and a display unit configured to display the tone-mapped image.
8. The device of claim 7, wherein the processor is further configured to perform face unlocking using the tone mapped image to determine whether the face unlocking was successful, and to display a result of the determination of the face unlocking.
9. The apparatus according to claim 7 or 8, wherein when the processor determines whether the photographing condition is the backlight condition, the processor is further configured to set a specific region on the image, calculate a first average luminance inside the specific region and a second average luminance outside the specific region to determine whether a difference between the first average luminance and the second average luminance is greater than a threshold value, determine that the photographing condition is the backlight condition when the difference is determined to be greater than the threshold value, and determine that the photographing condition is not the backlight condition when the difference is determined to be not greater than the threshold value.
10. The apparatus of any of claims 7 to 9, wherein the processor sets the region in such a way that: the center position of the region is located on a line in the direction of gravity.
11. The apparatus according to any one of claims 7 to 10, wherein when the photographing condition is determined not to be the backlight condition, the processor uses a camera parameter including f_value 2 The brightness is calculated by the following equation for exposure time and ISO sensitivity:
where C is the calibration contrast.
12. The apparatus according to any one of claims 7 to 11, wherein the image is a still image or one of a plurality of still images forming a moving image.
13. A computer usable medium storing software for causing a computer to implement the method for tone mapping an image according to any one of claims 1 to 6.
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| PCT/CN2020/127210 WO2022094945A1 (en) | 2020-11-06 | 2020-11-06 | Method and apparatus for tone mapping, and computer usable medium storing software for implementing the method |
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| US20240257325A1 (en) * | 2023-01-26 | 2024-08-01 | Samsung Electronics Co., Ltd. | Tone mapping in high-resolution imaging systems |
| CN116683986B (en) * | 2023-08-04 | 2023-10-27 | 武汉孚晟科技有限公司 | Ghost image identification method, system and medium of optical time domain reflectometer |
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