Exposure compensation method and system employing photometric matrix and flash

The present invention relates comprehensively to photography, and in particular to exposure compensation methods and systems using meter matrix and flash.

Photometers are commonly used in cameras to determine if there is enough light in the scene to produce a properly exposed image. Insufficient light in a scene, or scene, causes the camera's flash to fire to help expose the scene. Cameras have an automatic flash as a common feature. When the light meter indicates that the amount of light in the scene, which is usually the average brightness in the scene, is less than the threshold brightness level, the automatic flash circuit initiates a flash. Unfortunately, the average brightness in the scene is well above the threshold due to the bright background, but the subject may be dim. This type of exposure is commonly referred to as backlit exposure.

When shooting a dimly lit subject in a scene under ambient lighting conditions such as sunlight, incandescent lamps, or vehicle headlights at night, the subject is backlit. The resulting image of the subject is underexposed.

That is, when shooting a backlit subject without backlight compensation, the exposure is controlled according to the overall brightness of the scene without taking into account the brightness level of the object, thereby producing an underexposed image of the subject. Will be done. To compensate for this situation, the camera is provided with a backlight compensation function.

Some cameras have a backlight compensation function that is manually set by the user, while automatic backlight compensation that automatically detects backlight conditions and automatically adjusts the aperture to improve the resulting image. Some have a function. Unfortunately, both manual and automatic backlight compensation provide only tolerable results.

Patent Document 1 describes a backlight compensation area by selecting the most appropriate backlight compensation area from a plurality of predetermined backlight compensation areas for changes in ambient lighting and movement of an object, regardless of changes in ambient lighting. Describes a prior art backlight compensation technique that implements automatic backlight compensation without the need to manually respecify. Backlight compensation allows the user to adjust the position and size of the backlight compensation area to suit the surroundings of the monitoring camera, and automatically or manually select the most appropriate backlight compensation area according to changes in lighting and object position. This is done by controlling the aperture according to the brightness level of the selected backlight compensation area.

One drawback of this approach is that the use of aperture drivers and aperture drive signal generators along with the relevant tuning hardware complicates camera design and creates reliability issues. Moreover, the subject may still need to be illuminated by the flash, even if the aperture is adjusted to compensate for the backlight.

Patent Document 2 describes another prior art exposure control technique. This exposure control method and device for the camera has a brightness measurement system divided into two areas. The value of the central light is obtained based on the brightness of the central area of the shooting scene, and the value of the ambient light is obtained based on the brightness of the peripheral area of the scene. After determining whether the scene is backlit or forward-lit by comparing the central light value with the ambient light value, a correction factor specific to the backlight scene or a correction specific to the forward-lit scene. The coefficient is read from the memory. The appropriate exposure value for the main subject is calculated according to the following predetermined formula.<maths num="1"><img file="JP4068614B2_D0001.tif" /></maths>Where E_sRepresents the exposure value, and α represents the correction coefficient.

One drawback of this technique is that the memory needs to store the correction factors and additional logic in order to execute the above equation. As you can see, the additional hardware and / or software required complicates camera design and creates reliability issues. The flash still needs to illuminate the central subject.<patcit num="1"><text>U.S. Pat. No. 5,963,254</text></patcit><patcit num="2"><text>U.S. Pat. No. 6,389,232</text></patcit>

<p> Based on the above, there is still a need for exposure compensation methods and systems that overcome the shortcomings of the prior art described above.</p>

<p> According to one embodiment of the invention, to compensate for backlight conditions in a scene used in an image capture device that includes a flash and a flash control signal to serve or activate the flash when indicated. The method is described. First, a metric matrix for the scene is generated, each containing a plurality of points where each point can contain luminance information and distance information. Second, the flash control signal is selectively provided based on the metric matrix.</p><p> According to another embodiment of the invention, an image capture device (eg, a camera) for capturing a scene is described. Image capture devices include flashes that emit light in response to provided or indicated flash control signals. The image capture device also includes a metric matrix generator for generating a metric matrix based on the information received from the scene. The metric matrix can include, for example, a plurality of points where each point contains distance information and luminance information. The image capture device also includes a backlit compensation unit connected to a metric matrix generator for receiving the metric matrix and selectively providing or presenting a flash control signal based on the metric matrix.</p><p> Other features and advantages of the present invention will become apparent from the detailed description below.</p><p> The present invention is illustrated by examples in the accompanying drawings in which similar reference numbers point to similar elements, but is not limited by embodiment.</p>

Here, methods and systems for exposure compensation using a weighing matrix and a flash will be described. Although many specific details are provided for illustration purposes in the following description to provide a complete understanding of the invention, those skilled in the art will appreciate that the invention can be carried out without these specific details. it is obvious. In some cases, known structures and devices are shown in the form of block diagrams to avoid unnecessarily obscuring the invention.

It should be noted that aspects of the invention are described in the context of cameras. However, it should be understood that the teachings of the present invention extend to other film-based image capture devices or other film-free image capture devices (ie, digital image capture devices).

The exposure compensation system and method according to the present invention can be implemented in hardware, software, firmware, or a combination thereof. In one embodiment, the invention is practiced with software running on a general purpose or application processor.

In other embodiments, embodiments of the present invention may be implemented using a combination of hardware and software stored in memory and executed by an appropriate instruction execution system.

The hardware portion of the present invention includes discrete logic circuits including logic gates for performing logic functions on data signals, application specific integrated circuits (ASICs), programmable gate arrays (PGAs), and field programmable gates. It can be performed using one or more known techniques of an array (FPGA).

The software portion of the invention is stored in one or more memory elements and can be executed by a suitable general purpose or application processor. A program for exposure compensation that contains an ordered list of executable instructions for performing a logical function is an instruction execution system or device (for example, a computer-based system, a processor-based system, or It can be embodied by (another system) that can retrieve and execute instructions), or on any computer-readable medium used with it.

As used herein, the term "computer-readable medium" includes any program used by or with an instruction execution system or device that can be stored, transmitted, propagated, or carried. It may be the means of. Computer-readable media are, but are not limited to, for example, electrical connections with one or more wires, portable computer disks, random access memory (RAM), read-only memory (ROM), erasable programmable reads. It can be dedicated memory (EPROM or flash memory), fiber optics, and portable compact disk read-only memory (CDROM).

Note that the computer readable medium may be paper on which the program is printed or other suitable medium. The program can be electronically captured from paper or media (eg, by optical scanning), edited, interpreted, or processed in the appropriate format as needed, and then stored in computer memory. is there.

[Image Capture Device] FIG. 1 shows an image capture device (for example, a camera) 100 to which the backlight compensation mechanism 110 according to one embodiment of the present invention can be implemented. Image capture devices include optical components 120, distance meters 130, optical instruments 140, image processing electronic components 150, automatic focus electronic components 160, exposed electronic components 170, automatic flash electronic components 180, and user interface electronic components 190. These components are known to those of skill in the art and will not be mentioned herein.

The image capture device 110 is, but is not limited to, an image sensor for film cameras, digital cameras, machine vision applications, or images used in scientific (eg, remote detection) or manufacturing (eg, assembly line) applications. It can be a sensor.

The image capture device also includes a flash 104, and a flash control signal 108 for activating the flash 104 when provided.

The image capture device includes a backlight compensation mechanism (BCM) 110 for compensating for backlight conditions in the scene. The BCM110 can receive information and inputs from other components of the device capture device 100. For example, the BCM 110 can receive distance information about a group of points or points in a scene from a distance meter 130 and luminance information about a group of points or points in a scene from an optical meter 140. Hereinafter, the backlight compensation mechanism 110 will be described in more detail with reference to FIGS. 2 to 4.

The BCM110 can be implemented as a stand-alone mechanism or integrated with one or more of the above components. In one example, the backlight compensation mechanism 110 may be integrated with the automatic flash electronic component 180. In another example, the retrograde compensation mechanism 110 may be integrated with an autofocus electronic component 160 or an autoexposed electronic component 170.

[Backlight Compensation Mechanism (BCM) 110] FIG. 2 is a block diagram showing the backlight compensation mechanism 110 of FIG. 1 in more detail according to one embodiment of the present invention. The backlight compensation mechanism 110 compensates for the backlight condition in a certain scene by using the flash and more specifically providing a flash control signal for activating the flash.

The backlight compensation mechanism 110 includes a metric matrix generator 210 for generating a metric matrix 214 for the scene based on the information received from the scene. The metric matrix 214 includes a plurality of points, each of which contains luminance information and distance information. Hereinafter, the exemplary weighing matrix 214 will be described in more detail with reference to FIG.

The backlight compensation mechanism 110 receives the measurement matrix 214 and is connected to a measurement matrix generator 210 for selectively providing a flash control signal 108 based on the measurement matrix 214 (flash in the present specification). Also known as controller 220).

The backlight compensation unit 220 includes a scene divider 230 for dividing a plurality of points in the scene into a subject group and a background group. The backlight compensation unit 220 includes a brightness evaluator 240 for selectively providing a flash control signal based on the brightness information of points in the subject group and points in the background group. The backlight compensation unit 220 also includes a distance evaluator 250 for selectively providing a flash control signal based on distance information of points in the subject group and points in the background group.

It should be noted that the backlight compensation mechanism according to the present invention can determine whether to provide the flash control signal 108 using only distance information, only luminance information, or a combination thereof. Further, the backlight compensation mechanism according to the present invention includes 1) the distance between the camera and one or more points of the subject, 2) the distance between the camera and one or more points in the background, and 3) one in the subject. Or use the brightness of multiple points, 4) the brightness of one or more points in the background, 5) the overall brightness of the scene, or a combination thereof to determine whether to provide the flash control signal 108. Can be done. Two exemplary embodiments of how one or more of the above factors are used to selectively provide the flash control signal 108 are described with reference to FIGS. 3 and 4.

The backlight compensation unit 220 can also include a spot focus sensor 260 for measuring the distance between the camera and a point in the subject group, and an overall light sensor 270 for measuring the overall brightness level of the scene.

[Processing Step-1st Embodiment] FIG. 3 is a flowchart showing a step performed by the backlight compensation mechanism according to one embodiment of the present invention. First, a weighing matrix is generated for the scene. The metric matrix contains a plurality of points, each of which can include luminance information and distance information. The step of generating the metric matrix can include the following substeps. In step 310, the scene is divided into a plurality of points. In step 314, the plurality of points are classified into a subject group and a background group. An exemplary weighing matrix is shown below in more detail with reference to FIGS. 5-8.

Once generated, the metric matrix is used to selectively provide the flash control signal. The step of selectively providing the flash control signal using the metric matrix can include the following substeps. In step 320, the distance between the camera and the points in the background group and the brightness of the points in the background group are obtained. In step 330, the distance between the camera and the point in the subject group and the brightness of the point in the subject group are obtained.

In step 340, the difference between the distance between the camera and the points in the background group and the distance between the camera and the points in the subject group is calculated. In step 350, the difference between the brightness of the points in the background group and the brightness of the points in the subject group is also calculated. In step 360, it is determined whether the difference in distance exceeds a predetermined threshold value and whether the difference between the brightness of the points in the background group and the brightness of the points in the subject group exceeds the predetermined brightness threshold value. When the difference in distance exceeds a predetermined threshold and the difference between the brightness of the points in the background group and the brightness of the points in the subject group exceeds the predetermined brightness threshold, the flash control signal is provided in step 370. For example, when the background is farther away from the image capture device compared to the subject and the background is relatively bright compared to the subject, the flash is provided by the backlight compensation mechanism according to the present invention. Otherwise, no flash control signal is provided and processing continues in process step 310.

[Processing Step-Second Embodiment] FIG. 4 is a flowchart showing a step performed by the backlight compensation mechanism according to the second embodiment of the present invention. In step 410, a weighing matrix for the scene is generated. The metric matrix contains a plurality of points, each of which contains luminance information and distance information. In step 420, the flash control signal is selectively provided based on the weighing matrix. The step of selectively providing the flash control signal based on the measurement matrix can include the following substeps.

In step 430, the distance meter 130 determines the distance between the camera and a point (or group of points) in the subject group. In step 440, it is determined whether the distance between the camera and a point in the subject group is less than a predetermined distance. When the distance between the camera and the point in the subject group is not less than a predetermined distance, the process proceeds to step 410.

When the distance between the camera and a point in the subject group is less than a predetermined distance, step 450 requires the overall brightness level of the scene. The overall brightness level of the scene is provided by the optical meter 140 of the image capture device to determine the average brightness of all pixels in the scene or a given group of pixels at a given location (eg, a group of pixels near the center of the scene). Can include. In step 460, it is determined whether the overall luminance level exceeds a predetermined luminance threshold. When the overall luminance level exceeds a predetermined luminance threshold, step 470 provides a flash control signal.

Alternatively, a particular brightness level can be used in steps 450-470. In this case, the following steps can be performed. First, the brightness of the points in the background group is obtained. Next, the brightness of the points in the subject group is obtained. Next, the difference between the brightness of the points in the background group and the brightness of the points in the subject group is calculated. Next, it is determined whether or not the difference between the brightness of the points in the background group and the brightness of the points in the subject group exceeds a predetermined brightness threshold value. A flash signal is provided when the difference exceeds a predetermined threshold.

In another embodiment, steps 450-470 may be performed without performing steps 430 and 440. In this embodiment, distance is not used and the selective assertion of the flash control signal depends on the overall brightness level of the scene. The step of selectively providing the flash control signal may be based on distance information, luminance information (for example, the overall luminance difference between a point on the subject and a point on the background or a specific luminance difference). Please note.

[Exemplary Weighing Matrix] FIG. 5 shows an exemplary weighing matrix 500 that can be used according to the present invention. The matrix 500 includes a plurality of points 510 classified into a background point 520 indicated by "B" and a subject point 530 indicated by "S". Background point 520 is also referred to herein as a point within a peripheral point. It should be noted that the number of points, the pattern of points in the subject, and the pattern of points in the surroundings or background according to the present invention may be modified and adjusted to suit a particular application. In this embodiment, the points in the background form an upside-down "U" and the points in the subject form an "I" shape. However, it should be noted that the points in the background or surroundings, and the points in the subject, may be in the form of other continuous or discontinuous shapes and patterns. Further examples without limitation of the different metric matrices that can be used by the backlight compensation mechanism according to the invention are described herein below.

FIG. 6 shows another exemplary weighing matrix 600 that can be used by the present invention. The matrix 600 includes a plurality of points 610 classified into a background point 620 represented by "B" (also referred to herein as a "peripheral" point) and a subject point 630 represented by "S". The weighing matrix 600 is particularly suitable for subjects located near or along the left border of the scene. It should be noted that the number of points, the pattern of points in the subject, and the pattern of points in the surroundings or background according to the present invention may be modified and adjusted to suit a particular application.

FIG. 7 shows yet another exemplary weighing matrix 700 that can be used by the present invention. The matrix 700 includes a plurality of points 710 classified into a background point 720 (also referred to herein as a "peripheral" point) represented by "B" and a subject point 730 represented by "S". The weighing matrix 700 is particularly suitable for subjects located near or along the right border of the scene. It should be noted that the number of points, the pattern of points in the subject, and the pattern of points in the surroundings or background according to the present invention may be modified and adjusted to suit a particular application.

FIG. 8 shows another exemplary weighing matrix 800 that can be used by the present invention. The matrix 800 includes a plurality of points 810 classified into a background point 820 represented by "B" (also referred to herein as a "peripheral" point) and a subject point 830 represented by "S". The weighing matrix 800 is particularly suitable for subjects placed near the bottom of the scene. It should be noted that the number of points, the pattern of points in the subject, and the pattern of points in the surroundings or background according to the present invention may be modified and adjusted to suit a particular application.

For example, a metric matrix containing two rows of subject points and a third row of background points would be appropriate for a subject placed near the top of the scene.

Note that each area of the scene is indicated by a single circle or dot with either the "B" or "S" label. However, a single circle or dot can indicate a plurality of dots that represent either the subject or the background. The plurality of points can also form a shape other than the circular shape shown in the figure. For example, a shape having a straight edge or a non-straight edge can also be used in the weighing matrix.

Scenes with backlight conditions will benefit from the backlight compensation mechanism according to the present invention. For example, a scene with backlight conditions usually contains multiple points, these points are arranged at a background point or a peripheral point and a subject point, and the surrounding points are captured as compared with the points in the subject. It is far from the device and brighter in terms of brightness than it is on the subject. In contrast, points on the subject are less bright than points around them and are closer to the image capture device.

An example of a scene with backlight conditions is a scene in which a light source (eg, a streetlight or other natural or artificial light source) is present in the background. Such a scene with backlight conditions would, when captured, result in a poor quality photo with an undesirably bright background and dark subject. By automatically detecting the backlight condition and providing the flash, the exposure compensation mechanism of the present invention detects the backlight condition and enables the flash (for example, according to FIG. 4) to operate the flash, thereby capturing the photograph. Get the desired exposure (eg, a bright subject).

Scenes with slow synchronization conditions will benefit from the backlit compensation mechanism according to the invention. For example, a scene with slow sync conditions typically includes a plurality of points classified as a background or perimeter point and a subject point indicated by an "S". The surrounding points are farther from the image capture device than the points on the subject and are darker in terms of brightness than the points on the subject. In this case, the points on the subject are also darker in terms of brightness, but closer to the image capture device than the points around them. Without the exposure compensation mechanism of the present invention, a scene with slow synchronization conditions would result in a capture containing a poor quality photograph that would highlight the overexposed subject and the underexposed background.

In some cases, photographs taken with a flash show an undesired effect because they show a well-exposed foreground subject against a black or very dark background. The exposure compensation mechanism according to the present invention provides a slow synchronization mode that alleviates this problem by keeping the shutter open longer than usual and brightening the background.

For example, in one embodiment, the exposure compensation mechanism uses a slow shutter speed in a slow synchronized mode to make the blur resulting from a fast moving object or camera shake appear blurry in the image. To avoid blurring, you may use a tripod or simply shoot a stationary subject (eg, a non-moving subject).

The exposure compensation mechanism according to the present invention can be used to produce a special effect in photography. For example, a short flash burst combined with a long shutter speed provides an interesting special effect. A short flash burst makes the object sharply stationary, and then a dim ambient light blurs the image slightly, thereby making the moving light look like a streak in photography.

By automatically detecting slow synchronization conditions, invoking a flash, and adjusting the exposure, the exposure compensation mechanism of the present invention ensures that the captured photo has the desired exposure.

The exposure compensation mechanism according to the present invention detects a well-exposed foreground against a dark background and selectively controls the flash and shutter timings to compensate for this situation. For example, once a slow sync situation is detected, the exposure compensation mechanism according to the invention can set a longer exposure time to expose the flash to the subject and expose the background.

The principles of the present invention have been described for image capture devices (eg, film-based or filmless cameras). However, it should be noted that the teachings of the present invention can be applied to other sensors and other applications such as image sensors used in machine vision applications.

In the above specification, the present invention is described with reference to specific embodiments thereof. However, it is clear that various changes and modifications may be made without departing from the broader scope of the invention. Accordingly, the specification and drawings are viewed in an exemplary sense rather than in a limited sense.

<figref num="1">It is a figure which shows the camera which can carry out the back light compensation mechanism by one Embodiment of this invention.</figref><figref num="2">It is a block diagram which shows the back light compensation mechanism of FIG. 1 in more detail according to one Embodiment of this invention.</figref><figref num="3">It is a flowchart which shows the step performed by the backlight compensation mechanism according to one Embodiment of this invention.</figref><figref num="4">It is a flowchart which shows the step performed by the backlight compensation mechanism according to the 2nd Embodiment of this invention.</figref><figref num="5">It is a figure which shows the exemplary measurement matrix which can be used by this invention.</figref><figref num="6">It is a figure which shows another exemplary metric matrix which can be used by this invention.</figref><figref num="7">It is a figure which shows the still another exemplary metric matrix which can be used by this invention.</figref><figref num="8">It is a figure which shows the still another exemplary metric matrix which can be used by this invention.</figref>