Automatic exposure control for flash photography

A photographic flash unit comprises a direct flash unit and a bounce flash unit rotatably connected to the direct flash unit. Status and control lines coupled between a hot shoe and each flash unit enable independent triggering and control of each flash unit. The direct and bounce flash units may be a part of a digital camera adapted to make a first test exposure using direct flash illumination and second test exposure using bounce flash illumination, then computing an attenuation factor for compensating a selected flash exposure parameter by dividing the selected parameter by the attenuation factor. Steps in a method embodiment include making a first test image, making a second test image, selecting regions in the first and second test images, computing an attenuation factor from luminosity values for the first and second test images, and compensating settings for a final bounce flash image by the attenuation factor.

BACKGROUND

The present invention relates generally to flash photography, and more particularly to flash compensation for bounce illumination.

A flash unit outputs a controlled pulse of light in response to a trigger signal received from a camera, another flash unit, or other control device. A flash unit may be mechanically attached to a camera for primary or supplemental illumination of a photographic subject. One or more flash units may be positioned some distance away from the camera in addition to, or alternatively instead of, a flash unit mechanically attached to a camera. Each of the flash units receives a signal from the camera, or optionally from other flash units or control devices, for initiating and terminating light output. Light from the one or more flash units reflects from a photographic subject and the reflected light is collected by a camera lens for forming a photographic image. Controlling the light output from a flash unit, referred to as flash exposure control, and camera settings such as shutter speed, ISO sensitivity, and lens aperture allows a photographic image to be formed in which a range of tonal values from a photographic subject are captured in a corresponding range of tonal values. The range of tonal values in a captured image is generally smaller than the range of tonal values for the photographic subject represented in the image, and may be shifted more toward dark tones or light tones than tonal values for the subject.

A flash unit or a camera may include automatic flash exposure control for setting parameters such as flash duration, number of flashes, and other factors. Flash units with automatic flash exposure control (AFEC) may apply preprogrammed rules for controlling light output, for example by identifying the main subject in a photographic composition, by reducing the influence of very dark or very light regions on a photographic subject, or many other methods. A flash unit with AFEC may perform at least one test flash prior to a flash for making a final photographic image. The test flash may be used to account for surface reflectivity on different parts of the photographic subject and may take into account other parameters that influence flash settings used to make a final captured image. Many different algorithms have been proposed for controlling flash output to achieve different image results. For example, some flash units with AFEC determine an average tonal value for a photographic subject and adjust flash settings to render the average tonal value a predetermined gray level such as “18% gray” in the final captured image. However, if a photographic subject includes a high proportion of relatively dark areas, adjusting the flash output according to an 18% gray average tonal value may cause light areas to be overexposed in the captured image. Conversely, if the photographic subject includes a high proportion of relatively light areas, dark areas may be underexposed in the final image. Subject detail may be lost in underexposed and overexposed areas of a captured image.

A flash unit with AFEC may adjust flash output by accounting for such parameters as camera-to-subject distance, flash-to-subject distance, duration of flash pulses, and camera settings such as ISO sensitivity, lens aperture, and distance. A flash unit may receive distance information from the camera's autofocus system and use the distance information and the inverse square law for light to determine a time duration for a light pulse to be output from the flash unit to form a captured image with selected properties. This method may be applied in direct flash photography, an arrangement of camera, flash, and photographic subject in which the distance traveled by light from the flash to the subject is about the same as the camera-to-subject distance. With direct flash, a light pulse for illuminating the subject follows a path from the flash to the subject and then reflects from the subject to the camera lens, without reflecting from any intermediate surfaces between the flash and the subject. When a photographer using direct flash modifies a composition by changing the camera-to-subject distance, rearranging the photographic subject, changing camera lenses, or other changes, corresponding changes in flash settings may be predicted by using flash guide numbers, camera histograms, and other methods. For direct flash photography, there are known methods for creating a new image having tonal values comparable to a previous image when flash settings or camera settings are changed. Closely related methods permit a photographer to accurately predict new flash settings and camera settings for achieving a selected magnitude of change in captured tonal values for images created with direct flash exposures.

The larger the uncertainty in measured distances, the greater the difficulty flash units with AFEC may have in predicting correct flash settings for achieving a desired range of tonal values in a captured image. For example, in a configuration of a camera, photographic subject, and flash unit referred to as bounce flash, light output from the flash unit reflects (“bounces”) from an intermediate surface such as the ceiling in a room or a photographer's “bounce card” before illuminating a photographic subject and then reflecting toward a camera, where reflected light is captured in a photographic image. Some bounce flash units have a flash head that is rotatable relative to the camera or stand to which the flash is attached to permit the flash head to be aimed at a reflecting surface while the camera lens remains pointed at a photographic subject. Bounce flash is sometimes used to diffuse light falling on a photographic subject, creating a softening effect in the final image. Bounce flash may also be used to reposition a shadow or reflection that interferes with a desired aesthetic effect in a photograph.

When a photographic subject is illuminated by bounce flash, the length of the path traveled by light from the flash to the subject, referred to as flash-to-subject distance, may be substantially longer than camera-to-subject distance. Many guidelines have been proposed for predicting how flash settings and camera settings should be adjusted to compensate for illumination changes during bounce flash photography. However, precise compensation of bounce flash settings for a flash unit with AFEC is difficult partly because of the difficulty in measuring flash-to-subject distance, but also for other reasons such as color shifts and reflectivity of the surface from which light is bounced. Inaccurate compensation of bounce flash settings prevents accurate prediction of tonal values in the resulting image. Many photographers resort to “bracketing” flash settings recommended by an AFEC system by taking several photos, each photo representing the result of an incremental adjustment in at least one flash or camera parameter. However, bracketing may be inappropriate, distracting, or impractical depending on the photographic subject and its location. Camera histograms can be used to predict how much a change in flash settings or camera settings will affect a captured image, but it can be very difficult to associate a particular feature of a photographic subject with a particular point on a histogram plot, so predicting a change in the image of that feature can also be very difficult, especially for photographic subjects that comprise multiple tonal values for each feature of the subject. Flash units with AFEC systems which produce acceptable image results in direct flash photography may produce poor image results, for example loss of subject detail in highlight or shadow areas, when the AFEC system is allowed to control flash settings during bounce flash photography.

BRIEF SUMMARY

An example of an apparatus embodiment of the invention includes a direct flash unit, a bounce flash unit rotatably connected to the direct flash unit, a first group of status and control lines for controlling triggering and flash timing for the bounce flash unit, a second group of status and control lines for controlling triggering and flash timing for the direct flash unit, and a hot shoe adapted for attachment to a camera. The first and second groups of status and control lines are electrically connected from each of the direct and bounce flash units to the hot shoe. The example of the apparatus embodiment of the invention further includes a memory adapted for storing bounce flash luminosity factors for each pixel in a bounce flash test image, a memory adapted for storing direct flash luminosity factors for each pixel in a direct flash test image, a memory adapted for storing attenuation factors calculated from the bounce flash luminosity factors and the direct flash luminosity factors, and a central processing unit adapted for calculating the attenuation factors and compensated flash exposure settings.

In another example embodiment, an apparatus comprises a direct flash unit, a bounce flash unit, and a flash controller. The flash controller includes a memory adapted for storing bounce flash luminosity factors for each pixel in a bounce flash test image, a memory adapted for storing direct flash luminosity factors for each pixel in a direct flash test image, a memory adapted for storing attenuation factors calculated from the bounce flash luminosity factors and the direct flash luminosity factors, and a central processing unit adapted for calculating the attenuation factors and compensated flash exposure settings.

In another example embodiment, a method includes the steps of making a first test image using a digital camera, making a second test image using the digital camera, selecting a region in the first test image, and selecting a region in the second test image. The method further comprises the steps of computing a luminosity value for the region in the first test image, computing a luminosity value for the region in the second test image, computing an attenuation factor from the luminosity values for the first and second test images, dividing a selected control setting for a bounce flash unit by the attenuation factor to form a compensated control setting, and making a final bounce flash image using the digital camera and the compensated control setting for the flash unit.

DETAILED DESCRIPTION

Some embodiments of the invention comprise a flash unit adapted for matching a value of luminosity representing a selected region of an image captured during bounce photography to a value of from luminosities from corresponding regions in a direct flash test image and a bounce flash test image. Some embodiments of the invention comprise a combination of a camera and a flash unit for automatically compensating a bounce flash image from two test images, one test image from a direct flash exposure and one test image from a bounce flash exposure. Other embodiments of the invention comprise steps in a method for compensating bounce flash settings according to results of a direct flash test exposure and a bounce flash test exposure.

Briefly, embodiments of the invention operate by making two test images. A first test image (the “direct flash test image”) is made with direct flash illumination using flash exposure settings and camera exposure settings which may be determined by conventional methods, for example AFEC or other methods known to photographers. A second test exposure (the “bounce flash test image”) is made with bounce flash illumination using the same flash settings, camera settings, and camera positions relative to the subject as for the first test exposure, but with at least one bounce flash unit aimed to reflect light from a reflecting surface onto the photographic subject. After the second test exposure, the first test exposure may optionally be displayed, a region of the displayed image may optionally be selected, and a value representative of the luminosity of the selected region determined. Next, the second test exposure may optionally be displayed, a region of the displayed image may be selected, and a value representative of the luminosity of the selected region is determined. Regions in the first and second images may optionally be selected without displaying the first image, without displaying the second image, or without displaying either image. Then, a final image is captured with bounce flash illumination using flash settings adjusted by a value referred to as an attenuation factor. The attenuation factor is calculated from the luminosity values for the selected regions in the direct and bounce flash images. In one exemplary embodiment, an attenuation factor is the ratio of the luminosity value determined for the direct flash test image to the luminosity value determined for the bounce flash test image. The final image made with bounce flash illumination settings calculated from the attenuation factor as defined above will have a value of luminosity for the selected image region that matches the value of luminosity from the first test image made with direct flash illumination. In other embodiments, the attenuation factor is calculated by other methods.

Embodiments of the invention are advantageous for accurately predicting tonal values that will appear in a selected region of a photograph to be made with bounce flash illumination from two simple test exposures, without the necessity for bracketing exposures and without the difficulty and uncertainty of trying to relate a selected image feature to points on a camera histogram. Images having visible details in selected highlights or shadows can be made quickly with bounce flash illumination, without trial and error. Method embodiments of the invention may be used with camera equipment capable of controllable direct and bounce flash exposures and capable of accessing and optionally displaying a numerical value corresponding to luminosity for a region selected by a photographer in a photographic image.

Turning now to the figures,FIG. 1illustrates an example of a digital photography system in accord with an embodiment of the invention100. The example of a digital photography system100comprises a bounce flash208, optionally includes a direct flash210, optionally includes a camera104, and optionally includes a flash controller328. The camera104forms an image of a photographic subject (not illustrated) from light traveling along a straight-line path116from the photographic subject to the camera lens. A camera104in accord with an embodiment of the invention100is capable of outputting, and optionally displaying, a numerical value corresponding to the luminance of a selected portion of an image captured by the camera, for example by through-the-lens metering capable of reporting luminosity values at image locations selected by the photographer, by a light meter external to the camera that measures luminosity within a region of the photographic subject selected by the photographer (sometimes referred to as “spot metering”), or by the image sensor in a digital camera, in which digital values associated with each pixel are representative of luminosity in that portion of the image corresponding to the pixel's location in the image sensor.

The example of a direct flash210ofFIG. 1may output a light pulse along a direct flash path214that points directly toward a photographic subject. The direct flash path214represents the shortest travel path for light between the direct flash210and the photographic subject. Some of the light from the direct flash210reflects from the photographic subject and returns to the camera104along the path116from the subject to the camera lens. In comparison to the direct flash210, the bounce flash208optionally emits a light pulse along a bounce flash path212that points toward a reflecting surface (not illustrated). For bounce flash illumination, the bounce flash path212and the direct flash path214will be in different directions, although a bounce flash208may optionally be directed to emit a flash pulse directly at a photographic subject to supplement, or optionally to replace, the direct flash210.

The camera104and flash units (208,210) may exchange flash triggering signals, optional flash status signals, optional camera status signals, optional flash exposure timing signals, optional flash exposure intensity signals, and optional flash status signals along optional wired connections (solid lines) or optional wireless connections (dashed lines) inFIG. 1. Intensity as used herein refers to an amount of luminous flux per unit of solid angle in light emission from a flash unit. Wireless connections may be implemented to exchange optical, radio frequency, or acoustic signals. For example, the camera104may send a trigger signal, flash timing signals, and optionally other signals related to flash control along a wired connection220or a wireless connection222to direct flash210. The camera104may exchange similar signals along a wired connection224or a wireless connection226with the bounce flash208. The bounce flash208and direct flash210may optionally exchange signals with each other along wired connections216or wireless connections218. The camera104may optionally exchange trigger and other signals related to flash control parameters with a flash controller328on a wired connection338or a wireless connection340. In some examples of an embodiment of the invention100, the camera104exchanges flash trigger and control signals with a flash controller328over wired connections338or wireless connections340. In embodiments of the invention having a flash controller328, the flash controller and bounce flash208may exchange trigger, timing, and other signals such as status signals over a wired connection334or a wireless connection336.

FIG. 2illustrates an exemplary arrangement of an embodiment of the invention100and a photographic subject106for making bounce flash images with a camera104by reflecting light output from the flash unit102from a reflecting surface108for illuminating the photographic subject106. The camera is held steady with its lens118pointed at the photographic subject106. The photographic subject106is representative of any photographic subject a photographer may choose and includes a plurality of subject features (146,148,150). A subject feature may be any visually identifiable feature or region on a photographic subject. Each subject feature (146,148,150) comprises at least one tonal value and optionally includes many different tonal values corresponding to different colors, different shades of gray, and different reflectivities. Unless otherwise noted, discussion herein relating to different shades of gray, black, and white applies equally to different colors.

InFIG. 2, the flash unit102is mechanically connected to the camera104. The flash unit102may optionally be positioned away from the camera during flash photography. The flash unit102includes a bounce flash head120for directing light output from the flash unit in a selected direction. In the example illustrated inFIG. 2, the flash head120is pointed about 45 degrees away from the direction the camera lens118is pointed. A flash unit102with a bounce head120may be able to rotate the bounce head through an angle greater than90degrees relative to the direction in which the camera lens is pointed. Light output from the bounce head120is represented by a light path110from the bounce head to the reflecting surface108. Some of the light incident upon the reflecting surface is reflected toward the photographic subject on a light path112from the reflecting surface to the subject. The incident light path110and the reflected light path114for the bounce surface108comprise a bounce light path114. The flash head120may be rotated by a photographer to direct light from the bounce flash head120toward the photographic subject106along a selected bounce path114. A plurality of lines (110,112) represent light incident upon the reflecting surface and light incident upon each of the subject features. Light reflected from each of the subject features (146,148,150) toward the camera lens118is represented by a plurality of lines116.

The flash unit102optionally includes a direct flash unit in addition to the flash head120. A plurality of lines134inFIG. 2from the flash unit102to the subject106represent direct light paths from the direct flash unit to each of the subject features (146,148,150). An exemplary embodiment of the invention comprising a flash unit102with a bounce flash unit and a direct flash unit is illustrated inFIGS. 3-5. InFIG. 3, a bounce flash unit102includes a bounce flash head120rotatably coupled to a flash body130. The bounce flash head120includes an output window124, or alternatively an output lens124, through which light from a flash lamp (not illustrated) in the bounce flash head is emitted. The bounce flash unit102optionally includes a light sensor122. The light sensor122may optionally be part of a system incorporated into the flash unit102for measuring flash-to-subject distance. Flash trigger signals from a camera, flash synchronizer, flash controller, or other flash units may be received through a connector132.

Continuing withFIG. 3, a direct flash unit198may optionally be installed in the flash body130. The direct flash unit198and bounce flash unit120are controllable independently of one another, that is, each one may be triggered independently of the other and each may have its own settings for flash pulse timing and intensity. A guide number for the bounce flash unit may be different from a guide number for the direct flash unit. A connector132, also referred to as a hot shoe, is adapted for mechanical and electrical connection to a corresponding hot shoe connector on a camera. When the flash unit102is mechanically attached to a camera by the connector132, the direct flash unit198points in the same direction as the camera's lens. The bounce flash head120may be rotated about a bounce rotation axis126as shown for the flash unit102inFIG. 4. The bounce flash head may optionally be rotatable about a swivel rotation axis128as shown for the flash unit102inFIG. 5. InFIG. 3, the bounce flash head120and direct flash unit198are pointed in the same direction for making a direct flash image. Either one or both of the flash units in the bounce flash102inFIG. 3may be used for making a direct flash image. InFIGS. 4-5, the direct flash unit198is in position for making a direct flash image and the bounce flash head120is shown pointing in two different directions compared to the direct flash unit, for making bounce flash images.

FIG. 6illustrates an example of a flash unit with a bounce flash head120pointed directly at a photographic subject106for making a direct flash image. A plurality of lines134inFIG. 6represent a direct light path for light travelling from the bounce flash head120to the photographic subject106. Light reflecting from the subject106travels along paths116to the camera lens118as previously explained. In the example ofFIGS. 3-6, flash trigger, status, and control lines for both the direct and bounce flash units pass through the hot shoe connector132.

Operation of the embodiments of the invention may be understood in relation to the examples presented inFIGS. 7-10, which show a view toward the back side of a camera104having an image display136for displaying test images and final images captured by the camera. The image display136may also function as an electronic viewfinder for viewing a photographic subject before an image is captured and saved. InFIGS. 7-10, different gray shades are represented by different densities of stippling, with denser stippling representing darker grays. A black square or rectangular region represents a black (completely underexposed) region in an image, corresponding to a dark or nonreflective region on a subject. A white square or rectangular region without stippling represents a white (completely overexposed) region in an image, corresponding to a bright or highly reflective region on a subject.FIGS. 7-10further include exemplary image manipulation controls comprising a plurality of cursor control buttons140for repositioning a cursor152on the image display136and a select button142for initiating another action after the cursor152has been moved to a selected position on the image display. Although the image display136and control buttons (140,142) are shown on the camera104in the illustrated examples, these components are placed instead on the flash unit in some embodiments of the invention.

FIG. 7illustrates an example of a first test image, for example a direct flash test image, in which an image144of a photographic subject comprises a plurality of subject features (146,148,150), each subject feature having a different value of luminosity, black (region150, corresponding to subject feature150inFIG. 2), white (region146, corresponding to subject feature146inFIG. 2), or an intermediate gray (region148, corresponding to subject feature148inFIG. 2). A cursor, represented inFIGS. 7-8as a repositionable selection box152, is moved from an initial position to a subject feature148, thereby marking a boundary around a selected region162comprising an average luminosity corresponding to an intermediate gray value. Repositioning of the selection box152is represented by an arrow drawn with a dashed line. The selection box152is repositioned by depressing cursor control buttons140. The final selected position of the box152may be indicated by depressing a select button142. it will be appreciated that there are many alternative arrangements of cursor control and select buttons, compared to the exemplary arrangement in the figures herein.

FIG. 8represents an example of an image of the same photographic subject as shown in the example ofFIG. 7, but made with bounce flash illumination instead of direct flash illumination. The bounce flash image154of the photographic subject inFIG. 8is represented with darker tonal values compared to the direct flash image144inFIG. 7. A first region160, already black in the first test image (region150inFIG. 7) is also black in the second test image. A second test region (148inFIG. 7,158inFIG. 8) is significantly darker in the second test image than in the first test image, as is a third region (146inFIG. 7,156inFIG. 8).FIG. 8further illustrates the selection box152being repositioned to highlight the same region selected inFIG. 7, with the selection box152being moved from its initial position to a selected region164in the second image. The selected region164bounds the same subject feature (image feature158inFIG. 8) selected in the first test image (image feature148inFIG. 7). In some embodiments of the invention, the region selected in the first test image by an expert system or by a photographer is automatically re-selected in the second test image. For example, an expert system may select a human face in the first and second test images. However, a photographer or an expert system may optionally choose to highlight different features in the first and second test images.

FIGS. 9-10illustrate alternative methods for identifying regions of interest in test images. BothFIGS. 9 and 10include a same example of an image154A of a photographic subject. The image154A is representative of either a direct flash test image or a bounce flash test image. The image154A inFIGS. 9-10further includes a black region150, corresponding to a dark or low-reflectivity area on the photographic subject, a white region146, corresponding to a bright, highlight, or high-reflectivity area on the photographic subject, and an intermediate gray region148. In the example ofFIG. 9, the regions used for comparison of the direct flash and bounce flash images may be automatically selected from one or more zones202used by the camera's autofocus system. In the example ofFIG. 9, there are12autofocus zones202overlaying the image154A. The combined image area of all of the autofocus zones, or alternatively of any subset combination of selected autofocus zones, may optionally be used for comparing test images. Such a comparison could be made automatically, that is, without user input regarding image elements to be compared.

In the example ofFIG. 10, a grid204is overlaid on the test image154A. A repositionable selection box206may be moved with cursor buttons140. A selected grid location, for example a grid location including a subject feature of interest for comparing test images, may be marked with the select button142. Once the regions of interest have been selected in the direct flash test image and bounce flash test image, either by operating cursor control buttons140or automatic selection by an embodiment of the invention, the regions may be compared and an attenuation factor computed for compensation a bounce flash exposure for the final image. Alternatively, regions of interest may be determined by a flash unit, a camera, or a flash controller, instead of by a person operating the photographic equipment.

FIG. 11illustrates a simplified block diagram of an exemplary embodiment of a digital photography system for capturing two test images, comparing selected regions in each test region, and compensating a bounce flash exposure with an attenuation factor calculated from the selected regions in the test images. A direct flash lamp200is the light-emitting element of a direct flash unit, for example the direct flash unit198inFIGS. 3-5. A bounce flash lamp188is the light-emitting element of a bounce flash unit, for example the bounce flash head120inFIGS. 3-5. A flash lamp control circuit186drives each flash lamp independently, providing the electrical signals needed to turn each lamp on and off. The flash lamp control186optionally includes interface circuits for making measurements or receiving control inputs from a light sensor122. The light sensor122may receive light signals from other flash units or may receive reflected light116from a photographic subject.

The flash lamp control circuit186exchanges bounce flash status and control signals for the bounce flash lamp188over a set of lines194making electrical connections to a CPU166. Direct flash status and control signals are exchanged between the flash lamp control186and CPU166over lines196. The CPU166may send trigger, flash timing, and flash intensity signals to each flash lamp independently of the other.

The CPU166is connected to an image display136by a display data bus180. Light from a subject116enters a camera lens118which forms an image on an image sensor176. The image sensor176converts the image to rows and columns of pixels displayable on the image display136. Data for each pixel includes a value representative of image luminosity at the image location corresponding to the pixel. Luminosity data may be transferred from the image sensor176to the CPU166over pixel data lines178and then to a memory168over memory data and address lines182. The memory168includes separate storage locations for direct flash image luminosity values174, bounce flash image luminosity values172, and attenuation factors170calculated from selected luminosity values. Cursor control switches140and a select switch are connected to the CPU166over a plurality of lines184, operating as previously described to select regions of interest in the test images.

In some example embodiments of the invention, the CPU166, switches (140,142), memory168, and image display136are part of a camera. In some example embodiments, either the direct flash lamp200, the bounce flash lamp, or both, are part of a camera. In other example embodiments, any combination of these components may be located on a bounce flash unit capable of being removably attached to a hot shoe on a camera. In yet other example embodiments of the invention, the memory168, and optionally a second CPU167in signal communication with the memory168over electrical connections182and CPU166over electrical connections183, are part of an external flash control unit, for example the flash controller328ofFIG. 1. In embodiments of the invention in which the memory168is not part of the camera, for example when the memory168is part of a flash controller or a flash unit, a second CPU167may optionally be provided for managing the memory168and performing steps in accord with method embodiments of the invention, such as determining attenuation factors as will be explained in reference toFIG. 12. A second CPU may exchange signals representative of data and commands with the CPU166in the camera over a set of data and command lines183.

Another example of an embodiment of the invention comprises steps in a method for compensating a bounce flash exposure by making two test images and calculating an attenuation factor.FIGS. 12-14illustrate steps in an example of a method embodiment of the invention.

InFIG. 12, an example of a method embodiment of the invention300begins with step302, making a first test image using direct flash.

Next, at step304, the first test image may be displayed. The step304of displaying the first test image may optionally not be performed. In step306, the first test image is saved in memory. Saving the image refers to saving the luminosity value for each pixel in the image. Other data may optionally be saved with the pixel luminosity values.

At step308, a second test image is made using bounce flash illumination. The bounce flash image may be displayed at step310and saved at step312. The step310of displaying the second test image may optionally not be performed.

At step314, the first and second test images are displayed and compared. The comparison may optionally be made by a photographer or by an expert system running in a CPU in an embodiment of the invention.

At step316, a region is selected in the second test image, wherein a luminosity value for the selected region is to be achieved through suitable adjustment of bounce flash settings to match a luminosity value of a region to be selected from the first test image.

At step318, a region is selected in the first test image, wherein a luminosity value for the selected region in the first test image is to be matched in the corresponding region in a final exposure.

At optional step320, the same image region selected in the first test image is automatically selected in the second test image.

At step322, an attenuation factor is calculated by dividing a luminosity in a selected region of the second test image by a luminosity in a selected region of the first test image.

At step324, final bounce flash exposure output is determined by dividing bounce flash test flash output by the attenuation factor.

At step326, a final bounce flash image is made using compensated bounce flash exposure settings.

In other example embodiments of the invention, the steps above may be rearranged so that a region may be selected first in a bounce flash test image, then in a direct flash test image.

Step316inFIG. 12may include any of the following optional steps, as shown inFIG. 13:

At step316A, select the entire test image as the region for comparing luminosities.

At step316B, select the size of a selection box for comparison of image areas.

At step316C, select a color of pixels whose luminosities are to be compared throughout each test image.

At step316D, define a size of a region to be selected as corresponding to a preselected number of image pixels.

At step316E, define a region for comparison between test images as comprising at least one image location used by an autofocus system.

At step316F, divide a test image into rows and columns of rectangular regions and select a particular rectangular region for comparison. For purposes of this step, a square is considered to be a form of rectangle.

At step316G, use face detection to define and select a region.

At step316H, use pattern recognition to define and select a region.

At step316I, use an expert system to define and select a region.

Step322inFIG. 12may include any of the following optional steps, as shown inFIG. 14:

At step322A, compute attenuation factors for a predefined number of pixels near the center of each selected region.

At step322B, compute an average attenuation factor for all pixels within a selected region.

In each of the preceding examples, a direct flash test image preceded a bounce flash test image. It will be appreciated that any of the disclosed embodiments of the invention may be operated in the reverse order, that is, the bounce flash test image may be made first and the direct flash test image second.

Those skilled in the art will appreciate that various adaptations and modifications can be configured without departing from the scope and spirit of the embodiments described herein. Therefore, it is to be understood that, within the scope of the appended claims, the embodiments of the invention may be practiced other than as specifically described herein.