Digital Camera Patent AbstractA method of improving a digital image captured by a digital camera
includes using the digital camera to capture a first image of a
scene and having a display to display the first captured image;
identifying a portion of the displayed image of the first captured
image, which has exposure critical scene content; producing exposure
information from such portion and displaying such information on
the display which will permit a camera user to adjust the exposure
of the image; and adjusting the exposure of the camera based on
such exposure information and capturing a second image of the scene.
Digital Camera Patent ClaimsWhat is claimed is:
1. A method of improving a digital image captured by a digital
camera, comprising the steps of: a) using the digital camera to
capture and store in a non-volatile memory a first digital image
of a scene and displaying the first captured and stored image on
a display of the digital camera; b) providing a user interface which
permits the digital camera user to select a portion of the displayed
first captured and stored image, which the user identifies as having
exposure critical scene content, on the display; c) producing a
numerical value representative of exposure information from the
user selected exposure critical scene content portion of the first
captured and stored image and displaying the numerical value representative
of the exposure information which permits the user to adjust an
exposure value for capturing a second digital image of the scene
captured by the first image; and d) adjusting the exposure value
of the camera based on the numerical value representative of the
exposure information and capturing and storing the second image
of the scene in the non-volatile memory.
2. The method of claim 1, wherein selecting a portion of the displayed
first captured and stored image includes a user zooming in on a
particular portion of the displayed first image which the user identifies
as having critical scene content.
3. The method of claim 2, further including providing a zoom window
to allow the user to identify the region of interest.
4. The method of claim 3, further including analyzing pixels in
the particular region of interest to produce the exposure information.
5. A method of improving a digital image captured by a digital
camera, comprising the steps of: a) using the digital camera to
capture and store in a non-volatile memory a first digital image
of a scene and displaying the first captured and stored image on
a display of the digital camera; b) providing a user interface which
permits the digital camera user to select that portion of the displayed
first captured and stored image, which has exposure critical scene
content; c) producing a numerical value representative of exposure
information from the user selected exposure critical scene content
portion including photographic metrics of luminance values from
the portion and displaying the numerical value representative of
the exposure information on the display which permits the user to
adjust an exposure value for capturing a second digital image of
the scene captured by the first image; and d) adjusting the exposure
value of the camera based on the metrics and capturing and storing
the second image of the scene in the non-volatile memory.
6. The method of claim 5, wherein the metrics include relative
scene reflectance.
7. The method of claim 5, wherein the metrics include exposure
stop information.
8. The method of claim 7, wherein the exposure stop information
is relative to a normal exposure level.
9. The method of claim 5, wherein selecting that portion of the
displayed first captured and stored image includes a user zooming
in on a particular portion of the displayed first image which the
user identifies as having critical scene content.
10. The method of claim 5, further including providing a zoom window
to allow the user to identify the region of interest.
11. The method of claim 5, further including analyzing pixels in
the particular region of interest to produce the exposure information.
12. A method of improving a digital image captured by a digital
camera, comprising the steps of: a) using the digital camera to
capture and store in a non-volatile memory a first digital image
of a scene and displaying the first captured and stored image on
a display of the digital camera; b) providing a user interface identifying
a region of interest in the displayed first captured and stored
image and controls for user moving the region of interest to different
positions on the displayed first captured and stored image which
permits the user to select that portion of the displayed first captured
and stored image, which has exposure critical scene content; c)
producing a numerical value representative of exposure information
from the user selected portion of the first captured and stored
image and automatically adjusting at least one camera exposure parameter
to produce a second digital image; and d) producing a second digital
image based on the produced numerical value representative of the
exposure information and storing the produced second digital image
on the non-volatile memory.
13. The method of claim 12, further including capturing and storing
in the non-volatile memory another image using the automatically
adjusted camera exposure parameter.
14. A method of improving a digital image captured by a digital
camera, comprising the steps of: a) using the digital camera having
a display to capture an image of a scene, to store the captured
image in a non-volatile memory as a first digital image, and to
display the first digital image on the display; b) providing a user
interface identifying a region of interest in the displayed first
captured and stored image and controls for moving the region of
interest to different positions on the displayed first captured
and stored image which permits the user to select that portion of
the displayed first digital image, which has exposure critical scene
content; c) producing a numerical value representative of exposure
information from the selected portion and using the numerical value
representative of the exposure information to automatically adjust
the stored first digital image to produce a second digital image;
and d) producing a second digital image based on the produced numerical
value representative of the exposure information and storing the
second digital image in the non-volatile memory.
15. The method of claim 14, wherein identifying the region of interest
includes a user zooming in on a particular portion of the displayed
first image which the user identifies as having critical scene content.
16. The method of claim 14, further including providing a zoom
window to allow the user to identify the region of interest.
17. The method of claim 14, further including analyzing pixels
in the particular region of interest to produce the exposure information.
18. The method of claim 14, wherein the metrics include relative
scene reflectance.
19. The method of claim 14, wherein the metrics include exposure
stop information.
20. The method of claim 14, wherein the exposure stop information
is relative to a normal exposure level.
21. The method of claim 12, wherein identifying the region of interest
includes a user zooming in on a particular portion of the displayed
first image which the user identifies as having critical scene content.
22. The method of claim 12, further including providing a zoom
window to allow the user to identity the region of interest.
23. The method of claim 12, further including analyzing pixels
in the particular region of interest to produce the exposure in
formation. Digital Camera Patent DescriptionFIELD OF THE INVENTION
The present invention relates to producing improved digital images
captured by a digital camera.
BACKGROUND OF THE INVENTION
Digital cameras, such as the Kodak DCS 620 camera, capture images
of a scene using a solid state image sensor, and store the resulting
image data on a removable memory device, such as a PCMCIA type III
hard drive. Thumbnails of the captured images can be displayed on
the camera's color LCD screen. Since scenes can have a wide range
of illumination levels, these cameras include automatic exposure
controls in order to adjust the camera lens f/number and exposure
time to compensate for the scene illumination level. However, because
of the varying reflectance levels of objects within a scene, and
the limited dynamic range of image sensors, such automatic exposure
control often produces unacceptable results for professional photographers.
As a result, such digital cameras include manual exposure overrides.
The photographer can review a captured image on the camera's LCD
image display to determine if the captured scene appears lighter
or darker than desired, adjust the exposure settings, and can take
a second picture. However, because of the small size and limited
picture quality of the LCD display, it is impossible to make critical
exposure judgements using the displayed image. As a result, this
method is useful only for providing very coarse exposure adjustments.
Once the images are captured by a digital camera, such as the DCS
620, they can be downloaded to a computer and processed and displayed.
For example, an image processing program such as Photoshop version
6.0 or later by Adobe Systems Inc., San Jose, Calif. can be used
to display and edit a captured image. Photoshop version 6.0 or later
includes an "info tool" which displays the RGB code values
of a particular pixel when the user lingers the cursor over a particular
image area. The displayed values are the RGB code values of the
processed pixels from the camera, which may include many types of
non-linear quantization and processing. As a result, it is not possible
to easily relate the RGB code values to the sensor exposure values
of the camera when the scene was captured. Furthermore, these displayed
code values are available only after the images are downloaded to
the computer, and not as the images are being captured.
What is needed is a digital camera that provides an easy way for
the photographer to understand the sensor exposure values for different
areas of a scene as the scene is captured, so that any desired exposure
corrections can be made and the scene can be immediately recaptured.
SUMMARY OF THE INVENTION
It is an object of the present invention to allow a user to select
critical scene content from a displayed digital image on the camera
display and to provide information necessary to make exposure adjustments
and capture another image of the scene.
This object is achieved by a method of improving a digital image
captured by a digital camera, comprising the steps of:
a) using the digital camera to capture a first image of a scene
and having a display to display the first captured image;
b) identifying a portion of the displayed image of the first captured
image, which has exposure critical scene content;
c) producing exposure information from such portion and displaying
such information on the display which will permit a camera user
to adjust the exposure of the image; and
d) adjusting the exposure of the camera based on such exposure
information and capturing a second image of the scene.
ADVANTAGES
It is an advantage of the present invention that a photographer
can immediately view exposure information for areas of a scene having
exposure critical scene content.
It is a further advantage of the present invention to display exposure
information for areas of a scene having exposure critical scene
content using a metric which is well known to professional photographers.
It is a further advantage of the present invention to display exposure
information for areas of a scene having exposure critical scene
content and to use the exposure information to automatically adjust
the camera exposure settings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a digital camera which implements
the method of the present invention;
FIG. 2 is a flow diagram showing the steps of practicing a first
embodiment of the present invention;
FIG. 3 is another flow diagram showing the steps of practicing
the present invention in a different embodiment wherein the camera
settings are automatically modified based on critical scene content
in the first captured digital image;
FIG. 4 is another flow diagram showing the steps of practicing
the present invention in a different embodiment wherein the first
captured digital image is adjusted based on critical scene content;
FIG. 5 depicts the rear of the camera including the image display
and the user controls; and
FIG. 6 shows in more detail the steps included in block 60 of FIG.
2 for calculating the exposure information.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of a digital camera which implements
the method of the present invention. The digital camera 300 produces
digital images that are stored on the removable memory card 330.
The digital camera 300 includes a zoom lens 312 having zoom and
focus motor drives 310 and an electrically adjustable aperture 311
and an electrically driven mechanical shutter 313. The zoom lens
312 focuses light from a scene (not shown) on an image sensor 314,
for example, a single-chip color CCD image sensor, using the well
known Bayer color filter pattern. The aperture 311, shutter 313,
and image sensor 314 are controlled by drivers 306. The zoom and
focus motors 310 and the drivers 306 are controlled by control signals
supplied by a control processor and timing generator circuit 304.
The control processor and timing generator 304 receives inputs
from autofocus and autoexposure detectors 308 and controls a flash
302. The analog output signal from the image sensor 314 is amplified
and converted to digital data by the analog signal processing (ASP)
and analog-to-digital (A/D) converter circuit 316. The ASP and A/D
316 includes a programmable electrical gain that can be used to
adjust the effective ISO speed setting of the camera. This can be
done as described in commonly-assigned U.S. Pat. No. 5,610,654 to
Parulski, et. al., the disclosure of which is herein incorporated
by reference. The digital data is stored in a DRAM buffer memory
318 and subsequently processed by a processor 320 controlled by
the firmware stored in the firmware memory 328, which can be flash
EPROM memory. Alternatively, the processor 320 can be provided by
custom circuitry (e.g. by one or more custom integrated circuits
[ICs] design only for use in digital cameras), or by a combination
of programmable processor(s) and custom circuits.
The processed digital image file is provided to a memory card interface
324 which stores the digital image file on the removable memory
card 330. Removable memory cards 330 are known to those skilled
in the art. For example, the removable memory card 330 can include
memory cards adapted to the PCMCIA card interface standard, as described
in the PC Card Standard, Release 2.0, published by the Personal
Computer Memory Card international Association, Sunnyvale, Calif.,
September 1991, or to the CompactFlash Specification Version 1.3,
published by the CompactFlash Association, Palo Alto, Calif., Aug.
5, 1998. Other types of removable memory cards, including Smart
Memory cards, Secure Digital (SD) cards, and Memory Stick cards,
or other types of digital memory devices, such as magnetic hard
drives, magnetic tape, or optical disks, could alternatively be
used to store the digital images.
In some embodiments, the processor 320 performs color interpolation
followed by color and tone correction, in order to produce rendered
sRGB image data. The rendered sRGB image data is then JPEG compressed
and stored as a JPEG image file on the removable memory card 330.
In other embodiments, the processor directly compresses the Bayer
color image data from the image sensor, and stores the compressed
data on the removable memory card 330, and the image is later "finished"
by processing the compressed Bayer color image data using the host
PC 340.
The processor 320 also creates a "thumbnail" size image
that is stored in RAM memory 326 and supplied to the color LCD image
display 332, which displays the captured image for the user to review.
Instead of a color LCD image display, the digital camera 300 could
use an organic light emitting diode (OLED) display, or many other
types of image displays. The thumbnail image can be created as described
in commonly-assigned U.S. Pat. No. 5,164,831 to Kuchta, et. al.,
the disclosure of which is herein incorporated by reference. The
digital camera 300 is controlled by user controls 303, such as a
series of user buttons including a shutter release (e.g., capture
button) (not shown) which initiates a picture taking operation.
The graphical user interface displayed on the color LCD image display
332 is controlled by the user interface portion of the firmware
stored in the firmware memory 328.
After a series of images have been taken and stored on the removable
memory card 330, the removable memory card 330 can be inserted into
a card reader (not shown) in host PC 340. Alternatively, an interface
cable 342 can be used to connect between the host interface 322
in the digital camera 300 and the host PC 340. The interface cable
342 can conform to, for example, the well known IEEE 1394 interface
specification, the universal serial bus (USB) interface specification,
or other wired or wireless interface specifications.
Alternatively, the digital camera 300 could be comprised of a digital
back for a 35 mm or medium format film camera. In this case, the
zoom lens 312, aperture 311, and shutter 313 are provided as part
of the film camera body, and the other components, including the
image sensor 314, image processor 320 and color LCD image display
332, are provided as part of a separate digital camera back that
is connected to the film camera body. The connection preferably
includes an electrical connector (not shown), so that the zoom lens
312, aperture 311, and shutter 313 can be controlled by the control
processor and timing generator 304 in the digital back.
FIG. 2 is a flow diagram showing the steps of practicing a first
embodiment of the present invention. In block 10, the photographer
prepares to capture a digital image. Typically, this is done by
first determining the amount of light falling on the scene using
an incident light meter, or alternatively using a reflected light
meter to measure the amount of light reflected from various portions
of the scene. In controlled photography, such as studio photography,
the photographer may arrange lighting in order to illuminate the
scene in a desired manner.
In block 20, the photographer adjusts the camera settings based
on the scene to be captured. Typically, the photographer manually
adjusts the camera settings based on the meter readings made in
block 10, although the photographer may alternatively use the automatic
exposure mode to automatically set the camera settings. This eliminates
the need for the meter reading in block 10. The camera settings
that can be adjusted include the camera's exposure time (e.g. camera
shutter speed), the camera's effective ISO speed setting, and the
lens aperture.
In block 30, the photographer uses the digital camera 300 to capture
a first image of the scene. The photographer presses the camera
shutter button on the digital camera 300 to begin the exposure sequence.
The control processor and timing generator 304 controls the aperture
311, the shutter 313, and the gain of the ASP and A/D converter
316 in order to provide the camera settings that were manually or
automatically selected in block 20. Using these exposure settings,
an image is captured by the image sensor 314 and the resulting digital
image data is stored in DRAM buffer 318. The image is then processed
and stored on the removable memory card 330 as described earlier
in reference to FIG. 1.
In block 40, the photographer, using user controls 303, displays
the captured image on the color LCD image display 332. FIG. 5 depicts
the rear of the digital camera 300 including the color LCD image
display 332 and some of the user controls 303, including the four-way
controller (e.g. four-way switch buttons) 350, a cancel button 352,
and an OK button 354.
In block 50, the photographer selects a region of the displayed
image having exposure critical scene content, so that the exposure
related readings for this area of the scene can then be measured
and displayed in block 60. A region of an image having exposure
critical scene content can be, for example, the high specular reflections
off the portion of the face of the subject of a portrait image.
Another region of an image having exposure critical scene content
can also be, for example, the shadow region of a product that is
being captured for commercial advertising purposes. Still another
region of an image having exposure critical scene content can be,
for example, the neutral gray card of known reflectance positioned
in a test image in order to critically set the exposure of a subsequent
image. The neutral card can be used to achieve an appropriate color
balance for the image. The exposure-critical scene content may also
include a Macbeth Color Checker, or some other exposure-appropriate
reflectance test object that can be used to color balance or create
a custom profile for an image.
To select the region of the displayed image having exposure critical
scene content, the photographer can use the 4-way controller 350
to navigate to the camera's Zoom Mode. The Zoom Mode is accessed
by pressing the bottom or the top of the 4-way controller 350 until
the Zoom Mode is displayed. When the Zoom Mode is active, the current
image is displayed, overlaid with a disabled region of interest
(ROI) box 360. The region of interest (ROI) box 360 is a square-shaped
display overlay that serves two purposes: (1) it is an indicator
of the image area that is viewable on the LCD when zoomed to the
next level, and (2) its appearance serves as feedback regarding
the functional mode of the 4-way switch.
When the ROI box 360 is enabled, manipulation of the 4-way controller
350 results in corresponding movement of the ROI box 360. When the
ROI box 360 is enabled, pressing the cancel button 352 disables
the ROI box 360. When the ROL box 360 is disabled, manipulation
of the horizontal axis of the 4-way controller 350 results in forward-backward
navigation of image thumbnails. When the ROI box 360 is disabled,
manipulation of the vertical axis of the 4-way controller 350 results
in a change of Display Mode. When the ROI box 360 is disabled, pressing
the OK Button 354 enables the ROI box 360.
In order to maximize the visibility of the ROI 360, the borders
preferably consist of a dynamically moving series of black and white
patterns (i.e., marching ants). The default location of the ROI
box 360 is in the center of the image displayed on image display
332. When the position of the ROI box 360 for a thumbnail has been
moved during a previous zoom procedure, the last position of the
ROI box 360 is remembered and presented at the last-used location
when that thumbnail is presented again. This can be accomplished
by storing the last position of the ROI box 360, for each digital
image stored on removable memory card 330, along with each image
file, or alternatively in a table stored in RAM memory 326 or in
firmware memory 328.
By default, image thumbnails are displayed on color LCD image display
332 at a 10% (1:16) zoom level. There are two higher magnification
zoom levels with the Zoom Mode, 30% (1:4), and 100% (1:1). When
the Zoom Mode is active, the current image is displayed, overlaid
with the ROI box 360.
Once the photographer has zoomed the image and identified the exposure-critical
scene content (though zooming may not always be necessary), the
photographer places the luminometer crosshairs 362 over the exposure-critical
scene content to enable the digital camera 300 to extract the desired
information from the corresponding area of the captured image data,
as will be described relative to block 60. The luminometer values
370 provide information about the level of the luminance level of
the pixels at the location specified by the luminometer crosshairs
362.
The luminometer crosshairs 362 are normally located in the center
of the ROI box 360, and move with the ROI box 360 only when it is
moved. Movement of the crosshairs in a particular direction will
continue in that direction until the side of the ROI box reaches
the edge of the displayed thumbnail image. When the crosshairs reaches
the edge of the displayed thumbnail image, further manipulation
of the 4-way controller 350 will move the image thumbnail in the
opposite direction of the crosshairs movement, until the edge the
image is reached.
In block 60, the digital camera 300 displays the luminometer values
370 on the color LCD image display 332 for the exposure critical
scene content area of image selected in block 50. The luminometer
values 370 are preferably displayed in a lower portion of the color
LCD image display 332, which serves as an information area. The
luminometer values 370 preferably include two related metrics, the
"stops" exposure value 372, and the "percent scene
reflectance" value 374. The "stops" exposure value
372 preferably has a range of -3 to +3.25 stops, and changes in
tenth stop increments within its range. The "percent scene
reflectance" value 374 preferably has a range of 2% to 180%,
and changes in 1% increments. The "stops" exposure value
372 preferably indicates the exposure level in photographic stops
relative to the factory determined 18% gray level, so that 0 stops
equals intended signal level from a 18% reflectance object in the
scene.
In block 60, the exposure information that determines the luminometer
values 370 is calculated for the exposure critical area of the image
selected in block 50. The steps used to perform this calculation
are shown in detail in FIG. 6. In block 50, the user used the LCD
image display 332 to locate an exposure critical area of the image
to analyze. The user selected the exposure critical area by placing
the luminometer crosshairs 362 at the desired location. In block
62, the processor 320 determines the x/y coordinates of the first
captured digital image corresponding to the exposure critical scene
content selected by the user in block 50. In block 63, the linear
camera RGB code values of the first captured image that correspond
to the x/y coordinates determined in block 62 are obtained. In block
64, the linear camera RGB code values determined in block 63 are
then transformed to luminance values (Y) via equation 1.
where RL, GL, and BL are the red, green, and blue linear camera
code values captured by the image sensor at the x/y coordinate locations.
After the transformation to luminance (Y) in block 64, the luminometer
values 370 are presented in two metrics. One metric is "stops"
372 and the other metric is "percent scene reflectance"
374.
The first metric, "stops" 372 is calculated from the
area located by the luminometer crosshairs 362. The "stops"
are calculated in block 66 via equation 2.
where 18PGray is the factory determined 18% signal level.
In a preferred embodiment, a 12 bit A/D is used in ASP and A/D
converter 316, and the normal camera exposure is set to provide
1 stop of overexposure latitude, so that the factory determined
18% signal level is set equal to code value 369.
In block 68, the second metric, "percent scene reflectance"
374 is calculated from the same area located by the luminometer
crosshairs 362 that was used in determining the first metric "stops"
372. The "percent scene reflectance" 374 is calculated
using equation 3.
where 18PGray is the factory determined 18% signal level.
In block 60 of FIG. 2, after these two metrics are calculated as
just described related to FIG. 6, the "stops" 372 and
"percent scene reflectance" 374 are displayed on the LCD
image display 332.
In block 70, the photographer uses the information displayed by
the luminometer 370, to make a judgment regarding the exposure level
of the captured digital image. If the exposure level is too high,
or too low, and therefore does not meet the photographer's needs,
the photographer will manually adjust the camera settings based
on the information provided by the luminometer (block 80), and capture
a second image of the scene using the adjusted camera settings (block
90). For example, if the luminometer values 370 from the first captured
digital image of a scene having an 18% gray card provide a -1 value
for the "stop" value 372, this means that the exposure
was 1 stop underexposed, relative to the factory determined 18%
gray card values. In this case, the photographer can manually adjust
the exposure settings of the digital camera 300 to provide twice
as much exposure (e.g. 1 stop more exposure). This can be done by
manually doubling the exposure time, or alternatively by increasing
the aperture size by one stop (e.g. decreasing the f/number by 1
stop), or alternatively by doubling the effective ISO speed setting
of the camera, or by an appropriate combination of these settings.
FIG. 3 is a flow diagram showing the steps of practicing a second
embodiment of the present invention. In block 10, the photographer
prepares to capture a digital image as described earlier in reference
to FIG. 2. Typically, this is done by first determining the amount
of light falling on the scene using an incident light meter, or
alternatively using a reflected light meter to measure the amount
of light reflected from various portions of the scene. In controlled
photography, such as studio photography, the photographer may arrange
lighting in order to illuminate the scene in a desired manner.
In block 20, the photographer adjusts the camera settings based
on the scene to be captured as described earlier in reference to
FIG. 2. Typically, the photographer manually adjusts the camera
settings based on the meter readings made in block 10, although
the photographer may alternatively use the automatic exposure mode
to automatically set the camera settings. The camera settings that
can be adjusted include the camera's exposure time (e.g. camera
shutter speed), the camera's effective ISO speed setting, and the
lens aperture.
In block 30, the photographer uses the digital camera 300 to capture
a first image of the scene, as described earlier in reference to
FIG. 2.
In block 40, the photographer selects, using user controls 303,
to display the captured image on the color LCD image display 332,
as described earlier in reference to FIG. 2.
In block 50, the photographer selects a region of the displayed
image having exposure critical scene content, so that the exposure
related readings for this area of the scene can then be measured
and displayed in block 60, as described earlier in reference to
FIG. 2
In block 60, the digital camera 300 displays the luminometer values
370 on the color LCD image display 332 for the exposure critical
scene content area of the image, selected in block 50. The manner
in which the luminometer values are calculated and displayed on
the LCD image display 332 are identical to that described in reference
to block 60 in FIG. 2, and in reference to FIG. 6.
In block 70, the photographer uses the information displayed by
the luminometer 370, to make a judgment regarding the exposure level
of the captured digital image. If the exposure level is too high,
or too low, and therefore does not meet the photographer's needs,
the camera firmware will automatically calculate the camera adjustment
necessary to modify the exposure by the number of "stops"
indicated by the "stop" value 372.
In block 82, when the user selects the OK button 354, the control
processor and timing generator 304 automatically adjusts the camera's
exposure settings based on the information provided by the luminometer.
The photographer then captures a second image of the scene using
the adjusted camera settings (block 90). The photographer can also
capture additional images using these same camera exposure settings.
For example, if the luminometer values 370 from the first captured
digital image of a scene having an 18% gray card provide a -1 value
for the "stop" value 372, this means that the exposure
was I stop underexposed, relative to the factory determined 18%
gray card values. In this case, the control processor and timing
generator 304 will automatically adjust the exposure settings of
the digital camera 300 to provide twice as much exposure (e.g. 1
stop more exposure). This may be done by doubling the exposure time,
or increasing the aperture size (e.g. decreasing the f/number by
1 stop), or by adjusting the effective ISO speed of the camera.
Typically, the 18% grey card is included in the first picture captured
in block 30, so that it can be selected as the exposure critical
scene content in block 50, and is then removed when the second digital
image, and any additional images, are captured in block 90.
FIG. 4 is a flow diagram showing the steps of practicing a third
embodiment of the present invention. In block 10, the photographer
prepares to capture a digital image as described earlier in reference
to FIG. 2. Typically, this is done by first determining the amount
of light falling on the scene using an incident light meter, or
alternatively using a reflected light meter to measure the amount
of light reflected from various portions of the scene. In controlled
photography, such as studio photography, the photographer may arrange
lighting in order to illuminate the scene in a desired manner.
In block 20, the photographer adjusts the camera settings based
on the scene to be captured as described earlier in reference to
FIG. 2. Typically, the photographer manually adjusts the camera
settings based on the meter readings made in block 10, although
the photographer may alternatively use the automatic exposure mode
to automatically set the camera settings. The camera settings that
can be adjusted include the camera's exposure time (e.g. camera
shutter speed), the camera's effective ISO speed setting, and the
lens aperture.
In block 30, the photographer uses the digital camera 300 to capture
a first image of the scene, as described earlier in reference to
FIG. 2.
In block 40, the photographer selects, using user controls 303,
to display the captured image on the color LCD image display 332,
as described earlier in reference to FIG. 2.
In block 50, the photographer selects a region of the displayed
image having exposure critical scene content, so that the exposure
related readings for this area of the scene can then be measured
and displayed in block 60, as described earlier in reference to
FIG. 2.
In block 60, the digital camera 300 displays the luminometer values
370 on the color LCD image display 332 for the exposure critical
scene content area of image selected in block 50. The manner in
which the luminometer values are calculated and displayed on the
LCD image display 332 are identical to that described in reference
to block 60 in FIG. 2, and in reference to FIG. 6.
In block 70, the photographer uses the information displayed by
the luminometer 370, to make a judgment regarding the exposure level
of the captured digital image. If the exposure level is too high,
or too low, and therefore does not meet the photographer's needs,
in block 84 the processor 320 in the digital camera 300 can automatically
adjust (e.g. modify) the image data based on output provided by
the luminometer. The "stops" 372 metric is used to determine
how to adjust the image data. Since the "stops" 372 metric
is relative to 18% gray, the adjustment made to the image will be
in a metric that is very familiar to professional photographers.
In order to adjust the image, the captured image data will be processed
using equation 4.
where "stops" is the value from Eqn 2. Ecaptured is the
exposure value of each captured pixel of the x,y image array. E
adjusted is the adjusted exposure value of each pixel of the x,y
image array.
The adjustment processing provided by equation 4 adjusts the image
for either under or over exposure that occurred at the time of capture,
thus providing the user with a properly exposed image, relative
to the factory determined 18% point. For example, if the luminometer
values 370 from the first captured digital image of a scene having
an 18% gray card provide a -1 value for the "stop" value
372, this means that the exposure was 1 stop underexposed, relative
to the factory determined 18% gray card values. In this case, the
processor 320 will automatically adjust the image data by multiplying
the linear (e.g. exposure space) code values of the captured image
by 2, to provide the equivalent of 1 stop more exposure).
The invention has been described in detail with particular reference
to certain preferred embodiments thereof, but it will be understood
that variations and modifications can be effected within the spirit
and scope of the invention.
PARTS LIST 10 block 20 block 30 block 40 block 50 block 60 block
62 block 63 block 64 block 66 block 68 block 70 block 80 block 82
block 84 block 90 block 300 digital camera 302 flash 303 users controls
304 control processor and timing generator circuit 306 drivers 308
autofocus and autoexposure detectors 310 zoom and focus motor drives
311 aperture 312 zoom lens 313 shutter 314 image sensor 316 analog
signal processing and analog-to-digital converter
PARTS LIST (con't) 318 DRAM buffer memory 320 processor 322 host
interface 324 memory card interface 326 RAM memory 328 firmware
memory 330 removable memory card 332 color LCD image display 340
host PC 342 interface cable 350 4-way controller 352 cancel button
354 OK button 360 region of interest (ROI) box 362 crosshairs 370
luminometer values 372 stops exposure value 374 percent scene reflectance
value |