Digital Camera Patent Abstract
A digital camera, which captures images and transfers the captured
images to a host computer, includes an image sensor exposed to image
light for capturing the images and generating image signals; an
A/D converter for converting the image signals into digitized image
data; a digital interface for transferring the digitized image data
to the host computer; means for controlling the image sensor in
at least two different camera configurations, each configuration
including configuration information defining a plurality of camera
parameters; and means for communicating at least part of the configuration
information along with the digitized image data to the computer
via the digital interface. Digital Camera Patent Claims
What is claimed is:
1. A digital camera for capturing images and transferring the captured
images to a host computer, said camera comprising:
an image sensor exposed to image light for capturing the images
and generating image signals;
an A/D converter for converting the image signals into digitized
image data;
a digital interface for transferring the digitized image data to
the host computer;
means for controlling the image sensor in at least two different
camera configurations, each configuration including configuration
information defining a plurality of camera parameters;
means for storing the camera configuration information defining
the plurality of camera parameters for the at least two different
camera configurations;
means for selecting a camera configuration; and
means for communicating at least part of the selected configuration
information from the storage means along with the digitized image
data to the computer via the digital interface.
2. The camera as claimed in claim 1 wherein the digital interface
is a Universal Serial Bus (USB) interface.
3. The camera as claimed in claim 1 wherein said at least two different
configurations comprise separate modes for still and motion readout
of the sensor.
4. The camera as claimed in claim 1 wherein said at least two different
configurations comprise separate modes for motion readout of the
sensor.
5. The camera as claimed in claim 3 wherein, in the motion readout
mode, the sensor does not transfer all of the sensor image data
to the digital interface.
6. The camera as claimed in claim 1 wherein the configuration information
includes at least one of a color mode, a subsampling factor, a number
of bits per sample, and a cropping factor.
7. A digital camera for capturing images and transferring the captured
images to a host computer, said camera comprising:
an image sensor exposed to image light for capturing the images
and generating image signals;
an A/D converter for converting the image signals into digitized
image data;
a digital interface for transferring the digitized image data to
the host computer;
a memory for storing configuration information defining camera
parameters for at least two different camera configurations, each
configuration including camera parameters that apply to a current
image and a linkage parameter that indicates which configuration
to apply to a next image; and
means for controlling the image sensor in a selected one of said
at least two different camera configurations according to the configuration
information that applies to the current image, wherein the controlling
means is further responsive to the linkage parameter in the selected
configuration to determine which configuration to apply to the next
image.
8. The camera as claimed in claim 7 wherein a first value of the
linkage parameter requires staying in the same configuration and
a second value of the linkage parameter requires moving to another
configuration.
9. The camera as claimed in claim 8 wherein the first value of
the linkage parameter corresponds to capturing a sequence of continuous
images in a first configuration and a second value of the linkage
parameter corresponds to capturing a still image before moving to
said another configuration.
10. The camera as claimed in claim 9 wherein moving to another
configuration, as required by the second value of the linkage parameter,
comprises moving back to the first configuration.
11. A digital camera for capturing images and transferring the
captured images to a host computer, said camera comprising:
an image sensor exposed to image light for capturing the images
and generating image signals;
an A/D converter for converting the image signals into digitized
image data;
a digital interface for transferring the digitized image data to
the host computer;
a memory for storing configuration information defining camera
parameters for at least two different camera configurations, the
configuration information including a linking parameter that indicates
that the digital camera should shift to a second configuration after
a capture is initiated in a first configuration;
a timing generator for controlling the image sensor in said at
least two different camera configurations according to the configuration
information defining the camera parameters, wherein the timing generator
is responsive to the linking parameter to control the image sensor
in the second configuration; and
means for communicating at least some of the configuration information
stored in the memory from the camera to the computer via the digital
interface.
Digital Camera Patent Description
FIELD OF THE INVENTION
The invention relates generally to the field of electronic photography,
and in particular to a digital camera capable of interfacing with
a computer.
BACKGROUND OF THE INVENTION
There are generally two types of electronic cameras, those that
produce motion images and those that produce still images. Typical
motion cameras include motion video cameras and computer-connected
cameras like the Color QuickCam.TM. camera sold by the Connectix
Corporation, and typical still cameras include the Kodak line of
digital cameras, including the DC40 and DC50 cameras sold by the
Eastman Kodak Company. With motion video cameras, it is typical
to input images to a computer via a "frame grabber" board.
In this case still images and motion images are captured using a
single field or frame of the video. Therefore, the processing for
motion and still images, performed in hardware inside the camera,
is the same whether still or motion images are captured.
With electronic still cameras, the output processing is typically
oriented toward still images, since still image capture is the object
of the camera. U.S. Pat. No. 5,402,170, entitled "Hand-manipulated
Electronic Camera Tethered to a Personal Computer", describes
a digital still camera tethered to a computer for capturing an image
and providing the captured image to the computer for storage therewith.
Capture of images can be initiated from the camera, but its shutter
button, which is controlled pursuant to a status signal from the
computer, is used only to initiate the capture of still images.
If the electronic still camera provides another mode, it is typically
subsidiary to the main purpose. For example, in U.S. Ser. No. 08/367,399,
filed Dec. 30, 1994 (entitled "Electronic Camera Having Dual
Modes for Composing and Capturing Still Images" and assigned
to the same assignee as the present invention), an electronic still
camera is described in which a motion mode is used to provide a
"preview" image on an LCD viewfinder prior to still mode
capture. The camera does not output the motion image data, but simply
displays the motion data on the LCD display. Being part of its fixed
signal processing, the camera does not allow the user to affirmatively
elect between the motion and the still mode.
U.S. Pat. No. 5,301,244, entitled "Computer Input Scanner
Incorporating Multiple Scanning Modes", describes a film scanner
useful as an input device for a computer. The film scanner is operable
in two modes: the first mode is a low resolution monochrome prescanning
mode used for composing (zooming and cropping) the image, and the
second is a high-resolution color sequential mode in which three
successive high resolution color scans are obtained. Two user-controlled
switch functions on the scanner are used: one to continuously capture
low resolution frames in the prescan mode, and the second to initiate
a high-resolution scan. These switch functions, however, always
perform the same task, that is, either to initiate prescan or to
capture a high resolution image.
While describing two modes of operation in some cases, the prior
art does not allow flexibility in user selection of these modes,
or in the communication of mode information between a host computer
and the camera. As a result, the functionality of user-controlled
switches, e.g., the shutter button, remains fixed.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of
the problems set forth above. Briefly summarized, according to one
aspect of the present invention, a digital camera, which captures
images and transfers the captured images to a host computer, includes
an image sensor exposed to image light for capturing the images
and generating image signals; an A/D converter for converting the
image signals into digitized image data; a digital interface for
transferring the digitized image data to the host computer; means
for controlling the image sensor in at least two different camera
configurations, each configuration including configuration information
defining a plurality of camera parameters; and means for communicating
at least part of the configuration information along with the digitized
image data to the computer via the digital interface.
By providing two or more configurations that are immediately accessible
to the camera, and which can be set from the host computer, the
flexibility of the camera is increased. For example, the camera
may be configured for capturing still and motion images with a "shutter"
button that is used for different purposes in the different configurations.
In one case, pressing the shutter button changes the camera from
the motion mode to immediately capture a still image. In a second
case, pressing the shutter button keeps the camera in motion mode,
but enables the recording of a motion sequence in the computer hard
drive memory. It does so by sending a code along with the image
to indicate that the button has been pressed, thereby triggering
the storage of the image sequence on the computer's disk. When the
button is pressed a second time, this indicates to the computer
to stop the storage process. The digital camera output data includes
both the digital image data and a "configuration code"
that indicates which of the two configurations was used for the
image data presently being output by the camera. This indicates
to the host how to process the image data, whether to store the
image data, and/or simply display the image data. It also provides
a "sync code" that allows the computer to detect data
dropouts and resync the video stream by dropping a frame.
These and other aspects, objects, features and advantages of the
present invention will be more clearly understood and appreciated
from a review of the following detailed description of the preferred
embodiments and appended claims, and by reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a multi-mode digital camera with a
computer interface according to the invention.
FIG. 2 is a drawing of the camera encasement for the camera shown
in FIG. 1.
FIG. 3 shows illustrations of computer screens used as a camera
user interface for the camera shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Because imaging devices employing electronic sensors are well known,
the present description will be directed in particular to elements
forming part of, or cooperating more directly with, apparatus in
accordance with the present invention. Elements not specifically
shown or described herein may be selected from those known in the
art. Certain aspects of the embodiments to be described may be provided
in software. Given the system as described in the following materials,
all such software implementation needed for practice of the invention
is conventional and within the ordinary skill in such arts.
A block diagram of a multi-mode digital camera with computer interface
according to the invention is shown in FIG. 1. The camera 10 is
connected to a host computer 12 via a USB (universal serial bus)
digital host interface 14, which also provides power to the camera
10. USB is a well-known shared bus that can be connected to other
devices, such as keyboards, printers, etc. (USB is described in
the Universal Serial Bus Specification, 1.0 Final Draft Revision,
Nov. 13, 1995, which can also be viewed on the Web at http://www.teleport.com/-USB.)
The camera 10 can acquire both still and motion images. The camera
data is processed by the host computer 12 to create final images
that can be displayed on a computer monitor 16, e.g., transmitted
along with audio as part of a "computer videoconference",
etc. The camera 10 can produce both high quality (i.e., high resolution)
still images and high frame rate, reduced resolution motion images.
The camera 10 includes an optical section 18 for imaging light
from a subject upon an electronic image sensor 20. A preferred image
sensor is a Kodak KAI-0320CM interline transfer, progressive-scan
charge-coupled-device (CCD) image sensor with a usable active image
area having 640 columns and 480 rows of color photoelements arranged
in the well-known Bayer color filter array pattern (see U.S. Pat.
No. 3,971,065 for a description of the Bayer pattern). An analog
section 22 in the camera 10 includes the sensor 20, a CDS/gain block
24 for performing correlated double sampling (CDS) and setting the
analog gain, an analog-to-digital (A/D) converter 26 for converting
the analog output signal from the CCD sensor 20 to ,e.g., an 8-bit
digital signal, and CCD clock drivers 28 for clocking the sensor
20. A digital section 30 includes a CCD timing generator 32, a static
RAM memory 34, a line store timing generator 36, a microprocessor
38, and a USB device interface 40. The USB device interface 40 connects
to the USB host interface 14 by means of a USB cable 42.
The sensor 20 is controlled by the timing generator 32 via the
CCD clock driver 28. The digital data from the sensor 20 is temporarily
stored in the static RAM memory 34, preferably a 64K bit static
RAM memory (for example part number IDT7164 made by Integrated Device
Technology, Inc.) which is controlled by a line store timing generator
36 so as to serve as a line store. Besides controlling the sensor
20, the CCD timing generator 32 also controls the line store write
clock applied to the line store timing generator 36. The output
of the line store memory 34 is connected to the host computer 12
via the USB device interface 40, which operates at a maximum data
rate of 12 M bits/sec. (See the article "Universal Serial Bus
to Simplify PC I/O", by Michael Slater in Microprocessor Report,
Volume 9, Number 5, Apr. 17, 1995 for more detail about the benefits
of the USB interface.) The microprocessor 38, which may be the Intel
82930 microprocessor, reads data from the line store 34, and transfers
the data to the computer 12 via the USB interface 40 (which may
be incorporated as part of the microprocessor 38). The USB cable
42 includes four wires, one pair for sending data to and from the
host computer 12, and a second pair for supplying power to the camera
10 from the host computer 12.
As generally used, the USB interface has a clock rate of 12 MHz.
The clock is transmitted encoded along with the differential data,
and the data is transferred in packets. A SYNC field precedes each
data packet to allow the receiver(s) to synchronize their bit recovery
clocks. The basic unit of scheduling is 1 mSec. All bus transactions
involve the transmission of up to three packets, which include from
1 to 1024 bytes of data plus a 3 bytes header that includes an error
detection code word. Each transaction begins when the host computer
12, on a scheduled basis, sends a USB packet describing the type
and direction of transaction, the USB device address, and endpoint
number. This packet is referred to as the Token Packet. The USB
device that is addressed, e.g., the camera 10, selects itself by
decoding the appropriate address fields. In a given transaction,
data is transferred either from the host to a device or from a device
to the host. The direction of data transfer is specified in the
token packet. The source of the transaction then sends a Data Packet
or indicates it has no data to transfer. The destination in general
responds with a Handshake Packet indicating whether the transfer
was successful.
The USB data transfer model between a source or destination on
the host and an endpoint on a device is an abstraction referred
to as a "pipe". There are two types of pipes: stream and
message. Stream pipes are always unidirectional in their communication
flow. Stream data has no USB defined structure while message data
does. Additionally, pipes have associations of data bandwidth, transfer
service type, and endpoint characteristics like directionality and
buffer sizes. Pipes come into existence when a USB device is configured.
USB bandwidth is allocated among pipes. Multiple stream mode pipes
can be serviced at different intervals and with packets of different
sizes.
USB supports two types of pipes, "isochronous" (which
guarantees a continuous data stream using a subset of the USB data
rate) and "asynchronous" (which transfers blocks of data
but may incur a delay before the transfer can begin). The camera
USB interface has one pipe for transporting control data to the
camera and another for transporting image data from the camera.
The latter pipe is a "stream" pipe that can use either
"bulk" data transfer mode (asynchronous) or isochronous
(streaming real time data transfer) mode which occupies a prenegotiated
amount of USB bandwidth with a prenegotiated delivery latency. The
USB allocates bandwidth for isochronous pipes when the pipe is established.
Bulk and Isochronous mode pipes are stream pipes that deliver data
in the data packet portion of bus transactions with no USB required
structure on the data content.
The camera 10, as shown in FIG. 1, also includes a shutter button
44 for initiating an image capture sequence and a light emitting
diode (LED) 46 for indicating operation of the camera during the
capture sequence (i.e., to indicate that the camera is taking a
picture). A drawing of the camera encasement is shown in FIG. 2.
The camera 10 includes a detachable stand 50 which can be placed
on top of the computer monitor 16 for "hands-free" operation.
The camera 10 can also be removed from the stand 50 and used for
"hand-held" operation. The encasement of the camera 10
shows the shutter button 44 and the LED indicator light 46, which
is useful for the "hand-held" mode.
The host computer 12 controls the camera picture-taking process
by instructing the camera 10 when to take still or motion pictures,
and setting the electronic exposure time and the analog gain in
the CDS/gain block 24 via the microprocessor 38. The USB hardware
and software provides communication between the host 12 and the
camera 10 through the aforementioned abstraction called a "pipe".
When the camera 10 is connected to the host 12, camera driver software
running on the host 12 indicates the latency and bandwidth required
for the camera.
The operational modes of the camera 10 can be adjusted from the
host computer 12. More particularly, the microprocessor 38 includes
camera registers 72 that store at least two different camera configurations
communicated from the host computer 12 for controlling the image
sensor in at least two modes, wherein each configuration includes
information defining a plurality of camera parameters as shown in
the first column of Table 1. As further shown in the second column
of Table 1, the parameters may assume a number of allowed values
that are appropriate for either motion (continuous) or still (single
shot) modes.
TABLE 1 ______________________________________ Camera configuration
parameters Parameter Allowed values ______________________________________
Capture mode Continuous or single-shot Button mode Enabled or disabled
Link field Configuration 0, configuration 1, stop Color mode Color
or monochrome Number of bits per sample 8 or 4 Crop values Starting
line #, Ending line # Starting pixel #, Ending pixel # Green horizontal
1, 1/2, 1/4 (320, 160, or 80 subsampling factor pixels max.) Green
vertical subsampling 1, 1/2, 1/4, 1/8 (480, 240, factor 120, or
60 lines max.) Red/Blue horizontal 1, 1/2, 1/4, 1/8 (320, 160, subsampling
factor 80, or 40 pixels max.) Red/Blue vertical 1, 1/2, 1/4, 1/8
(240, 120, subsampling factor 60, or 30 pixels max.) Integration
time 1 msec to 100 msec Analog gain 1-7 unit adjustments ______________________________________
Many of these parameters are particularly useful in the continuous
(motion video) capture mode, in order to provide a higher video
frame rate, and in determining how the camera moves from one configuration
to the other. For example, the camera 10 is configured by input
from the host computer 12 by specifying the values of the group
of parameters shown in Table 1, as follows. (1) From the "color"
mode parameter, either a color image is selected, thereby causing
the camera to transfer RGB images, or a monochrome image is selected
by specifying the "monochrome" value, thereby causing
the camera to transfer only the green data. (2) By means of the
crop value parameter, the selected starting and ending lines and
pixels may be used to "crop" the image before it is transferred,
thereby further reducing the amount of data that has to be sent
to the computer 12. This also has the effect of acting as a "digital
zoom", and can be presented on screen as either a smaller image
than the non-cropped original, or as a "zoomed in" version
of the original. (3) By specifying the horizontal and vertical subsampling
factors (to be other than the allowed value of 1), the desired color
plane (Red, Green, and Blue) is accordingly subsampled as the data
is stored into the line store 34. Since the Bayer color filter pattern
is a mosaic of separate colors, the number of pixels obtained by
use of each subsampling factor corresponds to a fraction of the
number of red, green, and blue pixels in the pattern. (4) By specifying
the number of bits per sample, it is possible to select different
color depths (all 8 bits/color vs. using only 4 bits/color) as the
data is read from the line store 34 and transferred over the USB
interface 40. (5) The exposure of each image is determined by the
integration time and gain setting of the corresponding configuration,
i.e., taken together these parameters make up the exposure.
The button mode parameter determines whether the shutter button
44 is enabled or disabled. When the shutter button is disabled,
pressing the button does not change the mode. However, the camera
conveys the button status (pressed or not pressed) to the computer,
and this can be useful (as will be described) in instructing the
computer to save all the images transmitted or not. When the shutter
button is enabled, pressing the button causes the camera to automatically
shift to the other configuration stored in the camera registers
72, i.e., if presently in configuration 0, then the camera shifts
to configuration 1 or if presently in configuration 1, then the
camera shifts to configuration 0. The link field parameter determines
which configuration will be used to capture the next image frame.
For example, if the camera is in configuration 0 and the link field
is also configuration 0, the camera will examine the link field
after capturing each frame and see that it should always return
to the same configuration. Thus, the camera will continue to take
pictures in configuration 0 until the shutter button is pressed.
This is the typical operational sequence for the motion or continuous
capture mode. On the other hand, if the camera is currently in configuration
0 and the other configuration stored in the camera registers 72
is configuration 1 with a link field of 0, when the shutter button
is pushed the camera shifts from configuration 0 to configuration
1, takes one frame, looks at the new link field (which is 0), and
shifts back to configuration 0. This is the typical operational
sequence for a still capture. The "stops" value in the
link field parameter idles the camera such that it is not producing
pictures. This can be useful in shutting the camera down, e.g.,
after taking a still image until the shutter button is again pressed,
which restarts the motion mode.
As set forth in Table 1, the parameters include allowed values
appropriate for two different camera configurations: therein called
camera configuration 0 and camera configuration 1. Table 2 shows
a specific selection from the allowed values, wherein configuration
0 is a low resolution continuous (motion) configuration and configuration
1 is a full resolution single-shot (still) configuration. When the
camera is first powered up, default values are stored such as those
shown in the first column of Table 2 for the continuous capture
mode and in the second column for the single-shot capture mode.
Since the continuous mode (configuration 0) is used first and the
link field is set to configuration 0, the camera 10 begins sending
a series of color motion images, each with 320.times.240 green pixels
and 160.times.120 each red and blue pixels per image, with 4 bits
per color. This allows a frame rate of over 10 frames per second
at a data transfer rate of 5 Mbits per second. The user can hold
the camera while viewing the computer monitor display 16 to create
a motion sequence for videoconferencing, or in order to frame a
person, object, or document to be captured. When the user presses
the shutter button 44, the camera immediately moves to the single-shot
mode and uses the parameters from configuration 1, which in this
example captures a color image with 320.times.480 green pixels and
320.times.240 red and blue pixels, with 8 bits per color. Since
the link field parameter is set to configuration 0, a still is captured
and the camera immediately shifts back to configuration 0, the continuous
mode. Because the parameters for the two configurations are programmed
by the computer but stored in the camera mode registers 72, the
desired type of image can be immediately captured when the shutter
button 44 is pushed, without waiting for additional communications
between the host computer 12 and the camera 10.
TABLE 2 ______________________________________ An example of camera
configuration parameters for motion to still capture Configuration
0 Configuration 1 value value ______________________________________
Capture mode Continuous Single-shot Button press mode Enabled Enabled
Link field Configuration 0 Configuration 0 Color mode Color Color
Number of bits per 4 8 sample Crop values Starting line = 1, Starting
line = 1, Ending line = 480 Ending line = 480 Starting pixel = 1,
Starting pixels = 1, Ending pixel = 640 Ending pixel = 640 Green
horizontal 1 (320 pixels) 1 (320 pixels) subsampling factor Green
vertical 1/2 (240 lines) 1 (480 lines) subsampling Red and Blue
1/2 (160 pixels) 1 (320 pixels) horizontal subsampling factor Red
and Blue 1/2 (120 lines) 1 (240 lines) vertical subsampling factor
Integration time 30 msec 100 msec Analog gain 7 2 ______________________________________
Alternately, instead of using the default parameters for configurations
0 and 1 as shown in Table 2, the user can chose preferred parameter
values using the user interface screens shown in FIG. 3, which appear
on the computer monitor 16 when the user interface is enabled. More
specifically, the user clicks on a "camera adjustments"
icon 60 on a basic screen 62 in order to pull down a camera adjustments
screen 64. By then clicking on an "advanced camera settings"
icon 66, an advanced camera settings screen 68 is obtained, and
so on through as many additional screens 70 as are needed. The computer
would take the user settings and translate them into the appropriate
configuration settings for the camera, e.g., the zoom setting would
be translated into the crop windows. In this manner, the camera
configurations may be customized for the specific application.
For example, Table 3 shows a customized selection from the allowed
values, wherein configuration 0 is a low resolution continuous (motion)
monochrome configuration and configuration 1 is a low resolution
continuous (motion) color configuration. When the camera is powered
up, the continuous monochrome mode (configuration 0) is used first
and the link field is set to configuration 0. The camera 10 thus
begins sending a series of monochrome motion images, each with 320.times.240
green pixels, with 4 bits per pixel. This would allow a frame rate
of approximately two times the frame rate of a similar resolution
color image stream. The user can hold the camera while viewing the
computer monitor display 16 to create a motion sequence for videoconferencing,
or in order to frame a person, object, or document to be captured.
When the user presses the shutter button 44, the camera immediately
moves to the color motion mode and uses the parameters from configuration
1, which in this example captures a color image with 320.times.240
green pixels and 160.times.120 red and blue pixels, with 4 bits
per color. Since the link field parameter is set to configuration
1, the camera begins sending a series of color images in the continuous
mode. Because the parameters for the two configurations are programmed
by the computer but stored in the camera mode registers 72, the
desired type of motion sequence can be immediately captured when
the shutter button 44 is pushed, without waiting for additional
communications between the host computer 12 and the camera 10. When
the user presses the shutter button a second time, the camera reverts
back to configuration 0 operation and storage of the video stream
is terminated.
TABLE 3 ______________________________________ An example of camera
configuration parameters for monochrome motion to color motion capture
Configuration 0 Configuration 1 value value ______________________________________
Capture mode Continuous continuous Button press mode Enabled Enabled
Link field Configuration 0 Configuration 1 Color mode Monochrome
Color Number of bits per 4 4 sample Crop values Starting line =
1 Starting line = 1, Ending line = 480 Ending line = 480 Starting
pixel = 1, Starting pixels = 1, Ending pixel = 640 Ending pixel
= 640 Green horizontal 1 (320 pixels) 1 (320 pixels) subsampling
factor Green vertical 1/2 (240 lines) 1 (240 lines) subsampling
Red and Blue 1 (160 pixels) horizontal subsampling factor Red and
Blue 1 (120 lines) vertical subsampling factor Integration time
30 msec 30 msec Analog gain 7 7 ______________________________________
Other combinations of configurations can be readily implemented.
For example, configuration 0 (link field 0) could be a low resolution
motion mode (by use of the subsampling factors) and configuration
1 (link field 1) could be high resolution mode. The shutter button
would be used to toggle between the two odes. Another example would
use configuration 0 (link field 0) as a full resolution image and
configuration 1 (link field 1) as a cropped image (by appropriate
use of cropped values). Then the shutter button would be used to
toggle between a "conventional" image and a "zoomed"
image. Many other combinations are possible, e.g., high resolution
color to low resolution color, moderate subsampling to significant
subsampling, low resolution color motion to high resolution monochrome
still, and so on. Since the shutter button is used as a toggle to
move between configurations, it takes on a multiplicity of functions.
(Note that not all combinations need be exposed to the end user.)
The image data is transmitted to the host computer 12 via packets
of information, which may be 64 bytes per packet when the USB "bulk"
transfer mode is used. The first packet of data at the beginning
of each new frame includes the configuration and status information
shown in Table 4. The header begins with a 4 byte "Sync word"
(1) that identifies the image frame number, followed by a value
(2) that indicates how many bytes of image data are contained in
the frame. The color mode and number of bits per sample (3), cropping
values (4), and subsampling factors (5) provide the aforementioned
configuration values. The button status (6) indicates whether or
not the user is currently pressing the shutter button. (Note that
this status is independent of the button press mode shown in Tables
1, 2, and 3). Following the image header, packets containing the
image data are transmitted. The number of packets per frame depends
on the camera configuration.
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