Digital Camera Patent Abstract
A method and apparatus for capturing and printing an image of a
subject utilizes a tracking mechanism to allow an operator to print
the captured image onto a selected surface by manually manipulating
the apparatus across the surface. The apparatus is a print-capable
digital camera which can print the captured image in one of a range
of sizes. The printing process involves an operator placing the
digital camera on the surface and scanning the surface in order
for the digital camera to print a segment of the captured image
according to the location of the digital camera. The tracking mechanism
may be comprised of two trackball assemblies. The rotations of the
trackballs generate location data which is utilized by digital signal
processing circuitry to determine the position of the digital camera
relative to a start-print position. Once the location of the inkjet
printing head is determined, the digital signal processing circuitry
arranges print data to drive an inkjet cartridge to deposit droplets
of ink to form a particular segment of the captured image. The digital
camera also includes an optical lens for receiving the image of
the subject. The optical lens is optically coupled to an application
specific integrated circuit (ASIC). The ASIC contains a photosensor
array, analog-to-digital circuitry, a printer driver, timing control
circuitry, a memory, and digital signal processing circuitry. A
control interface is also included to allow the operator to control
functions of the digital camera. Digital Camera Patent Claims
What is claimed is:
1. An electronic imaging and printing apparatus comprising: a camera
housing; imaging means integral with said camera housing for defining
a field of vision and selectively generating a frame of digital
image data representative of subject matter within said field of
vision; camera-position tracking means located at an exterior surface
of said camera housing for generating location data that is responsive
to movement of said camera housing relative to a print medium during
a printing process, said camera-position tracking means including
a pair of trackballs; processor means located within said camera
housing for converting said frame of digital image data into print
data and dynamically arranging side-by-side segments of said print
data in response to receiving said location data during said printing
process, said processor means being cooperative with said pair of
trackballs to track movement of said camera housing in two perpendicular
axes within a plane aligned with said print medium and to track
variations in an angle of said camera housing relative to a direction
that is perpendicular to said plane, said processor means being
responsive to said tracking of said movement and said tracking of
said angle with respect to dynamically arranging said print data;
and printing means having a supply of print-forming matter for forming
an image on said print medium in response to receiving said dynamic
arrangement of said print data from said processor means, said printing
means being configured to deposit said print-forming matter as said
camera housing is moved in a direction of one of said segments.
2. The apparatus of claim 1 wherein said camera-position tracking
means includes circuitry having an input connected to said pair
of trackballs and having an output signal indicative of said movement
of said camera housing within an X,Y co-ordinate system.
3. The apparatus of claim 1 wherein said printing means includes
an inkjet cartridge and said supply of print-forming matter is ink
within said inkjet cartridge.
4. The apparatus of claim 3 wherein said inkjet cartridge contains
a plurality of colors inks.
5. The apparatus of claim 1 wherein said imaging means includes
a photosensor array and said processor means is a digital signal
processing circuitry, said photosensor array and said digital signal
processing circuitry being incorporated into an application specific
integrated circuit (ASIC).
6. The apparatus of claim 5 wherein said application specific integrated
circuit also includes memory, timing control cicuitry and analog-to-digital
cicuitry.
7. The apparatus of claim 5 wherein said application specific integrated
circuit utilizes CMOS techonology.
8. The apparatus of claim 1 further comprising memory having an
input that is connected to said imaging means to store said frame
of digital image data.
9. A method of printing an image utilizing a hand-held camera with
printing capability comprising steps of: capturing a frame of digital
image data utilizing an imaging device; storing said frame of image
data into internal memory of said hand-held camera; manually moving
said hand-held camera adjacent to a surface on which a printed image
is to be formed; tracking positions of said hand-held camera relative
to said surface and angles of said hand-held camera relative to
a direction that is perpendicular to said surface, including generating
position data indicative of said relative positions and said relative
angles; and depositing print-forming matter onto said surface in
a sequence determined by said position data and said meandering
path such that a composite printed image is representative of said
frame of image data, including limiting said depositing to a single
deposition of said print-forming matter onto any portion of said
surface, thereby preventing overlapping depositions onto portions
of said surface that are overlapped as said hand-held camera is
moved along said meandering path.
10. The method of claim 9 wherein said step of manually moving
said hand-held camera is executed in a manner free of physical constraints.
11. The method of claim 9 wherein said step of tracking positions
of said hand-held camera includes receiving signals from a trackball.
12. The method of claim 9 wherein said step of capturing said frame
of image data includes receiving signals from an array of optoelectrical
elements.
13. The method of claim 9 wherein said step of depositing print-forming
matter includes utilizing inkjet printer techniques.
Digital Camera Patent Description
TECHNICAL FIELD
The invention relates generally to digital cameras and more particularly
to a digital camera with printing capability.
BACKGROUND ART
A digital camera captures an image of a particular subject using
an imaging system that includes an optical lens and a photosensor
array, such as a charged coupled device (CCD). The imaging system
"captures" a set, or frame, of digital image data that
represents a particular subject at the time that the frame is captured.
Each frame of digital image data is stored in a memory of the digital
camera for subsequent viewing on a display or downloading to a computer
system for editing and printing.
In order to print the captured image, a host computer is typically
utilized. The frame of digital image data is transferred from the
digital camera to the host computer. Once the frame of digital image
data has been received, the host computer can display the captured
image represented by the frame of digital image data on a monitor
using photo-manipulation software. The host computer can then print
the captured image to any standard printer, or a special photography
printer, such as the Hewlett Packard (HP) PhotoSmart Photo Printer,
that is attached to the host computer. However, this typical approach
requires access to a host computer and the sophistication to utilize
the photo-manipulation software.
An alternative photo-printing approach is to employ a dedicated
printer that is directly connected to a digital camera. U.S. Pat.
No. 4,074,324 to Barrett describes an instant electronic camera
that is directly connected to an external mechanical scanning printer.
If digital image data is captured at a location distant from the
printer, the camera must be brought to the location of the printer
in order to print the image data.
Similarly, U.S. Pat. No. 4,827,347 to Bell describes an electronic
camera that is directly connected to a database/picture printer.
Unlike the instant electronic camera of Barrett, the electronic
camera of Bell has an array of display windows on the opposite side
of a lens assembly for viewing stored frames of digital image data
prior to printing or downloading.
Still another approach to printing the frame of digital image data
is to have a printer that is incorporated into the digital camera
or is attached physically to a camera housing of the digital camera.
U.S. Pat. No. 4,937,676 to Finelli et al. (hereinafter Finelli)
describes an electronic camera system with a detachable printer.
The detachable printer of Finelli utilizes a self-developing film
that is exposed according to the digital image data. Thus, photo-imageable
film is required to print an image. Moreover, the system described
in Finelli offers little flexibility with respect to photograph
manipulation (e.g., varying the size of a photo-print).
U.S. Pat. No. 5,493,409 to Maeda. et al. (hereinafter Maeda) describes
a still video camera having a printer. In one embodiment, a printing
mechanism is incorporated into a still video camera. In this embodiment,
a television set is utilized to view the electronic images. In another
embodiment, a printing mechanism is a detachable printer unit. In
both embodiments, the captured image can only be printed in one
size.
While the known devices for capturing and printing images operate
well for their intended purpose, an efficient and inexpensive camera
for capturing and printing frames of digital image data in various
sizes is desired. What is needed is a compact digital camera with
printing capability that could print the frame of digital image
data onto any of a variety of types of print media and preferably
within a range of different sizes.
SUMMARY OF THE INVENTION
A method and apparatus for capturing and printing an image includes
utilizing a tracking mechanism to allow an operator to print the
captured image onto a selected print medium by moving the apparatus
in a free-hand manner across a print medium. The changing location
of the apparatus is monitored in real time using navigation information
generated by the tracking mechanism. The apparatus is a print-capable
digital camera having conventional circuitry for capturing an image,
but also having a printing capability that is controlled by the
navigation information generated by the tracking mechanism.
In the preferred embodiment, the tracking mechanism is at least
one trackball that extends beyond an external surface of the digital
camera. Also in the preferred embodiment, the printing capability
is achieved by locating a printhead of an inkjet cartridge at the
external surface. Rotation of the trackball or trackballs is monitored
in real time to generate the navigation information that allows
determination of the position of the inkjet printhead relative to
a start position for the printing process. While inkjet printing
is preferred, other printing devices may be utilized.
In operation, a frame of digital image data is captured and stored
using conventional techniques. During a printing process, the frame
of image data is converted to print data compatible with the printing
device. The print data is dynamically arranged in segments in response
to receiving the navigation information. For example, if two trackball
assemblies generate navigation information, the location of the
printhead may be determined within X, Y coordinates, and segments
of the print data may be transmitted to the printhead accordingly.
As long as the trackball assemblies are in constant contact with
the surface on which the image is printed, the digital camera may
retrace any missed areas in order to complete the print image. Preferably,
the digital camera prints only the missed area when there is an
overlap, but duplicate printing may be utilized.
Rather than trackball assemblies, the navigation information may
be generated by an optical imaging structure. For example, during
a printing process, images of the surface on which the print material
is deposited may be repeatedly captured and compared to each other
to determine the direction of movement by the digital camera. Successive
determinations are used to arrange the print data for forming the
image of interest on a print medium, such as a sheet of paper.
The digital camera may include an optical lens for optically focusing
an image onto an array of elements that generate output signals
indicative of light received at a selected time. Collectively, the
signals form a frame of image data. In the preferred embodiment,
the imaging array is fabricated as part of an application specific
integrated circuit (ASIC) that also includes analog-to-digital circuitry,
timing control circuitry, memory and digital signal processing circuitry.
Also included on the ASIC is a printer driver, which is typically
implemented in computer software. The dynamic arrangement of segments
of print data may be implemented at the driver level, or at a level
above or below the driver level. That is, the printer driver may
direct print data in an arrangement of segments responsive to the
reception of navigation information. Alternatively, the dynamic
arrangement of segments may be implemented prior to the printer
driver by arranging the image information that is conducted to the
printer driver. As the third alternative, the print data from the
driver may be temporarily stored in a buffer, and the dynamic arrangement
may be the result of extracting print data from the buffer in an
arrangement dictated by the navigation information.
Preferably, the printer driver enables a user to select the size
of the image that is printed. The digital camera includes an interface
that allows magnification and demagnification of the image to be
printed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of a digital camera capable of printing
a captured image in various sizes in accordance with the invention.
FIG. 2 is a block diagram of the components of the print-capable
digital camera.
FIG. 3 is a bottom view of the digital camera.
FIG. 4 is a perspective view of the digital camera following a
meandering path on a printing medium in accordance with the invention.
FIG. 5 is a flow diagram of a method of capturing an image of a
subject and printing the captured image in accordance with the invention.
FIG. 6 is a conceptual representation of generating navigation
information using an optical approach.
DETAILED DESCRIPTION
With reference to FIG. 1, a print-capable digital camera 10 having
a camera housing 20 is shown. On the front portion of the digital
camera 10, an optical lens 12 and a flash device 22 are incorporated
into the camera housing 20. Print button 24 and capture button 26
are located on the top of the digital camera 10. Also shown in FIG.
1 are an inkjet printing head 14 and two trackballs 16 and 18 located
on the bottom of the digital camera 10. The inkjet printing head
14 and the two trackballs 16 and 18 can be covered by attaching
a printer case 28 (shown in phantom) to the camera housing 20.
Additional components of the print-capable digital camera 10 are
shown in FIG. 2. Optically coupled to the optical lens 12 is an
application specific integrated circuit (ASIC) 30. The ASIC 30 includes
a photosensor array 32, analog-to-digital circuitry 34, a printer
driver 35, timing control circuitry 37, memory 38, and digital signal
processing circuitry 36. The ASIC 30 utilizes complementary metal-oxide
semiconductor (CMOS) technology. As such, the photosensor array
32 is comprised of CMOS sensors. Compared to charged couple devices
(CCDs), CMOS sensors are less expensive and easier to fabricate.
In addition, CMOS sensors require less power than CCDs.
In an alternative embodiment, the memory 38 is contained in a detachable
memory card. The memory card can interface with a host computer
for downloading any stored information to the memory card.
The configuration of the ASIC 30 is not crucial to the present
invention. The photosensor array 32, the analog-to-digital circuitry
34, the timing control circuitry 37, the memory 38, and the digital
signal processing circuitry 36 may each, or in any combination thereof,
be incorporated on separate integrated circuits. The photosensor
array 32 may be a CCD instead of CMOS sensors. As is well known
in the art, the functions of a printer driver 35 are implemented
primarily in computer programming.
The inkjet cartridge 44, which is electrically controlled by the
ASIC 30, is also shown in FIG. 2. The inkjet printing head 14 shown
in FIG. 1 is a part of the inkjet cartridge 44. The inkjet cartridge
44 may be a commercially available inkjet cartridge, such as the
one utilized in the Hewlett Packard DeskJet 400 manufactured by
the assignee of the present invention. However, the inkjet cartridge
44 may be a miniature version of a conventional inkjet cartridge
in order to minimize the size of the print-capable digital camera
10. Although a black inkjet cartridge could be used, the preferred
embodiment utilizes a miniature color inkjet cartridge to produce
color pictures of the captured images.
Control interface 47 located at a surface of the camera housing
20 allows an operator to control most of the functions of the print-capable
digital camera 10. Control interface 47 may include an on/off switch,
a battery status readout, and a controller for lens focus, exposure,
shutter speed, and white balance. Printing controls included in
the control interface 47 may comprise a controller for selecting
stored images to be printed and selecting a print size of the image.
The control interface 47 may also include a display device for viewing
a captured image almost instantaneously.
First trackball assembly 46 and second trackball assembly 48 are
electrically coupled to the ASIC 30. First trackball assembly 46
includes trackball 16 shown in FIG. 1, while second trackball assembly
48 includes trackball 18. The trackballs 16 and 18 should be made
of rubber or other non-skidding material. The trackball assemblies
46 and 48 also include a detection mechanism for monitoring the
rotations of the trackballs 16 and 18. The detection mechanism may
include two rollers, such as the rollers utilized in a conventional
computer mouse, that are in constant contact with the trackball
16 or the trackball 18 to monitor movement of the digital camera
10 relative to a recording medium during a printing process. The
two trackball assemblies 46 and 48 also monitor the rotation of
the printable digital camera 10, or the angle of attack, during
the printing process. Although two trackball assemblies 46 and 48
are illustrated in FIG. 2, the invention could operate properly
with only one trackball assembly.
Lastly, a battery 42 is contained within the print-capable digital
camera 10 to supply power to the electronic components of the digital
camera 10. The battery 42 may be more than one conventional alkaline
battery, such as AAA size batteries, rechargeable nickel-cadmium
batteries, or nickel hydride batteries.
The image capturing operation of the print-capable digital camera
10 will be described with references to FIGS. 1 and 2. The optical
lens 12 is directed at a subject of interest. When the capture button
26 is depressed, an electronic shutter is activated and the image
of the subject is focused by the optical lens 12 onto the photosensor
array 32. The shutter speed and other timing functions are controlled
by the timing control circuitry 37. The photosensor array 32 is
a matrix of photosensitive pixels. Each photosensitive pixel generates
an electrical signal that is representative of the optical energy
that is directed at the pixel by the optical lens 12. Since the
resolution of an image that can be produced from the photosensor
array 32 is dependent upon the density of the pixels in the photosensor
array 32, a sufficient number of pixels should be contained in the
photosensor array 32 to achieve a desired resolution. The electrical
signals that are generated by the photosensor array are characterized
as image data or digital image data, wherein each image or "picture"
that is captured is considered one "set" or "frame"
of digital image data.
Once the image has been captured, the frame of digital image data
is processed by the analog-to-digital circuitry 34 and is stored
in the memory 38. The frame of digital image data may conduct through
the digital signal processing circuitry 36 prior to reaching the
memory 38. The digital signal processing circuitry 36 may be used
to enhance and compress the frame of digital image data prior to
storage in the memory 38.
The bottom of the print-capable digital camera 10 is shown in FIG.
3, illustrating the inkjet printing head 14 and the two trackballs
16 and 18 which were described with reference to FIG. 1. FIG. 4
shows the print-capable digital camera 10 in the incomplete stage
of the printing process in accordance with the present invention.
The print-capable digital camera 10 has taken a meandering path
52 beginning from a point 55 to print an image of a mountain scene
54 onto a recording medium 50.
The printing operation of the printable digital camera 10 will
be described with references to FIGS. 1, 2, and 4. Once the captured
image represented by the frame of digital image data has been stored
in the memory 38 as described above, the printable digital camera
10 is ready to print the captured image onto the printing medium
50. Using the control interface 47, the operator selects the captured
image to be printed and a print size. Print size selections may
vary from a high resolution, small scale choice to a low resolution,
large scale choice. The recording medium 50 may be a regular paper,
an inkjet-specific paper, a glossy photographic paper, or even a
surface of the operator's forearm.
After the selection of the print size, the printable digital camera
10 is placed on the printing medium 50 such that the inkjet printing
head 14 is at a desired starting point on the printing medium 50.
The desired starting point could be where the operator wants the
upper left corner of the image to be printed on the printing medium
50. However, the desired starting point could be any place on the
printing medium 50, as long as the print-capable digital camera
10 is programmed to know where that starting point is situated in
respect to the image to be printed. In FIG. 4, the starting point
is the point 55 which is located just left of the upper left corner
of the partially printed image.
The print-capable digital camera 10 begins to print when the print
button 24 is activated and the trackballs 16 and 18 start to rotate.
The depression of the print button triggers the digital signal processing
circuitry 36 to retrieve the frame of digital image data that is
to be printed from the memory 38. The frame of digital image data
is then converted into print data by the printer driver 35 in order
to drive the inkjet cartridge 44. Depending on the location of the
printable digital camera 10 with respect to the starting point,
a particular portion of the print data is sent to the inkjet cartridge
44. The location of the print-capable digital camera 10 is determined
by location data provided by the trackball assemblies 46 and 48
as the digital camera is moved along the surface of the medium.
Once the print data is received, the inkjet cartridge 44 operates
in a conventional manner to deliver droplets of color ink onto the
printing medium 50 using four jets with cyan, magenta, yellow and
black inks.
As the print-capable digital camera 10 travels across the printing
medium 50, the trackballs 16 and 18 of the trackball assemblies
46 and 48 rotate. The rotations of the trackballs 16 and 18 are
monitored and used to generate navigation data, which is sent to
the digital signal processing circuitry 36 to determine the position
of the print-capable digital camera 10 in real time or, more importantly,
the position of the inkjet printing head 14 with respect to the
starting point.
The use of trackballs to track movements of a device is known.
For example, a typical computer mouse has a single trackball for
tracking the computer mouse. The movement information of the computer
mouse is utilized to maneuver a cursor on a computer monitor. However,
using a single trackball method of the computer mouse only provides
two-directional information of the print-capable digital camera
10, i.e., movement in horizontal and vertical directions. If the
angle of attack of the digital camera during the printing process
changes because the digital camera is tilted by the user, this information
cannot be easily acquired using a single trackball. The present
invention could operate with only a single trackball, as long as
the digital camera 10 is positioned fairly vertical during the printing
process as shown in FIG. 4, or if the trackball is attached in a
manner that permits detection of rotational movement of the digital
camera 10. However, the rotational movement would be difficult to
detect using a single trackball due to slippage of the trackball
if the digital camera 10 is being pivoted with the trackball in
the center. The preferred embodiment is to have two trackballs to
acquire information on the change of the angle of attack.
Since the movement of the digital camera 10 is constantly being
tracked, the path taken to print the captured image is immaterial,
as long as the entire surface region on which the printed image
is to be printed is scanned. For example, the free-hand meandering
path 52 of FIG. 4 would have to be very precise if the digital camera
10 was printing in a traditional inkjet printing method. That is,
horizontal paths of the meandering path 52 would have to be perfectly
straight and evenly spaced. However, since the digital camera 10
is monitoring its position in real time, the digital camera 10 can
retrace and cover areas that were missed during the initial pass
with the inkjet printing head 14. When retracing an area that was
already printed, the digital camera 10 preferably does not print.
The segments of print data are marked or are discarded as each is
used in printing a segment of the image, thereby minimizing the
amount of ink that is used. However, in another embodiment, the
printing of image segments is duplicated when the free-hand movement
of the digital camera causes portions of the recording medium to
be overlapped.
Due to potential smearing of freshly deposited ink by contact with
the trackballs 16 and 18, the ideal path of the digital camera 10
during printing is the one illustrated in FIG. 4 as the meandering
path 52. The arrangement of the horizontal paths should minimize
the overlap of the inkjet printing head with a previous horizontal
path. This ensures that all the areas of the printed image are properly
covered, but minimizes any adverse effects of overlapping print.
The printing process is completed when the captured image is fully
printed on the print medium 50. The digital camera 10 is now ready
to print the same or another captured image on a different print
medium or to capture another new image.
The method of capturing an image of a subject and printing the
captured image in accordance with the invention will be described
with reference to FIGS. 1, 2, 3, and 5. At step 510 in FIG. 5, an
image is captured by directing the optical lens 12 at the subject
of interest and activating the image capturing device of the print-capable
digital camera 10. The captured image is converted into a frame
of digital image data by the photosensor array 32 and the analog-to-digital
circuitry 34 within the ASIC 30. The frame of digital image data
is enhanced and compressed by the digital signal processing circuitry
36.
The frame of digital image data is stored in the memory 38 at step
520. The memory 38 is preferably fabricated within the ASIC 30,
but may be on a separate integrated chip. Alternatively or additionally,
the memory 38 may be designed within a detachable memory card which
can be removed and interfaced with a host computer for viewing,
editing, and printing.
At step 530, the captured image to be printed is selected by the
operator using the control interface 47. The print size is also
selected by the operator utilizing the control interface 47.
Printing the captured image occurs during step 540. Printing takes
place when the print button 24 is activated and the trackballs 16
and 18 are rolling as a result of free-hand movement of the camera
while the trackballs are in contact with a print medium 50. Initially,
the inkjet printing head 14 of the printable digital camera 10 is
placed on a starting point on a print medium 50. The digital camera
10 is manually manipulated across the print medium 50, keeping the
trackballs 16 and 18 in constant contact with the print medium 50.
As described above, the activation of the print button 24 and the
movements of the trackballs 16 and 18 signal the electrical components
of the digital camera to start printing. As the digital camera 10
travels on the recording medium 50, the trackball assemblies 46
and 48 constantly monitor the navigation of the digital camera 10
by generating location data in real time. The location data is utilized
by the digital signal processing circuitry 36 to drive the inkjet
cartridge 44 to print the corresponding segment of the captured
image with respect to the location of the digital camera 10 on the
print medium 50. The inkjet printing head 14 is scanned across the
print medium 50 until the entire image is printed on the print medium
50.
The implementation of step 540 of printing a captured image requires
the dynamic arrangement of segments of print data in response to
receiving the navigation information. This can be carried out by
using the digital signal processing circuitry 36 in FIG. 2 to selectively
transfer segments of image data from memory 38 to the printer driver
35. Alternatively, the printer driver may be controlled to selectively
convert segments of the image data to print data that is compatible
with the inkjet cartridge 44. As a third alternative, the print
data from the printer driver 35 is collectively stored in a buffer
memory, not shown, and the print data is selectively extracted from
the buffer memory in a sequence dictated by the navigation information.
While the print device is shown in FIG. 2 as being an inkjet cartridge
44, other techniques for printing the image may be utilized. Moreover,
print-forming materials other than ink may be employed without diverging
from the invention.
The digital camera 10 has been described as being a still image
camera. However, the print capability described above may be added
to a camera that captures motion as digital data. A frame from a
camcorder may then be printed in the manner described above.
The use of trackball assemblies 46 and 48 may be replaced with
other mechanical devices. As an example, a roller may be substituted
and the roller may be limited to movement of the digital camera
in one direction along the surface on which an image is printed.
In this embodiment, the inkjet cartridge 44 may be mounted onto
a carriage that allows movement of the printhead in a direction
perpendicular to the direction of camera movement. A concern with
this implementation is that the motor that moves the inkjet cartridge
perpendicular to the movement of the camera will quickly deplete
the charge of the battery 42.
As an alternative to the mechanical tracking mechanism, an optical
approach may be utilized. U.S. Pat. No. 5,686,720 to Tullis, which
is assigned to the assignee of the present invention and is incorporated
by reference, describes a scanning device for simultaneously acquiring
image and navigation information. A hand-held scanning device is
moved relative to a document having an image to be captured. Simultaneously,
one or more optical sensors are used to view features on the scanned
document and to generate navigation information. This same approach
may be used in the printing process of FIG. 5. In a sophisticated
application of this approach, the features that are imaged and used
to determine position information may be paper fibers or illumination
patterns formed by highly reflective surface features and shadowed
areas between raised surface features. In a less sophisticated application,
the features that are imaged may be reference features, such as
graph paper lines on the surface to which the image is to be printed.
Referring to FIG. 2, the trackball assemblies 46 and 48 may be
replaced with a navigation sensor that is thirty-two pixels by sixty-four
pixels. Preferably, there are two such navigation sensors. A less
desirable alternative is to use the existing optical lens 12 and
imaging array 32, but this requires that the inkjet cartridge 44
be moved to the forward surface of the digital camera 10. The concepts
of the optical approach can be described with reference to FIG.
6. A reference frame 62 of a surface on which an image is to be
printed is shown as having a T-shaped feature 64. The size of the
reference frame depends upon factors such as the maximum scanning
speed of the digital camera, the dominant spatial frequencies of
the image of the structural features, and the image resolution of
the navigation sensor. A practical size of the reference frame for
a navigation sensor that is thirty-two pixels by sixty-four pixels
is 24.times.56 pixels.
At a later time (dt), the navigation sensor acquires a sample frame
66 of the surface on which the image is being printed. The sample
frame 66 is acquired after the digital camera 10 has been-displaced
with respect to the position in which frame 62 was acquired. The
duration dt is preferably set such that the relative displacement
of the T-shaped feature 64 is less than one pixel of the navigation
sensor and the velocity of translation of the scanning device. An
acceptable time period is 50 .mu.s for velocities of 0.45 meters/sec
at 600 dpi.
If the digital camera 10 has moved during the time period between
acquiring the reference frame 62 and the time at which the sample
frame 66 is acquired, the first and second images of the T-shaped
feature will be ones in which the feature has shifted. While the
preferred embodiment is one in which dt is less than the time that
allows a full-pixel movement, the schematic representation of FIG.
6 shows the feature 64 as having shifted upwardly and to the right
by one pixel. The full-pixel shift is assumed only to simplify the
representation.
Element 70 in FIG. 6 represents a sequential shifting of the pixel
values of frame 62 into the eight nearest-neighbor pixels. That
is, step "0" does not include a shift, step "1"
is a diagonal shift upward and to the left, step "2" is
an upward shift, etc. In this manner, the pixel-shifted frames can
be combined with the sample frame 66 to produce the array 72 of
position frames shown in FIG. 6. The position frame designated as
"Position 0" does not include a shift, so that the result
Is merely a combination of frames 66 and 62. "Position 7"
has the minimum number of shaded pixels, and therefore is the frame
with the highest correlation. Based upon the correlation results,
the position of the T-shaped feature 64 in the sample frame 66 is
determined to be a diagonal rightward and upward shift relative
to the position of the same feature in the earlier-acquired reference
frame 62, which implies that the digital camera has moved leftwardly
and downwardly during the time dt.
An advantage of the optical approach is that it may be possible
to temporarily remove the digital camera from being directly adjacent
to the surface on which the image is to be printed without adversely
affecting the printing process. That is, the printing process may
be interrupted. The imaging of a particular feature allows the process
to be performed in two steps, since correction may be achieved using
a previously imaged surface feature as a reference point. On the
other hand, the application in which trackball assemblies are used
for generating the navigation information requires that the trackballs
be precisely reseated if the printing process is temporarily halted. |