Method for transmitting multiresolution image data in a radio frequency communication system

The present invention relates to a method for transmitting multiresolution image data via wireless devices in a radio frequency communication system wherein images are decomposed into levels of resolution. The image data is stored in discrete information blocks in an image storage unit including a base image and one or more image details. The base image represents the coarsest resolution of the image. Each image detail, when added to the base image, improves the resolution of the image. An image display unit transmits a request for image data to the image storage unit. In response to the initial request, the base image is transmitted to the image display unit. If the base image is insufficient, the resolution can be increased incrementally by sending additional image data requests to transmit additional image detail. The additional image detail is then transmitted to the image display unit and recombined with the base image to provide a higher level of resolution to the image.

FIELD OF THE INVENTION 
The present invention relates to wireless communication systems and more 
particularly to a method for transmitting multiresolution image data via 
wireless devices in a radio frequency communication system. 
BACKGROUND OF THE INVENTION 
Multimedia applications are becoming an integral part in the design of 
wireline communication systems. These applications focus on the 
transmission of images, data, and speech over the same communication 
channel. A particular concern in multimedia applications is the 
transmission of images. An image comprises a two-dimensional signal that 
represents the relative luminances of objects in a scene. A scene may 
comprise, for example, a photograph, a video image, an X-ray image, or a 
radar image for a weather forecast. Two important parameters are the 
quality and the intelligibility of the image resulting from the 
transmission of the image data. 
A typical image consists of a matrix of 512.times.512 pixels. For uncolored 
images, each pixel is described by a gray level and uses 8 bits of memory 
to store this information. The result is that the entire image occupies 
approximately 2 Mbits of memory. For a colored image, each pixel uses 24 
bits and results in a image occupying approximately 6 Mbits of memory. 
Thus, a full-detail color image usually requires a lot of memory, 
bandwidth, and power consumption. 
As a natural result of advances in technology, attention is being given to 
the transmission of multimedia signals via radio frequency communication. 
In the near future, this communication vehicle will become an important 
part of the service requirements for radio frequency communication 
systems. However, unlike wireline communication systems, radio frequency 
systems tend to be spectrally limited. In addition, service costs, in 
terms of air time charges, are significantly higher for the consumer. 
Images usually occupy large quantities of device memory and the 
transmission of image signals take a correspondingly long time. As such, 
it becomes quite expensive to transmit images via radio frequency systems 
such as mobile cellular radio networks. These resources need not be wasted 
if high resolution image transmission is not required. Therefore, a system 
is needed whereby the air time necessary to transmit images via radio 
frequency systems can be minimized in order to minimize costs to the user. 
SUMMARY OF THE INVENTION 
The present invention relates to a method for transmitting multiresolution 
image data via wireless devices in a radio frequency communication system. 
This method uses wavelet techniques to decompose an image and store the 
image as discrete information blocks in an image storage unit. The 
information blocks include a base image, representing the lowest 
resolution of the image, and one or more image details which, when added 
to the base image, provide increasing levels of resolution. The maximum 
number of levels of resolution into which the image is decomposed may be 
determined by the resolution limits of the image storage unit or by 
artificial limitation on the image storage unit by the transmitting party. 
After establishing a communication channel, the base image is transmitted 
to the image display unit. The image display unit includes means for 
incrementing the resolution of the image by sending image data requests to 
the image storage unit. Additional image details are then transmitted to 
the image display unit. The additional image detail received by the image 
display unit is then combined with the base image, again using wavelet 
techniques, to create a detail image of higher resolution. The image 
display unit may send multiple requests for additional image details. Each 
time, the additional image detail is combined with the previous image to 
provide a new detail image of higher resolution. 
One advantage to decomposing the image into incremental levels of 
resolution is that only the level of resolution necessary to provide the 
agreed quality and intelligibility of the image is transmitted. For 
example, images such as handwritten notes may only require an intermediate 
or low level of image resolution to be intelligible. Bandwidth, power and 
transmission time are saved by transmitting a lower resolution. Images 
such as signatures or fingerprints may require high resolution to be 
effective for the purposes of the party receiving the communication. In 
such cases, the receiving party can request higher levels of resolution. 
The required level of resolution can be determined by either party to the 
communication or the by the resolution limits of the communication 
devices. Representative applications of this concept include transmission 
of images from hand-held cellular radio devices or from laptop computers 
connected via an interface to a hand-held cellular radio devices. 
Therefore, it can be seen that the main advantage of this method will be 
to minimize air time and associated costs of radio frequency communication 
while allowing the users of the devices to determine the optimal level of 
resolution necessary to suit their needs.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, FIG. 1 shows the multiresolution 
transmission system, indicated generally by the numeral 10. The basic 
elements of the multiresolution transmission system 10 are an image 
storage unit generally numbered as 20, an image display unit generally 
numbered as 40, and a communications media 70 providing a communications 
link between the image storage unit 20 and the image display unit 40. 
FIG. 2 shows the image storage unit in greater detail. The image storage 
unit 20 comprises an image input device 22, a main memory 24, an image 
processor 26, a transmitter module 28, a receiver module 30, and a counter 
module 32. The purpose of the image storage unit 20 is to decompose an 
image and store the decomposed image in discrete information blocks. An 
image is input into the main memory 24 via an image input device 22. An 
image input device 22 may include, for example, a disk reader, a scanner, 
or an electronic drawing pad. The image is then decomposed by the image 
processor 26 into discrete information blocks which are stored in the main 
memory 24. The image may be decomposed, for example, by using wavelet 
techniques or other pyramidal image decomposition schemes. Such methods 
are well-known to those skilled in the art and therefore are not described 
herein. For a more detailed explanation of wavelet techniques, see S. G. 
Mallat, A Theory for Multiresolution Signal Decomposition: The Wavelet 
Representation, IEEE Transactions on Pattern Analysis and Machine 
Intelligence, vol. 11, no. 7, pp. 674-693 (July, 1989), which is 
incorporated herein by reference. 
The transmitter module 28 is used to transmit the image data to a remotely 
located image display unit 40. Incoming requests for additional image 
details are directed through the receiver module 30. The main memory 24 is 
then ordered to transmit the requested data. The counter module 32 is also 
updated to maintain count of the number of transmitted information blocks. 
In practice, the image storage unit 20 may also be able to transmit 
additional image details without first receiving an image data request 
from the image display unit 40. This would be accomplished by a separate 
resolution control device incorporated into the image storage unit 20. In 
such instances, the user of the image storage unit 20 could transmit 
additional image details in response to a verbal request from the user of 
the image display unit 40. Control codes in the image data would then 
notify the display unit 40 of the nature of the incoming data. 
The display unit 40, shown in FIG. 3, comprises a receiver module 42, a 
switch 44, a main memory 46, an auxiliary memory 48, an image processor 
50, a display 52, a resolution control device 54, a timer 56, a counter 
module 58, a transmitter module 60, and a reset device 62. Image data 
transmitted by the image storage unit 20 is received at the receiver 
module 42. The switch 44 directs the image data received to the main 
memory 46 or the auxiliary memory 48 as will be described below. In 
general, the original or base image is directed to the main memory 46 
whereas any additional image details requested by the receiving party are 
routed to the auxiliary memory 48. The contents of both the main memory 46 
and the auxiliary memory 48 are combined by the image processor 50 to form 
a recomposed image. The recomposed image, referred to herein as a detail 
image, is then stored in the main memory 48 and directed to the display 
52. 
The resolution control device 54 is used to increment the resolution of the 
image. The resolution control device 54 may, for example, comprise a 
push-button. Pushing the button 54 causes an image data request to be sent 
via the transmitter module 60 and the switch 44 to be set accordingly for 
routing of the incoming data. The counter module 58 keeps a count of the 
number of image data requests sent. The timer 56 is used to delay the 
transmission of the image data request so that multiple presses of the 
button 54 can be accumulated and sent as a single request. The reset 
device 62 is used to reset the counter module 58 and to send a reset 
signal to the image storage unit 20. 
The communications media 70 illustrated in FIG. 1 comprises the means by 
which the image storage unit 20 communicates with the image display unit 
40. While the means of communication is not unique to the present 
invention, it may comprise such methods as wireline, radio frequency, 
infrared, or microwave. Subclasses to the means of communication may be 
any channels which are dedicated for specific roles in the communication 
between the image storage unit 20 and the image display unit 40. In the 
present invention, a radio frequency means of communication is assumed. 
To use the transmission system of the present invention, an image S is 
first decomposed using, for example, wavelet techniques into a base image 
S.sub.0 and a series of image details D.sub.1, D.sub.2, . . . D.sub.n. 
Both the base image S.sub.0 and the image details D.sub.1, D.sub.2, . . . 
D.sub.n are stored in the main memory 24 of the image storage unit 20. The 
image details D.sub.1, D.sub.2, . . . D.sub.n can be recombined with the 
base image S.sub.0 to provide detail images. For example, S.sub.0 combined 
with D.sub.1 would provide a detail image of one resolution level above 
the base image. Similarly, S.sub.0 combined with D.sub.1 and D.sub.2 would 
provide a detail image of two resolution levels above the base image. 
Following this concept, S.sub.0 combined with D.sub.1, D.sub.2, . . . and 
D.sub.n would provide a detail image with the highest available level of 
resolution corresponding to the maximum original level of decomposition. 
The image data stored in the image storage unit 20 is transmitted as 
discrete information blocks to the image display unit 40. When an image 
data request is received from the image display unit 40, the image storage 
unit 20 responds by sending the requested level of image data. Usually, 
only the base image is transmitted in response to the initial image data 
request. This image is most often an order of magnitude smaller than the 
original image. The initial image, however, may also comprise the base 
image and one or more details. In such case, the base image and the 
details are combined at the image storage unit 20 prior to transmission. 
If more detail is required, the recipient can send additional image data 
requests (in real time) for more details. For each additional image data 
request, the image storage unit 20 responds by sending an information 
block containing the next level of image detail. At the image display unit 
40, the image details are recombined with the base image and any previous 
image details received to improve the resolution of the image. If a 
request for multiple image details is received by the image storage unit 
20, the corresponding number of information blocks containing the next 
levels of image detail are transmitted sequentially to the image display 
unit 40 before being recombined with the previous image to further 
increase the resolution. 
Note that the user of the image storage unit 20 may be able to designate 
specific image display units 40 which would be able to receive 
multiresolution image data. In practice, an example of this imposed 
limitation in a radiotelephone communication system would be where the 
user of the image storage unit 20 programs certain authorized telephone 
numbers into the device. As a result, only callers from those specific 
telephone numbers with image display units 40 would have full 
multiresolution image data reception capability. Callers from numbers 
other than those specifically authorized by the user of the image storage 
unit 20 would receive either no image data or image data at a preset level 
of resolution. Thus, the blocking of all image data transmission would 
comprise a security feature to prevent reception of images by unauthorized 
parties. The transmission of only the marginally usable base image to 
unauthorized numbers may also have a similar security effect. However, 
transmission of any higher level of resolution, such as the base image 
combined with a number of image details, may be set by the user of the 
image storage unit 20 in order to limit air time required for 
transmission. The user of the image storage unit 20 may determine that an 
intermediate level of resolution is all that the receiving party needs and 
would transmit only that level. Therefore, this option will assist both in 
the security and in the optimization of bandwidth, power and transmission 
time parameters of image transmission. 
Referring now to FIGS. 4 and 5, the operations of the image storage unit 20 
and image display unit 40 are shown in greater detail. During the call 
initiation, each party to the communication establishes the initial level 
of resolution to be transmitted, such as S.sub.0 or S.sub.0 and D.sub.1, 
etc. The step of establishing the minimum level of resolution is indicated 
by function block 76 (FIG. 4) for the image storage unit 20 and function 
block 91 (FIG. 5) for the image display unit 40. Typically, this level 
would be preset in both the image storage unit 20 and the image display 
unit 40 by the respective user. If the level specified by each party is 
different, the minimum of the two values would be the limiting initial 
parameter. 
In addition to setting a minimum level of resolution, the transmitting 
party may also be able to specify the maximum level of resolution 
available to the receiving party. The maximum level of resolution set by 
the transmitting party may be less than the resolution of the original 
image when initially input into the system. For instance, the image may 
have originally been decomposed into a base image and seven additional 
image details. The transmitting party could limit the maximum available 
resolution to four additional image details. Accordingly, the receiving 
party would only be able to receive a maximum resolution of the base image 
with four additional image details, not the full resolution of the 
original image. This feature is useful where the transmitting party bears 
the cost of the communication and seeks to limit the air time required for 
the image transmission. 
After the minimum level of resolution has been established, image 
transmission starts when an image data request is sent from the image 
display unit 40 to the image storage unit 20 via a dedicated control 
channel DCC such as the fast associated control channel (FACCH) or the 
slow associated control channel (SACCH). Note that a dedicated control 
channel DCC may be utilized for the image data request since no image data 
is sent. An additional factor which would require such a dedicated control 
channel DCC is if a conversation was also in progress during the 
transmission of the imaging sequence. 
Referring now to FIG. 4, the operation of the image storage unit 20 is 
shown. When an image data request is received by the image storage unit 20 
(decision block 77), the image storage unit 20 transmits the requested 
number of information blocks to the image display unit 40. (function block 
80). As generally indicated by function block 78, when the first image 
data request is received, the image storage unit 20 transmits an 
information block containing the base image. Thereafter, the image storage 
unit 20 transmits an information block containing the next level of image 
detail in response to each image data request. If a request for multiple 
information blocks is received, the image storage unit 20 either combines 
the multiple details into a single information block or combines the 
requested number of blocks in a sequential string corresponding to the 
increasing level of detail over the base image (function block 78). As 
indicated by function block 79, each time a request for image data is 
received, the counter module 32 increments the count to ensure that the 
number of information blocks does not exceed the maximum levels of detail 
available for that image. 
After an acceptable image has been transmitted to the image display unit 
40, the receiving party may either send a reset signal to the image 
storage unit 20 or terminate the call. A reset signal indicates that the 
receiving party is satisfied with the previously-transmitted image and is 
now ready to receive a new image from the image storage unit 20. In the 
event of the receipt of a reset signal from the image display unit 40 
(decision block 81), the counter module 32 is reset as indicated by 
function block 82 and the image transmission process restarts. The reset 
signal is significant in that the parties may then initiate the 
transmission of another image, without reestablishing the line of 
communication, if there is another image to be transmitted. Otherwise, if 
the call is terminated (decision block 83), the counter module 32 is reset 
(function block 84) and the call ends. 
Referring now to FIG. 5, the operation of the image display unit 40 is 
shown. The image transmission process begins when the image display unit 
40 sends an image data request to the image storage unit 20 (decision 
block 92). If the image data request is the first such request, decision 
block 93 answered to the affirmative sets the routing switch 44 to main 
memory 46 data routing (function block 94). The counter module 58 is also 
incremented to take count of the number of information blocks requested 
(function block 95). After the image display unit 40 receives the 
requested image data from the image storage unit 20 (function block 96), 
the image data is directed by switch 44 into either the main memory 46 or 
the auxiliary memory 48. For the initial transmission, the switch 44 is 
set to route the data to the main memory 46 as shown in function block 97. 
The main memory 46 also serves as the storage site for the recomposed 
image. From there, the data is processed by the image processor 50, 
restored in the main memory 46, and then routed to the display 52 where 
the initial image S.sub.1 is displayed (function block 98). 
If not satisfied with the resolution after reception of the initial image 
S.sub.1, the receiving party may increase the resolution by pressing the 
button 54 the number of times corresponding to the number of additional 
detail levels desired. Activation of the button 54 (decision block 92) 
leads to three events: the timer 56 is activated, a increment 
corresponding to the extent of activation of the button 54 is registered 
by the counter module 58 (function block 100), and the switch 44 is set to 
route the incoming additional details to the auxiliary memory 48 (function 
block 99). After the specified time-out, the timer 56 commands the counter 
module 58 to send an image data request to the image storage unit 20 
corresponding to the increment registered by the counter module 58. For 
example, if the button 54 is pressed 2 times, a request for two 
information blocks is sent via the dedicated control channel DCC. 
Similarly, if the receiving party had activated the button 54 three times, 
the image storage unit 20 would be requested to transmit three information 
blocks containing additional image details. 
The transmitted information blocks containing the additional image details 
are received by the image display unit 40 (function block 101) and then 
routed by the switch 44 to the auxiliary memory 48 (function block 102). 
From there, the image processor 50 combines the image in the main memory 
46 with the additional image details in the auxiliary memory 48, again 
using wavelet techniques (function block 103). The resulting detail image 
is then stored in the main memory 46 (function block 104) before being 
routed to the display 52 (function block 98). 
The process of incrementally tuning the resolution of the image continues 
as specified in the preceding paragraph until the receiving party is 
satisfied or the maximum number of details has been reached. Note further 
that the maximum number of details available to the receiving party may be 
constrained by the resolution limit of the image storage unit 20 or by an 
artificial limitation in the image storage unit 20 established by the 
transmitting party. In addition, the maximum number of details may be 
constrained by a parameter in the image display unit 40 which limits the 
amount of additional details that may be simultaneously requested by 
multiple activations of the button 54. 
When the receiving party has procured the desired image, that party may 
either terminate the communication (decision block 108) or reset the image 
display unit 40 to receive another image (decision block 105). Even if the 
receiving party chooses to reset the image display unit 40, the 
communication may still be terminated (decision block 108). Resetting of 
the image display unit 40 ends the image transmission sequence for a 
particular image and may be accomplished by either of two means: (1) 
activation of the reset device 62 by the receiving party or (2) by the 
receiving party activating the button 54 more times than the maximum 
number of details that could be simultaneously requested. If an image 
transmission sequence for a particular image is terminated by any of these 
three methods, the counter module 58 is reset (function blocks 106 and 
109) and a signal is transmitted to the image storage unit 20 (function 
blocks 107 and 110) in order to reset the counter module 32. 
The described method for transmitting multiresolution image data 
illustrates the increased level of efficiency which may be realized by 
enabling the parties to the communication to determine the optimal level 
of resolution required when images are communicated. The interactive 
nature of this method also permits the parties to optimize the resolution 
of each image transmitted in a multi-image sequence. Thus, this method 
would result in significantly faster transmission of images, especially if 
the highest level of resolution is not required for the user's needs. 
Therefore, when applied to radio frequency communications, this method 
would serve to increase the efficiency of image communication by reducing 
memory requirements, bandwidth requirements, power consumption, and air 
time. 
The present invention may, of course, be carried out in other specific ways 
than those herein set forth without parting from the spirit and essential 
character of the invention. The present embodiments are, therefore, to be 
considered in all respects as illustrative and not restrictive, and all 
changes coming within the meaning and equivalency range of the appended 
Claims are intended to be embraced therein.