1. ABSTRACT
To eliminate the drawbacks of the conventional fax machines, this paper proposes a
new paperless fax machine equipped with a single-touch panel, replacing the
scanning and the printing units which not only take up most space but also are the
most costly and vulnerable parts. In the proposed paperless fax machine, a received
fax can be displayed and, if necessary, signed directly on the touch panel. The digital
signature is then pasted onto the fax document, which can be sent back or stored in
the memory for future references. Besides, a real handwriting reconstruction is
developed to make the appearance of the digital signature close to real handwriting
on the single-touch panel.
INTRODUCTION
Fax machines, connected to the public switched telephone networks (PSTN),
became popular around the world in the 1980s. In the recent decade, the traditional faxing
has faced increasing competitions from Internet based faxing systems. More and more
people consider fax machines are rarely used home electronics. However, fax machines
survive because they still retain some advantages that the Internet-based systems don’t
have. For example, documents sent and received over PSTN are much securer than those
done on Internet, and faxes are sent in real-time without delays. Most importantly, a
physical signature in the transmission of an official document has a legal effect.
Therefore, even though it is not frequently used, many home users still own a fax
machine.
A conventional fax machine usually consists of an image scanning unit, a printing
unit, a modem, and a telephone set. The image scanning unit converts the content printed
on a physical document into a digital image, the modem sends and receives the fax data
over PSTN analogly, and the printing unit produces a hard copy of the document image
received. Among all units, the image scanning unit and the printing unit not only take up
most space but also are the most costly and vulnerable parts.
Considering the occasions that a home user requires a fax machine, when a fax
document is received, it is quite often the recipient is asked to “sign it, and send it back”.
In this scenario, the fax document received is printed out just for signing it. This causes
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2. the unnecessary paper waste. To improve the efficiency and thus conserve paper, a new
type of fax machines is proposed to simplify the fax responding process stated above. In
this, a single-touch panel is added to a conventional fax machine to replace the scanning
and the printing units. The touch panel is a displaying device as well as an input device,
which can detect the location being touched within the display area. When a fax
document has been received, the recipient can read the content on the touch panel
directly, and if necessary, sign on it by using a stylus. Because of the fax document is
processed in the form of a digital image, the digital signature signed can be pasted onto
the document, as it is signed on the physical fax print-out. Then, the composite document
can be sent back immediately, printed, or, if desired, stored in the memory for future
references. The proposed touch panel fax machines can not only eliminate the drawbacks
from conventional ones, but also comply with the trend of paperless offices.
Furthermore, as a single-touch panel is integrated into a fax machine to deal with
signatures, something else needs to be taken into account. A signature on a fax document
is considered legal because it has been known that each person has a unique signature. If
a real signature is to be replaced by a digital signature signed on the single-touch panel,
the latter should be close to the former as much as possible. Since most of the currently
used touch panels, both the resistive and the capacitive types, are single-touch ones,
which can detect only one location being touched at a time. In this usage, all strokes of
the handwriting will be shown in same thickness, generally one pixel, no matter how hard
or how quick they were written. Therefore, how to make the digital signature close to the
original is a challenge. To make the proposed paperless touch panel fax machine feasible,
a pressure sensitive stylus is adopted to measure the pressure data while signing. In
addition, a handwriting reconstruction algorithm is also proposed to enhance the quality
of handwriting strokes shown on the touch panel.
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3. II. HARDWARE CONFIGURATION
Fig.1: Hardware of a single-touch panel fax machine
As shown in Fig. 1, the touch panel fax machine is composed of a modem
module, a micro-controller unit (MCU), a touch panel, a storage unit, an analog-to-digital
converter (ADC) module and a pressure sensitive stylus.
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4. The modem module, which is connected to MCU, is responsible for sending and
receiving faxes. Currently, the analog Group 3 (G3) fax machines connected to PSTN are
the most common faxing devices that have been in use for many years.
Since the paper less fax machine processes fax documents as digital images it is
required to convert the formats between G3 fax images and computer images (for
example, TIFF, BMP or JPG formats) in the MCU, after receiving or before sending
faxes. Besides, MCU manages the time synchronization with the fax machine at the other
end of the telephone line, displays the fax documents on the touch panel, stores the faxes
received in the storage, and accomplishes the handwriting reconstruction.
The touch panel is considered a peripheral device to MCU. It displays the fax
documents and accepts the handwriting signatures. The handwriting reconstruction
algorithm reconstructs the signature in real-time during a user’s signing act. Then, MCU
pastes the signature onto the fax document received. The composed document is shown
on the touch panel, ready to be sent back or saved in the storage unit. The storage unit,
which is also a peripheral device to MCU as shown in Fig. 1, is a removable read/write
memory for storing fax documents. There are three built-in folders in the storage unit, a
receiving folder, a composed folder and a transmitting folder.
The tip of the pressure sensitive stylus is connected to a pressure sensor through a
spring coil. During a signing act, the pressure at the tip is measured, digitalized by an
ADC, and finally sent to MCU for subsequent processing.
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5. III. OPERATING PROCEDURES
The proposed touch panel fax machine can operate in one of the three modes:
1. The fax receiving mode
2. The browsing and handwriting mode
3. The fax transmitting mode
A. Fax receiving mode
In the fax receiving mode, if the touch panel fax machine has received an
incoming fax, MCU converts the fax image to a popular image format used on
computers, and stores it in the receiving folder of the storage unit. At the mean time, the
touch panel shows the status to notify an incoming fax.
B. Browsing and handwriting mode
In the browsing and handwriting mode, any fax document stored in the folders of
the storage unit can be retrieved and displayed on the touch panel by MCU. Besides, the
user may sign on the touch panel in this mode. The data of the signing act are collected
from both the pressure sensitive stylus and the touch panel, and fed to the handwriting
reconstruction algorithm. Finally, the signature reconstructed is pasted on the fax
document, which can be shown on the touch panel, or if desired, sent back to original
sender or saved in the storage unit.
C. Fax transmitting mode
In the fax transmitting mode, MCU may retrieve any document from the storage
unit and display it on the touch panel. If the user wants to send out the document, MCU
converts it to the fax image format and hands it to modem module to transmit.
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6. IV. HANDWRITING RECONSTRUCTION
Fig.2: Signals flowing
In this section, the handwriting reconstruction algorithm, which could turn an
user’s signing act into a digital signature as close to the original as possible, is
introduced.
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7. During the signing act, both the data from the pressure sensitive stylus and the
touch panel are sampled by using timer interrupts in MCU. The readings from the
pressure sensitive stylus indicate how hard the user pushes the pen tip, and readings from
the touch panel show the locations where the pen touches. The sampled analog values are
then converted into digital values by ADCs and buffered in two FIFO queues in order, as
shown in Fig. 2. There are some issues to be addressed in data collection and processing.
A. Resolution of touch panels
A single-touch panel is composed of two major parts, an LCD screen for
displaying and a thin touch layer for inputs. Although the touch layer resides atop the
LCD screen, the ways to define resolutions of these two parts are different. The
resolution of an LCD screen is specified explicitly by enumerating the number of pixels
both in width and height. However, since a touch panel digitizes the analog readings by
using ADCs, the resolution of the touch panel is determined by the number of bits used in
the ADCs adopted. There are two ADCs used in a touch panel, one for horizontal and the
other for vertical direction respectively. For example, if a 10-bit ADC is used in one
direction, the resolution would be 1024 in that direction. Practically, the resolution of the
touch panel is higher than that of the LCD screen.
B. Signal synchronizations
In this, only the widely used single-touch panels are adopted. Single-touch panels
can response exact one location that is being touched at a time. The coordinates of the
touched location are digitalized and queued in a FIFO, waiting to be processed by MCU.
In most applications that use touch panels, the locations touched are the only parameter
required, whereas the pressures and the time duration are neglected. However, in order to
reconstruct a signature, both data of the locations and the pressures versus time during the
signing act are necessary.
The location and pressure data are collected by using timer interrupts in MCU.
The interrupt intervals are set to be constant. Therefore, the speed of the signing act can
be derived from the location data collected, in other words, how fast the user signs can be
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8. determined. If the signer makes a stop in the middle of signing, the location data will
remain unchanged, but the pressure may not. According to changes in the pressure data
measured, handwriting reconstruction algorithm can generate the strokes with different
thickness.
C. Pressures and Strokes
The single-touch panel detects and responses one location at a time, even though
there is actually an area of the panel is being touched. In order to reconstruct the different
stroke thickness as that in a real signature, the pressure data collected are analyzed. To
simplify the implementation, only positive pressures are considered valid. A simple two-
step calibration procedure for the stylus is performed before writing. First, press the pen
tip all the way down and record the pressure reading as PF. Then, let the tip off the touch
panel and record the pressure again as PE. During the signature reconstruction process,
the pressure ratio is used in the process. For any measured pressure P, the pressure ratio
(PR) is calculated as:
PR = (P − PE)/ (PF − PE).
Fig. 3(b) is the position data collected from a real handwriting stroke shown in
Fig. 3(a). While looking closer into the trajectory in Fig. 3(b), there is no way to know
how long it took and whether the pen stopped during the writing act. Fig. 3(c) shows the
corresponding pressure ratios of the same stroke over time. In this figure, it can be found
that starting from the beginning of the stroke (point A), the pressure ratio increases
rapidly, and then gradually decreases to zero at the end of the stroke (point B).
Comparing to the real stroke in Fig. 3(a), a relationship is found: at any point of the
trajectory, the thickness of the stroke is proportional to the pressure ratio measured at the
pixel. This finding is used to reconstruct the signature.
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9. Fig. 3 (a) Handwriting stroke (b) Position trajectory (c) Pressure ratio
D. Handwriting Reconstruction
Follow the relationship found in the above section, handwriting reconstruction
can be made. Intuitively, as shown in Fig. 4(a), a line extension method, which generates
the thickness of the stroke, may be applied on the laterally orthogonal directions of any
pixel in the trajectory. However, there will be a defect in the stroke, if a sharp corner
exists in the trajectory. Alternatively, a circle extension is adopted to replace the line
extension, as shown in Fig. 4(b). Though the strokes generated by circle extension
method are rugged, they can be smoothed by making sampling time intervals smaller.
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10. Fig. 4 (a) Line extension (b) Circle extension
To make a summary, the handwriting reconstruction algorithm includes:
(1) Sample the position trajectories and the corresponding pressures of all strokes.
(2) Determine the radius of the circle for each of the extension point on the trajectories
according to the pressure ratio calculated.
(3) Determine the pixel coordinates of the extension point on the touch panel, on which a
circle is generated and placed to form a handwriting image.
As shown in Fig. 5(a), the circle extension method is applied according to the
position trajectory in Fig. 3(b) and the pressure ratio in Fig. 3(c). Fig. 5(b) presents the
reconstructed result by sampling the stroke extending points densely.
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11. Fig. 5 (a) Circle extension applied (b) Real handwriting effects
Examples of signature trajectories are shown in both Fig. 6(a) and Fig. 7(a). They
were signed both in Chinese and English. Obviously, the thicknesses of the strokes in
both Fig. 6(a) and Fig. 7(a) were one pixel. Fig. 6(b) and Fig. 7(b) show the result
signature strokes generated from the handwriting reconstruction algorithm. Compare Fig.
6(b) to Fig 6(a), and also Fig. 7(b) to Fig. 7(a). The paperless fax machine is proven to be
feasible.
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12. Fig. 6 (a) Single-touch panel input (b) Handwriting reconstruction result
Fig. 7 (a) Single-touch panel input (b) Handwriting reconstruction result
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13. V. CONCLUSION
 By using handwriting reconstruction algorithm the signature can be exactly
reproduced.
 Circular extension is best method for handwriting reconstruction.
 Consumption of paper can be reduced.
 Transmitted and received fax documents can be stored into memory.
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14. VI. REFERENCES
 http://ieee.ieeexplore.org/
 ITU-T.37: Procedures for the Transfer of Facsimile Data via Store-and forward on
the Internet, 1998.
 ITU-T.38: Procedures for Real-time Group 3 Facsimile Communication over IP
Networks, Amendment 1, 1999.
 Handwriting Recognition Group, <hwr.nici.kun.nl>, May, 2008.
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15. VI. REFERENCES
 http://ieee.ieeexplore.org/
 ITU-T.37: Procedures for the Transfer of Facsimile Data via Store-and forward on
the Internet, 1998.
 ITU-T.38: Procedures for Real-time Group 3 Facsimile Communication over IP
Networks, Amendment 1, 1999.
 Handwriting Recognition Group, <hwr.nici.kun.nl>, May, 2008.
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