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                                                                   EXHIBIT 10.20

                            STOCK PURCHASE AGREEMENT


               THIS STOCK PURCHASE AGREEMENT (this "AGREEMENT") is entered into
as of this 22nd day of December 1999 (the "EFFECTIVE DATE") by and among
PROGRAPH SYSTEMS, INC., a Pennsylvania corporation (the "COMPANY"), and JOSEPH
J. WHANG (the "PURCHASER").

               WHEREAS, the Purchaser desires to purchase 1,018,278 shares of
the Company's common stock (the "COMMON STOCK") (such number of shares owned by
the Purchaser and any shares of capital stock of the Company acquired by the
Purchaser as a result of any subdivision, combination or reclassification of
outstanding shares of Common Stock into a greater or smaller number of shares,
recapitalization, reorganization, reclassification of shares, stock dividend or
like event (collectively, "RECAPITALIZATION EVENTS"), being hereinafter referred
to as the "SHARES");

               NOW, THEREFORE, in consideration of the mutual covenants and
representations herein set forth, the parties hereto hereby agree as follows:

               1. PURCHASE OF SHARES. As of the Effective Date and subject to
the terms and conditions of this Agreement, Purchaser hereby purchases from the
Company, and Company hereby sells to Purchaser, an aggregate of 1,018,278 shares
of the Company's common stock at an aggregate purchase price of $1,048,826.34
(the "PURCHASE PRICE") or $1.03 per Share (the "PURCHASE PRICE PER SHARE").

               2. PAYMENT OF PURCHASE PRICE; CLOSING.

                      (a) DELIVERIES BY PURCHASER. Purchaser hereby delivers to
the Company the full Purchase Price by signing and delivery the form of
promissory note attached as Exhibit A (the "PROMISSORY NOTE"). Purchaser also
hereby delivers to the Company two (2) copies of the Pledge Agreement in the
form of Exhibit B (the "PLEDGE AGREEMENT") a blank Stock Power and Assignment
Separate from Stock Certificate in the form of Exhibit C attached hereto (the
"STOCK POWERS"), both executed by Purchaser.

                      (b) DELIVERIES BY THE COMPANY. Upon its receipt of the
entire Purchase Price and all the documents to be executed and delivered by
Purchaser to the Company under Section 2(a), the Company will issue a duly
executed stock certificate evidencing the Shares registered in Purchaser's name
in accordance with Section 14 with such certificate to be placed in escrow as
provided in the Pledge Agreement.

               3. REPRESENTATIONS AND WARRANTIES OF PURCHASER. Purchaser
represents and warrants to the Company that:

                      (a) Purchase for Own Account for Investment. Purchaser is
purchasing the Shares for Purchaser's own account for investment purposes only
and not with a view to, or for sale in connection with, a distribution of the
Shares within the meaning of the Securities Act of 1933, as amended (the "1933
ACT"). Purchaser has no present intention of selling or otherwise disposing of
all or any portion of the Shares and no one other than Purchaser has any
beneficial ownership of any of the Shares.


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                      (b) Access to Information. Purchaser has had access to all
information regarding the Company and its present and prospective business,
assets, liabilities and financial condition that Purchaser reasonably considers
important in making the decision to purchase the Shares, and Purchaser has had
ample opportunity to ask questions of the Company's representatives concerning
such matters and this investment.

                      (c) Understanding of Risks. Purchaser is fully aware of:
(i) the highly speculative nature of the investment in the Shares; (ii) the
financial hazards involved; (iii) the lack of liquidity of the Shares and the
restrictions on transferability of the Shares (e.g., that Purchaser may not be
able to sell or dispose of the Shares or use them as collateral for loans); (iv)
the qualification and backgrounds of the management of the Company; and (v) the
tax consequences of investment in the Shares.

                      (d) Purchaser's Qualifications. Purchaser has a
preexisting personal or business relationship with the Company and/or certain of
its officers and/or directors of a nature and duration sufficient to make
Purchaser aware of the character, business acumen and general business and
financial circumstances of the Company and/or such officers and directors. By
reason of Purchaser's business or financial experience, Purchaser is capable of
evaluating the merits and risks of this investment, has the ability to protect
Purchaser's own interests in this transaction and is financially capable of
bearing a total loss of this investment. Purchaser is an "accredited investor"
as defined under Rule 501 promulgated under the Securities Act of 1933, as
amended.

                      (e) No General Solicitation. At no time was Purchaser
presented with or solicited by any publicly issued or circulated newspaper,
mail, radio, television or other form of general advertising or solicitation in
connection with the offer, sale and purchase of the Shares.

                      (f) Compliance with Securities Laws. Purchaser understands
and acknowledges that, in reliance upon the representations and warranties made
by Purchaser herein, the Shares are not being registered with the Securities and
Exchange Commission ("SEC") under the 1933 Act, but instead are being issued
under an exemption or exemptions from the registration and qualification
requirements of the 1933 Act or applicable state securities laws which impose
certain restrictions on Purchaser's ability to transfer the Shares.

                      (g) Restrictions on Transfer. Purchaser understands that
Purchaser may not transfer any Shares unless such Shares are registered under
the 1933 Act or qualified under the Law or unless, in the opinion of counsel to
the Company, exemptions from such registration and qualification requirements
are available. Purchaser understands that only the Company may file a
registration statement with the SEC and that the Company is under no obligation
to do so with respect to the Shares. Purchaser has also been advised that
exemptions from registration and qualification may not be available or may not
permit Purchaser to transfer all or any of the Shares in the amounts or at the
time proposed by Purchaser.

                      (h) Rule 144. In addition, Purchaser has been advised that
SEC Rule 144 promulgated under the 1933 Act, which permits certain limited sales
of unregistered securities, is not presently available with respect to the
Shares and, in any event, currently requires that the Shares be held for a
minimum of one year, and in certain cases two years, after


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they have been purchased and paid for (within the meaning of Rule 144), before
they may be resold under Rule 144. Purchaser understands that Rule 144 may
indefinitely restrict transfer of the Shares so long as Purchaser remains an
"affiliate" of the Company and "current public information" about the Company
(as defined in Rule 144) is not publicly available.

               4. RIGHTS AS STOCKHOLDER. Subject to the terms and conditions of
this Agreement, Purchaser will have all of the rights of a stockholder of the
Company with respect to the Shares from and after the date that Purchaser
delivers payment of the Purchase Price until such time as Purchaser disposes of
the Shares or the Company and/or its assignee(s) exercise(s) the repurchase
options hereunder. Upon an exercise of any right to repurchase hereunder,
Purchaser will have no further rights as a holder of the Shares so purchased
upon such exercise, except the right to receive payment for the Shares so
purchased in accordance with the provisions of this Agreement, and Purchaser
will promptly surrender the stock certificate(s) evidencing the Shares so
purchased to the Company for transfer or cancellation.

               5. RESTRICTIVE LEGEND AND STOP-TRANSFER ORDERS.

                (a)     LEGEND. Purchaser understands and agrees that the
                        Company will place the legend set forth below or a
                        similar legend on any stock certificate(s) evidencing
                        the Shares, together with any other legends that may be
                        required by state or federal securities laws, the
                        Company's Articles of Incorporation or Bylaws, any other
                        agreement between Purchaser and the Company or any
                        agreement between Purchaser and any third party:

                THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER
                THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE
                SECURITIES LAWS OF ANY STATE. THESE SECURITIES ARE SUBJECT TO
                RESTRICTIONS ON TRANSFERABILITY AND RESALE AND MAY NOT BE
                TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE ACT AND
                APPLICABLE STATE SECURITIES LAWS, PURSUANT TO REGISTRATION OR
                EXEMPTION THEREFROM.

                (b)     STOP-TRANSFER INSTRUCTIONS. Purchaser agrees that, in
                        order to insure compliance with the restrictions imposed
                        by this Agreement, the Company may issue appropriate
                        "stop-transfer" instructions to its transfer agent, if
                        any, and if the Company transfers its own securities, it
                        may make appropriate notations to the same effect in its
                        own records.

                (c)     REFUSAL TO TRANSFER. The Company will not be required
                        (i) to transfer on its books any Shares that have been
                        sold or otherwise transferred in violation of any of the
                        provisions of this Agreement or (ii) to treat as owner
                        of such Shares, or to accord the right to vote or pay
                        dividends, to any purchaser or other transferee to whom
                        such Shares have been so transferred.

               6. MARKET STANDOFF AGREEMENT. Purchaser agrees in connection with
any registration of the Company's securities under the 1933 Act that, upon the
request of the


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Company or the underwriters managing any registered public offering of the
Company's securities, Purchaser will not sell or otherwise dispose of any Shares
without the prior written consent of the Company or such managing underwriters,
as the case may be, for a period of time (not to exceed 180 days) after the
effective date of such registration requested by such managing underwriters and
subject to all restrictions as the Company or the managing underwriters may
specify for employee-shareholders generally.

               7. COMPLIANCE WITH LAWS AND REGULATIONS. The issuance and the
transfer of the Shares will be subject to and conditioned upon compliance by the
Company and Purchaser with all applicable state and federal laws and regulations
and with all applicable requirements of any stock exchange or automated
quotation system on which the Company's common stock may be listed or quoted at
the time of such issuance or transfer.

               8. SUCCESSORS AND ASSIGNS. The Company may assign any of its
rights under this Agreement, including its rights to repurchase Shares
hereunder. This Agreement will be binding upon and inure to the benefit of the
successors and assigns of the Company. Subject to the restrictions on transfer
herein set forth, this Agreement will be binding upon Purchaser and Purchaser's
heirs, executors, administrators, successors and assigns.

               9. GOVERNING LAW; SEVERABILITY. This Agreement will be governed
by and construed in accordance with the internal laws of the Commonwealth of
Pennsylvania, excluding that body of laws pertaining to conflict of laws. If any
provision of this Agreement is determined by a court of law to be illegal or
unenforceable, then such provision will be enforced to the maximum extent
possible and the other provisions will remain fully effective and enforceable.

               10. NOTICES. Any notice required or permitted hereunder will be
given in writing and will be deemed effectively given upon personal delivery,
three (3) days after deposit in the United States mail by certified or
registered mail (return receipt requested), one (1) business day after its
deposit with any return receipt express courier (prepaid), or one (1) business
day after transmission by telecopier, addressed to the other party at its
address (or facsimile number, in the case of transmission by telecopier) as
shown below its signature to this Agreement, or to such other address as such
party may designate in writing from time to time to the other party.

               11. FURTHER INSTRUMENTS. The parties agree to execute such
further instruments and to take such further action as may be reasonably
necessary to carry out the purposes and intent of this Agreement.

               12. HEADINGS. The captions and headings of this Agreement are
included for ease of reference only and will be disregarded in interpreting or
construing this Agreement. All references herein to Sections will refer to
Sections of this Agreement.

               13. ENTIRE AGREEMENT, AMENDMENT. This Agreement, together with
Employment Agreement and Proprietary Information and Inventions Assignment
Agreement, and all its Exhibits, constitutes the entire agreement and
understanding of the parties with respect to the subject matter of this
Agreement, and supersedes all prior understandings and agreements, whether oral
or written, between the parties hereto with respect to the specific subject
matter hereof. This Agreement may not be modified, amended, terminated or any
provision hereof


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waived in whole or in part except by a written agreement signed by the Company
and the Purchaser

               14. TITLE TO SHARES. The exact spelling of the name(s) under
which Purchaser will take title to the Shares is:

                                  JOSEPH WHANG

               15. WAIVERS. No waiver hereunder shall be deemed a waiver of any
subsequent breach or default of the same or a similar nature.

               16. HEADINGS. Headings are for convenience only and are not
deemed to be part of this Agreement.

               17. COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original, and all of which taken
together shall constitute one instrument.


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               IN WITNESS WHEREOF, this Agreement has been executed by the
undersigned as of the date and year first above written.



                                    COMPANY:



                                    PROGRAPH SYSTEMS, INC.





                                    By /s/ MARC OLIN
                                      -------------------------------
                                             Marc Olin, President







                                    PURCHASER:



                                     /s/ JOSEPH WHANG
                                    ---------------------------------
                                             JOSEPH WHANG





I, ________________, spouse of Joseph Whang, have read and hereby approve the
foregoing Agreement. In consideration of the Company's granting my spouse the
right to purchase the Shares as set forth in the Agreement, I hereby agree to be
bound irrevocably by the Agreement and further agree that any community property
or similar interest that I may have in the Shares shall hereby be similarly
bound by the Agreement. I hereby appoint my spouse my attorney-in-fact with
respect to any amendment or exercise of any rights under the Agreement.





                                    ---------------------------------
                                          Spouse of Joseph Whang

                                LIST OF EXHIBITS


<TABLE>
<S>            <C>
Exhibit A:     Promissory Note
Exhibit B:     Pledge Agreement
Exhibit C:     Stock Power and Assignment Separate from Stock Certificate
</TABLE>


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                                                                       EXHIBIT C


                           STOCK POWER AND ASSIGNMENT

                            SEPARATE FROM CERTIFICATE

               FOR VALUE RECEIVED and pursuant to that certain Stock Purchase
Agreement dated as of December 22 1999 and Pledge Agreement dated as of December
22, 1999 (the "Agreements"), the undersigned hereby sells, assigns and transfers
unto _______________, ___________ shares of the common stock of Prograph
Systems, Inc., a Pennsylvania corporation (the "Company"), standing in the
undersigned's name on the books of the Company represented by Certificate No(s).
___ delivered herewith, and does hereby irrevocably constitute and appoint the
Secretary of the Company as the undersigned's attorney-in-fact, with full power
of substitution, to transfer said stock on the books of the Company. THIS
ASSIGNMENT MAY ONLY BE USED AS AUTHORIZED BY THE AGREEMENTS.



Dated:______________________



                                    PURCHASER


                                    -------------------------------
                                    (Signature)


                                    -------------------------------
                                    (Please Print Name)


                                    -------------------------------
                                    (Spouse's Signature, if any)


                                    -------------------------------
                                    (Please Print Spouse's Name)