Patent Publication Number: US-2003228016-A1

Title: Image encryption apparatus, image encryption method, decryption apparatus, decryption method, program, and storage medium

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to an image encryption apparatus and method for encrypting an image, a decryption apparatus and method for decrypting an encrypted image, a program, and a storage medium.  
       BACKGROUND OF THE INVENTION  
       [0002] Upon delivering/distributing high-resolution color image data, an encryption/decryption technique is used to appropriately limit users.  
       [0003] However, in order to use an encrypted image, i.e., display it, print it out, and so forth, that image must be decrypted in advance, and an encrypted image cannot be directly used in a general image processing apparatus/image processing software program. In general, since decryption requires a dedicated software program, a user must install this program, learn its operation method, and execute decryption every time he or she uses an encrypted image. Also, users of a decrypted image cannot be limited.  
       [0004] The present invention has been made in consideration of the above problems, and has as its object to provide an image encryption apparatus, image encryption method, program, and storage medium, which can limit users of an image, and allow decryption without requiring any special software program or apparatus.  
       [0005] It is another object of the present invention to provide a decryption apparatus, decryption method, program, and storage medium, which can easily decrypt an encrypted image without requiring any special software program or apparatus.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention has been made in consideration of the above situation, and has as its object to reduce the influence of gaps between photoelectric conversion element arrays on a read image by a simple and inexpensive arrangement.  
       [0007] According to the present invention, the foregoing object is attained by providing an image encryption apparatus for encrypting an image, comprising: first conversion means for converting a color signal group that forms a first image into a color signal group, that is independent of a device supplying the first image, on the basis of a first profile; and second conversion means for converting the color signal group, converted by the first conversion means into a color signal group that forms a second image different from the first image, on the basis of a second profile used for encryption which is different from encryption by the first profile.  
       [0008] According to the present invention, a decryption apparatus for decrypting an image encrypted by the above-described image encryption apparatus comprises: conversion means for converting the second image into a color signal, that is independent of the device supplying the first image, on the basis of the second profile; and output means for generating output image data on the basis of the color signal group converted by the conversion means, and outputting the output image data to an image forming apparatus.  
       [0009] According to the present invention, the foregoing object is attained by providing an image encryption method for encrypting an image, comprising: a first conversion step of converting a color signal group that forms a first image into a color signal group, that is independent of a device supplying the first image, on the basis of a first profile; and a second conversion step of converting the color signal group, converted in the first conversion step into a color signal group that forms a second image different from the first image, on the basis of a second profile used for encryption which is different from encryption by the first profile.  
       [0010] According to the present invention, a decryption method for decrypting an image encrypted by the above-described image encryption method comprises: a conversion step of converting the second image into a color signal, that is independent of the device supplying the first image, on the basis of the second profile; and an output step of generating output image data on the basis of the color signal group converted in the conversion step, and outputting the output image data to an image forming apparatus.  
       [0011] According to the present invention, the foregoing object is attained by providing an image encryption apparatus for encrypting an image, comprising: first conversion means for converting a color signal group that forms a first image into a first color signal group, which is independent of a device, on the basis of a first profile; second conversion means for converting the first color signal group into a color signal group on a color space of an image forming apparatus on the basis of a second profile which is different from the first profile; third conversion means for converting the color signal group converted by the second conversion means into a second color signal group on the basis of a third profile, which is used for encryption which is different from encryption by the first and the second profiles; and fourth conversion means for converting the second color signal group into a color signal group that forms a second image by executing inverse conversion of the conversion by the first conversion means on the basis of the first profile.  
       [0012] According to the present invention, a decryption apparatus for decrypting an image encrypted by the above-described image encryption apparatus comprises: fourth conversion means for converting the color signal group which forms the second image into a third color signal group on the basis of the first profile; fifth conversion means for converting the third signal group into a color signal group on the color space of the image forming apparatus on the basis of the third profile; and output means for generating output image data based on the color signal group converted by the fifth conversion means, and outputting the output image data to the image forming apparatus.  
       [0013] According to the present invention, the foregoing object is attained by providing a first conversion step of converting a color signal group that forms a first image into a first color signal group, which is independent of a device, on the basis of a first profile; a second conversion step of converting the first color signal group into a color signal group on a color space of an image forming apparatus on the basis of a second profile which is different from the first profile; a third conversion step of converting the color signal group converted in the second conversion step into a second color signal group on the basis of a third profile, which is used for encryption which is different from encryption by the first and the second profiles; and a fourth conversion step of converting the second color signal group into a color signal group that forms a second image by executing inverse conversion of the conversion in the first conversion step on the basis of the first profile.  
       [0014] According to the present invention, a decryption method for decrypting an image encrypted by the above-described image encryption method comprises: a fourth conversion step of converting the color signal group which forms the second image into a third color signal group on the basis of the first profile; a fifth conversion step of converting the third signal group into a color signal group on the color space of the image forming apparatus on the basis of the third profile; and an output step of generating output image data based on the color signal group converted in the fifth conversion step, and outputting the output image data to the image forming apparatus.  
       [0015] According to the present invention, the foregoing object is attained by providing an image encryption apparatus for encrypting an image, comprising: first conversion means for converting a color signal group that forms a first image into a color signal group on a color space of an image forming apparatus on the basis of a first profile; and second conversion means for converting the color signal group converted by the first conversion means into a color signal group that forms a second image different from the first image, on the basis of a second profile which is used for encryption which is different from encryption by the first profile.  
       [0016] According to the present invention, a decryption apparatus for decrypting an image encrypted by the above-described image encryption apparatus comprises: conversion means for converting the second image into a color signal group on the color space of the image forming apparatus on the basis of the second profile; and output means for generating output image data on the basis of the color signal group converted by the conversion means, and outputting the output image data to the image forming apparatus.  
       [0017] According to the present invention, the foregoing object is attained by providing a first conversion step of converting a color signal group that forms a first image into a color signal group on a color space of an image forming apparatus on the basis of a first profile; and a second conversion step of converting the color signal group converted in the first conversion step into a color signal group that forms a second image different from the first image, on the basis of a second profile which is used for encryption which is different from encryption by the first profile.  
       [0018] According to the present invention, a decryption method for decrypting an image encrypted by the above-described image encryption method comprises: a conversion step of converting the second image into a color signal group on the color space of the image forming apparatus on the basis of the second profile; and an output step of generating output image data on the basis of the color signal group converted in the conversion step, and outputting the output image data to the image forming apparatus.  
       [0019] Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
     [0021]FIG. 1 is a block diagram showing the functional arrangement of an image processing apparatus used in the first embodiment of the present invention, and also the arrangement with its peripheral devices;  
     [0022]FIG. 2 is a block diagram showing the functional arrangement of an image processing unit  120 ;  
     [0023]FIG. 3 is a block diagram showing the functional arrangement of an input profile conversion unit  201 ;  
     [0024]FIG. 4 illustrates gamma conversion executed by a gamma converter  301 ;  
     [0025]FIG. 5 is a block diagram showing another functional arrangement of the input profile conversion unit  201 ;  
     [0026]FIG. 6 is a block diagram showing the functional arrangement of an image encryption apparatus according to the first embodiment of the present invention;  
     [0027]FIG. 7 shows an example of a setup user interface (GUI) of a typical color printer program, which is displayed on a display unit  1705 ;  
     [0028]FIG. 8 is a block diagram showing the basic arrangement of an image encryption apparatus according to the first embodiment of the present invention;  
     [0029]FIG. 9 is a flow chart of an image encryption process executed by the image encryption apparatus according to the first embodiment of the present invention;  
     [0030]FIG. 10 is a block diagram showing the functional arrangement of an image encryption apparatus according to the second embodiment of the present invention;  
     [0031]FIG. 11 is a block diagram showing the basic arrangement of an image encryption apparatus according to the second embodiment of the present invention;  
     [0032]FIG. 12 is a flow chart of an image encryption process executed by the image encryption apparatus according to the second embodiment of the present invention;  
     [0033]FIG. 13 is a block diagram showing the basic arrangement of the image processing apparatus used in the first embodiment of the present invention;  
     [0034]FIG. 14 is a block diagram showing the functional arrangement of an image processing apparatus according to the third embodiment of the present invention;  
     [0035]FIG. 15 is a block diagram showing the functional arrangement of an image encryption apparatus according to the third embodiment of the present invention;  
     [0036]FIG. 16 is a block diagram showing the basic arrangement of an image encryption apparatus according to the third embodiment of the present invention; and  
     [0037]FIG. 17 is a flow chart of an image encryption process executed by the image encryption apparatus according to the third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0038] Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.  
     First Embodiment  
     [0039] This embodiment will explain an image encryption apparatus which encrypts an image to be input to an image processing apparatus that receives an externally input image, and inputs an output instruction to an image output apparatus, which prints out the image on a print medium such as a paper sheet, OHP sheet, or the like. Of course, when an image to be input to the image processing apparatus is encrypted, the image processing apparatus cannot output satisfactory image data to the image output apparatus. Hence, this embodiment will explain a case wherein the image processing apparatus executes a decryption process for decrypting an image encrypted by the image encryption apparatus.  
     [0040] A general image processing apparatus used upon realizing advanced color reproduction will be explained first. FIG. 1 shows the functional arrangement of the image processing apparatus, and also the arrangement with its peripheral devices. Reference numeral  100  denotes an image processing apparatus which comprises an image input unit  110 , image processing unit  120 , and image output unit  130  (to be described later).  
     [0041] Reference numeral  101  denotes an image server which can make data communications with the image processing apparatus  100  via a network. Reference numeral  102  denotes an image recording medium such as a CD-ROM, DVD-ROM, or the like. Reference numeral  103  denotes an image output apparatus which prints an image, text, and the like on a print medium such as a paper sheet, OHP sheet, or the like on the basis of print data output from the image processing apparatus  100 , and outputs the printed print medium.  
     [0042] Image data loaded from the image server  101  on the network or the image recording medium  102  to the image processing apparatus  100  is input via the image input unit  100 , undergoes a color process by the image processing unit  120 , and is then output as print data via the image output unit  130 . The image output apparatus  103  prints an image, text, and the like on a print medium on the basis of this print data, and outputs the print medium. Typically, the image output apparatus  103  is a color printer which forms an image on a sheet surface using cyan (to be abbreviated as C hereinafter), magenta (to be abbreviated as M hereinafter), yellow (to be abbreviated as Y hereinafter), and black (to be abbreviated as K hereinafter) inks or toners.  
     [0043]FIG. 13 shows the basic arrangement of the image processing apparatus. Reference numeral  1701  denotes a CPU which controls the overall apparatus using programs and data stored in a RAM  1702  and ROM  1703 , and also executes respective image processes to be described later. Reference numeral  1702  denotes a RAM which has an area for temporarily storing program and data loaded from an external storage device  1707  and recording medium drive  1710 , and various data of processes in progress, and also a work area used when the CPU  1701  executes respective processes.  
     [0044] Reference numeral  1703  denotes a RAM which stores programs and data used to control the overall apparatus. Reference numeral  1704  denotes a console, which includes a keyboard and a pointing device such as a mouse or the like, and can input various instructions to the apparatus. Reference numeral  1705  denotes a display unit which comprises a CRT or liquid crystal display screen, and displays various GUIs, images, and text. Reference numeral  1706  denotes an I/F unit which connects to the image output apparatus  103 , and is used to output data to the image output apparatus  103 .  
     [0045] Reference numeral  1707  denotes an external storage device which saves an OS, a program (image processing program  1708 ) required to execute various image processes to be described later, and various profiles  1709  to be described later. Note that the image processing program  1708  includes a color management system (to be abbreviated as CMS hereinafter), and a color printer control program. Reference numeral  1710  denotes a recording medium drive, which reads various data including an image from the image recording medium  102 , and outputs them to the external storage device  1707  and RAM  1702 . Reference numeral  1711  denotes an I/F unit, which connects to the network, and is used to make data communications with the image server  101 . Reference numeral  1712  denotes a bus used to interconnect the aforementioned units.  
     [0046]FIG. 2 shows the functional arrangement of the image processing unit  120 , and processes in respective units which form the image processing unit  120  will be explained below. Color signals R, G, and B that form image data are converted into output color signals C, M, Y, and K by an input profile conversion unit  201 , input chromatic adaptation conversion unit  202 , input color space conversion unit  203 , color mapping unit  203 , output color space conversion unit  205 , output chromatic adaptation conversion unit  206 , output profile conversion unit  207 , and color separation conversion unit  208 .  
     [0047] The input profile conversion unit  201  converts input color signals R, G, and B into color signals X, Y, and Z on a CIEXYZ color space on the basis of a profile which represents the color reproduction characteristics of an input device, that is stored in an input profile storage unit  209 . In general, as a default of profiles (to be referred to as input profiles hereinafter) stored in the input profile storage unit  209 , sRGB specified by IEC61966-2-1 is used. In this case, the input profile conversion unit  201  converts input color signals R, G, and B into color signals X, Y, and Z on the CIEXYZ color space independent of image input/output devices (to be referred to as devices hereinafter) using a conversion formula based on sRGB. Use of sRGB as an input profile assumes that image data is based on sRGB.  
     [0048] The input chromatic adaptation conversion unit  202  corrects the influence of chromatic adaptation due to a different observation environment by a known method. For example, in environments of D65 and D50 white points, colors have different appearances even when color signals X, Y, and Z remain the same. Hence, the color signals are corrected to obtain the same appearance.  
     [0049] More specifically, color signals X, Y, and Z of an input image as tristimulus values in an observation environment are converted into tristimulus values X′, Y′, and Z′ that can obtain the same color appearance in a standard observation environment. In general, conversion based on the von Kries rules, chromatic adaptation model, color appearance model, or the like is used. When adaptation is not taken into consideration, the process of the input chromatic adaptation conversion unit  202  is omitted, and input color signals are directly output.  
     [0050] The input color space conversion unit  203  converts the input color signals X′, Y′, and Z′ on the CIEXYZ color space into color signals L, a, and b on a CIELAB color space on the basis of a conversion formula specified by Publication CIE No. 15.2. The color mapping unit  204  converts the color signals L, a, and b into color signals L′, a′, and b′ that can be reproduced by the image output apparatus  103 . The output color space conversion unit  205  converts the color signal L′, a′, and b′ on the CIELAB color space into color signals X″, Y″, and Z″ on the CIEXYZ color space on the basis of a conversion formula specified by Publication CIE No. 15.2.  
     [0051] The output chromatic adaptation conversion unit  206  converts the signals X″, Y″, and Z″ as tristimulus values in the standard observation environment into tristimulus values X′″, Y′″, and Z′″ that can obtain the same color appearance in an observation environment of an output image. When adaptation is not taken into consideration, the process of the output chromatic adaptation conversion unit  206  is omitted, and input color signals are directly output. The output profile conversion unit  207  converts input color signals X′″, Y′″, and Z′″ into color signals R′, G′, and B′ depending on the image output apparatus  103  on the basis of a profile (to be referred to as an output profile hereinafter) which is stored in an output profile storage unit  210  and represents the color reproduction characteristics of the image output apparatus  103 .  
     [0052] The output profile storage unit  210  typically stores color signals X′″, Y′″, and Z′″ corresponding to discrete color signals R′, G′, and B′ as a three-dimensional look-up table (to be abbreviated as 3D LUT hereinafter). The output profile conversion unit  207  searches the 3D LUT for data near the input color signals X′″, Y′″, and Z′″, and calculates output color signals R′, G′, and B′ based on the found data and input color signals using a known interpolation method. The color separation conversion unit  208  converts the input color signals R′, G′, and B′ into output color signals C, M, Y, and K by a known method using a color separation LUT stored in a color separation LUT storage unit  211 .  
     [0053]FIG. 3 shows the detailed functional arrangement of the input profile conversion unit  201 . Input color signals R, G, and B are converted into color signals X, Y, and Z by a gamma converter  301  and matrix converter  302 . When the input profile stored in the input profile storage unit  209  is based on sRGB, the gamma converter  301  converts input color signals R, G, and B into color signals RI, GI, and BI, which are linear with respect to luminance, by:  
     When ( R/ 255)≦0.03928,  
       RI= ( R/ 255)/12.92  (1)  
     When ( R/ 255)&gt;0.03928,  
       RI= ((R/255)+0.055)/1.055){circumflex over ( )}2.4  (2) 
     [0054] where x{circumflex over ( )}y indicates the y-th power of x. The gamma converter  301  generates GI and BI using equations (1) and (2) for the remaining signals G and B. When image data is based on color characteristics different from sRGB, for example, discrete input color signals (e.g., R) and corresponding output color signals (e.g., RI) are stored in the input profile storage unit  209  as a gamma conversion LUT. The gamma converter  301  converts arbitrary input color signals into output color signals with reference to the gamma conversion LUT.  
     [0055]FIG. 4 illustrates the relationship between the input and output color signals stored in the gamma conversion LUT. The abscissa plots a normalized input color signal (e.g., R/255), and the ordinate plots an output color signal (e.g., RI). Curve A represents the relationship between the input and output color signals of sRGB based on equations (1) and (2), and curve B represents the relationship between the input and output color signals based on other color characteristics different from sRGB. The values of input and output color signals at plot points are stored in the input profile storage unit  209  as a gamma conversion LUT, and an output color signal between neighboring plot points is calculated by interpolation.  
     [0056] When the input profile is based on sRGB, the matrix converter  302  converts the input color signals RI, GI, and BI into color signals X, Y, and Z by:  
                 [         X           Y           Z         ]          [         0.4124       0.3576       0.1805           0.2126       0.7152       0.0722           0.0193       0.1192       0.9505         ]            [         RI           CI           BI         ]             (   3   )                       
 
     [0057] When image data is based on color characteristics different from sRGB, an conversion matrix, which indicates the color characteristics, can be stored in the input profile storage unit  209 . The matrix converter  302  converts the color signals RI, GI, and BI into color signals X, Y, and Z using conversion matrix M stored in the input profile storage unit  209  by:  
               [         X           Y           Z         ]     =     M        [         RI           CI           BI         ]               (   4   )                       
 
     [0058]FIG. 5 shows another functional arrangement of the input profile conversion unit  201 . In this example, input color signals R, G, and B are converted into color signals X, Y, and Z by a 3D LUT converter  501 . In this case, output color signals corresponding to discrete input color signals R, G, and B are stored as a 3D LUT in the input profile storage unit  209 . For example, the input profile storage unit  209  stores colorimetric values X, Y, and Z corresponding to grid points {R, G, B}={0, 0, 0}, (0, 0, 32}, . . . , {0, 0, 224}, (0, 0, 255}, {0, 32, 0}, {0, 32, 32}, . . . , {255, 255, 255}. The 3D LUT converter  501  converts arbitrary input color signals R, G, and B into color signals X, Y, and Z using this 3D LUT and a known interpolation method.  
     [0059] Encryption in this embodiment will be described below. Image encryption in this embodiment amounts to reading a high-resolution color image by a virtual image input apparatus (to be referred to as an encryption apparatus hereinafter) which has unique color reproduction characteristics different from sRGB. Since the color reproduction characteristics of the encryption apparatus are different from sRGB, a default color process that uses sRGB in the input profile storage unit  209  cannot satisfactorily output an image (to be referred to as an encrypted image hereinafter) read by the encryption apparatus. The encrypted image can be output with high quality, i.e., can be decrypted, only when a profile (to be referred to as an encryption profile hereinafter) serving as a key of encryption is set in the input profile storage unit  209 . It should be noted that, when the decryption processing can not be done (the decryption processing using the encryption profile can not be done), one of cases as follow is happened.  
     [0060] 1. An image having poor color reproduction is reproduce.  
     [0061] 2. An image can not be reproduced.  
     [0062] According to type of encryption profile used for encryption, it is determined which case is happened.  
     [0063]FIG. 6 is a block diagram showing the functional arrangement of an image encryption apparatus in this embodiment. Color signals Ro, Go, and Bo which form an image to be encrypted (to be referred to as a to-be-encrypted image hereinafter) are converted by an input profile conversion unit  601  into color signals X, Y, and Z, which are converted by an encryption conversion unit  602  into color signals Re, Ge, and Be which form an encrypted image. The input profile conversion unit  601  executes the same process as that executed by the input profile conversion unit  201  shown in FIG. 2, and converts signals Ro, Go, and Bo of a to-be-encrypted image into color signals X, Y, and Z on a device-independent color space.  
     [0064] When the color characteristics of a to-be-encrypted image are based on sRGB, input color signals Ro, Go, Bo are converted into color signals X, Y, and Z by equations (1), (2), and (3) above. The encryption conversion unit  602  converts the input color signals X, Y, and Z into color signals Re, Ge, and Be on the basis of an encryption profile stored in an encryption profile storage unit  604 . This process executes inverse conversion of the conversion executed by the input profile conversion unit  201  when the encryption profile is stored in the input profile storage unit  209  in FIG. 2. When the encryption profile storage unit  604  stores a gamma conversion LUT and conversion matrix M based on the encryption profile, and the encryption conversion unit  602  executes inverse conversion of the conversion from color signals R, G, and B into color signals X, Y, and Z, which has been explained using FIG. 3, the encryption conversion unit  602  calculates RI, GI, and BI by:  
               [         RI           CI           BI         ]     =       M     -   1            [         X           Y           Z         ]               (   5   )                       
 
     [0065] as inverse conversion of equation (4).  
     [0066] Then, an inverse conversion process of the conversion executed by the gamma converter  301  is executed to convert the color signals RI, GI, BI into color signals Re, Ge, and Be. More specifically, conversion which has the ordinate of FIG. 4 as an input color signal and the abscissa of FIG. 4 as an output color signal is executed.  
     [0067] On the other hand, when the encryption profile storage unit  604  stores a 3D LUT based on the encryption profile and the encryption conversion unit  602  executes inverse conversion of the conversion from color signals R, G, and B into color signals X, Y, and Z which has been explained using FIG. 5, the encryption conversion unit  602  searches the 3D LUT for a grid point near the input color signals X, Y, and Z, and calculates output color signals Re, Ge, and Be using a known interpolation method on the basis of the found grid point data and the input color signals.  
     [0068]FIG. 8 shows the basic arrangement of the image encryption apparatus of this embodiment. As shown in FIG. 8, the image encryption apparatus of this embodiment comprises a data input unit  801 , data output unit  802 , input image holding unit  803 , output image holding unit  804 , input profile conversion unit  805 , input profile holding unit  806 , encryption conversion unit  807 , encryption profile holding unit  808 , and color signal buffer unit  809 .  
     [0069] The input image holding unit  803  stores to-be-encrypted image data input via the data input unit  801 . The input profile holding unit  806  stores an input profile (that which is stored in the input profile storage unit  603 ) input via the data input unit  801 . The encryption profile holding unit  808  stores an encryption profile (that which is stored in the encryption profile storage unit  604 ). The encryption profile holding unit  808  may pre-store an encryption profile or may store a new encryption profile input via the data input unit  801 .  
     [0070] The input profile conversion unit  805  converts color signals, which form an image stored in the input image holding unit  803 , into device-independent color signals, using an input profile stored in the input profile holding unit  806 , and stores them in the color signal buffer unit  809 . The encryption conversion unit  807  converts the color signals that the input profile conversion unit  805  stores in the color signal buffer unit  809  into color signals Re, Ge, and Be which form an encrypted image, using an encryption profile stored in the encryption profile holding unit  808 , and stores them in the output image holding unit  804 . The encrypted image stored in the output image holding unit  804  is externally output via the data output unit  802 , and is saved/distributed as in a normal image.  
     [0071] The image encryption process executed by the image encryption apparatus will be described below using FIG. 9 which is a flow chart of that process.  
     [0072] In step S 901 , an encryption profile to be used is set. The encryption profile may be set by selecting one of a plurality of encryption profiles pre-stored in the encryption profile holding unit  808  or inputting a new encryption profile via the data input unit  801 . In step S 902 , to-be-encrypted image data is input via the data input unit  801 , and is stored in the input image holding unit  803 . In step S 903 , an input profile of the to-be-encrypted image data is set. If the to-be-encrypted image data is scanned by a scanner, the profile of the corresponding scanner is set; if the to-be-encrypted image data is based on sRGB, an sRGB profile is set and stored in the input profile holding unit  806 . The input profile may be set by selecting one of a plurality of input profiles pre-stored in the input profile holding unit  806  or by inputting a new input profile via the data input unit  801 .  
     [0073] In step S 904 , an input profile conversion process is executed. The input profile conversion process converts color signals which form the input image data stored in the input image holding unit  803  in step S 902  into device-independent color signals X, Y, and Z using the input profile set in step S 903 . In step S 905 , an encryption conversion process is executed. The encryption conversion process converts the color signals X, Y, and Z into color signals Re, Ge, and Be, which form encrypted image data, using the encryption profile set in step S 901 . It is then checked in step S 906  if all color signals which form the input image data have been processed. If color signals to be processed still remain, the flow returns to step S 904 ; otherwise, the flow advances to step S 907 . In step S 907 , the generated encrypted image is output.  
     [0074] A process for decrypting the encrypted image data generated by the image encryption apparatus will be described below. The decryption process of this embodiment does not require any special apparatus or software program since it uses processes in the image processing apparatus. That is, in the general image process that has been explained using FIG. 2, the encryption profile used upon encrypting the to-be-encrypted image is set in the input profile storage unit  209 , and is used, thereby decrypting the encrypted image data.  
     [0075]FIG. 7 shows an example of a setup user interface (GUI) of a typical color printer program, which is displayed on the display unit  1705 . With this GUI, the types of input profile and color mapping are designated using an input profile list box  701  and color mapping list box  702 . The decryption process is implemented by designating the encryption profile in the input profile list box  701 .  
     [0076] As described above, the image encryption apparatus of this embodiment uses the color profile of a virtual image input apparatus having unique color reproduction characteristics as a key of decryption. As a result, simple image decryption that exploits the existing image process can be realized. The encrypted image data generated by the image encryption apparatus of this embodiment can be used in a general image processing apparatus/software program as in normal image data, and need not use any special software program. Furthermore, since the encrypted image data can be decrypted only when the user has the color profile as the key of decryption, secondary distributions are suppressed, and the limitation of users can be made securer.  
     Second Embodiment  
     [0077] In the first embodiment, an image encryption apparatus that exploits an input profile is formed. Likewise, an image encryption apparatus that exploits an output profile can be formed. The image encryption apparatus of this embodiment uses a color profile of a virtual image output apparatus having unique color reproduction characteristics as a key of decryption. An encrypted image generated by this image encryption apparatus can be decrypted by storing an encryption profile in the output profile storage unit  210  and using this encryption profile by the output profile conversion unit  207  in the image processing unit shown in FIG. 2.  
     [0078] Encryption in this embodiment will be described below. FIG. 10 shows the functional arrangement of the image encryption apparatus of this embodiment. Color signals Ro, Go, and Bo, which form a to-be-encrypted image, are converted into color signals Re, Ge, and Be, which form an encrypted image, by a pre-process conversion unit  1201 , output profile conversion unit  1202 , encryption conversion unit  1203 , and pre-process inverse conversion unit  1204 .  
     [0079] Note that the color signals Ro, Go, and Bo, and Re, Ge, and Be are those on a color space which form image data, color signals X′″, Y′″, and Z′″, and X″″, Y″″, and Z″″ are those on a device-independent color space, and color signals R′, G′, and B′ are those on a color space depending on the image output apparatus  103 . The pre-process conversion unit  1201  executes processes to be executed by the input profile conversion unit  201 , input chromatic adaptation conversion unit  202 , input color space conversion unit  203 , color mapping unit  204 , output color space conversion unit  205 , and output chromatic adaptation conversion unit  206  in the description using FIG. 2. Typically, a 3D LUT of color signals X′″, Y′″, and Z′″ corresponding to discrete color signals Ro, Go, and Bo is stored as a pre-process profile in a pre-process profile storage unit  1205 , and is used. The pre-process conversion unit  1201  converts input color signals Ro, Go, and Bo into output color signals X′″, Y′″, and Z′″ using the 3D LUT stored in the pre-process profile storage unit  1205 , and a known interpolation method.  
     [0080] The output profile conversion unit  1202  executes the same process as that of the output profile conversion unit  207  in FIG. 2, and converts the input color signals X′″, Y′″, and Z′″ into color signals R′, G′, and B′ on the basis of an output profile stored in an output profile storage unit  1206 .  
     [0081] The encryption conversion unit  1203  converts the input color signals R′, G′, and B′ into output color signals X″″, Y″″, and Z″″ using an encryption profile stored in an encryption profile storage unit  1207 . This process executes inverse conversion of the conversion to be executed by the output profile conversion unit  207  when the encryption profile is stored in the output profile storage unit  210  in FIG. 2.  
     [0082] The pre-process inverse conversion unit  1204  executes inversion conversion of the conversion executed by the pre-process conversion unit  1201 . Typically, the 3D LUT stored in the pre-process profile storage unit  1205  are searched for data near the input color signals X″″, Y″″, and Z″″, and output color signals Re, Ge, and Be are calculated using a known interpolation method on the basis of the found data and input color signals.  
     [0083]FIG. 11 shows the basic arrangement of the image encryption apparatus. As shown in FIG. 11, the image encryption apparatus of this embodiment comprises a data input unit  1301 , data output unit  1302 , input image holding unit  1303 , output image holding unit  1304 , pre-process conversion unit  1305 , pre-process inverse conversion unit  1306 , pre-process profile holding unit  1307 , encryption conversion unit  1308 , encryption profile holding unit  1309 , color signal buffer unit  1310 , output profile conversion unit  1311 , and output profile holding unit  1312 .  
     [0084] The input image holding unit  1303  stores to-be-encrypted image data input via the data input unit  1301 . The encryption profile holding unit  1309  stores the encryption profile. The encryption profile holding unit  1309  may pre-store the encryption profile or may store a new encryption profile input via the data input unit  1301 . The pre-process profile holding unit  1307  stores the pre-process profile. The pre-process profile holding unit  1307  may pre-store the pre-process profile or may store a new pre-process profile input via the data input unit  1301 .  
     [0085] The pre-process conversion unit  1305  converts color signals, which form an image stored in the input image holding unit  1303 , into color signals on a device-independent color space using the pre-process profile stored in the pre-process profile holding unit  1307 , and stores the converted color signals in the color signal buffer unit  1310 . The output profile conversion unit  1311  converts the color signals that the pre-process conversion unit  1305  stores in the color signal buffer unit  1310  into color signals on a color space depending on the image output apparatus  103  using the output profile stored in the output profile holding unit  1312 , and stores the converted color signals in the color signal buffer unit  1310 . The encryption conversion unit  1308  converts the color signals that the output profile conversion unit  1311  stores in the color signal buffer unit  1310  into color signals on a device-independent color space using the encryption profile stored in the encryption profile holding unit  1309 , and stores the converted color signals in the color signal buffer unit  1310 . The pre-process inverse conversion unit  1306  converts the color signals that the encryption conversion unit  1308  stores in the color signal buffer unit  1310  into color signals which form an encrypted image using the pre-process profile stored in the pre-process profile holding unit  1307 , and stores the converted color signals in the output image holding unit  1304 . The encrypted image stored in the output image holding unit  1304  is output via the data output unit  1302 .  
     [0086]FIG. 12 is a flow chart of the image encryption process executed by the image encryption apparatus of this embodiment.  
     [0087] In step S 1601 , an encryption profile to be used is set. The encryption profile may be set by selecting one of a plurality of encryption profiles pre-stored in the encryption profile holding unit  1309  or inputting a new encryption profile via the data input unit  1301 . In step S 1602 , a pre-process profile to be used is set. The pre-process profile may be set by selecting one of a plurality of pre-process profiles pre-stored in the pre-process profile holding unit  1307  or inputting a new pre-process profile via the data input unit  1301 . In step S 1603 , an output profile to be used is set. The output profile may be set by selecting one of a plurality of output profiles pre-stored in the output profile holding unit  1312  or inputting a new output profile via the data input unit  1301 .  
     [0088] In step S 1604 , to-be-encrypted image data is input via the data input unit  1301 , and is stored in the input image holding unit  1303 . In step S 1605 , pre-process conversion is executed. The pre-process conversion converts color signals, which form the input image data, into color signals X′″, Y′″, and Z′″ on a device-independent color space using the pre-process profile set in step S 1602 . In step S 1606 , output profile conversion is executed. The output profile conversion converts the color signals X′″, Y′″, and Z′″ into color signals R′, G′, and B′ on a color space depending on the image output apparatus  103  using the output profile set in step S 1603 .  
     [0089] In step S 1607 , encryption conversion is executed. The encryption conversion converts the color signals R′, G′, and B′ into color signals X″″, Y″″, and Z″″ on a device-independent color space using the encryption profile set in step S 1601 . In step S 1608 , pre-process inverse conversion is executed. The pre-process inverse conversion converts the color signals X″″, Y″″, and Z″″ into color signals Re, Ge, and Be which form encrypted image data using the pre-process profile set in step S 1602 . It is then checked in step S 1609  if all color signals that form the to-be-encrypted image data have been processed. If color signals to be processed still remain, the flow returns to step S 1605 ; otherwise, the flow advances to step S 1610 . Finally, in step S 1610  the generated encrypted image is output.  
     [0090] A-process for decrypting the encrypted image data generated by the image encryption apparatus will be explained below. The decryption process of this embodiment does not require any special apparatus or software program since it uses processes in the image processing apparatus. That is, in the general image process that has been explained using FIG. 2, the encryption profile used upon encrypting the to-be-encrypted image is set in the output profile storage unit  210 , and is used, thereby decrypting the encrypted image data.  
     Third Embodiment  
     [0091] Also, an image encryption apparatus which is compatible to an image processing apparatus that uses an input/output integrated profile that integrates input and output profiles may be formed. An image encryption apparatus of this embodiment uses an input/output integrated profile having unique color reproduction characteristics as a key of decryption.  
     [0092]FIG. 14 shows the functional arrangement of an image processing apparatus that uses an input/output integrated profile. The image processing apparatus comprises an input/output integrated color conversion unit  1401 , and integrated profile storage unit  1402 . The input/output integrated color conversion unit  1401  executes processes to be executed by the input profile conversion unit  201 , input chromatic adaptation conversion unit  202 , input color space conversion unit  203 , color mapping unit  204 , output color space conversion unit  205 , output chromatic adaptation conversion unit  206 , output profile conversion unit  207 , color separation conversion unit  208  in FIG. 2. Typically, a 3D LUT of color signals C, M, Y, and K corresponding to discrete input color signals R, G, and B is stored as an integrated profile in the integrated profile storage unit  1402 , and is used. An encrypted image generated by this image encryption apparatus is decrypted in such a manner that an encryption profile is stored in the integrated profile storage unit  1402 , and is used by the input/output integrated color conversion unit  1401 .  
     [0093] Encryption of this embodiment will be explained below. FIG. 15 shows the functional arrangement of the image encryption apparatus of this embodiment. Color signals Ro, Go, and Bo which form a to-be-encrypted image are converted into color signals Re, Ge, and Be that form an encrypted image by an input/output integrated color conversion unit  1501  and encryption conversion unit  1502 .  
     [0094] The input/output integrated color conversion unit  1501  executes the same process as in the input/output integrated color conversion unit  1401  in FIG. 14, and converts color signals Ro, Go, and Bo which form a to-be-encrypted image into color signals C, M, Y, and K to be output to the image output apparatus  103  on the basis of an integrated profile stored in an integrated profile storage unit  1503 .  
     [0095] The encryption conversion unit  1502  converts the input color signals C, M, Y, and K into color signals Re, Ge, and Be that form an encrypted image on the basis of an encryption profile stored in an encryption profile storage unit  1504 . This process executed inverse conversion of the conversion to be executed by the input/output integrated color conversion unit  1401  when the encryption profile is stored in the integrated profile storage unit  1402  in FIG. 14. Typically, a 3D LUT stored in the encryption profile storage unit  1504  is searched for data near the input color signals C, M, Y, and K, and output color signals Re, Ge, and Be are calculated using a known interpolation method on the basis of the found data and the input color signals.  
     [0096]FIG. 16 shows the basic arrangement of the image encryption apparatus. As shown in FIG. 16, the image encryption apparatus of this embodiment comprises a data input unit  1801 , data output unit  1802 , input image holding unit  1803 , output image holding unit  1804 , input/output integrated color conversion unit  1805 , integrated profile holding unit  1806 , encryption conversion unit  1807 , encryption profile holding unit  1808 , and color signal buffer unit  1809 .  
     [0097] The input image holding unit  1803  stores to-be-encrypted image data input via the data input unit  1801 . The integrated profile holding unit  1806  stores the integrated profile. The integrated profile holding unit  1806  may pre-store the integrated profile, or may store a new integrated profile input via the data input unit  1801 . The encryption profile holding unit  1808  stores the encryption profile. The encryption profile holding unit  1808  may pre-store the encryption profile, or may store a new encryption profile input via the data input unit  1801 .  
     [0098] The input/output integrated color conversion unit  1805  converts color signals that form the input image stored in the input image holding unit  1803  into color signals to be output to the image output apparatus  103  using the integrated profile stored in the integrated profile holding unit  1306 , and stores the converted color signals in the color signal buffer unit  1809 . The encryption conversion unit  1807  converts the color signals that the input/output integrated color conversion unit  1805  stores in the color signal buffer unit  1809  into color signals that form an encrypted image using the encryption profile stored in the encryption profile holding unit  1808 , and stores the converted color signals in the output image holding unit  1804 . The encrypted image stored in the output image holding unit  1804  is output via the data output unit  1802 .  
     [0099]FIG. 17 is a flow chart of the image encryption process executed by the image encryption apparatus of this embodiment.  
     [0100] In step S 1901 , an encryption profile to be used is set. The encryption profile may be set by selecting one of a plurality of encryption profiles pre-stored in the encryption profile holding unit  1808  or inputting a new encryption profile via the data input unit  1801 . In step S 1902 , an integrated profile to be used is set. The integrated profile may be set by selecting one of a plurality of integrated profiles pre-stored in the integrated profile holding unit  1806  or inputting a new integrated profile via the data input unit  1801 .  
     [0101] In step S 1903 , to-be-encrypted image data is input via the data input unit  1801 , and is stored in the input image holding unit  1803 . In step S 1904 , input/output integrated color conversion is executed. The input/output integrated color conversion converts color signals which form the input image data into color signals C, M, Y, and K to be output to the image output apparatus  103  using the integrated profile set in step S 1902 .  
     [0102] In step S 1905 , encryption conversion is executed. The encryption conversion converts the color signals C, M, Y, and K to be output to the image output apparatus  103  into color signals Re, Ge, and Be that form encrypted image data using the encryption profile set in step S 1901 . It is then checked in step S 1906  if all color signals which form the to-be-encrypted image data have been processed. If color signals to be processed still remain, the flow returns to step S 1904 ; otherwise, the flow advances to step S 1907 . Finally, in step S 1907  the generated encrypted image is output.  
     Another Embodiment  
     [0103] In the above embodiments, a color printer using four colors, i.e., C, M, Y, and K has been exemplified as the image output apparatus. However, the object of the present invention can also be achieved by color printers of other arrangements.  
     [0104] The objects of the present invention are also achieved by supplying a storage medium, which records a program code of a software program that can implement the functions of the above-mentioned embodiments to the system or apparatus, and reading out and executing the program code stored in the storage medium by a computer (or a CPU or MPU) of the system or apparatus.  
     [0105] In this case, the program code itself read out from the storage medium implements the functions of the above-mentioned embodiments, and the storage medium which stores the program code constitutes the present invention.  
     [0106] As the storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, and the like may be used. The functions of the above-mentioned embodiments may be implemented not only by executing the readout program code by the computer but also by some or all of actual processing operations executed by an OS (operating system) running on the computer on the basis of an instruction of the program code.  
     [0107] Furthermore, the functions of the above-mentioned embodiments may be implemented by some or all of actual processing operations executed by a CPU or the like arranged in a function extension board or a function extension unit, which is inserted in or connected to the computer, after the program code read out from the storage medium is written in a memory of the extension board or unit.  
     [0108] As described above, the present invention can implement image encryption that allows decryption without requiring any special software program or apparatus. Also, the present invention can decrypt an encrypted image without requiring any special software program or apparatus. As a result, users of a high-resolution image can be easily limited.  
     [0109] Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.  
     [0110] As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.