Abstract:
The present invention is in the field of digital imaging. It relates to a method and a system for selecting a subject of interest in a digital image, so as to be able to then display this subject of interest on the screen of a terminal with low display capacity. The present invention enables the display directly and automatically on the screen of a terminal with low display capacity, of subjects of interest, previously selected in an original image. This is done based on a simple operation or request executed from the terminal with low display capacity. This enables the image to be exploited correctly, by viewing the subjects of interest of the original image, in the best possible conditions of image rendering, given the display capacity of said terminal. The application of the present invention is in the area of the users of terminals with low display capacity.

Description:
FIELD OF THE INVENTION 
   The present invention is in the field of digital imaging. The present invention relates to a method and a system that enables the selection of a subject of interest in a digital image for displaying it in good conditions on terminal screens with low display capacity, and especially the screens of portable terminals. 
   BACKGROUND OF THE INVENTION 
   The combined development of networks, wireless communication means, terminals equipped with display screens and interface systems that enable these means to work together, provides users with the possibility of choosing and exchanging digital images through a network such as for example the internet. The screens of these terminals, and especially the screens of portable terminals, do not always have sufficient capacity to display directly an image with relatively high definition, given the number of displayable colors (for screens displaying colors) and the too restricted number of display pixels. “Low” display capacities are for example in the order of 96 by 44 pixels (NOKIA cell phone), 160 by 160 pixels (PALM Personal Digital Assistant). Consequently, the retrieved image, displayed for example on the screen of a cell phone, is often hardly, or even not exploitable visually. All the more so, part of the image constituting a special area of interest of the whole image displayed on the cell phone screen, is even less exploitable visually by a user of the telephone. Therefore it is of interest for the user to be able to view in good conditions all the special areas, or the subjects of interest of an original image. 
   Therefore, in order to visually exploit an image on terminal screens with low display capacity, the image rendering needs to be improved, i.e. obtain the best possible quality of plotting, given the fact that these devices offer poor display capacities. This improvement of the plotting can be provided by manually cutting out the subject of interest in the original digital image; but this technique has the major disadvantage of requiring prior knowledge of the shape factor of the display of the terminal with low display capacity used to view the image. An automatic means, independent of the terminal with low display capacity used, is thus desirable to determine and display the subject of interest. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a method for viewing on the screen of a terminal with low display capacity a subject of interest previously selected in an original still digital image, the method comprising the following steps:
         a) operate a request of the original image, from the terminal with low display capacity;   b) automatically determine the limits, in the original image, of an area in which the selected subject of interest is enclosed;   c) automatically save the pixel data characterizing the area of the subject of interest;   d) automatically determine, according to the display capacity of the terminal with low display capacity from which the request is operated, an optimal framing format of the area of the subject of interest; and   e) automatically display on the screen of the terminal with low display capacity, the optimized modified image corresponding to the framing area determined in step d).       

   In addition, the method of the invention also enables the successive display on the screen of a terminal with low display capacity of several optimized modified images corresponding to the subject of interest of each of the corresponding original images. Each of the original images can also contain several subjects of interest. 
   It is also an object of the present invention to provide a system to view a subject of interest of an original still digital image on the screen of a terminal with low display capacity, characterized in that it comprises:
         a) at least one terminal having a screen with low display capacity,   b) devices intercommunicating and enabling the display and saving of the original digital image;   c) an interface device linked to the terminal having a screen with low display capacity, the interface device enabling the communication of image digital data between the terminal and the devices enabling the display and saving of the original image; and   d) software enabling, based on a request operated from the terminal having a screen with low display capacity, the automatic display of an optimized modified image corresponding to an optimized framing area of the subject of interest of the original image on the screen of the terminal.       

   Thus it is the purpose of the present invention to provide a simplified user interface, that is user friendly and enables the optimization of the rendering of digital images, by displaying on the screen of a terminal with low display capacity, only parts or subjects of interest of an original digital image; this display corresponds to the visual exploitation of the image desired by the user of the terminal with low display capacity. Thus the best quality of plotting of the subjects of interest can be obtained, while reducing the number of manual operations for the user. The method and system of the invention enables improvement of the legibility and thus quality of the image displayed on the screen of the terminal with low display capacity; for example a zoom-in is performed to select the subject or the area of the original image that has a special interest. This selection of the subject of interest can be performed manually through the network interface for example, but this is not very user friendly. Conversely, the use of processes using fully automatic processing algorithms is not very robust and sometimes provides poor results, in terms of the transfer of digital images on terminals with low display capacity. 
   Other characteristics and advantages of the invention will appear on reading the following description, with reference to the drawings illustrating the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  represents diagrammatically a hardware environment of the system for implementing the invention. 
       FIG. 2  represents diagrammatically a still image illustrating a selection principle of two different subjects of interest of the image. 
       FIG. 3  represents diagrammatically a still image and different framing shapes of two subjects of interest of the image. 
       FIG. 4  represents diagrammatically a still image and the framing of a subject of interest comprising several homogeneous entities. 
       FIG. 5  represents the marking, segmentation and framing of a subject of interest in an original image. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is implemented in the environment diagrammatically represented by  FIG. 1 , and comprising a set of devices communicating one with another. A main server or terminal  1  enables the access to still digital images, forming part for example of a digital database of images stored or saved in the server. The digital images  8  saved in this database have relatively high definition. The server  1  is linked through a specific high speed link  10 , via an interface device  3 , to a network such as the internet. This enables for example the images at a URL address (Uniform Resource Locator) to be retrieved. The interface device  3  enables, via a cabled link  80 , the linking of the server  1  with terminals or computers  2 , of PC type (Personal Computer). These terminals  2  are fitted with screens with sufficient display capacity, for example in the order of 800 by 600 pixels or more. Other specific links  40 ,  50 ,  60 ,  70  enable, via the interface device  3 , communication with terminals with low display capacity  4 ,  5 ,  6 ,  7  to be ensured. These terminals with low display capacity are preferably mobile wireless terminals. Links  40   50 ,  60 ,  70  are for example WAP (Wireless Application Protocol) type wireless links. Terminals with low display capacity can be for example a portable microcomputer  4 , a PDA  5  (display capacity 160 by 160 pixels), a cell phone  6  (display capacity 96 by 44 pixels), a TV screen  7 , or any other portable terminal fitted with a display device for digital images. All the devices described above, and forming the environment represented by  FIG. 1 , work together to exchange information or digital data, by running a software program. This software enables the execution of the operations described below, algorithm operations for implementing the invention method. 
   In a first embodiment, the present invention enables a user, operating an initial request, to recover for example an original image  8  to terminal  2  with sufficient display capacity. The user sees the original image  8  on the screen  21  of the terminal  2 . The terminal  2  enabling the initial request to be operated is for example a PC that enables the display, on the screen  21 , of a set or subset representative of the pixels forming the original image  8  in good conditions. The user simply selects, for example by using a mouse  11  linked to the terminal  2 , a subject of interest in the original image  8 . This subject of interest has an interest special to the user.  FIG. 2  represents two examples of the types of selection of the subject of interest with the mouse  11 . Selection of the subject of interest is operated with the mouse  11 , either by placing for example a point  18  approximately in the main part of a first subject of interest  15  of the original image  12 , or by tracing a portion of line or a straight segment  19  approximately in the main part of a second subject of interest  20  of the image  12 . From this selection of one or more subjects of interest in the original image, the rest of the invention method operates automatically, without user intervention. The invention method enables the determination, loading, and then automatically saving, in the server  1 , of the original image  12  and the coordinates of the markers of the subjects of interest of the image. The coordinates of the marker  18 ,  19  of the subject of interest represent the position of the subject of interest  15 ,  20  in the original image  12 . The coordinates of the marker of the subject of interest are stored (saved) for example in the server  1 . The coordinates are stored for example in the form of a greyscale image, in which each marker identifying a subject of interest is defined by a particular greyscale; this greyscale of the marker is differentiated from the greyscale of the image background. The coordinates are stored for example in the form of a gray-scale image, in which each marker identifying a subject of interest is defined by a particular gray-scale; this gray-scale of the marker is differentiated from the gray-scale of the image background. 
   Based on the pixel data of the original digital image and the coordinates of the selected subjects of interest, the algorithm for implementing the invention method enables the original image to be analyzed to automatically determine the pixel limits  15 ,  20 , in the original image  12 , of the area of the selected subject of interest. To do this, the algorithm integrates a module enabling image segmentation operations to be performed. Segmentation enables elements or entities of a scene represented in the original digital image to be highlighted. This method, known to those skilled in the art, consists in fusing together, to form an entity or a uniform area, the pixels having a given value, or belonging to an interval of gray-scale or color values. For example, the transformation called “watershed transform” is a segmentation method known to those skilled in the art, and described in the publication by F. Meyer and S. Beucher of September 1990, The Journal of Visual Communication and Image Representation, entitled, Morphological Segmentation (Academic Press Ed.). This type of segmentation method enables the elements or entities of a digital image to be selected; said image elements or entities are selected using computer mouse type means enabling them to be pointed (point) or marked (line) on the screen. 
   According to a particular embodiment and according to  FIG. 5 , the algorithm called “watershed transform” is applied to the original image  12 ,  42 , to select the regions or areas of interest  15 ,  20 ,  45 , from the pixel gradient of the original image  12 ,  42  and the markers  18 ,  19 ,  44  of the regions of the image  12 ,  42 . Another implicit marker, automatically taken into account by the algorithm, is used in any original image; this implicit marker takes into account all the edge pixels  23  of the original image  12 . The implicit marker thus enables the automatic enclosing of the pixels forming the part  30  of the original image (background of the image) that has no interest. Based on the markers  19  of the subjects of interest and of the implicit marker of the background of the original image, the watershed transform operates a segmentation of the original image  12 . This segmentation enables an area of outlines or limits  31  of the subject of interest to be determined. The area  31  in which the subject of interest is enclosed is called the area of the subject of interest. The pixel data of the subject-of-interest area are automatically saved, for example in a database in a server, or in the metadata of the image file if the file format enables it, or if the encoding type of the image enables it, the region of interest is encoded directly in the image file. In the case of a database-in-a-server type storage, the server is for example the server  1 . The algorithm then enables the automatic selection and display of a framing format of the subject-of-interest region or area; this subject-of-interest area is represented for example by a polygon  20  circumscribing the limits  31  determined by the segmentation; the algorithm also enables the automatic determination of the area  30 , of the background of the original image  12 , which is not of any interest to the user. 
   According to a first embodiment, in order to automatically determine the limits of the subject-of-interest area, the invention method enables the segmentation to be operated, before a second request for the original image operated from the terminal with low display capacity  4 ,  5 ,  6 ,  7 . The step of automatic determination of the limits  31  of the area corresponding to the subject of interest is operated in a server (for example the server  1 ), by the segmentation module, according to the analysis of the original image and the coordinates  18 ,  19  of the subject of interest. Consequently, this step of determination of the limits is operated before the execution of the second request, from the terminal  4 ,  5 ,  6 ,  7 . Based on the second request effected for example later from the terminal with low display capacity  4 ,  5 ,  6 ,  7 , the user retrieves on this terminal  4 ,  5 ,  6 ,  7 , the original image  12  and the coordinates  18 ,  19  of the subject of interest stored in the server  1 . The algorithm of the invention method automatically determines, according to the terminal with low display capacity from which the second request is operated, an optimum format for framing the previously selected subject-of-interest area. That is, the invention method determines an optimized framing of the subject-of-interest area taking into account the display capacity of the terminal  4 ,  5 ,  6 ,  7 . 
   According to a second embodiment, the invention method enables the automatic operation, from the second request operated on the terminal  4 ,  5 ,  6 ,  7 , of the automatic determination of the limits of the subject-of-interest area, then the optimum framing format of the area. The operations of image rendering, for example filtering, trimming, decimation of the image and resizing the limits of the subject-of-interest area, are operated in real time (“on the fly”), according to the coordinates of the previously selected subject of interest. The user executes the second request from the terminal with low display capacity  4 ,  5 ,  6 ,  7 . When the user executes the second request, for example HTTP, to the server  1 , a header is inserted in the request. This header enables the server  1  to identify the type of terminal with low display capacity used to which to send for example digital image contents, and to format the contents appropriately. The invention method enables the user to retrieve in this way (following the second request) the optimized modified image, which represents the image of the previously selected subject of interest. The user recovers this modified image directly on the screen of their portable terminal with low display capacity. And this is with an image quality enabling the subject of interest to be viewed correctly. According to  FIG. 3 , the subject of interest of the original image  22  is for example either a face  24 , or a particularity of a geographic site  26 . According to an alternative, the embodiment of the invention is optimized, from a server database  9 , for example saved in the server  1 . The database  9  comprises for example the identifications and/or technical display characteristics of various types of terminals equipped with low display capacity screens. This optimized embodiment enables, from the terminal  4 ,  5 ,  6 ,  7 , and according to the display capacity characteristics recorded in the database  9 , the automatic determination of the optimum framing format of the subject-of-interest area, immediately after the step enabling the limits of this area corresponding to the subject of interest to be determined. 
   The present invention provides the advantage, for the user, of being totally free to use any type of terminal with low display capacity; i.e. the display capacity of the terminal  4 ,  5 ,  6 ,  7  used is taken into account automatically by the invention method, at the moment when the user makes the second request on the terminal. This is to display the subject of interest according to an optimum framing enabling good quality and good viewing of the optimized modified image, on the screen of the terminal  4 ,  5 ,  6 ,  7 . Another advantage of the invention method is to avoid the manual operation of searching and framing of the subjects of interest in the original image, while supplying the best results in terms of quality of the retrieved image on the screen of the terminal with low display capacity. The invention method thus enables the automatic determination of an optimum format of the framing area of the selected subject of interest, according to the type of terminal  4 ,  5 ,  6 ,  7 . This operation leads to supplying an optimum format of the framing area of the subject of interest enclosing the limits  31  previously defined automatically of the area of the subject of interest during the segmentation operation. The optimum framing format for the area of the subject of interest generally reveals a little more pixel data of the subject of interest than the limits  31  of the area automatically determined during the segmentation. But, if the type of terminal  4 ,  5 ,  6 ,  7  requires it, the optimized framing area, enabling good viewing to be obtained on the screen of the terminal  4 ,  5 ,  6 ,  7 , will not retrieve for example all the pixel data of the subject of interest previously determined during the segmentation. This is to favor the quality of the image rendering on the screen of the terminal  4 ,  5 ,  6 ,  7 . However, in this last case, the algorithm minimizes the difference between the number of pixels of the subject of interest determined during the segmentation and the number of pixels of the subject of interest effectively retrieved on the screen of the terminal  4 ,  5 ,  6 ,  7 . The user is thus not concerned with the capacity of the terminal  4 ,  5 ,  6 ,  7  they are using; the invention method operates the framing automatically, i.e. the ultimate adjustment to obtain the best display possible of the optimized modified image, on the terminal  4 ,  5 ,  6 ,  7 . The user is the person who executes the second request for an original image  12 ,  22 ,  42  saved on the server  1 , and which they generated. But the user is also the person who receives for example on their mobile phone  6  an image coming from another user; the original image  12 ,  22 ,  42  being sent by another person, for example as an electronic postcard; this mailing is operated for example by the internet or by using the MMS environment (Multimedia Messaging Service). 
     FIG. 2  represents for example an original image  12  stored on the server  1 . The original image  12  is for example recovered by the user (first request) on the screen  21  of the PC  2 . The image  12  comprises for example three image entities  14 ,  16 ,  17 . The user is for example more particularly interested in a particular element of the entity  14  located approximately in the middle of the image  12 , and in a particular element of the entity  17  located near the bottom of the image  12 . The implementation of the invention method involves for the user, from the PC  2 , for example using a simple click with the mouse  11 , pointing at  18  the first subject of interest  15  (particular element of the entity  14 ), then for example marking with a line  19  the second subject of interest  20  (particular element of the entity  17 ). The line segment  19  is executed by pressing on the mouse button and moving it simultaneously between the ends of the line segment  19  (click and drag). The user can operate, for example later, a second request for the original image  12  from for example their cell phone  6 , the phone  6  being equipped with a screen having a restricted number of display pixels, for example 96 by 44 pixels. The particular form of the entity  14 , represented by its subject of interest, cannot be viewed correctly on the screen of the cell phone  6  if the entire original image  12  is displayed. This is given the level of detail of the entity  14  in the original image  12 , and the insufficient display capacity of the cell phone  6  used. The invention method enables the automatic definition of the optimum framing format  15  that corresponds to the display capacity of the cell phone  6 , and enables good viewing of the optimized modified image (representing the subject of interest) to be rendered on the screen of the phone  6  used. 
   According to the choice of the subject of interest in the original image, the algorithm of the invention method also enables the automatic determination of an appropriate framing geometry. In other words, after the segmentation operations, framing areas of the subject of interest of different forms are obtained based for example on conventional geometric forms. The framing geometry encloses the form generated by the limits of the pixel area of the “segmented” subject of interest of the original image. According to a preferred embodiment of the invention method, and according to the illustration of  FIG. 3 , the forms used enable areas to be defined with rectangular  26 , or circular  24  shapes. But other types of framing form can also be used, for example square, elliptic, or whatever, i.e. for example polygonal and approximately following the outline of the entity characterizing the selected subject of interest. The forms, to define the framing areas of the subject of interest and to thus define the optimized modified image, are programmed according to the type of subject of interest that may appear in the image, as represented for example in  FIG. 3 : a rectangle  26  for a landscape, a circle  24  for a face, etc. 
   As illustrated in  FIGS. 2 &amp; 3 , the invention method enables the successive selection of several subjects of interest  15 ,  20 ,  24 ,  26  in one original image  12 ,  22 . When the user of the terminal with low display capacity wishes to retrieve these subjects of interest forming optimized modified images, to view them in good conditions on their cell phone  6  for example, they operate the (second) request for the original image from the cell phone. The invention method thus enables the automatic successive display of subjects of interest  15 ,  20 ,  24 ,  26  on the screen of the cell phone  6 . In a preferred embodiment, the display is executed in the chronological order of the initial selections of the subjects of interest operated on the terminal  2  with sufficient display capacity. The invention method also enables the programming of any other chronology of plotting the display of the subjects of interest on the terminal  4 ,  5 ,  6 ,  7 . Going from viewing for example the first plotted subject of interest  15  to the second subject of interest  20  is operated by a simple command executed manually by the user, from the terminal  4 ,  5 ,  6 ,  7 ; or this change is operated automatically, while following an automatic timing that is programmed and adjustable. 
   Another embodiment of the invention, as illustrated in  FIG. 4 , also applies to at least one subject of interest  45  from at least one original image  42 . The subject of interest  45  comprises several homogeneous image entities  47 ,  48 ,  49 . These homogenous entities represent, for the user, the interesting elements of the subject of interest  45 . The concept of homogenous image entities is defined and taken into account by the algorithm of the invention method. It integrates the operations of the “watershed transform” method, known to those skilled in the art. Based on an original image  42 , the user selects, for example with a simple click of the mouse  44 , or by drawing a line segment with the mouse, the subject of interest  45 . This subject of interest  45  corresponds for example to three homogenous entities  47 ,  48 ,  49 , which interest the user together. The algorithm of the invention method enables the subject of interest  45  to be selected by clicking in the original image  42 . The simple click is operated near the Barycenter of the homogenous entities  47 ,  48 ,  49 . The Barycenter thus defined is approximately the geometric Barycenter of the selected entities  47 ,  48 ,  49 . In a preferred embodiment, the user selects the subject of interest  45  by drawing a line that at least partially covers the homogenous entities  47 ,  48 ,  49 . The entities  47 ,  48 ,  49  are recognized as forming together a subject of interest  45  in the original image  42 , insofar as they are close and represent homogenous pixel areas having consistency of shapes or colors in relation to the neighboring pixels. 
   While the invention has been described with reference to preferred embodiments, it is clear that this application covers all modifications or variants which correspond with the purpose of the invention. Accordingly, the embodiments presented do not restrict the claimed protection.