Abstract:
A method of estimating an amount of an unconsumed part of a recording material wrapped on a core of a roll is implemented as an application program for an electronic device having a camera. A storage device stores reference data about the roll and the recording material in an unconsumed state. The method includes taking a picture of the recording material and the core with a camera, deriving from the picture characteristics of a first and second number of pixels representing the core and the unconsumed part of the recording material, respectively, requesting from a user an identification of the roll and the recording material, receiving the identification, matching the identification with the reference data, and calculating the amount of the unconsumed part of the recording material by means of the matched reference data and the characteristics of the first and second numbers of pixels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(a) to Application No. 13305438.7, filed in Europe on Apr. 4, 2013, the entire contents of which is hereby incorporated by reference into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of estimating an amount of recording material wrapped upon a core of a roll. 
     2. Description of Background Art 
     Image reproduction apparatus are nowadays equipped with sensors to estimate an amount of recording material wrapped upon a core of a roll positioned in a recording material unit of the image reproduction apparatus. However, these sensors are coupled to the image reproduction apparatus and the roll needs to be mounted in the recording material unit before the estimation can take place. The latter action results in a lower productivity of the operator. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for estimating the amount of recording material wrapped upon a core of a roll, which method is user-friendly and productive. 
     This object is achieved by a method implemented as an application program for an electronic device having a camera, the method comprising the steps of taking a picture of the recording material and the core with the camera; deriving from the picture characteristics of a first number of pixels representing the core; deriving from the picture characteristics of a second number of pixels representing the unconsumed part of the recording material; requesting from a user an identification of the roll and the type of recording material; receiving from the user the identification of the roll and the type of recording material; matching the identification with reference data about the core and the roll in an unconsumed state; and calculating the amount of the unconsumed part of the recording material by means of the matched reference data and the characteristics of the first number of pixels and the characteristics of the second number of pixels. 
     The characteristics of the first number of pixels are the amount of the first number of pixels and the shape of the first number of pixels, the circumference of the first number of pixels, etc. The characteristics of the second number of pixels are the amount of the second number of pixels and the shape of the second number of pixels, the circumference of the second number of pixels, etc. 
     Also, a relation between an area amount of the first number of pixels and an area amount of the second number of pixels may be taken into account. 
     According to an embodiment of the method, the reference data about the core and the roll in an unconsumed state comprises data of the dimensions of the core and data of the dimensions of the recording material in an unconsumed state. The reference data are used to compare the volume of the recording material in an unconsumed state with the amount of an unconsumed part of the recording material wrapped upon the core. The latter amount can be derived from the characteristics of the first number of pixels and the characteristics of the second number of pixels. 
     According to an embodiment of the method, the electronic device has a user interface screen and the method further comprises the step of displaying the calculated amount of the unconsumed recording material on the user interface screen. In this way, the user is able to immediately see the calculated amount of the unconsumed recording material. This amount can be used to estimate the remaining recording material amount to be sufficient for a specific job to be controlled by the user, for example a print job, a paint job or any other job that has the recording material as an input material for the camera; deriving from the picture a first number of pixels representing a core of the roll; deriving from the picture a second number of pixels representing the recording material of the roll; and estimating the length of the roll based on the reference data, the first number and the second number, wherein the reference data comprises at least the length of the unused roll. 
     According to an embodiment, the electronic device comprises a user interface screen and a camera, and is connectable to a server at which the reference data about a roll and a recording material in an unconsumed state and an application program for implementing the method according to present invention is stored, wherein said electronic device is configured to invoke the application program via the user interface screen and display the calculated amount of the unconsumed part of the recording material at the user interface screen. 
     By doing so, the length is estimated by taking a photograph with the camera of the electronic device and performing calculations with an application installed on the electronic device or on a server being connectable via a network with the electronic device. When a picture of the end grain of the roll is taken, the picture will show the core of the roll, the recording material on the roll and a background. The end grain of the roll is the short side of the roll. The core of the roll forms an inner part of the picture, while the recording medium forms an outer part of the picture circumventing the inner part of the picture representing the core of the roll. Usually, the core of the roll and the recording material on the roll are easily distinguishable from each other. Usually, the recording material on the roll and the background are also easily distinguishable. If the latter is not the case, a background may be selected having a deviating color than the color of the recording material. The core of the roll is delimited by a first ellipse. The recording material of the roll is delimited by a second ellipse. The eccentricity of the first ellipse and the second ellipse are the same. The pixels within the first ellipse are counted as a first number of pixels. The pixels between the first ellipse and the second ellipse are counted as a second number of pixels. By taking a quotient of the first number and the second number, a number is established which is independent of the angle and the distance from which the picture is taken. Such a quotient is beforehand established in a calibration phase as a reference quotient for an unused roll of the same kind and width and stored as part of the reference data. The reference data also contains the length of an unused roll of the same kind. Such a reference quotient is then used in a calculation with the quotient of the roll under investigation and the length of the unused roll. In this way, the remaining length is easily calculated for the roll under investigation. 
     A calibration phase may be envisioned for delivering the reference data to be stored at the electronic device or at the server. Calibration may take place for a plurality of types of rolls of recording material. The reference data will comprise identification data for each kind of roll. The identification data are requested to be entered and added to the reference data during the calibration phase. The roll from which the first picture is taken has to be identified by entering identification data before the calculation of the remaining roll is performed. The entered identification data will be compared with the identification data already present in the reference data. 
     The electronic device may a mobile phone, a smart phone, a tablet personal computer, a notebook computer, a laptop computer or the like. Nowadays, electronic devices may be provided with a built-in camera for taking pictures by the user. Pictures taken may be shown at a user interface screen of the electronic device, may be stored in memory of the electronic device or in memory of the server, or may be processed by applications installed at the electronic device or installed at the server. The user interface screen may be touchable by a finger, a pen or a stylus or clickable by a mouse. A touch screen may be sensitive for a single touch gesture or a multi-touch gesture. An application program—shortly named app—may be stored at the storage of the electronic device or at the server. The application program may include the reference data or the reference data may be stored separately and linked to the application program afterwards. 
     According to a further embodiment, the method comprises the additional step of determining the width of the roll and wherein the reference data comprises the diameter of the core of the roll. The picture of the end grain of the roll is taken from a position outside a virtual roll being an extension of the real roll in a direction of the width of the roll, the method comprises the further steps of deriving from the picture a third number of pixels representing the width of the roll and estimating the width of the roll based on the reference data, the first number, the second number and the third number, wherein the picture of the end grain of the unused roll has been taken at a predetermined angle between a line from the camera to the closest outer bound position of the media of the unused roll and the normal vector of the plane of the end grain of the unused roll and the reference data comprises the diameter of the core of the roll. Since a number of pixels is visible and the reference data comprises the diameter of the core of the roll and not the width of the unused roll, it is still possible to derive the actual width of the roll from the reference data, the first number of pixels, the second number of pixels and the third number of pixels established here-above. The picture of the end grain of the unused roll has been taken at the predetermined angle. This picture also shows some pixels representing the width of the roll. Pixels in the direction of the width of the unused roll are counted as a third number. It is possible to estimate the width of the used roll, which is equal to the width of the unused roll, based on the first number, the second number and the third number, and the diameter of the core of the roll. The predetermined angle may be equal to 30, 45 or 60 degrees since it simplifies the calculations to be performed for the estimation, but any other predetermined angle, e.g. between 30 and 60 degrees, is also envisaged. 
     According to an embodiment of the method, the electronic device is a mobile phone. Nowadays a mobile phone is usually equipped with a camera and an amount of storage suitable for storing reference data and the application program. An app, i.e. an application program, may be resident in the storage of the mobile phone for performing the calculations according to the present invention. 
     According to another embodiment, the mobile phone is connectable via a network to a server at which the reference data and the application program resides. 
     According to another embodiment, part of the application program resides on the mobile phone and part of application program resides on the server. The mobile phone is compact and may be used to take the picture according to the method of the present invention. 
     According to an embodiment of the method, the electronic device is an image reproduction apparatus comprising a recording material unit suitable for comprising the camera, the recording material and the core of the roll, and a control unit for comprising storage for the application program and the reference data. 
     According to an embodiment of the method, the electronic device is an image reproduction apparatus comprising a recording material unit suitable for comprising the camera, the recording material and the core of the roll, and a control unit for controlling a connection to a server for storage of the application program and the reference data. 
     The present invention also relates to an electronic device comprising a user interface screen, a camera and a storage device configured to store reference data about a roll and a recording material, and the application program for implementing the method according to the present invention, said electronic device is configured to invoke the application program via the user interface screen and to display the calculated amount of the unconsumed part of the recording material at the user interface screen. 
     The present invention also relates to an electronic device comprising a user interface screen and a camera, wherein the user interface screen and the camera are connectable to a server on which reference data about a roll and the recording material in an unconsumed state are stored, wherein the application program for implementing the method according to the present invention is stored, and wherein said electronic device is configured to invoke the application program via the user interface screen and to display the calculated amount of the unconsumed part of the recording material at the user interface screen. 
     The present invention also relates to an image reproduction apparatus comprising a user interface screen, a recording material unit suitable for comprising a camera and a roll of recording material, an engine unit for consuming the roll of recording material, and a control unit for comprising a storage device for storing reference data about the roll of recording material in an unconsumed state and for storing the application program for implementing the method according to the present invention, wherein said image reproduction apparatus is configured to invoke the application program via a user action by means of the user interface screen and to display the calculated amount of the roll at the user interface screen. 
     The present invention also relates to an image reproduction apparatus comprising a user interface screen, a recording material unit suitable for comprising a camera and a roll of recording material, an engine unit for consuming the roll of recording material, and a control unit for controlling a connection to a server for storing reference data about the roll of recording material in an unconsumed state and for storing the application program for implementing the method according to the present invention, said image reproduction apparatus configured to invoke the application program via a user action by means of the user interface screen and to display the calculated amount of the roll at the user interface screen. 
     The present invention also relates to a computer program product embodied on a non-transitory computer readable medium that, when executed on a processor, performs a method according to the present invention. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic view of an image reproduction apparatus comprising a roll of media; 
         FIG. 2  is a schematic view of an electronic device according to the present invention; 
         FIG. 3  is a schematic view of a picture taken of an end grain of the roll; 
         FIG. 4  is a picture taken from an end grain of the roll and the width of the roll; 
         FIGS. 5-8  are schematic views of a picture taken of the end grain of the roll and a representation of the width of the roll; and 
         FIG. 9  is a schematic view of a picture taken of a top side of a recipient filled with a remaining amount of fluidum. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described with reference to the accompanying drawings, wherein the same or similar elements are identified with the same reference numerals throughout the several views. 
       FIG. 1  shows a reproduction system comprising workstations  8 A- 8 C connected to a network N. A reproduction apparatus  5  is available for a user working with one of the workstations  8 A- 8 C and intending to send a print job comprising a set of documents from one of the workstations  8 A- 8 C to the reproduction apparatus  5 . The reproduction apparatus  5  is connected to the network N and suited for receiving print jobs from the workstations  8 A- 8 C. The network N may be wireless. The reproduction apparatus  5  comprises a local user interface unit  2  suitable for displaying print jobs, selecting a print job and editing settings of a print job. A control unit  3  is suited to store a queue of print jobs, to check whether or not the queue is empty and to submit a document from a queued print job to the print engine of the reproduction apparatus  5  in order to be printed. Documents of a print job are stored in a storing device  7  contained in the control unit  3  at least for the time period that the document is printed by the print engine and finished by a finisher. 
     The reproduction apparatus  5  works up a roll  1  of media having a width indicated by an arrow  1   c  and a length. The length of the media on the roll is defined as a dimension of the media perpendicular to the width of the media in the plane of the media when completely unrolled. Media material may be paper, textile, metal plates, printed circuit plates, solar cell plates, overhead sheet material, plastic or any other kind of suitable receiving material or substrate. The roll  1  has been put in a holder. An end grain of the roll  1  comprises a part  1   a  of the core of the roll  1  and a side part  1   b  of the media of the roll  1 . In  FIG. 1 , the core of the roll  1  and the side part of the media on the roll  1  are visible, but image reproduction apparatuses exist that have a housing that shields the roll such that the core of the roll and the media on the roll are not visible from the outside of the reproduction apparatus  5 . 
       FIG. 2  is a schematic view of an electronic device  11  according to the present invention. The electronic device  11  comprises a user interface screen  15  for displaying user interactive dialogs and for requesting data to be input by a user, a storage unit  13  for storing pictures, applications, etc., and a camera  14  for taking pictures of objects in front of the eye of the camera  14 . The storage unit  13  may comprise the reference data according to the present invention. When an application program according to the present invention is started, a picture is asked to be taken by means of the camera  14  from an end grain of a roll to be investigated. The picture is stored in the storage unit  13  for further pixel counting and calculations. The user interface screen  15  is used to display the result of the method according to the present invention, i.e. the at least one characteristic of the roll comprising the remaining media. 
     In another embodiment, the electronic device  11  is connected via a network to a server. The reference data and/or the application program resides on the server. According to this embodiment, the picture is transmitted to the server for further pixel counting and calculations and the results of the calculations are transmitted to the electronic device  11 . 
       FIG. 3  is a schematic view of a picture  20  taken of an end grain of the roll  1  at a background represented by a grey color. (Roll  1  has been removed from the image reproduction apparatus  5  or has been taken from a stock of rolls). The picture is taken in front of the end grain of the roll, so that no part of the roll that is behind the end grain is visible in the picture  20 . A core of the roll is represented by a black filled-up ellipse  21 . Media on the roll are represented by a white area  22  between the black filled-up ellipse  21  and another larger ellipse  23 . 
     A picture like  FIG. 3  may be taken by the camera  14  of the electronic device  11  for an unused roll and stored in the storage unit  13  of the electronic device  11  as a second picture. The picture in  FIG. 3  is taken by the camera  14  of the electronic device  11  for a used roll and stored in the storage unit  13  of the electronic device  11 . 
     An application stored in the storage unit  13  is able to count the pixels of the picture  20  which represent the core of the roll, i.e. the pixels within and on the black filled-up ellipse  21  resulting in a first number N 1  of pixels. The application is also able to count the pixels of the picture  20  which represent the remaining media on the roll, i.e. the pixels of the picture  20  which have a white color within the larger ellipse  23 , resulting in a second number N 2  of pixels. The pixels of the grey background are not counted. 
     Such counting of a first number and a second number is also established for the second picture of an unused roll—in the storage unit  13  or at an external server—resulting in a first reference number N 1ref  and a second reference number N 2ref . The second picture may be taken from another angle and/or from another distance. The storage unit  13  also has stored a number L ref  of the length of an unused roll of the same kind as roll  1 . The goal of the present invention is to estimate a length L of the remaining media on the roll  1 . 
     The following formula (1) reveals the calculation of the wanted length L:
 
 L=L   ref *( N   2   /N   1 )/( N   2ref   /N   1ref )  (1)
 
     For convenience reasons, the picture  20  has been taken just in front of the end grain of the roll  1 , but may be taken from any angle as long as the end grain is still visible for the camera&#39;s eye. The concentric ellipses  21 ,  23  will become elongated or broadened. At each angle shot at each distance, the eccentricity of the smaller ellipse  21  will be the same as the eccentricity of the larger ellipse  23 . Therefore the elongation or broadening of the ellipses  21 ,  23  does not effect the truth of the formula (1) here-above. It is noted that a change in distance from the camera to the end grain also does not effect the truth of formula (1) 
     The term N 2ref /N 1ref  may be stored as a quotient Q ref  in the reference data. The quotient Q ref  and the term N 2 /N 1  are invariant qua shot angle with the end grain and qua shot distance to the end grain. 
       FIG. 4  shows a picture  30  taken of the end grain of the roll and the width of the roll, wherein the picture of the end grain of the roll is taken from a position outside a virtual roll being an extension of the real roll. A picture of the entire roll is taken. First, the remaining media length on the roll is calculated. Then, the width of the roll is calculated. 
     It is noted that the calculation of the remaining media length described here-below differs from the calculation of the remaining media length corresponding to  FIG. 3 , in that the picture according to  FIG. 3  is taken from directly above the roll standing on end. The calculation described here-below is done from a picture taken at an angle (around 45°) to the horizontal plane in order to make the calculation of the roll width with the same picture. 
     It is assumed that the picture is taken in a way so the roll axis is more or less in the widest direction of the picture frame (in order to maximize the roll image on the picture) called “y-direction” or “ordinate axis”. The axis orthogonal to “y-direction” is called the “x-direction” or “abscissa axis”. It is also assumed that a reference calibration of the Q ratio of a full roll (Q ref  as introduced before) has been done as described with regard to  FIG. 3 . In the shot conditions of the picture, the perspective effect (due to the camera focal length) in the roll core plan is neglected. The picture is binarized to transform all the paper pixels  31  as white pixels, and the roll core  32  and background pixels as black pixels. 
     A computation of the remaining length on the core is now elucidated on behalf of  FIG. 5 . Assuming that in the picture the apparent roll width (along the y-direction) is larger than the apparent diameter of the roll (in the x-direction), a roll axis  33  can be found by calculating a linear regression on the position of the white pixels from the binarized bitmap. The Cartesian equation of the axis  33  is: b=y−ax. 
     The ‘a’ and ‘b’ coefficients are estimated in the following way. The white pixels coordinates are named (x w ,y w ). We define the usual averages, centered variances and covariance on these coordinates: 
     
       
         
           
             
               
                 
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     The estimator of ‘b’ is then:
 
 {tilde over (b)}   w   =y   w   −ā   w   ·x   w  
 
     After the binarization, the roll core appears as a black ellipse  32  included totally inside the white pixels  31  on the processed picture as shown in  FIG. 6 . The ellipsis parameters are determined: center coordinates (x k ,y k ), a semi-major axis q k  and a semi-minor axis p k . 
     The black pixels coordinates are named (x k ,y k ) and, similar to the white pixels, the averages, centered variances and covariance are calculated:
 
   x   k   ;   y   k   ;σ x     k     2 ;σ y     k     2 ;σ xy     k   ;
 
     The estimators for x k ,y k ,p k  and q k  are: 
     
       
         
           
             
               
                 
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     Like the white pixels, the semi-major axis equation of the core ellipse is evaluated from: 
     
       
         
           
             
               
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                   _ 
                 
               
             
           
         
       
     
     As shown in  FIG. 7 , by construction, the ellipse  32  of the roll core (in black) and the ellipse of the roll paper seen from aside (in white) have a common center and common semi-axis lines  34 . 
     We compute the projected length 2 q   w  of the remaining paper semi-axis  34  (in dark color on  FIG. 7 ) by searching the minimal and maximal abscissas x w     min    and x w     max    of the white pixels on the semi-axis equation:
 
 {tilde over (b)}   k   =y−ã   k   ·x  
 
2 {tilde over (q)}   w =( x   w     max     x   w     min   )·√{square root over (1 |ã   k   2 )}
 
     The area ratio Q m  of the paper ellipse area by the core ellipse area is then: 
     
       
         
           
             
               Q 
               m 
             
             = 
             
               
                 
                   q 
                   ~ 
                 
                 w 
                 2 
               
               
                 
                   q 
                   ~ 
                 
                 k 
                 2 
               
             
           
         
       
     
     An estimation of the remaining length can be deduced as described with regard to  FIG. 3 . 
     Secondly, the roll width is computed. Since it is assumed that the core is physically a circle, the estimated angle θ between the camera optical axis and the roll core plan is evaluated with: 
     
       
         
           
             
               θ 
               ~ 
             
             = 
             
               
                 sin 
                 
                   - 
                   1 
                 
               
               ⁡ 
               
                 ( 
                 
                   
                     
                       p 
                       ~ 
                     
                     k 
                   
                   
                     
                       q 
                       ~ 
                     
                     k 
                   
                 
                 ) 
               
             
           
         
       
     
     It is also assumed that the user provides by the application program the physical diameter of the core Φ c . Therefore, the {tilde over (p)} k  estimator can be used to calibrate the scale factor f c  and to measure the lengths on the semi-minor axis of the core: 
     
       
         
           
             
               f 
               c 
             
             = 
             
               
                 Φ 
                 σ 
               
               
                 2 
                 ⁢ 
                 
                   
                     p 
                     ~ 
                   
                   k 
                 
               
             
           
         
       
     
     Minimal and maximal ordinates and y w     min    are y w     max    determined of the white pixels on the roll axis equation:
 
 {tilde over (b)}   w =   y   w   − ã   w ·   x   w   .
 
     The semi-minor axis  35  of the white ellipse according to  FIG. 8  is deduced from its semi-major axis and the black ellipse eccentricity: 
     
       
         
           
             
               
                 p 
                 ~ 
               
               kw 
             
             = 
             
               
                 
                   q 
                   ~ 
                 
                 W 
               
               · 
               
                 
                   
                     p 
                     ^ 
                   
                   k 
                 
                 
                   
                     q 
                     ~ 
                   
                   k 
                 
               
             
           
         
       
     
     The projected width W pr  of the roll  36  is then given by: 
     
       
         
           
             
               W 
               pr 
             
             = 
             
               
                 
                   
                     ( 
                     
                       
                         y 
                         
                           w 
                           max 
                         
                       
                       - 
                       
                         y 
                         
                           w 
                           min 
                         
                       
                     
                     ) 
                   
                   · 
                   
                     
                       1 
                       + 
                       
                         
                           a 
                           ~ 
                         
                         w 
                         2 
                       
                     
                   
                 
                 
                   
                     a 
                     ~ 
                   
                   w 
                 
               
               - 
               
                 2. 
                 ⁢ 
                 
                   
                     
                       
                         p 
                         ~ 
                       
                       k 
                     
                     · 
                     
                       
                         q 
                         ~ 
                       
                       w 
                     
                   
                   
                     
                       q 
                       ~ 
                     
                     k 
                   
                 
               
             
           
         
       
     
     In this evaluation, the perspective effect is neglected and an evaluator {tilde over (W)} r  of the physical roll width is: 
     
       
         
           
             
               
                 W 
                 ~ 
               
               r 
             
             = 
             
               
                 f 
                 c 
               
               × 
               
                 
                   
                     W 
                     pr 
                   
                   
                     cos 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       θ 
                       ~ 
                     
                   
                 
                 . 
               
             
           
         
       
     
     A similar method may be used to estimate a remaining fluidum in a non-translucent recipient by means of an electronic device having a camera and storage means comprising reference data about an empty recipient. The reference data may also be stored on a server that has a connection to the electronic device via a network. At the server, the reference data and/or the application program resides. 
     The recipient has an opening at a top side of the recipient. The area of the opening is wider than or equal to the area of a bottom of the recipient. The reference data comprises the dimensions of the recipient and the method comprises the steps of taking a picture of the maximal opening at the top side of the recipient by means of the camera, deriving from the picture a first number of pixels representing a visible part of the recipient, deriving from the picture a second number of pixels representing the visible part of the fluidum in the recipient, and estimating the volume of the remaining fluidum in the recipient based on the reference data, the first number and the second number, wherein the reference data comprises at least the volume of the fluidum when the recipient is fully filled. The volume of the fluidum when the recipient is fully filled is equal to the volume of the recipient. 
     By doing so, the volume is estimated by taking a photo with the camera of the electronic device and performing calculations with an application installed on the electronic device or on an external server connected to the electronic device. When a picture of the opening at the top side of the recipient is taken, the picture will show the recipient, the fluidum in the recipient and a background. The fluidum forms an inner part of the picture, while the recipient forms an outer part of the picture circumventing the inner part of the picture representing the fluidum. Usually, the fluidum and the recipient are easily distinguishable from each other. If this is not the case, a recipient may be selected having a deviating color than the color of the fluidum. Usually, the recipient and the background are also easily distinguishable. If this is not the case, a background may be selected having a deviating color than the color of the recipient. A vertical axis of the recipient is to be deduced from the picture. From this vertical axis, a first part corresponds to a distance from the top of the recipient to the fluidum and a second part corresponds to a distance from the bottom of the recipient to the top of the recipient. Knowing this, a simple formula for the remaining volume of the fluidum may be derived from these distances, and a volume of the recipient that is contained in the reference data. 
     If in a calibration phase more than one recipient is measured, the reference data will comprise identification data for each kind of recipient having a wide opening at the top side of the recipient. The identification data are requested to be entered and added to the reference data during the calibration phase. The identification may be performed by scanning an identification code on the recipient. The recipient from which the first picture is taken may also be identified by entering identification data before the calculation of the remaining fluidum is performed. The entered identification data will be compared with the identification data already present in the reference data. According to a further embodiment, the amount of the fluidum in the recipient is expressed as a number of volume units of the fluidum in the recipient. 
     Such a method comprises the steps of taking a picture from above the recipient with the camera, deriving from the picture a first number of pixels representing a fluidum in the recipient, deriving from the picture a second number of pixels representing the shape of the recipient, and estimating the remaining amount of fluidum in the recipient based on the reference data, the first number and the second number. The reference data may comprise the dimensions of the empty recipient and/or data derived from a picture of the empty recipient. 
     For example, the volume of coffee in a cup or the amount of paint remaining in a bucket may be estimated by taking a picture from above as shown in  FIG. 9 , comparing with reference data present at the smart phone or at a server connected to the smart phone and deriving the remaining amount from the reference data and the recognition of the shape  40  of the recipient and an amount of the fluidum in the recipient  40  from the picture. 
     The reference data contains the dimensions of the recipient object  40 , i.e. a total volume V total  of the recipient is known. An image processing algorithm suitable for recognizing the shape of the recipient  40  and an amount of fluidum in the recipient is used to detect a level  43  of remaining fluidum in the recipient and the recipient shape. The recipient dimensions can be different due to the angle of the camera when taking the picture, but the deformations are isomorphic. Therefore, it is possible to estimate the remaining fluidum in the recipient from the liquid level. 
       FIG. 9  shows a 3-dimensional container as a recipient and 2-dimensional shape on a top  41  of the recipient and a bottom  42  of the recipient. For convenience reasons, the top  41  and the bottom  42  are parallel, e.g. a bucket of paint. The total volume V total  of the recipient  40  is known. The fluidum to be measured can be differentiated from the inside of the recipient  40 . The diameter of the recipient is small enough to make negligible the difference of the apparent heights of the front side and the rear side. The recipient  40  is not translucent. However, for convenience reasons  FIG. 9  shows all line curves necessary to explain the estimation of the remaining fluidum. 
     The linear regression for detecting the vertical axis  33  in  FIG. 5  explained in the previous embodiment is applied to detect the vertical axis of the recipient  40 . From the vertical axis we can count the number of pixels of the height  44  of the front of the recipient (H) and we can count the number of pixels from the rear top edge to the inside-level of the contents (h) on line segment  45 . 
     The remaining volume of the fluidum is computed to be equal to:
 
 V   remaining   =h/H*V   total .
 
     In  FIG. 9  the vertical sides  46 ,  47  are assumed to be parallel, but a recipient having a top opening that is wider than the bottom of the recipient may be envisaged. The formula of V remaining  mentioned here-above is easily to be adapted to be suitable for such a recipient. For such a recipient the area size of the top opening and the area size of the bottom (determining an angle between two sides similar to the vertical sides  46 ,  47 ) may be part of the reference data and may be used in the calculations. If the diameter of the top opening equals X and the diameter of the bottom equals x, then the volume of the complete filled recipient is 1/12*π*(X 3 −x 3 ). If the same heights H and h are deducted from the picture, we get the following approximating formula for the remaining fluidum:
 
 V   remaining = 1/12*π*(( X −( X−x )*( h/H )) 3   −x   3 ).
 
     It may be clear to the skilled person that the various embodiments of the method, the electronic devices and the image reproduction apparatuses may be combined in one way or another in order to establish an appropriate and applicable embodiment of the method according to the invention. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.