Abstract:
A printer and a method are provided for determining a type of print medium in a printer. The method comprises the steps of: obtaining a first set of reflectance data from a first side of the print medium; obtaining a second set of reflectance data from a second side of the print medium; comparing the first set of reflectance data to the second set of reflectance data; and categorizing the print medium as being in one of a plurality of print medium categories based upon the comparison of the first set of reflectance data and second set of reflection data.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is related to printers and to methods for determining a type of print medium loaded therein.  
       BACKGROUND OF THE INVENTION  
       [0002]     There are a wide variety of items upon which images can be printed by modem printers such as papers, films, transparencies, packaging materials, solid objects, and the like. Even within relatively focused use printers such as home and office printers that typically print only on relatively flat papers or transparencies there is an increasingly bewildering assortment of available print mediums such as a wide variety of colored papers, white papers, transparencies and photo papers. To ensure that a printer can print in a manner that yields a desired level of quality, it is useful to adapt the printing process to conform to the print medium that is to be used in the printing process.  
         [0003]     Accordingly it is highly advantageous to determine a print medium type before printing. Generally, two types of approaches have been developed for doing this. A first approach for doing this is to provide data with the print medium that is to be read by a separate reader in the printer. Such data can be provided the form of visible or invisible markings on the medium. Such data can also be provided in the form of a mechanical, electromechanical or electronic memory device that stores information identifying the print medium that can be read to provide a medium type. Such markings or memories can be stored on the medium itself or on packaging associated with the medium. These approaches while highly useful can add cost to both the printer and to the medium.  
         [0004]     A second approach seeks to avoid the costs of providing data with the medium by supplying equipment in a printer to determine a print medium type based upon analysis of a non-marked print medium prior to its use in printing. One example of this approach can be found in U.S. Pat. No. 6,561,643 entitled Advanced Media Determining System for Inkjet Printing, filed by Walker et al. The &#39;643 patent provides a system that is said to be capable of categorizing a type of incoming media entering an inkjet or other printing mechanism to identify the media without requiring any special manufacturer markings.  
         [0005]     In &#39;643 patent, the leading edge of the incoming media is optically scanned using a blue-violet light to obtain both diffuse and specular reflectance values. A Fourier transform of these reflectance values generates a spatial frequency signature for the incoming media. The spatial frequency is compared with known values for different types of media to categorize the incoming media according to major categories, such as transparencies, glossy photo media, premium paper and plain paper, as well as specific types of media within these categories, such as matte photo premium media and high-gloss photo media. An optimum print mode is selected according to the determined media type to automatically generate outstanding images without unnecessary user intervention. A printing mechanism constructed to implement this method is also provided. Such a mechanism is complicated and costly as it requires the measurement of both specular and diffuse reflection, complex statistical analysis of the same in real time and an accurate library of signatures of particular print mediums. And it is still very difficult for such a system to discriminate certain media types such as colored plain paper vs. photo paper.  
         [0006]     What is needed in the art is a system that enables, at low cost, simple detection of a print medium type without requiring frequency specific light detection or analysis of the reflectance data.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect of the invention, a method of determining a type of print medium in a printer is provided. The method comprises the steps of: obtaining a first set of reflectance data from a first side of the print medium; obtaining a second set of reflectance data from a second side of the print medium; comparing the first set of reflectance data to the second set of reflectance data; and categorizing the print medium as being in one of a plurality of print medium categories based upon the comparison of the first set of reflectance data and second set of reflection data.  
         [0008]     In another aspect of the invention, a printer comprises: a medium transport for conveying a print medium from a supply to a printing area; a printhead at the print area for forming an image using a print medium; a first reflectance sensor positioned in the medium transport path to confront the print medium before the print medium is conveyed to the print area, the first reflectance sensor having a first light source adapted to supply light to a first side of the print medium and a first detector adapted to generate a first reflectance signal that is indicative of an amount of the supplied light that is reflectively returned to the first detector; a second reflectance sensor positioned in the medium transport path to confront the print medium before the print medium is conveyed to the print area, the first reflectance sensor having a second light source adapted to supply light to a rear side of the print medium and a second detector adapted to generate a second reflectance signal that is indicative of an amount of the supplied light that is reflectively returned to the second detector; and a controller for causing the medium transport to transport the print medium to the printing area, for causing the first light source to supply light to the first side of the print medium and to detect the amount of the supplied light that is reflectively returned thereto, for causing the second light source to supply light to the back side of the print medium and to detect the amount of the supplied light that is reflectively returned thereto; the controller further being adapted to receive the first reflectance signal and the second reflectance signal and to determine a category for the print medium from a plurality of categories based upon a comparison of the reflectance of the first side of the print medium and the second side of the print medium as indicated by the first reflectance signal and the second reflectance signal.  
         [0009]     In yet another aspect of the invention, a printer comprises: a medium transport for moving a print medium through a medium transport path to a printing area; a first light source and first detector positioned on a first side of the medium transport path for collecting a first set of reflectance data from a first side of the print medium; a second light source and a second detector positioned on a second side of the medium transport path for collecting a second set of reflectance data from a second side of the print medium; and wherein a controller causes the first and second sets of reflectance data to be collected prior to a point where a print medium in the print medium transport path is moved to the printing area.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a first embodiment of a printer of the invention;  
         [0011]      FIG. 2  provides a flow diagram showing one embodiment of a method for operating the printer of  FIG. 1 ;  
         [0012]      FIG. 3  is an illustration of an example distribution of first side reflectance values of an image receiving side of a hypothetical set of possible print mediums;  
         [0013]      FIG. 4  is an illustration of an example distribution of first side reflectance values and second side reflectance values of a hypothetical set of possible print mediums;  
         [0014]      FIG. 5  is an illustration of an example distribution of the differences between the first sides of each print medium of the hypothetical set of possible print mediums;  
         [0015]      FIG. 6  is an illustration of first side reflectance values of an image receiving side of a low differential category of print mediums within the hypothetical set of possible print mediums;  
         [0016]      FIG. 7  is an illustration of first side reflectance values of an image receiving side of a high differential category of print mediums within the hypothetical set of possible print mediums;  
         [0017]      FIG. 8  illustrates one possible arrangement of reflectance sensor that can be used in the present invention and in which a common light source provides light to both of a first side reflecting mirror and a second side reflecting mirror which in turn direct a portion of this light as first side source light onto first side and a portion of this light as second side source light onto second side respectively of receiver medium;  
         [0018]      FIG. 9  illustrates another possible arrangement of reflectance sensor that can be used in the present invention;  
         [0019]      FIG. 10  illustrates another possible arrangement of a reflectance sensor that can be used in the present invention; and  
         [0020]      FIG. 11  illustrates still another possible arrangement of a reflectance sensor that can be used in the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]      FIG. 1  shows a first embodiment of a printer  20  of the invention. In the embodiment of  FIG. 1 , printer  20  comprises a housing  21  having a print engine  22  that applies markings or otherwise forms an image on a print medium  24 . Print engine  22  can record images on print medium  24  using a variety of known technologies including, but not limited to, conventional four color offset separation printing or other contact printing, silk screening, dry electrophotography such as is used in the NexPress  2100  printer sold by Eastman Kodak Company, Rochester, New York, USA, thermal printing technology, drop on demand ink jet technology and continuous inkjet technology. For the purpose of the following discussions, print engine  22  will be described as being of a type that generates color images. However, it will be appreciated that this is not necessary and that the claimed methods and apparatuses that are described herein can be practiced with a print engine  22  that is adapted to form monotone images such as black and white, grayscale or sepia toned images. Similarly, the methods and apparatuses that are described herein can be practiced with a print engine  22  that is adapted to deliver images in the form of a pattern of one or more functional materials on print medium  24 . Examples of such functional materials include but are not limited to electrically conductive, insulating, semi-conductive or resistant materials of a type that can be used in combination to form electrical circuits and the like, optical materials of a type that are adapted for form optical conductors, reflectors, lenses and pathways. Other examples of functional materials include polymers, ceramics, metals and other such functional materials that can be used to form mechanical structures using print medium  24  as a support.  
         [0022]     Print medium  24  can take any of a wide variety of forms including but not limited to a plain paper, photo-paper, non-photo paper, glossy paper, glossy paper, matte paper, transparency, translucent film, transparent film, packaging material, ceramic product, wood product, metal product, fabric, or a glass or glass fiber product, a polymer product, a mono-mer product or any other flexible, rigid or other material of a type that can cooperate with print engine  22  and a medium advance  26  so that an image can be recorded thereon. The image formed thereon can be of a type that is intended for viewing, a type that is machine readable or type that comprises a functional pattern of functional material such as an optical or electrical circuit or any combinations of such images.  
         [0023]     Medium advance  26  is used to position print medium  24  and/or print engine  22  relative to each other to facilitate recording of an image on print medium  24 . In the embodiment illustrated in  FIG. 1 , medium advance  26  moves print medium  24  through a printing area  27  so that print engine  22  can print an image on print medium  24 . Medium advance  26  can comprise any number of well-known systems for moving receiver medium  24  within printer  20 , including a motor  28 , driving pinch rollers  30 , a motorized platen roller (not shown) or other well-known systems for the movement of paper or other types of print medium  24 .  
         [0024]     Print engine  22  and medium advance  26  are operated by a processor  34 . Processor  34  can include, but is not limited to, a programmable digital computer, a programmable microprocessor, a programmable logic processor, a series of electronic circuits, a series of electronic circuits reduced to the form of an integrated circuit, or a series of discrete components. Processor  34  operates printer  20  based upon input signals from a user input system  36 , sensors  40 , a memory  60  and a communication system  74 .  
         [0025]     User input system  36  can comprise any form of transducer or other device capable of receiving an input from a user and converting this input into a form that can be used by processor  34 . For example, user input system  36  can comprise a touch screen input, a touch pad input, a 4-way switch, a 6-way switch, an 8-way switch, a stylus system, a trackball system, a joystick system, a voice recognition system, a gesture recognition system or other such systems. In the embodiment illustrated in  FIG. 1 , user input system  36  includes a keypad  37  and mouse  38  for receiving input from a user. A display  39  is connected to processor  34  and provides information to a user so that the user can interact with printer  20 . Various components of user input system  36  and/or display  39  can be located within housing  21  or can be separate therefrom. Where separate, user input system  36  and display  39  can exchange signals with processor  34  by way of wired or wireless signals and connections.  
         [0026]     Sensors  40  are provided in printer  20  to sense environmental, operating and other conditions relevant to the operation of printer  20  and to convert this information into a form that can be used by processor  34  in governing operation of print engine  22 , and/or other systems of printer  20 . Sensors  40  can include audio sensors adapted to capture sounds. Sensors  40  can also include print medium positioning sensors (not shown) and other sensors used internally to control printer operations.  
         [0027]     Sensors  40  also include a first side reflectance sensor  42  and a second side reflectance sensor  44 . Generally, reflectance sensors  42  and  44  can comprise any combination of visible or non-visible light sources known in the art that can be used to supply light and any light detectors known in the art that can sense an amount of the light from the light sources that is reflectively returned to the detectors.  
         [0028]     It will be appreciated that first side light detector  48  and second side light detector  52  can be arranged to measure either specular reflectance or diffuse reflectance and/or both specular and diffuse reflectance. Specular reflectance is generally referred to herein as an amount of source light that is applied to a surface at an angle of incidence and that is reflected by the print medium at an angle that is generally equal to the angle of incidence, however, it will be appreciated that there are a number of generally accepted variations of the definition of specular reflectance known in the art for particular applications and that there are a variety methods for measuring specular reflectance, any of which can be used in determining the specular reflectance of the print medium  24 . Diffuse reflectance is generally referred to herein as a measure of an amount of light reflected by a surface in a broad range of directions and in that sense can be considered to be a measure of the light scattering properties of a surface such as first side  24   a  of print medium  24 . Here too, there are a number of generally accepted definitions of diffuse reflectance known in the art for particular applications and that there are a variety methods for measuring diffuse reflectance, any of which can be used in determining the diffuse reflectance of print medium  24 .  
         [0029]     In the embodiment shown in  FIG. 1 , first side reflectance sensor  42  has a first side light source  46  that directs first side source light SL 1  at first side  24   a  of receiver medium  24  and a first side light detector  48  that receives first side reflected light RL 1  comprising that portion of source light SL 1  that is reflected by first side  24   a . Similarly, second side reflectance sensor  44  has a second side light source  50  that directs second side source light SL 2  onto a second side  24   b  of receiver medium  24  and a second side light detector  52  that receives second side reflected light RL 2  comprising that portion of second side source light SL 2  that is reflected by second side  24   b.    
         [0030]     The angular relationships between first side light source  46  and first side light detector  48 , between second side light source  50  and second side light detector  52  shown in  FIG. 1  are exemplary only and a wide variety of other arrangements can be used so long as the desired type of reflectance of each side of print medium  24  can be measured with a degree of accuracy necessary for repeatable measurements. In this exemplary example, first side light detector  48  and second side light detector  52  are arranged to receive light that is reflected by first side  24   a  of print medium  24  and second side  24   b  of print medium  24  at an angle that is equal to an angle of incidence of first side source light SL 1  and second side source light SL 2 , respectively. Accordingly, in this example embodiment, first side light detector  48  and second side light detector  52  are positioned so that they can provide a meaningful indication of the specular reflectance of first side  24   a  and second side  24   b  of print medium  24 , respectively.  
         [0031]     First side light source  46  and second side light source  50  can comprise any of a number of light sources including but not limited to one or more of a light emitting diode, a laser, a laser diode, a monochromatic light source, or a polychromatic light source. The light emitted can be in the visible or non-visible wavelengths or a combination thereof In certain embodiments, at least one of the first side light source  46  and second side light source  50  has two or more light sources wherein the lights sources have different optical properties such as emitting light of different wavelengths. In such an embodiment, first side light detector  48  or second side light detector  52  can be capable of detecting light of each of the wavelengths, or a set of more than one detector can be provided so that a range of wavelengths of reflected light can be detected. In another embodiment, some of which are shown in greater detail below, at least one of the first side light source  46  and second side light source  50  can contain two or more light sources with the light sources being arranged to have a different orientation so that they apply source light to print medium  24  at different angles of incidence.  
         [0032]     As shown in the embodiment of  FIG. 1 , print medium  24  is a paper type material that is moved from a print medium storage area  76  to printing area  27 . Such a print medium  24  of this type can comprise any of a number of different types of print mediums  24 . For example, a commercial or home printer of a type that uses paper type print mediums  24  are often called upon to print using any of a number of types of such print medium  24  such as plain paper, colored paper, matte finish paper, a gloss paper, and transparencies. Each of these different types of print medium  24  forms images or other patterns having highly desirable characteristics when processor  34  causes print engine  22  to print in a manner that is adapted for use with such a print medium  24 . As will be described in greater detail below, processor  34  is adapted to determine a print medium type based upon the signals from sensors  40 .  
         [0033]     As is also shown in  FIG. 1 , printer  20  has a memory  60 . Memory  60  can include conventional memory devices including solid state, magnetic, optical or other data storage devices. Memory  60  can be fixed within printer  20  or it can be removable. In the embodiment of  FIG. 1 , memory  60  is shown having a hard drive  62 , a disk drive  64  for a removable disk such as an optical, magnetic or other disk memory (not shown) and a memory card slot  66  that holds a removable memory  68  such as a removable memory card and has a removable memory interface  70  for communicating with removable memory  68 . Data including but not limited to control programs, digital images and metadata can also be stored in a remote memory system  72 .  
         [0034]     In the embodiment shown in  FIGS. 1 and 2 , printer  20  has a communication system  74  for communicating with, for example, remote memory system  72 . Communication system  74  can be for example, an optical, radio frequency circuit having a transducer and appropriate signal processing circuitry to convert image and other data into a form that can be conveyed to a remote device such as remote memory system  72  by way of an optical signal, radio frequency signal or other form of signal. Communication system  74  can also be used to receive a digital image and other information from a host computer or network (not shown). Communication system  74  provides processor  34  with information and instructions from signals received thereby.  
         [0035]      FIG. 2  provides a flow diagram showing one embodiment of a method for operating printer  20  of  FIG. 1 . As is shown in the embodiment of  FIG. 2 , a print order is received by printer  20  (step  80 ). The print order provides instructions sufficient for processor  34  to begin a print sequence and can include an instruction to print an image, the image data for the image to be printed, print quantity information or information identifying a selected print medium  24  upon which the image is to be printed. The print order can also contain other information including but not limited to as delivery date, delivery destination information, consumer information, and point of sale information.  
         [0036]     Processor  34  can receive a print order in a variety of ways including but not limited to a receiving entries made at user input system  36 , receiving signals received at communication system  64 , or in response to data provided by way of memory  50  including but not limited to data provided by way of a removable memory card  68 .  
         [0037]     As shown in  FIG. 2 , when processor  34  receives the print order, processor  34 , initiates a print medium loading process (step  82 ). During the print medium loading process (step  82 ) processor  34  sends signals causing medium advance  26  to move a print medium  24  from a storage location  76  to a printing area  27 . In the embodiment illustrated in  FIG. 1 , print medium  24  is passed through a scanning area  78  as it is moved from a storage location  76  to printing area  27 . First side reflectance sensor  42  and second side reflectance sensor  44  are arranged so that reflectance data can be obtained and processed while print medium  24  is advanced through scanning area  78 . In other embodiments, scanning area  78  can be located at printing area  27 .  
         [0038]     A set of first side reflectance data is obtained from a first side of the print medium (step  84 ) using first side reflectance sensor  42 . In the embodiment of  FIG. 1 , processor  34  generates a first side illumination signal that cause first side light source  46  to radiate first side source light SL 1  having a known intensity and/or wavelength at a time when print medium  24  is positioned in scanning area  78 . First side light detector  48  receives first side reflected light RL 1 , generates a first intensity signal which indicating an intensity of first side reflected light RL 1 . The first intensity signal is received by processor  34 . Processor  34  uses the first intensity signal to determine a first set of reflectance data. In one embodiment, the absolute value of the first intensity signal or an intensity of the first side reflected light determined therefrom is used to form the first set of reflectance data. In other embodiments, the intensity of the first side reflected light RL 1  indicated by the first intensity signal is compared to a known intensity or range of intensities of the first side source light SL 1  to determine a first set of reflectance data.  
         [0039]     The first set of reflectance data can comprise a single data point or a plurality of data points and can be based upon the reflectance of a single area of print medium  24  defined by an area of first side  24   a  of print medium  24  that is exposed to first side source light SL 1  when print medium  24  is held in a stationary position during the reflectance determination. The first set of reflectance data can also be based upon the reflectance of a larger area of first side  24   a  of print medium  24  such as might be obtained by measuring reflectance of first side  24   a  over a period of time while print medium  24  is being moved. In the latter embodiment, the reflectance data can comprise a set of more than one reflectance measurements that indicate the reflectance of portions of first side  24   a  that that are illuminated by first side source light  24   a  during reflectance measurements. Alternatively, the first set of reflectance data can comprise an average, mean, or other overall measure of the reflectance that can be determined based upon statistical analysis of more than one reflectance measurement. In certain embodiments, first side light detector  48  can be adapted to detect light in a manner that averages the intensity of the first side reflected light over a period of time during which different portions of first side  24   a  of print medium  24  are exposed to first side source light SL 1  and to generate a first side reflectance signal indicative of an average or overall reflectance of first side  48 . As noted above, first side light detector  48  can be adapted to sense specular reflection, diffuse reflection, or both. Accordingly, the first set of reflectance data can be based upon sensed specular reflection, diffuse reflection or both.  
         [0040]      FIG. 3  illustrates an example distribution of first side reflectance values of an image receiving side of a representative set of possible print medium types that could be used in a particular printer. In this example, the set of representative print mediums includes a first photo paper  100 , a second photo paper  102 , a third photo paper  104 , a fourth photo paper  106 , a fifth photo paper  108 , a first plain paper  110 , a second plain paper  112 , a third plain paper  114 , a fourth plain paper  116 , a fifth plain paper  118 , a first transparency  120  and a second transparency  122 .  
         [0041]     As can be seen from  FIG. 3 , it can be difficult to establish that a particular print medium is of a particular print medium type based upon the first side reflectance values because there are situations wherein the first side reflectance values for one print medium type are quite similar to the first side reflectance values of another print medium type. For example, in the example of  FIG. 3 , first side reflectance values for fifth photo paper  108 , first transparency  120  and second transparency  122  are quite similar and fifth photo paper  108  could be mistakenly determined to be a transparency. Similarly, third plain paper  114  could mistakenly be determined to be a photo paper such as photo paper  102 . Accordingly, there is a need to obtain additional data that can be used to allow better print medium type discrimination and to do so in a manner that is reliable, cost effective and efficient.  
         [0042]     In the present invention, a second set of reflectance data is obtained from a second side  24   b  of print medium  24  (step  86 ) using second side reflectance sensor  44 . In the embodiment of  FIG. 1 , processor  34  generates a second side illumination signal that causes second side light source  50  to radiate second side source light SL 2  having a known intensity and/or wavelength at a time when print medium  24  is positioned in scanning area  78 . Second side light detector  52  receives second side reflected light RL 2 , generates a second intensity signal which indicates indicating an intensity of second side reflected light RL 2 . The second intensity signal is received by processor  34 . Processor  34  uses the second intensity signal to determine a second set of reflectance data. In one embodiment, the absolute value of the second intensity signal or an intensity of the second side reflected light RL 2  determined therefrom is used to form the second set of reflectance data. In other embodiments, the intensity of the second side reflected light RL 2  indicated by the second intensity signal is compared to a known intensity or range of intensities of second side source light SL 2  to determine the second set of reflectance data.  
         [0043]     The second set of reflectance data can comprise a single data point or a plurality of data points and can be based upon the reflectance of a single area of print medium  24  defined by an area of second side  24   b  of print medium  24  that is exposed to second side source light SL 2  when print medium  24  is held in a stationary position during the reflectance determination. The second set of reflectance data can also be based upon the reflectance of a larger area of second side  24   b  of print medium  24  such as might be obtained by measuring reflectance of second side  24   b  mover a period of time when print medium  24  is being moved. In the latter embodiment, the second set of reflectance data can comprise a set of more than one reflectance measurements that indicate the reflectance of portions of second side  24   b  that are illuminated by second side source light SL 2  during reflectance measurements. Alternatively, the second set of reflectance data can comprise an average, mean, or other overall measure of second side reflected light RL 2  that can be determined based upon statistical analysis of more than one reflectance measurement. In certain embodiments, second side light detector  52  can be adapted to detect light in a manner that averages the intensity of second side reflected light RL 2  over a period of time during which different portions of second side  24   b  of print medium  24  are exposed to second side source light SL 2  and to generate a second side reflectance signal indicative of an average or overall reflectance of second side  24   b.    
         [0044]     As noted above, second side light detector  52  can be adapted to sense specular reflection, diffuse reflection or both, accordingly the first set of reflectance data can be based upon sensed specular reflection, diffuse reflection or both.  
         [0045]      FIG. 4  shows a side by side comparison of the first side reflectance and second side reflectance of the hypothetical set of print medium types of  FIG. 3 . As can be seen from  FIG. 4 , there are variations in the second side reflectance measures that can be used to help discriminate between print mediums. In one embodiment, first set of reflectance data and second set of reflectance data are then compared (step  88 ) and print medium  24  is assigned to one of a plurality of print categories based upon the comparison of the first set of reflectance data and the second set of reflectance data.  
         [0046]     In step  88  a first side/second side reflectance comparison is used to associate a print medium with, for example, one of at least two categories of print mediums, with each category including only a subset of the possible types of print mediums that can be used in printer  20 . This categorization can be made by determining a difference between first side reflectance values and second side reflectance values for each of the print mediums in the set of representative print mediums and establishing a first/second side reflectance differential threshold that can be used to categorize the print medium types.  
         [0047]     As can be seen from  FIGS. 4 and 5 , plain papers  110 - 118  each have a relatively high second side reflectance value and because these relatively high second side reflectance values are subtracted from first side reflectance values that are somewhat lower in general than the first side reflectance values of the photo papers, the differential reflectance values of the plain papers shown in  FIG. 5  are generally much lower than the differential reflectance values of either of the photo papers  102 - 108 . This allows, generally, a threshold to be determined to segregate plain papers and photo papers into a low differential reflectance category and a high- differential reflectance categories.  
         [0048]     Similarly, because transparencies  120  and  122  typically have a first side reflectance and a second side reflectance that are quite similar, the differential reflectance values are typically low and thus transparencies  120  and  122  can be separated into the low differential reflectance category with the plain papers also using threshold  130 .  
         [0049]     Accordingly, as shown in  FIG. 4 , processor  34  can use a threshold,  130  to identify with an acceptable degree of precision whether a print medium  24  is in a category that generally includes transparencies and plain paper or in a category that generally includes photo papers. This information can be used by processor  34  to in printing operations.  
         [0050]     This categorization also greatly facilitates the optional step (step  92 ) of making a further determination as to the type of medium by limiting the number of print medium types that must be considered when determining a medium type for a particular medium so that discrimination between medium types can be accomplished. Within each category, discrimination can be made on the basis of first side reflectance values and, optionally, second side reflectance values or combined reflectance values can be used to provide greater discrimination of medium type within a category.  
         [0051]     For example, as shown in  FIG. 6 , there is little overlap of first side reflectance values within the category of low combined reflectance medium types. Similarly, as shown in  FIG. 7 , there is little overlap of first side reflectance values within the category of high combined reflectance medium types.  
         [0052]     Further, even where the potential for such overlap exists, comparison of differential reflectance values for such print mediums can be used to better discriminate between medium types. For example, as illustrated in  FIG. 6 , the fourth plain paper  116  and the fifth plain paper  118  have similar first side reflectance values, however, discrimination therebetween can be made based upon the differential reflectance values shown in  FIG. 5 . For example, as shown in  FIG. 6 , once that it is known that a print medium  24  is in a low differential reflectance category discrimination between medium types with that category can be made for example by applying a print medium type detection threshold  132  to the first side reflectance data for the print mediums in that category. Further categorization between print medium types can be performed using one or more additional thresholds. An example of such an additional threshold is threshold  134  that separates photo paper  100  from plain papers  112 - 118 . Or alternatively, additional categories can be established for such print mediums.  
         [0053]     Specifically, in  FIG. 6 , a determined first side reflectance value of a print medium within the low differential reflectance category can be compared against first threshold  132  to determine if a print medium is a transparency  120  or  122  and additional threshold  134  can be used to determine whether the print medium is first photo paper  100 . The value of first threshold  132  or additional threshold  134  can be in a range that is also associated with certain photo-papers. This would create uncertainty if such photo papers  102 - 108  had not been excluded from consideration as a possible print medium type. However, with these papers excluded from consideration, reliable discrimination becomes possible.  
         [0054]     Once that a category has been determined for print medium  24  and optionally the type of the print medium has been determined, processor  34  can use this information regarding the category of a print medium  24  and/or type of a print medium  24  in the performance of at least one printing function (step  94 ). Examples of such a printing function include determining colors to be printed on print medium  24 , determining a printing speed for printing using print medium  24 , determining whether an image can be printed using print medium  24 , determining whether there is a need to reload the a print medium supply  66 , selecting a dye or colorant set for use in printing using print medium  24  or for other purposes related to printing an image. Other examples of such a printing function include determining before printing, whether printer  20  has been loaded with a desired type of print medium  24 .  
         [0055]     For example, a print medium  24  can be received that requests that a particular type of print medium  24  is to be used during the satisfaction of a particular print order. For example, a print order can request that an image is to be printed on a transparency and the reflectance values from of a print medium drawn from print medium source  76  can be obtained an compared to verify that the requested medium type is being used. Additionally, where the quality of the print medium is of importance, controller  34  is further adapted to use the reflectance data to determine whether the print medium is has a quality level required for a particular print medium. For example, a print medium  24  comprises a photo paper that is to be used to render a glossy print, the reflectance data can be obtained and analyzed in a manner that allows a determination of the evenness of the gloss to be made.  
         [0056]     A further printing function can include determining whether a print medium  24  is loaded into printer  20  with a desired side positioned so that it can be printed on. For example, a glossy type photo paper will have one side that is treated to have a glossy surface texture. An image is to be recorded on this side. A comparison of a first side reflectance and a second side reflectance can be used to identify whether such a photo paper type is loaded with the proper side facing print engine  22  by detecting reflectance values that are the inverse of what is expected.  
         [0057]     Where the print medium  24  in printer  20  does not comprise a proper print medium type, where the print medium  24  has been mis-loaded or where print medium  24  has an unacceptable level of quality, controller  34  can prevent printing until the problem is corrected and/or can cause a warning to be presented using for example display  39 .  
         [0058]     Other types of comparison can be used to compare the first set of reflectance data to the second set of reflectance data. For example, the ratio of specular and diffuse reflectance can be used as a measure of reflectance and compared in similar fashion. Alternatively, the standard deviation of either specular or diffuse reflectance over a wide area can be used as a measure of reflectance of a side of print medium  24  and compared, or the ratio of reflectance between two or more different light sources (either optical properties or orientation) can be compared in like fashion.  
         [0059]     Further, it will be appreciated that, in the embodiment of  FIG. 1 , first side reflectance sensor  42  and second side reflectance sensor  44  each have an individual and separate light source and light detector. In other embodiments of the invention, common components can be used for radiating source light or for detecting reflected light. For example, arrangement of mirrors, optical fibers, light pipes or other structures well known to one of ordinary skill in the art can be provided that direct source light from a common source to both first side  24   a  and second side  24   b  of print medium  24 .  
         [0060]      FIG. 8  illustrates one possible arrangement of a reflectance sensor of this type comprising an embodiment of first side reflectance sensor  42  and second side reflectance sensor  44  wherein a common light source  138  provides light to both of a first side reflecting mirror  140   a  and a second side reflecting mirror  140   b  which in turn direct a portion of this light as first side source light SL 1  onto first side  24   a  and a portion of this light as second side source light SL 2  onto second side  24   b  respectively of receiver medium  24 . First side light detector  48  and second side light detector  52  senses first side reflected light RL 1  and second side reflected light RL 2 .  
         [0061]      FIG. 9  also shows another arrangement of a reflectance sensor such as first side reflectance sensor  42  of the invention. In this embodiment, first side reflectance sensor  42  has a first side light detector  48  that is adapted to detect specular reflectance and diffuse reflectance. In this regard, a first side light source  46  applies first side source light SL 1  to a first side  24   a  of medium  24  and a portion of first side reflected light RL 1  is reflected by first side  24   a  of medium  24  in a specular fashion to a first side specular reflectance sensor  144  while another portion of first side reflected light RL 1  is reflected in a diffuse fashion to a first side diffuse reflectance sensor  146 . As a shown in the embodiment of  FIG. 9 , first side specular reflectance sensor  144  is positioned relative to medium  24  at an angle that is equal to an angle of incidence of first side source light SL 1 . As is also shown in the embodiment of  FIG. 9 , first side diffuse reflectance sensor  146  is positioned relative to medium  24  at a position wherein first side diffuse reflectance sensor  146  will receive a portion of source light SL 1  that is reflected by medium  24  at an angle that is other than an angle that is equal to be angle of incidence of source light SL 1 .  
         [0062]      FIG. 10  shows another embodiment of a reflectance sensor such as first side reflectance sensor  42 . In this embodiment, first side reflectance sensor  42  is adapted to sense the diffuse reflectance and the specular reflectance of first side  24   a  of print medium  24  using a single first side light detector  48 . As can be seen in this embodiment, a first side light source  46  has a light source  150  is provided that applies a portion of source light SL 1  to first side  24   a  of print medium  24  at an angle of incidence that is equal to an angle at which first side light detector  48  is arranged relative to first side  24   a  of print medium  24 , and an additional light source  152  that is arranged relative to first side  24   a , to apply an additional portion of source light SL 1  at an angle of incidence that is not equal to the angle at which first side light detector  48  is arranged relative to first side  24   a . Accordingly, first side reflected light RL 1  comprises light from both sources and thus is indicative of both the specular and diffuse reflectance of first side  24   a . It will be appreciated that a similar structure can be used, as desired, to provide a second side reflectance sensor  44  that senses the diffuse and specular reflectance of second side  24   b  of print medium  24 .  
         [0063]      FIG. 11  shows still another embodiment of a reflectance sensor such as first side reflectance sensor  42  useful in the present invention. In this embodiment, first side reflectance sensor  42  is adapted to sense the diffuse reflectance of first side  24   a  using a single first side light detector  48  and at least two sources of light. As can be seen in this embodiment, a first side light source  154  is provided that applies a portion of source light SL 1  to first side  24   a  of print medium  24  at an angle of incidence that is different from an angle at which first side light detector  48  is arranged relative to print medium  24   a , and an additional first side light source  156  is arranged relative to print medium  24   a , to apply further portion of source light SL 1  to light print medium  24   a  at an angle of incidence is different from the angle at which first side light detector  48  is arranged relative to medium  24   a . This allows a first side light detector  48  to be used determine diffuse reflectance of first side  24   a  of print medium  24  at more than one point on surface  24   a  without moving print medium  24 . It will be appreciated that a similar structure can be used, as desired, to sense the diffuse and specular reflectance of second surface  24   b  of print medium  24 .  
         [0064]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0000]    
       
           20  printer  
           21  housing  
           22  print engine  
           24  print medium  
           24   a  first side of print medium  
           24   b  second side of print medium  
           26  medium advance  
           27  printing area  
           28  motor  
           30  pinch roller  
           32  image capture system  
           34  processor  
           36  user input system  
           37  keypad  
           38  mouse  
           39  display  
           40  sensors  
           42  first side reflectance sensor  
           44  second side reflectance sensor  
           46  first side light source  
           48  first side light detector  
           50  second side light source  
           52  second side light detector  
           60  memory  
           62  hard drive  
           64  disk drive  
           66  memory card slot  
           68  removable memory  
           70  removable memory interface  
           72  remote memory system  
           74  communication system  
           76  print medium storage area  
           78  scanning area  
           80  receive print order step  
           82  load print medium step  
           84  obtain first side reflectance step  
           86  obtain second side reflectance step  
           88  compare step  
           92  determine type step  
           94  perform print function step  
           100  first photo paper  
           102  second photo paper  
           104  third photo paper  
           106  fourth photo paper  
           108  fifth photo paper  
           110  first plain paper  
           112  second plain paper  
           114  third plain paper  
           116  fourth plain paper  
           118  fifth plain paper  
           120  first transparency  
           122  second transparency  
           130  threshold  
           132  threshold  
           138  common light source  
           140   a  first side mirror  
           140   b  second side mirror  
           144  first side specular reflectance sensor  
           146  first side diffuse reflectance sensor  
           150  light source  
           152  additional light source  
           154  light source  
           156  additional light source  
          SL 1  first side source light  
          RL 1  first side reflected light  
          SL 2  second side source light  
          RL 2  second side reflected light