Abstract:
A method and system for automatically classifying a print medium entering a printing device as being a print medium type having known properties relevant to print operations. A detection system captures data indicative of optical characteristics of the incoming medium. The data is spectrally examined to derive frequency-related information. At least one neural network utilizes the frequency-related information to determine a medium type. In one embodiment, a major category network determines the medium type as one of five major medium types. Subsequently, the medium is subjected to analysis with a specific neural network for differentiating the identified major media type into narrower categories. Each neural network comprises a layer of adaptive decision-making nodes. Each node includes an activation function for processing the sum of multiple weighted inputs for generating an output. The output is directed to the output level that is at least partially utilized for a medium type determination.

Description:
TECHNICAL FIELD 
     The invention relates generally to printing mechanisms and more particularly to a system for determining the type of print media, so that the printing mechanism can automatically select an optimal print mode for a specific type of incoming media without requiring user intervention. 
     BACKGROUND ART 
     For printers on the commercial market today, such as laser and inkjet printers, automated selection for the type of print media (e.g., transparency media, premium media, glossy photo media, matte photo media, etc.) is not always present. Rather than using a close-loop feedback system for automated selection, these printers use an open-loop process by relying on a user to select the type of print media through the software driver in his/her personal computer (PC). Without correctly selecting the proper type of print media, there is no assurance that the media corresponds to the type selected for a particular print request. Consequently, the type of print media used for printing may not always correspond to an optimal operational mode of the printer. 
     Printing with an incorrectly selected media often produces poor quality images. The problem primarily stems from the fact that most users do not change the media type settings, even assuming that they are aware of the existing settings. Instead, the typical users print with a default setting of the plain paper-normal mode. This is unfortunate, because if a user inserts an expensive photo media into the printer, the resulting image is sub-standard when the normal mode rather than a photo mode is selected, leaving the user effectively wasting the expensive photo media. Besides photo media, other types of media such as transparencies yield particularly poor image quality when they are printed in the plain paper-normal mode. 
     One proposed system for a printer to automatically adopt an optimal print mode for a specific type of incoming media without requiring user intervention utilizes an invisible ink code. The code is printed on each sheet of incoming media where it is read by a sensor onboard the printer. The code supplies the printer driver with practical information, such as the media type, manufacturer, orientation and properties. Armed with this information, the system is both reliable and economical in properly selecting the correct type of print media for optimal performance. Thus, the user is no longer burdened by media selection through his/her PC. A concern with the invisible ink code system is that the pre-printed invisible code can become visible when printed over. To avoid this problem, the code is placed at the margin of the print medium. However, since market demand is pushing printers into becoming high-quality photo generators, the invisible code becomes an undesirable artifact for a photographic finish requiring printing up to the edge of the paper. Consequently, placing the invisible code at the margin creates a print defect for printing in the photo-mode. 
     Another system for print media type determination utilizes a combination of transmissive and reflective sensors. The transmissive sensor measures the amount of light that has passed through the print media and is very effective for some media type determinations, such as the identification of a transparency. The reflective sensors receive light reflected off the surface of the print medium at different angles and are used to measure the specular reflectance and the diffuse reflectance of the medium. By analyzing the ratio of these two reflectance values, a specific medium type is identified. To implement this system, a database having a look-up table of the reflective ratios is used to correlate the ratios with various types of print media. A concern with this system is that new, non-characterized medium is often misidentified, leading to print quality degradation. Another concern is that several different types of media could generate the same reflectance ratio, yet have different print mode classifications. 
     What is needed is a method and system for reliably determining the type of incoming print medium, so that the printing mechanism can automatically select a proper print mode without requiring user intervention. 
     SUMMARY OF THE INVENTION 
     The invention is a method and system that uses neural network techniques for automatically selecting a print medium type without requiring user intervention. A media detection system captures data indicative of characteristics of an incoming medium. The data is spectrally analyzed to derive frequency-related information. At least one media-identifying neural network utilizes the frequency-related information to determine a print medium type. A “neural network” is herein defined as an adaptive arrangement which is specifically designed to adapt on the basis of prior decisions in order to increase the accuracy of decisions. Utilizing a feedforward architecture, the media-identifying neural network includes a layer of decision making nodes (i.e., the “hidden” layer). Each decision making node includes an activation function for processing a sum of multiple weighted inputs to the node. The output from each decision-making node may be directed to a node within the same layer for continuous processing or to a node in an output layer. Each node at the output layer corresponds to a major type of print medium selection, including a transparency type, premium-paper type, plain-paper type, photo-quality type, and default type. Subsequent to identifying the print medium as one of the major medium types, a specific neural network is utilized to narrow the identified type of medium into a more specific category. 
     The media-identifying neural network comprises an input layer of nodes, an output layer of nodes and one “hidden” layer of nodes sandwiched between the input and output layers. In a first embodiment in which a major network is used to identify an incoming print medium as one of the five major media print types, each node of the input layer is configured to receive one frequency component from the media detection system. Each frequency component is derived by spectrally analyzing (e.g., performing Fourier Transform) the data captured by the media detection system. If there are 84 diffuse frequency components and 84 specular frequency components, the input layer comprises 168 input nodes, with each node being configured to receive one frequency component and to impose a weight on the received component. 
     The outputs from the input nodes are directed to the “hidden” or decision-making layer. Actual computations utilizing algorithms are performed at the decision-making layer to determine a print medium type. The optimal number of decision-making nodes utilized in this layer is dependent on the nature of the classification. A task requiring greater accuracy may use a greater number of decision-making nodes, while a task requiring greater speed may use a fewer number of nodes. In one embodiment, the decision-making layer comprises at least six decision-making nodes. In a second embodiment, the layer comprises at most ten decision-making nodes. Each decision-making node may be configured to receive 168 weighted inputs and emit one output. An activation function is applied to the sum of the weighted inputs, together with a bias weight for each decision-making node to produce one output. 
     The decision-making nodes are configured to generate a decision for designating a print medium type for the incoming medium. Each of the nodes in the output layer corresponds to one of the major media types. While the process may designate the subject print medium as one of a transparency type, premium-paper type, plain-paper type, photo-quality type and default type, other types of categorization can be selected without diverging from the scope of the invention. 
     In the first embodiment, the print medium is further subjected to analysis within a specific neural network to differentiate the selected major media type into narrower categorizes. For example, after a determination by a major network that an incoming print medium is a “photo-quality type,” a specific neural network is utilized to further differentiate the “photo-quality type” as one of a: (1) default type, (2) Gossimer type, (3) combined type, and (4) very glossy type. 
     In a second embodiment, the 168 frequency components are analyzed to determine a print media type of the incoming print medium utilizing other categorizing means, without being subjected to analysis within a major neural network. Specifically, after identifying the print medium as one of the major media types utilizing other categorizing techniques, the incoming medium is subjected to the specific neural network to more clearly differentiate the medium as being one that fits within a narrower category. 
     The media-identifying network architecture is dependent on the types of training algorithms used for defining the network. During training in the “supervised” mode, a training set of print media for a particular class (e.g., a transparency type) is provided to the printing mechanism. The decision-making nodes are set to be “ON” for that particular class and “OFF” for the other classes. Each node is associated with a bias term, i.e., a weight, to be applied to each input value. A weight determines how much relative effect an input value has on an output value for a given node. Initially, the values for the weights are selected at random. As training continues, error reduction algorithms adjust the actual outputs to the target outputs by reducing the error space for each of the connections in the network. The adjustment utilizes a genetic algorithm or a simulated annealing algorithm to determine a global minima for each connection. An associated weight corresponding to the global minima reduces the measure of error in the network&#39;s results. Finally, a conjugate descent is performed to determine the direction of the global minima. The training process continues until the error value is within an acceptable target range. 
     In one aspect of the invention, an incoming print medium that does not correspond to one of a desired type (i.e., transparency type, premium-paper type, plain-paper type and photo-quality type) is directed to an output node designated as the default type. A faulty training set of print media that does not correspond to one of the desired types may be input to the printing mechanism to teach the system to recognize a non-desired type of incoming print medium. 
     One of the advantages of the invention is that by utilizing a media-identifying neural network, the system is flexible and can easily be updated to detect other types of print media. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a process flow diagram for classifying an incoming print medium into pre-determined categories entering a printing device in accordance with the invention. 
     FIG. 2 is a print media detection system of the printing device of FIG. 1 for capturing data reflected off the incoming print medium. 
     FIG. 3 is a major media-identifying neural network in accordance with the invention for categorizing an incoming print medium as one of the five major media types. 
     FIG. 4 is a media type table listing exemplary specific media types for each of the five major media types. 
     FIG. 5 is a process flow of steps for training the neural network of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     In accordance with the invention, FIG. 1 is a process flow of steps for classifying an incoming print medium entering a printing device into pre-determined categories without requiring user intervention. In step  10 , data indicative of characteristics of the incoming medium is collected. A transformation step  12  is performed to place the data collected in step  10  into a suitable format for subsequent analysis. Following the transformation step  12 , a major category determination step  14  and a subsequent specific category determination step  16  are performed utilizing at least one media-identifying neural network. In one embodiment, the incoming print medium is categorized by an adaptive major neural network as one of the following major media types in step  14 : (1) transparency type, (2) premium-paper type, (3) plain-paper type, (4) photo-quality type and (5) default type. Subsequent to identifying a major media type, the incoming print medium is subjected to an adaptive specific neural network for identifying a specific media type in step  16 . Subsequently, an operational print mode is selected in step  18 . In response to the selection in step  18 , the printing device is configured to utilize a particular set of print parameters. The printing device may be any type of device utilized for printing, such as inkjet printers and laser printers. 
     With reference to step  10  of FIG. 1, FIG. 2 shows a print media detection system  20  of a printer  21  comprising: (1) an illuminating source  22  configured to direct a modified light beam  24  onto an incoming print medium  26  at a region of interest  28 , (2) a diffuse sensor  30  configured to receive a diffuse reflectance light beam  32  reflected off from the region of interest and (3) a specular sensor  34  configured to receive a specular reflectance light beam  36  reflected off from the region of interest. For capturing print medium data, the illuminating source may be an LED (light emitting diode) for emitting a single pulse of light for each sampling. The emitted pulse may be diffracted by an optical element (not shown) into the modified beam that is focused onto the region of interest. After striking the region of interest, the modified beam is reflected off the medium as both the diffuse reflectance beam and the specular reflectance beam. The diffuse deflected beam has a flame-light scattering of rays arranged in a Lambertian distribution. The specular deflected beam is reflected off the region of interest at the same angle at which the modified beam impinges the region of interest. The diffuse sensor  30  and the specular sensor  34  convert the detected beams into signals for subsequent processing. A controller  38  that is operationally coupled to the illuminating source, diffuse sensor and specular sensor by respective channels  40  controls the illumination of the light source and the capturing of the data reflected off from the illuminated region of interest. 
     With reference to step  12  of FIG. 1, the signals corresponding to the detected diffuse reflectance beam  32  and the specular reflectance beam  36  are subjected to data transformation into a suitable format for subsequent analysis. Prior to the transformation, the signals may be subjected to a Hanning or Welch windowing function, but this is not critical to the invention. Following the windowing function, a discrete Fourier Transform function is performed on the data to provide 84 frequency-related components for the diffuse reflectance signals and 84 frequency-related components for the specular reflectance signals. A subsequent pre-scaling step, such as subjecting each of the 168 frequency component to a log(n) or sqrt(n) function, may be performed. 
     The selection of a major media type under the major category determination step  14  of FIG. 1 can be performed by either of two different embodiments. In a first embodiment with reference to FIG. 3, the 84 diffuse frequency components and the 84 specular frequency components are analyzed within a major media-identifying neural network  42  for categorizing the incoming print medium as one of the five major media print types. The major neural network  42  is configured to process the data in a feedforward direction. It comprises an input layer of nodes  44 , a “hidden” or decision-making layer of nodes  46  and an output layer of nodes  48 . The neural network processes in the feedforward direction when the nodes in one layer send their outputs to the nodes in a next layer (e.g., decision-making layer) without receiving any input back from the nodes in the next layer. This is shown by the direction of signals flowing in a “forward” direction from layer  44  to layer  46  and finally to layer  48 . Since there are a total of 168 frequency-related components (84 for the diffuse reflectance data and 84 for the specular reflectance data), there are a total of 168 corresponding nodes in the input layer, with each node configured to receive each of the 168 frequency components. No processing is performed by any node in the input layer. Rather, the input nodes are a semantic construct utilized to represent the input layer. 
     Within the decision-making layer  46 , there are six decision-making nodes. Each decision-making node may be configured to receive weighted values from the nodes in the preceding layer (i.e., the input layer  44 ) and from the nodes within the same layer (i.e., decision-making layer  46 ). Each decision-making node has a connective weight associated with each input, multiplies each input value by its associated weight, and sums these values for all of the inputs. The sum is then used as input to an activation function to produce an output for that node. An associated bias term for each function may be utilized for adjusting the output. The activation function is typically a sigmoid function, such as a logistic function or a hyperbolic tangent function. The output from the selected activation function may be directed to a node within the same layer (i.e., decision-making layer) for further processing or to a node in the next layer (i.e., output layer). 
     While the invention is shown as comprising six decision-making nodes within the decision-making layer, there can be a greater or lesser number of nodes. In an alternative embodiment, the number of decision-making nodes is ten. The optimal number of nodes is dependent on various factors, such as the types of training algorithms utilized and the desired accuracy for the classification scheme. Moreover, there can be a greater number of decision-making layers  46  within the network. Again, the optimal number of layers may be dependent on the types of training algorithms and the desired accuracy of the classification system. 
     In the preferred embodiment, there are five nodes at the output layer  48 . Each output node corresponds to a particular print medium type. An incoming print medium subjected to analysis with the neural network is categorized as one of the five print media types. They include: (1) a transparency type, (2) a premium-paper type, (3) a plain-paper type, (4) a photo-quality type and (5) a default type. While the invention is described as having five major media print types, there can be a fewer number or a greater number of major media print types. Moreover, there can be other types of print media selected for categorization, such as a bonded-paper type, without diverging from the scope of the invention. 
     Referring to the specific category determination step  16  of FIG. 1, the print medium is further subjected to analysis within a specific media-identifying neural network after being categorized as one of the five major media types by the major neural network  42 . Analysis within the specific neural network differentiates a major media type selection into narrower categories. As an example, after determining that the incoming print medium is a “transparency type,” a specific neural network is utilized to further differentiate the “transparency type” as either a “default type” or a “HP type.” FIG. 4 shows a media type table  52  listing exemplary specific media types for each of the five major media types on row  54 . 
     The architecture of the specific neural network is similar to the architecture of the major neural network  42  of FIG.  3 . Specifically, the specific neural network comprises an input layer, at least one decision-making layer and an output layer. The number of nodes used in each layer as well as the number of layers and the connective weights associated with each node in the decision-making layer of the specific neural network are dependent on the same factors identified when referring to the major neural network. 
     Referring to FIG. 2, the major neural network  42  is configured to receive frequency data from the controller  38  for a major media type determination. After identifying the incoming medium  26  as one of the five major media types, the medium is further subjected to analysis within the specific media-identifying neural network  43  for a specific media type determination. Subsequently, a print mode is selected by a printer driver  45  for the incoming medium. 
     In a second embodiment under the major category determination step  14  of FIG. 1, the 168 frequency components are categorized as one of the five major media types without being subjected to the major media-identifying neural network  42  of FIG.  3 . Rather, other categorizing techniques that do not include a neural network are utilized for the media type selection in step  14 . In an exemplary embodiment, the ratio of the spectral signals corresponding to the diffuse reflectance light beam  32  (FIG. 2) and the specular reflectance light beam  36  are analyzed to determine a major print medium type. Following a determination of the incoming print medium as being one of the five major media types, the print medium is subjected to analysis within the specific media-identifying neural network  43  (FIG. 2) in the specific category determination step  16  of FIG.  1 . 
     As was previously stated, each decision-making node is associated with a connective weight. For a given decision-making node, the associated weight corresponding to an input determines the relative strength an input value has on the output value. Consequently, the weights determine the classification for a given set of input data. The weights assigned to each input are determined during the training phase. 
     FIG. 5 shows a process flow of steps for training the neural network  42  of FIG.  3 . In step  56 , the weights are initialized to random values or to preselected values. In step  58 , a set of training data for a particular class (e.g., transparency type) is provided to the input nodes of the network for training. In supervised training, many samples pertaining to a specific class are input to the network to “teach” the system and recognize characteristics indicative of the selected class. A media detection system similar to the detection system  20  of FIG. 2 captures the diffuse and specular reflectance data reflected off a training medium. A discrete Fourier Transform function is performed on the data to produce 84 frequency-related components for the diffuse reflectance signals and 84 frequency-related components for the specular reflectance signals. Analysis by the decision-making nodes for that particular set of training data input to the network in step  58  results in the network outputting a value corresponding to that particular class. 
     In step  60 , error reduction algorithms adjust the actual outputs to the target outputs by reducing the error space for each of the connective weights in the network. The adjustment utilizes genetic algorithms or simulated annealing algorithms to determine a global minima for each connection. An associated weight corresponding to a global minima reduces the measure of error in the network&#39;s results. Finally, a conjugate descent is performed to determine the direction of the global minima. While the invention is described as utilizing a combination of genetic or simulating annealing algorithms in conjunction with performing a conjugate descent, other error reduction means, such as back propagation means without utilizing the identified algorithms, may be used to approximate the actual associated weights to the target values. 
     In step  62 , test samples are applied to the network to validate the accuracy of the system. If the error space is greater than the predetermined threshold value, the training process continues until the error space is found to be less than the pre-determined value. This process is repeated with the training data until the number of mistaken classifications is lower than the pre-determined threshold value. A separate training set may be used for each of the major media types, requiring steps of FIG. 5 to be repeated. 
     Moreover, faulty training sets of print media having characteristics not indicative of a transparency type, premium-paper type, plain-paper type, or photo-quality type are provided to the network to train the system to classify a corresponding incoming print medium as a “default type.” Finally, while FIG. 5 is described as training the major neural network  42  for categorization, the same sequence of steps can be used for training the specific neural network for differentiating an identified major media type into narrower categories.