Abstract:
A system and method for generating training images. An existing training image is associated with a classification. The system includes an image processing module that performs color-space deformation on each pixel of the existing training image and then associates the classification to the color-space deformed training image. The technique may be applied to increase the size of a training set for training a neural network.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/745,713, filed on Dec. 24, 2012, the contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The following relates generally to training image classification neural networks and more specifically to generating training cases for image classification neural networks. 
     BACKGROUND 
     Given current processing capability, it is now practical to implement complex neural networks to perform various tasks, such as image classification. Neural networks are configured through learning, which can be referred to as a training stage. In the training stage for image classification, training data (a training set of images each having a known classification) is processed by the neural network. Thus, it is intended that the neural network learn how to perform classification for new images by generalizing the information it learns in the training stage from the training data. 
     One problem that can occur when training a particularly complex neural network (i.e., a neural network having a large number of parameters) is overfitting. Overfitting occurs when the neural network simply memorizes the training data that it is provided, rather than generalizing well to new examples. Generally, the overfitting problem is increasingly likely to occur as the complexity of the neural network increases. 
     Overfitting can be mitigated by providing the neural network with more training data. However, the collection of training data is a laborious and expensive task. One proposal has thus been to synthetically and automatically generate new training data from the existing training data. For vision tasks, this can be accomplished by label-preserving two-dimensional spatial deformations of existing training data and adding these spatially deformed images to the training set. However, the generated images will be correlated, likely highly correlated, with the original training images. Furthermore, the increase in size of the training set is limited in this approach. Thus, this technique is generally accepted to be inferior to actually collecting more independent training data. 
     It is an object of the following to obviate or mitigate at least one of the foregoing issues. 
     SUMMARY 
     In one aspect, a system for generating a training image is provided, the system comprising an image processing module operable to perform color-space deformation on an existing training image. 
     In another aspect, a method for generating a training image is provided. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: 
         FIG. 1  is an architecture diagram of a system capable of generating training data; and 
         FIG. 2  is a flowchart for generating training data. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be described with reference to the figures. It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein. 
     It will also be appreciated that any module, unit, component, server, computer, terminal or device exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of the device or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media. 
     It has been found that, in general, object identity in a natural image (that is, an image capturing a scene comprising natural features, such as faces and objects, for example) is invariant to changes in image intensity and color. Correspondingly, it is described herein that a training set of images can be generated by performing one or more color-space deformations on an existing training set. In aspects, the specific deformations applied make use of the dimensions in color-space along which images vary most. The generated training set may be used to augment an existing training set. 
     Referring now to  FIG. 1 , an image processing module ( 100 ) is shown. The image processing module ( 100 ) is operable to perform color-space deformation processes. The image processing module ( 100 ) may comprise a random number generator (RNG) ( 102 ), principal component analysis (PCA) module ( 104 ), and an arithmetic logic unit (ALU) ( 106 ). A memory ( 108 ) linked to the image processing module ( 100 ) may further be provided for storing existing training images (also referred to herein as base images) ( 110 ) and for enabling the storage of generated training images ( 112 ). Training images comprise image data (e.g., pixel data) and classification data (e.g., labels). 
     Referring now to  FIG. 2 , in one aspect, the image processing module ( 100 ) is operable to obtain from the memory one or more base images ( 200 ), perform one or more color-space deformations to the image data for each obtained base images to generate a respective deformed image ( 202 ), associate the classification data of each base image with the respective generated image ( 204 ) and store the generated image with classification data to the memory ( 206 ). 
     In one aspect, the image processing module may perform more than one color-space deformation for any particular existing training image. It will be appreciated that an increase in the number of deformations applied to training images correspondingly increases the size of the training set, which may be beneficial in various implementations. In this example, it is preferred that such deformations be not identical to reduce correlation in the resulting training set. 
     In one aspect, the color-space deformation process comprises applying PCA followed by altering the intensities of RGB (red green blue) channels in the training image set. In this example, prior to performing a deformation on the images, the image processing module ( 100 ) obtains from the memory the training image set, or a subset thereof and provides the obtained training image set to the PCA module. The PCA module ( 104 ) performs PCA on the set of RGB pixel values thoughout the obtained training image set. The PCA module ( 104 ) applies PCA to provide the image processing module ( 100 ) with at least one principal component each represented by an eigenvalue-eigenvector pair. Preferably, the image processing module uses all principal components. Preferably still, the image processing module rescales noise added to the principal components by the square roots of their eigenvalues. 
     The image processing module ( 100 ) may subsequently multiply the eigenvalues for the selected principal components by a random variable generated by the RNG ( 102 ). The RNG ( 102 ) may generate the random variable from a Gaussian with mean zero and a preconfigured standard deviation. An example of a suitable standard deviation value is 0.1, although other values may be suitable. 
     Thus, in this example, the ALU ( 106 ) deforms each RGB image pixel I xy =[I xy   R , I xy   G I xy   B ] T  by adding the following quantity:
 
[p 1 ,p 2 ,p 3 ][α 1 √λ 1 ,α 2 √λ 2 ,α 3 √λ 3 ] T  
 
where p i  and λ i  are ith eigenvector and eigenvalue of the 3×3 covariance matrix of RGB pixel values, respectively, and α i  is the random variable generated by the RNG ( 102 ).
 
     In one aspect, the RNG ( 102 ) generates each α i  only once for all the pixels of a particular training image until that image is used for training again, which point the RNG generates a new α i . 
     Given the color-space deformed image pixels, the image processing module ( 100 ) generates the image, associates the label from the base image with the generated image, and stores to the memory ( 108 ) the generated image with corresponding label. 
     In a further aspect, the image processing module may apply a plurality of intensity transformations to different regions of the images, rather than to apply a single intensity transformation to an entire image. 
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. The entire disclosures of all references recited above are incorporated herein by reference.