11-05-2011, 02:58 PM
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CBIR - Content Based Image Retrieval Using Shape & Color Characteristics
Introduction
Content-based image retrieval (CBIR), also known as query by image content (QBIC) and content-based visual information retrieval (CBVIR) is the application of computer vision to the image retrieval problem, that is, the problem of searching for digital images in large databases.
"Content-based" means that the search will analyze the actual contents of the image. The term 'content' in this context might refer colors, shapes, textures, or any other information that can be derived from the image itself. Without the ability to examine image content, searches must rely on metadata such as captions or keywords, which may be laborious or expensive to produce.
History
The term CBIR seems to have originated in 1992, when it was used by T. Kato to describe experiments into automatic retrieval of images from a database, based on the colors and shapes present. Since then, the term has been used to describe the process of retrieving desired images from a large collection on the basis of syntactical image features. The techniques, tools and algorithms that are used originate from fields such as statistics, pattern recognition, signal processing, and computer vision.
Technical progress
There is growing interest in CBIR because of the limitations inherent in metadata-based systems, as well as the large range of possible uses for efficient image retrieval. Textual information about images can be easily searched using existing technology, but requires humans to personally describe every image in the database. This is impractical for very large databases, or for images that are generated automatically, e.g. from surveillance cameras. It is also possible to miss images that use different synonyms in their descriptions. Systems based on categorizing images in semantic classes like "cat" as a subclass of "animal" avoid this problem but still face the same scaling issues. Potential uses for CBIR include:
• Art collections
• Photograph archives
• Retail catalogs
• Medical records
Query by example
Query by example is a query technique that involves providing the CBIR system with an example image that it will then base its search upon. The underlying search algorithms may vary depending on the application, but result images should all share common elements with the provided example.
Options for providing example images to the system include:
• A preexisting image may be supplied by the user or chosen from a random set.
• The user draws a rough approximation of the image they are looking for, for example with blobs of color or general shapes.
This query technique removes the difficulties that can arise when trying to describe images with words.
Content comparison techniques
The sections below describe common methods for extracting content from images so that they can be easily compared. The methods outlined are not specific to any particular application domain.
Color: Examining images based on the colors they contain is one of the most widely used techniques because it does not depend on image size or orientation. Color searches will usually involve comparing color histograms, though this is not the only technique in practice.
Texture: Texture measures look for visual patterns in images and how they are spatially defined. Textures are represented by texels which are then placed into a number of sets, depending on how many textures are detected in the image. These sets not only define the texture, but also where in the image the texture is located.
Shape: Shape does not refer to the shape of an image but to the shape of a particular region that is being sought out. Shapes will often be determined first applying segmentation or edge detection to an image. In some cases accurate shape detection will require human intervention because methods like segmentation are very difficult to completely automate.
Aim
• To build a Content Based Retrieval System based on color as well as generic shape information.
• User must be able to execute a query by example (i.e. specify a sample image to be used as query input)
• User must also be able to execute a query by sketch (i.e. draw a sample sketch to be used as query input)
• The system must provide facility to the user to be able to use multi-resolution images.
• The system must support both color and grayscale images.
• The system must use digital signature database for fast execution of queries.
• User must be able to see multiple results in ascending order of comparison results.
• The system must provide easy database management. i.e. addition and deletion of images to database.
