Multimedia Databases

Content-based retrieval (CBR)of a multimedia data is retrieval that uses the text of the document rather than any added metadata. Free text searching is a good example of content-based text retrieval for text documents. The words making up the content of the document are indexed and used as the basis for retrieval, sometimes in conjunction with quite sophisticated “intelligent” software used to satisfy the query. But in case of images and videos CBR is difficult. The difficulty is that an image is an collection of pixels with color specified for each pixels but need to interpret them automatically and see meaningful regions of colour, recognise objects and identify scenes which can usefully form the basis of effective image matching processes.
How can CBR be performed for images :

• Image Retrieval By Color : The colour histogram has been a simple and popular representation which captures the relative amounts of each colour in an image. But it is a global measure and does not give information about colour variations at local positions in the image. Color Histogram gives the proportio of pixels of each color within a image. Now we define a distance color set distance d^(set)=(c_q-c_t)^tA(c_q-c_t) where
  • c_q: Query color histogram
  • c_t: Target color histogram
  • A is the color similarity matrix.
    
  Now for a query we search for minimum value of this distance.
• Region Query for Images by Spatial description : Image may be divided into some regions. Here we can perform triangulation of image. Now region location can be found using Euclidean distance of centroids. When we query for an region of an image we can make the weighted sum of
  • Color set
  • Location
  • Area
  • Spatial extent
  as a criterion. We may also need to define spatial relation between regions for example
  • Adjacency
  • Nearness
  • Overlap
  • Surround
    

How can we perform CBR :
1. The application provides us a drawing tool so that we can draw image and calculate feature of query image and search accordingly in database.
2. Or we can prform Query By Example : in this case we provide an example image so that an iomage from database should be similar to it.