Image Databases

Definition

Ø  Computer system where image files are kept in an organised form.

Ø  Software that facilitates organised storage and retrieval of digital images is called Image database system.

Characteristics of Image Database

The main characteristics of image database system

1. possibility to handle large amount of images of different types.
2. possibility for content and similarity based retrieval.
3. possibilities to compose the query of text, images, sketches and making use of colour palette.
4. The query response time is fast.

Global Image Representation

            Traditionally there have been two major approaches for global image representation.

ü  The parametric approach.

ü  The syntactic approach

In the parametric approach image elements are represented by vectors of features ((e.g., colour, Size, etc.), which features can be measured from the images.

In the syntactic representation the image features are represented as sets of symbolic entities, that is an alphabet of image primitives is used.

The image indexing mechanism combines the two approaches and allows quick search based on multilevel index.

The user can make use besides of simple text-based queries, also of tools for drawing sketches, picking colour from colour palette, drawing image element, extracting parts from example images, etc. The searching mechanism combines image and text description of colour, shape and attribute of the image and its elements. The overall description reduces the search.

Image Indexing

The basis of image indexing is a semantic image representation. The total image representation is defined as: Global image representation and Image Elements representation,

where

Global image representation = {Image Name, Image Colour, Image Attribute}

And Image Elements representation includes the Image element representations and their places.

Image Element representation = {Element name, Element colour, Element shape, Element attribute}.

An Element is a small patch in the image with descriptive power. The best choice for an ensemble element is to form a set from which the image is composed.

The different elements in the semantic image representations are defined as:

1.      Name description.

Name of an image or elements in it could be given during the image entering.

2.      Attribute description.

It is borrowed from outside sources concerning the image elements. In the case of geographic maps, if the element represents a legend sign for a town, the user could enter the town population. The attribute description could be text or number.

3.      Colour description.

Each image voxel is considered as a point in a 3D colour space (Red, Green, Blue).

Content-Based Retrieval of Image

ü  System retrieves images that best match the description.

ü  Image content can be defined at different levels of abstraction

Lowest level

o   Image is a collection of pixels.

o   Rarely used.

The raw data can be processed to produce numeric descriptors capturing specific visual characteristics called features.

–     Color,

–     Texture, and

–     Shape

Features can be extracted from entire images describing global visual characteristics

                  Portions of images describing local characteristics

Highest Level

–     Images are often accompanied by metadata.

–     Metadata may contain information that cannot be obtained directly from the image, as well as an actual description of the image content.

–     Medical images.

Radiological report

Multidimensional Indexing

ü  Multidimensional descriptors

–     colour or

–     texture

ü  Search task can be made significantly more efficient by relying on multidimensional indexing structures.

  

ü  RDBMS should not support Multidimensional indexes.

Image Element representation = {Element name, Element colour, Element shape, Element attribute}.

By using this the images are retrieved

Image Retrieval

ü  Image retrieval in the Image database system

  1.“direct query”

- the user specifies the query by directly picking colour from the colour palette

  2.“image query”

- the user asks for images similar to a given image or containing given image.

              3.“textual query”

- the user specifies a textual description of the search image.

              4.combination of all of the above.

Creating the Image Databas

ü  Creating image database in MySQL

–     Create a MySQL database called Database_Image.

–     Create a table called images with two rows

•      Imageid

•      Description.

–     Query

CREATE TABLE  Images

( imgid          INT                 NOT NULL AUTO_INCREMENT ,

  description LONGTEXT   NOT NULL ,

  PRIMARY KEY ( imgid ) );