基于内容的图像检索

1 . Content-Based Image Retrieval • Queries • Commercial Systems • Retrieval Features • Indexing in the FIDS System • Lead-in to Object Recognition 1 

2 .Content-based Image Retrieval (CBIR) Searching a large database for images that match a query:  What kinds of databases?  What kinds of queries?  What constitutes a match?  How do we make such searches efficient? 2 

3 .Applications  Art Collections e.g. Fine Arts Museum of San Francisco  Medical Image Databases CT, MRI, Ultrasound, The Visible Human  Scientific Databases e.g. Earth Sciences  General Image Collections for Licensing Corbis, Getty Images  The World Wide Web Google, Microsoft, etc 3 

4 .What is a query?  an image you already have  a rough sketch you draw  a symbolic description of what you want e.g. an image of a man and a woman on a beach 4 

5 . Some Systems You Can Try • Corbis sells sold high-quality images for use in advertising, marketing, illustrating, etc. Corbis was sold to a Chinese company, but  Getty images now provides the image sales. • http://www.gettyimages.com/search/2/image?excludenudity=true&sort=best 5 

6 . Google Image •Google Images http://www.google.com/imghp Try the camera icon. 6 

7 . Microsoft Bing • http://www.bing.com/ 7 

8 . Problem with Text-Based Search • Retrieval for pigs for the color chapter of my book • Small company (was called Ditto) • Allows you to search for pictures from web pages 8 

9 . Features • Color (histograms, gridded layout, wavelets) • Texture (Laws, Gabor filters, local binary pattern) • Shape (first segment the image, then use statistical or structural shape similarity measures) • Objects and their Relationships This is the most powerful, but you have to be able to recognize the objects! 9 

10 .Color Histograms 10 

11 . Gridded Color Gridded color distance is the sum of the color distances in each of the corresponding grid squares. 1 2 1 2 3 4 3 4 What color distance would you use for a pair of grid squares? 11 

12 . Color Layout (IBM’s Gridded Color) 12 

13 . Texture Distances • Pick and Click (user clicks on a pixel and system retrieves images that have in them a region with similar texture to the region surrounding it. • Gridded (just like gridded color, but use texture). • Histogram-based (e.g. compare the LBP histograms). 13 

14 .Laws Texture 14 

15 . Shape Distances • Shape goes one step further than color and texture. • It requires identification of regions to compare. • There have been many shape similarity measures suggested for pattern recognition that can be used to construct shape distance measures. 15 

16 . Global Shape Properties: Projection Matching 0 4 1 Feature Vector 3 (0,4,1,3,2,0,0,4,3,2,1,0) 2 0 0 4 3 2 1 0 In projection matching, the horizontal and vertical projections form a histogram. What are the weaknesses of this method? strengths? 16 

17 . Global Shape Properties: Tangent-Angle Histograms 135 0 30 45 135 Is this feature invariant to starting point? Is it invariant to size, translation, rotation? 17 

18 . Boundary Matching • Fourier Descriptors • Sides and Angles • Elastic Matching The distance between query shape and image shape has two components: 1. energy required to deform the query shape into one that best matches the image shape 2. a measure of how well the deformed query matches the image 18 

19 .Del Bimbo Elastic Shape Matching query retrieved images 19 

20 . Regions and Relationships • Segment the image into regions • Find their properties and interrelationshipsLike what? • Construct a graph representation with nodes for regions and edges for spatial relationships • Use graph matching to compare images 20 

21 .Blobworld (Carson et al, 1999)  Segmented the query (and all database images) using EM on color+texture  Allowed users to select the most important region and what characteristics of it (color, texture, location)  Asked users if the background was also important 21 

22 . Tiger Image as a Graph (motivated by Blobworld) sky image above above adjacent inside tiger grass above above adjacent sand abstract regions 22 

23 .Andy Berman’s FIDS System multiple distance measures Boolean and linear combinations efficient indexing using images as keys 23 

24 .Andy Berman’s FIDS System: Use of key images and the triangle inequality for efficient retrieval. d(I,Q) >= |d((I,K) – d(Q,K)| 24 

25 . Andy Berman’s FIDS System: Bare-Bones Triangle Inequality Algorithm Offline 1. Choose a small set of key images 2. Store distances from database images to keys Online (given query Q) 1. Compute the distance from Q to each key 2. Obtain lower bounds on distances to database images 3. Threshold or return all images in order of lower bounds 25 

26 .Andy Berman’s FIDS System: 26 

27 . Andy Berman’s FIDS System: Bare-Bones Algorithm with Multiple Distance Measures Offline 1. Choose key images for each measure 2. Store distances from database images to keys for all measures Online (given query Q) 1. Calculate lower bounds for each measure 2. Combine to form lower bounds for composite measures 3. Continue as in single measure algorithm 27 

28 .Demo of FIDS  http://www.cs.washington.edu/research/ imagedatabase/demo/  Try this and the other demos on the same page.  First, in the Java control panel, add a site exception: http://imagedatabase.cs.washington.edu/demo/fids/  Then make sure you are running 32 bit Firefox (or IE) with 32 bit Java (64 not tested)  For IE, may have to enable Java plugins 28 

29 .Different Features