Evaluation.Of.Texture.Feature.For.CB.ppt
- 1. Zahra Mansoori z_mansoori@ce.sharif.edu Evaluation of Texture Features for Content-based Image Retrieval Computer Department Sharif University of Tech. Spring 2008 1
- 2. Contents Introduction to image retrieval Introduction to texture Methods of Extracting Evaluation of some approaches and results References 2
- 3. Content-based Image Retrieval An image search engine Works by image content (Color, texture, shape) instead of annotated texts Consist of: 1. Database of Primitive Image 2. Feature Extraction Module 3. Indexing Module 4. Search and Retrieval Module 5. User interface (Input: query image, Output: Similar images) Examples: IBM QBIC, Virage, VisualSEEK, … 3
- 4. CBIR CBIR modules and flowchart Row Images Query Image Feature Extraction Feature Vectors Feature Vector DB Feature Vector Feature Vector Search and retrieval Similarity Measure Results to User 4
- 5. What is texture? A key component of human visual perception about the nature and three dimensional shape of physical objects Can be regarded as a similarity grouping in an image One of essential Features to consider when querying image database Normally defined by grey levels 5
- 6. Texture analyzing Rottenly : it is required to convert image into gray scald mode Inspecting batch of pixels in order to find the relationship between them 6
- 7. Methods of analyzing Approaches to texture analysis are usually categorized into Structural, Statistical, Model-based and Transform 7
- 8. Structural approaches Represent texture by well-defined primitives called microtexture and a hierarchy of spatial arrangements of those primitives Define the primitives and the placement rules to define the texture 8
- 9. Statistical approaches Represent the texture indirectly by the non- deterministic properties These properties govern the distributions and relationships between the grey levels of an image 9
- 10. Model-based approaches Attempt to interpret an image texture by use of, respectively, generative image model 10
- 11. Transform approaches Represent an image in a space whose co-ordinate system (such as frequency or size) Interpretation in this space will be closely related to the characteristics of its texture 11
- 12. Problem & Experimental Set up To Evaluate three texture extraction method to use in Content-based Image Retrieval Image Collection: Corel Collection Similarity Measure: Manhattan Metric 12
- 13. Co-occurrence matrix Definition One of the earliest methods Also called GLCM stands for Gray-level Co-occurrence Matrix Extract 2nd -order statistics from an image Very successful method 13
- 14. Co-occurrence matrix (cont.) Let C be the GLCM, so Ca,d(i,j) will be the co-occurrence of pixels with grey values i and j at a given distance d and in a given direction α Should be symmetric or asymmetric Usually: All pixel intensities are quantized into smaller number of available gray levels (8, 16, 64, …). For example if 8 is selected, the target matrix will be 8 x 8. Values of α are one of values such as 0, 45, 90 and 135. Using all of them may bring more accuracy. 14
- 15. Co-occurrence matrix Calculating Co-occurrence matrix from a gray scaled image 15
- 16. Co-occurrence matrix (cont.) Feature Extraction: Once the GLCM has been created, various features can be computed from it. All these features are supported by MATLAB 16
- 17. Co-occurrence matrix – Evaluation Results Distance between 1 and 4 pixels gave the best performance There was no significant differences between symmetrical and asymmetric matrices Tiling of the image gave a large increase in retrieval which flatted out by 9 x 9 tiles The concatenated (cat) features gave better result at all points than the rotationally invariant summed matrices (sum) The best feature was homogeneity 17
- 18. Co-occurrence features Mean average precision Retrieval 18
- 19. Tamura Extract features that correspond to human perception Contains six textural features: 1. Coarseness 2. Contrast 3. Directionality 4. Line-likeness 5. Regularity 6. Roughness 19
- 20. Tamura (cont.) 20 First three are most important Coarseness direct relationship to scale and repetition rates calculated for each points of image Contrast dynamic range of gray levels in an image calculated for non-overlapping neighborhoods Directionality Measure the total degree of directionality calculated for non-overlapping neighborhoods
- 21. Tamura (cont.) 21 Another approach: Tamura CND Image Spatial joint of coarseness-contrast-directionality distribution (view as RGB distribution) Extract color histogram style feature from Tamura CND Image
- 22. Tamura – Evaluation Results 22 Increasing k value for coarseness decrees the performance Optimum value = 2 Performance of directionality is poor
- 23. Tamura features Mean average precision Retrieval 23
- 24. Gabor filter Special case of the short-time Fourier transform Time-frequency analysis It is used to model the responses of human visual system A two dimensional Gabor function Advantage/disadvantage: Very popular Time consuming calculation Generate complete but non orthogonal basic set so redundancy of data will be occurred 24
- 25. Gabor filter (cont.) Manjunath et al reduced redundancy by using Gabor wavelet functions The Features is computed by 1. Filtering the image with a bank of orientation and scale sensitive filters and, 2. Computing the mean and standard deviation of the output in the frequency domain 25
- 26. Gabor filter – Evaluation Results 26 Better for homogeneous textures with fixed size because of specific filter dictionary Widely used to search for an individual texture tile in an aerial images database Best response Usage: Process image for 7x7 tiling and apply filters on Just 2 scales and 4 orientations
- 27. Gabor wavelet Mean average precision Retrieval 27
- 28. References 1) Howarth P. and Ruger S., "Evaluation of Texture Features for Content- Based Image Retrieval," in Third International Conference, CIVR 2004, Dublin, Ireland, 2004. 2) Deselaers Th., "Features for Image Retrieval," 2003 3) Materka A. and Strzelecki M. , "Texture Analysis Methods – A Review," Technical University of Lodz, Institute of Electronics, Brussels, COST B11 1998. 4) Manjunath B.S. and Ma W.Y., "Texture features for browsing and retrieval of image data," Transactions on Pattern Analysis and Machine Intelligence, vol. 18, pp. 837-842, 1996. 5) Schettini R. ; Ciocca G. and Zuffi S., "A Survey of Methods for Color Image Indexing and Retrieval in Image Databases." 28
- 29. Appendix: Performance measures of an Information Retrieval System Every document is known to be either relevant or non-relevant to a particular query 1. Precision: The fraction of the documents retrieved that are relevant to the user's information need Precision = (Relevant images ∩ Retrieved Images) / Retrieved Images 2. Recall: The fraction of the documents that are relevant to the query that are successfully retrieved Recall = (Relevant images ∩ Retrieved Images) / Relevant images 3. Average Precision: The precision and recall are based on the whole list of documents returned by the system. Average precision emphasizes returning more relevant documents earlier. It is average of precisions computed after truncating the list after each of the relevant documents in turn: AveP = Ʃr = 1:n (P(r) . rel(r)) / Relevant images where r is the rank, N the number retrieved, rel() a binary function on the relevance of a given rank, and P() precision at a given cut-off rank. 29