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indexImages

Create image search index

Syntax

imageIndex = indexImages(imds)
imageIndex = indexImages(imds,bag)
imageIndex = indexImages(___,Name,Value)

Description

example

imageIndex = indexImages(imds) creates an invertedImageIndex object, imageIndex, that contains a search index for imds. Use imageIndex with the retrieveImages function to search for images.

example

imageIndex = indexImages(imds,bag) returns a search index that uses a custom bagOfFeatures object, bag. Use this syntax with the bag you created when you want to modify the number of visual words or the feature type used to create the image search index for imds.

imageIndex = indexImages(___,Name,Value) uses additional options specified by one or more Name,Value pair arguments, using any of the preceding syntaxes.

This object supports parallel computing using multiple MATLAB® workers. Enable parallel computing from the Computer Vision System Toolbox Preferences dialog box. To open Computer Vision System Toolbox™ preferences, on the Home tab, in the Environment section, click Preferences. Then select Computer Vision System Toolbox.

Examples

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Create an image set.

setDir  = fullfile(toolboxdir('vision'),'visiondata','imageSets','cups');
imds = imageDatastore(setDir);

Index the image set.

imageIndex = indexImages(imds)
Creating an inverted image index using Bag-Of-Features.
-------------------------------------------------------

Creating Bag-Of-Features.
-------------------------

* Selecting feature point locations using the Detector method.
* Extracting SURF features from the selected feature point locations.
** detectSURFFeatures is used to detect key points for feature extraction.

* Extracting features from 6 images...done. Extracted 1708 features.

* Keeping 80 percent of the strongest features from each category.

* Balancing the number of features across all image categories to improve clustering.
** Image category 1 has the least number of strongest features: 1366.
** Using the strongest 1366 features from each of the other image categories.

* Using K-Means clustering to create a 20000 word visual vocabulary.
* Number of features          : 1366
* Number of clusters (K)      : 1366

* Initializing cluster centers...100.00%.
* Clustering...completed 1/100 iterations (~0.06 seconds/iteration)...converged in 1 iterations.

* Finished creating Bag-Of-Features


Encoding images using Bag-Of-Features.
--------------------------------------

* Encoding 6 images...done.
Finished creating the image index.
imageIndex = 
  invertedImageIndex with properties:

         ImageLocation: {6x1 cell}
            ImageWords: [6x1 vision.internal.visualWords]
         WordFrequency: [1x1366 double]
         BagOfFeatures: [1x1 bagOfFeatures]
        MatchThreshold: 0.0100
    WordFrequencyRange: [0.0100 0.9000]

Display the image set using the montage function.

thumbnailGallery = [];
for i = 1:length(imds.Files)
    I = readimage(imds,i);
    thumbnail = imresize(I,[300 300]);
    thumbnailGallery = cat(4,thumbnailGallery,thumbnail);
end

figure
montage(thumbnailGallery);

Select a query image.

queryImage = readimage(imds,2);
figure
imshow(queryImage)

Search the image set for similar image using query image. The best result is first.

indices = retrieveImages(queryImage,imageIndex)
indices = 

     2
     1
     5
     3
     4

bestMatchIdx = indices(1);

Display the best match from the image set.

bestMatch = imageIndex.ImageLocation{bestMatchIdx}
bestMatch = 
'/mathworks/devel/bat/Bdoc17b/build/matlab/toolbox/vision/visiondata/imageSets/cups/blueCup.jpg'
figure
imshow(bestMatch)

Create an image set.

setDir  = fullfile(toolboxdir('vision'),'visiondata','imageSets','cups');
imgSets = imageSet(setDir, 'recursive');

Display image set.

thumbnailGallery = [];
for i = 1:imgSets.Count
    I = read(imgSets, i);
    thumbnail = imresize(I, [300 300]);
    thumbnailGallery = cat(4, thumbnailGallery, thumbnail);
end

figure
montage(thumbnailGallery);

Train a bag of features using a custom feature extractor.

extractor = @exampleBagOfFeaturesExtractor;
bag = bagOfFeatures(imgSets,'CustomExtractor',extractor);
Creating Bag-Of-Features.
-------------------------
* Image category 1: cups
* Extracting features using a custom feature extraction function: exampleBagOfFeaturesExtractor.

* Extracting features from 6 images in image set 1...done. Extracted 115200 features.

* Keeping 80 percent of the strongest features from each category.

* Using K-Means clustering to create a 500 word visual vocabulary.
* Number of features          : 92160
* Number of clusters (K)      : 500

* Initializing cluster centers...100.00%.
* Clustering...completed 26/100 iterations (~1.66 seconds/iteration)...converged in 26 iterations.

* Finished creating Bag-Of-Features

Use the trained bag of features to index the image set.

imageIndex = indexImages(imgSets,bag,'Verbose',false) 
imageIndex = 
  invertedImageIndex with properties:

         ImageLocation: {6x1 cell}
            ImageWords: [6x1 vision.internal.visualWords]
         WordFrequency: [1x500 double]
         BagOfFeatures: [1x1 bagOfFeatures]
        MatchThreshold: 0.0100
    WordFrequencyRange: [0.0100 0.9000]

queryImage = read(imgSets,4);

figure
imshow(queryImage)

Search for the image from image index using query image.

indices = retrieveImages(queryImage,imageIndex);
bestMatch = imageIndex.ImageLocation{indices(1)};
figure
imshow(bestMatch)

Input Arguments

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Images, specified as an imageDataStore object. The object stores a collection of images.

Bag of visual words, specified as a bagOfFeatures object.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (' '). You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'Verbose',true sets the 'Verbose' property to true

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Save feature locations, specified as the comma-separated pair consisting of 'SaveFeatureLocations' and a logical scalar. When set to true, the image feature locations are saved in the imageIndex output object. Use location data to verify spatial or geometric image search results. If you do not require feature locations, set this property to false to reduce memory consumption.

Display progress information, specified as the comma-separated pair consisting of 'Verbose' and a logical scalar.

Output Arguments

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Image search index, returned as an invertedImageIndex object.

Algorithms

imageIndex uses the bag-of-features framework with the speeded-up robust features (SURF) detector and extractor to learn a vocabulary of 20,000 visual words. The visual words are then used to create an index that maps visual words to the images in imds. You can use the index to search for images within imds that are similar to a given query image.

Introduced in R2015a