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LearningOpenCV

All the code are compiled against OpenCV 3.2.0 on Ubuntu 16.04LTS.

"DisplayImage" and "HelloWorld" are two example OpenCV Eclipse projects given in the tutorial http://docs.opencv.org/3.2.0/d7/d16/tutorial_linux_eclipse.html.

1. DisplayImage

This OpenCV project is created in Eclipse from scratch.

2. HelloWorld

This OpenCV project is firstly created with CMake and then imported into Eclipse.

3. DisplayPicture

Modified from Example 2-2 in the book "Learning OpenCV 3: Computer Vision in C++ with the OpenCV Library".

4. PlayVideo

Modified from Example 2-3 in the book "Learning OpenCV 3: Computer Vision in C++ with the OpenCV Library".

5. SimpleTransformation

Modified from Example 2-5 in the book "Learning OpenCV 3: Computer Vision in C++ with the OpenCV Library".

6. FlannMatching1to1

Modified from the based on the tutorial "Feature Matching with FLANN" at http://docs.opencv.org/3.2.0/d5/d6f/tutorial_feature_flann_matcher.html.

Given two images, the executable will detect the keypoints via the SURF detector and compute the descriptors. Then it will match the descriptor vectors using the match() method of the FLANN matcher. At the end, it will find the "good" matches and display them by connecting the "good"-matched keypoints between the best matched source image and the target image.

./FlannMatching1to1 [image1] [image2]

One example:

./FlannMatching1to1 ../../Pictures/airplanes/image_0001.jpg ../../Pictures/image_0001-new.jpg

7. FlannKnnMatching1to1

This executable is similar to FlannMatching1to1 where the main difference is that it uses the knnMatch() method of the FLANN matcher.

./FlannKnnMatching1to1 [image1] [image2]

One example:

./FlannKnnMatching1to1 ../../Pictures/airplanes/image_0001.jpg ../../Pictures/image_0001-new.jpg

8. FlannMatching1toN

Given a directory of source images and a single target image, the executable will detect the keypoints via the SURF/ORB detector and compute the descriptors. Then it will match the descriptor vectors between each source image and the target image using the knnMatch() method of the FLANN matcher. At the end, it will find the "good" matches and display them by connecting the "good"-matched keypoints between the best matched source image and the target image.

Note that the executable has two modes: slow and fast. While it will do the match between the target image and each source image one-by-one in the slow mode, it will do the match between the target image and all the source images as a whole once in the fast mode. It is expected to see a significant running time reduction in the fast mode.

./FlannMatching1toN [surf/orb] [slow/fast] [source-image-directory] [target-image]

Two examples:

./FlannMatching1toN surf slow ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannMatching1toN surf fast ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannMatching1toN orb slow ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannMatching1toN orb fast ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg

9. FlannKnnMatching1toN

This executable is similar to FlannMatching1to1 where the main difference is that it uses the knnMatch() method of the FLANN matcher.

./FlannKnnMatching1toN [slow/fast] [source-image-directory] [target-image]

Two examples:

./FlannKnnMatching1toN surf slow ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannKnnMatching1toN surf fast ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannKnnMatching1toN orb slow ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg
./FlannKnnMatching1toN orb fast ../../Pictures/airplanes ../../Pictures/image_0001-new.jpg

10. BowSvmClassifier

This executable implements a simple object classifier with Bag-of-Word (BOW) and 1-vs-all SVM using OpenCV as introduced in http://www.morethantechnical.com/2011/08/25/a-simple-object-classifier-with-bag-of-words-using-opencv-2-3-w-code/. After the SVM classification, it does a 1vn (e.g., n = 2, 3, 5) knnMatch of the SURF descriptors with n candidate classes selected by the SVM classification. Note that for the FLANN-based 1v1 knnMatch, each class has only one high-quality image, and the set of the high-quality images for the FLANN-based 1vn knnMatch is a subset of the images for building the BOW vocabulary and training the SVM classifiers. If one class has more than one image for training the FLANN-based 1vn knnMatch, the repetitive descriptors in multiple images will invalidate the good match selection in knnMatch.

If

(1) the maximum percentage of the good matches exceeds a certain threshold, (2) the count of good matches is greater than or equal to a certain number,

then evaluate the class as the one with the maximum knnMatch percentage; otherwise evaluate the class as "unknown".

To display the information about the available commands and options, please run the help command.

$ ./BowSvmClassifier help

Besides the help command, this executable has three other commands: build, train, and test.

10.1 Build the vocabulary.

Below is an example build command.

./BowSvmClassifier build -d ./train-images -e ./descriptors.yml -v ./vocabulary.yml

The SURF descriptors of the images are written to descriptors.yml and the BOW vocabulary is written to vocabulary.yml. Note that the labelled images need to be stored in the following hierachical tree:

train-images
├── label1
│   ├── image11
│   ├── image12
│   └── image13
└── label2
    ├── image21
    └── image22

10.2 Train the 1-vs-all SVM classifiers and save the FLANN-based matcher.

Below is an example train command.

./BowSvmClassifier train -p ./SvmClassifier -e ./descriptors.yml -v ./vocabulary.yml -d ./match-images -m ./matcher-descriptors.yml

The SURF descriptors of the train images are loaded from descriptor.yml, so they don't need to be computed again. The BOW vocabulary is loaded from vocabulary.yml. The 1-vs-all SVM classifiers are saved in a set of yml files with the common prefix "SvmClassifier". The images for training the FLANN-based matcher are stored in the same hierachical way as those for building the vocabulary, and the descriptors for the FLANN-based matchers are saved in the yml file "./matcher-descriptors.yml".

10.3 Test the 1-vs-all SVM classifiers and the knnMatch of the trained FLANN-based matchers.

(1) To test one image,

./BowSvmClassifier test -p ./SvmClassifier -c label -i ./test.jpg -r ./result.yml -m ./matcher-descriptors.yml -v ./vocabulary.yml

The option "-c" specifies the true class or the expected class of the test image. The evaluated class and the decision function values of all the 1-vs-all SVM classifiers are written to result.yml as well as the match percentage of the two class candidates.

(2) To test a set of images,

./BowSvmClassifier test -p ./SvmClassifier -d ./test-images -r ./results.yml -m ./matcher-descriptors.yml -v ./vocabulary.yml

Note that the test images need to be stored in a tree similar to the one for building the vocabulary above, where the true class or the expected class of each image is given by its directory name.

11. SimpleHsvHistComparison

This executable converts two BGR-colored images into HSV, computes their single-channel or multi-channel histograms, and then compares their histograms via various methods. Note that

  • While BGR is Blue, Green, and Red, HSV is Hue, Saturation, and Value.

  • Any combination of the three h, s, and v channels may be specified for computing and comparing the histograms. If not specified, the default value "hs" will be used. Also, if only one channel is specified, the two histograms will be drawn up and down, next to each other.

  • One of the following comparison methods may be specified:

    correl = Correlation (method = CV_COMP_CORREL), chisqr = Chi-Square (method = CV_COMP_CHISQR), chisqr_alt = Alternative Chi-Square (method = CV_COMP_CHISQR_ALT), intersection = Intersection (method = CV_COMP_INTERSECT), bhattacharyya or hellinger = Bhattacharyya distance (method = CV_COMP_BHATTACHARYYA or method = CV_COMP_HELLINGER), kl_div = Kullback-Leibler divergence (method = CV_COMP_KL_DIV),

    If "all" is specified, the histograms will be compared via all the above methods. If not specified, the default value "correl" will be used.

To get the help info,

$./SimpleHsvHistComparison -h

Below are a couple of sample commands.

$./SimpleHsvHistComparison ./image1.jpg ./image2.jpg
$./SimpleHsvHistComparison ./image1.jpg ./image2.jpg -c h -m chisqr_alt
$./SimpleHsvHistComparison ./image1.jpg ./image2.jpg -c hs -m all

12. EmdHsvHistComparison

This executable converts two BGR-colored images into HSV, computes their single-channel or double-channel histograms, and then compares their histograms via the Earth Mover's Distance (EMD) method. Note that

  • Only one or two of the HSV channels may be specified for computing and comparing the histograms. If not specified, the default value "hs" will be used. Also, if only one channel is specified, the two histograms will be drawn up and down, next to each other.

  • The current EMD implementation in OpenCV supports the following three definitions of distance:

    l1: Manhattan distance, l2: Euclidean distance, c: Checkboard distance,

    If "all" is specified, the histograms will be compared with all the above distances. If not specified, the default value "l1" will be used.

To get the help info,

$./EmdHsvHistComparison -h

Below are a couple of sample commands.

$./EmdHsvHistComparison ./image1.jpg ./image2.jpg
$./EmdHsvHistComparison ./image1.jpg ./image2.jpg -c h -m l1
$./EmdHsvHistComparison ./image1.jpg ./image2.jpg -c hs -m all

13. BgrHistComparison

This executable computes the single-channel (Blue, Green, or Red) histograms of two BGR-colored images and then compares their histograms via various methods. Note that

  • Any combination of the three b, g, and r channels may be specified for computing and comparing the histograms. If not specified, default bgr.

  • One histogram is generated for each specified channel.

  • One of the following comparison methods may be specified:

    correl = Correlation (method = CV_COMP_CORREL), chisqr = Chi-Square (method = CV_COMP_CHISQR), chisqr_alt = Alternative Chi-Square (method = CV_COMP_CHISQR_ALT), intersection = Intersection (method = CV_COMP_INTERSECT), bhattacharyya or hellinger = Bhattacharyya distance (method = CV_COMP_BHATTACHARYYA or method = CV_COMP_HELLINGER), kl_div = Kullback-Leibler divergence (method = CV_COMP_KL_DIV), emd = Earth Mover's Distance

    If "all" is specified, the histograms will be compared via all the above methods. If not specified, the default value "correl" will be used.

  • The current EMD implementation in OpenCV supports the following three definitions of distance:

    l1: Manhattan distance, l2: Euclidean distance, c: Checkboard distance,

    If "all" is specified, the histograms will be compared with all the above distances. If not specified, the default value "l1" will be used.

To get the help info,

$./BgrHistComparison -h

Below are a couple of sample commands.

$./BgrHistComparison ./image1.jpg ./image2.jpg
$./BgrHistComparison ./image1.jpg ./image2.jpg -c b -m emd -d l2
$./BgrHistComparison ./image1.jpg ./image2.jpg -c bgr -m all

14. SimpleTemplateMatching

This executable matches a template image patch against an input image by "sliding" the patch over the input image using one of cv::matchTemplate()'s available matching method. The best match for the template image will be marked by a black rectangle in the input image. Note that

  • Although both images are always loaded as BGR images, the template matching can be done with four different channel type: bgr, grayscale, hsv, and hs.

  • The cv::matchTemplate()'s available matching methods are as below:

    Square Difference (method = cv::TM_SQDIFF) Normalized Square Difference (method = cv::TM_SQDIFF_NORMED) Cross Correlation (method = cv::TM_CCORR) Normalized Cross Correlation (method = cv::TM_CCORR_NORMED) Correlation Coefficient (method = cv::TM_CCOEFF) Normalized Correlation Coefficient (method = cv::TM_CCOEFF_NORMED)

    The matching method can be changed by moving the track bar at the top of the input image window.

To get the help info,

$./SimpleTemplateMatching -h

Below are a couple of sample commands.

$./SimpleTemplateMatching ./inputImg.jpg ./templateImg.jpg
$./SimpleTemplateMatching ./inputImg.jpg ./templateImg.jpg -c grayscale
$./SimpleTemplateMatching ./inputImg.jpg ./templateImg.jpg -c hs

15. TemplateHsHistComparison

This executable first matches a template image patch against a source image by "sliding" the patch over the source image using the cv::matchTemplate()'s Normalized Correlation Coefficient matching method, and then computes and compares the histograms of the template image patch and the best match. Note that

  • To minimize the effects of brightness, we convert the BGR images into HSV and only use the hue and saturation channels for template matching and histograms.

  • One of the following comparison methods may be specified:

    correl = Correlation (method = CV_COMP_CORREL), chisqr = Chi-Square (method = CV_COMP_CHISQR), chisqr_alt = Alternative Chi-Square (method = CV_COMP_CHISQR_ALT), intersection = Intersection (method = CV_COMP_INTERSECT), bhattacharyya or hellinger = Bhattacharyya distance (method = CV_COMP_BHATTACHARYYA or method = CV_COMP_HELLINGER), kl_div = Kullback-Leibler divergence (method = CV_COMP_KL_DIV), emd = Earth Mover's Distance

    If "all" is specified, the histograms will be compared via all the above methods. If not specified, the default value "correl" will be used.

  • The current EMD implementation in OpenCV supports the following three definitions of distance:

    l1: Manhattan distance, l2: Euclidean distance, c: Checkboard distance,

    If "all" is specified, the histograms will be compared with all the above distances. If not specified, the default value "l1" will be used.

To get the help info,

$./TemplateHsHistComparison -h

Below are a couple of sample commands.

$./TemplateHsHistComparison srcImg templImg
$./TemplateHsHistComparison srcImg templImg -m emd -d l2
$./TemplateHsHistComparison srcImg templImg -m all -d all

16. FindMostDescriptivePatch

This executable detects the keypoints of the source image and computes their SURF descriptors. Then it slides a fixed-size window over the source image and finds the window with the most number of keypoints in its internal area. The result window is called the characteristic patch of the source image. Note that

  • By default, both the width and the height of the window is 100 if not specified.
  • The boundary area of the window where the keypoints are not counted is called "buffer zone". By default, both the width and the height of the buffer zone is 10 if not specified.

To get the help info,

$./FindMostDescriptivePatch -h

Below are a couple of sample commands.

$./FindMostDescriptivePatch srcImg characteristicPatch
$./FindMostDescriptivePatch srcImg characteristicPatch -w 50 -g 50
$./FindMostDescriptivePatch srcImg characteristicPatch -w 200 -g 200 -b 20 -d 20

17. FindMaxConvexContour

This executable finds the contour with the maximum area and its convex hull. Below is a sample usage.

$./FindMaxConvexContour srcImg

18. FlannKnnSavableMatching1toN

Similar to FlannKnnMatching1toN, this executable detects the SURF keypoints of a given image, computes the corresponding descriptors, and then matches the descriptors with those of a set of training images using the knnMatch() method of the FLANN-based matcher. But the major difference is that it can save the trained FLANN-based matcher in two files (one for the matcher and the other for the FLANN index of the matcher) and load the trained FLANN-based matcher from the two files later. Note that

  • Since the write/read method of the FLANN-based matcher doesn't save/load the trained descriptors and FLANN index, we have to create a customized savable matcher inherited from the FLANN-based matcher which can save/load the trained descriptors and FLANN index.
  • The FLANN index file is assumed to be in the same directory as the matcher file.

To get the help info,

$ ./FlannKnnSavableMatching1toN help

To train the FLANN-based matcher and save the matcher,

$ ./FlannKnnSavableMatching1toN train -d [training-image-directory] -m [matcher-yml-file]

To load the FLANN-based matcher and do the matching,

$ ./FlannKnnSavableMatching1toN match -i [image-file] -m [matcher-yml-file]

19. FlannKnnSavableMatchingM2N

This executable extends FlannKnnSavableMatching1toN such that it can do the SURF knnMatching of multiple images in a single "match" command. It can also write detailed match results into a yml file. Note that the labelled training images need to be stored in the following hierachical tree:

train-images
├── label1
│   └── image11
├── label2
│   └── image21
└── label3
    └── image31
  • For version 1.0, we do only one knnMatching between the query image and all the training images.
  • For version 1.1, if the good match percentage of the first knnMatching is marginally low, we will do second pairwise knnMatching between the query image and the best matched training image; otherwise, we still do only one knnMatching as for version 1.0.
  • For version 1.2, we revert to one knnMatching between the query image and all the training images, but calculate two good match percentages per each query-training image pair and adopt a slightly more complicated criterion for determining the best matched training image.

To get the help info,

$ ./FlannKnnSavableMatchingM2N help

To train the FLANN-based matcher and save the matcher,

$ ./FlannKnnSavableMatchingM2N train -d [training-image-directory] -m [matcher-yml-file]

To load the FLANN-based matcher and do the matching of multiple images,

$ ./FlannKnnSavableMatchingM2N match -d [training-image-directory] -m [matcher-yml-file] -r [result-yml-file]

To load the FLANN-based matcher and do the matching of a single image,

$ ./FlannKnnSavableMatchingM2N match -i [image-file] -l [expected-label] -m [matcher-yml-file] -r [result-yml-file]

where the option "-l" specifies the expected label of the input image.

20. LineFollowingCannyEdge

This executable recognizes the "maximum" black line in a white paper where the maximum is in the sense of the area (i.e., the number of pixels) occupied by the line. It uses the Canny Edge Detection to generate the contours.

$ .\LineFollowingCannyEdge [image-file]

21. LineFollowingHoughTf

This executable recognizes the "maximum" black line in a white paper where the maximum is in the sense of the line length.

$ .\LineFollowingHoughTf [image-file]

22. LineFollowingThresholding

This executable recognizes the "maximum" black line in a white paper where the maximum is in the sense of the area (i.e., the number of pixels) occupied by the line. It uses the simple invert thresholding to generate the contours.

$ .\LineFollowingThresholding [image-file]

23. GroupHsvHistComparison

Slightly different from SimpleHsvHistComparison which compares the histograms of two BGR-colored images, this executable compares the histogram of each BGR-colored image within a given directory with the histograms of two BGR-colored images, respectively. Note that although it supports the same comparison methods as SimpleHsvHistComparison, only one comparison method can be specified in each run.

To get the help info,

$ ./GroupHsvHistComparison -h

Below are a couple of sample commands.

$ ./GroupHsvHistComparison ./image1.png ./image2.png -d ./image-dir/
$ ./GroupHsvHistComparison ./image1.png ./image2.png -d ./image-dir/ -c h -m chisqr_alt