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How to select a bounding box ( ROI ) in OpenCV (C++/Python) ?

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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I know here already some questions were asked but they did't help me to solve my problem.

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I will appreciate any help to solve my problem. I'm new to opencv. I have an image and apply some code to get contours from image.

python roipoly

Now i want to get the RGB color values from detected contours. How can i do that? I do research on it and find that it could be solved by using contours so i try to implement contours and now finally i want to get the color values of the contours.

python roipoly

As asked in the comments, here's a possible solution to extract the BGR! The proper detecting of the desired, colored stripes is omitted here as also discussed in the comments. Having an image and a filled mask of a contour, for example from cv2.

Here's a short code snippet, that uses NumPy's savetxt to store all values in some txt file:. The resulting values. Attention: Values are BGR values; e. Learn more. How can i get the rgb color values from inside of a contour in image using opencv? Ask Question.Documentation Help Center. Use the new Polygon object instead. You can also use the new ROI creation convenience function drawpolygon.

Another option is the Polyline object, which enables you to create an open polygon, or polyline shape. For more information, see Compatibility Considerations. An impoly object encapsulates an interactive polygon over an image. You can add vertices and adjust the size and position of the polygon by using the mouse. The polygon also has a context menu that controls aspects of its appearance and behavior.

For more information, see Usage. Handle to parent object, specified as a handle. The parent is typically an axes object, but can also be any other object that can be the parent of an hggroup object. Position of polygon vertices, specified as an n -by-2 matrix.

The two columns define the x - and y -coordinate, respectively, of each of the n vertices. Specify optional comma-separated pairs of Name,Value arguments.

Name is the argument name and Value is the corresponding value. Name must appear inside quotes.

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You can specify several name and value pair arguments in any order as Name1,Value1, Position constraint function, specified as the comma-separated pair consisting of 'PositionConstraintFcn' and a function handle. You can use this function to control where the polygon can be dragged. See the help for the setPositionConstraintFcn function for information about valid function handles. Polygon is closed, specified as the comma-separated pair consisting of 'Closed' and true or false.

When set to true the defaultimpoly creates a closed polygon, that is, it draws a straight line between the last vertex specified and the first vertex specified to create a closed region. When Closed is falseimpoly does not connect the last vertex with the first vertex, creating an open polygon or polyline. ROI can be deleted, specified as true or false.Can anyone tell me roipoly matlab function equivalent in OpenCV?? In my case I want to extract triangular roi from the image, so c and r are of size 3x1.

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Instead, OpenCV provides functions like cv2. If you have the coordinates of the vertices, as shown in matlab you can create a numpy array with them. Then draw this polygon on a black image, which gives you the mask image as returned by roipoly.

An example is demonstrated below :. Asked: Do all opencv functions support in-place mode for their arguments? What is the most effective way to access cv::Mat elements in a loop? Is stereoRectifyUncalibrated efficient?

python roipoly

Sobel derivatives in the 45 and degree direction. Conversion between IplImage and MxArray. Saving an image with unset pixels. How to enable vectorization in OpenCV?

Vrm to obj

First time here? Check out the FAQ! Hi there! Please sign in help. Or how to get the same functionality using OpenCV? There is no corresponding inbuilt function like roipoly in OpenCV. T cv2. Question Tools Follow. Related questions Do all opencv functions support in-place mode for their arguments? Object detection slow. Copyright OpenCV foundation Powered by Askbot version 0.

Please note: OpenCV answers requires javascript to work properly, please enable javascript in your browser, here is how. Ask Your Question.In this tutorial, we will learn how to select a bounding box or a rectangular region of interest ROI in an image in OpenCV. In the past, we had to write our own bounding box selector by handling mouse events. I am always amazed by the weird choices made in the OpenCV library. You would think that selectROI would be part of highgui that has functions for displaying images, drawing on images etc.

As you will notice later in the post, the choices made while writing selectROI are a bit odd. But, before we criticize we gotta be thankful that someone produced something useful even though it is not perfect. It allows you to select a rectangle in an image, crop the rectangular region and finally display the cropped image.

If you are like me, you would prefer to drag a rectangle from the top left corner to the bottom right corner instead of the dragging it from the center. Well, we can easily fix that by replacing the highlighted line with the following line. Well here you go.

Now, suppose you do not like the crosshair and would like to see the rectangle without it. You can modify the code to not show the crosshair. The function selectROI also allows you to select multiple regions of interest, but there appear to be two bugs.

However, there appears to be a bug in the implementation in OpenCV 3. Bug Alert 2 : I could not get the python version to work and there is no documentation. The following code runs, but the variable rects is not populated. The function also does not return anything. If you find a fix, please let me know in the comments below.

You will also receive a free Computer Vision Resource Guide. Subscribe Now. Skip to primary navigation Skip to main content Skip to primary sidebar In this tutorial, we will learn how to select a bounding box or a rectangular region of interest ROI in an image in OpenCV. We will modify the highlighted line to try different options. Python Note this code does not work.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I need to create a numpy 2D array which represents a binary mask of a polygon, using standard Python packages. Larger context: I want to get the distance transform of this polygon using scipy.

As a slightly more direct alternative to Anil's answer, matplotlib has matplotlib. You should be able to pass grid to any of the scipy. An update on Joe's comment. Matplotlib API has changed since the comment was posted, and now you need to use a method provided by a submodule matplotlib.

As a slight alternative to Yusuke N. Useful me? And the result image is below, where dark area is Falsebright area is True. First you initialize the canvas. Then you create a drawing object, and you start making lines. Learn more. Asked 9 years, 7 months ago. Active 1 month ago.

Viewed 33k times. Can anyone show me how to do this? Isaac Sutherland. Isaac Sutherland Isaac Sutherland 2, 4 4 gold badges 23 23 silver badges 35 35 bronze badges.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

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I am getting a similar issue with this example. I ran this example after cloning the package. When I click I will not see any polygon lines showing up. Right-clicking to close the screen doesn't seem to work either. Only when I close the screen manually, I will receive the following error log:.

python roipoly

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I cloned the project from git and run it on my Mac. This comment has been minimized. Sign in to view. Line2D self. Are you using spyder? Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. Linked pull requests. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. The program itself is based on a simple discrete version of the Jordan curve theorem: if a point is inside of a polygon, then a ray emanating from it in a direction that is not parallel to any of the edges of the polygon will cross the polygon boundary an odd number of times.

If the point is not inside the polygon, the ray will cross the polygon boundary an even number of times. The boundary intersection calculation logic is described here and then here.

Through a code review I performed here, we determined that it was unlikely we could optimize that function anymore. After I changed the boundary intersection logic, I spend a lot more time in calculateNumberOfBoundaryIntersectionswith a small performance gain over the old algorithm.

So, while it is unlikely that performance can be squeezed out of findAnglesBetweenTwoVectors I suppose the other functions are still up for grabs. Is my NumPy usage good?

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EDIT: I just achieved a moderate gain by changing the organization of the code so that it is like this:. So here is my implementation of roipoly:. I am not completely sure point and polygonVertexCoords are going to be in the same format, but maybe this would be a start.

One may also solve for the generalized barycentric coordinates: at least one of them must be negative for points outside the convex hull of the polytope, see for example this thesis on On Generalized Barycentric Coordinates Sign up to join this community.

The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Calculating if a point is within a polygon, or outside of it Ask Question. Asked 5 years, 10 months ago. Active 5 years, 9 months ago. Viewed 4k times. Let's use whatever we can to get as much performance as we can! How come that algorithm works by always choosing the same fixed direction?


Python roipoly

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