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74 lines
3.0 KiB
74 lines
3.0 KiB
Adding a Trackbar to our applications! {#tutorial_trackbar} |
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- In the previous tutorials (about *linear blending* and the *brightness and contrast |
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adjustments*) you might have noted that we needed to give some **input** to our programs, such |
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as \f$\alpha\f$ and \f$beta\f$. We accomplished that by entering this data using the Terminal |
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- Well, it is time to use some fancy GUI tools. OpenCV provides some GUI utilities (*highgui.hpp*) |
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for you. An example of this is a **Trackbar** |
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- In this tutorial we will just modify our two previous programs so that they get the input |
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information from the trackbar. |
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Goals |
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----- |
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In this tutorial you will learn how to: |
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- Add a Trackbar in an OpenCV window by using @ref cv::createTrackbar |
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Code |
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---- |
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Let's modify the program made in the tutorial @ref tutorial_adding_images. We will let the user enter the |
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\f$\alpha\f$ value by using the Trackbar. |
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This tutorial code's is shown lines below. You can also download it from |
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[here](https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp) |
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@include cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp |
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Explanation |
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----------- |
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We only analyze the code that is related to Trackbar: |
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-# First, we load two images, which are going to be blended. |
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@snippet cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp load |
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-# To create a trackbar, first we have to create the window in which it is going to be located. So: |
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@snippet cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp window |
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-# Now we can create the Trackbar: |
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@snippet cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp create_trackbar |
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Note the following: |
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- Our Trackbar has a label **TrackbarName** |
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- The Trackbar is located in the window named **Linear Blend** |
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- The Trackbar values will be in the range from \f$0\f$ to **alpha_slider_max** (the minimum |
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limit is always **zero**). |
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- The numerical value of Trackbar is stored in **alpha_slider** |
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- Whenever the user moves the Trackbar, the callback function **on_trackbar** is called |
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-# Finally, we have to define the callback function **on_trackbar** |
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@snippet cpp/tutorial_code/HighGUI/AddingImagesTrackbar.cpp on_trackbar |
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Note that: |
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- We use the value of **alpha_slider** (integer) to get a double value for **alpha**. |
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- **alpha_slider** is updated each time the trackbar is displaced by the user. |
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- We define *src1*, *src2*, *dist*, *alpha*, *alpha_slider* and *beta* as global variables, |
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so they can be used everywhere. |
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Result |
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------ |
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- Our program produces the following output: |
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- As a manner of practice, you can also add two trackbars for the program made in |
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@ref tutorial_basic_linear_transform. One trackbar to set \f$\alpha\f$ and another for \f$\beta\f$. The output might |
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look like: |
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