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75 lines
3.0 KiB
Markdown
75 lines
3.0 KiB
Markdown
Adding a Trackbar to our applications! {#tutorial_trackbar}
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======================================
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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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