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72 lines
3.1 KiB
Markdown
72 lines
3.1 KiB
Markdown
---
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title: 'OpenCV tools'
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linkTitle: 'OpenCV tools'
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weight: 14
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description: 'Guide to using Computer Vision algorithms during annotation.'
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---
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The tool based on [Open CV](https://opencv.org/) Computer Vision library
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which is an open-source product that includes many CV algorithms.
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Some of these algorithms can be used to simplify the annotation process.
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First step to work with OpenCV is to load it into CVAT. Click on the toolbar icon, then click `Load OpenCV`.
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Once it is loaded, the tool's functionality will be available.
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### Intelligent scissors
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Intelligent scissors is an CV method of creating a polygon
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by placing points with automatic drawing of a line between them.
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The distance between the adjacent points is limited by the threshold of action,
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displayed as a red square which is tied to the cursor.
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- First, select the label and then click on the `intelligent scissors` button.
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- Create the first point on the boundary of the allocated object.
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You will see a line repeating the outline of the object.
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- Place the second point, so that the previous point is within the restrictive threshold.
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After that a line repeating the object boundary will be automatically created between the points.
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To increase or lower the action threshold, hold `Ctrl` and scroll the mouse wheel.
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Increasing action threshold will affect the performance.
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During the drawing process you can remove the last point by clicking on it with the left mouse button.
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- You can also create a boundary manually (like when
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[creating a polygon](/docs/manual/advanced/annotation-with-polygons/manual-drawing/)) by temporarily disabling
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the automatic line creation. To do that, switch blocking on by pressing `Ctrl`.
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- In the process of drawing, you can select the number of points in the polygon using the switch.
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- You can use the `Selected opacity` slider in the `Objects sidebar` to change the opacity of the polygon.
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You can read more in the [Objects sidebar](/docs/manual/basics/objects-sidebar/#appearance) section.
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- Once all the points are placed, you can complete the creation of the object
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by clicking on the `Done` button on the top panel or press `N` on your keyboard.
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As a result, a polygon will be created (read more about the polygons in the [annotation with polygons](/docs/manual/advanced/annotation-with-polygons/)).
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### Histogram Equalization
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Histogram equalization is an CV method that improves contrast in an image in order to stretch out the intensity range.
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This method usually increases the global contrast of images when its usable data
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is represented by close contrast values.
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It is useful in images with backgrounds and foregrounds that are both bright or both dark.
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- First, select the image tab and then click on `histogram equalization` button.
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- Then contrast of current frame will be improved.
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If you change frame, it will be equalized too.
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You can disable equalization by clicking `histogram equalization` button again.
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