Clipping Techniques

Introduction of Clipping Techniques

• The clipping technique is used in computer graphics to limit the portion of an image that is visible.

Definition of Clipping Techniques

• Clipping in multimedia graphics refers to the process of removing the parts of an object or image that lie outside the visible or viewing area or viewport. (The viewing area of the image is called the Viewport.)
• Clipping in graphics refers to the process of selecting and rendering only a portion of an image or object that falls within a specified region or boundary.

Characteristics of Clipping Techniques

• Clipping is used to improve the rendering speed and efficiency of graphics by reducing the amount of processing required to render the full image or object.
• clipping is an important process in multimedia graphics that helps to optimize performance and ensure that only the visible parts of an object or image are displayed on the screen.
• Clipping is performed to ensure that only the visible portions of an object are displayed on the screen.
• Clipping is important to prevent unnecessary computation, which can be very expensive in terms of processing power and memory.
• In computer graphics, clipping can be applied in two different ways:
  • Clip space clipping:
    • It involves clipping the geometry of an object before it is projected onto the screen.
    • This ensures that only the visible parts of the object are rendered, which can save valuable computation time.
  • Screen space clipping:
    • It involves clipping the pixels of an image that falls outside of the viewing area.
    • This is commonly used in 2D graphics to prevent unnecessary processing of pixels that will not be visible on the screen.

Types of Clipping Techniques 

• Each Clipping technique has its own advantages and disadvantages, and the optimal choice depends on factors such as performance, accuracy, and visual quality.
• There are several types of clipping techniques used in multimedia graphics. These are:-

  • Viewport Clipping:

    • This technique clips an object or image to the edges of the viewport, ensuring that only the visible parts of the object or image are displayed on the screen.

  • Image Clipping:

    • This technique clips an image to a specific shape or path. This is commonly used in photo editing to create a more appealing or interesting composition.

  • Alpha Clipping:

    • This technique clips an image based on its transparency level. It removes the pixels that are completely transparent, leaving only the visible parts of the image.

  • Z-Clipping:

    • This technique is used in 3D graphics to remove the parts of an object that are behind another object or are hidden from view.

• • Point Clipping:

    • This technique is used to determine whether a point lies within a specified boundary or region. If the point is within the boundary, it is rendered; otherwise, it is discarded.

  • Line Clipping:

    • This technique is used to determine whether a line segment intersects a specified boundary or region. If the line segment intersects the boundary, it is clipped to the boundary; otherwise, it is discarded.

  • Polygon Clipping:

    • This technique is used to determine whether a polygon intersects a specified boundary or region. If the polygon intersects the boundary, it is clipped to the boundary; otherwise, it is discarded.

  • Curve Clipping:

    • This technique is used to determine whether a curve intersects a specified boundary or region. If the curve intersects the boundary, it is clipped to the boundary; otherwise, it is discarded.

  • Text Clipping:

    • This technique is used to determine whether text falls within a specified boundary or region. If the text falls within the boundary, it is rendered; otherwise, it is discarded.

Clipping Algorithms

• The choice of clipping algorithm depends on the nature or type of object being clipped and or the image being rendered, as well as the specific requirements of the application or system.
• Some algorithms are more efficient for certain types of objects and can handle more complex shapes than others.
• There are several types of clipping techniques used in computer graphics. Some of the commonly used ones are:

1. Cohen-Sutherland algorithm:

   • This algorithm divides the screen into nine regions and assigns a binary code to each point based on its location with respect to the viewport. This code is used to determine whether a point lies inside or outside the viewport.
   • The algorithm steps for Cohen-Sutherland Line Clipping are:
     1. Compute the region codes for both endpoints of the line.
     2. Check if both endpoints are inside the viewport. If so, render the line and exit.
     3. Check if both endpoints are outside of a single edge of the viewport. If so, discard the line and exit.
     4. If the line intersects an edge of the viewport, compute the intersection point and update the region code for the endpoint that is outside the viewport.
     5. Repeat steps 2-4 until the line is either rendered or discarded.

2. Liang-Barsky algorithm:

   • This algorithm is an improvement over the Cohen-Sutherland algorithm.
   • It computes the intersections of the object edges with the viewport boundaries and uses these intersections to determine the visible portion of the object.

3. Sutherland-Hodgman algorithm:

   • This algorithm clips a polygon against one edge of the viewport at a time.
   • It performs the clipping process in a series of steps until the entire polygon has been clipped against all four edges of the viewport.

4. Cyrus-Beck algorithm:

   • This algorithm uses vector operations to clip an object against a convex clipping window.
   • It is efficient and can handle objects with curved surfaces.

Use/Applications of Clipping Techniques

• In multimedia graphics, clipping is commonly used in video editing, 3D modeling, and animation to optimize performance and reduce processing time.