10. Write the difference between object space method and image space method. Explain Z-buffer algorithm for visible surface detection. [5+5=10]

Object Space Method vs Image Space Method:

1. Object Space Method: In this method, the visibility of a surface is decided by comparing surfaces of objects. It is more suitable for less complex scenes. The calculations are performed at the vertices and edges of an object. The main advantage of this method is that it can handle any type of surface including polygons, curves, and surfaces. However, it is computationally expensive for complex scenes.

2. Image Space Method: In this method, the visibility is decided pixel by pixel at the image space. It is more suitable for complex scenes with a large number of objects. The calculations are performed at each pixel of the screen. The main advantage of this method is that it is less computationally expensive for complex scenes. However, it can only handle polygonal surfaces.

Z-buffer Algorithm for Visible Surface Detection:

The Z-buffer algorithm is a type of image space method for visible surface detection. It works by storing the z-depth of each object for every pixel in the frame buffer. The steps of the Z-buffer algorithm are as follows:

1. Initialize the depth buffer and frame buffer such that for all pixels, the depth is set to the maximum value and the frame buffer is set to the background color.

2. For each polygon surface in the scene, do the following: a. Calculate the depth z for each pixel (x, y) inside the polygon. b. If z is less than the depth currently stored in the depth buffer for pixel (x, y), then replace the depth in the depth buffer with z and set the color of the pixel in the frame buffer to the color of the polygon.

3. The final image is formed by using the colors in the frame buffer.

The Z-buffer algorithm is simple and easy to implement. However, it requires a lot of memory to store the depth information for each pixel.