Which of the following statements is/are INCORRECT about the Z-buffer…

i) It is an image space method to detect visible surface.

True. Image space methods loops through pixel positions on the screen $(x, y)$ to determine which object is visible at that specific pixel. This is exactly how Z-buffer works, unlike object space methods which compare polygons to each other in 3D space.

• ii) In this method, a depth buffer is used to store the depth values of each position and a refresh (frame) buffer is used to store the intensity values or colour values for each position.

  True. The algorithm requires two arrays of memory: the Z-buffer (depth buffer) to track how close an object is to the viewer, and the frame buffer to store the actual RGB color that will be displayed on the screen.

iii) In this method, object edges can be anti-aliased.
The standard Z-buffer algorithm operates strictly on a pixel-by-pixel basis. For each pixel, it performs a simple binary comparison: is the new polygon closer than the previous one? It either replaces the pixel completely or discards the new one. Because it works with these sharp, "all-or-nothing" boundaries at the pixel level, it inherently causes jagged edges (aliasing or "jaggies"). Standard Z-buffering cannot perform anti-aliasing on its own.

• iv) This method can only find one visible surface at each pixel position.

  True. The Z-buffer only keeps track of the single closest depth value and the single corresponding color for any given pixel. It completely discards information about surfaces that are hidden behind the closest one.