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Mapping Depth Values to the near / far range

Started by wolf Nov 21, 2009 at 1:00 AM 1 replies 2.6k views

Original Post

Nov 21, 2009 at 1:00 AM

Hi, I have a projection matrix that is w, 0, 0, 0, 0, h, 0, 0, 0, 0, (f + n) / (f - n), -(2 * f* n) / (f - n), 0, 0, 1, 0); This matrix is a OpenGL projection matrix. I would like to map the values that I can read from the depth buffer into the near / far plane range of the view frustum in camera space. This is useful for camera based effects like Depth of Field. Many websites suggest a solution like this: -f * n /(z * (f-n) -f) where z is the depth buffer value and f and n the far and near plane. Any references where I can read up on this?

Erik Rufelt

Nov 21, 2009 at 8:28 AM

As I'm sure you're aware, the depth buffer is not linear, as it needs more precision closer to the viewer, and that equation transforms the depth back to the linear range from near to far.

The following site explains the process a bit: http://www.sjbaker.org/steve/omniv/love_your_z_buffer.html.
And http://www.opengl.org/resources/faq/technical/depthbuffer.htm has a lot of information.

Halifax2

Dec 5, 2009 at 10:27 PM

Sorry to bump, but this link would be good for you and any future prosperity when they search the forums. It does a very good explanation of the derivation of the perspective projection matrix, thus explaining why the depth map is not linear: Deriving Projection Matrices: Perspective Projection.

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