As opposed to direct volume rendering, which requires every sample value to be mapped to opacity and a color, maximum intensity projection picks out and projects only the voxels with maximum intensity that fall in the way of parallel rays traced from the viewpoint to the plane of projection.
This technique is computationally fast, but the 2D results do not provide a good sense of depth of the original data. To improve the sense of 3D, animations are usually rendered of several MIP frames in which the viewpoint is slightly changed from one to the other, thus creating the illusion of rotation. This helps the viewer's perception to find the relative 3D positions of the object components. This implies that two MIP renderings from opposite viewpoints are symmetrical images, which makes it impossible for the viewer to distinguish between left or right, front or back and even if the object is rotating clockwise or counterclockwise even though it makes a significant difference for the volume being rendered.
MIP imaging was invented for use in nuclear medicine by Jerold Wallis, MD, in 1988, and subsequently published in IEEE Transactions in Medical Imaging.
Surprisingly, an easy improvement to MIP is Local maximum intensity projection. In this technique we don't take the global maximum value, but the first maximum value that is above a certain threshold. Because - in general - we can terminate the ray earlier this technique is faster and also gives somehow better results as it approximates occlusion.
Read more about this topic: Volume Rendering
Famous quotes containing the words maximum, intensity and/or projection:
“I had a quick grasp of the secret to sanity—it had become the ability to hold the maximum of impossible combinations in one’s mind.”
—Norman Mailer (b. 1923)
“We may say that feelings have two kinds of intensity. One is the intensity of the feeling itself, by which loud sounds are distinguished from faint ones, luminous colors from dark ones, highly chromatic colors from almost neutral tints, etc. The other is the intensity of consciousness that lays hold of the feeling, which makes the ticking of a watch actually heard infinitely more vivid than a cannon shot remembered to have been heard a few minutes ago.”
—Charles Sanders Peirce (1839–1914)
“In the case of our main stock of well-worn predicates, I submit that the judgment of projectibility has derived from the habitual projection, rather than the habitual projection from the judgment of projectibility. The reason why only the right predicates happen so luckily to have become well entrenched is just that the well entrenched predicates have thereby become the right ones.”
—Nelson Goodman (b. 1906)