5 · Display and windowing

5.1 The density window

A CBCT voxel is a density value in Hounsfield units (HU). The window maps a chosen HU range onto the screen's gray scale: everything below the window renders black, everything above renders white, and the range in between gets the full gray ramp. A narrow window shows subtle density differences; a wide window shows the whole span at once.

Caution. CBCT HU calibration is approximate by nature. The presets and every HU readout in the program are starting points and raw values, not calibrated CT numbers.

5.2 Presets

For a 2D radiograph the HU presets do not apply (the gray scale is display-normalized, not HU); center, width, gamma, and invert work the same way on its 0 to 4095 scale.

The desktop app opens every CT volume on the preset you last picked (section 2.6); the website opens each volume on Auto.

5.3 Manual control

• Histogram: the current volume's value distribution, with the black and white cut lines draggable directly on it. Below the black line renders black; above the white line renders white. Double-clicking a cut line returns it to the automatic window. The histogram is computed when the volume loads, so it is available in every mode.
• One window, every mode: the Window section governs the whole app. Every reading mode, including the virtual cephalogram, renders with the same center, width, gamma, and invert you see here; there are no per-mode duplicates of these controls.
• Double-click resets: every slider in the app resets on double-click (window sliders to the automatic values, gamma to 1).
• Center and width sliders: the same window numerically. The sliders span this image's actual value range, and width moves on a logarithmic scale, so narrow windows adjust finely while the far end still reaches the full span.
• Gamma: bends the gray ramp; 1 is linear. Double-click the slider to reset.
• Invert: white-on-black to black-on-white.

5.4 Slab and MIP

Each MPR pane can thicken its slice into a slab (0.1 to 20 mm). The slab averages the voxels through its thickness; ticking MIP (maximum intensity projection) takes the brightest voxel instead, which pulls high-density structures such as roots, canals walls, and metal through the slab. Slab and MIP are per pane, so an averaged axial can sit next to a MIP sagittal.

5.5 Resetting

R (or the reset control) returns the cameras to the standard orthogonal orientation. A full reset additionally returns window, inversion, and gamma to their defaults; over the agent connection this is the reset_view verb with full (chapter 9).