Preview Prefrence
Automatically enabled after OpenGL1.2. Without 3D texture, each texture for x-y, y-z and z-x plane must be prepared and it is not efficient.
Mutual hiding among multiple channels. If disabled, later channel overwrite the former ones.
Open GL format for texture.
ALPHA (transparency only. 1 byte per boxel.)
LUMINANCE_ALPHA (luminocity and transparency. 2 byte per boxel.)
RGBA (4 byte per boxel. Best image quality.)
Alpha Blend is normal drawing method, forground layer hide background layers according to its alpha.
In Add mode, color is just accumulated.
Also, interpolation method can be selected.
If "Lattice like" is selected, Open GL draws the scene without 3D texture. (Slower and not efficient).
Layers normal to the camera
The volume is rendered as the sequence of cross sections.
Left image shows the border of each cross section layers.
You can select the base number of layers.
Larger number makes the image better, but larger time to render.
(Note actual number of layers varies according to the relative camera position)
Shade Setting
When emboss shading is selected, a copy is drawed in somewhat shifted position with negative luminocity.
Below image is the example of emboss in 2D image.
With this pseudo-shading, contrast of data can be emphasized.
Absorption factor is the amount of "shadow".
Complement determines the color modification for shadow.
Shade Factor is scale of positional offset.
Since this method is just overlapping of two data, rendering is much faster than ray-traced shadows.
Belows are samples of previews and PovRay rendered images with emboss shadow.
Since default "shade" has same color of the original one, when white core and red envelop exist, envelop absorb red component and looks like blue.
To modify the color of shade copy, set complement factor more than 0.
Empirically, 0.3～0.5 is good.
The graph at the bottom shows the level distribution of the data. (number of boxels of given value).
Y-axis of the graph is log scaled.
Second line is correction curve that comes from Level and Gamma Correction Filter
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