Normal & Cavity Map Tab

From ZBrush Info

This section describes the normal map creation options found under the Normal & Cavity Map tab. These are the settings you'll most commonly use to affect a generated normal map.

• Flip Image Vertically: The generated normal map texture will be flipped top to bottom. Some external programs or renderers will need to use vertically flipped normal maps.
• Flip Red Channel: Vertically flips just the red channel of the normal map.
• Flip Green Channel: Vertically flips just the green channel of the normal map.
• Switch Red and Green Channels: Switches the red and green channels of the normal map. This is used with programs or renderers that switch the x-y coordinate space mapping of the color channels opposite to the "usual" way of doing things.
• RGB Blur: If you find artifacts when rendering using a ZMapper normal map, increasing the Blur value may eliminate these artifacts. Try this particularly if you find 'black speckles' in the model when displayed using the created normal map. (This has to do with limitations inherent in the process of mapping 3D geometry to a normal map representation, and will be encountered in some form in all normal map creation programs that employ the high-resolution/low-resolution subdivision correspondence used by ZBrush.)
• RGB Sharp: Inverse of RGB Blur. This is another control that may allow you to change the final map to be of higher quality.
• Seam Overpaint: When renderers are processing normal map information (or almost any other type of map information, for that matter), they need to handle UV seam issues. These issues arise because adjacent polygons in the model may be mapped to areas of the normal map that are not adjacent. A renderer that in some sense averages nearby map pixels in its calculations may need to go outside the actual group/polygon area of the map in these cases. As a result, some maps (including normal maps) may need to have valid map information outside of and around the borders of the map areas actually corresponding to points on the model. This option controls how many pixels outside of a map area such information may be written. You can try increasing it to handle artifacts that appear at UV seams.

• Samples, Subdivide: These affect the quality of the final map. Higher values are likely to produce higher quality, at the expense of increased map generation time.
• Inflat Hires Mesh Details and Inflat Bumpmap Details: Both of these exaggerate the bumps or wrinkles in the mesh by inflating them, depending on the intensity of the settings. The first control causes inflation before any bumps have been processed into the model's geometry, and so causes inflation of only geometric details; the second causes inflation after bumps have been processed into the model's geometry, and so inflates both geometric and bump details. Both may be used at the same time, but doing so will often lead to artifacts. Using these settings is definitely a matter of artistic judgment. Some screenshots are shown in below to try to give an idea of what the settings do.

Figure: Close-ups of effects of 'Inflat Hires Mesh Details' and 'Inflat Bumpmap Details' controls.

Inflat Hires Mesh Details at max, Inflat Bumpmap Details at max. Artifacts are clearly visible.

Inflat Hires Mesh Details at max, Inflat Bumpmap Details at 0. Notice that the headband and some folds around the eye are more prominent, but that the headband dots (which are bump map details) are unchanged from frame 1.

Inflat Hires Mesh Details at 0, Inflat Bumpmap Details at max. Now not only Now not only the geometric details, but also the bump map details, have been inflated.

Inflat Hires Mesh Details at, Inflat Bumpmap Details at. This is the base model.

• Sharpen Bumpmap Details: Allows elements of the bump map to be presented more clearly, but possibly with a more pixilated effect. This is shown below.

Figure: Elephant ear rendered at low and high values of 'Sharpen Bumpmap'.

• Sharpen Hires Mesh Details: Similar to the previous setting, but applies to mesh rather than bumpmap details.
• Cavity Intensity: One commonly used technique to achieve realistic or dramatic renders is the idea of ambient occlusion, where recessed areas of a surface become darker, even if a model is lit only with diffuse light. Cavity shading is a way of simulating this effect, and of incorporating it into the generated normal map. Cavity Intensity controls the degree of this effect; higher settings will result in darker cavities. If this setting is 0, no cavity shading will be done.

Figure: Section of troll used to illustrate cavity mapping.

The portion of the troll model shown below will be used to illustrate how the different cavity settings affect the final cavity map. This area was chosen because it has both wrinkled areas, flat areas, and blends between the two.

When viewing a normal-mapped model with standard shading, it's difficult to separate the effect of cavity shading from the effect of standard shading. Accordingly, in the examples below we have presented the cavity effects with cavity mapped models, rather than with normal-mapped models. Cavity maps may be created with the Create CavityMap button, described later.

Figure: Effects of 'Cavity Intensity' setting.

The three images below show the effects of rendering a cavity map with the cavity intensity set to 0.25, 0.5, and 0.75 of its maximum value, respectively. Other cavity-related settings held constant. Higher settings will result in darker cavities in final rendered images.

• Cavity Coverage: Affects what is considered a cavity. In practical terms, you can think of the 'cavity ratio' of a recessed area as the ratio of the depth of the recess to its width. The higher this ratio, the more of a cavity a recess is. As cavity coverage is increased, more recesses that are shallow in relation to their width will be considered and shaded as cavities. In particular, note the effect of this setting on the wrinkles in the relatively smooth area under the troll's collarbone.

Figure: Effects of 'Cavity Coverage' setting.

Cavity maps rendered with cavity coverage set to approximately 0.5, 0.75, and maximum of full intensity, respectively. Other cavity-related settings were held constant. Higher settings will result in more geometry being affected by cavity darkening in final rendered images.

• Cavity Blur: Use this to compensate for artifacts that might appear when using cavity shading, or to cause an effect that does not follow the contours of the model as closely as it otherwise would.

Figure: Effects of 'Cavity Blur' setting.

Cavity maps rendered with a blur setting 0.25, and 0.75 of maximum, respectively. Other cavity-related settings were held constant. Higher settings will cause cavities to appear softer and larger in final rendered images.

• Raytrace, Interpolate: Normal map generation is done somewhat differently depending on which of these modes is on. Map generation times will differ somewhat between modes. More importantly, the different generation modes may have an effect on the final appearance of the normal-rendered low-resolution mesh, depending on the tools and techniques you used when refining the model in ZBrush. (Using tools such as Nudge, which cause a vertex in the high-resolution model to be displaced significantly across a surface, compared to the same vertex in the low-res model, will be most likely to produce visible differences using these modes.) Often, the results using one method will be effectively identical to the results using the other method. Inspecting renders whose normal maps have been generated in each way is the best way to see which mode fits with your workflow.

Figure: Normal map generated with interpolated mode.

Details around the eyes are not quite as desired.

Figure: Normal map generated with raytraced mode.

Note how the eyes are slightly rounder, compared with the previous picture.

• Create NormalMap: Create a normal map using the specified settings, and write it to the texture chosen when ZMapper was started. (If no texture was chosen, or one of the built-in textures was chosen, a new texture will be created with a default size.) The model will be displayed in ZMapper using the generated map, once the map is complete.
• Create CavityMap: Like Create NormalMap, except that a grayscale map showing the calculated cavity intensities is produced (and will be available as a texture after quitting ZMapper). This can be useful in a number of ways. Looking at the cavity map in ZMapper makes clear what effect the cavity settings have on where shading takes place, which is not obvious from inspecting a normal mapped surface. A cavity map can also be produced separately from a normal map, and modified by hand to produce other effects, before being included in the rendering pipeline.