Creating Normal Maps
High Frequency Detailing differentiates from High Resolution Sculpting as the process will generally require a completed Medium to High Resolution Sculpt in which the model’s topological structure can be retained. As High Resolution Sculpting is used to produce details that require geometric displacement (such as wrinkling and lower level detail), High Frequency Detailing serves the purpose of displacing light rays (such as with pores in a character’s skin) and therefore makes the effect more subtle as it will only be visible in sufficiently illuminated areas. Retaining a models topological structure while creating High Frequency Details, should also preserve the underlying High Resolution Sculpt detail and the model’s UV Layout.
The image above depicts High Frequency Detail (HFD) applied at a character’s skin level. Creating this level of detail has been achieved by sculpting with a modifier that retains the geometry loops that comprise the model’s topology, despite geometric subdivision. As the model’s High Resolution Sculpting should be completed at this stage, the purpose of using this modifier is multi-part as it will not only preserve details from High Resolution Sculpting (HRS) but also preserve UV layouts that were performed on the underlying geometry. It is therefore significant that geometry displacement deeper than wrinkling, is not targeted for High Frequency Detailing as this will potentially result in distortion of UV’s and HRS detail loss.
In the case of Blender, model topology preservation while sculpting can be achieved with a Multires Modifier.
Closer inspection of the detailing in the above image will reveal excessively boosted details in some areas (such as around the eyes and under the nose). It is important that details are boosted in these regions during High Frequency Detail Sculpting as much of the detail produced at this level is prone to becoming washed out either by a lack of sufficient illumination or Sub-Surface Scattering of light rays during render-time. Boosting details at this point increases the chances of their visibility in the final render, as a result it is therefore recommended that this technique is used sparingly in combination with the Mulitres and Normal Map method for HFD as noted below.
Multires in Conjunction with Normal Mapping for Rendering HFD
The creation of a set of custom made brushes for sculpting HFD should be determined by the requirements of the specific models. Nonetheless, there are certain brushes I’ve found to be consistent for many human-based characters such as skin pore brushes, cracked lip brushes etc. Below are several custom brushes used for sculpting this character’s High Frequency Details, you are free to download and use these brushes in your own projects permissible by CC0 (Creative Commons Zero) licensing.
Skin on Forehead and wrinkles around eyes (above) with finger skin (below).
Detail context (below)
When Sculpting of High Frequency Detail is completed a Normal Map can then be Baked from the result.
A Normal map should, however, not replace sculpted HFD but provide an additional level of control for HFD which is ultimately controlled with the Multires modifier in conjunction with the baked Normal Map.
When the Normal Map is applied to the appropriate texture channel (typically the Normal Map Channel) of the model’s material, and with the model’s modifier stack retaining the HFD in a Multires modifier, an additional level of control can be used to balance the model’s render times with details required for the final shot.
In other words using this method provides an additional degree of control over the model’s Level Of Detail (LOD), whereby mixing the results can decrease render times (by reduction of Multires subdivisions at render-time) for areas where this detailing does not prevail in the final render.
Use of the Multires modifier at this stage is also beneficial in terms of keeping viewport interactivity at realtime speeds as the modifier’s Preview setting can be set to 0.
Normal mapping can also render significantly faster than the excessively, sub-divided geometry required for HFD.
This set-up is particularly useful during animation when the same model is required for Wide to Extreme Close-up’s (ECU) but also useful when the effects of the Multires Modifier, Normal Mapping and High Resolution Sculpting are mixed for static imagery.