To create more immersive renders, ZBrush allows the loading of a background image for use as an environment map, projected onto a sphere that surrounds your scene. The background utilities are located in the Light > Background sub-palette.
An image used in this manner must be a panorama with a ratio of 2:1. In other words, the width must be twice the size of the height. For this feature, ZBrush uses the Equirectangular Projection method for the environment — the same one used for most HDRI (High Dynamic Range Image) work. This means that ZBrush is now able to load HDRI images. This includes support for 32-BIT color depth, which stores a wider range of color and light information compared to a classic 8-BIT image like a jpg.
Rather than simply serving as a great-looking background, these images can also be used by ZBrush to create a LightCap. This process uses the data within the image to extract color and light intensity which is then used as actual lights by the ZBrush rendering engine. In other words, rather than painstakingly creating lights to fit the background image, LightCap does the work automatically.
Note: For a high quality background, it is advised to use a large image such as a size of 8000×4000 pixels. Also, the quality of the LightCap created from a background image is controlled by the Details slider in the Render >> Render Properties sub-palette. When the Detail slider is set to 1 ZBrush will create 512×512 environment maps. When set to 2, 1024×1024 environment maps are created and when set to 3 ZBrush will create 2048×2048 environment maps.
8-Bit versus 32-Bit Background Images
ZBrush can now load 32-BIT images in HDR (radiance) file format for the background. The main benefit of a 32-BIT image is to allow you to adjust the image exposure. This is a dramatic improvement from an 8-BITs per channel image where the exposure range is really limited.
Put another way, a standard JPG has 255 steps in brightness between black and white. HDR can have thousands of steps. This more closely matches lighting conditions in the real world while simultaneously giving far more data to manipulate on the fly – data that you can use to dramatically alter your renders.
ZBrush now converts all images to 32-BIT depth, including JPG files. This means that any image of the appropriate dimensions can be used as a background image from which to create a LightCap. HDR images will result in the best quality render but JPG requires less memory and disk space usage. For this reason it is recommended to use JPG whenever the highest quality is not required. For example, you can convert an HDR image to JPG for use while sculpting and setting up your scene, then switch to the HDR version for the final render.
Snapshot Objects to Background
Objects in Edit mode can be snapshot to the Background by pressing the Transform > Snapshot button or shortcut Shift+S. With the Rotate With Object option turned on, different views of a model or different models can be snapshot at different locations, building up a complex scene.
Background controls are explained fully in the Reference Guide.