Background
From ZBrush Info
To create more immersive renders, ZBrush 4R2 allows the loading of a background image for use as an environment map, projected on a sphere that surrounds your scene. These 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 what is called 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 4 R2 rendering engine. In other words, rather than painstakingly creating lights to fit the background image, LightCap does the work automatically.
A model integrating in a Background image and using its information to light the model through a LightCap.
Note: For a high quality background, it is advised to use a large image such as a size of 8000x4000 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 512x512 environment maps. When set to 2, 1024x1024 environment maps are created and when set to 3 ZBrush will create 2048x2048 environment maps.
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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.
Background menu controls
On Button
The On button enables or disables display of the background texture. This option is only available if a background texture has been loaded.
Texture Popup Window
When clicking the Texture selector, you can choose which background image to apply from the Texture palette. If the desired image has not already been loaded, click the Import button at the bottom left of the popup window to browse for the texture you wish to use.
A texture loaded in the Background palette and its preview in the floating window.
Zoom Slider
The Zoom slider lets you zoom within the background image. It is only possible to zoom in; you cannot zoom out.
Exposure Slider
The Exposure slider lets you define the exposure value of the image. This is useful when working with 32-BIT images like HDRI since they contain multiple exposure ranges.
Gamma Slider
The Gamma slider lets you change the gamma value of the loaded background texture. This affects the darker regions of the image without affecting the brighter regions, allowing you to make shadows darker or to bring out details that are hidden by shadows.
Longitude and Latitude Sliders
The Longitude and Latitude sliders let you rotate the background image on the horizontal and vertical axes. This makes it possible to find the best point of view for integrating your model with the image.
LightCap
The LightCap function lets you create a LightCap (Light Capture) based on the shading information within the background image. Once this has been done the LightCap image can be accessed and applied using the Light palette.
LightCap creation is based on two settings: the Samples slider and Reflect mode.
Samples slider
The Samples slider defines the number of lights which will be created for the LightCap :
- 0 creates 2 lights
- 1 creates 3 lights
- 2 creates 5 lights
- 3 creates 9 lights
- 4 creates 17 lights
- 5 creates 33 lights
The more lights that are created, the more closely your LightCap will match the image’s lighting and color information. However, this also means that if you wish to modify the LightCap information you will need to adjust the values of more lights.
From let to right, a LightCap created with a Sample of 2, 3, 4 and 5. More samples produce a more accurate LightCap.
Reflect Mode
When Reflect is enabled, specular information will be calculated from the image and created as part of the LightCap. This specular data will then be added to each light. This option is useful when you want to use a reflective material on your model.
On the left, a Specular created with the Reflect mode on and on the right, with the Reflect mode off.
