Copy-paste from luxrender wiki
In LuxRender an environment map serves two purposes:
- environment lighting map
- reflection map
In LuxRender both maps are one and referred to as environment map. As such it is recommended to choose detailed HDR images in case reflective surfaces are present in a scene.
Apart from above options a background image might be required. For this several options exist. These are:
- postpro addition (in eg. GIMP or Photoshop)
- win- or camera-mapped image
- self made sphere in the hosting 3d-application around the scene
- usage of highly detailed HDR images of usually 16+ Megapixels which can also serve as a background image
- much more additional options depending on the 3D host application.
A distinct support for background images is not offered by LuxRender.
Background and preconsiderations
Using environment maps in general follows these recommendations:
The HDR should have a resolution suitable for the needs of the scene
- Lighting: For a pure environment lighting map almost any size works. Common for environment maps are eg 360x180 pixel for a latlong HDR (see further down). A viewer like eg. qtpfsgui, GIMP or Photoshop will show a HDR at that resolution as a blurry image without details. For lighting this is sufficient.
- Reflection: Reflection maps are usually mirrored on shiny surfaces, like eg a shiny metal spoon, a glass or only blurry on a gold coin. Only with a complex environment a material with a reflective surface looks believable (this especially applies to metal and water/glass materials). A typical size for a latlong reflection map is 3200x1600 pixels and at this size a lot of distinct details of the surroundings will become visible.
- Background: Background images are usually seen in detail eg. through a mirror or directly towards the horizon. In some cases they are the whole scene, where only a few 3D objects are added. Using LuxRender environment map also for background usually requires resolutions of 6,000 x 3,000 and more depending on the scene's finaly requirements. Other strategies for a rich background should be considered.
HDR images come in varying quality. Some with already applied Gamma (compliant to pre-linear workflows), some with already adjusted multipliers or both. This applies to both commercial and freely available HDRIs. HDR images of poor quality lack contrast or offer poor lighting information. HDR images generated out of LDR images, eg. a HDR from a HiRes jpg-image almost always provide poor lighting. LuxRender offers to compensate such issues, but this can be tricky and results might still be poor in case of too low quality HDRs.
LuxRender accepts latlong, angular and vcross projected HDR images. SkyDome mapped HDRs should only be used in LuxRender with an appropriate geometry in the scene, which "hides" the lower half (eg a ground area with thickness). Still due to different aspect ratios in common supplied SkyDome HDRs, weird results usually happen. SkyDome HDRs are set to LatLong in LuxRender if used that way. File:PanoConversion Names.png
The following images show how the axis directions are mapped using the environment map. (Note, LuxRender uses the Z-axis as the up-axis internally, so that is what these images show. Some 3D apps use the Y-axis as the up-axis instead, usually an exporter for these apps would "flip" the scene automatically to make this transparent)
Up to version 0.6 LuxRender supports only the OpenEXR-format (.exr). LuxRender 0.7 supports also the Radiance-format(.hdr). LDR-images can be used, but this is not recommended. In case of a LDR-image as environment map in LuxRender additional lighting sources or some heavy modification upon creating the HDR out of an LDR should be considered.
IBL Image information
Some HDR images are supplied with the corresponding gain and gamma value, which have already been applied. HDR images with IBL or sIBL descriptions have a seperate text file (ending .ibl or .sibl), which lists all relevant information. siBL HDRIs can safely always assumed to be at 1.0 Gamma (linear), whereas the corresponding Gamma and multiplier values in the sIBL files list the values for non-linear workflows.
In case those are not supplied, HDR images usually are supplied as follows:
- - "old" HDRIs (for non-lienear workflows): Gamma at 1.8 or 2.2 already applied.
- - linear HDRIs (for linear workflows): always linear at 1.0 Gamma