What is sIBL and what is in an sIBL set?
- sIBL stands for Smart Image Based Lighting, a file convention published by Christian Bloch of HDR Labs.
- An sIBL set is a folder with the full HDRI, a half-resolution reflection map, a small blurred light map, a tonemapped background JPEG, a preview, and a .ibl text file that describes them and the sun position.
- 149 of the 359 HDRI download packages on HDRI Hub include an sIBL set next to the full-resolution HDRI.
- You do not need sIBL-GUI. Every set also works when you load the .hdr or .exr file directly.
sIBL was created to make image based lighting a one-click setup: instead of loading an HDRI, a reflection map and a sun light by hand, a loader reads one small text file and builds the whole rig. Many HDRI Hub skies ship with such a set. This page explains what is in the folder and how to use it with and without sIBL-GUI.
What is inside an HDRI Hub sIBL set?
Every package that includes an sIBL set contains the full-resolution HDRI plus a folder with the set. Taking HDR 001 Meadow 1 as delivered:
- HDR_001_Meadow_1.hdr: the full HDRI, 10240 x 5120 pixels, Radiance format, 178 MB. This is the file you load for lighting and reflections in any renderer.
- HDR_001_Meadow_1_Ref.hdr: half-resolution copy, 5120 x 2560 pixels, 45 MB, used by sIBL loaders for reflections and refractions.
- HDR_001_Meadow_1_Env.hdr: blurred light map, 512 x 256 pixels, 316 KB, used as the diffuse environment light.
- HDR_001_Meadow_1_Bg.jpg: tonemapped background JPEG at full width, 10240 pixels, for the camera background when the sky is visible.
- HDR_001_Meadow_1_Preview.jpg (600 x 300) and HDR_001_Meadow_1_Thumb.tga (128 x 128): browsing images only.
- HDR_001_Meadow_1.ibl: the description file, 870 bytes of plain text.
The whole package is 254 MB. Newer skies (HDR 142 and up) are delivered as OpenEXR instead of Radiance, see .hdr or .exr.
What does the .ibl file contain?
A .ibl file is an INI-style text file that any editor can open. It has a [Header] with name, author, location and date, then a [Background], [Reflection] and [Environment] section that each name a file, its height in pixels, a multiplier and a gamma. The [Sun] section stores the sun's position on the panorama as u and v coordinates between 0 and 1, its colour and a multiplier. For HDR 001 Meadow 1 the sun sits at u 0.70, v 0.43 with colour 255,211,186. A loader uses these values to place a directional light exactly where the sun is in the image, which gives crisp shadows without a manual search for the brightest pixel.
Which software supports sIBL?
sIBL-GUI, the free, open-source browser and loader from HDR Labs, ships loader scripts for 3ds Max, Maya, Softimage, Cinema 4D, Modo and LightWave. It has not been updated for several years, so on current operating systems and renderer versions the direct route is usually simpler: load the .hdr or .exr as the environment map in V-Ray, Corona, Arnold, Cycles, Redshift, Octane, Enscape, Twinmotion, Unreal or Unity, and add a sun light at the position given in the .ibl file if you want a separate sun. The Ref and Env maps are an optimisation from a time when a 10K HDRI was slow to sample; current renderers handle the full map directly.
Do I need the sIBL set at all?
No. The full HDRI is always in the package and is the better file for lighting. The set is useful if you work in sIBL-GUI, if you want the ready-made tonemapped background JPEG, or if you want the sun position without measuring it yourself.