Appendix 2 High Dynamic Range Images
From ShadeCamp
Normal image formats contain 8 bits of data per channel, including 8 bits each for the RGB colors plus 8 bits for the alpha channel. This results in color values between 0 and 255 for each of the RGB channels. HDRI (High Dynamic Range Images) provides at least 16 bits of data per color channel, making it possible to express finer gradations of color, preserving detail in very dark or very bright areas of an image.
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HDRI Effects
Using HDRI with Image Based Lighting (IBL) can create some very realistic effects. Greater detail in environment maps and highlights can also be achieved using HDR images.
An example of IBL using an HDR image
An example of IBL using a normal image
The surface attributes in the two above images are identical, but you can see a difference between the two images in the caustics and in the specular of the rightmost bear.
The Lighting factor in the Background window is set to 1.0 in the HDRI example above. In the example of the normal image, the Lighting factor is set to 8.0. To use IBL in an image, set the rendering method to “Path tracing” (in the Basics tab of the Rendering Settings window), and in the Global Illumination (G.I.) tab select “Path tracing” from the Global illumination pull-down menu. Also verify that the image you want to use for IBL is set as the background image in the Background window.
As noted above, using an HDR image for IBL can preserve greater detail in dark or light areas of the image. If you use an HDR image for IBL, there are several settings that may improve your results: Noise reduction may block out very bright pixels in HDR images, so in the Global Illumination tab of the Rendering Settings window, set Noise reduction to 0.00. If noise appears in your image, try raising the Ray tracing quality in the Miscellaneous (Misc.) tab to a higher value.
Loading HDR Images in the Background
There are several methods for using HDR images in the background. Both methods involve adjusting settings in the Background window.
Light Probe Images
An example of a light probe image
From the Background window’s Pattern pull-down menu (the pull-down menu labeled “None” by default) select Image. Next, click the Edit image pull-down menu and load a light probe image.
Now make the following settings: Set the Area pulldown menu to Whole. Set the Projection pull-down menu to Light probe. Set the Direction pull-down menu to whichever direction you deem appropriate based on the orientation of the image.
Spherical Maps
An example of a spherical map
Select Image from the Pattern pull-down menu in the Background window, and load a spherical map by choosing Load from the Edit image pull-down menu.
Now make the following settings: Set the Area pulldown menu to Whole. Set the Projection pull-down menu to Sphere.
Cube Maps
Select Image from the Pattern pull-down menu in the Background window, and load a cube map by choosing Load from the Edit image pull-down menu.
Now make the following settings: Set the Area pull-down menu to Whole.
Set the Projection pull-down menu to Cube Map.
Vertical Cross Maps
Select Image from the Pattern pull-down menu in the Background window, and load a cube map by choosing Load from the Edit image pull-down menu. Now make the following settings: Set the Area pulldown menu to Whole. Set the Projection pull-down menu to Vertical Cross.
Supported Formats
Shade supports OpenEXR, HDR, PFM (Portable Float Map) and raw HDRI formats. The following table shows the differences between the three:
