HDRi Skies

HDRi Skies

HDRi Skies are special images to represent skies which contain extra information about intensities of the colors.

HDRi (high dynamic range imaging)is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRi is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.

IRender nXt offers support for HDRi Skies - used as visible skies, as sky reflections and for illumination from the Sky.

HDRi skies for background, illumination and/or reflection

HDRI Skies are special 360 degree images of background imagery such as skies, trees, sunsets and buildings that also contain illumination information such as the intensity and color of light based on the background imagery chosen.

What HDRi Skies means to you...

Accurately illuminate a scene.
Create realistic reflections.
Increase realism.
Featured in IRender nXt and nXtRender.

HDRI (high dynamic range imaging)is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.

1 HDRi Sky Tutorial
2 Using HDRI skies in IRender nXt
3 Resolution Issues
4 See also
5 Sources

HDRi Sky Tutorial

Exterior rendering with HDRi Sky Preset

This tutorial show you how to use the HDRi Sky Lighting default, to add a quick HDRi sky background to a model.

You can easily choose a different HDRi sky, or mke other changes after you view a sample rendering.

See HDRi Sky Tutorial

Using HDRI skies in IRender nXt

We added a new Lighting Preset to IRender nXt - HDRi Sky

Because of the new Image Layer Wizard - which make it easy to rotate and position HDRi skies, more and more people are using HDRi skies in the models.

This new Lighting Preset automatically makes the best settings for HDRi skies, and selects a nice sky with a mountain, background trees, sky and clouds.

If you want to use a different HDRi sky - just choose this preset and then go to the HDRi Setup tab to choose a different sky.

IRender contains several HDRI skies from various sources, including ArchVision, AccuStudio and EverMotion. You can click on the plus sign to cycle between the included HDRI skies.

If you want to make HDRI Skies visible, or just reflective, use the Sun/Sky Tab to adjust the settings

In order to see the HDRI skies, you need to turn the sky on, and select an HDRI sky. None of the 4 lighting defaults selects HDRI sky and makes the sky visible, so you need to do this manually on the Sun/Sky tab. In the example on the right, we selected the Exterior Default, then turned off the sun, and turned on HDRI sky mode. (We selected the HDRI sky to use from the HDRI tab)

Resolution Issues

HDRI skies don't work well for backgrounds unless you have a very high resolution HDRi, or use a very large Field of View.

If you use a standard FOV of 35, then you're only using 10% of the width of the HDRi image and stretching part of the image that across the background of your rendering. (35 degrees is about 10% of 360 degrees)

So if you do the math, for a 1000 pixel rendering, you would need a 10,000 pixel HDRi image for a 35 degree FOV to render at highest quality.

If the FOV is small, it will look like you are zoomed in on the background image, the wrong scale. So it's better to use a larger FOV for exterior scenes for which you want to use a HDRi sky for the background.

If you set the FOV to 90, then you will see 1/4 th of the HDRi image as a background. That kind of works, but of course you may get distortion from the 90 FOV in the perspective view. 2 Pt Perspective may help with this.

Here I used StJohns_09_2.hdr, one of the highest resolution HDRi files that are included with the librairies. It has a width of 4096 pixels. And I used a FOV of 90 and turned on 2 pt perspective.