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INSIDE / TUTORIALS : |
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For those of you that are new to HDRI - here's a quick description of what all the fuss is about !
HDRI stands for high dynamic range image - sometimes refered to as a radiance map. The dynamic range of a scene is the contrast ratio between its brightest and darkest parts. A HDR image therefore has a greater dynamic range than a standard image file such as a jpeg, tiff etc., which is a low dynamic range image.
HDR images have the important property that their pixel values are proportional to the amount of light in the original environment where the HDRI was captured. So the benefit of the HDR format is that it stores the amount of luminance data of a scene, instead of just on-screen colour values that normal bitmaps do.
There are two good reasons for using HDRI in 3d and exploiting the special properties of HDR images - A. for producing realistic looking reflections and B. for lighting a scene. (The aim of this tutorial is to show you how to get great looking reflections using Splutterfish's free HDRI Bitmap I/O plug-in for 3ds MAX. To exploit HDRIs for lighting you need a render engine such as Brazil by Splutterfish - this is not the subject of this tutorial).
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1. To carry out this tutorial you'll need the following:
a. The demonstration scene above can be downloaded for FREE here !
b. You'll need a lightprobe (HDR) image such as those available at Paul Debevec's Light Probe Gallery - I used the kitchen probe for this scene.
c. You will also need HDRShop - an image processing tool that lets you view and modify HDR images, along with other standard bitmap formats. Get it here...
d. Finally you'll need to download and install the Splutterfish free I/O plugin for max - available on the Splutterfish website !
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2. To begin with take a look at these two scenes for comparison. The red ball is 100% reflective, the black ball is 66% reflective and the blue ball 33%. The scenes are rendered with default lighting and no shadows to concentrate on the reflections being produced.
Fig.1
The scene in fig.1 uses a HDR image as an environment map, whereas in the scene shown in fig.2 the HDRI has been replaced by the same image in jpeg format. In the HDRI scene you can see how the strength of the reflections is nicely adapted depending on the reflective properties of each ball. In the ....ball (100% reflective) the windows appear "blown out" that is to say over exposed. However in the .... ball (% reflective) the reflected window appears less exposed, and you can even see the detail of the trees outside the window. In comparison in fig.2 you can see that the reflections resulting from the use of a jpeg bitmap don't have the same adaptive exposure characteristics that HDR images produce !
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Fig.2
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To quote something that I read on Neil Blevin's website - reflections only look as good as the environment the object is reflecting ". Now take another look at the results achieved using a HDRI at the top of the page ... get the point ?
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Fig.3
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3. If you've downloaded all the files etc., you can make yourself a nice cup of tea and get started on the tutorial !
First of all you need to convert your lightprobe image into a HDR format that can be used by 3ds MAX. This is where HDRShop comes in handy. Start HDRshop and load the kitchen light probe image. To create the "latitude/logitude" type image required by 3dsMAX you select Image... Panorama... Panoramic transformations, then choose Latitude/Longitude from the drop down list under Destination Image. Make sure that the Source Image Format is set to Lightprobe. Click OK to save out your new image.
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4. Install the splutterfish plugin simply by copying the HDRI.bmi file to your MAX plugin directory, e.g. C:\program files\3dsmax4\plugins.
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5. Fire up max and load the pool.max file. Now you can load the HDRI image as an environment bitmap. Choose Rendering... Environment... and under Environment Map click None then Bitmap. Choose Radiance Image File (HDRI) from the format type drop down list (its the splutterfish plugin that allows you to load this type of image). Select the kitchen latitude image that you created in HDRshop. See fig.4 below
BEFORE YOU CLICK ON OPEN you need to setup the HDR image ! Click Setup.
Fig.4
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Fig.5
6.Take a look at the Linear White Point under the HDRI Load Settings. As you increase this value you'll notice the magenta areas in the preview image decrease in size. These magenta areas indicate the pixels that are clamped to white - that means their value is fixed and interpreted by MAX as being white. Alot of magenta will limit the amount of luninance data being exploited from the HDRI - with a HDR image you need to cover the highest range of luminance data possible whilst maintaining precision. You therefore need to increase the Linear White Point until the last pixel of magenta disappears. I found a value of 120 worked fine with my HDR Latitude image. NOW you can click on OK then Open !
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7.You now need to boost the HDR texture's output. To do this, open the Material Editor. Drag and drop the kitchen.hdr image from the Environment Map button to a free material slot. Make sure you copy as Instance.
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Fig.6
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In the material editor under the Output rollout change the RGB Level to 120 - the same value indicated in the "Linear White Point" spinner earlier. This determines the bit range used for each pixels color channel. See fig.7
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Fig.7
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8.Still in the materials Editor - change the Coordinates to Mapping... Spherical Environment. (3dsMAX defaults the mapping to Screen, which is wrong).
Now render your image and you'll see the reflections created by the HDRI environment map ! Open up the pool-final.max file to see my finished scene with lights and shadows added. The End ! Have fun...
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Fig.8
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