Occasionally its nice to be able to use a HDRi environment together with a vraysun, for when you want stronger shadows than the HDRi supplies. The trick is in aligning the sun with the HDRi so that the shadows from each match up. You can do this through trial and error, but if you want to change the rotation of the HDRi then its a pain. Rather than try to explain the steps involved, I thought it would be quicker doing a video tutorial. I’m afraid it turned out to be 13 mins long, but hopefully it will help.
Thought I should do a quick tutorial on how I use these HDRi Skydomes I’m selling. Note that this is just one of many possible workflows, and there are probably lots of tricks I’m missing and even things I do completely wrong. I should also say that I work mostly with still images, not animations.
1. Here is a typical architectural scene. It is a model I made of Waro Kishi’s Fukaya house in Japan that never really went anywhere.
2. I use a gamma 2.2 workflow together with reinhard color mapping, so not strictly LWF but shares some of the advantages. I don’t want this to turn into a LWF tutorial or discussion, but this post on cgpov.com pretty much sums up how I feel a gamma corrected workflow helps us as visualisation artists.
The reinhard color mapping helps to control burnt out (overexposed) areas. Screenshot of my color mapping set up: The burn value of the reinhard color mapping typically ranges from .75 for an exterior to 0.05 for an interior. You need to experiment with the value until you gain control over the burnt out areas. Here is an example with a camera pointing at the HDR sky:
For the final render, I use the Vray Frame Buffer, and add a slight s-curve to the output to compensate for the lack of contrast that the gamma corrected workflow introduces:
3. Add a vray dome light and load the exr/hdr using the max bitmap loader. Set the mapping type to environment/spherical. If you are using .hdr files, you can use the vrayHDRi loader instead. It makes no difference whether you use the bitmap loader or the vrayHDRi loader, the vrayHDRi adds a bit more control in that you can control the render multiplier independently from the viewport multplier. Set the output of the .exr to 1 and the vraylight multiplier to 1. If your hdr/exr has no alpha channel it seems you can save quite a bit of memory while rendering (approx 200mb in my case) if you load the exr/hdr as realpixel float rgb rather than the rgba option.
[Click for original size]
4. To rotate the HDR you need to enter a U offset value from 0-1, so to rotate 180 degrees with would enter 0.5, 270 degrees 0.75 etc.
5. Add a vrayphysicalcamera, and set the aperture and shutter speed to something that would work for a typical outdoor scene, like F4, 1/200th & ISO 100. Remember that you are in effect using a completely manual camera, there is no ‘P’ or automatic mode so you need to experiment with different exposures until you get a good result.
[Click for original size]
6. Hit render and see what you get. If it looks too dark/bright I tend to adjust the bitmap’s output rather than the vraylight multiplier, so that I can have a couple of ready setup HDRi’s ready to drag and drop onto the dome light. In the examples below I use an output value of 1.5.
For the 7 shots used to make this HDR skydome I used a Canon 1ds mk3 which has superb auto bracketing abilities as well as being very fast and having 21 megapixels. The lens used for these shots was a sigma 8mm fisheye which gives a complete circular image on a full frame dslr. I set the AEB to 7 shots 2 stops apart, which gave exposure times of 0.5s, 1/8, 1/30, 1/125, 1/500, 1/2000 & 1/8000 all at F20. This range of exposures is crucial for capturing the full dynamic range of the sun, which will eventually mean you get good strong shadows when you use the HDR image to light a 3d scene.
- Process raw files to remove chromatic aberration & to ensure white balance is consistent. I do this in Adobe Lightroom (pictured below), where you can copy the develop settings from the first file, and then batch process the remaining ones to save time.
- Export as 16 bit TIFFs
- Load TIFFs into Photomatix or Photoshop to blend into a single HDR, I use Photomatix as it seems to do a better job of removing ghosting artifacts (from moving clouds).
- Load HDR image file into Hugin. Choose lens type as fisheye when importing, and set the Horizontal field of view to 285 degrees (I arrived at this mostly through trial and error!)
- Hugin will complain that more than 1 image is required - ignore.
- Set pitch of image to 90, and adjust yaw so that sun is centred. If you know where the sun is, it helps later on when you come to rotating the skydome in your 3d application.
- in the stitcher tab, I take off soft blending as there is only 1 image, and press the ‘calculate optimal size’ button. Then hit ‘Stitch Now!’ (saving as a tif)
- Open 32bit tif in photoshop, clone out anything you dont want (dust in my case), save as 32 bit exr. Image below shows how the HDR should look when you drag the exposure slider in photoshop.
(click image for high res version on flickr)
Sometime, I’ll follow this up with something about how I use these in 3dsmax & Vray!
