This tutorial is far from done, it’s full of typo’s, but I’m already posting it for I might not be able to work on it the next few days. I will fix the text and add images somewhere in the next week. Hope it’s handy still!
Create your own HDR Light Probe.
Sander Wit
11-22-2008
This tutorial
In this tutorial I will explain how to create a High Dynamic Range Image to use as a background image in Blender for reflections and lighting information. I’m no rocket scientist and I’m not English either so it will not be very accurate. However it may help you when you want nice reflections or light-setups with home-made lighting images.
What will you need
Simple digital camera.
Reflective sphere (the more reflective and spherical the better).
Picturenaut 2 or newer.
PhotoShop.
What is ‘HDR’ and ‘Probe’
HDR or HDRI means High Dynamic Range Image. It’s nothing more or less than an image with more lighting information than in a normal image. For example, most photo’s or images on the internet have a lighting range per pixel of 8 bit. A HDR image contains a larger range of varieties in lighting like 16 or 32 bit. It’s like 8 bit is a photo of a set where there is a bit underexposed (details are unclear and dark like a place under a couch) and where another bit is overexposed (details are unclear and bright like a lamp or window). The nice thing about a high dynamic range image is that you have a more wide range of lighting information meaning you can either make the photo darker so that the window isn’t overexposed any more, or brighter so that the dust underneath the couch is visible. This is handy when lighting a scene in 3D for you want as much lighting information from the background as possible to simulate actual environment lighting. You will see that we will do some very logical steps to create such an image.
Another thing you want to have when lighting a scene in 3D is a background image covering the complete background in all directions. Not only behind the scene, or 360 degrees around it, but also from the top and bottom like in real life. This is where the probe bit comes in. A probe in this case means a sphere-ish shape. Meaning the image will be not like a 360 degree panorama, but a image in all directions. It’s like a sphere around your 3D scene that’s fully textured so that you can have pretty accurate reflections. The HDR bit adds the fact that you can also use it as a all-directional light source.
The steps
First get yourself a digital camera and a reflective sphere. Place them both in the place you want to be capture for further use. Place the sphere in the middle of the space for it will be the eye looking in pretty much all directions. Place the camera pretty far away from the sphere so that you and the camera will not be visible too much in the reflection of the sphere. Also you will see more of the sphere and there for more of the environment in the reflection when standing far away. Make sure to zoom in (without using digital zoom for it will decrease your image quality dramatically) to capture the sphere as big as possible in your shot. Make sure that the sphere and camera are really stationary when taking the shots for you might need a slow closing-time and there for a steady ground/tripod. With everything set up you need to change the settings of the camera to manual, set the focus to be so that the reflections in the sphere are sharp (the reflections in the sphere are further away than the sphere itsselve!) and make sure it stays like it without autofocussing everytime you take a new shot for it might often not be able to focus automatically. Make sure the white-balance is correct and not changing when making multiple shots. Get the aperture to be pretty open (like F3 depending on the camera you are using) and get the ISO number to be as low as possible (like a hundred). This to get as less grain as possible. Now set the closing-time to pretty long so that the darkest spot in your scene is fully visible. It’s okay if bright areas are way overexposed. Make more test-photos if necessary. Now make the same shot again but with a less long closing-time. Do the same thing like 8 times (sometimes less is okay, sometimes more is needed) to capture the brightest thing in your set without overexposing it. Now it’s okay if a dark area is underexposed. Now we are done with the camera and sphere, toss them away. Load the photo’s to your pc and start Picurenaut. Go to File - Generate HDRI… and select your photo’s with the Add button. (Not the test-photo’s obviously, only the photo’s of the complete range of lighting.) If you listened carefully and had the white-balance and camera and probe-setup locked, you won’t need to tick the ‘Color balancing’ and ‘Image alignment’ boxes. If you did deviate from my advice you will want to tick these… Leave the rest of the settings unharmed and press Ok. Now the program will work it’s butt off to make your 32 bit image. Go to View - HDR Display Options… To slide the Exposure and Gamma sliders to see that all the lighting information is stored in this one image. Neat ey! Now save the image as something.hdr (another one is also okay, but to be able to edit it nicely in Photoshop, choose .hdr. Remember the location of the file carefully, start Photoshop and load your hdr image. Now make the Rules visible with Ctrl + R and drag two rulers to the top and left side of your sphere. Now grab your ‘Elliptical Marquee Tool’ in other words the round selection tool. Select the sphere from the top left (where the two rulers meet) to the bottom right holding Shift. You might find that your perfect shiny sphere is not actually a sphere. If that’s the case select just your ‘sphere’ without Shift and resize the image so that the height and width are the same. If your sphere is actually spherical, here’s what you do. After selecting the sphere select Image - Crop. If you’re sphere was non-spherical, resize your image to become spherical now. You might also consider resizing it to 640 pixels wide and high if that’s the HDR size you prefer. (That size is often used with HDR Probes.) Make sure Constrain Proportions is turned off when your sphere was non-spherical.
That’s pretty much about it! Save your HDR and load it into Blender as a background with Spherical and Hori turned on. Good luck and have fun!
Additional tips
Create some photos of the floor the 3D model will be standing on. Make yourself a nice texture using these photo’s, perhaps even with a bump and specular map on it and put them on a plane underneath the 3D model. This will make the reflections a bit more believable since the floor is often directly underneath the model. Using a photo from the ground in the exact location as the HDR probe will help making the reflection more nice and also because a ground is often visible around the 3D model, not only in the reflection, you might wanna have it visible in the render.
Another useful tip is to use two series of photos with different exposures to create two HDR images and than overlapping them in Photoshop to get rid of the ugly seam. It’s not very easy but maybe very useful in some cases.
The last not at all least tip is a complicated one. If you want to have a square size image like below to be able to project the image more easily to an actual sphere, load the photos, before making them HDR to Photoshop, and choose Filter - Distort - Polar Coordinates. And than Polar to Rectangular. Now you have a square sized image which you can easily modify and fix and color correct and tile and what not. Also choose UV Project with U and than Sphere from view with the view being from the side (num3) to project the faces to a square. Now load your image and see it projected on the sphere. Rotate the sphere if needed.