Not only of domes can an artist leave of. The fisheye mode shown in the previous post is sufficient for planetarium productions, but may not satisfy artists looking for ‘real’ fisheye lens. The most common lens found in today’s market are ‘equisolid’ lens (ref: HDRI for CGI).
After a productive holiday we now have something new to play with 😉
model by Jar-Artist
model by Jar-Artist
Models/scene gently provided by Jar-Artist
http://www.blendswap.com/blends/author/jay-artist/
The proof is in the pudin
It’s “easy” to put up a nice artistic effect together and simply assume everything is working as it should. However, I wanted to make a system that could match the effect produced by real lens. For that I had to build a fail proof experiment. People not into coding may not know, but building a reliable testing and debugging setup is one of the keys for efficient coding. In my opinion it’s always worthy to put time into this. Note: this is also why Blender users can help a lot with bug fixing by simply building proper test files for the (also carefully/methodologically) reported bugs).
1 – Photoshooting
Take some pictures with a tripod rotating the camera on its center (the focal centre actually). We have been doing this for the past two weeks so it was smooth. Those pictures were taken by Aldo Zang in the Visgraf Lab at IMPA.
2 – Stiching
I don’t get tired of recommending Hugin for stitching and panorama making – hugin.sourceforge.net. This open source project sometimes works better even than autopano pro (a pretty good commercial alternative).
3 – Rendering
I put the panorama as a background plate, calibrated the aligment, added a simple floor + spheres. This was done with the (yet to be released) IBL Toolkit. Apart from that my Blender camera needs to match the settings of the real camera+lens I’m aiming at.
In this case all the pictures for the stitching were taken with a Nikon DX2S and a fisheye 10.5mm lens. I created new presets for the sensor dimensions and the render output.
4 – Results
I was quite pleased when I compared the rendered output with the original image. The aspects we should be looking at are only field of view and line distortion across the lens:
Also note the bottom left corner of the photo. This subtle shadowing is due to the vignetting of the lens. This is not present in the cycles render because I’m not implementing a real camera model (as shown here and here).
Algorithm
The complete patch can be found here. The core is the following function (simplified here). I elaborated this from the ‘classic’ fisheye equisolid formula: radius = 2 * focallens * sin ( angle / 2):
__device float3 fisheye_equisolid_to_direction(
float u, float v, float lens, float width, float height)
{
u = (u - 0.5) * width;
v = (v - 0.5) * height;
float r = sqrt(u*u + v*v);
float phi = acos(u/r);
float theta = 2 * asin(r/(2 * lens));
if (v < 0) phi = -phi;
return make_float3(
cos(theta),
-cos(phi)*sin(theta),
sin(phi)*sin(theta)
)
I hope you like it. If you can share any work you did with this feature I would love to see it.
Dalai
