Having more of the history of SSAO, and measuring some rendered images in the same way, would help this article..<p>Several corrections here:<p>1) Historically, SSAO was never intended solve wall corners. That was already being done with baked textures, in games like Doom and Quake. It was first used in CryEngine to show deep crevices in fabric folds, and plants. Objects that capture light.<p>2) The examples of 'ugly' artifacts are just that, incorrect implementations. There should be no halo or shadow around objects, which is caused by not implementing a smart-blur, which is required for SSAO.<p>3) Even in scenes containing walls, SSAO is often better because - other than baked lighting - the alternative was just straight Phong illumination, which gives essentially a straight line profile using the technique the author describes. Analyze corners for regular Phong and SSAO in the same way, and you'll find Phong is the worse of them.
For example, regarding the images where the author says "And sure enough, the darkening is way less prominent here than I think it is visually.." What is not realized is that, with basic phong rendering, those gradual curves >would be flat lines< since the surface normals are constant. So yes, the effect is quite subtle, but we are still seeing a profile curve which has a 'curve' to it, and we notice (feel/see) that.<p>4) SSAO is now replaced by HBAO, and even further by VXGI (Voxel cone tracing) and other GI methods that truly solve wall corners in the correct way. Most of what the author is measuring here is multi-bounce lighting, which is correctly simulated by these new techniques.<p>Each method has its particular uses, and SSAO fits into that history for specific needs.<p>(Full disclosure: I work for NVIDIA, but the thoughts expressed here are my own.)
You can criticize SSAO/SAO as much as you want, but it can add spectacular details.<p>Here is a Viking Shield that I setup shading on:<p><a href="https://clara.io/view/01529814-3164-449a-8765-61a77cf780e0" rel="nofollow">https://clara.io/view/01529814-3164-449a-8765-61a77cf780e0</a><p>Then I added this SAO/SSAO pass:<p><a href="https://clara.io/view/966d2196-8573-47df-b9c2-bd6e1ad65a73" rel="nofollow">https://clara.io/view/966d2196-8573-47df-b9c2-bd6e1ad65a73</a><p>And the result is this, which I think is dramatically better than what I began with:<p><a href="https://clara.io/view/d59d26ab-c26e-4fa0-8907-d52c0c8acc1a" rel="nofollow">https://clara.io/view/d59d26ab-c26e-4fa0-8907-d52c0c8acc1a</a><p>I find the end result has significantly more detail and feeling of depth than what I started out with.
If you run a real radiosity renderer, you get proper darkening at corners. Here's a Blender rendering with a good radiosity renderer. Note that some inside corners have darkening, and some don't, depending on how they're lighted.[1][2]<p>Full radiosity renderers are slow. The image is rendered over and over again, each pass using the previous result, with all surfaces now being light sources. Each pass thus shows the result of light being reflected one more time. The corner-darkening effect comes from indirect lighting from the opposite face, an effect which gets smaller as you approach the corner. With some renderers, you can watch the passes, as the image changes from starkly lit to very realistic. Render farms for movie production spend most of their time doing just this.<p>Game hardware cannot yet do true radiosity in real time, so there are many ways to fake it. Some better than others.<p>[1] <a href="http://s10.photobucket.com/user/RCRuiz/media/3dTest/IlluminationInternalRadiosmallAO01.png.html" rel="nofollow">http://s10.photobucket.com/user/RCRuiz/media/3dTest/Illumina...</a>
[2] <a href="http://wiki.blender.org/index.php/Doc:2.4/Manual/Lighting/Radiosity" rel="nofollow">http://wiki.blender.org/index.php/Doc:2.4/Manual/Lighting/Ra...</a>
A common abuse of SSAO I see among early users: using it everywhere. SSAO is technically only supposed to occur where there is a lack of lighting (where there is only <i>ambient</i> lighting). That said I think it is still fine to apply it unrealistically if the results look "good" -- maybe even preferable for some people as I tend to enjoy stylized rendering over totally realistic rendering.
These graphs make things look more official, but the fact that he's judging luminosity in sRGB (a non-linear space) makes me think they're basically rubbish.<p>I mean, yeah, SSAO is a gimmicky trick... but so what?
I think HDR photography has some influence too. "Normal" photo-realism isn't necessarily the benchmark for renders anymore. Not when HDR looks so good when done right (subtle).<p>Take this photo of a room. The HDR is subtle, and reveals shadows in the corners that wouldn't be there without HDR.<p><a href="http://www.vangviet.com/wp-content/uploads/lovely-separation-house-bedroom-interior-graphy.jpg" rel="nofollow">http://www.vangviet.com/wp-content/uploads/lovely-separation...</a><p>Game graphics aren't known for subtlety. So the cheesy overdone HDR photography that burns our eyes, has found its way into gaming graphics. GTA5 generally looks great, but I noticed the overcooked corner shadows.
If I were a neural net learning to tell real light vs ambient occlusion, I'd immediately learn to look for the spider webs. I was fascinated by this article and loved the author's approach of graphing real photos. But I got a giggle when I started seeing the prominent spider webs.