Hi Greg! Unfortunately, I don’t have a Mac, so I can’t download it. I did download the hdrgen for Linux, but I’m not sure if that’s what you’re referring to, as it looks as though it actually creates HDRs. I’m not sure how to use it exactly in my scenario and can’t work it out from the man page.
Meanwhile, here’s an update, and happy new year! Updates includ:
- New saw-horses in the room. Yes, I, uh, do have saw-horses in the room.
- Shoes on the shoe rack. There are my black work shoes.
- Fixed the trees on the right. Previously I made a mistake which meant that the textures were distorted because I didn’t multiply frac(Lu) by the aspect ratio of the texture. Now it is fixed and looks much nicer. They are alpha mapped plane trees.
- I replaced the alpha mapped plane bushes in the background with the photogrammetrically scanned and reconstructed bush that I had shown earlier in the thread, calibrated with macbethcal. This gives a much better sense of depth and shadow compared to a alpha mapped plane approach, which is expected.
- I modelled the grass in the backyard! There are also dead leaves, flowers, and weeds, but unfortunately at this perspective you can hardly see them. However, all that subtlety adds up to create what I think is now a pretty convincing backyard.
- Added some bricks in the back yard. There is actually a pile of bricks on a concrete plinth in the back, but it is so overexposed you can’t even see it. This is obviously incorrect for the human eye, the human eye can certainly see it. A photo, on the other hand, can not.
For those who haven’t seen the other thread where I test rendering out grass in detail, you can read it here.
Here is a rough comparison of the real space in greyscale. Apologies for the absolute mess in the room. It’s something of a workshop. Also, I didn’t match up the images perfectly in terms of viewpoint, the screendoor is open, there are obviously more objects, and the time of day is also not quite the same, even though it is roughly in the afternoon.
… and a colour comparison. I did tweak the white balance of the photo to match the render in this case, but nothing else, only white balance. I think that is allowed, eh? 
I’m pretty happy with it so far and I think the simulation is pretty close. Of course it will never be 100% perhaps, what with not having a spectrometer, modeling errors, human eye correction, etc.
I am considering whether to model more objects and fill up the room with junk, or to call it a day and move on to doing things like creating BIM models, classifying objects and releasing them for free online, and other tangential experiments.