Shooting HDRI's With Ricoh THETA Z1

I needed to capture HDRI’s on set at night with minimal lighting, to send to a remote VFX post-production team in Germany. We needed something up to the team’s standards that would also be quick and reliable on set. Although I’ve used stock HDRI’s to light 3D scenes, I had never successfully created any myself.

The workflow isn’t complicated, but there are a lot of steps to forget if we don’t do it often. I’m documenting the process here so I can remember how in the hell we did it.

By HDRI, I am referring to a spherical image with brightness values higher than the limits of a normal image. In 3D compositing we can use that lighting information to illuminate a scene and create reflections, like I’ve done in the image above.

With some quick research, we decided the Ricoh THETA Z1 would be a great fit.

The Z1 is a compact 360-degree camera, which uses two fisheye lenses and some tech-magic to create a complete spherical view around the camera.

I grabbed one from LensRentals and ran to downtown Spartanburg to shoot a bunch of test images with my friend Kavin Bradner (an epic photographer and 3D enthusiast).

Here’s one of our tests from Daniel Morgan Square, the one I’m using used to light the scene in the previous image:

To turn a sphere into a rectangle, the Z1 creates an equirectangular image. In this style, an image is squeezed at the top and the bottom. It looks weird to us, but technically it’s a normal image you can open in any editor. (3D software can stretch it back into a sphere later.)

This alone doesn’t make it an HDRI; for it to be “high dynamic range” we need to add multiple exposures together and save to a file that is capable of holding that extra information.

There are a few methods for making HDRI’s with the Z1.

Method 1: HDRI Plugin

The first method is to install the official HDRI Plugin. The plugin takes a series of images at different exposures, then merges them together into an HDRI. It’s fast, automated, and provides an .exr or .hdr file for immediate use.

My day tests came out great.

Unfortunately, my night tests were terrible.

This could be user error, but I could not get meaningful dynamic range at night using the plugin. Everything was underexposed, leaving no shadow detail and insufficient brightness from the lamps.

Method 2: AE Bracket Mode

So I switched to the Z1’s built-in AE Bracket mode, again taking a series of images at different exposures. This time, I merged these images myself in postproduction.

This method worked great for us, and the night / low light images worked great.

AE Bracket had other advantages compared to the plugin:

• More control over the exposures, including manual white balance, and “ISO priority” which meant I could keep the ISO fixed at a low number (less grainy) and allow the camera to take long exposures to make up for the low light.
• Allowed preview and control from the phone app, and review of the image when complete. (The HDRI plugin did not offer visual confirmation on the phone app.)

That last detail alone makes this approach worthwhile. On set, we could move on after each setup with confidence that we had captured what we needed.

Here’s how I set up the Z1 for bracketing at night:

1. Press power button on THETA for 1sec
   • Make sure THETA is broadcasting wifi signal
2. Open THETA app:
   • Shooting Mode
   • Access point mode (Join THETA wifi network)
3. Shooting settings:
   • Shooting method: AE Bracket
   • Step: 1.7 (indicates EV steps)
   • Num of shots: 9
   • Format: JPEG
   • ISO sensitivity upper limit: 6400 (max)
   • Camera settings (bottom of shooting screen)
     • ISO priority
     • ISO set to 100
     • WB Auto

The Z1 has a minimal interface, so you may have noticed that the workflow here requires pairing with an app on a compatible smartphone. I generally avoid apps, especially in a production environment,✦ but in this case I’ll admit it was great to have control of the camera remotely and to be able to preview and rotate a 360 image on a smartphone screen. I borrowed a spare iPhoneXs, which was compatible with the app at that time (December 2023).✦✦

Rig and Placement

The Z1 weighs so little, I used a cheap light stand to support it. This kept the whole rig very light, easy for one person to set up quickly. The light stand’s minimal footprint is ideal too, because whatever you use as a stand will be visible at the ‘bottom’ of the 360-degree image.

It’s important to plan ahead for where you’ll position the camera on set and what height / vertical position is best. The short answer is: place it roughly in the center of where you plan to add 3D objects, avoid having any large objects close by, and clear the cast/crew from the scene because you don’t want motionless people to show up in reflections.

Merging the HDRI in Post

As you can see in this image, nine exposures 1.7 EV steps apart produced a few useful images and a few that pretty much look identical. I could probably reduce the number of shots, but I prefer to risk overshooting rather than undershooting.

The built-in bracketing mode creates a series of images we now had to merge to create an HDRI. For this, I used Photoshop.

1. Open all the exposures in Photoshop
2. File > Automate > HDR Merge
3. Deselect/Remove any redundant exposures. Although I took 9 exposures, there were always two or three at the extremes which looked indistinct to me so I excluded them.
4. Click ‘Tone in ACR’ (Adobe Camera Raw)
5. You shouldn’t need to make any changes, so hit ‘Cancel’ ACR.
6. Adjust exposure and contrast if desired, but make sure the document stays in 32-bit mode to keep the dynamic range.
   • Exposure worked for adjusting exposure
   • Curves worked for adjusting contrast
7. Save the file as .EXR or .HDR (these retain 32-bit data)

Notice that you don’t need to use Photoshop’s 3D workflow for this process, since we’re still just looking at equirectangular images.

These images are pretty big compared to normal photos, because there is so much detail to preserve. It can be a burden on slower computers, so be prepared for that possibility. If you have a tripod/stand visible in the ‘bottom’ of your image, you might need to use Photoshop’s 3D workflow to view and edit that area accurately. That process can be really buggy even on reasonably fast computers.

Footnotes:

Alex Pearce has an intro video about the Z1 and HDRI’s here and a series of follow-up videos if you want an idea of what an entire workflow might look like.

✦ I prefer systems that have minimal dependencies and are built to last, which seems antithetical to the smartphone industry. I generally run the oldest phone my carrier will tolerate, so my iPhone 6 was not compatible with the THETA app. Since I’m an outlier here, other people’s “old” phones are usually an upgrade for me. Don’t let anyone convince you the latest smartphone is necessary for your film production journey. Put your money towards some nice gear instead.

✦✦ An “old” phone with no carrier service can be a useful tool on set, where it can be dedicated to a specific task. This means it will not be impacted by interruptions or battery drain from other uses. A dedicated phone can be disconnected from data networks and sometimes disconnected from wifi or bluetooth, which further reduces battery drain, reduces the likelihood of unexpected software updates, and eliminates the security risks associated with old devices.

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