Hydra HDRI Pro - Make a 32-bit HDRI From an 8-bit Image

Hydra Design Labs' Hydra HDRI Pro plugin claims to convert an ordinary 8-bit image such as a JPG into a usable 32-bit per pixel image, suitable for High Dynamic Range Image based rendering. Snap a panoramic with your phone and use it as as an HDRI light source in your renders. In their own words:

"Hydra HDRI Pro is a photoshop plugin that will convert an 8-bit image into a 32-bit HDRI. Create your own spherical HDRI's for use in 3D rendering programs. Take your 8-bit spherical image, edit it in Photoshop, and then with a click of a button convert it into an HDRI."

I was skeptical. I had to have a closer look! Hydra Design Labs sent me a copy of Hydra HDRI Pro Photoshop plugin to evaluate. Hydra HDRI Pro retails for around $150. This review is my thoughts after testing it on Windows 7 using Photoshop CS6 and using Autodesk Maya's Mentalray for the rendering aspects, but you could use any modern renderer.

This image was rendered with an HDRI light source created from an 8-bit per pixel image. Image courtesy Hydra Design Labs.

A little background: (Advanced readers can skip ahead.) A High Dynamic Range Image (HDRI) contains wider range of exposures than ordinary JPGs. A JPG can hold 0-255 possible luminance values, i.e. 256 in total. (That's 2^8, because a JPG is 8-bits per color component.) If we adjust the luminance of a JPG image, we simply can't recover areas of black shadow or blown-out highlights, the data simply isn't there.

If we took an exposure using "RAW" mode we would get roughly 14-bits per channel of luminance data per pixel. We then have to convert these "RAW"s to TIFFs or openEXR or some other format our renderer can read. Even so, that's only 16,384 luminance values. We can do so much better.

If we instead took a series of 14-bits per channel images and spaced the exposure times out to cover a wider range, we could have a potentially unlimited dynamic range. Typically we use a 32-bit per pixel image format such as TIFF, HDR, or openEXR. This gives us potentially 4,294,967,296 luminance values.

Who Cares?

Contrast cares! By the time light emitted from an HDRI bounces around the scene, gets reflected and refracted a few times, there's potential for a very wide range of luminance values. If we use only an 8-bit per pixel image as a light source we often end up with poor contrast.

Shouldn't we just use a proper HDRI in the fist place?

If possible, yes. However not everyone owns a DSLR camera and the software to make a 'true' HDRI. The idea behind Hydra HDRI Pro is you can use a ordinary camera like your phone to capture 8-bit images and then convert them to 32-bit per channel HDRIs that are "good enough" for rendering. It's a convenience vs. quality tradeoff.

An added benefit is you can use ordinary image editing tools on the 8-bit version and only convert it to a 32 bit HDRI after all edits are done. Even Photoshop as of CS6 is limited in its ability to manipulate 32-bit images. Therefore this technique opens the possibility to use all available tools.

Image courtesy Hydra Design Labs.

How is this different from Image -> Mode -> 32-Bits?

The output file is re-normalized to a 32-bit space, not simply converted! You could accomplish the same feat by duplicating the image several times, adjusting the luminance values of each layer to approximate a traditional HDRI and re-stack them. In fact, that's what the plugin appears to do, it's just it does it much faster than doing so by hand. There's probably some other magic in there too.

Does it actually work?

Yes, to the extent possible it works rather well! Understand that no computation can ever recover luminance information that wasn't there in the first place. Hydra HDRI Pro makes no claim to do so. What it does accomplish however, is better contrast in the resulting renders than using the virgin 8-bit versions images as light sources. If all you have in your arsenal, or on your person, is a smart phone you're usually stuck with 8-bit per pixel images. These situations are where Hydra HDRI Pro can help you turn those 8-bit images into suitable 32-bit HDRIs.

Image courtesy Hydra Design Labs.

Hydra HDRI Pro is cake to use. There's no settings and only a single button. Once installed, you simply open an ordinary 8-bit JPG, such as a panoramic you captured (The plugin itself does not stitch panoramics. That's another subject entirely.). You then select File -> Scripts -> Hydra HDRI Pro, click Convert and let the script work.

Image courtesy Hydra Design Labs.

A few moments later it spits out a 32-bit version of the same image, saved as Untitled_HDR2.hdr, in the same directory as the original image. We then apply this new 32-bit image as a light source in a renderer that supports HDRI based lighting.

Image courtesy Hydra Design Labs.

Show Me The Goods

Below is a comparison render. The image on the left uses an ordinary JPG as an HDR light source, both rendered with Autodesk Mentalray. Notice how the contrast is lower and the highlights a bit blown out on the left car.

Left is ordinary JPG used as a light source. Right is same JPG converted into an HDRI used as a light source.

The image on the right used the same exact JPG source image, but it was first converted into an HDRI file by Hydra HDRI Pro. Note the improvement in contrast, especially around the headlights. This is a subtle example but the difference is still readily apparent. The effect becomes even more dramatic when you start to boost the Color Gain to brighten or darken the image used as the light source.

Bottom Line

It's a quality vs. convenience tradeoff. Due to the ubiquity of cameras that capture at 8-bits per pixel, such as most phone cameras, Hydra HDRI Pro opens up the possibility of taking an impromptu panoramic and then using it as an HDRI light source. There's also the ubiquity of tools to manipulate 8-bit per pixel images. You can use any tool you want to tweak your images prior to HDRI conversion.

Hydra HDRI Pro also means that mere mortals can create their own HDRI library using inexpensive tools. These are the main selling points and rightfully so. Hydra HDRI Pro does indeed do what it claims. The rendered results in most cases are acceptable for production use such as product shots, etc.

Cons: Hydra HDRI Pro can never match the quality of an image taken at higher bit depth in the first place. If you have all the expensive cameras and other tools to make "proper" HDR images, Hydra HDRI Pro can't beat them for quality. With Hydra HDRI Pro you also don't have as much flexibility of tweaking the luminance of the HDR image in your render engine. You can do it, but you don't retain the full spectrum of color that you would have with a higher bit depth source image because the data simply wasn't in the 8-bit image to begin with.

The plugin itself has some minor thorns. The most notable is that you can't name the output image. It always gets named Untitled_HDR2.hdr, even if you have an image in the source folder that is already using that name - It will be silently overwritten. I would also love to see a stand-alone command line version of the program that can conveniently operate on batches of files in the background.

Again, quality vs. convenience. Hydra HDRI Pro is indeed convenient. Are the resulting HDR images high quality enough for your needs? Only you can decide that (I'd say 90% of the time, yes.). Unfortunately, there isn't a demo of Hydra HDRI Pro at this time, but I bothered Jon Hull, President of Hydra Design Labs enough that we just might see one in the near future!

System Requirements

Hydra HDRI Pro is compatible with the following versions of Adobe Photoshop:

-Windows: 32 & 64 bit CS4, CS5, CS6, CC

-Mac: 32 & 64 bit CS5, CS6, CC

Check out Hydra HDRI Pro here.

Kurt Foster (Modulok) falls somewhere between programmer and visual effects artist. When not sifting through technical manuals, he takes on freelance roles in both programming and visual effects, attempting to create a marriage of technical knowledge with artistic talent. He can be seen helping out on the Renderosity Maya forum, when time permits.