New paper: Enhancing LDR video with HDR stills

Ok, we had a few exciting posts about HDR video here. Current approaches are either complicated, time-consuming, or just plain expensive.

In the meantime Francesco Banterle, researcher at the official Visual Computing Lab of Italy and most known for his free Picturenaut plugins, has figured out a technique that is easy, fast and cheap. And it seems like he had quite some fun in the process:

Read the research paper and see more examples on the project page.

In quick summary, he's extracting an alpha mask for the over-exposed areas, and then layers the video on top of an HDR image. A simple and efficient approach. In the VFX world this is know as "Sky Replacement" and has been practiced forever. Especially given the premise that the camera is perfectly locked on a tripod, a shot like this would typically be a job for the intern. If you want to try it for yourself in After Effects, I recommend checking out this tutorial from

Still, Francesco's paper is a really good read: definitely an inspiration for your own experiments, and with a good summary of existing HDR video technologies. And the actual prospect is that this could be done via fully automatic processing in webcams. Which would classify as awesome.

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Philip Bloom's HDR timelapse: 24 hours of Neon

British cinematographer Philip Bloom has already made himself a name in the DSLR filmmaker scene. When confronted with the absurd orchestra of light and color that is called Las Vegas, he picked HDR timelapse as the weapon of choice. Check it out:

24 Hours of Neon from Philip Bloom on Vimeo.

There is an abundance of making-of material and commentary on Philip Bloom's blog.

In short, he used Photomatix's batch processing and manhandled flickering problems by simply omitting the worst shots. Flickering is indeed a common problem when abusing Photomatix as image sequencer, because Photomatix does not have a concept of temporal consistency. There are better ways to tone video in After Effects, working directly on the 32-bit HDR footage with the Atlas plugin and manual exposure adjustments based on roto masks. But then again, this is more labor-intensive than just running it through Photomatix...

Now that the RED Epic camera has an HDRx mode, you can expect options for toning HDR footage to open up soon. Which actually brings me to an announcement:

RED Los Angeles User Group meeting

If you're in the LA area, come to the RED User Group meeting on June 11, 9:00 am-noon!

You'll get to see the high-end Nucoda color grading system with full OpenEXR capabilities, the amazing Dolby reference monitor, and I will teach a class on the fundamentals of HDR imaging. The event is free, your only investment is a Saturday morning.

Full program and sign-up here.

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Easter Egg #2: Group control points in Nik HDR Efex

Yes, it is a mini-series of undocumented features.
In part 2 we will have a closer look at Nik Software's HDR Efex Pro.

Especially for grungy/artistic styles HDR Efex is fantastic, because of one killer feature: U-Point. It allows you to set control points for targeted adjustments in specific areas. Each point acts as a soft circular selection of similar colors. To see exactly what part of the image is being affected, turn on the mask view in the control point list.

The mask view is a pretty helpful insight into in the way Nik’s U-Point system works, indispensable for double-checking the effectiveness of a control point. We can change the size of the circular area, but unfortunately we can neither change the range of selected colors, nor the shape of the soft selection.

In practice, however, you will often want a larger, non-circular area affected. The trick is to
  • hold the ALT key,
  • click on a control point,
  • and drag to tear off a copy.
  • Clone a control point multiple times and
  • select them all with the SHIFT key held down.
Now they will all be in sync. You can change a slider on either one of the control points, and the setting will apply to the entire group.

But this is all public knowledge.
The easter egg is an undocumented feature, that will permanently link control points together:
After shift-selecting them, press Command + G (or Ctrl + G on PC) to form a group. Now only the first point will have the controller fishbone, the rest of the group is represented by tiny dots. Power users might find this mode helpful to nail down the selection to a complex shape or manage large amounts of control points.

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Personally, I don’t really like it as much as the plain old Shift-selection, because these secondary dots are so easily overlooked. It's also pretty hard to remember the antidote:
To explode the group again, press Command + Shift + G (or Ctrl + Shift + G on PC).

Happy Easter!
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Easter Egg #1: Unlock all file formats in HDR Express

HDR Express is a refreshingly simple tonemapper, powered by the same high-quality engine like its big brothers HDR Expose and 32Float.

But it also shares their lame HDR merger, inferior to Photoshop CS5, Photomatix, and a dozen other alternatives out there. If you want better alignment, clean ghost reduction, or batch processing you're better off baking EXR files elsewhere. But wait - you can't load these EXR files in HDR Express, or can you?

Yes, you can! It's all in there: OpenEXR, Radiance HDR, 32-bit TIFF. You just have to unlock it.

The super-secret unlock code goes like this:

  • Start HDR Express while holding the Command key (CTRL on Windows).
  • Keep it held until the start screen comes up, then press the F key in addition.
  • HDR Express will now kindly offer to enable extended file formats, hit OK and voila!

From now on HDR Express will load and save all common HDR file formats. Nifty trick, eh? You'll only have to do it once, and it also works with the the 30-day demo.

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By the way, this will also enable saving in standard HDR formats. Which is the reason why it's locked away in the first place: it may confuse HDR beginners (the main target audience of this program). However, if you know what you're doing, this is a great way to boost details in an HDR image, change white balance or saturation - without actually converting it down to 16 bits. For using it in this manner, I do recommend starting out with all settings on zero, though. Here's a handy preset for that.

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Artifact-free Ghost Removal algorithms? Yes, please!

It's been a while since I pointed out some interesting white papers. Time to catch up.

Let's start out with the centerpiece of last blog post: Ghost Removal. How does that work under the hood, and why is Photoshop CS5 so much better at it?

As general rule of thumb: However tempting, you should not get into the habit to leave Ghost Removal checked “just in case”. That’s because this option will tell a software to use as little information from as few source images as possible. It will operate under the assumption that blending pixel values from different exposures is a bad thing. Instead it will try to establish a single exposure as the dominant source of information, and use the rest of the exposures as supplemental sources only. The result is more noise and less color fidelity, most noticeable in the extreme ends of the dynamic range. For that reason, ghost removal should only be used when an exorcism is really necessary.

But when we really have a ghost at hand, then the things that set good ghost removal apart from lousy ghost removal, are these:
  • How well can it detect a moving object?
  • How successful is it in masking the moving part out of all the other images?
  • How much information can it still use from the non-ghosted, clean areas?
Photoshop CS5 excels in these key areas, and that's why it delivers so well. If you care about the exact formulas used in Photoshop's algorithm, have a peek at the HDR tech bible / 2nd revision. But it's definitely inspired by this very readable paper:

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Artifact-free High Dynamic Range Imaging

by Orazio Gallo and some folks from Nokia Research.

All examples in this post are taken from this paper. What they do is to cleverly isolate the treatment only to the ghosted areas, otherwise they just proceed with averaging as many good pixels as possible.

The funky colormap on the right shows how many source images actually contribute to the final HDR image, for each area. As you see, the algorithm gathers plenty of detail on the ground, but uses one image less for the spot where people walk through.

The result comes out pretty clean.

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Gallo's paper explains how they do it. Read it!
Read it twice and very thoroughly if you're an HDR software developer, please!

PS: Hui, another one of those long blog posts. Tipped by David in the Forum. Thanks!
Guess it would be easier if I'd just post a pretty image every now and then, like everybody else does. But I promised you hard facts in the title of this blog, and so I'll just stay on course...

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Aprils Updates: Nik HDR Efex, Oloneo & Gigapan

Another month, another flood of updates in the ever-spinning world of HDR imaging.

Nik HDR Efex Pro 1.2

HDR Efex is finally supposed to be rock stable on 32-bit operating systems. I can neither confirm nor deny, never actually witnessed any crashes, but that's because I'm in the warm embracement of 64-bit WinXP / Mac OS for a while. As a bonus, Nik also threw a new ghostbuster in the mix. Heard nice things about it, but I can hardly see a difference myself.

Here is a little deghosting test with a tough example:

Bottom line: Can't beat Photoshop CS5's Automatic Ghost Removal! But that's no wonder, since Adobe had this feature done by El Maestro Greg Ward himself. HDR Efex seems pretty much on par with Photomatix's automatic mode, but that's actually their lame option. Photomatix's user-guided Selective Deghosting is the good one, it comes in second-best overall. Although in this case it requires a lot of extra work, and still ends up clipping the blacks on the palm leaves. Or the whitecaps on the waves, that's your selective choice, basically.

Oloneo PhotoEngine 1.04

PhotoEngine goes into the next beta round, merrily inviting everybody. This is one of the most raved about new-school tonemappers, providing excellent speed, a fistful of great color tools, and an innovative ReLight mode. The new beta includes:

  • Look Presets, ranging from "Natural Soft" all the way to "I love Halos!"
  • Natural Mode, that doesn't seem to do anything (but sure sounds good)
  • Batch Processing, that allows in-between image reviews (awesome)
  • Panorama-safe mode, which I still have to test. (please please work!)
  • and several bug fixes.
Still, no Mac version in sight, and no word on the final pricing yet. For now, it's free and fully functional until June 1st. Grab it!

Gigapan Firmware Updater:

Our good friend Googlebot has snooped out the secret download page of the new Gigapan EPIC firmware. As mentioned last month, this update adds the highly anticipated HDR bracketing option. For some strange reason it's not linked anywhere on the Gigapan homepage, but when you google for "Gigapan Firmware Upgrade" it will happily take you there.

PS: Atlas, the freeware tone-mapping plugin for After Effects, now works on 64-bit Windows. Hurray for Open Source!

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