HDR on moving subjects

[sjl]

Or, more specifically, fire.

Those in Melbourne should be familiar with the area in question; those that aren't may need a bit of a description. Basically, we have a casino in the city. This casino likes to throw its money around in gaudy displays of various kinds; the one I'm thinking of in particular is a series of some eight or nine towers just outside the casino on the south bank of the Yarra River. At the top of these towers one can find gas burners.

Every hour, on the hour, when the sun is down, these towers belch flames. Small ones, big ones, in unison and in sequence. Naturally, when photographing them, they blow out the camera's range, in a very big way. No surprise there.

The only way I can think of getting a decent photo of the flames without having the surroundings almost black is through HDR (see the side note below). Trouble is, flame is, by its nature, a moving object; I'm not going to get an exact duplicate shot at a greater exposure. The best solution I have is to shoot the fire at two (or maybe even three) stops below what the camera thinks is right, and follow it up with shots of the building at slower shutter speeds and/or larger apertures.

As somebody pointed out, though, that would, in its turn, lose some of the natural look, as the follow-up shots wouldn't have the reflections from the flames coming from the buildings and/or the water (depending on where, exactly, I place the camera.)

Anybody have any better suggestions? I suppose I'm going to be better off to just suck it and see; after all, it's digital, I'm out nothing except time by trying.

On a side note: I've looked into software for doing HDR. There seem to be many offerings: Photoshop, Photomatix, Photogenics, and CinePaint are the obvious ones. CinePaint is free, but I don't know what its quality is like. I'm not comfortable buying Photoshop since Adobe introduced product activation, either ... Suggestions on what's good, and what's not so good?

Thanks,

S.

 

[TheAnswer]

Well...

I would suggest some putting together some type of assembly with three cameras all focused (roughly) on subject and then some kind of way to trigger them all to fire at once. Then set them up with the -2(0)+2 HDR range. Crop them in photoshop to all show the same exact subject (by pixelmatching), then do the HDR voodoo on them.

Since this isn't the type of thing you are likely to shoot all the time, probably renting a couple of extra bodies and lens is the way to go. A couple of friends to help you lug all the equipment to your shooting point and I would think the infrared remote on most systems can be used to have them all fire at once (but that might not be as precise as a wired connection since it's counting on all the sensors to see the signal at once).

Now hopefully someone a little brighter than myself is going to come in here and tell you a cheaper way to do it. Be sure to make a thread once you have some pics...the idea sounds really cool.

Good luck!

 

[sjl]

I would suggest some putting together some type of assembly with three cameras all focused (roughly) on subject and then some kind of way to trigger them all to fire at once. Then set them up with the -2(0)+2 HDR range. Crop them in photoshop to all show the same exact subject (by pixelmatching), then do the HDR voodoo on them.

Very nice thought. It'd work for one of two shots I have in mind - from a bridge near the casino - but not for the other, where I'm trying to get in up close and personal with the flame tower using a wide angle lens. The latter would mean the difference in angle would render the shots useless for this purpose. Look at the image below, for instance. Now imagine the flame belching out of the top of that tower in the foreground. There's no way I could get three cameras setup for that shot simultaneously; even a slight change in position would make it close enough to impossible to get a good lineup on the pixels. (This shot was taken at 17mm on the 20D, so around 27-28mm on a 35mm camera equivalent.)



Against that, of course, is the point that there'd not be a great deal of reflection in this instance, since most of the light from the flames would bounce off away from the camera, so merging two different exposures could well work.

 

[epicwelshman]

Shoot in RAW. Make 3 or so exposures from the single RAW file. Merge them as HDR. Ta da.

 

[beavo451]

Shoot in RAW. Make 3 or so exposures from the single RAW file. Merge them as HDR. Ta da.

This doesn't really work. If you did the above, it is essentially the same as opening the image with a linear curve. The only thing you might gain is that the shadow and highlight detail may be slightly clearer. You will not gain any dynamic range and would look very flat and lifeless.

 

[spicyapple]

RAW is sort of like HDR-lite, since all the luminance values are contained in the file; although you can't view it on an 8-bit monitor. Then there's really no way to capture HDR with one exposure, unless some new imaging technology like an array of overlapping transparent CMOS sensors can capture the information in one exposure.

 

[sjl]

This doesn't really work. If you did the above, it is essentially the same as opening the image with a linear curve. The only thing you might gain is that the shadow and highlight detail may be slightly clearer. You will not gain any dynamic range and would look very flat and lifeless.

Yup. I just downloaded Lightroom for a quick play with the tone curve (which is, ultimately, what such a merge would do). No matter what I did, I couldn't get a shot that I was happy with - the flame was excessively saturated, or the background detail was too low, or the whole thing looked too artificial, or ...

We're talking about an incredibly bright object set against a very dark background. To give you an idea, the shot I posted earlier in this thread was taken at f/4, with a 1.6 second exposure time. In comparison, a photo of a relatively small flame was at f/4, with a 1/10 second exposure time.

Sixteen times the speed. That's four stops, and even then, the flame was overexposed. I'd say (at a first guess, without having gone out to play more) that I want about five, six, maybe even seven stops of dynamic range, over and above that that JPEG can provide, followed by careful flattening of the image. There is no way that I'm going to get that out of a single raw image.

 

[sjl]

Further to the subject ...



That shows the sort of thing I'm trying to achieve; I'd like to have the flame a little less saturated, and the tower a little more pronounced. As I said: there's four stops difference between the two shots I've posted in this thread, and I'm still not really happy with the flame; I'd like it to have more detail, less "clipping".

Maybe I'm dreaming. I know what I want to achieve; I'm just not sure on how best to achieve it ...

 

[maxi]

Maybe it´s too obvious, but if the flames go up every hour or so, why don´t you set up a tripod and take a long exposure while the flames aren´t there and then do another shot, exposing the flames together. You can even do a 3rd one, exposing for the reflections of the flame.

Then, I´d personally use photoshop to have more control in the merging of the images.

 

[epicwelshman]

This doesn't really work. If you did the above, it is essentially the same as opening the image with a linear curve. The only thing you might gain is that the shadow and highlight detail may be slightly clearer. You will not gain any dynamic range and would look very flat and lifeless.

Hmm, fair enough

 

[Sdashiki]

Quick little side question...

Am I to understand HDR is, on the lowest terms, taking multiple exposures from very under to very over exposed, and then using photoshop to create a single image where everything is properly exposed, as one would see in reality but certainly not in a typical photo?

 

[ATD]

Quick little side question...

Am I to understand HDR is, on the lowest terms, taking multiple exposures from very under to very over exposed, and then using photoshop to create a single image where everything is properly exposed, as one would see in reality but certainly not in a typical photo?

Yes to a point. I would rewrite your sentence to "HDR is, on the lowest terms, taking multiple exposures from very under to very over exposed, and then using photoshop to create a single image." The difference is this new image has a far greater bit depth. This will allow you to adjust the shot so you can retain detail in the brightest highlights and the deepest shadows where as in a single exposure that might be a trade off. That trade off is losing one in favor of the other, highlights or shadows. Some people will adjust the shot to get a normal looking exposure, others push it to look surreal, not something you would see in reality.