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Author Topic: How many brackets are needed for HDR photos?  (Read 11340 times)
jnmoore
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« on: April 06, 2012, 11:55:27 PM »
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I've been shooting HDR regularly for a few years using a Canon 5D Mark11. The Canon only allows a 3 exposure auto image exposure bracket and I'm too lazy/rushed to do more manually.

I'm happy with most of my results using Photomatix but wonder if I'm missing something by not doing more exposures? I recognize that each scene is lit differently but is there an ideal exposure number that I'm missing?

I note that there is an external control (may be others ?) called Promote (http://www.promotesystems.com/products/Promote-Control.html) that will allow more exposures plus time lapse and other things. The down side is that you have to hook up two cables but this no big issue for me because the camera is on my tripod. Anyone used this device or similar?

Are my three exposures enough or am I missing out? Any advice appreciated.

John

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Steve Weldon
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« Reply #1 on: April 07, 2012, 01:03:20 AM »
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Here's the thing about HDR.

Probably, imo, most people shooting HDR are shooting it unnecessarily because they don't understand what they're really doing.  By that I mean, you shoot HDR only when the dynamic range of the scene exceeds the capability of the camera to capture.  What you don't do is shoot HDR just because you see a good scene and want to create a "wow" image.

With that said, it becomes obvious you only need to shoot enough images to cover the entire dynamic range of the scene, with caveats.  For the best quality you don't want to extend that dynamic range with more than one stop per image, and for economy of shootings sake more than one stop per image enters the 'point of marginal returns' realm. 

So, let's say you have a nine stop scene and your camera can only capture 7 stops, then you'll shoot that one 7 stop image, then go up one stop with another image, and up again (or down depending on where you choose to start) for another.   If you're trying to compensate for 2 stops, you shoot three images.  3 stops, 4 images.  4 stops, 5 images.

I'm assuming you know how to read your scene?
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Walter Schulz
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« Reply #2 on: April 07, 2012, 01:03:57 AM »
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Take a look at Magic Lantern software hack. It's known for video but contains some enhancements for still shooters, too.

Ciao, Walter
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Tony Jay
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« Reply #3 on: April 07, 2012, 05:18:50 AM »
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Meter the darkest and lightest parts of the scene.
Work out the dynamic range of the scene.
If you know the dynamic range of the camera then proceed as already explained.

Regards

Tony Jay
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BartvanderWolf
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« Reply #4 on: April 07, 2012, 08:57:05 AM »
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Here's the thing about HDR.

Probably, imo, most people shooting HDR are shooting it unnecessarily because they don't understand what they're really doing.  By that I mean, you shoot HDR only when the dynamic range of the scene exceeds the capability of the camera to capture.

Hi Steve,

Not necessarily so. By shooting longer exposures in addition to a regular exposure, one gains improved shot-noise performance in those longer exposed  brackets because more photons were collected. This will offer an opportunity to do heavier procssing on the darker tones with a lower risk of amplifying noise. A +2 EV exposed frame will have half the photon shot-noise in the non-clipped range.

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With that said, it becomes obvious you only need to shoot enough images to cover the entire dynamic range of the scene, with caveats.

It still won't hurt to add more exposures to improve the shadow noise. The practical limit would be dictated by things like exposure time, and reducing storage requirements.

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For the best quality you don't want to extend that dynamic range with more than one stop per image, and for economy of shootings sake more than one stop per image enters the 'point of marginal returns' realm.

While an exposure delta of one stop gives good results for HDR assembly, I regularly use 1.33 stops if I need to cover a larger range, this can be increased up to 2 stops when using certain exposure blending applications. 

Cheers,
Bart
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Guillermo Luijk
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« Reply #5 on: April 07, 2012, 09:17:54 AM »
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I'm happy with most of my results using Photomatix but wonder if I'm missing something by not doing more exposures? I recognize that each scene is lit differently but is there an ideal exposure number that I'm missing?

If you are wondering this you are surely not missing anything.

Do you often get clipped highlights and/or too much noise in your final images? if this is not the case, I can guarantee you that you are not missing anything for not bracketing wider.

Regards
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Steve Weldon
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« Reply #6 on: April 07, 2012, 11:28:48 AM »
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Hi Steve,

Not necessarily so. By shooting longer exposures in addition to a regular exposure, one gains improved shot-noise performance in those longer exposed  brackets because more photons were collected. This will offer an opportunity to do heavier procssing on the darker tones with a lower risk of amplifying noise. A +2 EV exposed frame will have half the photon shot-noise in the non-clipped range.

It still won't hurt to add more exposures to improve the shadow noise.
The practical limit would be dictated by things like exposure time, and reducing storage requirements.

While an exposure delta of one stop gives good results for HDR assembly, I regularly use 1.33 stops if I need to cover a larger range, this can be increased up to 2 stops when using certain exposure blending applications. 

Cheers,
Bart

1.  The operative word I used was "most" and I stand by this.  But you are right, there are other reasons to shoot HDR under perfect circumstances. 

2.  True, but I think the "practical" part is more than time and storage space.. You're just not "necessarily" going to gain significant image quality by adding more frames.  There's a point, which depends on the scene, where you just won't gain enough to care about.  I think a good rule of thumb would be 1 frame per stop.  There will be exceptions, but the OP shouldn't be left with the impression he needs to shoot more with every scene.

3.  Agreed.   All of what you said is true, and it comes down to reading the scene.  The OP should start with an acceptable rule of thumb (one frame per stop) and go up/down from there depending on the scene.
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Chris_Brown
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« Reply #7 on: April 08, 2012, 10:33:11 AM »
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Are my three exposures enough or am I missing out? Any advice appreciated.

I use Photomatix when fussing with HDR work and found that three exposures works best in almost every instance. I vary exposures range from 2/3 stop to 2 stops depending on the scene. I've tried using up to 7 exposures, and get different results than 3 exposures, but not necessarily better results.
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