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Author Topic: Photomatix HDR  (Read 3581 times)

sanfairyanne

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Photomatix HDR
« on: December 19, 2009, 02:49:40 pm »

I've done a few HDR images now hopefully I've just attached my latest effort. I'm just wondering is there a disadvantage of doing an HDR from a single image. With Photomatix Pro there is the facility to do just this.

You may wonder why I'm asking and well it's just because on occasion I can't carry enough back up space on location so taking a single image and HDRing it later would potentially save me lots of memory.  

Maybe taking a single image HDR restricts your EV spacing.


Any thoughts...



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walter.sk

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Photomatix HDR
« Reply #1 on: December 19, 2009, 04:54:33 pm »

Quote from: sanfairyanne
I've done a few HDR images now hopefully I've just attached my latest effort. I'm just wondering is there a disadvantage of doing an HDR from a single image. With Photomatix Pro there is the facility to do just this.

You may wonder why I'm asking and well it's just because on occasion I can't carry enough back up space on location so taking a single image and HDRing it later would potentially save me lots of memory.  

Maybe taking a single image HDR restricts your EV spacing.


Any thoughts...
The main differences between actual bracketed exposures and the one-image "HDR" are as follows, in no particular order:

For single-image:
1) If there are any truly blown highlights they will not be recovered.
2) Increasing the exposure will increase the noise in the shadows.
3) If the image did not cover the entire contrast range, the results will still lack the whole contrast range.
4) If the image did capture the whole contrast range of the scene, but, say, had pale skies and too-dark lower tones, such a pseudo HDR may improve the look of the image but it will not be as rich as a real HDR made from bracketed exposures of the same contrast range.

For a properly bracketed series of RAW's for HDR:
1) The entire contrast range of the scene will be captured.
2) any part of the scene will occur on 2 or more images, and the likelihood of the final tonemapped image reproducing the range of tonalities will be very good, depending on your skill and the HDR program.
3)  Most of the work can be done in the 32 bit HDR file before converting down to 16 bit color, giving smoother reults tone-wise.

I'm sure there are more differences.  As far as shooting single images only, for the reason of storage space, the price of CF or other flash cards has come way down.  In addition, if you have a laptop with you, there are 2.5 inch portable drives with huge capacity for not very much money (compared to a few years ago).

Don't forget that if you were shooting film and wanted to bracket the shots you would have been spending larger amounts on the film and processing.

The only advantage I can think of in doing single-image HDR's is the elimination of ghosting caused by either subject or camera motion.

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gardenvalley

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Photomatix HDR
« Reply #2 on: December 20, 2009, 06:39:32 am »

Quote from: sanfairyanne
I've done a few HDR images now hopefully I've just attached my latest effort. I'm just wondering is there a disadvantage of doing an HDR from a single image. With Photomatix Pro there is the facility to do just this.

You may wonder why I'm asking and well it's just because on occasion I can't carry enough back up space on location so taking a single image and HDRing it later would potentially save me lots of memory.  

Maybe taking a single image HDR restricts your EV spacing.


Any thoughts...


When I first started using HDR software I followed the "standard" advice of bracketing over and under the metered exposure. I then asked myself what I was trying to achieve by doing this and realised that I could get decent results simply by taking one shot exposed to the left and one shot exposed to the right thereby effectively doubling the DR of the sensor and I continue to use this method. Works for me and doesn`t take up that much space on the memory card. I have read of people taking a series of bracketed exposures from -2 to +2 at 1/3 intervals but I don`t see the point of this if the object of the exerc ise is simply to record all the shadows and all the highlights. The fewer shots to achieve this the better, I think. Perhaps though, as in everything photographic, more is better.
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walter.sk

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Photomatix HDR
« Reply #3 on: December 20, 2009, 10:56:14 am »

Quote from: gardenvalley
When I first started using HDR software I followed the "standard" advice of bracketing over and under the metered exposure. I then asked myself what I was trying to achieve by doing this and realised that I could get decent results simply by taking one shot exposed to the left and one shot exposed to the right thereby effectively doubling the DR of the sensor and I continue to use this method. Works for me and doesn`t take up that much space on the memory card. I have read of people taking a series of bracketed exposures from -2 to +2 at 1/3 intervals but I don`t see the point of this if the object of the exerc ise is simply to record all the shadows and all the highlights. The fewer shots to achieve this the better, I think. Perhaps though, as in everything photographic, more is better.
In a high contrast scene, 2 exposures may not capture enough of the range to prevent some ugly artifacts, such as black blotches in highlight areas, etc.  While I have not heard of people shooting a series from -2 to +2 at 1/3 stop intervals, I have found that in most moderate-to-high contrast scenes, shooting brackets 2 ev apart does not give as smooth and artifact-free results as a greater number of images.  I usually space them at either 1 or 1 1/3 ev apart, and 5 images works in most cases.
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Guillermo Luijk

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Photomatix HDR
« Reply #4 on: December 26, 2009, 06:47:10 pm »

Quote from: walter.sk
In a high contrast scene, 2 exposures may not capture enough of the range to prevent some ugly artifacts, such as black blotches in highlight areas, etc.  While I have not heard of people shooting a series from -2 to +2 at 1/3 stop intervals, I have found that in most moderate-to-high contrast scenes, shooting brackets 2 ev apart does not give as smooth and artifact-free results as a greater number of images.  I usually space them at either 1 or 1 1/3 ev apart, and 5 images works in most cases.

The optimum number of EV's apart for HDR is an interesting debate:

- If we look at the results produced by Photomatix and most HDR programs, the resulting image will vary a lot depending on how many and how much spaced in EV your shots are
- From a technical point of view, there is no reason to justify such big differences but this one: Photomatix and most HDR programs are not optimised to obtain the best from the input images

Bracketing {-2,0,+2} provides almost the same amount and quality of information as just taking the extreme shots {-2,+2} (in this case there should be just some extra noise in the middle tones). But the reality is that if you feed the {-2,+2} bracketing into Photomatix it's very likely that the result will be much worse than using the entire series {-2,0,+2}.

In general there should be no reason to shoot at smaller than 2EV or even 3EV intervals. In practice, since Photomatix is that bad at taking the best from the provided information, shooting at wider intervals than 2EV is a high risk with those software tools.

Just a sample: 2 shots, the most exposed of them 4+1/3EV apart from the least exposed:

Optimum blend (+anti ghost masking):


Photomatix blend:



Funily, if we perform first the optimal blend, next we make several replicas of it at 2EV (or less) intervals, then the result in Photomatix is fine.
Conclusion: Photomatix doesn't manage to optimally blend the source information unless it is provided at short exposure gaps.
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