What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: What I learned from Gollywop -- and what I wonder

richarddd wrote:

Anders W wrote:

richarddd wrote:

Anders W wrote:

secretworld wrote:

Thanks everyone, useful stuff!

You are welcome.

I already had a good grasp of ETTR and even use uniWB sometimes, thanks to DM. But for the situations that that is not adequate, could someone share their preferred ways of stacking and merging? And maybe explain some of the differences....not the implications, of equal and HDR exposure, I get that, just how do you stack and merge and with what settings if needed.

Not sure exactly what more you'd like to know apart from what I already said. But practically speaking, the software I use at present is LR/Enfuse which works quite well in my experience so far and has the advantage of a) being cheap (a "donation" of 2 GBP is required) and integrated with LR (LR plug-in). The only significant disadvantage I have noticed this far is that it takes a while for it to do the number-crunching (we are talking minutes rather than seconds) even on my new and pretty fast PC. But I don't know if other options are faster.

I would normally use the default merging parameters, which in the case of exposure bracketing weighs the contribution of the various shots to the rendering of a particular area in the frame based on how optimal the exposure of that area is. When merging shots at the same exposure, it doesn't matter what parameters you use since the shots are practically identical.

Apart from LR/Enfuse, applications that can do stacking/merging include recent versions of PS, PhotoAcute, and Photomatix. I am sure there are others as well but I don't know enough to tell you what the very best options might be.

One thing that might be worth mentioning here, apart from what has already been said, is that you can stack/merge for more than one reason. What we have been discussing here is stacking for the purpose of improving DR/SNR and minimizing noise. But you can also stack for the purpose of extending the sharp area of a photo (focus stacking). And you can of course combine these two if you want. In a recent exchange with kenw, we discussed the possibility of doing this for landscape photos where it is important to have the foreground as well as background tack sharp and where you would also like to maximize DR.

Photomatix will do "Exposure Fusion" which does a nice job of merging images for low noise. This is a different method then "Tone Mapping" which is the usual HDR mode.

The "exposure fusion" mode of Photomatix is similar to what LR/Enfuse does. The resulting image is already tonemapped. Another approach ("the HDR mode") is to first merge the images into a special 32-bit HDR file that isn't tonemapped and then let a RAW converter (e.g., LR) do the tone mapping. Photomatix can create such a file too, but LR/Enfuse can't.

Exposure Fusion is defined as "Combination of photos of the same scene taken under different exposure settings in such a way that highlight details are taken from the underexposed photos and shadow details from the overexposed ones." This seems a good way to combine bracketed images to produce a low noise result, as you described.

The manual includes "Strictly speaking, an HDR image is an intermediary image with 32 bits per color channel (96 bits per pixel). An HDR image is the result of merging photos of the same scene taken under different exposure settings and stored in special HDR image format. The 32-bit intermediary HDR image must be processed with tone mapping for proper display on standard monitors and prints. It has become very common to define "HDR image" as the result of processing the 32-bit HDR image with tone mapping, i.e. the tone mapped output, but this is not technically correct."

The program gives you the option of viewing and saving the intermediary 32-bit HDR image before giving the choice of the two processes, HDR Tone Mapping and Exposure Fusion.

FWIW, the manual also defines exposure as "The amount of light that enters a camera for the length of time the shutter is open. Exposure depends on aperture and shutter speed, as well as the camera’s sensitivity to light (controlled by the ISO). "Exposure" is also shorthand for a photograph or frame (a frame of film)."

Thanks Richard! I guess some people might want to take issue with their definition of "HDR image" (who is really to decide what the proper definition is in this case) and most certainly with their definition of "exposure".

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