# HDR in LR 6 without base exposure?



## pknight (May 28, 2015)

Victoria Bampton mentioned on her website that the base exposure is not needed to merge to HDR in LR 6/cc.  The notion is that, in a 3-exposure bracket situation, you only need the over- and under-exposed shots to create the entire HDR dynamic range.  I played around with this, and found that it generally works, and concluded that I will never do things this way.

First off, it does seem to work in terms of dynamic range.  Just as with three bracketed shots (-2/0/+2), when you only use two (-2/+2) exposures the resulting LR 6 HDR looks just like the original base exposure (0) before making adjustments. The HDR image based on two exposures is roughly the same size as one created with all three exposures (in fact, slightly larger in my case), and the Develop module adjustments have the same effects on both images.

The problem is that if you are in a situation where you need to use higher ISO settings, the two-exposure HDR is likely to be noisier in the midtones.  I was bracketing 3 shots at Eastern State Penitentiary in Philadelphia.  Some of the cellblocks are completely abandoned, with only skylights for illumination.  This results in very high contrast between the skylights themselves and the shadows almost everywhere else.  With no tripod, I was hand-holding these brackets, and to keep the shutter fast enough I had to use ISOs up to 3200.  My three-exposure HDRs look good, but there is substantially more noise in the two-exposure images.  This makes sense, as LR is having to boost the underexposed image to retrieve this part of the dynamic range, and that leads to noise.

Since my camera (and all cameras, I believe) always shoots a base exposure when bracketing, I see no advantage to creating HDRs without using that exposure, and in some situations there is a penalty for doing so.


----------



## clee01l (May 28, 2015)

To me it would be an extra step to omit the base exposure in LR HDR.  My camera has a bracket mode. Three is the minimum. I have found that 5 & 7 brackets shots do a nice job when there is considerable spread in stops between the darkest shadows and the brightest highlights.


----------



## pknight (May 29, 2015)

clee01l said:


> To me it would be an extra step to omit the base exposure in LR HDR.  My camera has a bracket mode. Three is the minimum. I have found that 5 & 7 brackets shots do a nice job when there is considerable spread in stops between the darkest shadows and the brightest highlights.



I agree that more brackets would be better in this case, but I had to handhold, and even at ISO 3200+, the additional overexposed shots would have been way too long.


----------



## RikkFlohr (May 29, 2015)

According to the engineering team - if your two exposures are three or less stops apart, (ie 0, -1.5, +1.5), a third exposure is not needed. In this case, merging the -1.5 and the +1.5 and ignoring the 0 should give you as good or better results than using all three exposures.  In the example cited in the OP, the -2/0/+2, the spread is 4 stops and requires a third exposure. See the guide below.

Under to Over Optimum number of exposures:

Up to:
-1.5 to 1.5 = 2 exposure
-3.0 to 3.0 = 3 exposure
-4.5 to 4.5 = 4 exposure
-6.0 to 6.0 = 5 exposure


----------



## Jim Wilde (May 29, 2015)

Rikk, you should add that post into the Tip, Tricks & Starter Kit forum.


----------



## RikkFlohr (May 29, 2015)

I expect a white paper document from Adobe shortly that will address HDR in depth-including this concept. We should probably wait for that.


----------



## Jim Wilde (May 29, 2015)

Sounds good!


----------



## Hoggy (Jun 1, 2015)

RikkFlohr said:


> According to the engineering team - if your two exposures are three or less stops apart, (ie 0, -1.5, +1.5), a third exposure is not needed. In this case, merging the -1.5 and the +1.5 and ignoring the 0 should give you as good or better results than using all three exposures.  In the example cited in the OP, the -2/0/+2, the spread is 4 stops and requires a third exposure. See the guide below.
> 
> Under to Over Optimum number of exposures:
> 
> ...



VERY good info to know!

I remember, I think from another site, where someone mentioned a post from the developers explaining exactly why fewer exposures are better from a very technical standpoint.  Does anybody here know where to find such a post? I've been unsuccessful with any Google attempts so far.  The guy that mentioned it just said 'that it was too technical' and didn't link to it, unfortunately.  However, it would help me understand exactly what is going on.


----------



## Hoggy (Mar 7, 2017)

RikkFlohr said:


> I expect a white paper document from Adobe shortly that will address HDR in depth-including this concept. We should probably wait for that.



Sorry for bringing up an old topic, but does Rikk or anyone know if this white paper ever materialized?


----------



## RikkFlohr (Mar 7, 2017)

I have never seen the paper issued that was discussed previously. 

Here are my current notes on the subject of HDR and Panos.


HDR Exposures

According to the engineering team - if your two exposures are three or less stops apart, (ie 0, -1.5, +1.5), a third exposure is not needed. In this case, merging the -1.5 and the +1.5 and ignoring the 0 should give you as good or better results than using all three exposures. In the example cited in the OP, the -2/0/+2, the spread is 4 stops and requires a third exposure. See the guide below.
Under to Over optimum number of exposures:
Up to:
-1.5 to 1.5 = 2 exposure
-3.0 to 3.0 = 3 exposure
-4.5 to 4.5 = 4 exposure
-6.0 to 6.0 = 5 exposure

HDR/Pano Settings 

Please note that the settings that are copied over will differ between the HDR and Panorama cases. 

For a Panorama, the merge tool is changing geometric attributes, and will therefore not copy over existing geometric settings such as Lens Corrections/Upright (with the exception of Defringe settings). 

For HDR, the merge tool is expanding tonal range, so existing primary tone settings (such as Exposure, Contrast, Highlights, Shadows, Whites, and Blacks) are not copied over. 

Settings cleared for both the HDR & Pano cases: 
- Local Corrections 
- Red Eye 
- Upright 
- Crop 

Settings that are copied over (with some exceptions): 
- Basic Panel (except primary tone adjustments for HDR) 
- Tone Curves (HDR no, Pano yes) 
- HSL/Color/B&W 
- Split Toning 
- Detail Panel 
- Lens Correction (HDR yes, Pano only Defringe) 
- Effects Panel 
- Camera Calibration (except Process Version, which must always be current for HDR) 
- Spot Healing (retained for Panos only)


----------



## LouieSherwin (Mar 8, 2017)

Thanks Rik, 

This is useful information to know. It really should be included in the online help if you could. I'm sure Victoria will be adding it into her book as well.

-louie


----------



## Victoria Bampton (Mar 8, 2017)

The HDR info's on page 294, although I might add Rikk's specific examples in a future update.

The panorama info's on page 291, although again, I hadn't listed it out in quite such detail (just says "If you do choose to edit the photos before merging, Lightroom automatically copies some of the Develop settings from the active photo onto the merged photo. It skips things like the crop, lens corrections and local adjustments as they may not end up in the right place on the merged photo.")


----------



## LouieSherwin (Mar 8, 2017)

As usual you are way ahead of us.


----------

