# New plugin - adjust exposure based on curve/function



## paulgodard (Mar 8, 2010)

Hi everyone,I am doing some time-lapse and I would like to know from the plugin/LR gurus if there is a way to do the following.Select a series of images that are ordered chronologically and show a scene where the light varies from day to night. Apply some kind of a 'match total exposure' but not linear for all the images but based on a predefined curved (i.e. typical log curve) in order to automatically adjust the exposure of each image. This will produce a smooth transition from day to night, and remove flickering artifacts.Timothy mentioned that plug-in can not modify the develop settings. So is there a solution to my problem?


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## Victoria Bampton (Mar 8, 2010)

Paul, there's a guy I've seen on the U2U forum who's been writing some kind of plugin to change Develop settings using xmp sidecar files. Something along those lines might work. The guy's name is Rob Cole: http://www.robcole.com/Rob/ProductsAndServices/XmpEditLrPlugin/


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## paulgodard (Mar 9, 2010)

Thank you Victoria... I am already following the lead.


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## paulgodard (Mar 9, 2010)

This plugin sounds really interesting but I am not sure it will work yet... waiting for Rob to reply.
Meanwhile I have just done a quick test with LR where I have the same jpg image in 2 different LR catalogs. If I change the exposure of an image in LR (exposure + 2 in Develop), save the metatag to file in catalog 1. Then I open catalog 2 and read metatag from file. My image picks up the exposure correction done in catalog 1. This means that the exposure correction was saved inside the metatag (obviously, everyone knows that...).
If I look at the jpg metatag before and after, there is only the aperture metatag that has changed. Unfortunately EXIFTool can not overwrite that metatag.
So I need to confirm that aperture is really the metatag storing the exposure change, or understand what happen in the metatag after correcting the exposure in LR, and ultimately find a program (ideally PHP-OS-X-compatible) that can modify that metatag outside of LR.


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## paulgodard (Mar 10, 2010)

Rob helped me to figure out something new.
When the exposure slider is changed in LR/Develop (+2) and metatag save to file, the jpg file stores the value in crs:Exposure="+2.''", and a whole new set of metadata are created as saved settings with the old values.
However, if I modify the crs:Exposure="+2.''" to crs:Exposure="+4.''" metadata in a hex editor, save the file and read the metadata again in LR, then the exposure is not adjusted.
That is question I try to solve now...


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## Victoria Bampton (Mar 10, 2010)

Perhaps it's limited to the adjustments that the QD panel can make?


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## Brad Snyder (Mar 11, 2010)

Paul, I played around with raw/XMPs. I didn't realize at first you were talking about JPGs. With the raw/XMP pairs, I didn't have any trouble with the +4.'' Exposure adjustment. 

I realize that may not have any bearing on the JPG problem, but I have to run right now, out of time to play with JPG. One quick thought, make sure you're writing the crs:Exposure adjustment into the mainline XMP segment, and not into a &lt;crss&gt; Snapshot segment.


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## areohbee (Apr 10, 2010)

Hey Paul, long time no email.

In addition to making sure you tweak the "non-shapshot" setting, when editing jpegs, you _must_ make sure you don't change the length of the setting, or if you do, that you change the block length to match (the block length is the pair of bytes after the FF E1 that precedes the aforementioned setting(s).

Rob


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