Time-lapse Deflicker - Creative Uses of CHDK - CHDK Forum
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Time-lapse Deflicker

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Offline c_joerg

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Time-lapse Deflicker
« on: 15 / March / 2016, 11:23:07 »
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 From my side, I found a really efficient way, to deflicker timelapse which I want to share here. Just now it works only for Adobe Lightroom.

Even rawopint gets in some situation, in oscillation. Especially on overexposed scene or if you have ocean waves. This is not much but oscillation from around 1/32EV can be seen.

The log file from rawopint delivers already useful information. The meter96 divided by 96 gives you the different in EV steps from a neutral picture (Is this correct?). The first picture shows you the values from my example video. Yes of course, the example is the worst case.

If you develop you RAW with Lightroom, you can write all information (meta data) in a XMP file. This file includes the following value:

crs:Exposure2012="0.00"

I modified this values by adding the (-meter96/96) values from the rawopint log file. If meter96 is around 0, I use them directly. When not, I have to remove an offset (by calculation background normalization).

My working sequence:
- Developing the RAW File in Lightroom
- Saving the meta data (XMP File)
- Using a smart ‘search and replace’ to change the Exposure2012 values in the XMP File
- Reading the XMP Files in Lightroom
- Developing the RAW Files in Lightroom to JPG.

The second picture shows you the difference from JPG’s with (red curve) and without (blue curve) correction. As you can see on the video, it works very well. As you can see on the video, it works very well:



I have not tested it with JPG pictures, because they have no additional XMP file. The meta data is in the JPG itself. This is a little bit more complicated.

This method can be also used for other thinks like smooth exposure changes when the scene goes to bright…


Questions on everybody here:
I do the ‘search and replace’ in MATLAB. This is a little bit complicated but it works. Does somebody knows a smart ‘search and replace’ which can do this? Yes of course I could write a C Application…
Does somebody Knows other RAW converters which write there develop information in a text readable file?
I could not read the files from Canon DPP…

« Last Edit: 15 / March / 2016, 11:34:18 by c_joerg »
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Offline reyalp

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Re: Time-lapse Deflicker
« Reply #1 on: 15 / March / 2016, 17:44:57 »
This is a very good idea, and the results speak for themselves :)
Quote from: c_joerg on 15 / March / 2016, 11:23:07
The meter96 divided by 96 gives you the different in EV steps from a neutral picture (Is this correct?).
Approximately at least, the definitions aren't very rigorous.

Quote
Does somebody Knows other RAW converters which write there develop information in a text readable file?
Raw therapee pp3 "sidecar" files are in something like windows .ini format.


This reminds me of an idea I had for rawopint a long time ago:
Instead of using Bv / Ev shift to follow changes in scene brightness, just expose the maximum amount possible within the over-exposure limits. Since the actual Bv and exposure parameters are in the log, the "correct" scene brightness can be reconstructed in post processing. One reason I didn't pursue this was I couldn't think of a workflow that didn't require writing image processing software, but your approach of generating / modifying processing parameter files should work.
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Offline c_joerg

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Re: Time-lapse Deflicker
« Reply #2 on: 16 / March / 2016, 03:41:38 »
 
Quote
This is a very good idea, and the results speak for themselves
Well, just the idea using the meter96 values comes from me ;)
The idea to modify the XMP files comes from.
This tool is basically designed to compensate the 1/3EV jumps from a DSLR.
It works only with Litheroom and is free for up to 400 pictures.
He calculates the correction for deflicker from the JPG which is not so accurate. My understanding was, you have to calculate (Correction values from JPG -> RAW development) a couple of times (iterative) to get good results.
Quote
Instead of using Bv / Ev shift to follow changes in scene brightness, just expose the maximum amount possible within the over-exposure limits. Since the actual Bv and exposure parameters are in the log, the "correct" scene brightness can be reconstructed in post processing. One reason I didn't pursue this was I couldn't think of a workflow that didn't require writing image processing software, but your approach of generating / modifying processing parameter files should work.
Well, I was thinking about the same. I wasn’t very happy with the Bv / Ev shift. That’s the reason why I haven’t used it anymore on my last runs. Doing it on post processing gives you more possibilities.
LRTimelapse does similar thinks in the following way:
You have to decide a couple of ‘Key Frames’ in you Timelapse. You have only developed this ‘Key Frames’. Than the tool synchronize and soothes the meta data for you. And this isn’t just working for exposure.
If you want to change the white balance from a day to night run you have only to set the two different values for two ‘Key Frames’. The tool does the smooth changeover.
Same with virtual zooming. You set on crop on one picture and another crop on another picture.
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Offline c_joerg

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Re: Time-lapse Deflicker
« Reply #3 on: 01 / August / 2016, 07:30:01 »
Hello,
I’m looking about a smart way to synchronize the meter96 values from log files with my pictures.

If the number of pictures are same as entries in the log file, I have no problems.
But sometimes I use only every second or third picture or only a part of them. Then I got sometimes mismatches.

Not sure if I could use the time from log and from picture to synchronize. May be on short intervals it does not work.

Not sure if the filename in the log file would be helpful…

Great Joerg
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Offline reyalp

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Re: Time-lapse Deflicker
« Reply #4 on: 01 / August / 2016, 13:44:57 »
Quote from: c_joerg on 01 / August / 2016, 07:30:01
Not sure if the filename in the log file would be helpful…
The "exp" column is the image counter, so you should be able to generate the filename from that. You would have to handle the counter resetting, but in normal use that should only happen once per run at most.
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Offline c_joerg

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Re: Time-lapse Deflicker
« Reply #5 on: 01 / August / 2016, 14:52:55 »
Quote from: reyalp on 01 / August / 2016, 13:44:57
The "exp" column is the image counter, so you should be able to generate the filename from that. You would have to handle the counter resetting, but in normal use that should only happen once per run at most.

Ok, exp is the get_exp_count(). That’s great. I have not notice this. I thought it’s just a counter. That’s really helpful. 
Thank a lot…
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