Frank I.
 lvl.2
Germany
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Hi there,
sorry this is a bit long, but i hope it will help some of you doing aerial photography with the Mavic.
(Note: A similar "fix" may be possible for videos, but this here is about RAW/DNG fotos and
Lightroom only (i'm not into video - yet...). A simple LUT will not fix it, though - from what
i have understood LUTs are applied to the entire frame, so this won't work here.)
1. Cause of the problem
There are several threads here about a "warm" spot in the center of images taken with the Mavic.
Depending on the light situation and the dominant color in the frame it can be "red-ish" or
"yellow-ish". In some pictures it's hardly visible, in other shots it's very dominant.
DJI Ken posted some links to a PDF from DJI R&D that explains the origin of this issue (thanks!!).
Most of the links i found don't work (any more? at least not for me), this one did:
https://forum.dji.com/forum.php? ... &fromuid=422787
In a nutshell, it's an optical/physical problem, caused by the very compact dimensions of Mavic's
camera. This results in a very short distance between the lens that's closest to the sensor and the
infrared filter that sits right before the sensor.
So, it's a problem of the camera's construction in the first place - and no firmware update and
no DJI Go App V.27 or whatever can fix that. Bummer.
2. Variations of the problem
Whether or not this becomes a problem to you as a photographer seems to depend on several factors:
2.a) the individual Mavic you use
The combination of more-or-less misaligned lenses and/or IR filters in your Mavic can add up to
making it a "bad" problem - or not. If you're lucky, your sample lies in the center of manufacturing
tolerances, so maybe you will not even notice there's a problem at all.
(i have sent my Mavic in for repair two times - the first "repair" was a completely different unit,
but the "red spot problem" was even worse than with the one i sent in. In the second "repair"
it seems only the camera was replaced. It still has the issue, but not so bad, and i can fix it
in the DNGs in post (see below)). So i'll keep this one - it's just so damn fun to fly! :-)
2.b) the colors in the scene
False color rendition becomes most visible when you have very little different colors in the frame
in the first place. To test your Mavic, take test shots of a white or grey piece of paper that
is evenly lightened(!). Shots of snow-covered landscapes are more prone to show it than an
"indian summer forest". When you take landscape shots, the different colors of the landscape
can "cover up" the problem and make it less visible ( if you have it at all - see a) )
2.c) light source(s)
Since the problem is related to the frequencies of light the camera has to capture, results can be
completely different when you shoot landscapes outdoors (esp. in golden/blue hours) vs. a studio
scene with "controlled" light amounts and spectrums.
3. How to "color-fix" your "red-spot" images (DNGs) in Lightroom
Lightroom presets can fix those nasty color casts. Forum member FlyLight posted a Lr preset here:
https://forum.dji.com/forum.php? ... &fromuid=422787
(This was a good starting point - as stated in your post - big thanks for that!)
I built up on that and refined it.
3.a) understand how Lightroom presets work
You can do a lot with Lr presets. Open any image, shift all the sliders all the way you want, add
Gradient or Radial filters, and when you're happy with the result - click on the "plus" sign next
to "presets" on the right and save your edit as a preset.
HERE'S THE CATCH:
Lr can save ALL or only PARTS OF the changes you made during development into a preset.
This depends on what checkboxes you check/uncheck in the "new preset" window.
If you check only the "Radial filter" checkbox (and nothing else), than Lr will only apply
that part of your development to any image you apply this preset to(!). All other settings
you may have done before will remain. All settings that you add in by applying other presets
later on will also apply, UNLESS they have Radial Filters incorporated - these will override
the preset's values.
Appliying Lr presets works in an _additive_ way: if you apply a preset that only adjusts Contrast,
only Contrast will be set to the preset's value.
3.b) Find "your" best correction profile for "your" Mavic
Because of 2.a) there's likely no "universal" correction profile that you can download and
just be happy with it. You will have to tweak it a bit for your Mavic's camera.
(You may even have to make different presets, e.g. for indoor/outdoor shots, or for "mid day"
vs. "golden hour" vs. "blue hour" shots.)
The basic procedure is this:
- take a picture of a white (or light grey) plane (piece of paper, cardboard...) with Mavic's Cam
- import that into Lightroom. Do NOT apply any presets(!)
- you'll see the "warm spot" in the middle. Leave all the sliders (Saturation, Dynamic) as they are.
- go to "radiant filters". Create a radiant filter that's as high / wide as your image and is ROUND.
- in the filter's properties, check the "invert mask" checkbox
- set "temperature" to -25
- set "toning" to -25
- these are just starting values: adjust "temparature", "toning" until the image looks "even"
(i.e. you don't see any colour casts any more)
- click the "plus" sign on the right side next to "user presets" to create a new user preset
- make sure ONLY "radial filters" is checked (and nothing else!)
- name it "Mavic V1" (you will likely need V2, V3 etc....) and Save
- open any of your Mavic pics and apply that preset. It should make the image more "color neutral".
- repeat the above steps until you have the best preset for your own Mavic figured out.
3.c) use Lr presets "conservatively"
Once you have this "personal Mavic preset" figured out, i would suggest to apply it to all
Mavic images right during the import into Lr. There may be variations, it will not be perfect
for all shots under each condition, but you've got a starting point that's more "neutral" than
what the DNG's come with (without any correction).
Any other presets you make ("lights down", "warmer" or whatever you think of) can be "clicked in".
4.) a final word for panorama shooters
In a single image, the "red spot" is often overlooked or not much of an issue.
If you are doing aerial panoramas, this can drive you nuts: the "warm spot" is present in all of the
initial pictures, and often you don't even see it.
Unless you try to build a panorama shot from several "red-spot-affected" single images.
The stitching software will decide what part of which image will make it into the final pano image.
If you haven't corrected the "red spot" BEFORE letting the stitching SW do it's job...
good luck! ;-)
cheers, Frank
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First Officer
lvl.3