Hi all,
since I am doing photomapping of terrain,
I have experienced, that the light tends to change progressively as I shot photos.
The problem is, the flight is following zig-zag or spiral shape and as a result I have gradual variation
of brightness and contrast across ortophotomap.
In my case I am striving for fast response, not for HDR quality, and it might be difficult to repeat a mission
that takes up to 2h of UAV flight.
The question is, are there any tools that can linearly/gradually or maybe automatically apply some correction to a list of images?
We are talking abotu 300-3000 photos per flight, up to a few times per day. A real mill.
I am aware of ImageMagick toolset, but it is not a solution:
The problem is that any automatic method I know gathers statistics over a single image, then applies the correction to one or many.
Also ImageMagick scripts I tried to apply by merging photos etc show insufficient processing speed of Image Magick (it is general tool, with dozens of intermediary memory copies/logic layers during processing a script).
What is needed is a tool that analyses 3..tens..all neighboring images (consecutive in the list) and applies slowly changing correction.
I know that somebody will advise fixing exposition in the camera but thsi is NOT the way to go in 50% cloud cover changing the lighting 8 times during the flight.

What is needed is something like Deflicker algorithm used in movies, but this would be ideal but I doubt it exist for photos.
At the moment I am looking for anything that works.

I know the issue could be known to ppl doing Timelapses but I have no idea what are the solutions (I guess they usually merge the results into a movie, then apply Deflicker filter in movie processing soft, but the resolution, compression and quality is lost).

At the moment typical application of autobalance or histogram equalize/anything leads to photos where 1 out of 20 pops up with very off colors or other parameters.
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  • T3

    I have tried Grass for 1 week 4 months and found myslef in deep Forest. The problem is that I can do interfacing on my side, preprocessing, but the core data processing fucntionality I want to leave for the others. What is interesting to me is to removing minor obstacles in almost-working solution either by UAV mission planning, autopilot export processing etc.

  • @ Brakar : When I was working on that project, I tried Grass (on many differents modules). My conclusion was it's very powerfull on many functions, but a lot of remaining bugs (or difficult to understand parameters ??). Really time consuming and not enough to a complete toolchain.

    Documentation was poor and GUI very complex 2 years ago, but Grass is still in development, perhaps it's easier today !

  • GRASS GIS can probably do the blending (also); http://grass.osgeo.org/gdp/html_grass63/r.blend.html

    The problem that remains to solve is to line up the individual photos correctly, and to export the image coordinats to a propor file-format. For this, I think the use of algorithms like SIFT or SURF will be neccessary.

  • I have a collegue who works with thousands of photo's and stitches them together:


    to enhance pictures to give them the same "look": lightroom (aprox $300)

    to mosaic photo's photoshop (aprox $700).

    Personally i find photoshop not a product for an amateur but hey who am i (townsfool?)

    These adobe products dont have a problem with photos with a size of 18 Mb and can calculate in batch.

    In lightroom you work on 1 photo, select the photo's that will have the same treatment and press go.

  • Yes your true about tie points, they become GCP at the really end of the treatement.

    Of course you can export tie points in 3D, in a first step.

    There is another step in wich very dense point cloud is generated after 1st pass orthorectification is complete, but very very long step. Everything is possible I think with a so huge amount of data, but for the second pass I believe you'll wait for weeks if you need the top quality 3D reconstruction (final step) !

    What are your overlapping proportions ?

  • @Rocca: Well I saw some results where GPU SIFT was used on large number of images that hasn't any kind of georeference information. Its speed is impressive. Almost 1 image (5Mpx) per second. Anyway, there are two working options for me:

    1. 640x480 px and several thousand, sometimes even more than 10k images (thermal camera)

    2. 12-16Mpx and approx. thousand images

    Can you export also a point cloud of so called "GCP". I would like to name those points as tie points because they are not GCPs due to lack of measured real world coordinates as far as I understand your process of course.

  • @Lojze : There is no GPU support at the moment, and honestly I don't know how to do it ! Do you plan to do real time processing ? Because the step to detect GCPs between all the pictures is not the longer one (25% computing time approx, if I remeber well) with the CPU.

    About the total size of final blend, there is just no limit (there's a trick of course...) ! What final resolution and initial number of picture in your work ?

  • @Rocca: Are you also using a GPU SIFT approach and what is maximum image size (pixels) that you can put trough whole process?
  • @Rocca: I'm primary looking for a software. And I'm a fan of command line. Batching processes is priceless for my lazy nature ;-)
  • Yes I made it too in my software, absolutely crucial when you are dealing with several hundreds pictures.
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