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Warning re low res images

In trying to develop a standard processing stream for MME I do the following:

  1. Plan mission using PC based Litchi Flight Planner.
  2. Fly the mission (several flights may be required).
  3. Compress the .jpg images with Jpegmini - this normally reduces image size by 40% to 70% without visible change in quality of the image.
  4. Adjust colour balance using Photoshop.

Invariably I get a message that either says images are of low quality and the job will probably fail or a message saying that some other program has messed around with the EXIF info.

Despite these messages, the jobs run successfully and as can be seen below, there is no change to the EXIF information (or at least the information that you require for processing).

The reasons for flying/processing this way are:

  1. Missions are created via a VBA app which creates a CSV file which is easily loaded into Litchi. Also Litchi give complete control over location and altitude of individual images unlike Map Pilot.

  2. Images are normally uploaded to MME from a minesite with poor internet comms. For this reason JPEGmini is used to compress the files before uploading.

  3. The Phantom 4, 4 Pro and Mavic are notoriously bad at maintaining colour balance using the auto white balance (see attached image showing consecutive images flown over a relatively consistent ground). If a particular white balance is used (eg sunny), then colour balance of images still varies if the sun goes behind the clouds and then reappears. Using the Photoshop Match Color option corrects for this prior to processing.

The warning messages don't concern me other than the fact that your software appears to be making incorrect assumptions about what has been changed and the effect that has on processing (as you can see from above, all the EXIF values which could potentially affect processing -resolution, camera settings, location, altitude etc, remain the same).

I am just hoping you understand why, for some people, modifying the images prior to uploading is essential.

Brutus Cooper

Official comment


The uploader is not making "incorrect assumptions" about the data. It is looking at the data density of the images which is how many megabytes are present to represent how many pixels. If this number is below a certain threshold it is deemed to be of low quality. Low quality images are prone to fail in our system since the details of the images are no longer reliably transmitted to the system since they have been replaced by compression approximations. 

The changes compression makes to the human eye can be small but those changes make a big impact to the performance of our system's feature detection algorithms. 

If you have figured out a way for it to work, great! There are automated messages to let users know that other software has touched the images/tags. We don't stop you from uploading them but we let you know about it. 

If you are having issues with the auto white balance why not try just setting it to sunny or cloudy so it doesn't change mid flight? The color is always going to change if the lighting conditions are variable. 

We do not in any way prohibit doing color corrections. We just let users know that the source image tags may have been altered since this happens frequently.

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