====== Idea ======


To be able to efficiently send the image data over a wireless datalink, one option is to compress the video data using h264/h265 encoders. Those two are often implemented in a hardware-accelerated way on the onboard computers like RPI and Jetson Nano. We can use these encoders to compress the video data to about 1000kBit/s and keep some kind of acceptable quality in the images to be processed by the image analysis algorithms ( to be tested! ) on a basestation computer.
These kind of compression is also used in existing solutions mentioned in https://www.hs-augsburg.de/homes/beckmanf/dokuwiki/doku.php?id=searchwing-wifibroadcast.

====== Tests ======

I conducted a first test using real images from a flight to check how well data could be compressed. I used gstreamer to compress a series of images to a videofile. Following settings choosen:

  * Imagesize 8MP - 3280x2464
  * Framerate 1Hz
  * Interframerate 1Hz / Didnt work with H265 so i choose 0.5Hz

H264

''
gst-launch-1.0 -e multifilesrc location="%04d.jpg" caps="image/jpeg,framerate=1/1" ! jpegdec ! x264enc bitrate=1000 speed-preset=2 key-int-max=2 ! avimux ! filesink location="out264.avi"
''

H265

''
gst-launch-1.0 -e multifilesrc location="%04d.jpg" caps="image/jpeg,framerate=1/1" ! jpegdec ! x265enc bitrate=1000 speed-preset=2 key-int-max=2 ! h265parse ! filesink location=out265.h265  
''

====== Results ======

Images are still looking okay for a human beeing. If the algorithms are also okay with that reduced quality need to be tested. 

{{ :comparison.png?1000 |}}

H264s filesize is in line with to the specified bitrate.  H265 somehow is ~4x bigger that the specified bitrate and also the quality is not really better than H264, so there are still some errors to find. 

Testimages and results can be found here: https://cloud.hs-augsburg.de/s/sm6taLQCAyWMY6F

====== Image compression in general ======

  *  [[https://ieeexplore.ieee.org/document/818515|Comparison of lossless image compression algorithms]]