ZoneMinder Forums

I'm looking for advice on the image quality front. I have a system that monitors a busy rural road corner and would like to do license plate detection, manual or automatic. In the manual case, the still image quality from a Amcrest 4k camera is barely enough. Remove storage size as a limitation ... what is the best way to get a high quality image from the h264 stream?

I have used the stills directly from the zoneminder UI and extracting images using ffmpeg from the event mp4 but the quality isn't great. If you had a 4k still image at 20 feet, license plate detection would be easy. I'm currently using 10 fps at full resolution (3840x2160) and variable bit rate. I've read that many license detection systems use 30+ fps. Are there some good rules to live by when trying to find the balance between size and quality?

Any input appreciated.

Thanks

Reading documentation from OpenALPR and Phd papers seems to imply I should reduce my resolution and increase the FPS.

VBR with cap is recommended.

Trying reduced resolution 2304x1296 @ 30fps.

"Location, Location, Location." A good placement for license plate camera would be right next to an entrance of a building (i.e. a parking garage). You want good lighting, and to be close to the car as possible. Think of how the highway automated toll cameras work. They are right above the road pointing down. I'd be willing to guess those are somewhere around 4K (since they've been around a couple years at this point, in my region). If it's good enough for them, it means that the tech works.

The ability to isolate the plate with a tight crop on the actual camera would do the trick, of course. My system has managed ANPR with a wide angle lens, but the cars slow down for this part of the road.

Is the problem due to motion? Is it encoding artefacts? Do you have control over the shutter speed?

I didn’t find openALPR as good as Plate Recognizer.

Appreciate the input.

I don't have a great perspective on the road .. as in no overhead perspective. Reading the best practices for detection indicates off center more than 30 degrees is not optimal. I only have a roadside perspective.

I will experiment with fps and see if image quality is better.

As always ... thanks to everyone involved in the zoneminder project. Such a great tool.