Sunday, August 11, 2019

Doing the math on pixels per inch at a distance for your cam

Seeing a lot of posts where people are talking up 1080p cams with wide angle. Let's do the math on that. There is a simple calculator online to get the width of the area being viewed by a cam with a given view angle. For example let's take my old work hours the Foscam 9800 series that is 720p and 70 deg view angle.

So at 20 feet the view width is 24.4 feet or 293 inches. 720p resolution is actually 1,280 pixels so when we divide the pixels by the view width you get  4.3686 pixels per inch. So a face, about 6 inches wide will be 26 pixels across at 20 feet with this cam. 40 is considered to be the min. So even with the best lens focused for 20 feet this is still not going to cut it.

For convenience I worked up the charts below from my compare sheet. Note these charts assume the camera is focused for the target distance and not the upscaled resolution some cams advertise. Despite claims, outdoor fixed focus cams seem to be focused at around 20 to 30 feet. You might get a "decent 2X screen grab" of targets within +- 10 feet of that. Of course for a large range of  depth you really should look at a camera with autofocus like the Reolink RLC-411WS I've tried. Though it has had the occasional glitch as well. For long distance something adjustable like the Microseven 6-22mm 3MP Manual Zoom Varifocal Len HD 1080P.







Not those are best case numbers under perfect conditions. While 7 pixels per inch is bare min 14 is the more accepted min. If I change the wanted pixels per inch to 14 the last chart becomes

Note 12 degrees is a fairly extreme telephoto lens in the range of 22mm
70 is standard though up to 90
between 90 and 130 is often called wide angle
180 to 360 are often called 360 view cameras

For a more indepth info look here.

Sunday, August 4, 2019

Should you get a Wyze cam?

I'm seeing that question a fair bit these days. The answer is of course it all depends on what you want to do with a cam. For instance 6 of the 51 cams I currently have online are Wyze. And I have a 7th I'm planning on replacing an old 720p cam at the gate watching the mailbox with. But you need to think about what you plan to use it for.  They are great for places you want to setup something quickly to monitor something. Or in a place like out at the gate where it might be easily stolen so you want something with audio but cheap. For example only 2 of the 7 will be mounted in a permanent way. Compared to others here are the pros and cons I've see running them 24/7 in RTSP mode.

Wyze Pros:


  • Cheap (~$30 with shipping) though for the "3 times the price" I often see quoted you can get some really killer cameras. I just picked up 2 Amcrest IP4M-1026EWs for $64 each for example. For ~4X the price you can get 5 MP with zoom and auto focus or even 4K for example.
  • Can record local and to free cloud (and to NVR with hacks or one off supported firmware)
  • Easy to setup. I have 3 in the barn just stuck on walls by the magnetic base.
  • Wide 110° view. Good for getting a good bit of the room though not as good for distance without a lot more pixels.
  • They are adding person recognition to cut down on "bad" notifications. I have not had a change to try this personally though so not sure how well it is going to work given the limitations of the camera hardware and bandwidth if attempting a cloud solution. Update 8/10: Went to add a Wyze V2 out by the gate now that I have power and found they updated the RTSP firmware so ti now does person notifications. It is disappointing video compared to the 720p Foscam I hoped to replace. And the sensors seem iffy but I'll leave it a bit to see how well the person notifications work.

Cons:


  • Only WiFi and the WiFi is weak. Expect a lot of drop outs if you plan to stream to a NVR. I suggest putting any WiFi cam on a smart plug so you can restart it remotely if not automatically.
  • Just 1080p which is the bare minimum these days given how cheap cameras have become. Especially with a 110° view. Remember one of the main factors in recognition is pixels per inch at the target distance.
  • USB powered which generally means power nearby.Though some have reported being able to use POE to USB adapters. At that point though you are talking similar price of cams with POE built in.
  • Indoor cam by design. While there are cases that are supposed to shield it from weather again that negates most cost savings. Also this does not change the in focus range of the camera which is setup for medium size rooms. Having the target in the focus range of the camera is the other main factor in being able to recognize the target. Though focus range can also be an issue with many cameras since most these days are not just fixed focus but glued in place to prevent altering so it is important to match the camera to the target. 


Note for non RTSP use:

It only triggers once in 5 minutes and only uploads the first 12 seconds of that. Does record local 24/7 though and you should absolutely do that. While the cloud recording is a nice backup you really should not count on it catching anything, especially outdoors, since the odds the movement the first triggers it will get the best 12 seconds of video for you are about the same as hitting green light in city traffic when you are in a hurry.

More info:

To see more of what I've done with Wyze cams see my other posts here and samples I've posted on YouTube.