Zoom/PPF for human readable?

[Bitslizer]

Newbie here so forgive my ignorance.

Read through as much as I can and I understand that for Machine recognition like ALPR it is recommend to have 200PPF. But if I'm not doing ALPR or plate recognizer and only want to record and be able to look up the Date/Time/Plate manaully and be able to read it reliably by human, whats the min PPF I would need?

I want to get 2 cameras for LP but I can't justify $500+ for 2x of the Dahua 12x bullet everyone rave about here. Seems there are a few Dahua 13.5mm within my budget but I'm not sure those have enough zoom or not. Looking at about 60-100ft or so.

 

[samplenhold]

A 13.5mm for getting plates at 60-100 feet is probably not going to work unless you are at about 0-5 degrees. You could use the IPVM calculator to see a calculated image for a specific cam. The only real way to tell though, is to set up a cam and test it in your particular setup.

IPVM Camera Calculator V3

See these threads to get an idea about LPR and it's challenges.

LPR Case Study: Scoping, Planning, Proof of Concept, Installation, & Results

Introduction This thread is about my journey into LPR (License Plate Recognition) after having about 18 months of experience with IP cams and having quite a bit of my system finished. I am not an expert on LPR, or IP cameras either. But I have spent a lot of time working with my system and...

ipcamtalk.com

New to LPR? Considerations Before You Begin

Thought I would throw together a post on my experiences so far with LPR in an effort to help others that are considering running down that rabbit hole. There are some practical considerations you should know about LPR. I am approaching this from the position of using Blue Iris and Plate...

ipcamtalk.com

 

[richardgohth]

Newbie here so forgive my ignorance.

Read through as much as I can and I understand that for Machine recognition like ALPR it is recommend to have 200PPF. But if I'm not doing ALPR or plate recognizer and only want to record and be able to look up the Date/Time/Plate manaully and be able to read it reliably by human, whats the min PPF I would need?

I want to get 2 cameras for LP but I can't justify $500+ for 2x of the Dahua 12x bullet everyone rave about here. Seems there are a few Dahua 13.5mm within my budget but I'm not sure those have enough zoom or not. Looking at about 60-100ft or so.

say the stroke width of the characters in the plate is 1cm, then theorectical ( nyquist criterion) minimum is 2 pixels per cm or 200 pixels per metre

 

[Bitslizer]

So managed to pick up a toy for testing.... a RevoTech 3mp 6-22mm with a 1/3" sensor (no IR) for like $35. fully zoomed at 22mm (IPVM says 12degree HFOV) with about a 45 degree horizontal angle from my porch to the street need about 100ppf (according to the IPVM calculator), distance roughly 80ft to be human readable during day time on a fairly consistent basis. tried going under 30 degree but not enough zoom to be human readable. Not exactly sure what shutter speed the camera is using but I set it to go no slower than 1/4000.

Will see if i can get anything at night but probably need a miracle since this cam doesn't have any IR. I can see if another of my camera with IR pointing in the same direction can help or not, but that's about 130ft for the IR maybe too far to reach. saving grace is that it is more or less under a street lamp

 

[wittaj]

If the camera does not have an IR filter then it will not see the IR...

 

[Bitslizer]

If the camera does not have an IR filter then it will not see the IR...

you are right, but it is possible for me to remove the IR-cut filter based on other online info

 

[wittaj]

You need to add an IR filter not remove one