Mat do diem anh trong CCTV
Mat do diem anh (PPM) xac dinh chat luong hinh anh va lien quan den viec ban co the nhan dien khuon mat, doc bien so xe, hay chi phat hien chuyen dong. Tim hieu chi so quan trong nay.
Mat do diem anh la gi?
Mat do diem anh, do bang pixel tren met (PPM), mo ta so luong pixel do phan giai video tren moi met khoang cach tu camera. PPM cang cao nghia la cang nhieu chi tiet.
PPM duoc tinh bang: PPM = (do phan giai x 1000) / khoang cach tinh bang met
Mat do diem anh huu ich hon do phan giai thuan tuy vi no tinh ca khoang cach. Camera 4MP o khoang cach 30 met co PPM hieu qua thap hon camera 2MP o khoang cach 5 met.
Mat do diem anh va cac cap do DORI
Tieu chuan DORI (phat hien, quan sat, nhan dien, dinh danh) dua tren mat do diem anh. Moi cap do yeu cau PPM cu the:
| Cap do DORI | PPM toi thieu | Mo ta |
|---|---|---|
| Phat hien | 40+ PPM | Ban thay co vat the hien dien |
| Quan sat | 80+ PPM | Xac dinh loai, mau sac, huong di |
| Nhan dien | 160+ PPM | Nhan dien nguoi quen biet |
| Dinh danh | 300+ PPM | Dinh danh nguoi la, doc bien so xe |
Cach tinh mat do diem anh
Cong thuc tinh ca do phan giai camera va khoang cach quan sat:
PPM = (can bac hai cua do phan giai x 1000) / khoang cach
Vi du: camera 4MP (2688 x 1520 pixel) o khoang cach 10 met
PPM = (can bac hai cua 4 086 720 x 1000) / 10 = 203 PPM
Camera 4MP nay dat tieu chuan nhan dien (160+ PPM) o khoang cach 10 met.
Vi du thuc te
Loi vao cua hang (2 met)
Can cap do nhan dien (160+ PPM). Camera 2MP dat 80 PPM o 2m (chua du). Camera 4MP dat 160 PPM (vua du).
Bai dau xe (30 met)
Can dinh danh bien so xe (300+ PPM). Camera 2MP: 27 PPM (qua thap). Camera 4MP: 54 PPM (van thap). Camera 8MP: 108 PPM (van thap). Camera 12MP: 162 PPM (van thap). Can camera chuyen dung 25MP.
Loi di kho hang (15 met)
Can cap do quan sat (80+ PPM). Camera 2MP dat 54 PPM (chua du). Camera 4MP dat 108 PPM (du).