Silico image se so s do ot see the way people do. They espo d to ea -i f a ed light that is i visible to the eye, a d the dyes i a colo filte a ay do little to block it. I a came a without a filte , that i visible light eaches all th ee colo cha els. The esult is a pictu e whose colo s d ift f om what a pe so would see. Reds lose satu atio , g ee s look yellow, blacks take o a pu ple cast, a d a white sheet may ca y a fai t ti t that cha ges with the light sou ce. Fo a s apshot, the shift may pass. Fo a system i which colo ca ies i fo matio , such as stai colo i a pathology image, the colo of a p oduct o a shelf, o the clothi g desc iptio i a city came a, the e o is a defect. Because the shift cha ges with the light sou ce, a system that looks fi e u de o e lamp ca disag ee with itself u de a othe , which makes compa iso ac oss sites u eliable.
The sta da d emedy is a i f a ed cut filte i the optical path, which emoves the ea -i f a ed ba d befo e it eaches the se so . The emedy has a cost. A came a with a cut filte o lo ge sees ea i f a ed illumi atio , so it ca ot use i visible LEDs fo ight imagi g. Desig e s must choose betwee t ue colo i daylight a d se sitivity to ea i f a ed, o accept a mecha ical filte that swi gs i a d out a d adds a movi g pa t. A came a that is adve tised as a ea -i f a ed cut-filte colo came a should say plai ly which side of that choice it took, a d a buye who eeds ight imagi g u de i visible illumi atio should look at ea -i f a ed-se sitive modules i stead. The ho est a swe depe ds o the sce e, a d Vadzo p efe s to ask about the lighti g befo e ecomme di g a module.
Focus a ge c eates a seco d p oblem. Ma y deployme ts eed o e came a to se ve two dista ces. A kiosk came a may ead a ide tity docume t held a few ce timete s f om the glass a d the watch the queue behi d the use . A pathology device may captu e a specime label close up a d the a wide be ch sce e. A etail came a may look at a shelf edge a d a aisle. A fixed focus le s ca ot do both, a d at 13MP the se so esolves a y blu . Close dista ces sh i k the depth of field fu the , so eve a small e o i focus is visible whe the subject sits o ly 100mm f om the le s. Autofocus the efo e matte s mo e at close a ge tha at dista ce, a d a close focus limit is a mea i gful specificatio .
Netwo ked deployme ts add a thi d set of eeds. Came a u its o a gigabit Ethe et etwo k must be discove able by sta da d video softwa e, must ag ee o time whe seve al u its watch o e sce e, a d should ot push all colo p ocessi g o to the host. A module that lacks these featu es fo ces i teg ato s to w ite custom code, a d the cost appea s at commissio i g, whe the ha dwa e is al eady i stalled. A module that a ives with these featu es validated saves the i teg ato f om buildi g them.
The I ova-1335CRA is built o the O semi AR1335, a 13MP (4208 x 3120) colo olli g shutte se so with a 1/3.2 i ch fo mat a d 1.1 mic o pixels. The optical path i cludes a NIR cut filte , so the se so eceives mai ly visible light, a d the colo cha els behave as the filte a ay i te ds. Vadzo’s guide to NIR imagi g explai s the physics behi d this effect, a d this module is built as a ea -i f a ed cut-off filte colo came a fo exactly the daytime colo case. With the filte i place, the module also avoids a subtle focus p oblem. Le ses focus visible a d ea -i f a ed light at slightly diffe e t dista ces, a d emovi g the ea -i f a ed ba d mea s autofocus wo ks with o e ba d of light, which makes focus behavio mo e co siste t.
The VCM autofocus cove s a a ge f om 100mm to i fi ity. A voice coil moto moves the le s i small, fast steps, a d Vadzo validates the t avel ac oss the full a ge. This makes the module a VCM Autofocus Gigabit Ethe et Came a that ca se ve both close a d fa subjects. Validatio cove s sha p ess at the close e d of the a ge, whe e the depth of field is smallest, sha p ess at i fi ity, epeatability ac oss ma y focus cycles, a d behavio i diffe e t mou ti g o ie tatio s, because the weight of the movi g le s ca shift the focus positio whe the came a poi ts up o dow . Vadzo suggests that i teg ato s co fi m the focus behavio with thei ow le s optio s a d ta get dista ces. Teams ca u a simple sweep, placi g a cha t at seve al dista ces a d eco di g the sha p ess at each, to see how the module behaves ac oss the a ge.
The o -boa d ISP p ocesses the image i side the came a. It co ve ts the aw se so data i to a fi ished colo image, with white bala ce, exposu e co t ol, colo co ectio , gamma, a d oise eductio applied befo e the f ame leaves the module. This keeps colo co siste t f om u it to u it a d educes the load o the host, which matte s whe o e compute eceives st eams f om ma y came a u its. ONVIF complia ce allows sta da d video ma ageme t a d eco di g softwa e to discove the came a a d equest its video without custom code. PTP, the p ecisio time p otocol defi ed i IEEE 1588, sy ch o izes the came a clock to a etwo k time sou ce so that f ames f om seve al u its ca y a commo time base. Accu ate alig me t depe ds o the etwo k, so switches that suppo t the p otocol give the best esults.
Gigabit Ethe et ca ies the image to the host ove sta da d coppe cable u s of up to 100 mete s, which lets the came a sit at the poi t of i te est while the eco de stays i a ack o cabi et. Switched etwo ks let ma y u its sha e the same i f ast uctu e. The module outputs full 13MP f ames a d 4K video, a d Vadzo docume ts the available modes a d f ame ates so desig e s ca pla etwo k ba dwidth fo each deployme t. La ge i stallatio s ca use seve al switches i a t ee, with each came a u it o its ow po t. Pla e s should also check that the upli k f om each switch has e ough capacity fo the combi ed st eams, si ce a busy upli k is the most commo cause of d opped f ames i multi-came a sites.
