Tap chiKHKTMo Dig chat, so 34, 4/2011, (Chuyen de Trac dia), tr 1 5 C O N G T A C T H I E T K E C H U P A N H SO T R O N G D O A N H M A T D A T 6 M O L O T H I E N TRAN TRUNG ANH, Trudng Dai hoc Md D[.]
Tap chiKHKTMo - Dig chat, so 34, 4/2011, (Chuyen de Trac dia), tr.1-5 C O N G T A C T H I E T K E C H U P A N H SO T R O N G D O A N H M A T D A T M O LO THIEN TRAN TRUNG ANH, Trudng Dai hoc Md - Dia chat Tom tat: Bdi bdo de cap den cong tdc thiet ke chup anh so mat dat tai cdc md 16 thien nham phuc vu tot cong tdc anh mat dat d phong Cdc cong viec bao gdm: tinh toan phdn gidi khong gian cua anh chup tic may chup anh so, thiet ke dudng day chup anh, bd tri va noi cdc diem khong che anh, cai dat cdc tham sd chup anh cho may chup anh so Cong tdc thiet ke chup anh phai dam bdo cho chinh xac ve ban do, xdy ditng cdng thitc tinh toan va so lieu cung cap cho thiet ke don gian de thuc hien Day la cong tdc rdt quan trong, anh hudng den chinh xac vd khd ndng ve cua anh img dung cong nghe anh so lap binh dia hinh d cdc md Id thien l.Mddau Sir dung may chup anh so thong cong vao cong tac chup anh mat dat la dieu da duoc khang djnh bdi nhieu nghien ciiu nude va tren the gidi Sir khac biet Idn nhat giua may chup anh so va may chup anh dung phim quang hoc la phim Halozel Bac duoc thay the bang mang nhan anh CCD (Charge-Coupled Device) hoac CMOS (Complimentary MetalOxide Semiconductor) chua cac detector chuyen cudng anh sang tin hieu dien va ma hda don vj thdng tin cua cac phan tii anh (pixels) May chup anh so khdng can diing phim quang hoc bd qua cdng doan trang l ira phim va quet anh, chi diing the nhd de luu tru d& lieu anh chup va chuyen true tiep vao may tinh Trong cdng nghe anh so ling dung ve dia hinh tai cac md Id thien, viec thu nhan tu lieu anh tir cac may anh so phd thong la rat quan trong, can duoc tinh toan thiet ke trudc Vdi mdi loai may anh sd khac thi cac sd lieu thiet ke khac nham dap ung mot yeu cau chung la dam bao chinh xac ve cho ty le ban tuong img, cdng thiic tfnh toan don gian, sd lieu dau vao cho thiet ke don gian Do vay bai bao trinh bay co so khoa hoc va cac cdng thiic tinh toan thiet ke chup anh cho may anh so phd thdng Cac thong so co" ban ciia may chup anh so May anh sd phd thdng (non-metric digital camera) la loai may anh phd bien tren thj trudng Loai may sir dung don gian, gon nhe, anh chup dang sd, phan giai cang cao va gia re Ve nguyen ly xay dung hinh anh ciia loai may anh gidng co ban vdi cac loai may anh cd dien va chuyen dung cho anh dd la nguyen ly ciia phep chieu xuyen tam Mang nhan anh gdm cac pixel ddng vai trd nhu phim chup, ghi nhan lai gia tri phan xa cudng biic xa va chuyen ddi sang tin hieu so Hinh May chup anh so va mang nhan anh so vdi vdng trdn hinh anh < 36mm > Hinh Mang nhan anh anh so va phim 35mm truyen thong Tu kich co thuc te ciia mang nhan anh va so lup'ng diem anh tren mang nhan anh thi co the tinh toan kich thuoc thuc te ciia pixel theo cong thiic: H W s =— =— , (1) n n do: s - la kich thuoc thuc te ciia pixel; W - la rong thuc te ciia mang nhan anh; H - la chieu cao thuc te ciia mang nhan anh; n - la so pixel tren chieu ngang (so cot p w H p w cua mang nhan anh); n - la so pixel tren chieu doc (so hang cua H mang nhan anh) Do co sir khac giua cac kich thuoc thuc te (W, H) ciia cac loai mang nhan anh va la nhung so rat kho nho nen cac nha san xuat thuong quy tuong duong (equivalence) kich thuoc ve co phim 35mm ciia cac may anh truyen thong dung phim Halozel Bac de de so sanh va quy chuan cac thong so khac (thuong la tieu cu ciia he thong kinh vat) Cach quy doi tuong duong khong lam thay doi tinh dong dang ciia quy luat tao hinh, ty so ciia tieu cu thuc t i (f) tren kich co pixel thuc te va ty so ciia tieu cir tuong duong ( f ) tren kich co pixel tuong duong (s ) la khong doi eq eq f f« -eq 35 (mm) (2) (3) Thiet ke cac thong so chup anh 3.1 Dp phdn gidi khong gian vd khodng each chup anh Voi khai niem truyen thong, phan giai khong gian la kich co tren thuc te ciia pixel tren anh so Tuy nhien theo dinh ly lay mau ciia Nyquist thi phai co it nhat pixels tren mang nhan anh moi phat hien duoc doi tuong nho nhat tren thuc dia theo khoang each chup anh [2] Do vay khoang each chup anh den doi tuong quan he voi phan giai khong gian nhu sau: S R ^ R (4) 2s„ 2s p «q do: D - khoang each tu tam chup den doi tupng; SR - phan giai khong gian (kich ca nho nhat ciia doi tuong tren thuc dia theo khoang each chup ma tren anh nhan biet duoc); Thay cong thiic (3) vao (4) nhan duoc cong thiic (5) sau: SR.n (5) 70 f >m do: f tfnh theo don vj mm; SR tinh theo don vi m Cong thiic (5) la moi quan he giua khoang each chup anh (D) voi phan giai khong gian (SR) lien quan den cac thong s6 ciia nha san xuat may chup anh s6 cong bo la s6 cot ciia mang nhan anh (n ) va tieu cu tuong duong ( f ) Day la cong thiic don gian d l uoc tinh khoang each ve ciia anh chua can din kiem dinh dai thuc t l ciia may anh, giiip cho uoc tfnh kha nang ve cua may anh phii hop voi ty le ban cin lap va su lira chon may chup anh duoc de dang hon Luu y rang tieu cu tuong duong f duoc chon la tieu cu a vi tri mac dinh va 6n dinh nhat D = f = f eq w D eq eq w eq e q Hinh Mdi quan he hinh hoc giua pixel tren anh va thuc dja 3.2 Thiit ki dudng day chup anh, diem khong che anh Duong day chup anh (B) la khoang each giua tam chup (Si, S2) ciia cap anh lap the Thiet k6 dudng day chup anh chii yeu phu thudc vao dia hinh khu do, chinh xac ciia ban dd cin lap, chinh xac ciia may do, dam bao kha nang nhin lap the ciia mat ngudi (gdc giao hdi y < 16°) va phai chii y tan dung tdi da kha nang ky thuat ciia may anh (khoang each chup anh xa nhat) V j tri dudng day chup anh cin bd tri d dia diem kha bang phang (chenh cao giua hai dau dudng day khdng qua Idn, thudng quy djnh la nhd hon 0,15B), vj tri cd quan sat rong, han che tdi thieu phan "khdng gian chit" (khdng gian khuit, ddi tuong khong ghi nhan duoc hinh anh) Thay (4) vao (6) se nhan duoc cdng thiic : D„ D„