KEY SEN­SOR TECH­NOLOGI ES

HWM (Malaysia) - - LAB TEST -

1 CCD

A charge-cou­pled de­vice (CCD) im­age sen­sor uses a global shut­ter to cap­ture an en­tire frame in one in­stance. It is the more ma­ture tech­nol­ogy and was used in early dig­i­tal cam­eras, but has since been over­shad­owed by the rise of CMOS sen­sors in re­cent years. CCD sen­sors are prone to ver­ti­cal smear, where bright lights can cre­ate a ver­ti­cal line from the top to the bot­tom of the im­age, but it does not suf­fer from the rolling shut­ter ef­fect that plague CMOS sen­sors.

2 BACKSIDEILLUMINATION

Back­side-il­lu­mi­nated (BSI) sen­sors move the light-block­ing wires on CMOS sen­sors to the back of the sen­sor, mak­ing them more ef­fi­cient at cap­tur­ing light in low-light sit­u­a­tions, pro­duc­ing less im­age noise in the process.

3 CMOS

Com­ple­men­tary me­tal-ox­ide semi­con­duc­tor (CMOS) im­age sen­sors are the pre­dom­i­nant tech­nol­ogy used in dig­i­tal cam­eras to­day. It uses a rolling shut­ter to cap­ture a frame from top to bot­tom, record­ing each pixel one-by-one.

With CMOS sen­sors, ad­di­tional cir­cuitry can be built onto the sen­sor to per­form ad­di­tional tasks, like fo­cus­ing and im­age-pro­cess­ing. Com­pared to CCDs, CMOS sen­sors are more power ef­f­cient and cheaper to pro­duce. CMOS sen­sors how­ever, are prone to the ‘rolling-shut­ter ef­fect’, which makes the im­age tilt and dis­tort when cap­tur­ing video of a fast­mov­ing sub­ject or when pan­ning the cam­era while shoot­ing.

4 BAYER AR­RAY

The pho­to­sites on a sen­sor cap­ture light, but a color lter is re­quired to cap­ture color im­ages. The most com­mon color fil­ters is the Bayer Ar­ray, which con­sists of al­ter­nat­ing rows of red-green and blue­green fil­ters. Bayer de­mo­saic­ing is the process of trans­lat­ing th­ese pri­mary col­ors into a full-color im­age, by de­duc­ing each pixel’s color from the value cap­tured by it and its neigh­bours. How­ever, this process can re­duce im­age res­o­lu­tion, be­cause of the blur­ring that in­evitably oc­curs when com­bin­ing cap­ture data.

The Leica M Monochrom is fa­mously known for re­mov­ing the color lter ar­ray en­tirely, shoot­ing only black and white im­ages. Re­mov­ing the color lter brings cer­tain ad­van­tages, like re­duc­ing im­age noise and in­creas­ing ne res­o­lu­tion, as none of the pix­els need to be de­mo­saiced.

6 OP­TI­CAL LOW-PASS FIL­TER

The op­ti­cal low-pass lter, also known as the AA lter, is found in al­most ev­ery dig­i­tal cam­era. It re­duces the ap­pear­ance or moiré ar­ti­facts, which can ap­pear in pho­to­graphs of re­peat­ing pat­terns, at the cost of blur­ring of ne de­tail. The op­ti­cal low-pass lter is signi cant to­day, not so much for its in­clu­sion, but its ex­clu­sion from cam­eras like the Leica M9 and the Sony RX1R. By re­mov­ing the lter, the sen­sor can cap­ture more ne de­tails.

7 X-TRANS SEN­SOR

To do away with the op­ti­cal low­pass lter and re­duce the risk of moiré ar­ti­facts, FUJIFILM in­vented the X-Trans sen­sor, found in its cam­eras like the X-Pro1 and X100S. In­spired by the ran­dom ar­range­ment of ne lm grain, the new ar­ray’s RGB pix­els are ar­ranged in 6 x 6 pixel sets with a high de­gree of ran­dom­ness when com­pared to con­ven­tional sen­sors. This elim­i­nates the in­ci­dence of moiré, as well as re­sult­ing in bet­ter color re­pro­duc­tion.

5 FOVEON SEN­SOR

The Foveon CMOS sen­sor is sig­nif­i­cantly dif­fer­ent from the dig­i­tal sen­sors found in most cam­eras to­day. De­signed by Foveon, the sen­sor’s pho­to­sites con­sist of three ver­ti­cally stacked RGB pho­to­di­odes. Each pho­to­di­ode re­sponds to dif­fer­ent wave­lengths of light, and the re­sult­ing data pro­duces the nal color in­for­ma­tion of the pixel.

Be­cause de­mosiac­ing is not re­quired to pro­duce a full-color im­age, a Foveon sen­sor doesn’t suf­fer from the disad­van­tages of hav­ing a Bayer ar­ray lter, like loss of de­tail. The op­ti­cal low-pass lter is also not needed in a Foveon sen­sor, which means the sen­sor can cap­ture a high amount of de­tail.

How­ever, Foveon sen­sors can have prob­lems with color ac­cu­racy, due to pos­si­ble color con­tam­i­na­tion within the stacked pho­to­di­odes. Be­cause more light is ab­sorbed by the stacked pho­to­di­odes, a Foveon sen­sor can also be prone to im­age noise in low-light shoot­ing.

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A Bayer Ar­ray color fil­ter.

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