Digital Camera TAVITA SU’A. Overview ◦Digital Camera ◦Image Sensor ◦CMOS ◦CCD ◦Color ◦Aperture ◦Shutter Speed ◦ISO

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Digital Cameras

Digital CameraTavita suaOverviewDigital CameraImage SensorCMOSCCDColorApertureShutter SpeedISODigital CameraAllows images to be captured and stored in a digital format SensorA device that converts an optical image (incoming light) into an electronic signal. Small silicon chip that contain photosensitive diodes called photosites2 TypesCCD (Charge Coupled Device)CMOS (Complimentary Metal Oxide Semiconductor)Both perform similarly in absorbing light photonsConfusion as these photosites are often referred to as pixels, pels or picture elementsCCD (Charge Coupled Device) sensors convert pixel measurements sequentially using circuitry surrounding the sensor. CMOS (Complementary Metal Oxide Semiconductor) sensors convert pixel measurements simultaneously, using circuitry on the sensor itself.4

Image Sensor - CCDAdvantagesMore sensitive to lightProduces better images in low lightProduces images with less noise

DisadvantagesRequires more battery than CMOSMore expensive than CMOSMay suffer vertical smearing on bright light sources

Image Sensor - CMOSAdvantagesRequire less power than CCDCheaper to manufacture

DisadvantagesMore susceptible to noiseLess sensitive to light than CCD photosite is colorblindMost sensors use a filter to get a full color imageLight must be separated and recorded in its primary colorsColor is usually recorded using:Beam SplitterSpinning DiskBayer Filter

Filter in this case is just transparent body that allows only a certain color to pass

7Bayer Filter

Pattern of alternating color filtersBlue and green, then green and red50% green, 25% blue, 25% redOnly requires 1 sensor eye is not equally sensitive to all 3 coloursIt is necessary to create more information about the green pixels to create an image that will be perceived as true color8Bayer Filter

hole or an opening through which light travelsAperture size is referred to in f-stopsIt controls thedepth of field thelens'socal lengthto the diameter of theentrance pupil.Depth of fieldis the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph10Aperture depth of field is the distance of sharp focus in an imageThe wider the aperture, the shallower the depth of filedThe narrower the aperture, the deeper the depth of fieldratioof thelens'socal lengthto the diameter of theentrance pupil.Depth of fieldis distance of sharp focus within an image11Shutter Speedlength of time the digital sensor is exposed to lightA typical shutter speed for photographs taken in sunlight is 1/125th of a second.Very short shutter speeds can be used to freeze fast-moving subjectsLong shutter speeds can be used to blur a moving object12Shutter Speed of sensitivity of thecamerato available lightthe lower the ISO number, the less sensitive to light and vice-versaIncreasing sensitivity adds grain or noise to picturesBest to use lower ISO when there is ample lightincrease the ISO when there is not enough light for the camera to be able to quickly capture an image

ISO rule of thumb is to use a low ISO whenever possible 15ISO

Low light environment with high ISO (1600) rule of thumb is to use a low ISO whenever possible 16Potential Exam QuestionsDiscuss the advantages and disadvantages of CMOS and CCD image sensors.Explain how a bayer filter is used to filter light.What is the function of the aperture? How can it be used to modify images?Which camera function(s) should be adjusted to freeze an object moving at high speeds?What are the effects of increasing camera ISO?If the amount of light in an object scene is raised, how should the camera be adjusted to compensate for it?