Transcript スライド 1
Sensory Information Processing Introduction to imaging sensors How the image is recorded electrically? What is the artifact of CCD? How to select the CCD? Camera CCD CCD driver / Signal processing Digital Capture lens What is principal parameter of the lens? What is aberration? What is the image degradation by lenses? How to select the lenses? the Synchronize and CameraHow Sampling is performed? CCD CCD driver / Signal processing Digital Capture lens How to drive the CCD? How the color value is recovered? Measuring the light • History of light measurement – Exposure meter for cameras (Human can not percept absolute amount of the light) Leica MC meter (1954) Contaflex(1935) : world’s first camera with exposure meter Before that.. • Rely on inspiration and experience.. Senoguide Device to measure the amount of light • Transducing energy of light to electricity – Photo diode – Solar cell (similar to photo diode) • Change of resistance according to the light – CdS (sulfureted cadmium) cell – Photo tube • Light displacement, speed, etc.. – So weak, very difficult CdS cell • Change of resistance of sulfureted cadmium (compound semiconductor) – Free electrons are emerged by the light, and conducts electric current well – Wide range of sensitivity – Slow reaction – cheap Inadequate for image sensor CdS cell(2) electrode • Winding CdS area Relative sensitivity Electric current (mA) – Wider width, shorter path Wavelength(nm) ・very good linearity Burn out Voltage (V) phototube(1) • Photoelectric effect – electron is kicked off from metal by photon ephoton metal • Characteristics of photoelectric effect – No electron for the light with longer wavelength than threshold which depends on materials – Number of electron is proportional to the intensity of light phototube(2) • Capturing the electron out from the metal – Material: Ag, Cs, Na, Te, Ga, As – Very high speed of response : up to 10ps •Electron is attracted by electric potential by high voltage Phototube(3) • Very high sensitivity (photomultiplier) •Dynodes (SbCs, AgHg etc.) emit lots of electron by hitting the accelerated electron． •http://en.wikipedia.org/wiki/Photomultiplier photomultiplier(4) • Super-kamiokaNDE (observing facility of http://en.wikipedia.org/wiki/Kamiokande neutrino) • Broken photomultiplier of kamiokaNDE photodiode(1) • Major light sensing device – Photoelectron emerged between p and n semiconductor – No vaccum! history of exposure meter • Solar cell type : require no battery – １９５０ Leica MC meter • CdS type : high sensitivity (but slow) – １９６０ Leica MR meter • Photodiodes – １９７０ Current products 2-D image sensor • How to capture the 2-D distibution of light? Array of sensors? Connecting all sensors each? 2-D image sensors • To reduce the wiring cost, scanning mechanism is necessary Electric signal Camera tube • Magnetic field is used to deflection (scanning) Camera and TV tubes • Magnetic field for scanning Image orthicon CCD (charge coupled device) • Electrostatic effect is used to transfer the electron – Not limited to the imaging device – CCD is the term of the way to transfer the electron – http://en.wikipedia.org/wiki /Charge-coupled_device Aside : delay line (1) • How to delay temporal signal? – “dead time component” Aside : delay line (1) Aside : delay line (1) • Delay line is a memory – Recording information for a short time – No sampling, no quantization Delay line (2) • SAW (surface acoustic wave) filter – http://en.wikipedia.org/wiki/Surface_acoustic_wave Delay line (3) BBD • BBD = Bucket Brigade delay Predecessor of CCD MN3004 Delay line (4) current standard AD converter CPU DA converter RAM • Long time delay for sound, video is based on digital technology CCD types • • • • Full frame Interline transfer Frame transfer Frame interline transfer • http://laser.physics.sunysb.edu/~jose/CCD Info.html • CCD university – http://www.ccd.com/ccdu.html Full frame • While transfer, CCD should be covered • (mechanical shutter is necessary) • High aperture ratio • Easy to manufacture • Commonly used in digital SLR Interline transfer • Most popular • Mechanical shutter is not necessary • Very short exposure is possible • Used in most video cameras Frame transfer • Image is transferred to the storage array quickly Image degradation in CCD • smear – Highlight spreading to the transfer direction (vertical) • blooming – Highlight spreading to the peripherals • Thermal noise – Electron is emerged by the thermal agitation of free electron smear Source of smear mask mask mask mask mask • Imperfect mask of transfer CCD areas, spilling out of electron to the transfer area Anti-blooming • Discarding too much electrons by highlight X-Y address image sensor photodiodes are connected by wire and transistor CMOS transistor is used, therefore, commonly called as CMOS sensor CMOS image sensor JFET type CMOS image sensor • Low power consumption – CCD needs high voltage to attract the electron • Other circuit can be embedded on a chip (usual LSI process is used) – AD converter, image processor can be embedded • Noise was more than CCD – Now it is well improved • Flexibility to access to each pixel Rolling shutter • For most CMOS sensors, exposure timing is varied pixel by pixel – Called “rolling shutter” – If all pixels are exposed simultaneously, it is called “global shutter” Shutter types and image skew Lens shutter （interchanging the lens is not easy) Focal plane shutter （suit for interchanging lens) SLR (single lens reflex) etc. Skew of moving object • Shape of the object is skewed by the varied timing of exposure Ancient example of skew • Lartigue “A.C.F grand prix” World’s most famous example of skew Color image • Sequencial shots of R, G, B – filter wheel • Split R, G, B to three image sensors optically – ３ tubes, 3-CCD • Each pixel is sensitive either R, G or B – Primal color, complementary color – Foveon Filter wheel ３ tubes prism Camera tube lens ３-CCDcamera Each surface in the prism is “interference filter” which consist of transparent materials with different refractive index, and interference of light reflect or transmit the energy of the light without loss. • No loss of light energy, high sensitivity • Color reproduction is good Single CCD R G R G R G R G Cy Ye Cy Ye Cy Ye Cy Ye G B G B G B G B G Mg G Mg G Mg G Mg R G R G R G R G Cy Ye Cy Ye Cy Ye Cy Ye G B G B G B G B Mg G Mg G Mg G Mg G R G R G R G R G Cy Ye Cy Ye Cy Ye Cy Ye G B G B G B G B G Mg G Mg G Mg G Mg Primal color （Bayer pattern) Complementary color • Each pixel of CCD is colored – Primal color ○natural color reproduction – Complementary color ○high light efficiency Color reproduction (2) • Simple method (interpolation) G G G G G G G G G G G G G G R R R G R R R R G R R R R Low resolution G G G R G G G G G • See Fredo Durand and Bill Freeman’s slide – http://groups.csail.mit.edu/graphics/classes/CompPho to07/index2.html – 03_colorInterpCP.ppt