What will be on the midterm CS 178 Spring 2011 Marc Levoy Computer Science Department Stanford University General information Monday 7 9pm Hewlett 200 across the hall from us closed book no notes calculators ok but you won t need them on lectures and assigned chapters in London list of formulas will be provided on exam sheets practice problems in weekly assgns and sections this week 2 attached are some review slides to help you study treat these as a non exhaustive summary of the course look also at the applets and the recap slides in each lecture emphasis will be on the concepts behind the formulas and on the tradeoffs they imply for the photographer Marc Levoy Image formation the laws of perspective pinhole imaging 3 especially natural perspective versus linear perspective tradeoff between aperture size and blur imaging uses lenses Gauss s ray tracing construction be able to draw it tradeoffs between focal length sensor size and FOV changing the focal length vrs changing the viewpoint exposure tradeoffs between aperture shutter speed motion blur and depth of field study Eddy s diagrams tradeoffs that include ISO and noise covered later Marc Levoy Lenses and apertures orange lecture slides and items starred here are fair game for extra credit Q s qualitative understanding of the approximations we make geometrical optics instead of physical optics spherical lenses instead of hyperbolic lenses thin lens representation of thick optical systems paraxial approximation of ray angles the Gaussian lens formula know it and be able to use it changing the focal length vrs changing the subject distance understand lens power and transverse magnification center of perspective ignore the other thick lens terms convex vrs concave lenses real vrs virtual images depth of field formula know its parts how they vary and the tradeoffs they imply hyperfocal distance and how to use it Marc Levoy 4 Practical photographic lenses aberrations without the algebra be able to recognize them by a name or sketch how is each one fixed which are correctable in software which are reducible by stopping down the aperture other lens artifacts be able to recognize them by a name or sketch understand the geometry of vignetting cos4 falloff diffraction sharpness and MTF qualitatively special purpose lenses 5 what are they and what factors do they depend on some of this was covered in the sampling pixels lecture principles not detailed derivations of telephoto zoom Marc Levoy Sampling and pixels frequency representations of images resolution and human perception be able to manipulate FOV dpi retinal arc cycles degree sampling and aliasing what is aliasing when does it happen especially in a camera how can aliasing be avoided prefiltering vrs postfiltering definition and uses of spatial convolution understand the integral and summation forms of this equation be able to work out a simple convolution like two rects no calculus manipulations will be required on the exam 6 sampling versus quantization understand how aliasing differs from quantization artifacts Marc Levoy Autofocus AF view cameras understand eliminating vanishing points understanding tilting the focal plane understand real versus fake tilt shift effects passive autofocus techniques understand the principle of phase detection understand the principle of contrast detection when are they used what are the tradeoffs don t worry about the details of lenslets ray geometry etc active autofocus techniques tradeoffs between time of flight and triangulation be able to manipulate the geometry of triangulation at least for right angle triangles 7 Marc Levoy Automatic exposure metering AE what makes metering hard understand qualitatively the dynamic range problem gamma transforms what is it when is it applied what effect does it have when can you compare intensity levels in image files metering technologies what problems are caused by having few metering zones tradeoffs between typical shooting modes A P Av Tv M 8 Marc Levoy Image stabilization IS what are the causes of camera shake treating camera shake as a 2D convolution of the image and how can you avoid it without having an IS system understand the geometry of this approximation image stabilization systems be able to define mechnical optical electronic IS understand the principles of lens shift vrs sensor shift IS understanding the ray geometry in detail is not required how much does stabilization help what is lucky imaging and how can a photographer use it 9 Marc Levoy Photons and sensors basic concepts qualitatively photons quantum efficiency blooming smearing analog to digital conversion relationship of gamma transforms to of bits required don t worry about specific circuits how does aliasing and filtering apply to a digital camera fill factor per pixel microlenses antialiasing filters be able to explain how exposure time is a temporal prefilter color sensing technologies be able to recognize them from a name or sketch tradeoffs between the technologies qualitatively what is demosaicing 10 Marc Levoy Noise and ISO what are the sources of noise in digital cameras be able to recognize them by a name or description which ones grow with exposure time or with temperature which ones can be fixed in software benefit of downsizing an image or averaging multiple shots signal to noise ratio and dynamic range be able to apply the formulas correctly we ll give you a list ISO what is it and how is it implemented in digital cameras tradeoffs between ISO and noise study Eddy s diagram from the image formation lecture 11 Marc Levoy List of important formulas will be replicated on exam sheets f N A xi xt DTOT sin i sin t nt ni 1 1 1 so si f MT yi si yo so FOV 2 arctan h 2 f 12 2NCU 2 f2 f2 U H NC SNR dB 20 log10 SNR DR P Qe t P Qe t D t N r2 saturation level D t D t N r2 Marc Levoy