Class Note for OPTI 696D at UA
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This 35 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 16 views.
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Date Created: 02/06/15
VJDI Id39S Larg nvelLDrI of c momma an 5910199 What is Machine Vision The merging of imaging and computing Collecting data analysis and making a decision based on image information mom san wumpammmnmnz llll gmens Where 5 Mac ne on Used mom san wumpammmnmnz Ill gmens Where is Machine Vision Used soudo Emsnpm punmpa mrmaog ma Where is Machine Vision Used mag 2 an punmp mew 103 mo II gmum Where is Machine Vision Used Biometrics mac mtisnpu mnmpa mmaoo vooz an gmgnsi e is Machine Vision Used sauclO ramser nunmni mamas vooz What is Machine Vision Used for Dimensional Measurement Part Presence Defect Detection Sorting Part Orientation mom san wumpammmnmnz llll gmens Turning the Application into a Speci cation Determine the fundamental parameters of an imaging system Determine the required image quality Design a solution mom san wumpammmnmnz llll gmens Fundamental Parameters of an Imaging System Field of View How much do you need to see Working Distance How much clearance do you need Why not Mag Wailing mum sum mum anpi wmanomnz Km mmn ll Edmemi Image Quality Resolution 3 Depth of Field quot Distortion L 39 erspectiv soudo lelJlsnpuI punwpa lu lmdoo 17002 These 5 p kfaitleters define the Ithage quality IBII How Much Image Quality is Necessary An imaging system should create sufficient image quality to allow one to extract desired information about the object from the image Note that what may be adequate image quality for one application may prove inadequate in another mom san wumpammmnmnz llll 591mm How Do We Define Resolution SENSOR SENSOR 4 Pixels LENS OBJECT LinePair Resolution is a measurement of the smallest discernable feature Note software people often define in Pixel density Optical people define in Ipmm all 13901939 soudo EUISHPW puma lHWdOO vooz How Do We Use Object Space and Image Space Resolution Object Space resolution defines the size elements in the object that can be resolved Image space resolution is the resolution at the image plane CCD sensor Image space resolution and object resolution are related by the Primary Magni cation PMAG Image Space Resolution pm Object Space Resolutionij PMAG Object Space Resolutionlpmm PMAG x Image Space Resolutionlpmm Image Space Resolution is a combination of the Lens resolution and the camera resolution Camera resolution pm 2 x Pixel Sizeij resolution is always defined by pairs saldolmlsnpul wumpammmnmnz ll gmens Converting Resolution Resolutionuml1000 Resolutionmm 1Resolutionmm Resolutionlplmm llll gmens As you know from earlier lectures resolution is actually described at a specific contrast value and can be plotted out as MTF mom san wumpammmnmnz Illl gmens How Do We Define Contrast Contrast defines the separation of intensity of blacks and whites o Contrast max Imin ImagingPixels39 I I V 4 max 11 White Square Wuve I 1 Black soudo lewsnpul Punwpa NEHWOO vooz an gmwg Example of Contrast in Imaging Red and green pills back lit viewed on BampW camera Red pills are on the ends green are in the middle Sampllng Area quot quot9 quotquot3 045 f1 155 u 156 A A A A A u 75 Gaysrale mm a soudo 2 an punmp m uxdoo m0 With a green filter on the lens II 99399 Example of the Need for High Contrast across the Field Cosinetothefourth fall off for any lens the relative intensity of any portion of the image will be limited to a cosine 40 where 0 is the the chief ray angle RI45 25 RI235 70 mom san wumpammmnmnz llll gmens Relative Contrast Two lenses the one on the right has a near zero degree chief ray angle and no fall off the on the left has a 235 Degree chief ray angle and ahout a 70 relative intensity ara MT F Le less than modulation gures to ye with the spectrum 0 My during blooming s fer efficiency and cm TF dependina upon Io llll gmens mom san wumpammmnmnz Relative Contrast Cont Same images it you make them binary with a 140 count threshold am MT F Le less tha modulation gures fox 9 with the spectrum 0 idly during blooming s d er efficiency and cm TF depending unon lo 5 35 Ill gmen mom san wumpammmnmnz Defining Depth of Field The depth of field DOF of a lens is its ab to maintain a desired amount of image quality as the object is moved from best locus pos on DOF also appl s to objects with depth since a lens with high DOF will allow the whole object to be imaged clearly As the object is moved either closer or further than the working distance both contrast and resolution suffer The amount of depth must be de ned at both a contrast and a resolution mom san wumpammmnmnz Depth of Field Cont DOF is often calculated using diffraction limlt however this is often flawed if the lens is not working at the diffraction limit Increasing the F t 39 crease the depth of field may limit the overall resolution of the imaging system Therefore the application constraints must be considered An alternative to calculating DOF is to test it for the specific resolution and contrast for an application mom san wumpammmnmnz How Do We Test Depth of Field By placing a target at an angle toward from the optical axis you can measure the depth of field directly Choose the frequency of the target to match the resolution you are defining the DoF at remember there is a sine factor between what is on the face of the target and what is in the plane of the image To the left is an image of DOF test target object 5 space resolution being tested is 15 lpmm at a m contrast of less than K N Dow 10 350 I 15mm I 15lpmm zoo We can either see visually where the image blurs out or we can look ml at a line spread function and calculate contrast from the grayscale values Ell solido lE HiShPUI punwpa NEHdoc vooa Defining Distortion ADPD x 1 on PD Distortion o39oooooooob39o vdoeeeeoebb Above is an example of negative distortion AD is Actual Distance that an image point is from center of the field PD is the Predicted Distance that an image point would be from the center of the field if no distortion were present solldo lewsnpul punrupa ru uldog 7002 II 319199 Distortion Continued Distortion is a misplacing of image information Very little information is lost so the information can be remapped to the proper location in software to correct the error mom san wumpammmnmnz llll gmens Defining Perspective error Perspective error also called parallax is change in magnification with a change in working distance Conventional Lens Telecenlriclens 0 This is how we perceive distance with our eyes i 0 Though useful for perceiving distance this is harmful when trying to make measurements Telecentric lenses are designed to minimize perspective error oUnlike distortion information is lost and can not be corrected with software soudo lewsnpul punpr MESHdos 17003 II Edema An Example of Telecentric Error Test piece is the depth of field target looking at the paral I IInes running down the 45 degree target The right side w II he farthest from the camera Telecentricity is demonstrated hy the line converging as they get farther from the lens llll gmens mom san wumpammmnmnz Measurement With a Telecentric Lens ma mamas vooz Measurement with a Conventional Lens mamas vooz Prospective error Edmund Where Does Perspective Error Come From chief ray angle The chief ray angle will determine how much the eld of view grows as the working distance increases mom san WM llll gmens Telecentric Lens In a telecentric lens the stop is projected to in nity which causes all the chief rays to he parallel to the optical axis By placing the stop a focal length away from you front lens group it will he projectedTout at in nity 4 mom san wumpammmnmnz Illl Edm ns Symmetric blurring Because the defocus will blur symmetrically around the parallel chief rays finding edges and centers of holes becomes more accurate with a telecentric lens mom san wumpammmnmnz llll gmens Limitations of a Telecentric Lens Due to the need for the chief ray angles to be parallel the front lens group must be larger than the object mom san wumpammmnmnz llll gmens The Engineer can find an imaging solution once they have translated the application into specifications that they can design to The speci cations we use are the Field of View Working Distance Resolution Contrast Depth of Field Distortion and Perspective Error mom san wumpammmnmnz Illl gmens
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