10/19/200611ENGG 167 MEDICAL IMAGINGLecture 9: Thursday Oct. 12Image Processing I Image Types & Linear TransformsReference: Gonzalez, Woods, EddinsDigital Image Processing using MATLAB, Prentice Hall, (2004)2Preparation -Review Imaging Processing Toolbox Help Manual(on your computer)Download NIHImage (Mac) / ImageJ (Windows)(from the web… just do a Google search)Most of the next two lectures are adapted from Textbook by Gonzalez, Woods, EddinsDigital Image Processing using MATLAB, Prentice Hall, (2004)10/19/200623Human light perception is sensitive but not linear Ref: Gonzalez et al, TextGray scale perception is not linear4This leads to ‘optical illusion’ in certain cases Ref: Gonzalez et al, TextGray scale perception is not linearContrast, length, orientation are not entirely linear10/19/200635Image sensors – quantization of light from imagesRef: Gonzalez et al, Text6Grey scale values… humans can discriminate about 128 levels (7 bit digitization needed)Ref: Gonzalez et al, Text25612864321684210/19/200647Enhancing images – Intensity transformsRef: Gonzalez et al, TextNegative transformContrast StretchingLogarithm transform – gamma factorThresholding (upper and lower)8Enhancing images – imadjust transformRef: Gonzalez et al, TextNegative transform of image fg = imadjust(f, [low_in high_in], [low_out high_out], gamma);g = imadjust(f, [0 1], [1 0]); or g = imcomplement(f);10/19/200659Enhancing images – contrast stretching(Radiology: windowing)Ref: Gonzalez et al, TextImage inImage outLow I high ILow I high IImage inImage outLow I high ILow I high IImage inImage outLow I high ILow I high I10Enhancing images – gamma factorRef: Gonzalez et al, TextImage inImage inImage outLow I high ILow I high Igamma = 1Image outLow I high ILow I high Igamma < 1Image inImage outLow I high ILow I high Igamma > 110/19/2006611Enhancing images – Histogram transforms –in paint shop pro…Ref: visible human projectmidtone compressionmidtone expansionHistogram stretch12Enhancing images – Histogram transform (histogram equalization, stretching)h(rk) = nkthe histogram, h, is the number of pixels, n, at each k intensity level, with r being the new scale level ordinate Grey scale values0255# of pixelsGrey scale values2550# of pixelsRef: visible human project10/19/2006713Enhancing images – Histogram processing & resulting transform curvesRef: Gonzalez et al, Text14Enhancing images – Histogram processing & resulting transform curvesRef: Gonzalez et al, TextScanned image ^(text on either side of page is showing through!)Removing this large peak at the top of the intensity range eliminates all this ‘crosstalk’Repeating again on this edge corrects this locally10/19/2006815Enhancing images – Histogram processing global vs local processingRef: Gonzalez et al, Text16Enhancing images – Spatial Filtering & ProcessingRef: Gonzalez et al, Text1) Linear spatial filtering 2) Nonlinear spatial filtering3) Geometric transformations10/19/2006917Spatial Filtering with a filter mask to map the initial image onto a new calculated image Ref: Gonzalez et al, TextSmoothing masks18Spatial Smoothing Filter masks Ref: Gonzalez et al, TextIncreasing mask size “blurs” the image.10/19/20061019Edge enhancement filter masks - LaplacianRef: Gonzalez et al, Text20Edge enhancement filter masks – other derivatives Ref: Gonzalez et al, Text10/19/20061121Image enhancement via multistage processing Ref: Gonzalez et al, Text22Assignments this weekImage Processing with MATLAB: Due Wed. Oct. 18.Download assignement.Choose one Function in MATLAB Image processing toolbox and describe and demonstrate the function, with an example.Options :Dilation and ErosionImage DeblurringColor space transformLinear Filter designRadon TransformSegmentationSomething else…?1) Use an image and show the effect that can be achieved with the MATLAB function. 2) Show when the effect is dominant and when it is not dominant (what are the main control parameters). 3) Include all MATLAB programs in your handed in work, as well as all images Journal Club Presentations: Monday, Oct. 16.Image processing
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