MATLAB

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MATLAB

• Image Processing Toolbox

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Introduction

• Collection of functions (MATLAB files) that
  supports a wide range of image processing
  operations
• Documentation
• www.mathworks.com

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Read an Image

• Read in an image
• Validates the graphic format
• (bmp, hdf, jpeg, pcx, png, tiff, xwd)
• Store it in an array
• clear, close all
• I imread(pout.tif)
• X, map imread(pout.tif)

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Display an Image

• imshow(I)

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Check the Image in Memory

• lt Name, Size, Bytes, Class gt
• whos
• Name Size Bytes Class
• ans 291x240 69840 uint8 array
• Grand total is 69840 elements using 69840 bytes

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Histogram Equalization

• Histogram distribution of intensities
• figure, imhist(I)
• Equalize Image (contrast)
• I2 histeq(I)
• figure, imshow(I2)
• figure, imhist(I2)

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Histogram Equalization (cont.)
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Histogram Equalization (cont.)
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Write the Image

• Validates the extension
• Writes the image to disk
• imwrite(I2, pout2.png)
• imwrite(I2, pout2.png, BitDepth, 4)

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Morphological Opening

• Remove objects that cannot completely contain a
  structuring element
• Estimate background illumination
• clear, close all
• I imread(rice.tif)
• imshow(I)
• background imopen(I, strel(disk, 15))
• imshow(background)

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Morphological Opening (cont.)
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Subtract Images

• Create a more uniform background
• I2 imsubtract(I, background)
• figure, imshow(I2)

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Adjust the Image Contrast

• stretchlim computes low hight to be mapped into
  bottom top
• I3 imadjust(I2, stretchlim(I2), 0 1)
• figure, imshow(I3)

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Apply Thresholdingto the Image

• Create a binary thresholded image
• Compute a threshold to convert the intensity
  image to binary
• Perform thresholding creating a logical matrix
  (binary image)
• level graythresh(I3)
• bw im2bw(I3, level)
• figure, imshow(bw)

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Apply Thresholdingto the Image (cont.)
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Labeling Connected Components

• Determine the number of objects in the image
• Accuracy
• (size of objects, approximated background,
  connectivity parameter, touching objects)
• labeled, numObjects bwlabel(bw, 4)
• numObjects 80
• max(labeled())

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Select and DisplayPixels in a Region

• Interactive selection
• grain imcrop(labeled)
• Colormap creation function
• RGB_label label2rgb(labeled,
• _at_spring, c, shuffle)
• imshow(RGB_label)
• rect 15 25 10 10
• roi imcrop(labeled, rect)

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Object Properties

• Measure object or region properties
• graindata regionprops(labeled, basic)
• graindata(51).Area 296
• graindata(51).BoundingBox 142.5 89.5 24.0
  26.0
• graindata(51).Centroid 155.3953 102.1791
• Create a vector which holds just one property for
  each object
• allgrains graindata.Area
• whos

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Statistical Propertiesof Objects

• max(allgrains) 695
• Return the component label of a grain size
• biggrain find(allgrains 695) 68
• Mean grain size
• mean(allgrains) 249
• Histogram (bins)
• hist(allgrains, 20)

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Statistical Propertiesof Objects (cont.)
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Storage Classes

• double (64-bit), uint8 (8-bit), and uint16
  (16-bit)
• Converting (rescale or offset)
• double
• im2double (automatic rescale and offsetting)
• RGB2 im2uint8(RGB1)
• im2uint16
• imapprox (reduce number of colors indexed
  images)

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Image Types

• Index
• Data matrix (uint8, uint16, double)
• Colormap matrix (m x 3 array of double 0 1)
• Intensity (black 0, white ?)
• Binary (0, 1)
• B logical(uint8(round(A))) (logical flag on)
• B A (logical flag off)
• RGB (m x n x 3 of truecolor)

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Converting Image Types

• dither
• gray2ind
• grayslice
• im2bw
• ind2gray

• ind2rgb
• mat2gray
• rgb2gray
• rgb2ind

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Multiframe Image Arrays

• Same size, planes, colormap
• Store separate images into one multiframe array
• A cat(4, A1, A2, A3, A4, A5)
• Extract frames from a multiframe array
• FRM3 MULTI(, , , 3)
• Display a frame
• imshow(MULTI(, , , 7))

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Image Arithmetic

• imabsdiff
• imadd
• imcomplement
• imdivide

• imlincomb
• immultiply
• imsubtract

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Adding Images

• I imread(rice.tif)
• J imread(cameraman.tif)
• K imadd(I, J)
• imshow(K)
• Brighten an image results saturation
• RGB imread(flowers.tif)
• RGB2 imadd(RGB, 50)
• subplot(1, 2, 1) imshow(RGB)
• subplot(1, 2, 2) imshow(RGB2)

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Adding Images (cont.)
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Adding Images (cont.)
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Subtracting Images

• Background of a scene
• rice imread(rice.tif)
• background imopen(rice, strel(disk, 15))
• rice2 imsubtract(rice, background)
• imshow(rice), figure, imshow(rice2)
• Negative values
• imabsdiff

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Subtracting Images (cont.)
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Multiplying Images

• Scaling multiply by a constant
• (brightens gt1, darkens lt1)
• Preserves relative contrast
• I imread(moon.tif)
• J immultiply(I, 1.2)
• imshow(I)
• figure, imshow(J)

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Multiplying Images (cont.)
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Dividing Images (Ratioing)

• I imread(rice.tif)
• background imopen(I, strel(disk, 15))
• Ip imdivide(I, background)
• imshow(Ip, )
• Linear combination only truncates the final
  result
• K imlincomb(.5, I, .5, I2)

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Dividing Images (cont.)
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Coordinate Systems

• Pixel Coordinates
• Discrete unit (integer)
• (r, c)
• ? (1, 1)

• Spatial Coordinates
• Continuous unit
• (x, y)
• ? (0.5, 0.5)

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Non-default Spatial Coordinate System

• A magic(5)
• x 19.5 23.5
• y 8.0 12.0
• image(A, xData, x, yData, y), axis image,
  colormap(jet(25))

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Spatial Transformations

• Map pixel locations in an input image to new
  locations in an output image
• Resizing
• Rotation
• Cropping

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Resizing Images

• Change the size of an image
• I imread(ic.tif)
• J imresize(I, 1.25)
• K imresize(I, 100 150)
• figure, imshow(J)
• figure, imshow(K)

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Resizing Images (cont.)
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Rotating Images

• Rotate an image by an angle in degrees
• I imread(ic.tif)
• J imrotate(I, 35, bilinear)
• imshow(I)
• figure, imshow(J)

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Rotating Images (cont.)
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Cropping Images

• Extract a rectangular portion of an image
• imshow ic.tif
• I imcrop