basics (Spring 2015)

Contents

iminfo

info = imfinfo(filename) returns a structure whose fields contain information about an image in a graphics file. filename is a string that specifies the name of the graphics file

clear
close all
filename = '2013_0115_163116AA.JPG';
info = imfinfo(filename);
disp(info)

            Filename: 'C:\Users\jloomis1\Google Drive\ece564\2015\basics20...'
         FileModDate: '16-Jan-2013 22:31:05'
            FileSize: 607096
              Format: 'jpg'
       FormatVersion: ''
               Width: 2048
              Height: 1536
            BitDepth: 24
           ColorType: 'truecolor'
     FormatSignature: ''
     NumberOfSamples: 3
        CodingMethod: 'Huffman'
       CodingProcess: 'Sequential'
             Comment: {}
                Make: 'FUJIFILM'
               Model: 'FinePix6900ZOOM'
         Orientation: 1
         XResolution: 72
         YResolution: 72
      ResolutionUnit: 'Inch'
            Software: 'Digital Camera FinePix6900ZOOM Ver1.00'
            DateTime: '2013:01:15 16:31:16'
    YCbCrPositioning: 'Co-sited'
           Copyright: '    '
       DigitalCamera: [1x1 struct]
       ExifThumbnail: [1x1 struct]

additional fields

which leads us to enter:

disp('info.DigitalCamera');
disp(info.DigitalCamera);
if isfield(info,'GPSInfo')
    disp('info.GPSInfo');
    disp(info.GPSInfo);
end
disp('info.ExifThumbnail');
disp(info.ExifThumbnail);

info.DigitalCamera
                     FNumber: 2.8000
             ExposureProgram: 'Normal program'
             ISOSpeedRatings: 100
                 ExifVersion: [48 50 49 48]
            DateTimeOriginal: '2013:01:15 16:31:16'
           DateTimeDigitized: '2013:01:15 16:31:16'
     ComponentsConfiguration: 'YCbCr'
      CompressedBitsPerPixel: 1.5000
           ShutterSpeedValue: 6
               ApertureValue: 3
             BrightnessValue: 3.1100
           ExposureBiasValue: 0
            MaxApertureValue: 3
                MeteringMode: 'Pattern'
                       Flash: 'Flash fired, no strobe return detection fun...'
                 FocalLength: 9.7000
                   MakerNote: [1x238 double]
             FlashpixVersion: [48 49 48 48]
                  ColorSpace: 'sRGB'
            CPixelXDimension: 2048
            CPixelYDimension: 1536
         InteroperabilityIFD: [1x1 struct]
       FocalPlaneXResolution: 2678
       FocalPlaneYResolution: 2674
    FocalPlaneResolutionUnit: 3
               SensingMethod: 'One-chip color area sensor'
                  FileSource: 'DSC'
                   SceneType: 'A directly photographed image'

info.ExifThumbnail
                    Compression: 'OJPEG'
                    Orientation: 1
                    XResolution: 72
                    YResolution: 72
                 ResolutionUnit: 'Inch'
          JPEGInterchangeFormat: 1102
    JPEGInterchangeFormatLength: 9225
               YCbCrPositioning: 'Co-sited'

imread

A = imread(filename) reads a grayscale or color image from the file specified by the string filename.

rgb = imread(filename);
whos rgb

  Name         Size                  Bytes  Class    Attributes

  rgb       1536x2048x3            9437184  uint8              

imshow

imshow(RGB) displays the truecolor image RGB.

small = imresize(rgb,0.3);
imshow(small);

imcrop

I = imcrop creates an interactive Crop Image tool associated with the image displayed in the current figure, called the target image. The Crop Image tool is a moveable, resizable rectangle that you can position interactively using the mouse.

rect = [637.5  484.5  732  470];
imshow(rgb);
if exist('rect','var')
    out = imcrop(rgb,rect);
    hold on
    x1 = rect(1);
    y1 = rect(2);
    x2 = x1+rect(3);
    y2 = y1+rect(4);
    plot([x1 x2  x2 x1 x1],[y1 y1 y2 y2 y1],'b-','Linewidth',2);
    hold off
else
    [out rect] = imcrop;
    rect
end

Warning: Image is too big to fit on screen;
displaying at 33% 

imwrite

imwrite(A,filename) writes the image A to the file specified by filename in the format specified the file extension.

imwrite(out,'cropped_target.jpg');
imshow(out);

rgb2gray

I = rgb2gray(RGB) converts the truecolor image RGB to a grayscale intensity image I. rgb2gray converts RGB images to grayscale by eliminating the hue and saturation information while retaining the luminance.

g = rgb2gray(out);
imshow(g);

imhist

imhist(I) displays a histogram for the image I above a grayscale colorbar. The number of bins in the histogram is specified by the image type. If I is a grayscale image, imhist uses a default value of 256 bins.

imhist(im2double(g));

graythresh

level = graythresh(I) computes a global threshold (level) that can be used to convert an intensity image to a binary image with im2bw. level is a normalized intensity value that lies in the range [0, 1].

%The graythresh function uses Otsu's method, which chooses the threshold
% to minimize the intraclass variance of the black and white pixels.

level = graythresh(g);
fprintf('threshold %g\n',level);
hold on
plot([level level],[0 1000],'k-','Linewidth',2);
hold off

threshold 0.521569

im2bw

BW = im2bw(g,level);
imshow(BW);

bwconncomp

CC = bwconncomp(BW) returns the connected components CC found in BW. The binary image BW can have any dimension. CC is a structure with four fields.

CC = bwconncomp(~BW);
disp(CC)

    Connectivity: 8
       ImageSize: [471 733]
      NumObjects: 21
    PixelIdxList: {1x21 cell}

labelmatrix

L = labelmatrix(CC) creates a label matrix from the connected components structure CC returned by bwconncomp. The size of L is CC.ImageSize. The elements of L are integer values greater than or equal to 0.

L = labelmatrix(CC);
whos L

  Name        Size              Bytes  Class    Attributes

  L         471x733            345243  uint8              

label2rgb

RGB = label2rgb(L) converts a label matrix into an RGB color image for the purpose of visualizing the labeled regions.

RGB = label2rgb(L);
imshow(RGB);

histogram (integer based)

imhist(g);
hold on
plot([100 100],[0 1000],'k-','Linewidth',2);
plot([170 170],[0 1000],'k-','Linewidth',2);
hold off

simple mask operations

show "inbetween" values;

msk1 = g>100;
msk2 = g<170;
imshow(msk1&msk2);

Published with MATLAB® R2014a