ll = dir('lab3pic/*.jpg');
addpath ./lab3pic/
I = imread(ll(1).name);
figure, imshow(I);
type ColorGradients.m

% Compute color gradients, use p order binomial filter, and threshold t

function [Gx,Gy,m] = ColorGradients(I,p,t);

Ir = BiSmooth(I(:,:,1),p);
Ig = BiSmooth(I(:,:,2),p);
Ib = BiSmooth(I(:,:,3),p);
[rx,ry] = Gradient(Ir, p);
[gx,gy] = Gradient(Ig, p);
[bx,by] = Gradient(Ib, p);

cx = rx+gx+bx;
cy = ry+gy+by;

aa = rx.^2 + gx.^2 + bx.^2;
cc = ry.^2 + gy.^2 + by.^2;

tr = aa + cc;

% eigenvalues cannot be bigger than a+c (trace)
ind = find(tr >= t);

Gx = zeros(size(rx));
Gy = zeros(size(rx));
m = zeros(size(rx));

% NEW Vectorized implementation: 2x2 eigenvalues and eigenvectors computed
% directly

%eigenvalues
a = aa(ind);
c = cc(ind);
b = rx(ind).*ry(ind) + gx(ind).*gy(ind) + bx(ind).*by(ind);

D = sqrt((a+c).^2 - 4*(a.*c-b.^2));
lmax = 0.5*((a+c) + D);
% lmin = 0.5*((a(ind)+c(ind)) - D);

% eigenvectors
ex = zeros(length(ind),1);
ey = zeros(length(ind),1);

% zero out low threshold  edges

% ind1 = find(lmax<t);
% lmax(ind1) = 0;      % ignore those points

ind1 = find(lmax>0);
ex(ind1) = 1;
xx = a - lmax;
ind1 = find((lmax>0) & (abs(xx)>=0.00001));

% compute normalized eigenvectors
x = -b(ind1)./xx(ind1);
xd = 1./sqrt(x.^2+1);
ex(ind1) = x.*xd;
ey(ind1) = xd;
ind1 = find((ex.*cx(ind)+ey.*cy(ind))<0);
ex(ind1) = -ex(ind1);
ey(ind1) = -ey(ind1);
m(ind) = sqrt(lmax);
Gx(ind) = ex.*m(ind);
Gy(ind) = ey.*m(ind);



% 
% OLD NON-VECTORIZED VERSION: eigenvalues and eigenvectors computed using
% eig; may be a bit slow due to the sequential nature of the implementation
% 
% Gx1 = zeros(size(rx));
% Gy1 = zeros(size(rx));
% m1 = zeros(size(rx));
% a = rx.^2 + gx.^2 + bx.^2;
% c = ry.^2 + gy.^2 + by.^2;
% b = rx.*ry + gx.*gy + bx.*by;
% length(ind)
% 
% for i=1:length(ind),
%     S = [a(ind(i)) b(ind(i)); b(ind(i)) c(ind(i))];
%     [V,D] = eig(S);
%     if (D(2,2) > D(1,1))
%         m11 = D(1,1);
%         D(1,1) = D(2,2);
%         D(2,2) = m11;
%         e = V(:,1);
%         V(:,1) = V(:,2);
%         V(:,2) = e;
%     end;
%     m1(ind(i)) = sqrt(D(1,1));
%     e = V(:,1)*m1(ind(i));
%     Gx1(ind(i)) = e(1);
%     Gy1(ind(i)) = e(2);
%     if (cx(ind(i))*Gx1(ind(i))+cy(ind(i))*Gy1(ind(i))<0)
%         Gx1(ind(i)) = -Gx1(ind(i));
%         Gy1(ind(i)) = -Gy1(ind(i));
%     end;
% end;
% 
% Gx = Gx1;
% Gy = Gy1;
% m = m1;


[Gx,Gy,m] = ColorGradients(I,2,2);

X =

     1     2     1


c =

     4


X =

     1     2     1


c =

     4


X =

     1     2     1


c =

     4

figure, imagesc(m);
colorbar
figure, imhist(uint8(m))
max(max(m))

ans =

  138.8986

help imthresh

imthresh not found.

Use the Help browser Search tab to <a href="matlab:docsearch imthresh">search the documentation</a>, or
type "<a href="matlab:help help">help help</a>" for help command options, such as help for methods.

help imahes

imahes not found.

Use the Help browser Search tab to <a href="matlab:docsearch imahes">search the documentation</a>, or
type "<a href="matlab:help help">help help</a>" for help command options, such as help for methods.

help images
  Image Processing Toolbox
  Version 6.1 (R2008a) 23-Jan-2008
 
  Image display and exploration.
    <a href="matlab:help colorbar">colorbar</a>       - Display colorbar (MATLAB Toolbox).
    <a href="matlab:help image">image</a>          - Create and display image object (MATLAB Toolbox).
    <a href="matlab:help imagesc">imagesc</a>        - Scale data and display as image (MATLAB Toolbox).
    <a href="matlab:help immovie">immovie</a>        - Make movie from multiframe image.
    <a href="matlab:help implay">implay</a>         - Play movies, videos, or image sequences.
    <a href="matlab:help imshow">imshow</a>         - Display image in Handle Graphics figure.
    <a href="matlab:help imtool">imtool</a>         - Display image in the Image Tool.
    <a href="matlab:help montage">montage</a>        - Display multiple image frames as rectangular montage.
    <a href="matlab:help movie">movie</a>          - Play recorded movie frames (MATLAB Toolbox).
    <a href="matlab:help subimage">subimage</a>       - Display multiple images in single figure.
    <a href="matlab:help warp">warp</a>           - Display image as texture-mapped surface.
 
  Image file I/O.
    <a href="matlab:help analyze75info">analyze75info</a>       - Read metadata from header file of Mayo Analyze 7.5 data set.
    <a href="matlab:help analyze75read">analyze75read</a>       - Read image file of Mayo Analyze 7.5 data set.
    <a href="matlab:help dicomanon">dicomanon</a>           - Anonymize DICOM file.
    <a href="matlab:help dicomdict">dicomdict</a>           - Get or set active DICOM data dictionary.
    <a href="matlab:help dicominfo">dicominfo</a>           - Read metadata from DICOM message.
    <a href="matlab:help dicomlookup">dicomlookup</a>         - Find attribute in DICOM data dictionary.
    <a href="matlab:help dicomread">dicomread</a>           - Read DICOM image.
    <a href="matlab:help dicomuid">dicomuid</a>            - Generate DICOM Unique Identifier.
    <a href="matlab:help dicomwrite">dicomwrite</a>          - Write images as DICOM files.
    dicom-dict.txt      - Text file containing DICOM data dictionary (2007).
    dicom-dict-2005.txt - Text file containing DICOM data dictionary (2005).
    <a href="matlab:help hdrread">hdrread</a>             - Read Radiance HDR image.
    <a href="matlab:help imfinfo">imfinfo</a>             - Information about image file (MATLAB Toolbox).
    <a href="matlab:help imread">imread</a>              - Read image file (MATLAB Toolbox).
    <a href="matlab:help imwrite">imwrite</a>             - Write image file (MATLAB Toolbox).
    <a href="matlab:help interfileinfo">interfileinfo</a>       - Read metadata from Interfile files.
    <a href="matlab:help interfileread">interfileread</a>       - Read images from Interfile files.
    <a href="matlab:help isnitf">isnitf</a>              - Check if file is NITF.
    <a href="matlab:help nitfinfo">nitfinfo</a>            - Read metadata from NITF file.
    <a href="matlab:help nitfread">nitfread</a>            - Read NITF image.
 
  Image arithmetic.
    <a href="matlab:help imabsdiff">imabsdiff</a>      - Absolute difference of two images.
    <a href="matlab:help imadd">imadd</a>          - Add two images or add constant to image.
    <a href="matlab:help imcomplement">imcomplement</a>   - Complement image.
    <a href="matlab:help imdivide">imdivide</a>       - Divide two images or divide image by constant.
    <a href="matlab:help imlincomb">imlincomb</a>      - Linear combination of images.
    <a href="matlab:help immultiply">immultiply</a>     - Multiply two images or multiply image by constant.
    <a href="matlab:help imsubtract">imsubtract</a>     - Subtract two images or subtract constant from image.
    <a href="matlab:help ippl">ippl</a>           - Check for presence of Intel Performance Primitives Library (IPPL).
 
  Spatial transformations.
    <a href="matlab:help checkerboard">checkerboard</a>   - Create checkerboard image.
    <a href="matlab:help findbounds">findbounds</a>     - Find output bounds for spatial transformation.
    <a href="matlab:help fliptform">fliptform</a>      - Flip input and output roles of TFORM structure.
    <a href="matlab:help imcrop">imcrop</a>         - Crop image.
    <a href="matlab:help impyramid">impyramid</a>      - Image pyramid reduction and expansion.
    <a href="matlab:help imresize">imresize</a>       - Resize image.
    <a href="matlab:help imrotate">imrotate</a>       - Rotate image.
    <a href="matlab:help imtransform">imtransform</a>    - Apply 2-D spatial transformation to image.
    <a href="matlab:help makeresampler">makeresampler</a>  - Create resampling structure.
    <a href="matlab:help maketform">maketform</a>      - Create spatial transformation structure (TFORM).
    <a href="matlab:help tformarray">tformarray</a>     - Apply spatial transformation to N-D array.
    <a href="matlab:help tformfwd">tformfwd</a>       - Apply forward spatial transformation.
    <a href="matlab:help tforminv">tforminv</a>       - Apply inverse spatial transformation.
 
  Image registration.
    <a href="matlab:help cpstruct2pairs">cpstruct2pairs</a> - Convert CPSTRUCT to control point pairs.
    <a href="matlab:help cp2tform">cp2tform</a>       - Infer spatial transformation from control point pairs.
    <a href="matlab:help cpcorr">cpcorr</a>         - Tune control point locations using cross-correlation. 
    <a href="matlab:help cpselect">cpselect</a>       - Control Point Selection Tool. 
    <a href="matlab:help normxcorr2">normxcorr2</a>     - Normalized two-dimensional cross-correlation.
 
  Pixel values and statistics.
    <a href="matlab:help corr2">corr2</a>          - 2-D correlation coefficient.
    <a href="matlab:help imcontour">imcontour</a>      - Create contour plot of image data.
    <a href="matlab:help imhist">imhist</a>         - Display histogram of image data.
    <a href="matlab:help impixel">impixel</a>        - Pixel color values.
    <a href="matlab:help improfile">improfile</a>      - Pixel-value cross-sections along line segments.
    <a href="matlab:help mean2">mean2</a>          - Average or mean of matrix elements.
    <a href="matlab:help regionprops">regionprops</a>    - Measure properties of image regions (blob analysis).
    <a href="matlab:help std2">std2</a>           - Standard deviation of matrix elements.
 
  Image analysis.
    <a href="matlab:help bwboundaries">bwboundaries</a>    - Trace region boundaries in binary image.
    <a href="matlab:help bwtraceboundary">bwtraceboundary</a> - Trace object in binary image.
    <a href="matlab:help edge">edge</a>            - Find edges in intensity image.
    <a href="matlab:help hough">hough</a>           - Hough transform.
    <a href="matlab:help houghlines">houghlines</a>      - Extract line segments based on Hough transform.
    <a href="matlab:help houghpeaks">houghpeaks</a>      - Identify peaks in Hough transform.
    <a href="matlab:help qtdecomp">qtdecomp</a>        - Quadtree decomposition.
    <a href="matlab:help qtgetblk">qtgetblk</a>        - Get block values in quadtree decomposition.
    <a href="matlab:help qtsetblk">qtsetblk</a>        - Set block values in quadtree decomposition.
 
  Image enhancement.
    <a href="matlab:help adapthisteq">adapthisteq</a>    - Contrast-limited Adaptive Histogram Equalization (CLAHE).
    <a href="matlab:help decorrstretch">decorrstretch</a>  - Apply decorrelation stretch to multichannel image.
    <a href="matlab:help histeq">histeq</a>         - Enhance contrast using histogram equalization.
    <a href="matlab:help imadjust">imadjust</a>       - Adjust image intensity values or colormap.
    <a href="matlab:help imnoise">imnoise</a>        - Add noise to image.
    <a href="matlab:help medfilt2">medfilt2</a>       - 2-D median filtering.
    <a href="matlab:help ordfilt2">ordfilt2</a>       - 2-D order-statistic filtering.
    <a href="matlab:help stretchlim">stretchlim</a>     - Find limits to contrast stretch an image.
    <a href="matlab:help intlut">intlut</a>         - Convert integer values using lookup table.
    <a href="matlab:help wiener2">wiener2</a>        - 2-D adaptive noise-removal filtering.
 
  Linear filtering.
    <a href="matlab:help convmtx2">convmtx2</a>       - 2-D convolution matrix.
    <a href="matlab:help fspecial">fspecial</a>       - Create predefined 2-D filters.
    <a href="matlab:help imfilter">imfilter</a>       - N-D filtering of multidimensional images.
 
  Linear 2-D filter design.
    <a href="matlab:help freqspace">freqspace</a>      - Determine 2-D frequency response spacing (MATLAB Toolbox).
    <a href="matlab:help freqz2">freqz2</a>         - 2-D frequency response.
    <a href="matlab:help fsamp2">fsamp2</a>         - 2-D FIR filter using frequency sampling.
    <a href="matlab:help ftrans2">ftrans2</a>        - 2-D FIR filter using frequency transformation.
    <a href="matlab:help fwind1">fwind1</a>         - 2-D FIR filter using 1-D window method.
    <a href="matlab:help fwind2">fwind2</a>         - 2-D FIR filter using 2-D window method.
 
  Image deblurring.
    <a href="matlab:help deconvblind">deconvblind</a>    - Deblur image using blind deconvolution.
    <a href="matlab:help deconvlucy">deconvlucy</a>     - Deblur image using Lucy-Richardson method.
    <a href="matlab:help deconvreg">deconvreg</a>      - Deblur image using regularized filter.
    <a href="matlab:help deconvwnr">deconvwnr</a>      - Deblur image using Wiener filter.
    <a href="matlab:help edgetaper">edgetaper</a>      - Taper edges using point-spread function.
    <a href="matlab:help otf2psf">otf2psf</a>        - Convert optical transfer function to point-spread function.
    <a href="matlab:help psf2otf">psf2otf</a>        - Convert point-spread function to optical transfer function.
 
  Image transforms.
    <a href="matlab:help dct2">dct2</a>           - 2-D discrete cosine transform.
    <a href="matlab:help dctmtx">dctmtx</a>         - Discrete cosine transform matrix.
    <a href="matlab:help fan2para">fan2para</a>       - Convert fan-beam projections to parallel-beam.
    <a href="matlab:help fanbeam">fanbeam</a>        - Fan-beam transform.
    <a href="matlab:help fft2">fft2</a>           - 2-D fast Fourier transform (MATLAB Toolbox).
    <a href="matlab:help fftn">fftn</a>           - N-D fast Fourier transform (MATLAB Toolbox).
    <a href="matlab:help fftshift">fftshift</a>       - Reverse quadrants of output of FFT (MATLAB Toolbox).
    <a href="matlab:help idct2">idct2</a>          - 2-D inverse discrete cosine transform.
    <a href="matlab:help ifft2">ifft2</a>          - 2-D inverse fast Fourier transform (MATLAB Toolbox).
    <a href="matlab:help ifftn">ifftn</a>          - N-D inverse fast Fourier transform (MATLAB Toolbox).
    <a href="matlab:help ifanbeam">ifanbeam</a>       - Inverse fan-beam transform.
    <a href="matlab:help iradon">iradon</a>         - Inverse Radon transform.
    <a href="matlab:help para2fan">para2fan</a>       - Convert parallel-beam projections to fan-beam.
    <a href="matlab:help phantom">phantom</a>        - Create head phantom image.
    <a href="matlab:help radon">radon</a>          - Radon transform.
 
  Neighborhood and block processing.
    <a href="matlab:help bestblk">bestblk</a>        - Optimal block size for block processing.
    <a href="matlab:help blkproc">blkproc</a>        - Distinct block processing for image.
    <a href="matlab:help col2im">col2im</a>         - Rearrange matrix columns into blocks.
    <a href="matlab:help colfilt">colfilt</a>        - Columnwise neighborhood operations.
    <a href="matlab:help im2col">im2col</a>         - Rearrange image blocks into columns.
    <a href="matlab:help nlfilter">nlfilter</a>       - General sliding-neighborhood operations.
 
  Morphological operations (intensity and binary images).
    <a href="matlab:help conndef">conndef</a>        - Default connectivity array.
    <a href="matlab:help imbothat">imbothat</a>       - Bottom-hat filtering.
    <a href="matlab:help imclearborder">imclearborder</a>  - Suppress light structures connected to image border.
    <a href="matlab:help imclose">imclose</a>        - Morphologically close image.
    <a href="matlab:help imdilate">imdilate</a>       - Dilate image.
    <a href="matlab:help imerode">imerode</a>        - Erode image.
    <a href="matlab:help imextendedmax">imextendedmax</a>  - Extended-maxima transform.
    <a href="matlab:help imextendedmin">imextendedmin</a>  - Extended-minima transform.
    <a href="matlab:help imfill">imfill</a>         - Fill image regions and holes.
    <a href="matlab:help imhmax">imhmax</a>         - H-maxima transform.
    <a href="matlab:help imhmin">imhmin</a>         - H-minima transform.
    <a href="matlab:help imimposemin">imimposemin</a>    - Impose minima.
    <a href="matlab:help imopen">imopen</a>         - Morphologically open image.
    <a href="matlab:help imreconstruct">imreconstruct</a>  - Morphological reconstruction.
    <a href="matlab:help imregionalmax">imregionalmax</a>  - Regional maxima.
    <a href="matlab:help imregionalmin">imregionalmin</a>  - Regional minima.
    <a href="matlab:help imtophat">imtophat</a>       - Top-hat filtering.
    <a href="matlab:help watershed">watershed</a>      - Watershed transform.
 
  Morphological operations (binary images).
    <a href="matlab:help applylut">applylut</a>       - Neighborhood operations using lookup tables.
    <a href="matlab:help bwarea">bwarea</a>         - Area of objects in binary image.
    <a href="matlab:help bwareaopen">bwareaopen</a>     - Morphologically open binary image (remove small objects).
    <a href="matlab:help bwdist">bwdist</a>         - Distance transform of binary image.
    <a href="matlab:help bweuler">bweuler</a>        - Euler number of binary image.
    <a href="matlab:help bwhitmiss">bwhitmiss</a>      - Binary hit-miss operation.
    <a href="matlab:help bwlabel">bwlabel</a>        - Label connected components in 2-D binary image.
    <a href="matlab:help bwlabeln">bwlabeln</a>       - Label connected components in N-D binary image.
    <a href="matlab:help bwmorph">bwmorph</a>        - Morphological operations on binary image.
    <a href="matlab:help bwpack">bwpack</a>         - Pack binary image.
    <a href="matlab:help bwperim">bwperim</a>        - Find perimeter of objects in binary image.
    <a href="matlab:help bwselect">bwselect</a>       - Select objects in binary image.
    <a href="matlab:help bwulterode">bwulterode</a>     - Ultimate erosion.
    <a href="matlab:help bwunpack">bwunpack</a>       - Unpack binary image.
    <a href="matlab:help makelut">makelut</a>        - Create lookup table for use with APPLYLUT.
 
  Structuring element (STREL) creation and manipulation.
    <a href="matlab:help getheight">getheight</a>      - Get STREL height.
    <a href="matlab:help getneighbors">getneighbors</a>   - Get offset location and height of STREL neighbors
    <a href="matlab:help getnhood">getnhood</a>       - Get STREL neighborhood.
    <a href="matlab:help getsequence">getsequence</a>    - Get sequence of decomposed STRELs.
    <a href="matlab:help isflat">isflat</a>         - True for flat STRELs.
    <a href="matlab:help reflect">reflect</a>        - Reflect STREL about its center.
    <a href="matlab:help strel">strel</a>          - Create morphological structuring element (STREL).
    <a href="matlab:help translate">translate</a>      - Translate STREL.
 
  Texture analysis.
    <a href="matlab:help entropy">entropy</a>        - Entropy of intensity image.    
    <a href="matlab:help entropyfilt">entropyfilt</a>    - Local entropy of intensity image.
    <a href="matlab:help graycomatrix">graycomatrix</a>   - Create gray-level co-occurrence matrix.
    <a href="matlab:help graycoprops">graycoprops</a>    - Properties of gray-level co-occurrence matrix.  
    <a href="matlab:help rangefilt">rangefilt</a>      - Local range of image.  
    <a href="matlab:help stdfilt">stdfilt</a>        - Local standard deviation of image.
 
  Region-based processing.
    <a href="matlab:help poly2mask">poly2mask</a>      - Convert region-of-interest polygon to mask.
    <a href="matlab:help roicolor">roicolor</a>       - Select region of interest based on color.
    <a href="matlab:help roifill">roifill</a>        - Fill in specified polygon in grayscale image.
    <a href="matlab:help roifilt2">roifilt2</a>       - Filter region of interest.
    <a href="matlab:help roipoly">roipoly</a>        - Select polygonal region of interest.
 
  Colormap manipulation.
    <a href="matlab:help brighten">brighten</a>       - Brighten or darken colormap (MATLAB Toolbox).
    <a href="matlab:help cmpermute">cmpermute</a>      - Rearrange colors in colormap.
    <a href="matlab:help cmunique">cmunique</a>       - Eliminate unneeded colors in colormap of indexed image.
    <a href="matlab:help colormap">colormap</a>       - Set or get color lookup table (MATLAB Toolbox).
    <a href="matlab:help imapprox">imapprox</a>       - Approximate indexed image by one with fewer colors.
    <a href="matlab:help rgbplot">rgbplot</a>        - Plot RGB colormap components (MATLAB Toolbox).
 
  Color space conversions.
    <a href="matlab:help applycform">applycform</a>     - Apply device-independent color space transformation.
    <a href="matlab:help hsv2rgb">hsv2rgb</a>        - Convert HSV color values to RGB color space (MATLAB Toolbox).
    <a href="matlab:help iccfind">iccfind</a>        - Search for ICC profiles by description.
    <a href="matlab:help iccread">iccread</a>        - Read ICC color profile.
    <a href="matlab:help iccroot">iccroot</a>        - Find system ICC profile repository.
    <a href="matlab:help iccwrite">iccwrite</a>       - Write ICC color profile.
    <a href="matlab:help isicc">isicc</a>          - True for complete profile structure
    <a href="matlab:help lab2double">lab2double</a>     - Convert L*a*b* color values to double.
    <a href="matlab:help lab2uint16">lab2uint16</a>     - Convert L*a*b* color values to uint16.
    <a href="matlab:help lab2uint8">lab2uint8</a>      - Convert L*a*b* color values to uint8.
    <a href="matlab:help makecform">makecform</a>      - Create device-independent color space transformation structure (CFORM).
    <a href="matlab:help ntsc2rgb">ntsc2rgb</a>       - Convert NTSC color values to RGB color space.
    <a href="matlab:help rgb2hsv">rgb2hsv</a>        - Convert RGB color values to HSV color space (MATLAB Toolbox).
    <a href="matlab:help rgb2ntsc">rgb2ntsc</a>       - Convert RGB color values to NTSC color space.
    <a href="matlab:help rgb2ycbcr">rgb2ycbcr</a>      - Convert RGB color values to YCbCr color space.
    <a href="matlab:help whitepoint">whitepoint</a>     - XYZ color values of standard illuminants.
    <a href="matlab:help xyz2double">xyz2double</a>     - Convert XYZ color values to double.
    <a href="matlab:help xyz2uint16">xyz2uint16</a>     - Convert XYZ color values to uint16.
    <a href="matlab:help ycbcr2rgb">ycbcr2rgb</a>      - Convert YCbCr color values to RGB color space.
 
  Interactive mouse utility functions.
    <a href="matlab:help getline">getline</a>        - Select polyline with mouse.
    <a href="matlab:help getpts">getpts</a>         - Select points with mouse.
    <a href="matlab:help getrect">getrect</a>        - Select rectangle with mouse.
 
  ICC color profiles.
    lab8.icm       - 8-bit Lab profile.
    monitor.icm    - Typical monitor profile.
                     Sequel Imaging, Inc., used with permission.
    sRGB.icm       - sRGB profile.
                     Hewlett-Packard, used with permission.
    swopcmyk.icm   - CMYK input profile.
                     Eastman Kodak, used with permission.
 
  Array operations.
    <a href="matlab:help circshift">circshift</a>      - Shift array circularly (MATLAB Toolbox).
    <a href="matlab:help padarray">padarray</a>       - Pad array.
 
  Image types and type conversions.
    <a href="matlab:help demosaic">demosaic</a>       - Convert Bayer pattern encoded image to a truecolor image.
    <a href="matlab:help dither">dither</a>         - Convert image using dithering.
    <a href="matlab:help gray2ind">gray2ind</a>       - Convert intensity image to indexed image.
    <a href="matlab:help grayslice">grayslice</a>      - Create indexed image from intensity image by thresholding.
    <a href="matlab:help graythresh">graythresh</a>     - Global image threshold using Otsu's method.
    <a href="matlab:help im2bw">im2bw</a>          - Convert image to binary image by thresholding.
    <a href="matlab:help im2double">im2double</a>      - Convert image to double precision.  
    <a href="matlab:help im2int16">im2int16</a>       - Convert image to 16-bit signed integers.    
    <a href="matlab:help im2java">im2java</a>        - Convert image to Java image (MATLAB Toolbox).
    <a href="matlab:help im2java2d">im2java2d</a>      - Convert image to Java BufferedImage.
    <a href="matlab:help im2single">im2single</a>      - Convert image to single precision.     
    <a href="matlab:help im2uint8">im2uint8</a>       - Convert image to 8-bit unsigned integers.
    <a href="matlab:help im2uint16">im2uint16</a>      - Convert image to 16-bit unsigned integers.  
    <a href="matlab:help ind2gray">ind2gray</a>       - Convert indexed image to intensity image.
    <a href="matlab:help ind2rgb">ind2rgb</a>        - Convert indexed image to RGB image (MATLAB Toolbox).
    <a href="matlab:help label2rgb">label2rgb</a>      - Convert label matrix to RGB image.
    <a href="matlab:help mat2gray">mat2gray</a>       - Convert matrix to intensity image.
    <a href="matlab:help rgb2gray">rgb2gray</a>       - Convert RGB image or colormap to grayscale.
    <a href="matlab:help rgb2ind">rgb2ind</a>        - Convert RGB image to indexed image.
    <a href="matlab:help tonemap">tonemap</a>        - Render high dyanmic range image for viewing.
 
  Toolbox preferences.
    <a href="matlab:help iptgetpref">iptgetpref</a>     - Get value of Image Processing Toolbox preference.
    <a href="matlab:help iptsetpref">iptsetpref</a>     - Set value of Image Processing Toolbox preference.
 
  Toolbox utility functions.
    <a href="matlab:help getrangefromclass">getrangefromclass</a> - Get dynamic range of image based on its class.
    <a href="matlab:help iptcheckconn">iptcheckconn</a>      - Check validity of connectivity argument.
    <a href="matlab:help iptcheckinput">iptcheckinput</a>     - Check validity of array.
    <a href="matlab:help iptcheckmap">iptcheckmap</a>       - Check validity of colormap.
    <a href="matlab:help iptchecknargin">iptchecknargin</a>    - Check number of input arguments.
    <a href="matlab:help iptcheckstrs">iptcheckstrs</a>      - Check validity of text string.
    <a href="matlab:help iptnum2ordinal">iptnum2ordinal</a>    - Convert positive integer to ordinal string.
 
  Modular interactive tools.
    <a href="matlab:help imageinfo">imageinfo</a>           - Image Information tool.
    <a href="matlab:help imcontrast">imcontrast</a>          - Adjust Contrast tool.
    <a href="matlab:help imdisplayrange">imdisplayrange</a>      - Display Range tool.
    <a href="matlab:help imdistline">imdistline</a>          - Draggable Distance tool.
    <a href="matlab:help imgetfile">imgetfile</a>           - Open Image dialog box.
    <a href="matlab:help impixelinfo">impixelinfo</a>         - Pixel Information tool.
    <a href="matlab:help impixelinfoval">impixelinfoval</a>      - Pixel Information tool without text label.
    <a href="matlab:help impixelregion">impixelregion</a>       - Pixel Region tool.
    <a href="matlab:help impixelregionpanel">impixelregionpanel</a>  - Pixel Region tool panel.
    <a href="matlab:help imputfile">imputfile</a>           - Save Image dialog box.
    <a href="matlab:help imsave">imsave</a>              - Save Image tool.
 
  Navigational tools for image scroll panel.
    <a href="matlab:help imscrollpanel">imscrollpanel</a>       - Scroll panel for interactive image navigation.
    <a href="matlab:help immagbox">immagbox</a>            - Magnification box for scroll panel.
    <a href="matlab:help imoverview">imoverview</a>          - Overview tool for image displayed in scroll panel.
    <a href="matlab:help imoverviewpanel">imoverviewpanel</a>     - Overview tool panel for image displayed in scroll panel.
 
  Utility functions for interactive tools.
    <a href="matlab:help axes2pix">axes2pix</a>                  - Convert axes coordinate to pixel coordinate.  
    <a href="matlab:help getimage">getimage</a>                  - Get image data from axes.
    <a href="matlab:help getimagemodel">getimagemodel</a>             - Get image model object from image object.
    <a href="matlab:help imagemodel">imagemodel</a>                - Image model object.
    <a href="matlab:help imattributes">imattributes</a>              - Information about image attributes.
    <a href="matlab:help imhandles">imhandles</a>                 - Get all image handles.  
    <a href="matlab:help imgca">imgca</a>                     - Get handle to most recent current axis containing an image.
    <a href="matlab:help imgcf">imgcf</a>                     - Get handle to most recent current figure containing an image.
    <a href="matlab:help imellipse">imellipse</a>                 - Create draggable, resizable ellipse.
    <a href="matlab:help imfreehand">imfreehand</a>                - Create draggable freehand region.
    <a href="matlab:help imline">imline</a>                    - Create draggable, resizable line.
    <a href="matlab:help impoint">impoint</a>                   - Create draggable point.
    <a href="matlab:help impoly">impoly</a>                    - Create draggable, resizable polygon.
    <a href="matlab:help imrect">imrect</a>                    - Create draggable, resizable rectangle.
    <a href="matlab:help iptaddcallback">iptaddcallback</a>            - Add function handle to callback list.
    <a href="matlab:help iptcheckhandle">iptcheckhandle</a>            - Check validity of handle.
    <a href="matlab:help iptgetapi">iptgetapi</a>                 - Get Application Programmer Interface (API) for handle.
    <a href="matlab:help iptGetPointerBehavior">iptGetPointerBehavior</a>     - Retrieve pointer behavior from HG object.
    <a href="matlab:help ipticondir">ipticondir</a>                - Directories containing IPT and MATLAB icons.
    <a href="matlab:help iptPointerManager">iptPointerManager</a>         - Install mouse pointer manager in figure.
    <a href="matlab:help iptremovecallback">iptremovecallback</a>         - Delete function handle from callback list.
    <a href="matlab:help iptSetPointerBehavior">iptSetPointerBehavior</a>     - Store pointer behavior in HG object.
    <a href="matlab:help iptwindowalign">iptwindowalign</a>            - Align figure windows.
    <a href="matlab:help makeConstrainToRectFcn">makeConstrainToRectFcn</a>    - Create rectangularly bounded position constraint function.
    <a href="matlab:help truesize">truesize</a>                  - Adjust display size of image.
 
  Demos.
    <a href="matlab:help iptdemos">iptdemos</a>       - Index of Image Processing Toolbox demos.
 
  See also <a href="matlab:help imdemos">imdemos</a>, <a href="matlab:help imuitools">imuitools</a>, <a href="matlab:help iptformats">iptformats</a>, <a href="matlab:help iptutils">iptutils</a>, <a href="matlab:help medformats">medformats</a>.

help graythresh
 GRAYTHRESH Global image threshold using Otsu's method.
    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].
    GRAYTHRESH uses Otsu's method, which chooses the threshold to minimize
    the intraclass variance of the thresholded black and white pixels.
 
    [LEVEL EM] = GRAYTHRESH(I) returns effectiveness metric, EM, as the
    second output argument. It indicates the effectiveness of thresholding
    of the input image and it is in the range [0, 1]. The lower bound is
    attainable only by images having a single gray level, and the upper
    bound is attainable only by two-valued images.
 
    Class Support
    -------------
    The input image I can be uint8, uint16, int16, single, or double, and it
    must be nonsparse.  LEVEL and EM are double scalars. 
 
    Example
    -------
        I = imread('coins.png');
        level = graythresh(I);
        BW = im2bw(I,level);
        figure, imshow(BW)
 
    See also <a href="matlab:help im2bw">im2bw</a>.

    Reference page in Help browser
       <a href="matlab:doc graythresh">doc graythresh</a>




g = graythresh(uint8(m))

g =

    0.1765



g*255

ans =

    45





length(find(m>10))

ans =

        8623

length(find(m>5))

ans =

       16458

[M,N] = size(m)

M =

   240


N =

   320

M*N

ans =

       76800

length(find(m>45))

ans =

        2162

type NMS2.m

% This is vectorized version

% Non-maximum suppression for a gradient image;
% magnitudes under t are ignored
% returns a binary image where maximal gradient values are non-zero
function [m1] = NMS2(Gx,Gy,m,t);

[M,N] = size(Gx);

% m = sqrt(Gx.^2+Gy.^2);  % magnitude
I1 = find(m<t);
m(I1) = 0;    % zero values under t

[I,J] = find(m>0);
aGx = abs(Gx);
aGy = abs(Gy);

Z = zeros([M,N]);  % binary image

for i=1:size(I),
	if I(i)>1 & I(i)<M & J(i)>1 & J(i)<N
           if Gx(I(i),J(i))>0 
              dx = 1;
           else 
              dx = -1;
           end;
           if Gy(I(i),J(i))>0 
              dy = 1;
           else
	      dy = -1;
           end;

        if aGx(I(i),J(i))>aGy(I(i),J(i)) % x is dominant direction
	   m01 = m(I(i),J(i)+dx);
           m11 = m(I(i)-dy,J(i)+dx);
           m_01 = m(I(i),J(i)-dx);
           m_11 = m(I(i)+dy,J(i)-dx);
           m1 = (aGx(I(i),J(i))-aGy(I(i),J(i)))*m01 + aGy(I(i),J(i))*m11;
           m2 = (aGx(I(i),J(i))-aGy(I(i),J(i)))*m_01 + aGy(I(i),J(i))*m_11;
           mag = m(I(i),J(i))*aGx(I(i),J(i));
           if (mag>m2) & (mag>=m1) 
              Z(I(i),J(i)) = 1;
           end
	else % y is dominant direction
	   m01 = m(I(i)-dy,J(i));
           m11 = m(I(i)-dy,J(i)+dx);
           m_01 = m(I(i)+dy,J(i));
           m_11 = m(I(i)+dy,J(i)-dx);
           m1 = (aGy(I(i),J(i))-aGx(I(i),J(i)))*m01 + aGx(I(i),J(i))*m11;
           m2 = (aGy(I(i),J(i))-aGx(I(i),J(i)))*m_01 + aGx(I(i),J(i))*m_11;
           mag = m(I(i),J(i))*aGy(I(i),J(i));
           if (mag>m2) & (mag>=m1) 
              Z(I(i),J(i)) = 1;
	   end
	end
      end % if
end % for

I1 = find(Z==0);  % only keep points where Z=1
m(I1)=0;
m1 = uint8(m);




m1 = NMS2(Gx,Gy,m,5);
lenght(find(m1>0))
??? Undefined function or method 'lenght' for input arguments of type 'double'.

length(find(m1>0))

ans =

        4976

type Hysteresis.m

% Hysteresis thresholding: keep all points with m>t connected to 
% points with m>t2 (=2.5t)
function [m1] = Hysteresis(m, t)

[L, numc] = bwlabel(m);  
t2 = 2.5*t;

[I,J] = find((L>0) & (m>t2));  % find labeled points with mag>t2
comps = zeros(numc,1);  % initialize comps

for i=1:size(I),        % components with at least one point mag.>t2
  comps(L(I(i),J(i))) = 1;
end

[I,J] = find(L>0);         % find non-zero points
for i=1:size(I),       
  L(I(i),J(i)) = comps(L(I(i),J(i)));  %replace connected components labels
end;
   
m1 = zeros(size(m));     % initialize m
I2 = find(L>0);          % L can be treated as a vector
m1(I2) = m(I2);

% for i=1:numc,    % remove connected components that are too small
%     i, comps(i)
%     if comps(i)>0
%         ind = find(L == i);
%         i, length(ind)
%         if (length(ind) < MinEdgeLen) 
%             comps(i) = 0;
%         end;
%     end;
% end;
        



m2 = Hysteresis(m1,5);
length(find(m2>0))

ans =

        3724

figure, imagesc(m2);
figure, imshow(m2>0);
m2 = Hysteresis(m1,3);
figure, imshow(m2>0);
ind = find(m2>0);


alpha = atan2(Gy(ind),Gx(ind));
figure,hist(alpha,36);
ind2=find(alpha<0);
alpha(ind2) = alpha(ind2)+2*pi;
whos alpha
  Name          Size            Bytes  Class     Attributes

  alpha      4546x1             36368  double              

ei = rint(alpha/10);
??? Undefined function or method 'rint' for input arguments of type 'double'.

ei = round(alpha/10);
ei = round(alpha*18/pi);
max(ei)

ans =

    36

min(ei)

ans =

     0

ind2 = find(ei == 0);
ei(ind2) = 36;
m3(ind) = m(ind);
clear m3
m3 = m(ind);
whos m3 ei
  Name         Size            Bytes  Class     Attributes

  ei        4546x1             36368  double              
  m3        4546x1             36368  double              

h1 = histc(ei,0:36);
sum(h1)

ans =

        4546

figure, stem(h1);
figure, stem(h1);clear h1
max(max(ei))

ans =

    36

max(ei)

ans =

    36


h1(37)
??? Undefined function or method 'h1' for input arguments of type 'double'.

h1
??? Undefined function or variable 'h1'.

h1 = histc(ei,1:36);
whos h1
  Name       Size            Bytes  Class     Attributes

  h1        36x1               288  double              

h1(1)

ans =

    81

h1(36)

ans =

   356

sum(h1)

ans =

        4546

h2 = zeros(size(h1))

h2 =

     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0

for i=1:36,
ind2 = find(ei==i);
h2(i) = sum(m3(ind2));
end;
figure, stem(h2);
figure, stem(h1);
help histc
 HISTC Histogram count.
    N = HISTC(X,EDGES), for vector X, counts the number of values in X
    that fall between the elements in the EDGES vector (which must contain
    monotonically non-decreasing values).  N is a LENGTH(EDGES) vector
    containing these counts.  
 
    N(k) will count the value X(i) if EDGES(k) <= X(i) < EDGES(k+1).  The
    last bin will count any values of X that match EDGES(end).  Values
    outside the values in EDGES are not counted.  Use -inf and inf in
    EDGES to include all non-NaN values.
 
    For matrices, HISTC(X,EDGES) is a matrix of column histogram counts.
    For N-D arrays, HISTC(X,EDGES) operates along the first non-singleton
    dimension.
 
    HISTC(X,EDGES,DIM) operates along the dimension DIM. 
 
    [N,BIN] = HISTC(X,EDGES,...) also returns an index matrix BIN.  If X is a
    vector, N(K) = SUM(BIN==K). BIN is zero for out of range values. If X
    is an m-by-n matrix, then,
      for j=1:n, N(K,j) = SUM(BIN(:,j)==K); end
 
    Use BAR(EDGES,N,'histc') to plot the histogram.
 
    Example:
       histc(pascal(3),1:6) produces the array [3 1 1;
                                                0 1 0;
                                                0 1 1;
                                                0 0 0;
                                                0 0 0;
                                                0 0 1]
 
    Class support for inputs X,EDGES:
       float: double, single
 
    See also <a href="matlab:help hist">hist</a>.

    Reference page in Help browser
       <a href="matlab:doc histc">doc histc</a>

diary