Segment extraction from an image in any direction

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Alejandro 2014-7-4

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https://ww2.mathworks.cn/matlabcentral/answers/140190-segment-extraction-from-an-image-in-any-direction

评论： Alejandro 2014-7-5

Hi, i'm trying to extract a segment from an image in any direction. Suppose i have an 800X600 image (RGB) and i want to read a segment from point A(500,200) to point B(300,600). Is there any way i can get a column vector which contains the pixels values in that "diagonal"? i think it has to be some sort of interpolation between the nearest pixels. I don´t want to rotate the image, i need the values as they are. Regards.

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Image Analyst 2014-7-4

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Yes. You can use improfile()

x = [200, 600];
y = [500, 300];
values = improfile(grayImage, x, y);

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Image Analyst 2014-7-4

在 MATLAB Online 中打开

Well you need to put some thought into this. You're taking a profile from two points somewhere in the image, right? Now the number of samples taken along that line would not necessarily be the same as the number of rows in the image, would it? Of course not, so you don't want to append the line to the entire original RGB image (the poorly-named "A") like you tried to do. That makes no sense.

You said you need to do lots of these lines: "I need to apply this to a number of images and create a matrix which contains all the vectors from those images" So how can we do that? Well how about we loop over all the images and in the loop we have a call to improfile. On the first image, there is nothing to append to so the first one we just take the profile itself to get started. Only if the loop index if >=2 do we append. So don't you think you'll need to do something like this inside your loop

rgbImage = imread(filenames(k).name); % read kth image.
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
x = [100, 1400];
y = [700, 200];
redValues=improfile(redChannel,x,y,'bicubic');
if k == 1
    redProfiles = redValues;
else
    redProfiles = [redProfiles, redValues];
end

Do the same for the green and blue channels. Then make an RGB image from them like

rgbProfiles = cat(3, redProfiles, greenProfiles, blueProfiles);

If you don't know how to loop over the filenames, see the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Alejandro 2014-7-4

编辑：Alejandro 2014-7-4

在 MATLAB Online 中打开

ok, i did it, but i couldn't initialize an array and display it as the final image. I'm trying to do that because i think the process would be faster. Is that correct?

weel, here's the array %vect_foto = zeros(abs(x(2)-x(1))+1,n2,3); and here is the code.

 lee_archivos2 = dir('*.jpg');
  dimension2 = length(lee_archivos2);
  n2 = dimension2;
  B2 = 1:n2; %B2 es un vector fila
for k=1:n2
ttt=sscanf(lee_archivos2(k).name(7:end),'%ld');
B2(k)=ttt;
end
%disp(B2);
[sorted_array2,orden2] = sort(B2);%B = sort(A) sorts the elements along different dimensions of an array, 
%and arranges those elements in ascending order. a can be a cell array of strings
x = [100, 1400];
y = [700, 200];
%vect_foto = zeros(abs(x(2)-x(1))+1,n2,3);
wbr = waitbar(0,'1','Name','Espere Por Favor',...
            'CreateCancelBtn',...
            'setappdata(gcbf,''canceling'',1)');
setappdata(wbr,'canceling',0)
for j = 1:n2 %recorre número de archivos guardados en el directorio
      ima_read = imread(lee_archivos2(orden2(j)).name); %se lee cada imagen ascendentemente 
      redChannel = ima_read(:, :, 1);
      greenChannel = ima_read(:, :, 2);
      blueChannel = ima_read(:, :, 3);
      redValues=improfile(redChannel,x,y,'bicubic');
      greenValues=improfile(greenChannel,x,y,'bicubic');
      blueValues=improfile(blueChannel,x,y,'bicubic');
if j == 1
    redProfiles = uint8(redValues);
    greenProfiles =  uint8(greenValues);
    blueProfiles = uint8(blueValues);
else
   redProfiles = [redProfiles, redValues];
   greenProfiles =  [greenProfiles, greenValues];
   blueProfiles = [blueProfiles, blueValues];
end
      %Do the same for the green and blue channels. Then make an RGB image from them like
      rgbProfiles = cat(3, redProfiles, greenProfiles, blueProfiles);
      if getappdata(wbr,'canceling')
          break
      end
      waitbar(j/n2,wbr,{sprintf('%g%%Completado',...
              fix(100*(j/(n2))))});
      fclose('all');
      clear ima_read rotate_ima vect1 ttt B2 sorted_array2
end
 delete(wbr);
 %size(rgbProfiles)
imshow(rgbProfiles);

Alejandro 2014-7-5

在 MATLAB Online 中打开

lee_archivos2 = dir('*.jpg');
dimension2 = length(lee_archivos2);
n2 = dimension2;
B2 = 1:dimension2; %B2 es un vector fila
for k=1:n2
ttt=sscanf(lee_archivos2(k).name(7:end),'%ld');
B2(k)=ttt;
end
%disp(B2);
[sorted_array2,orden2] = sort(B2);%B = sort(A) sorts the elements along different dimensions of an array, 
%and arranges those elements in ascending order. a can be a cell array of strings
x = [100, 1400];
y = [700, 200];
wbr = waitbar(0,'1','Name','Espere Por Favor',...
            'CreateCancelBtn',...
            'setappdata(gcbf,''canceling'',1)');
setappdata(wbr,'canceling',0)
cx = zeros(abs(x(2)-x(1))+1,n2);
cy = zeros(abs(x(2)-x(1))+1,n2);
cx2 = zeros(abs(x(2)-x(1))+1,n2);
cy2 = zeros(abs(x(2)-x(1))+1,n2);
cx3 = zeros(abs(x(2)-x(1))+1,n2);
cy3 = zeros(abs(x(2)-x(1))+1,n2);
redValues = zeros(abs(x(2)-x(1))+1,n2);
greenValues = zeros(abs(x(2)-x(1))+1,n2);
blueValues = zeros(abs(x(2)-x(1))+1,n2);
for j = 1:n2 %recorre número de archivos guardados en el directorio
      ima_read = imread(lee_archivos2(orden2(j)).name); %se lee cada imagen ascendentemente 
      redChannel = ima_read(:, :, 1);
      greenChannel = ima_read(:, :, 2);
      blueChannel = ima_read(:, :, 3);
[cx(:,j),cy(:,j),redValues(:,j)]=improfile(redChannel,x,y,'bicubic');
      [cx2(:,j),cy2(:,j),greenValues(:,j)]=improfile(greenChannel,x,y,'bicubic');
      [cx3(:,j),cy3(:,j),blueValues(:,j)]=improfile(blueChannel,x,y,'bicubic');
%if j == 1
  % redProfiles = uint8(redValues);
  % greenProfiles =  uint8(greenValues);
   % blueProfiles = uint8(blueValues);
%else
  % redProfiles = [redProfiles, redValues];
  % greenProfiles =  [greenProfiles, greenValues];
   %blueProfiles = [blueProfiles, blueValues];
%end
 redProfiles = uint8(redValues);
 greenProfiles =  uint8(greenValues);
 blueProfiles = uint8(blueValues);
      %Do the same for the green and blue channels. Then make an RGB image from them like
      rgbProfiles = cat(3, redProfiles, greenProfiles, blueProfiles);
      if getappdata(wbr,'canceling')
          break
      end
      waitbar(j/n2,wbr,{sprintf('%g%%Completado',...
              fix(100*(j/(n2))))});
      fclose('all');
      clear ima_read rotate_ima vect1 ttt B2 sorted_array2
end
 delete(wbr);
imshow(rgbProfiles);

Image Analyst 2014-7-5

That's using the same spacing as the original sampling. You can go higher for more "resolution" though it's just giving you more samples, not necessarily giving more information, or you can use a smaller number if you want a sampling less frequent than you have in the image. It's your choice. Do whatever you want considering the time to process and what you want to do with the final image you're building up.

Alejandro 2014-7-5