can you plot a image? (line by line or pixel by pixel)

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Fatima prv
Fatima prv 2012-7-17
for this matrix:
>> A=rand(10,7)
>> A=im2bw(A)
Can you write a code like this? And with this method to write an image of the matrix A?(This is a simple form of what is going)
>> for i=1:10
>> for j=1:7
>> imshow(A(i,j))
>> end
>> end
And finally the results are similar to this picture?
>> imshow(A)

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回答（4 个）

Teja Muppirala
Teja Muppirala 2012-7-17
编辑：Teja Muppirala 2012-7-17
One idea would be to use the AlphaData property. This sets the transparency of each pixel:
A = im2bw(rand(10,7));
M = zeros(size(A'));
h = imshow(A, 'InitialMagnification' ,2000);
for n = 1:numel(M);
M(n) = 1;
set(h,'AlphaData',M');
drawnow;
end
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Fatima prv
Fatima prv 2012-7-20
编辑：Fatima prv 2012-7-20
this code has a error :
Warning: Dimensions of AlphaData must be 1x1, or must match CData..
what mean?
Walter Roberson
Walter Roberson 2012-7-20
It means that for no good reason that I can see, Teja transposed M when building it, and transposed again when using it, but that I did not take that into account when I adjusted Teja's code.
A = im2bw(rand(10,7));
M = zeros(size(A'));
h = imshow(A, 'InitialMagnification' ,2000);
for n = 1:size(A,1);
M(:,n) = 1; %corrected line
set(h,'AlphaData',M');
drawnow;
end
I would not have written the code this way myself, but you did specifically ask for the speed up to be against Teja's code.

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Walter Roberson
Walter Roberson 2012-7-17
Yes, it is possible, just very very inefficient. You can create one patch object per pixel, with the edge turned off, and the facecolor set to the pixel color. This is the closest thing MATLAB has to a pixel object.
It might take a few hours to render a single image this way: MATLAB is not designed for efficiency when it comes to having thousands of graphics objects on a single figure.
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Walter Roberson
Walter Roberson 2012-7-17
You would certainly get delays if you used this mechanism ;-)
Fatima prv
Fatima prv 2012-7-17
编辑：Fatima prv 2012-7-17
I write this code, but I can not see where I'm going to put every pixel
A=rand(10,7)
A=im2bw(A)
s=size(A);s=s/2;
for i=1:10
for j=1:7
x=[((-1/7)*s(2))+.5*i (s(2)./7)+.5*i];
y=[((-.1)*s(1))+.5*j (s(1)./10)+.5*j];
image(A(i,j),'XData',x,'YData',y), axis image,
hold on
end
end

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Fatima prv
Fatima prv 2012-7-22
in a image :Can I change data of a pixel ? without drawing all of picture again, and re show only one pixel?
  1 个评论
Walter Roberson
Walter Roberson 2012-7-22
Normally, if you change the CData property of the image, all of the changes show up simultaneously (unless possibly the figure has many many objects in it.)
This behavior can be changed by altering the "erasemode" property of individual graphic objects; see for example the description of erasemode for lines
Images also have erasemode but note that there is no provided method to change only individual pixels, no way to say "change the pixel at (172,48) to green": one can only set the entire CData at once. The erasemode properties of images is more about what should happen if you move or resize or delete the image as a whole.
MATLAB's graphics model is not pixel-oriented. There is no (documented) user-accessible frame buffer.

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Image Analyst
Image Analyst 2012-7-22
Why do you want to do this? Plot one pixel at a time? Your code shows one pixel only, not a whole image with just one pixel in the image changing. Maybe you'd be interested in the FAQ about making a movie of your data: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_a_movie_from_my_MATLAB_figures.3F

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