Convert matrix number into png image

2012 4 15
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Hello i'm new on package "Image Processing Toolbox". I have a matrix of number ( http://dl.dropbox.com/u/59868217/matlab.mat) obtained by this script ( http://dl.dropbox.com/u/59868217/show_im_GR.m) I would be able to convert an image to grayscale or black and white. Possibly in png format.
How can I do ?

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Image Analyst
Image Analyst 2012-4-15

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I looked at your m-file. You get your data like this:
A = fread(fid,size,'*uint16');
img = reshape(A,width,height); %ok-->poi trasponi
Did you know you can get the 2D matrix directly like this:
img = fread(fid, [width, height], '*uint16');
% It will be a 2D array after this.
No reshaping will be necessary. Anyway, to get it into PNG format you have to save it out to disk as a PNG format image file because when it's in MATLAB it's simply an array of numbers and format doesn't really apply.
baseFileName = 'My matrix.png';
fullFileName = fullfile(folderName, baseFileName);
imwrite(img, fullFileName);

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Geppo Batt
Geppo Batt 2012-4-15

0 个投票

but the png file is completely black, while if use figure,image(img);colormap(gray); title(filename); obtained this image : http://dl.dropbox.com/u/59868217/untitled.jpg

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Image Analyst
Image Analyst 2012-4-15
If you look at img in the variable editor, are the values all zero (completely black)? If they are, then how do you get that image with spots?
Geppo Batt
Geppo Batt 2012-4-16
no,the values are reported in the "img" matrix are those in the file .mat http://dl.dropbox.com/u/59868217/matlab.mat than the values are all different zero
Image Analyst
Image Analyst 2012-4-16
I downloaded your mat file and tried it and it was fine. It read the .mat file fine, it displayed fine, and I could write it out and recall a PNG file fine. Here is my code. Does this work for you?
By the way, you should not save "ans" to the .mat file. This is matlab's default variable name. You should accept the output of your operation into some variable with a name and save that - don't just save "ans" itself.
s = load('matlab.mat')
image16 = s.ans;
minValue = min(image16(:))
maxValue = max(image16(:))
imshow(image16, []);
axis on;
impixelinfo;
% Save it out to a PNG file.
imwrite(image16, 'matlab.png');
% Recall the image from the PNG file.
i2=imread('matlab.png');
figure;
imshow(i2, []);
Geppo Batt
Geppo Batt 2012-4-17
ok perfect, thank you very much. you saved me. the last question minvalue and maxvalue what does they for ?
Image Analyst
Image Analyst 2012-4-17
I just called them to see if you had integer or floating point values and if they were in the range 0-255, 0-1, or something else. which might cause me to call mat2gray() or uint8().

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