Save an image from a matrix

Question

Federico Fioretti 2022-1-4

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https://ww2.mathworks.cn/matlabcentral/answers/1622225-save-an-image-from-a-matrix

回答： Image Analyst 2022-1-9

Hi. I have a matrix of data type double in matlab. I have to save this matrix as an image in .jpg or .png format, but when i try to save it, the image saved is completely white. I would like the saved image to have a specific colormap as a function of the values of the starting matrix. How can i do? thanks in advance

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Federico Fioretti 2022-1-4

编辑：Federico Fioretti 2022-1-4

I forgot to say that the starting matrix is made of noninteger values.

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Answer 1

Turlough Hughes 2022-1-4

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Here's one way - convert to an 8 bit array with values between 0 and 255 and then save:

I2 = 255*(I - min(I(:))) ./ (max(I(:)) - min(I(:))); %scale values between 0 and 255
I2 = cast(I2,'uint8');
imwrite(I2,'myImage.png')

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Federico Fioretti 2022-1-4

编辑：Federico Fioretti 2022-1-4

Thank you. This is a progress. But i would the pixels of the saved image to have the same values of the elements of the starting matrix. Is this possible?

Furthermore, i would know how can I change the saved image with a different color palette from the grayscale one.

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Answer 2

Image Analyst 2022-1-9

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To save a floating point image as a TIFF format file:

% Create floating point image.
rgbImage = rand (10, 20, 3);
% Image must be single precision.
rgbImage = single(rgbImage);
% Display it.
imshow(rgbImage, 'InitialMagnification', 1000)
axis('on', 'image');
% Create tiff object.
fileName = '_floatingPointImage.tif';
tiffObject = Tiff(fileName, 'w')
% Set tags.
tagstruct.ImageLength = size(rgbImage,1); 
tagstruct.ImageWidth = size(rgbImage,2);
tagstruct.Compression = Tiff.Compression.None;
tagstruct.SampleFormat = Tiff.SampleFormat.IEEEFP;
tagstruct.Photometric = Tiff.Photometric.MinIsBlack;
tagstruct.BitsPerSample = 32;
tagstruct.SamplesPerPixel = size(rgbImage,3);
tagstruct.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tiffObject.setTag(tagstruct);
% Write the array to disk.
tiffObject.write(rgbImage);
tiffObject.close;
% Recall image.
m2 = imread(fileName)
% Check that it's the same as what we wrote out.
maxDiff = max(max(m2-rgbImage)) % Should be zero.