Convert data on a TIFF image and save it

Hi,

I made some calculations regarding data I use for my research in image analysis.

Since I wanted to have an image that showed the variations of my variable, I transformed my data into values between 0-65535. I can not work with 0-255, because it is a very small range for what my original data is.

My problem is: I tried to create a grayscale image, and save it into a .tiff file. However not only I cannot obtain the file, but the image that MatLab is showing me does not have any variations. Is either all black or all white.

I'm sure my data is correct. I looked into the original variable, and everything is correct. I also looked into the variable that transforms those original data into values between 0-65535. I found several values ranging, primarily, between 10000 and 50000, so everything looks fine.

Does anyone knows how to convert N² data into an image of NxN size and show those variations? Also how to save it, .tiff file to be more specific?

My code up until now, regarding the problem:

% shows my grayscale image

figure;

image(tcrho); %tcrho is my variable, already in 0-65535 scale

colormap(gray(65536); %grayscale colormap

cbh = colorbar('location', 'SouthOutside'); %just location and name of my colorbar

set(cbh, 'Units', 'normal');

text(3.5, -1, 'Densidade crescente', 'Parent', cbh);

%save my image. I need to save several images - that explains the %04d.

rtc = sprintf('rho%04d.tiff',d);

imwrite(tcrho,gray(65536),rtc,'tiff')

Answer 1

[Image Analyst]

What does

whos tcrho

show? I want to know if it's uint16 or double. By the way, you can't have a colormap with 65536 entries in it. Simply display your image like this:

imshow(tcrho, []);

and don't use a colormap at all.

[Haimon]

Whos tcrho shows double.

The imshow function worked well. The image is showing properly.

Now I need to save it as a .tiff format, grayscale, with a colorbar, if possible. Do you know how?

My original code, considering I had created an image with a colorbar was:

rtc = sprintf('rho%04d.tiff',d);

imwrite(tcrho,gray(65536),rtc,'tiff')

What do I substitue gray(65536) for?

Thanks

[Image Analyst]

You have to convert tcrho to uint8. If the range is outside 0-255 then you should call mat2gray:

imwrite(uint8(mat2gray(tcrho)), filename);

[Haimon]

It did not work.

The matrix range is 0-65535. When it saves the file, it shows only black, but the original matrix has values going from 10000 to 50000.

Uint16 worked though, just tried that. Without the mat2gray.

[Walter Roberson]

colormaps larger than 256 are not certain to work in MS Windows.

I would suggest that you use

imwrite( uint16(tcrho(:,:,[1 1 1])), rtc, 'tiff' );

The tcrho(:,:,[1 1 1]) is a short form of repmat(tcrho, 1, 1, 3) which is to say to convert the grayscale to rgb by duplicating the data into all three planes.

[Image Analyst]

Sorry - it turns out mat2gray scales between 0 and 1, not 0 and 255. So if you want a regular 8 bit image, you have to multiply by 255. So if you want a 16 bit image, you have to multiply by 65535.

imwrite(uint8(255*mat2gray(tcrho)), filename);

[Haimon]

Thank you for your help!