How to save 12 bit PNG images

Hi, I have a grayscale camera that takes 8 and 12 bit images. Im taking images via MATLAB gentl. I noticed that imwrite saves the image as 16-bit PNG files. I was wondering if this affects the intensity for each pixel in the picture someway? Is it ok that it saves as 16 bit image? I notied that my almost maxed out intensity scale (4049 = 12 bit) looks very pale in the saved 16-bit images.

[Jan]

How do you import the images? I do not know "MATLAB gentl". If the image is store in double format, the output should scale the intensities automatically. But perhaps you import the data as UINT16 with the 4 last bit unused?

[Happy PhD]

I basically use the app "Image Acquisition" with the following code. I have a GigE Camera connected to the computer.

% % Calling the camera
vid = videoinput('gentl', 1, 'Mono12');
src = getselectedsource(vid);

% .. + some code to set exposure time and frames etc ...

% % Taking images
start(vid);
img_var = getdata(vid);

% %  Saving image
imwrite(img_var,'image.png')

Answer 1

[Akshay Khadse]

MATLAB scales the image intensity values from 12-bit to 16-bit after it loads a 12-bit image via the following algorithm:

% W contains the the 12-bit data loaded from file. Data is stored in 16-bit unsigned integer
% First 4 bits are 0. Consider 12-bit pixel color value of ABC
% Then W = 0ABC
X = bitshift(W,4); % X = ABC0
Y = bitshift(W,-8); %Y = 000A
Z = bitor(X,Y); %Z = ABCA 
% Z is the variable that is returned by IMREAD.

Please refer to the following MATLAB Answer for more explanation:

https://www.mathworks.com/matlabcentral/answers/93578#answer_102928

However, Please note that this article was originally answerd for MATLAB R2010a. The workaround mentioned might produce different results for later releases.

I am not sure if you can save 12-bit PNGs from MATLAB as the data is internally stored as 16-bit.