MATLAB M x N x 24 array to bitmap

Question

I am working in MATLAB.

I have a an array of M x N and I fill it with 1 or 0 to represent a binary pattern. I have 24 of these "bit planes", so my array is M x N x 24.

I want to convert this array into a 24 bit M x N pixel bitmap.

Attempts like:

test = image(1:256,1:256,1:24);
imwrite(test,'C:\test.bmp','bmp')

Produce errors.

Any help and suggestions would be appreciated.

Answer 1

Let's assume A is the input M x N x 24 sized array. I am also assuming that those 24 bits in each of its 3D "slices" have the first one-third elements for the red-channel, next one-third for the green-channel and rest one-third as blue-channel elements. So, with these assumptions in mind, one efficient approach using the fast matrix multiplication in MATLAB could be this -

%// Parameters
M = 256;
N = 256;
ch = 24;

A = rand(M,N,ch)>0.5; %// random binary input array

%// Create a 3D array with the last dimension as 3 for the 3 channel data (24-bit)
Ar = reshape(A,[],ch/3,3);

%// Concatenate along dim-3 and then reshape to have 8 columns, 
%// for the 8-bit information in each of R, G and B channels
Ar1 = reshape(permute(Ar,[1 3 2]),M*N*3,[]);

%// Multiply each bit with corresponding multiplying factor, which would
%// be powers of 2, to create a [0,255] data from the binary data
img = reshape(Ar1*(2.^[7:-1:0]'),M,N,3); %//'

%// Finally convert to UINT8 format and write the image data to disk
imwrite(uint8(img), 'sample.bmp')

Output -