In this example MS Paint file was saved as a truecolor BMP file (Paint's default setting), whereas the MATLAB file was saved as a 256 Color Bitmap. 256 Color Bitmaps save a colormap along with the image data; this is why the file size is so much larger. If you go into MS Paint and instead save the image as a 256 Color Bitmap, you will see that the resultant file size is comparable with the MATLAB file. The colormap may be different, however, so the file contents are not exactly the same.
To generate a truecolor BMP from MATLAB, the array containing the image data must be a 3 dimensional RGB array. As an example, the following code will generate from MATLAB the truecolor BMP file that was generated from MS Paint:
for k = 1:3
b(:,:,k) = uint8([128 128 128; 128 128 128; 128 128 128]);
end
imwrite(b, 'imTC.bmp', 'bmp')
