Error while changing image bit depth in MATLAB

I'm trying to convert RGB image with some bit depth to BMP image of bit depth 8. here is my code

    a = imread('DSC01684_5.bmp');
    [x,map] = rgb2ind(a,32); 
    imwrite(x,map,'C:\Documents and Settings\Home\Desktop    \DSC01684_5.bmp.','bitdepth', 8);

and I'm getting error like

    ??? Error using ==> imformats>find_in_registry at 507
    Format specifier must be a 1-D character array.

    Error in ==> imformats at 114
        varargout{1} = find_in_registry(fmts, varargin{1});

    Error in ==> imwrite>get_format_from_filename at 550
    fmt_s = imformats(ext);

    Error in ==> imwrite at 389
    format = get_format_from_filename(filename);

is the error in imwrite function or in changing bit depth?

However if i use

    output_filename = 'C:\Documents and Settings\Home\Desktop\DSC01684_5.bmp.'
    imwrite(x, map, output_filename, 'bmp', 'bitdepth', 8);

I'm getting error like

    ??? Error using ==> imagesci\private\writebmp
     Too many input arguments
     Error in ==> imwrite at 429 
     feval(fmt_s.write, data, map, filename, paramPairs{:});

Answer 1

[Jan]

The first error is caused by the trailing dot in "DSC01684_5.bmp.", such that omitting it allows to recognize the file type by the extension.

Because RGB2IND replies an UINT8 for 32 colors, you do not have to specify the bitdepth explicitly:

file = 'C:\Documents and Settings\Home\Desktop\DSC01684_5.bmp'
imwrite(x, map, file);
imfinfo(file)
% >> ... BitDepth: 8

Answer 2

[Walter Roberson]

'bitdepth' only applies to JPEG and PNG formats. There are no supported options for bmp files.

[Chethan]

Please check this image http://s1273.photobucket.com/user/Chethan_tv/media/DSC00947_zps342d216d.png.html This image is 8 bit and BMP format

[Walter Roberson]

imwrite() chooses the depth from the datatype in this situation. It only allows that automatic depth choice to be overridden via the 'bitdepth' option for JPEG and PNG