matlab code for bit map picture

1. function [X,map,out3]=bmpread(filename);
%BMPREAD Read a BMP (Microsoft Windows Bitmap) file from disk.
% [X,MAP]=BMPREAD('filename') reads the file 'filename' and
% returns the indexed image X and associated colormap
% MAP. If no extension is given for the filename, the
% extension '.bmp' is assumed.
% [R,G,B]=BMPREAD('filename') reads the 24-bit BMP file
% from the file 'filename'.
% BPP=BMPREAD('filename') returns the number of bits per
% pixel in the BMP file.
%
% BMPREAD does not read 1-bit or compressed BMP files.
%
% See also: BMPWRITE, GIFREAD, HDFREAD, PCXREAD, TIFFREAD,
% XWDREAD.
% Mounil Patel 3/10/94
% Revised Steve Eddins February 9, 1995
% Copyright (c) 1994 by The MathWorks, Inc.
% $Revision: 1.14 $ $Date: 1996/06/14 12:39:07 $
if (nargin~=1)
error('Requires a filename as an argument.');
end;
if (isstr(filename)~=1)
error('Requires a string filename as an argument.');
end;
if (isempty(findstr(filename,'.'))==1)
filename=[filename,'.bmp'];

2. end;
fid=fopen(filename,'rb','l');
if (fid==-1)
error(['Error opening ',filename,' for input.']);
end;
bfType=fread(fid,2,'uchar');
if (bfType~=[66;77])
fclose(fid);
error('Not a BMP file.');
end;
bfSize=fread(fid,1,'uint');
bfReserved1=fread(fid,1,'ushort');
bfReserved2=fread(fid,1,'ushort');
bfOffBytes=fread(fid,1,'uint');
biSize=fread(fid,1,'uint');
if (biSize~=40)
fclose(fid);
error('Not a MS Windows Device Independent Bitmap BMP file.');
end;
biWidth=fread(fid,1,'uint');
biHeight=fread(fid,1,'uint');
biPlanes=fread(fid,1,'ushort');
biBitCount=fread(fid,1,'ushort');
if (biBitCount == 1)
error('BMPREAD does not read 1-bit BMP files.');
end
biCompression=fread(fid,1,'uint');

3. if biCompression~=0
error('Can''t load compressed format bitmaps.');
end;
biSizeImage=fread(fid,1,'uint');
biXPels=fread(fid,1,'uint');
biYPels=fread(fid,1,'uint');
biClrUsed=fread(fid,1,'uint');
biClrImportant=fread(fid,1,'uint');
if (nargout <= 1)
X = biBitCount;
map = [];
fclose(fid);
return;
end
if ((nargout == 2) & (biBitCount == 24))
error('Three output arguments required for 24-bit BMP file.');
end
if ((nargout == 3) & (biBitCount < 24))
error('Only two arguments needed for 4- and 8-bit BMP files.');
end
if (biBitCount == 24)
if (rem(biWidth,4)~=0)
XSize=biWidth+(4-rem(biWidth,4));
else
XSize=biWidth;
end
YSize=biHeight;
Size=XSize*YSize;

4. fseek(fid, bfOffBytes, 'bof');
X=fread(fid,Size*3,'uchar');
out3 = rot90(reshape(X(1:3:length(X)), XSize, YSize)) * (1/255);
map = rot90(reshape(X(2:3:length(X)), XSize, YSize)) * (1/255);
X = rot90(reshape(X(3:3:length(X)), XSize, YSize)) * (1/255);
if (rem(biWidth,4)~=0)
X=X(:,1:biWidth);
map = map(:,1:biWidth);
out3 = out3(:,1:biWidth);
end;
fclose(fid);
return;
end
if (biClrUsed==0)
nColors=2.^biBitCount;
else
nColors=biClrUsed;
end;
% load color map now
if (biClrUsed>256)
map=[]; % 24-bit images have no colormap
else
map=fread(fid,4*nColors,'uchar');
map=reshape(map,4,nColors);
map=map';
map=map(:,1:3);
map=fliplr(map);
end;

5. map=map./255;
% read in 8-bit image data
if (biBitCount==8)
if (rem(biWidth,4)~=0)
XSize=biWidth+(4-rem(biWidth,4));
else
XSize=biWidth;
end
YSize=biHeight;
Size=XSize*YSize;
fseek(fid, bfOffBytes, 'bof');
X=fread(fid,Size,'uchar');
X=reshape(X,XSize,YSize);
X=rot90(X);
X=X+1;
if (rem(biWidth,4)~=0)
X=X(:,1:biWidth);
end;
end;
if (biBitCount==4)
XSize=ceil(biWidth/2);
if (rem(XSize,4)~=0)
XSize=XSize+rem(XSize,4);
end;
YSize=biHeight;
Size=XSize*YSize;
fseek(fid, bfOffBytes, 'bof');
X=fread(fid,Size,'uchar');

6. X=reshape(X,XSize,YSize);
X=X';
loX=X;
index=loX>127;
loX(index)=loX(index)-128;
index=loX>63;
loX(index)=loX(index)-64;
index=loX>31;
loX(index)=loX(index)-32;
index=loX>15;
loX(index)=loX(index)-16;
X=X-loX;
X=X./16;
[m,n]=size(X);
X(:,1:2:(n*2))=X;
X(:,2:2:(n*2))=loX;
X=flipud(X);
X=X+1;
end;
cmax=max(max(X));
map=map(1:cmax,:);
fclose(fid);

7. X=reshape(X,XSize,YSize);
X=X';
loX=X;
index=loX>127;
loX(index)=loX(index)-128;
index=loX>63;
loX(index)=loX(index)-64;
index=loX>31;
loX(index)=loX(index)-32;
index=loX>15;
loX(index)=loX(index)-16;
X=X-loX;
X=X./16;
[m,n]=size(X);
X(:,1:2:(n*2))=X;
X(:,2:2:(n*2))=loX;
X=flipud(X);
X=X+1;
end;
cmax=max(max(X));
map=map(1:cmax,:);
fclose(fid);