I got wrong result when I read some bitmap file!!!

I want to read bitmap file by fread in Matlab. For some bmp file, the result is correct, but for others, the result is wrong.

Attached are the code, bitmap files and result.doc. For Desert.bmp, the code can get correct result.

The code is following:

A= fopen('wrong.bmp');

type = fread(A,2,'char=>char')'; % BM

size = fread(A,1,'int32'); %The size of the BMP file in bytes

reserved = fread(A,1,'int32');%Reserved

offset= fread(A,1,'int32');%offset

bisize = fread(A,1,'int32'); %the size of this header

width= fread(A,1,'long');%width

height= fread(A,1,'long'); %height

planes = fread(A,1,'int16'); %planes

bitcount = fread(A,1,'int16'); %BitCount

compression= fread(A,1,'int32');%Compression

sizelmage= fread(A,1,'int32'); %The size of bitmap data

xpelspermeter = fread(A,1,'long'); %the horizontal resolution of the image

ypelspermeter= fread(A,1,'long'); %the vertical resolution of the image

clrused= fread(A,1,'int32'); %the number of colors in the color palette

clrlmportant=fread(A,1,'int32');%the number of important colors used

b=zeros(height,width,'uint8');

g=zeros(height,width,'uint8');

r=zeros(height,width,'uint8');

for i=1:height

    for j=1:width

        b(i,j)=fread(A,1,'uint8');

        g(i,j)=fread(A,1,'uint8');

        r(i,j)=fread(A,1,'uint8');

    end

end

%extra pixels for 'test.bmp'

%----------------------------

% t=zeros(1,10);

% for k=1:10

%     t(k)=fread(A,1,'uint8');

% end

%----------------------------

rgb=zeros(height,width,3,'uint8');

rgb(:,:,1)=flipud(r);

rgb(:,:,2)=flipud(g);

rgb(:,:,3)=flipud(b);

imshow(rgb);

///////////////////////////////////////////////////////////////////////////////////////////

However, for test.bmp, a 5*6 image, the result is wrong. The code get r, g, b matrix as follows.

r =

    172  131  226  227  224  221

     72    0  163  172  177  176

      0  194  192  191  155  102

    228  178   98   47   34   51

    193  142   62   22   19   34

g =

    199  160    0  163  168  171

     83    0  197  203  206  203

     27  215  209  204  167  112

      0  182  139   64   20    8

    219  164   82   40   38   50

b =

    216  178    0  198  202  203

     78   45  222  224  224  220

     48    0  163  165  165  131

      0  209  165   88   40   29

    236  177   89   44   36   47

The extra pixels beside r, g, b matrix.

 201  170  218  197  166  226  201  169  0  0

The correct r, g, b matrix as follows.

r

163  168  171  170  166  169

163  172  177  176  172  131

163  165  165  131  78  45

182  139  64  20  8  27

193  142  62  22  19  34

g

198  202  203  201  197  201

197  203  206  203  199  160

194  192  191  155  102  72

209  165  88  40  29  48

219  164  82  40  38  50

b

226  227  224  221  218  226

222  224  224  220  216  178

215  209  204  167  112  83

228  178  98  47  34  51

236  177  89  44  36  47

///////////////////////////////////////////////////////////////////////////////////////////

when read the following bmp file, I will get a wrong result.

the wrong result is folowing

Answer 1

[Matthew Eicholtz]

I suggest using imread instead.

[lee rama]

Thanks Matthew! I know imread, but I just want to see what's the file structure of the bitmap.

What puzzles me is why the bitmap files with the same format have the different file structure?