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

Question

lee rama 2017-5-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/339971-i-got-wrong-result-when-i-read-some-bitmap-file

评论： lee rama 2017-5-15

readbmp.zip

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 =
131  226  227  224  221
  0  163  172  177  176
194  192  191  155  102
178   98   47   34   51
142   62   22   19   34
g =
160    0  163  168  171
  0  197  203  206  203
215  209  204  167  112
182  139   64   20    8
164   82   40   38   50
b =
178    0  198  202  203
 45  222  224  224  220
  0  163  165  165  131
209  165   88   40   29
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
168  171  170  166  169
172  177  176  172  131
165  165  131  78  45
139  64  20  8  27
142  62  22  19  34
g
202  203  201  197  201
203  206  203  199  160
192  191  155  102  72
165  88  40  29  48
164  82  40  38  50
b
227  224  221  218  226
224  224  220  216  178
209  204  167  112  83
178  98  47  34  51
177  89  44  36  47