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題目：實作bitmap的讀取
本程式僅供參考，如欲使用請自便 XD
=================================================================
function [I M] = bmpread(filename)
% open file
fid = fopen(filename, 'r');
if fid == -1
error('File "%s" does not exist.', filename);
end
% reading header
Signature = fread(fid, 2, 'uchar');
if Signature(1) ~= 66 || Signature(2) ~= 77
fclose(fid);
error('Not a bitmap file.');
end
% continue reading header
FileSize = fread(fid, 1, 'uint32');
Reserved = fread(fid, 1, 'uint32');
DataOffset = fread(fid, 1, 'uint32');
Size = fread(fid, 1, 'uint32');
Width = fread(fid, 1, 'uint32');
Height = fread(fid, 1, 'uint32');
Planes = fread(fid, 1, 'uint16');
BitCount = fread(fid, 1, 'uint16');
Compression = fread(fid, 1, 'uint32');
ImageSize = fread(fid, 1, 'uint32');
HorizontalRes = fread(fid, 1, 'uint32');
VerticalRes = fread(fid, 1, 'uint32');
ColorsUsed = fread(fid, 1, 'uint32');
ImportantColors = fread(fid, 1, 'uint32');
% reading color map
if DataOffset > 54
tmp = fread(fid, DataOffset-54, 'uint8');
tmp = reshape(tmp, 4, 2^BitCount)';
tmp(:,4) = [];
ColorMap = fliplr(tmp) / 255;
else
ColorMap = [];
end
% reading bitmap data
if Compression == 0
if BitCount == 1 || BitCount == 4 || BitCount == 8
cmd = sprintf('fread(fid, (FileSize-DataOffset)*8/BitCount,
''ubit%d=>uint8'')', BitCount);
tmp = eval(cmd);
tmp = reshape(flipud(reshape(tmp, 8/BitCount, [])), Width, Height);
Image = rot90(tmp);
elseif BitCount == 16
Image = uint8(zeros(Height, Width, 3));
tmp = fread(fid, (FileSize-DataOffset)/2, 'uint16=>uint16');
tmp = reshape([bitshift(tmp,-10) mod(bitshift(tmp,-5),2^5)
mod(tmp,2^5)]', 3, Width, Height);
tmp = 255 * tmp / (2^5-1); % normalise
tmp = shiftdim(tmp,1); % shift rgb to 3rd dimension
Image(:,:,1) = rot90(tmp(:,:,1));
Image(:,:,2) = rot90(tmp(:,:,2));
Image(:,:,3) = rot90(tmp(:,:,3));
elseif BitCount == 24
Image = uint8(zeros(Height, Width, 3));
tmp = fread(fid, FileSize-DataOffset, 'uint8=>uint8');
tmp = reshape(tmp, 3, Width, Height);
tmp = shiftdim(tmp,1); % shift rgb to 3rd dimension
Image(:,:,1) = rot90(tmp(:,:,3));
Image(:,:,2) = rot90(tmp(:,:,2));
Image(:,:,3) = rot90(tmp(:,:,1));
else
fclose(fid);
error('File type does not support.');
end
else
fclose(fid);
error('Compressed bitmap does not support.');
end
fclose(fid);
if nargout == 0
imshow(Image, ColorMap);
else
I = Image;
M = ColorMap;
end
--
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