function?descriptors?=?do_descriptor（octave?...?%?一組的高斯尺度空間
??????????????????????????????????????oframes?...??%?frames?包含關鍵點相關的尺度和主方向
??????????????????????????????????????sigma0?...???%?基本?sigma?值
??????????????????????????????????????S?...????????%?該組的尺度層數
??????????????????????????????????????smin?...?????
??????????????????????????????????????varargin）

for?k=1:2:length（varargin）
	switch?lower（varargin{k}）
??????case?‘magnif‘
????????magnif?=?varargin{k+1}?;
????????
??????case?‘numspatialbins‘
????????NBP?=?varargin{k+1}?;??
????????
??????case??‘numorientbins‘
????????NBO?=?varargin{k+1}?;???
????????
??????otherwise
????????error（[‘Unknown?parameter?‘?varargin{k}?‘.‘]）?;
?????end
end?
??????
???????????????????????????????
num_spacialBins?=?NBP;
num_orientBins?=?NBO;
key_num?=?size（oframes?2）;
%?計算該圖的向量和方向
[M?N?s_num]?=?size（octave）;?%?M?是圖像的高度?N?是圖像的寬度;?num_level?is?the?number?of?scale?level?of?the?octave
descriptors?=?[];
magnitudes?=?zeros（M?N?s_num）;
angles?=?zeros（M?N?s_num）;
%?compute?image?gradients
for?si?=?1:?s_num
????img?=?octave（::si）;
????dx_filter?=?[-0.5?0?0.5];
????dy_filter?=?dx_filter‘;
????gradient_x?=?imfilter（img?dx_filter）;
????gradient_y?=?imfilter（img?dy_filter）;
????magnitudes（::si）?=sqrt（?gradient_x.^2?+?gradient_y.^2）;
%?????if?sum（?gradient_x?==?0）?>?0
%?????????fprintf（‘00‘）;
%?????end
????angles（::si）?=?mod（atan（gradient_y?./?（eps?+?gradient_x））?+?2*pi?2*pi）;
end

x?=?oframes（1:）;
y?=?oframes（2:）;
s?=?oframes（3:）;
%?round?off
x_round?=?floor（oframes（1:）?+?0.5）;
y_round?=?floor（oframes（2:）?+?0.5）;
scales?=??floor（oframes（3:）?+?0.5）?-?smin;

for?p?=?1:?key_num??%對各個關鍵點處理

????s?=?scales（p）;
????xp=?x_round（p）;
????yp=?y_round（p）;
????theta0?=?oframes（4p）;%關鍵點的主方向
????sinth0?=?sin（theta0）?;
????costh0?=?cos（theta0）?;
????sigma?=?sigma0?*?2^（double?（s?/?S））?;
????SBP?=?magnif?*?sigma;
????%W?=??floor（?sqrt（2.0）?*?SBP?*?（NBP?+?1）?/?2.0?+?0.5）;
????W?=???floor（?0.8?*?SBP?*?（NBP?+?1）?/?2.0?+?0.5）;
????
????descriptor?=?zeros（NBP?NBP?NBO）;
????
????%?within?the?big?square?select?the?pixels?with?the?circle?and?put?into
????%?the?histogram.?no?need?to?do?rotation?which?is?very?expensive
????%在大正方形中用高斯加權圓選擇像素點放入方向直方圖中，不需要做昂貴的圖像旋轉
????for?dxi?=?max（-W?1-xp）:?min（W?N?-2?-?xp）
????????for?dyi?=?max（-W?1-yp）?:?min（+W?M-2-yp）
????????????mag?=?magnitudes（yp?+?dyi?xp?+?dxi?s）;?%?當前點（yp?+?dyi?xp?+?dxi）的梯度幅值
????????????angle?=?angles（yp?+?dyi?xp?+?dxi?s）?;??%?當前點（yp?+?dyi?xp?+?dxi）的梯度幅角
%???????????angle?=?mod（-angle?+?theta0?2*pi）;??????%?用關鍵點的主方向調整角度?并且?mod?it?with?2*pi
????????????angle?=?mod（angle?-?theta0?2*pi）;
?????????????dx?=?double（xp?+?dxi?-?x（p））;????????????%?x（p）?是關鍵點的精確位置?（浮點數）.?dx?相對于該關鍵點當前像素的位置
????????????dy?=?double（yp?+?dyi?-?y（p））;????????????%?dy?相對于該關鍵點當前像素的位置
????????????
????????????nx?=?（?costh0?*?dx?+?sinth0?*?dy）?/?SBP?;?%?nx?是旋轉（dx?dy）后的規格化位置?with?the?major?orientation?angle.?this?tells?which?x-axis?spatial?bin?the?pixel?falls?in?
????????????ny?=?（-sint

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????目錄???????????0??2019-02-17?18:18??dosift\
?????文件????????5412??2013-03-14?16:27??dosift\do_descriptor.m
?????文件?????????464??2013-03-14?16:27??dosift\do_diffofg.m
?????文件????????4322??2013-03-14?16:27??dosift\do_extrefine.m
?????文件????????2964??2013-03-14?16:27??dosift\do_gaussian.m
?????文件????????2133??2013-03-14?16:27??dosift\do_localmax.m
?????文件????????2505??2013-03-14?16:27??dosift\do_orientation.m
?????文件????????3838??2013-03-14?16:27??dosift\do_sift.m
?????文件?????????378??2019-02-17?18:24??dosift\run_demo.m
?????文件?????????215??2013-03-14?16:27??dosift\smooth.m