vlfeat 的 sift 函数中这个角度参数是什么意思？
what is the meaning of this angle parameter in vlfeat's sift function?
我想知道输出参数angles是什么，为什么angle的长度是4？
查看 original paper 第 5 部分。方向分配：
An orientation histogram is formed from the gradient orientations of sample points within a region around the keypoint [...] Peaks in the orientation histogram correspond to dominant directions of local gradients. The highest peak in the histogram is detected, and then any other local peak that is within 80% of the highest peak is used to also create a keypoint with that orientation. Therefore, for locations with multiple peaks of similar magnitude, there will be multiple keypoints created at
the same location and scale but different orientations.
VLFeat 实现也解释了这一点（参见sift.c）：
This histogram is then smoothed and the maximum is selected. In
addition to the biggest mode, up to other three modes whose amplitude
is within the 80% of the biggest mode are retained and returned as
additional orientations.
我想知道输出参数angles是什么，为什么angle的长度是4？
查看 original paper 第 5 部分。方向分配：
An orientation histogram is formed from the gradient orientations of sample points within a region around the keypoint [...] Peaks in the orientation histogram correspond to dominant directions of local gradients. The highest peak in the histogram is detected, and then any other local peak that is within 80% of the highest peak is used to also create a keypoint with that orientation. Therefore, for locations with multiple peaks of similar magnitude, there will be multiple keypoints created at the same location and scale but different orientations.
VLFeat 实现也解释了这一点（参见sift.c）：
This histogram is then smoothed and the maximum is selected. In addition to the biggest mode, up to other three modes whose amplitude is within the 80% of the biggest mode are retained and returned as additional orientations.