关于 VLFeat 的说明可参考：

[1] - VLFeat指南——SIFT检测器和描述子 - 2014.11.20

[2] - 图像检索(1): 再论SIFT-基于vlfeat实现 - 2018.06.13

VLFeat 的参数说明可见：https://www.vlfeat.org/api/sift_8h.html

1. 命令行实现

1.1. 下载编译vlfeat

下载： https://www.vlfeat.org/download.html

Github：https://www.github.com/vlfeat/vlfeat.git

由于 VLFeat 0.9.21 编译后运行 sift 输出的结果为空，这里采用 VLFeat 0.9.20.

wget https://www.vlfeat.org/download/vlfeat-0.9.21.tar.gz
tar -xzvf vlfeat-0.9.21.tar.gz
cd vlfeat-0.9.20
make

即可以在 vlfeat-0.9.20/bin 路径生成 sift 工具.

1.2. Python 调用命令行

Vlfeat sift：https://www.vlfeat.org/man/sift.html

import os 
from PIL import Image 

def vlfeat_sift_extract(img_file, params="--edge-thresh 10 --peak-thresh 1"):
    img_pil = Image.open(img_file).convert('L')
    gray_imgfile = os.path.basename(img_file) + '.pgm'
    img_pil.save(gray_imgfile) 

    #
    sift_file = os.path.basename(img_file) + '.sift'
    cmd_str = "vlfeat-0.9.20/bin/glnxa64/sift {} --output={} {}".format(gray_imgfile, sift_file, params)
    msg = os.system(cmd_str)
    print('[INFO]msg: ', msg)

2. Cyvlfeat 实现

2.1. 安装

Github - menpo/cyvlfeat

Conda 安装(推荐)：

#https://anaconda.org/menpo/cyvlfeat
conda install -c conda-forge cyvlfeat
# 或pip
#pip install cyvlfeat (调用时可能会出错)

2.2. 示例

import numpy as np
from cyvlfeat.sift import sift as vlsift

def vlfeat_sift_extract(img_file):
    img_cv2 = cv2.imread(img_file)
    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY).astype(np.float32)
    kp, des = vlsift(gray, peak_thresh=5.0, compute_descriptor=True, float_descriptors=True)
    sift_vector = kp + des
    #
    sift_file = os.path.basename(img_file) + '.sift'
    np.savetxt(sift_file, np.array(sift_vector), fmt='%0.8f')

3. SIFT 可视化

import numpy as np 
import matplotlib.pyplot as plt 
from PIL import Image 

def vis_sifts(imgfile, locs, circle=True):
    def draw_circle(c,r):
        t = np.arange(0,1.01,.01)*2*np.pi
        x = r*np.cos(t) + c[0]
        y = r*np.sin(t) + c[1]
        plt.plot(x,y,'b',linewidth=2)
    
    plt.figure(figsize=(10, 8))
    img_pil = Image.open(imgfile)
    plt.imshow(img_pil)
    if circle:
        for p in locs:
            draw_circle(p[:2],p[2]) 
    else:
        plt.plot(locs[:,0],locs[:,1],'ob')
    plt.axis('off')
    plt.title('{} sift features'.format(len(locs)))
    plt.show()

参考：vlfeat python