python - sift算法颜色不变吗？

Question

我将使用 sift 来识别某种类型的对象，如果该对象的颜色发生变化，它能识别出来吗？我将使用 opencv 库进行筛选 cv2.xfeatures2d.SIFT_create()

Answer 1

SIFT 仅对灰度图像进行操作。在 Lowe's 的结论中paper ，他指出:

The features described in this paper use only a monochrome intensity image, so further distinctiveness could be derived from including illumination-invariant color descriptors (Funt and Finlayson, 1995; Brown and Lowe, 2002).

OpenCV implementation在提取特征之前将彩色图像转换为灰度图像。

static Mat createInitialImage( const Mat& img, bool doubleImageSize, float sigma )
{
    /* ... */
    Mat gray, gray_fpt;
    if( img.channels() == 3 || img.channels() == 4 )
    {
        cvtColor(img, gray, COLOR_BGR2GRAY);
        gray.convertTo(gray_fpt, DataType<sift_wt>::type, SIFT_FIXPT_SCALE, 0);
    }
    else
        img.convertTo(gray_fpt, DataType<sift_wt>::type, SIFT_FIXPT_SCALE, 0);
    /* ... */
}