对于图像聚类或分类等任务，我们通常将图像转换为数字特征向量。现在，我不想为整个图像计算特征向量，而是为图像的片段生成特征（不限于矩形片段）。例如，使用 SLIC 算法 (skimage.segmentation.slic) 我可以将图像分割成超像素。现在我想为每个段生成特征（区域大小、位置、颜色、形状和纹理特征），如 5.3 节所述
古尔德、斯蒂芬等人。 “具有先验相对位置的多类分割。”国际计算机视觉杂志 80.3（2008 年）：300-316。
在给定图像和片段掩码的情况下，python 中是否存在可以帮助我生成这些特征的库？我可以使用 skimage 做到这一点吗？
【问题讨论】：
标签： python opencv image-processing classification scikit-image
对于python，我建议使用fast_slic，尽管只使用CPU，但速度很快。至于访问各个片段，请尝试阅读 Adrian Rosebrock 关于 PyImageSearch 的教程并使用边界框算法来查找您感兴趣的特定 roi。如果您的工作只需要图像本身而不需要零填充，那么您可以尝试 @987654322 @ 以及仅保留跨通道不为零的图像块的条件。
【讨论】：
我不知道有任何此类库。但是，我前段时间需要自己计算特征，您可以在下面找到一些代码 sn-ps。虽然代码不在 Python 中，但它可能对您有所帮助。请注意，我尝试了超体素；因此，您可能会在其中找到一些 PCL 参考。
如果您开始自己实现功能，请查看以下出版物以了解一些想法（两种情况下的表 1）：
Derek Hoiem, Andrew N. Stein, Alexei A. Efros, Martial Hebert:
Recovering Occlusion Boundaries from a Single Image. ICCV 2007: 1-8
Joseph Tighe, Svetlana Lazebnik:
Superparsing - Scalable Nonparametric Image Parsing with Superpixels. International Journal of Computer Vision 101(2): 329-349 (2013)
请注意，并非头文件中的所有定义都实际实现；但是，它们可以作为灵感。
标题：
#ifndef SUPERPIXELFEATURES_H
#define SUPERPIXELFEATURES_H
#include <opencv2/opencv.hpp>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>
#include <Eigen/Dense>
#include <string>
namespace features {
/**
* Class SuperpixelFeatures represents a set of features computed for
* each superpixel in a given image.
*/
class SuperpixelFeatures {
public:
/**
* Construct superpixel features form only an image.
*
* @param image
* @param labels
*/
SuperpixelFeatures(const cv::Mat &image, int** labels);
/**
* Construct superpixel features from the image and its depth and
* a given superpixel segmentation.
*
* @param image
* @param depth
* @param labels
*/
SuperpixelFeatures(const cv::Mat &image, const cv::Mat &depth, int** labels);
/**
* Constructu superpixel features form the image and a point cloud and
* a given superpixel segmentation.
*
* @param image
* @param pointCloud
*/
SuperpixelFeatures(const cv::Mat &image, pcl::PointCloud<pcl::PointXYZ>::Ptr pointCloud, int** labels);
/**
* Destructor.
*/
~SuperpixelFeatures();
/**
* Add maximum color in each channel to the features.
*
* @return
*/
Eigen::Vector2i addMaximumColor();
/**
* Add minimum color in each channel to the features.
*
* @return
*/
Eigen::Vector2i addMinimumColor();
/**
* Add mean color to the features.
*
* @return
*/
Eigen::Vector2i addMeanBGRColor();
/**
* Add mean position to the features.
*
* @return
*/
Eigen::Vector2i addMean3DPosition();
/**
* Add mean position (pixel coordinates) to the features.
*
* @return
*/
Eigen::Vector2i addMean2DPosition();
/**
* Add the surface normal (mean normal) to the features.
*
* @return
*/
Eigen::Vector2i addMeanNormal();
/**
* Add a 3D bounding box of the superpixel to the features.
*
* @return
*/
Eigen::Vector2i addBoundingBox();
/**
* Add the compactness of the superpixel in its 2D sens to the features.
*
* @return
*/
Eigen::Vector2i addCompactness();
/**
* Add the area in pixels to the features.
*
* @return
*/
Eigen::Vector2i addArea();
/**
* Add the color covariance matrix to the features.
*
* @return
*/
Eigen::Vector2i addColorCovariance();
/**
* Add the position covariance matrix to the features.
* @return
*/
Eigen::Vector2i addPositionCovariance();
/**
* Add point-ness, curve-ness and surface-ness to the features.
*
* @return
*/
Eigen::Vector2i addSuperpixelStatistics();
/**
* Add a color histogram of the given number of bins to the features.
*
* @param bins
* @return
*/
Eigen::Vector2i addColorHistogram(int bins);
/**
* Add the ground truth label to the features.
*
* @param labels
* @return
*/
Eigen::Vector2i addGroundTruth(int** labels);
/**
* Get the dimension of the computed features.
*
* @return
*/
int getFeatureDimension() const;
/**
* Get the total number of superpixels.
*
* @return
*/
int getNumberOfSuperpixels() const;
/**
* Get pointer to comptued features.
*
* @return
*/
Eigen::MatrixXd* getFeatures() const;
protected:
void appendFeatures(Eigen::MatrixXd features);
cv::Mat* image;
int height;
int width;
int** labels;
int numberOfSuperpixels;
pcl::PointCloud<pcl::PointXYZ>::Ptr pointCloud;
bool pointCloudAvailable;
Eigen::MatrixXd* features;
};
}
来源：
#include <pcl/features/normal_3d.h>
#include <pcl/features/integral_image_normal.h>
#include "Tools.h"
#include "SuperpixelFeatures.h"
SuperpixelFeatures::SuperpixelFeatures(const cv::Mat &image, int** labels) {
this->image = new cv::Mat();
int channels = image.channels();
assert(channels == 1 || channels == 3);
if (channels == 1) {
image.convertTo(*this->image, CV_8UC1);
}
else if (channels == 3) {
image.convertTo(*this->image, CV_8UC3);
cv::cvtColor(*this->image, *this->image, SEEDS_REVISED_OPENCV_BGR2Lab, 3);
}
this->height = image.rows;
this->width = image.cols;
this->pointCloudAvailable = false;
// Copy labels.
this->labels = new int*[this->height];
for (int i = 0; i < this->height; ++i) {
this->labels[i] = new int[this->width];
for (int j = 0; j < this->width; ++j) {
this->labels[i][j] = labels[i][j];
}
}
this->numberOfSuperpixels = seeds_revised::tools::Integrity::countSuperpixels(this->labels, this->height, this->width);
seeds_revised::tools::Integrity::relabel(this->labels, this->height, this->width);
this->features = new Eigen::MatrixXd(this->numberOfSuperpixels, 1);
// Initialize first column with labels.
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
(*this->features)(label, 0) = label;
}
}
SuperpixelFeatures::SuperpixelFeatures(const cv::Mat &image, pcl::PointCloud<pcl::PointXYZ>::Ptr pointCloud, int** labels) {
assert(image.rows == (int) pointCloud->height);
assert(image.cols == (int) pointCloud->width);
this->image = new cv::Mat();
int channels = image.channels();
assert(channels == 1 || channels == 3);
if (channels == 1) {
image.convertTo(*this->image, CV_8UC1);
}
else if (channels == 3) {
image.convertTo(*this->image, CV_8UC3);
cv::cvtColor(*this->image, *this->image, SEEDS_REVISED_OPENCV_BGR2Lab, 3);
}
this->pointCloud = pointCloud;
this->height = pointCloud->height;
this->width = pointCloud->width;
this->pointCloudAvailable = true;
// Copy labels.
this->labels = new int*[this->height];
for (int i = 0; i < this->height; ++i) {
this->labels[i] = new int[this->width];
for (int j = 0; j < this->width; ++j) {
this->labels[i][j] = labels[i][j];
}
}
this->numberOfSuperpixels = seeds_revised::tools::Integrity::countSuperpixels(this->labels, this->height, this->width);
seeds_revised::tools::Integrity::relabel(this->labels, this->height, this->width);
this->features = new Eigen::MatrixXd(this->numberOfSuperpixels, 1);
// Initialize first column with labels.
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
(*this->features)(label, 0) = label;
}
}
SuperpixelFeatures::~SuperpixelFeatures() {
delete this->image;
for (int i = 0; i < this->height; ++i) {
delete[] this->labels[i];
}
delete[] this->labels;
}
Eigen::Vector2i SuperpixelFeatures::addMeanBGRColor() {
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 3);
double meanB = 0;
double meanG = 0;
double meanR = 0;
int count = 0;
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
meanB = 0;
meanG = 0;
meanR = 0;
count = 0;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
meanB += this->image->at<cv::Vec3b>(i, j)[0];
meanG += this->image->at<cv::Vec3b>(i, j)[1];
meanR += this->image->at<cv::Vec3b>(i, j)[2];
++count;
}
}
}
(*this->features)(label, cols) = meanB/count;
(*this->features)(label, cols + 1) = meanG/count;
(*this->features)(label, cols + 2) = meanR/count;
}
return Eigen::Vector2i(cols, cols + 2);
}
Eigen::Vector2i SuperpixelFeatures::addMean3DPosition() {
assert(this->pointCloudAvailable);
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 3);
double meanX = 0;
double meanY = 0;
double meanZ = 0;
int count = 0;
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
meanX = 0;
meanY = 0;
meanZ = 0;
count = 0;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
meanX += (*this->pointCloud)(j, i).x;
meanY += (*this->pointCloud)(j, i).y;
meanZ += (*this->pointCloud)(j, i).z;
++count;
}
}
}
(*this->features)(label, cols) = meanX/count;
(*this->features)(label, cols + 1) = meanY/count;
(*this->features)(label, cols + 2) = meanZ/count;
}
return Eigen::Vector2i(cols, cols + 2);
}
Eigen::Vector2i SuperpixelFeatures::addMean2DPosition() {
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 2);
double meanX = 0;
double meanY = 0;
int count = 0;
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
meanX = 0;
meanY = 0;
count = 0;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
meanX += j;
meanY += i;
++count;
}
}
}
(*this->features)(label, cols) = meanX/count;
(*this->features)(label, cols + 1) = meanY/count;
}
return Eigen::Vector2i(cols, cols + 1);
}
Eigen::Vector2i SuperpixelFeatures::addMeanNormal() {
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 3);
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
std::vector<int> indices;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
indices.push_back(i*cols + j);
}
}
}
Eigen::Vector4f superpixelCentroid;
Eigen::Matrix3f superpixelCovariance;
Eigen::Vector3f superpixelNormal;
pcl::compute3DCentroid(*pointCloud, indices, superpixelCentroid);
pcl::computeCovarianceMatrix(*pointCloud, indices, superpixelCentroid, superpixelCovariance);
Eigen::SelfAdjointEigenSolver<Eigen::Matrix3f> superpixelEigenValues(superpixelCovariance);
superpixelNormal = superpixelEigenValues.eigenvectors().col(0);
(*this->features)(label, cols) = superpixelNormal(0);
(*this->features)(label, cols + 1) = superpixelNormal(1);
(*this->features)(label, cols + 2) = superpixelNormal(2);
}
return Eigen::Vector2i(cols, cols + 2);
}
Eigen::Vector2i SuperpixelFeatures::addArea() {
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 1);
int area = 0;
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
area = 0;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
++area;
}
}
}
(*this->features)(label, cols) = area;
}
return Eigen::Vector2i(cols, cols);
}
Eigen::Vector2i SuperpixelFeatures::addSuperpixelStatistics() {
assert(this->pointCloudAvailable);
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + 3);
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
std::vector<int> indices;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (this->labels[i][j] == label) {
indices.push_back(i*cols + j);
}
}
}
Eigen::Vector4f superpixelCentroid;
Eigen::Matrix3f superpixelCovariance;
Eigen::Vector3f superpixelNormal;
pcl::compute3DCentroid(*pointCloud, indices, superpixelCentroid);
pcl::computeCovarianceMatrix(*pointCloud, indices, superpixelCentroid, superpixelCovariance);
Eigen::SelfAdjointEigenSolver<Eigen::Matrix3f> superpixelEigenValues(superpixelCovariance);
// Point-ness:
(*this->features)(label, cols) = superpixelEigenValues.eigenvalues()(0);
(*this->features)(label, cols + 1) = superpixelEigenValues.eigenvalues()(2) - superpixelEigenValues.eigenvalues()(1);
(*this->features)(label, cols + 2) = superpixelEigenValues.eigenvalues()(1) - superpixelEigenValues.eigenvalues()(0);
}
return Eigen::Vector2i(cols, cols + 2);
}
Eigen::Vector2i SuperpixelFeatures::addColorHistogram(int bins) {
assert(bins > 0 && bins < 10);
int histogramSize = std::pow(bins, 3);
int cols = this->features->cols();
this->features->resize(this->numberOfSuperpixels, cols + histogramSize);
int* normalization = new int[this->numberOfSuperpixels];
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
normalization[label] = 0;
for (int k = 0; k < histogramSize; ++k) {
(*this->features)(label, cols + k) = 0;
}
}
int denominator = ceil(256./((double) bins));
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
int bin = this->image->at<cv::Vec3b>(i, j)[0]/denominator + bins*(this->image->at<cv::Vec3b>(i, j)[1]/denominator) + bins*bins*(this->image->at<cv::Vec3b>(i, j)[2]/denominator);
++(*this->features)(this->labels[i][j], cols + bin);
++normalization[this->labels[i][j]];
}
}
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
for (int k = 0; k < histogramSize; ++k) {
(*this->features)(label, cols + k) /= normalization[label];
}
}
return Eigen::Vector2i(cols, cols + histogramSize);
}
Eigen::Vector2i SuperpixelFeatures::addGroundTruth(int** labels) {
int numberOfLabels = 0;
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
if (labels[i][j] > numberOfLabels) {
numberOfLabels = labels[i][j];
}
}
}
// Remember that zero may be a label as well.
numberOfLabels = numberOfLabels + 1;
Eigen::MatrixXi intersection(this->numberOfSuperpixels, numberOfLabels);
for (int i = 0; i < this->height; ++i) {
for (int j = 0; j < this->width; ++j) {
assert(this->labels[i][j] < this->numberOfSuperpixels);
assert(labels[i][j] < numberOfLabels);
++intersection(this->labels[i][j], labels[i][j]);
}
}
for (int label = 0; label < this->numberOfSuperpixels; ++label) {
int maxIntersection = 0;
int maxGTLabel = 0;
for (int gtLabel = 0; gtLabel < numberOfLabels; ++gtLabel) {
if (intersection(label, gtLabel) > maxIntersection) {
maxIntersection = intersection(label, gtLabel);
maxGTLabel = gtLabel;
}
}
(*this->features)(label, 0) = maxGTLabel;
}
return Eigen::Vector2i(0, 0);
}
int SuperpixelFeatures::getFeatureDimension() const {
return this->features->cols();
}
Eigen::MatrixXd* SuperpixelFeatures::getFeatures() const {
return this->features;
}
【讨论】：