Artifacts in image generated with cv::fillPoly #22012
Description
System information (version)
- OpenCV => 3.4.1, 4.5.5
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
Detailed description
Result image of cv::fillPoly contains artifacts at the corner of the polygon. In the following image there are small black dots at the right top of the white area.
It seems like this mostly happenes if some of the polygon coordinates are outside of the image, but only in rare cases. And it seems that it doesn't happen with line mode cv::LineTypes::LINE_4
Steps to reproduce
UnitTest to reproduce and to generate the image shown above.
TEST(OpenCVTests, CvFillPolyCheckForArtifacts)
{
unsigned imageWidth = 256;
unsigned imageHeight = 256;
for (int y = imageHeight/2; y > -50; y -= 1)
{
// define polygon
std::vector<cv::Point> polygonPoints;
polygonPoints.push_back(cv::Point(100, imageHeight - y));
polygonPoints.push_back(cv::Point(imageWidth, imageHeight));
polygonPoints.push_back(cv::Point(imageWidth, 0));
// convert data
std::vector<const cv::Point*> polygonPointPointers(polygonPoints.size());
for (size_t i = 0; i < polygonPoints.size(); ++i)
{
polygonPointPointers[i] = &polygonPoints[i];
}
auto data = &polygonPointPointers.front();
int size = (int)polygonPoints.size();
const int* npts = &size;
int ncontours = 1;
cv::Mat img(imageWidth, imageHeight, CV_8UC1);
img = 0;
int lineType = cv::LineTypes::LINE_8;
int shift = 0;
cv::Point offset(0, 0);
// generate image
cv::fillPoly(img, data, npts, ncontours, 255, lineType, shift, offset);
// check for artifacts
cv::Mat binary = img < 128;
cv::Mat labelImage(binary.size(), CV_32S);
cv::Mat labelStats;
cv::Mat labelCentroids;
auto labels = cv::connectedComponents(binary, labelImage, 4);
EXPECT_EQ(2, labels);
if (labels > 2)
{
cv::imwrite("C:\\temp\\BadFilledPolygon.png", img);
}
}
for (int x = imageWidth / 2; x > -50; x -= 1)
{
// define polygon
std::vector<cv::Point> polygonPoints;
polygonPoints.push_back(cv::Point(imageWidth-x, 100));
polygonPoints.push_back(cv::Point(imageWidth, imageHeight));
polygonPoints.push_back(cv::Point(0, imageHeight));
// convert data
std::vector<const cv::Point*> polygonPointPointers(polygonPoints.size());
for (size_t i = 0; i < polygonPoints.size(); ++i)
{
polygonPointPointers[i] = &polygonPoints[i];
}
auto data = &polygonPointPointers.front();
int size = (int)polygonPoints.size();
const int* npts = &size;
int ncontours = 1;
cv::Mat img(imageWidth, imageHeight, CV_8UC1);
img = 0;
int lineType = cv::LineTypes::LINE_4;
int shift = 0;
cv::Point offset(0, 0);
// generate image
cv::fillPoly(img, data, npts, ncontours, 255, lineType, shift, offset);
// check for artifacts
cv::Mat binary = img < 128;
cv::Mat labelImage(binary.size(), CV_32S);
cv::Mat labelStats;
cv::Mat labelCentroids;
auto labels = cv::connectedComponents(binary, labelImage, 4);
EXPECT_EQ(2, labels);
if (labels > 2)
{
cv::imwrite("C:\\temp\\BadFilledPolygon.png", img);
}
}
}
Issue submission checklist
- I report the issue, it's not a question
- I checked the problem with documentation, FAQ, open issues,
forum.opencv.org, Stack Overflow, etc and have not found any solution - I updated to the latest OpenCV version and the issue is still there
- There is reproducer code and related data files: videos, images, onnx, etc