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Added a height filter to character analysis -- helps remove noise so that a good plate doesn't get rejected

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Matt Hill
2014-04-08 14:56:04 -05:00
parent 004f7a5bd8
commit 58d57fc12d
1 changed files with 47 additions and 5 deletions
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52
src/openalpr/characteranalysis.cpp
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@@ -733,6 +733,7 @@ vector<bool> CharacterAnalysis::filterByParentContour( vector< vector< Point> >
vector<bool> CharacterAnalysis::filterBetweenLines(Mat img, vector<vector<Point> > contours, vector<Vec4i> hierarchy, vector<Point> outerPolygon, vector<bool> goodIndices)
{
static float MIN_AREA_PERCENT_WITHIN_LINES = 0.88;
static float MAX_DISTANCE_PERCENT_FROM_LINES = 0.15;
vector<bool> includedIndices(contours.size());
for (int j = 0; j < contours.size(); j++)
@@ -754,15 +755,17 @@ vector<bool> CharacterAnalysis::filterBetweenLines(Mat img, vector<vector<Point>
// Create a white mask for the area inside the polygon
Mat outerMask = Mat::zeros(img.size(), CV_8U);
Mat innerArea = Mat::zeros(img.size(), CV_8U);
Mat innerArea(img.size(), CV_8U);
fillConvexPoly(outerMask, outerPolygon.data(), outerPolygon.size(), Scalar(255,255,255));
// For each contour, determine if enough of it is between the lines to qualify
for (int i = 0; i < contours.size(); i++)
{
if (goodIndices[i] == false)
continue;
// get rid of the outline by drawing a 1 pixel width black line
innerArea.setTo(Scalar(0,0,0));
drawContours(innerArea, contours,
i, // draw this contour
cv::Scalar(255,255,255), // in
@@ -777,7 +780,7 @@ vector<bool> CharacterAnalysis::filterBetweenLines(Mat img, vector<vector<Point>
vector<vector<Point> > tempContours;
findContours(innerArea, tempContours,
CV_RETR_EXTERNAL, // retrieve the external contours
CV_CHAIN_APPROX_SIMPLE ); // all pixels of each contours );
CV_CHAIN_APPROX_SIMPLE ); // all pixels of each contours );
double totalArea = contourArea(contours[i]);
double areaBetweenLines = 0;
@@ -787,12 +790,51 @@ vector<bool> CharacterAnalysis::filterBetweenLines(Mat img, vector<vector<Point>
areaBetweenLines += contourArea(tempContours[tempContourIdx]);
}
if (areaBetweenLines / totalArea >= MIN_AREA_PERCENT_WITHIN_LINES)
if (areaBetweenLines / totalArea < MIN_AREA_PERCENT_WITHIN_LINES)
{
// Not enough area is inside the lines.
continue;
}
// now check to make sure that the top and bottom of the contour are near enough to the lines
// First get the high and low point for the contour
// Remember that origin is top-left, so the top Y values are actually closer to 0.
int highPointIndex = 0;
int highPointValue = 999999999;
int lowPointIndex = 0;
int lowPointValue = 0;
for (int cidx = 0; cidx < contours[i].size(); cidx++)
{
if (contours[i][cidx].y < highPointValue)
{
highPointIndex = cidx;
highPointValue = contours[i][cidx].y;
}
if (contours[i][cidx].y > lowPointValue)
{
lowPointIndex = cidx;
lowPointValue = contours[i][cidx].y;
}
}
// Get the absolute distance from the top and bottom lines
Point closestTopPoint = topLine.closestPointOnSegmentTo(contours[i][highPointIndex]);
Point closestBottomPoint = bottomLine.closestPointOnSegmentTo(contours[i][lowPointIndex]);
float absTopDistance = distanceBetweenPoints(closestTopPoint, contours[i][highPointIndex]);
float absBottomDistance = distanceBetweenPoints(closestBottomPoint, contours[i][lowPointIndex]);
float maxDistance = lineHeight * MAX_DISTANCE_PERCENT_FROM_LINES;
if (absTopDistance < maxDistance && absBottomDistance < maxDistance)
{
includedIndices[i] = true;
}
innerArea.setTo(Scalar(0,0,0));
}
return includedIndices;