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Refine segmentation mask with morphological operations to improve detection of quadrilateral

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This commit is contained in:
Pierre-Yves Nicolas
2025-07-26 16:38:02 +02:00
parent fad6802ed7
commit d8697b5cb3
1 changed files with 29 additions and 1 deletions
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30
app/src/main/java/org/mydomain/myscan/DocumentDetection.kt
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@@ -33,8 +33,10 @@ fun detectDocumentQuad(mask: Bitmap, minQuadAreaRatio: Double = 0.02): Quad? {
val gray = Mat()
Imgproc.cvtColor(mat, gray, Imgproc.COLOR_BGR2GRAY)
val refinedMask = refineMask(gray)
val blurred = Mat()
Imgproc.GaussianBlur(gray, blurred, Size(5.0, 5.0), 0.0)
Imgproc.GaussianBlur(refinedMask, blurred, Size(5.0, 5.0), 0.0)
val edges = Mat()
Imgproc.Canny(blurred, edges, 75.0, 200.0)
@@ -69,6 +71,32 @@ fun detectDocumentQuad(mask: Bitmap, minQuadAreaRatio: Double = 0.02): Quad? {
return createQuad(vertices)
}
/**
* Applies morphological operations to improve a document mask.
*/
fun refineMask(original: Mat): Mat {
// Step 0: Ensure the mask is binary (just in case)
val binaryMask = Mat()
Imgproc.threshold(original, binaryMask, 0.0, 255.0, Imgproc.THRESH_BINARY)
// Step 1: Closing (fills small holes)
val kernelClose = Imgproc.getStructuringElement(Imgproc.MORPH_ELLIPSE, Size(5.0, 5.0))
val closed = Mat()
Imgproc.morphologyEx(binaryMask, closed, Imgproc.MORPH_CLOSE, kernelClose)
// Step 2: Gentle opening (removes isolated noise)
val kernelOpen = Imgproc.getStructuringElement(Imgproc.MORPH_ELLIPSE, Size(5.0, 5.0))
val opened = Mat()
Imgproc.morphologyEx(closed, opened, Imgproc.MORPH_OPEN, kernelOpen)
// Step 3: Light dilation (connects almost touching parts)
val kernelDilate = Imgproc.getStructuringElement(Imgproc.MORPH_ELLIPSE, Size(5.0, 5.0))
val dilated = Mat()
Imgproc.dilate(opened, dilated, kernelDilate, org.opencv.core.Point(-1.0, -1.0), 1)
return dilated
}
fun extractDocument(originalBitmap: Bitmap, quad: Quad, rotationDegrees: Int): Bitmap {
val widthTop = norm(quad.topLeft, quad.topRight)
val widthBottom = norm(quad.bottomLeft, quad.bottomRight)