Save about 400ms at capture by delegating the rotation to OpenCV

app/src/androidTest/java/org/mydomain/myscan/DocumentDetectionTest.kt

@@ -57,7 +57,7 @@ class DocumentDetectionTest {
                 if (quad != null) {
                     val resizedQuad =
                         quad.scaledTo(mask.width, mask.height, bitmap.width, bitmap.height)
-                    outputBitmap = extractDocument(bitmap, resizedQuad)
+                    outputBitmap = extractDocument(bitmap, resizedQuad, 0)
                     val file = File(context.getExternalFilesDir(null), imageFileName)
                     FileOutputStream(file).use {
                         outputBitmap.compress(Bitmap.CompressFormat.JPEG, 95, it)

app/src/main/java/org/mydomain/myscan/DocumentDetection.kt

@@ -15,7 +15,9 @@
 package org.mydomain.myscan
 
 import android.graphics.Bitmap
+import androidx.core.graphics.createBitmap
 import org.opencv.android.Utils
+import org.opencv.core.Core
 import org.opencv.core.Mat
 import org.opencv.core.MatOfPoint
 import org.opencv.core.MatOfPoint2f
@@ -24,7 +26,6 @@ import org.opencv.imgproc.Imgproc
 import kotlin.math.abs
 import kotlin.math.max
 import kotlin.math.sqrt
-import androidx.core.graphics.createBitmap
 
 fun detectDocumentQuad(mask: Bitmap): Quad? {
     val mat = Mat()
@@ -65,7 +66,7 @@ fun detectDocumentQuad(mask: Bitmap): Quad? {
     return createQuad(vertices)
 }
 
-fun extractDocument(originalBitmap: Bitmap, quad: Quad): Bitmap {
+fun extractDocument(originalBitmap: Bitmap, quad: Quad, rotationDegrees: Int): Bitmap {
     val widthTop = norm(quad.topLeft, quad.topRight)
     val widthBottom = norm(quad.bottomLeft, quad.bottomRight)
     val maxWidth = max(widthTop, widthBottom).toInt()
@@ -96,11 +97,23 @@ fun extractDocument(originalBitmap: Bitmap, quad: Quad): Bitmap {
 
     val enhanced = enhanceCapturedImage(outputMat)
 
-    return toBitmap(enhanced, maxWidth, maxHeight)
+    return toBitmap(rotate(enhanced, rotationDegrees))
 }
 
-private fun toBitmap(mat: Mat, width: Int, height: Int): Bitmap {
+fun rotate(input: Mat, degrees: Int): Mat {
-    val outputBitmap = createBitmap(width, height)
+    val output = Mat()
+    when ((degrees % 360 + 360) % 360) {
+        0 -> input.copyTo(output)
+        90 -> Core.rotate(input, output, Core.ROTATE_90_CLOCKWISE)
+        180 -> Core.rotate(input, output, Core.ROTATE_180)
+        270 -> Core.rotate(input, output, Core.ROTATE_90_COUNTERCLOCKWISE)
+        else -> throw IllegalArgumentException("Only 0, 90, 180, 270 degrees are supported")
+    }
+    return output
+}
+
+private fun toBitmap(mat: Mat): Bitmap {
+    val outputBitmap = createBitmap(mat.cols(), mat.rows())
     Utils.matToBitmap(mat, outputBitmap)
     return outputBitmap
 }

app/src/main/java/org/mydomain/myscan/MainViewModel.kt

@@ -17,7 +17,6 @@ package org.mydomain.myscan
 import android.content.Context
 import android.graphics.Bitmap
 import android.graphics.BitmapFactory
-import android.graphics.Matrix
 import androidx.camera.core.ImageProxy
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
@@ -109,25 +108,19 @@ class MainViewModel(
 
     private suspend fun processCapturedImage(imageProxy: ImageProxy): Bitmap? = withContext(Dispatchers.IO) {
         var corrected: Bitmap? = null
-        val bitmap = imageProxy.toBitmap().rotate(imageProxy.imageInfo.rotationDegrees)
+        var bitmap = imageProxy.toBitmap()
         val segmentation = imageSegmentationService.runSegmentationAndReturn(bitmap, 0)
         if (segmentation != null) {
             val mask = segmentation.segmentation.toBinaryMask()
             val quad = detectDocumentQuad(mask)
             if (quad != null) {
                 val resizedQuad = quad.scaledTo(mask.width, mask.height, bitmap.width, bitmap.height)
-                corrected = extractDocument(bitmap, resizedQuad)
+                corrected = extractDocument(bitmap, resizedQuad, imageProxy.imageInfo.rotationDegrees)
             }
         }
         return@withContext corrected
     }
 
-    fun Bitmap.rotate(degrees: Int): Bitmap {
-        if (degrees == 0) return this
-        val matrix = Matrix().apply { postRotate(degrees.toFloat()) }
-        return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
-    }
-
     fun addPage(bitmap: Bitmap, quality: Int = 75) {
         val resized = resizeImage(bitmap)
         val outputStream = ByteArrayOutputStream()

app/src/main/java/org/mydomain/myscan/view/Camera.kt

@@ -131,6 +131,7 @@ fun CameraScreen(
         pageCount = viewModel.pageCount(),
         liveAnalysisState,
         onCapture = {
+            Log.i("MyScan", "Pressed <Capture>")
             viewModel.liveAnalysisEnabled = false
             showPageDialog.value = true
             isProcessing.value = true
@@ -140,6 +141,7 @@ fun CameraScreen(
                         viewModel.processCapturedImageThen(imageProxy) {
                             isProcessing.value = false
                             viewModel.liveAnalysisEnabled = true
+                            Log.i("MyScan", "Capture process finished")
                         }
                     } else {
                         Log.e("MyScan", "Error during image capture")