Resize and compress bitmaps to decrease PDF size

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

@@ -1,19 +1,27 @@
 package org.mydomain.myscan
 
 import android.graphics.Bitmap
+import android.graphics.BitmapFactory
 import android.graphics.pdf.PdfDocument
 import android.util.Log
+import androidx.core.graphics.scale
+import java.io.ByteArrayOutputStream
 import java.io.File
 import java.io.FileOutputStream
 import java.io.IOException
+import kotlin.math.max
 
 fun createPdfFromBitmaps(bitmaps: List<Bitmap>, outputFile: File): Boolean {
     val document = PdfDocument()
     try {
-        for ((index, bitmap) in bitmaps.withIndex()) {
+        for ((index, bitmap) in bitmaps.map { resizeImage(it) }.withIndex()) {
+            val jpegStream = ByteArrayOutputStream()
+            bitmap.compress(Bitmap.CompressFormat.JPEG, 72, jpegStream)
+            val compressedBytes = jpegStream.toByteArray()
+            val compressedBitmap = BitmapFactory.decodeByteArray(compressedBytes, 0, compressedBytes.size)
             val pageInfo = PdfDocument.PageInfo.Builder(bitmap.width, bitmap.height, index + 1).create()
             val page = document.startPage(pageInfo)
-            page.canvas.drawBitmap(bitmap, 0f, 0f, null)
+            page.canvas.drawBitmap(compressedBitmap, 0f, 0f, null)
             document.finishPage(page)
         }
         FileOutputStream(outputFile).use { outputStream ->
@@ -27,3 +35,16 @@ fun createPdfFromBitmaps(bitmaps: List<Bitmap>, outputFile: File): Boolean {
         document.close()
     }
 }
+
+fun resizeImage(original: Bitmap): Bitmap {
+    val targetMax = 1500
+    if (max(original.width, original.height) < targetMax)
+        return original;
+    var targetWidth = targetMax
+    var targetHeight = original.height * targetWidth / original.width
+    if (original.width < original.height) {
+        targetHeight = targetMax
+        targetWidth = original.width * targetHeight / original.height
+    }
+    return original.scale(targetWidth, targetHeight)
+}