try filling the screen with the default back camera photo resolution

app/src/main/kotlin/com/simplemobiletools/camera/Config.kt

@@ -39,7 +39,7 @@ class Config(context: Context) : BaseConfig(context) {
         set(enabled) = prefs.edit().putBoolean(LAST_FLASHLIGHT_STATE, enabled).apply()
 
     var backPhotoResIndex: Int
-        get() = prefs.getInt(BACK_PHOTO_RESOLUTION_INDEX, 0)
+        get() = prefs.getInt(BACK_PHOTO_RESOLUTION_INDEX, -1)
         set(backPhotoResIndex) = prefs.edit().putInt(BACK_PHOTO_RESOLUTION_INDEX, backPhotoResIndex).apply()
 
     var backVideoResIndex: Int

app/src/main/kotlin/com/simplemobiletools/camera/Preview.kt

@@ -164,13 +164,17 @@ class Preview : ViewGroup, SurfaceHolder.Callback, MediaScannerConnection.OnScan
     }
 
     private fun getSelectedResolution(): Camera.Size {
-        val index = getResolutionIndex()
+        var index = getResolutionIndex()
         val resolutions = if (mIsVideoMode) {
             mParameters!!.supportedVideoSizes ?: mParameters!!.supportedPreviewSizes
         } else {
             mParameters!!.supportedPictureSizes
         }.sortedByDescending { it.width * it.height }
 
+        if (index == -1) {
+            index = getDefaultFullscreenResolution(resolutions) ?: 0
+        }
+
         return resolutions[index]
     }
 
@@ -183,6 +187,18 @@ class Preview : ViewGroup, SurfaceHolder.Callback, MediaScannerConnection.OnScan
         }
     }
 
+    private fun getDefaultFullscreenResolution(resolutions: List<Camera.Size>): Int? {
+        val screenAspectRatio = mActivity.realScreenSize.y / mActivity.realScreenSize.x.toFloat()
+        resolutions.forEachIndexed { index, size ->
+            val diff = screenAspectRatio - (size.width / size.height.toFloat())
+            if (Math.abs(diff) < RATIO_TOLERANCE) {
+                config.backPhotoResIndex = index
+                return index
+            }
+        }
+        return null
+    }
+
     fun setTargetUri(uri: Uri) {
         mTargetUri = uri
     }

app/src/main/kotlin/com/simplemobiletools/camera/extensions/size.kt

@@ -4,7 +4,7 @@ import android.content.Context
 import android.hardware.Camera
 import com.simplemobiletools.camera.R
 
-private val RATIO_TOLERANCE = 0.1f
+val RATIO_TOLERANCE = 0.1f
 
 fun Camera.Size.isSixteenToNine(): Boolean {
     val selectedRatio = Math.abs(width / height.toFloat())