[image_picker]Fixed losing transparency of PNGs

packages/image_picker/android/src/main/java/io/flutter/plugins/imagepicker/ImageResizer.java

@@ -85,7 +85,9 @@ private File resizedImage(String path, Double maxWidth, Double maxHeight) throws
 
     Bitmap scaledBmp = Bitmap.createScaledBitmap(bmp, width.intValue(), height.intValue(), false);
     ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
-    scaledBmp.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);
+    boolean saveAsPNG = bmp.hasAlpha();
+    scaledBmp.compress(
+        saveAsPNG ? Bitmap.CompressFormat.PNG : Bitmap.CompressFormat.JPEG, 100, outputStream);
 
     String[] pathParts = path.split("/");
     String imageName = pathParts[pathParts.length - 1];

packages/image_picker/ios/Classes/ImagePickerPlugin.m

@@ -162,9 +162,12 @@ - (void)imagePickerController:(UIImagePickerController *)picker
       image = [self scaledImage:image maxWidth:maxWidth maxHeight:maxHeight];
     }
 
-    NSData *data = UIImageJPEGRepresentation(image, 1.0);
+    BOOL saveAsPNG = [self hasAlpha:image];
+    NSData *data =
+        saveAsPNG ? UIImagePNGRepresentation(image) : UIImageJPEGRepresentation(image, 1.0);
+    NSString *fileExtension = saveAsPNG ? @"image_picker_%@.png" : @"image_picker_%@.jpg";
     NSString *guid = [[NSProcessInfo processInfo] globallyUniqueString];
-    NSString *tmpFile = [NSString stringWithFormat:@"image_picker_%@.jpg", guid];
+    NSString *tmpFile = [NSString stringWithFormat:fileExtension, guid];
     NSString *tmpDirectory = NSTemporaryDirectory();
     NSString *tmpPath = [tmpDirectory stringByAppendingPathComponent:tmpFile];
 
@@ -254,4 +257,11 @@ - (UIImage *)scaledImage:(UIImage *)image
   return scaledImage;
 }
 
+// Returns true if the image has an alpha layer
+- (BOOL)hasAlpha:(UIImage *)image {
+  CGImageAlphaInfo alpha = CGImageGetAlphaInfo(image.CGImage);
+  return (alpha == kCGImageAlphaFirst || alpha == kCGImageAlphaLast ||
+          alpha == kCGImageAlphaPremultipliedFirst || alpha == kCGImageAlphaPremultipliedLast);
+}
+
 @end