Base64 encoding in Swift will not decode in Android

Question

I have an Android app which uses Base64 to encode images, and encoded strings are stored on a server. I am now making an iOS client for the same app and am struggling to make it encode images in the same way Images encoded on the android end will decode in Swift iOS but images encoded in Swift will NOT decode in Android, or here http://www.freeformatter.com/base64-encoder.html (the resulting file isn't a valid image)

Images encoded in iOS WILL decode in iOS

In Android, I am using the following to encode and decode

public static String encodeBitmap(Bitmap bitmap) {
    Bitmap immagex = bitmap;
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    immagex.compress(Bitmap.CompressFormat.PNG, 100, baos);
    byte[] b = baos.toByteArray();
    String imageEncoded = Base64.encodeToString(b, Base64.DEFAULT);
    return imageEncoded;
}

public static Bitmap decodeBitmap(String encodedString) {
    byte[] decodedByte = Base64.decode(encodedString, Base64.DEFAULT);
    Bitmap b = BitmapFactory.decodeByteArray(decodedByte, 0,
            decodedByte.length);
    return b;
}

And the following on the iOS side

static func decodeImage(str: String) -> UIImage?{
    if let decodedData = NSData(base64EncodedString: str, options: NSDataBase64DecodingOptions.IgnoreUnknownCharacters){
        var iconValue:UIImage? = UIImage(data: decodedData)
        return iconValue
    }
    return nil
}

static func encodeImage(image: UIImage) -> String{
    var imageData = UIImagePNGRepresentation(image)
    let base64 = imageData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.Encoding76CharacterLineLength)
    return base64
}

}

I am willing to change either client to make it work

Example: take this image for example https://pbs.twimg.com/profile_images/522909800191901697/FHCGSQg0.png

On Android it encodes to http://pastebin.com/D41Ldjis

And on iOS to http://pastebin.com/fEUZSJvF

iOS one has a much larger character count

Answer 1

The Base64 provoided are from different PNG encodings. The headers are different, Android has a "sBIT" chunk and iOS has a "sRGB" chunk.

Thus the problem is not Base64 but the representatins prpovided by the two systems.

Decoded portions

Android:
âPNG

IHDR††≠zsBIT€·O‡ÑIDAT

iOS:
âPNG

IHDR»»≠XÆûsRGBÆŒÈiDOTd(ddp`ùıºIDAT