How to know the type of a image file

Question

Given a file path (without extension) I'd like to know if the image inside the file is a JPEG or a PNG.

How can I do it?

Answer 1

Try looking for the image headers, somewhat like this:

File file = /* (get your file) */;
byte[] data = new byte[2];
try {
    new FileInputStream(file).read(data);
} catch (Exception e) {
    // handle the error somehow!
}

if (data[0] == 0xFF && data[1] == 0xD8) {
    // jpeg
} else if (data[0] == 0x89 && data[1] == 0x50) {
    // png
} else {
    // error?
}

JPEG headers will always be FFD8, and PNG headers are 89504E470D0A1E0A (for which we only need to look at the first two bytes to distinguish from JPEG).

Answer 2

You can find it like this:

step 1: You just get the image bounds only....

step 2: You can change your image with your corresponding size using the below method

    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    in.mark(in.available());
    BitmapFactory.decodeStream(in, null, options);
    (or)
    BitmapFactory.decodeFile(pathName);
    (or)
    BitmapFactory.decodeResource(MainActivity.this.getResources(), R.drawable.ic_launcher);
    String name = options.outMimeType;

this below method is used to get the large bitmaps loading with efficiently re-sizing the image with your required height and width

public static Bitmap decodeSampledBitmapFromResource(InputStream in,
            int reqWidth, int reqHeight) throws IOException {

        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        in.mark(in.available());
        BitmapFactory.decodeStream(in, null, options);
        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, reqWidth,
                reqHeight);
        in.reset();
        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeStream(in, null, options);
    }

    public static int calculateInSampleSize(BitmapFactory.Options options,
            int reqWidth, int reqHeight) {
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;
            // Calculate the largest inSampleSize value that is a power of 2 and
            // keeps both
            // height and width larger than the requested height and width.
            while ((halfHeight / inSampleSize) > reqHeight
                    && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }
        }

        return inSampleSize;
    }

Answer 3

Do you search for this? Why don't you have the extension?

"In Java 7 you can now just use

 Files.probeContentType(path)"

-> source but we are not sure if it's supported in android.

So why don't you just get the full path and extract the file extension with substring?