Reading EXIF data from byte array in android

The Camera app includes an EXIF class which can do this:

http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android-apps/4.1.1_r1/com/android/camera/Exif.java

The code is nice and short, so I’ve reproduced it here in case that link breaks. Note that it doesn’t handle the mirrored orientations, but you can see that it is pretty trivial to change.

import android.util.Log;

public class Exif {
    private static final String TAG = "CameraExif";

    // Returns the degrees in clockwise. Values are 0, 90, 180, or 270.
    public static int getOrientation(byte[] jpeg) {
        if (jpeg == null) {
            return 0;
        }

        int offset = 0;
        int length = 0;

        // ISO/IEC 10918-1:1993(E)
        while (offset + 3 < jpeg.length && (jpeg[offset++] & 0xFF) == 0xFF) {
            int marker = jpeg[offset] & 0xFF;

            // Check if the marker is a padding.
            if (marker == 0xFF) {
                continue;
            }
            offset++;

            // Check if the marker is SOI or TEM.
            if (marker == 0xD8 || marker == 0x01) {
                continue;
            }
            // Check if the marker is EOI or SOS.
            if (marker == 0xD9 || marker == 0xDA) {
                break;
            }

            // Get the length and check if it is reasonable.
            length = pack(jpeg, offset, 2, false);
            if (length < 2 || offset + length > jpeg.length) {
                Log.e(TAG, "Invalid length");
                return 0;
            }

            // Break if the marker is EXIF in APP1.
            if (marker == 0xE1 && length >= 8 &&
                    pack(jpeg, offset + 2, 4, false) == 0x45786966 &&
                    pack(jpeg, offset + 6, 2, false) == 0) {
                offset += 8;
                length -= 8;
                break;
            }

            // Skip other markers.
            offset += length;
            length = 0;
        }

        // JEITA CP-3451 Exif Version 2.2
        if (length > 8) {
            // Identify the byte order.
            int tag = pack(jpeg, offset, 4, false);
            if (tag != 0x49492A00 && tag != 0x4D4D002A) {
                Log.e(TAG, "Invalid byte order");
                return 0;
            }
            boolean littleEndian = (tag == 0x49492A00);

            // Get the offset and check if it is reasonable.
            int count = pack(jpeg, offset + 4, 4, littleEndian) + 2;
            if (count < 10 || count > length) {
                Log.e(TAG, "Invalid offset");
                return 0;
            }
            offset += count;
            length -= count;

            // Get the count and go through all the elements.
            count = pack(jpeg, offset - 2, 2, littleEndian);
            while (count-- > 0 && length >= 12) {
                // Get the tag and check if it is orientation.
                tag = pack(jpeg, offset, 2, littleEndian);
                if (tag == 0x0112) {
                    // We do not really care about type and count, do we?
                    int orientation = pack(jpeg, offset + 8, 2, littleEndian);
                    switch (orientation) {
                        case 1:
                            return 0;
                        case 3:
                            return 180;
                        case 6:
                            return 90;
                        case 8:
                            return 270;
                    }
                    Log.i(TAG, "Unsupported orientation");
                    return 0;
                }
                offset += 12;
                length -= 12;
            }
        }

        Log.i(TAG, "Orientation not found");
        return 0;
    }

    private static int pack(byte[] bytes, int offset, int length,
            boolean littleEndian) {
        int step = 1;
        if (littleEndian) {
            offset += length - 1;
            step = -1;
        }

        int value = 0;
        while (length-- > 0) {
            value = (value << 8) | (bytes[offset] & 0xFF);
            offset += step;
        }
        return value;
    }
}

By the way, I highly recommend every Android developer downloads the source for all the stock apps, and the GoogleIO app. They’re full of nice code/hacks that Google have written to get around weaknesses in Android.