Exif.java

/*

 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.fanfou.app.opensource.ui.widget;

import android.util.Log;

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

    public static int getOrientation(final 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)) {
            final 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 = Exif.pack(jpeg, offset, 2, false);
            if ((length < 2) || ((offset + length) > jpeg.length)) {
                Log.e(Exif.TAG, "Invalid length");
                return 0;
            }

            // Break if the marker is EXIF in APP1.
            if ((marker == 0xE1) && (length >= 8)
                    && (Exif.pack(jpeg, offset + 2, 4, false) == 0x45786966)
                    && (Exif.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 = Exif.pack(jpeg, offset, 4, false);
            if ((tag != 0x49492A00) && (tag != 0x4D4D002A)) {
                Log.e(Exif.TAG, "Invalid byte order");
                return 0;
            }
            final boolean littleEndian = (tag == 0x49492A00);

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

            // Get the count and go through all the elements.
            count = Exif.pack(jpeg, offset - 2, 2, littleEndian);
            while ((count-- > 0) && (length >= 12)) {
                // Get the tag and check if it is orientation.
                tag = Exif.pack(jpeg, offset, 2, littleEndian);
                if (tag == 0x0112) {
                    // We do not really care about type and count, do we?
                    final int orientation = Exif.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(Exif.TAG, "Unsupported orientation");
                    return 0;
                }
                offset += 12;
                length -= 12;
            }
        }

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

    private static int pack(final byte[] bytes, int offset, int length,
            final 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;
    }
}