android - 从android中的字节数组中读取EXIF数据

Question

我想从相机输出的字节数组数据中读取 EXIF 数据。我知道我可以使用 exifInterface 从文件中读取 EXIF 数据。但这需要我将字节数组数据写入文件，读取 EXIF 数据，然后删除文件。我想读取 EXIF 数据而无需先写入文件。

有人有什么想法吗？

Answer 1

相机应用程序包含一个 EXIF 类，它可以做到这一点:

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

代码又好又短，所以我在这里复制了它，以防链接中断。请注意，它不处理镜像方向，但您可以看到更改非常简单。

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;
    }
}

顺便说一句，我强烈建议每个 Android 开发人员下载所有库存应用程序和 GoogleIO 应用程序的源代码。它们充满了 Google 编写的用于绕过 Android 弱点的漂亮代码/黑客。