Exifpublic class Exif extends Object
| Fields Summary |
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| private static final String | TAG |
| Methods Summary |
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| public static int | getOrientation(java.io.InputStream inputStream, long byteSize)Returns the degrees in clockwise. Values are 0, 90, 180, or 270.
if (inputStream == null) {
return 0;
}
/*
Looking at this algorithm, we never look ahead more than 8 bytes. As long as we call
advanceTo() at the end of every loop, we should never have to reallocate a larger buffer.
Also, the most we ever read backwards is 4 bytes. pack() reads backwards if the encoding
is in little endian format. These following two lines potentially reads 4 bytes backwards:
int tag = pack(jpeg, offset, 4, false);
count = pack(jpeg, offset - 2, 2, littleEndian);
To be safe, we will always advance to some index-4, so we'll need 4 more for the +8
look ahead, which makes it a +12 look ahead total. Use 16 just in case my analysis is off.
This means we only need to allocate a single 16 byte buffer.
Note: If you do not pass in byteSize parameter, a single large allocation will occur.
For a 1MB image, I see one 30KB allocation. This is due to the line containing:
has(jpeg, byteSize, offset + length - 1)
where length is a variable int (around 30KB above) read from the EXIF headers.
This is still much better than allocating a 1MB byte[] which we were doing before.
*/
final int lookAhead = 16;
final int readBackwards = 4;
final InputStreamBuffer jpeg = new InputStreamBuffer(inputStream, lookAhead, false);
int offset = 0;
int length = 0;
if (has(jpeg, byteSize, 1)) {
// JPEG image files begin with FF D8. Only JPEG images have EXIF data.
final boolean possibleJpegFormat = jpeg.get(0) == (byte) 0xFF
&& jpeg.get(1) == (byte) 0xD8;
if (!possibleJpegFormat) {
return 0;
}
}
// ISO/IEC 10918-1:1993(E)
while (has(jpeg, byteSize, offset + 3) && (jpeg.get(offset++) & 0xFF) == 0xFF) {
final int marker = jpeg.get(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) {
// Loop ends.
jpeg.advanceTo(offset - readBackwards);
break;
}
// Get the length and check if it is reasonable.
length = pack(jpeg, offset, 2, false);
if (length < 2 || !has(jpeg, byteSize, offset + length - 1)) {
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;
// Loop ends.
jpeg.advanceTo(offset - readBackwards);
break;
}
// Skip other markers.
offset += length;
length = 0;
// Loop ends.
jpeg.advanceTo(offset - readBackwards);
}
// 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;
}
final 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;
// Offset has changed significantly.
jpeg.advanceTo(offset - readBackwards);
// 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?
final 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;
// Loop ends.
jpeg.advanceTo(offset - readBackwards);
}
}
return 0;
| | public static int | getOrientation(byte[] jpeg)
return getOrientation(new ByteArrayInputStream(jpeg), jpeg.length);
| | private static boolean | has(InputStreamBuffer jpeg, long byteSize, int index)
if (byteSize >= 0) {
return index < byteSize;
} else {
// For large values of index, this will cause the internal buffer to resize.
return jpeg.has(index);
}
| | private static int | pack(InputStreamBuffer 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.get(offset) & 0xFF);
offset += step;
}
return value;
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