Flip the image saved as an array of bytes

Question

I have an image that is stored as a byte [] array, and I want to flip the image vertically before writing bytes to another disk.

Image bytes come from a compressed jp2 image file. I was looking for an implementation of something like a Flip image stored as a byte [] array , but I do not work in android and do not have access to BitmapFactory. I also looked at converting a byte array to a BufferedImage, and then flipped it over, but the height and width of the image are unknown in the current context (EDIT: I changed the code so that the height and width are now known).

Is there a way to do this only with strict array manipulation?

EDIT: Attempting a Flip Code

public static byte[] flip(byte[] imageBytes) { //separate out the sub arrays byte[] holder = new byte[imageBytes.length]; byte[] subArray = new byte[dimWidth];//dimWidth is the image width, or number of matrix columns int subCount = 0; for (int i = 0; i < imageBytes.length; i++) { subArray[subCount] = imageBytes[i]; subCount++; if (i% dimWidth == 0) { subArray = reverse(subArray); if (i == (dimWidth)) { holder = subArray; } else { holder = concat(holder, subArray); } subCount = 0; subArray = new byte[dimWidth]; } } subArray = new byte[dimWidth]; System.arraycopy(imageBytes, imageBytes.length - dimWidth, subArray, 0, subArray.length); holder = concat(holder, subArray); imageBytes = holder; return imageBytes; } 

Answer 1

No matter guys, I earned it. I just needed to flip the upper and lower bytes BEFORE MOVING to the last array. For those with the same problem as me, use the above dump function in arrays with high and low bytes separately before interleaving them.

Thank you for your help!

Answer 2

I also looked at converting a byte array to BufferedImage first and then flipping it, but the height and width of the image are not known in the current context.

You can simply check the height and width directly from the header section of the JP2 file.

 import java.io.IOException; import java.io.FileInputStream; import java.io.File; import java.nio.ByteBuffer; import javax.xml.bind.DatatypeConverter; public class parse_Header_JP2 { static File myFile; static FileInputStream fileInStream = null; static byte[] myBytes; static String myString = ""; static int myNum = 0; static int myWidth = 0; static int myHeight = 0; static ByteBuffer byteBuff; public static void main(String[] args) { myFile = new File("c:/test/image.jp2"); myBytes = getBytes_Header_JP2(myFile); checkBytes_Header_JP2(myBytes); //# update myWidth & myHeight //# Shows HEX of whole bytearray System.out.println("First 64 bytes (as HEX) : \n" + bytesToHex( myBytes ) ); } private static byte[] getBytes_Header_JP2(File file) { myBytes = new byte[64]; //will hold first 64 bytes of file as header bytes try { //# convert file into array of bytes fileInStream = new FileInputStream(file); fileInStream.read(myBytes, 0, 64); //# Read only first 64 bytes fileInStream.close(); } catch (Exception e) { e.printStackTrace(); } //# error catching byteBuff = ByteBuffer.wrap(myBytes); //associate ByteBuffer with bytes return myBytes; } public static void checkBytes_Header_JP2(byte[] bytes) { int offset = 0; myHeight = 0; myWidth = 0; // resets while(true) { //# set as byte value reading from offset myNum = bytes[offset]; myString = Integer.toHexString(myNum).toUpperCase(); //# Check byte as : Hex value System.out.println("Byte Value at [" + offset + "] : " + decimalToHex(myNum) ); //# Check byte as : Decimal value //System.out.println("Byte Value at [" + offset + "] : " + myNum ); //# Find byte 0x69 (or Decimal = 105) which is letter "i" from "ihdr" if (myNum == 0x69) //# if "i" is found at this offset within bytes { //# From this offset check if reading 4 bytes gives "ihdr" (as bytes 69-68-64-72) if ( byteBuff.getInt(offset) == 0x69686472 ) //# if the 4 bytes make "ihdr" { System.out.println("found \"ihdr\" section at offset : " + offset ); //# extract Width or Height from this offset myHeight = byteBuff.getInt(offset+4); //# +4 from "ihdr" is Height entry myWidth = byteBuff.getInt(offset+8); //# +8 from "ihdr" is Width entry //# check values System.out.println("Image Width : " + myWidth); System.out.println("Image Height : " + myHeight); break; //# end the While loop (otherwise runs forever) } } offset++; //# increment offset during While loop process } } //# Convert byte values to Hex string for checking private static String bytesToHex(byte[] bytes) { myString = ""; myString = DatatypeConverter.printHexBinary(bytes); return myString; } private static int bytesToNumber( ByteBuffer input ) //throws IOException { input.rewind(); myNum = input.getInt(); return myNum; } private static String decimalToHex(int input) { input = input & 0xFF; myString = Integer.toHexString(input); if(myString.length() == 1) {myString="0"+myString;} return myString.toUpperCase(); } } //end Class