[veenit33]

Hello friends

I am creating a project in J2ME which requires me to select a PNG image from the filesystem of the mobile phone

I load this image in memory

I want to know whether the PNG file data is compressed or no?

When i use the Image.getRGB() method i will be getting the int[] in hand.

Also how do i proceed converting the int[] to byte[]?

I want to use this byte[] to hide bits of data in it..

Actually i am performing Image Steganography in mobile phones.

So whatever text the user enters will be hidden behind the image.
I am using the LSB technique of hiding data ie in each pixel i will be hiding 1 bit.

What is a PNG Encoder?
Also i would like to know will i be needing the PNG Encoder?


Til now what ever image i create i cannot read that back from my application
So if i could get any help from u will be appreciable.

[niujianwei]

You can use a tool to convert a BMP file into a PNG format file.

[veenit33]

I dont need to convert a BMP file to a PNG file
I want to work with PNG images.

My problem is how do i get the byte[] data of PNG file so dat i can modify it according to my need.

What are the steps in doin so...?

[jitu_goldie]

Hi,
Please try out the following link. there is something for ur problem:

http://www.j2meforums.com/forum/inde...;topic=20468.2


hope this will help u somewhile..

thanks,
jitu_goldie..

[mikemoore]

A much better solution to this is at http://www.java-tips.org/java-me-tip...-from-rms.html

- Mike
NAVTEQ Network for Developers
The community for developing innovative location-based applications
http://NN4D.com

[veenit33]

Hello jitu

i am modifying the bits of the PNG data in byte[] and then creating a datachunk.

i use this data chunk to create a byte[] which contains the signature header trailer.

How do i go back to find out as to where did i start modifying the bits

the PNG encoder i am using is as follows:





/*
* Minimal PNG encoder to create MIDP images from RGBA arrays.
*
* Copyright 2006 Christian Froeschlin
*
* Changelog:
*
* 09/22/08: Fixed Adler checksum calculation and byte order
* for storing length of zlib deflate block. Thanks
* to Miloslav R?ži?ka for noting this.
*
* www.chrfr.de
*
*/

import java.io.*;
import javax.microedition.lcdui.Image;

public class PNG
{

public static Image toImage(int width, int height, byte[] alpha, byte[] red, byte[] green, byte[] blue)
{
try
{
byte[] png = toPNG(width, height, alpha, red, green, blue);
return Image.createImage(png, 0, png.length);
}
catch (IOException e)
{
return null;
}
}

public static byte[] toPNG(int width, int height, byte[] alpha, byte[] red, byte[] green, byte[] blue) throws IOException
{
byte[] signature = new byte[] {(byte) 137, (byte) 80, (byte) 78, (byte) 71, (byte) 13, (byte) 10, (byte) 26, (byte) 10};
byte[] header = createHeaderChunk(width, height);
byte[] data = createDataChunk(width, height, alpha, red, green, blue);
byte[] trailer = createTrailerChunk();

ByteArrayOutputStream png = new ByteArrayOutputStream(signature.length + header.length + data.length + trailer.length);

png.write(signature);
png.write(header);
png.write(data);
png.write(trailer);
return png.toByteArray();
}

public static byte[] toPNG(byte[] img_data,int width, int height, byte[] alpha, byte[] red, byte[] green, byte[] blue) throws IOException
{
byte[] signature = new byte[] {(byte) 137, (byte) 80, (byte) 78, (byte) 71, (byte) 13, (byte) 10, (byte) 26, (byte) 10};
byte[] header = createHeaderChunk(width, height);
byte[] data = img_data;
byte[] trailer = createTrailerChunk();

ByteArrayOutputStream png = new ByteArrayOutputStream(signature.length + header.length + data.length + trailer.length);

System.out.println("Signature Length === "+signature.length);
System.out.println("Header Length === "+header.length);
System.out.println("Trailer Length === "+trailer.length);

png.write(signature);
png.write(header);
png.write(data);
png.write(trailer);
return png.toByteArray();
}

public static byte[] createHeaderChunk(int width, int height) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream(13);
DataOutputStream chunk = new DataOutputStream(baos);
chunk.writeInt(width);
chunk.writeInt(height);
chunk.writeByte(8); // Bitdepth
chunk.writeByte(6); // Colortype ARGB
chunk.writeByte(0); // Compression
chunk.writeByte(0); // Filter
chunk.writeByte(0); // Interlace
return toChunk("IHDR", baos.toByteArray());
}

public static byte[] createDataChunk(int width, int height, byte[] alpha, byte[] red, byte[] green, byte[] blue) throws IOException
{
int source = 0;
int dest = 0;
byte[] raw = new byte[4*(width*height) + height];
for (int y = 0; y < height; y++)
{
raw[dest++] = 0; // No filter
for (int x = 0; x < width; x++)
{
raw[dest++] = red[source];
raw[dest++] = green[source];
raw[dest++] = blue[source];
raw[dest++] = alpha[source++];
}
}
return toChunk("IDAT", toZLIB(raw));
}

public static byte[] createTrailerChunk() throws IOException
{
return toChunk("IEND", new byte[] {});
}

public static byte[] toChunk(String id, byte[] raw) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream(raw.length + 12);
DataOutputStream chunk = new DataOutputStream(baos);

chunk.writeInt(raw.length);

byte[] bid = new byte[4];
for (int i = 0; i < 4; i++)
{
bid[i] = (byte) id.charAt(i);
}

chunk.write(bid);

chunk.write(raw);

int crc = 0xFFFFFFFF;
crc = updateCRC(crc, bid);
crc = updateCRC(crc, raw);
chunk.writeInt(~crc);

return baos.toByteArray();
}

static int[] crcTable = null;

public static void createCRCTable()
{
crcTable = new int[256];

for (int i = 0; i < 256; i++)
{
int c = i;
for (int k = 0; k < 8; k++)
{
c = ((c & 1) > 0) ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
}
crcTable[i] = c;
}
}

public static int updateCRC(int crc, byte[] raw)
{
if (crcTable == null)
{
createCRCTable();
}

for (int i = 0; i < raw.length; i++)
{
crc = crcTable[(crc ^ raw[i]) & 0xFF] ^ (crc >>> 8);
}

return crc;
}


// Creates a single zlib block contain a single
// uncompressed deflate block. Must be < 64K!
public static byte[] toZLIB(byte[] raw) throws IOException
{
byte tmp;
ByteArrayOutputStream baos = new ByteArrayOutputStream(raw.length + 5 + 6);
DataOutputStream zlib = new DataOutputStream(baos);
tmp = (byte) (8 + (7 << 16));
zlib.writeByte(tmp); // Compression + Flags
zlib.writeByte((31 - ((tmp << 8) % 31)) % 31); // FCHECK (compr/dict 0)

//Uncompressed deflate block
zlib.writeByte((byte) 1); //Final flag set, Compression type 0
char length = (char) raw.length;
zlib.writeByte((byte)(length & 0xFF)); //Length LSB
zlib.writeByte((byte)((length & 0xFF00) >> 8)); //Length MSB
zlib.writeByte((byte)(~length & 0xFF)); //Length 1st complement LSB
zlib.writeByte((byte)((~length & 0xFF00) >> 8)); //Length 1st complement MSB
zlib.write(raw); //Data

// zlib block check sum
zlib.writeInt(calcADLER32(raw));
return baos.toByteArray();
}

// Unverified (the Java PNG loader did not complain at any value)
public static int calcADLER32(byte[] raw)
{
int s1 = 1;
int s2 = 0;
for (int i = 0; i < raw.length; i++)
{
int abs = raw[i] >=0 ? raw[i] : (raw[i] + 256);
s1 = (s1 + abs) % 65521;
s2 = (s2 + s1) % 65521;
}
return (s2 << 16) + s1;
}
}