A Java class to determine image width, height and color depth for a number of image file formats. Written by Marco Schmidt

gistfile1.java

/*
 * ImageInfo.java
 *
 * Version 1.9
 *
 * A Java class to determine image width, height and color depth for
 * a number of image file formats.
 *
 * Written by Marco Schmidt 
 *
 * Contributed to the Public Domain.
 */

import java.io.DataInput;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.IOException;
import java.net.URL;
import java.util.Vector;

/**
 * Get file format, image resolution, number of bits per pixel and optionally 
 * number of images, comments and physical resolution from 
 * JPEG, GIF, BMP, PCX, PNG, IFF, RAS, PBM, PGM, PPM and PSD files 
 * (or input streams).
 * <p>
 * Use the class like this:
 * <pre>
 * ImageInfo ii = new ImageInfo();
 * ii.setInput(in); // in can be InputStream or RandomAccessFile
 * ii.setDetermineImageNumber(true); // default is false
 * ii.setCollectComments(true); // default is false
 * if (!ii.check()) {
 *   System.err.println("Not a supported image file format.");
 *   return;
 * }
 * System.out.println(ii.getFormatName() + ", " + ii.getMimeType() + 
 *   ", " + ii.getWidth() + " x " + ii.getHeight() + " pixels, " + 
 *   ii.getBitsPerPixel() + " bits per pixel, " + ii.getNumberOfImages() +
 *   " image(s), " + ii.getNumberOfComments() + " comment(s).");
 *  // there are other properties, check out the API documentation
 * </pre>
 * You can also use this class as a command line program.
 * Call it with a number of image file names and URLs as parameters:
 * <pre>
 *   java ImageInfo *.jpg *.png *.gif http://somesite.tld/image.jpg
 * </pre>
 * or call it without parameters and pipe data to it:
 * <pre>
 *   java ImageInfo &lt; image.jpg  
 * </pre>
 * <p>
 * Known limitations:
 * <ul>
 * <li>When the determination of the number of images is turned off, GIF bits 
 *  per pixel are only read from the global header.
 *  For some GIFs, local palettes change this to a typically larger
 *  value. To be certain to get the correct color depth, call
 *  setDetermineImageNumber(true) before calling check().
 *  The complete scan over the GIF file will take additional time.</li>
 * <li>Transparency information is not included in the bits per pixel count.
 *  Actually, it was my decision not to include those bits, so it's a feature! ;-)</li>
 * </ul>
 * <p>
 * Requirements:
 * <ul>
 * <li>Java 1.1 or higher</li>
 * </ul>
 * <p>
 * The latest version can be found at <a href="http://schmidt.devlib.org/image-info/">http://schmidt.devlib.org/image-info/</a>.
 * <p>
 * Written by Marco Schmidt.
 * <p>
 * This class is contributed to the Public Domain.
 * Use it at your own risk.
 * <p>
 * <a name="history">History</a>:
 * <ul>
 * <li><strong>2001-08-24</strong> Initial version.</li>
 * <li><strong>2001-10-13</strong> Added support for the file formats BMP and PCX.</li>
 * <li><strong>2001-10-16</strong> Fixed bug in read(int[], int, int) that returned
 * <li><strong>2002-01-22</strong> Added support for file formats Amiga IFF and Sun Raster (RAS).</li>
 * <li><strong>2002-01-24</strong> Added support for file formats Portable Bitmap / Graymap / Pixmap (PBM, PGM, PPM) and Adobe Photoshop (PSD).
 *   Added new method getMimeType() to return the MIME type associated with a particular file format.</li>
 * <li><strong>2002-03-15</strong> Added support to recognize number of images in file. Only works with GIF.
 *   Use {@link #setDetermineImageNumber} with <code>true</code> as argument to identify animated GIFs
 *   ({@link #getNumberOfImages()} will return a value larger than <code>1</code>).</li>
 * <li><strong>2002-04-10</strong> Fixed a bug in the feature 'determine number of images in animated GIF' introduced with version 1.1.
 *   Thanks to Marcelo P. Lima for sending in the bug report. 
 *   Released as 1.1.1.</li>
 * <li><strong>2002-04-18</strong> Added {@link #setCollectComments(boolean)}. 
 *  That new method lets the user specify whether textual comments are to be  
 *  stored in an internal list when encountered in an input image file / stream.
 *  Added two methods to return the physical width and height of the image in dpi: 
 *   {@link #getPhysicalWidthDpi()} and {@link #getPhysicalHeightDpi()}.
 *  If the physical resolution could not be retrieved, these methods return <code>-1</code>.
 *  </li>
 * <li><strong>2002-04-23</strong> Added support for the new properties physical resolution and
 *   comments for some formats. Released as 1.2.</li>
 * <li><strong>2002-06-17</strong> Added support for SWF, sent in by Michael Aird.
 *  Changed checkJpeg() so that other APP markers than APP0 will not lead to a failure anymore.
 *  Released as 1.3.</li>
 * <li><strong>2003-07-28</strong> Bug fix - skip method now takes return values into consideration.
 *  Less bytes than necessary may have been skipped, leading to flaws in the retrieved information in some cases.
 *  Thanks to Bernard Bernstein for pointing that out.
 *  Released as 1.4.</li>
 * <li><strong>2004-02-29</strong> Added support for recognizing progressive JPEG and
 *  interlaced PNG and GIF. A new method {@link #isProgressive()} returns whether ImageInfo
 *  has found that the storage type is progressive (or interlaced). 
 *  Thanks to Joe Germuska for suggesting the feature.
 *  Bug fix: BMP physical resolution is now correctly determined.
 *  Released as 1.5.</li>
 * <li><strong>2004-11-30</strong> Bug fix: recognizing progressive GIFs 
 * (interlaced in GIF terminology) did not work (thanks to Franz Jeitler for 
 *   pointing this out). Now it should work, but only if the number of images is determined.
 *  This is because information on interlacing is stored in a local image header.
 *  In theory, different images could be stored interlaced and non-interlaced in one 
 *  file. However, I think  that's unlikely. Right now, the last image in the GIF file 
 *  that is examined by ImageInfo is used for the "progressive" status.</li>
 * <li><strong>2005-01-02</strong> Some code clean up (unused methods and variables
 *  commented out, missing javadoc comments, etc.). Thanks to George Sexton for a long list.
 *  Removed usage of Boolean.toString because
 *  it's a Java 1.4+ feature (thanks to Gregor Dupont).
 *  Changed delimiter character in compact output from semicolon to tabulator
 * (for better integration with cut(1) and other Unix tools).
 *  Added some points to the <a href="http://schmidt.devlib.org/image-info/index.html#knownissues">'Known
 *  issues' section of the website</a>. 
 *  Released as 1.6.</li>
 * <li><strong>2005-07-26</strong> Removed code to identify Flash (SWF) files.
 *  Has repeatedly led to problems and support requests, and I don't know the
 *  format and don't have the time and interest to fix it myself.
 *  I repeatedly included fixes by others which didn't work for some people.
 *  I give up on SWF. Please do not contact me about it anymore.
 *  Set package of ImageInfo class to org.devlib.schmidt.imageinfo (a package
 *  was repeatedly requested by some users).
 *  Released as 1.7.</li>
 *  <li><strong>2006-02-23</strong> Removed Flash helper methods which weren't used elsewhere.
 *   Updated skip method which tries "read" whenever "skip(Bytes)" returns a result of 0.
 *   The old method didn't work with certain input stream types on truncated data streams.
 *   Thanks to Martin Leidig for reporting this and sending in code.
 *   Released as 1.8.</li>
 *  </li>
 *  <li><strong>2006-11-13</strong> Removed check that made ImageInfo report JPEG APPx
 *   markers smaller than 14 bytes as files in unknown format. Such JPEGs seem to be
 *   generated by Google's Picasa application. First reported with fix by 
 *   Karl von Randow. Released as 1.9.</li>  
 * </ul>
 * @author Marco Schmidt
 */
public class ImageInfo {
  /**
	 * Return value of {@link #getFormat()} for JPEG streams.
	 * ImageInfo can extract physical resolution and comments
	 * from JPEGs (only from APP0 headers).
	 * Only one image can be stored in a file.
	 * It is determined whether the JPEG stream is progressive 
	 * (see {@link #isProgressive()}).
	 */
	public static final int FORMAT_JPEG = 0;

	/**
	 * Return value of {@link #getFormat()} for GIF streams.
	 * ImageInfo can extract comments from GIFs and count the number
	 * of images (GIFs with more than one image are animations).
	 * It is determined whether the GIF stream is interlaced (see {@link #isProgressive()}).
	 */
	public static final int FORMAT_GIF = 1;

	/**
	 * Return value of {@link #getFormat()} for PNG streams.
	 * PNG only supports one image per file.
	 * Both physical resolution and comments can be stored with PNG,
	 * but ImageInfo is currently not able to extract those.
	 * It is determined whether the PNG stream is interlaced (see {@link #isProgressive()}).
	 */
	public static final int FORMAT_PNG = 2;

	/**
	 * Return value of {@link #getFormat()} for BMP streams.
	 * BMP only supports one image per file.
	 * BMP does not allow for comments.
	 * The physical resolution can be stored.
	 */
	public static final int FORMAT_BMP = 3;

	/**
	 * Return value of {@link #getFormat()} for PCX streams.
	 * PCX does not allow for comments or more than one image per file.
	 * However, the physical resolution can be stored.
	 */
	public static final int FORMAT_PCX = 4;

	/**
	 * Return value of {@link #getFormat()} for IFF streams.
	 */
	public static final int FORMAT_IFF = 5;

	/**
	 * Return value of {@link #getFormat()} for RAS streams.
	 * Sun Raster allows for one image per file only and is not able to
	 * store physical resolution or comments.
	 */
	public static final int FORMAT_RAS = 6;

	/** Return value of {@link #getFormat()} for PBM streams. */
	public static final int FORMAT_PBM = 7;

	/** Return value of {@link #getFormat()} for PGM streams. */
	public static final int FORMAT_PGM = 8;

	/** Return value of {@link #getFormat()} for PPM streams. */
	public static final int FORMAT_PPM = 9;

	/** Return value of {@link #getFormat()} for PSD streams. */
	public static final int FORMAT_PSD = 10;

/*	public static final int COLOR_TYPE_UNKNOWN = -1;
	public static final int COLOR_TYPE_TRUECOLOR_RGB = 0;
	public static final int COLOR_TYPE_PALETTED = 1;
	public static final int COLOR_TYPE_GRAYSCALE= 2;
	public static final int COLOR_TYPE_BLACK_AND_WHITE = 3;*/

	/**
	 * The names of all supported file formats.
	 * The FORMAT_xyz int constants can be used as index values for
	 * this array.
	 */
	private static final String[] FORMAT_NAMES =
		{"JPEG", "GIF", "PNG", "BMP", "PCX", 
		 "IFF", "RAS", "PBM", "PGM", "PPM", 
		 "PSD"};

	/**
	 * The names of the MIME types for all supported file formats.
	 * The FORMAT_xyz int constants can be used as index values for
	 * this array.
	 */
	private static final String[] MIME_TYPE_STRINGS =
		{"image/jpeg", "image/gif", "image/png", "image/bmp", "image/pcx", 
		 "image/iff", "image/ras", "image/x-portable-bitmap", "image/x-portable-graymap", "image/x-portable-pixmap", 
		 "image/psd"};

	private int width;
	private int height;
	private int bitsPerPixel;
	//private int colorType = COLOR_TYPE_UNKNOWN;
	private boolean progressive;
	private int format;
	private InputStream in;
	private DataInput din;
	private boolean collectComments = true;
	private Vector comments;
	private boolean determineNumberOfImages;
	private int numberOfImages;
	private int physicalHeightDpi;
	private int physicalWidthDpi;

	private void addComment(String s) {
		if (comments == null) {
			comments = new Vector();
		}
		comments.addElement(s);
	}

	/**
	 * Call this method after you have provided an input stream or file
	 * using {@link #setInput(InputStream)} or {@link #setInput(DataInput)}.
	 * If true is returned, the file format was known and information
	 * on the file's content can be retrieved using the various getXyz methods.
	 * @return if information could be retrieved from input
	 */
	public boolean check() {
		format = -1;
		width = -1;
		height = -1;
		bitsPerPixel = -1;
		numberOfImages = 1;
		physicalHeightDpi = -1;
		physicalWidthDpi = -1;
		comments = null;
		try {
			int b1 = read() & 0xff;
			int b2 = read() & 0xff;
			if (b1 == 0x47 && b2 == 0x49) {
				return checkGif();
			}
			else
			if (b1 == 0x89 && b2 == 0x50) {
				return checkPng();
			}
			else
			if (b1 == 0xff && b2 == 0xd8) {
				return checkJpeg();
			}
			else
			if (b1 == 0x42 && b2 == 0x4d) {
				return checkBmp();
			}
			else
			if (b1 == 0x0a && b2 < 0x06) {
				return checkPcx();
			}
			else
			if (b1 == 0x46 && b2 == 0x4f) {
				return checkIff();
			}
			else
			if (b1 == 0x59 && b2 == 0xa6) {
				return checkRas();
			}
			else
			if (b1 == 0x50 && b2 >= 0x31 && b2 <= 0x36) {
				return checkPnm(b2 - '0');
			}
			else
			if (b1 == 0x38 && b2 == 0x42) {
				return checkPsd();
			}
			else {
				return false;
			}
		} catch (IOException ioe) {
			return false;
		}
	}

	private boolean checkBmp() throws IOException {
		byte[] a = new byte[44];
		if (read(a) != a.length) {
			return false;
		}
		width = getIntLittleEndian(a, 16);
		height = getIntLittleEndian(a, 20);
		if (width < 1 || height < 1) {
			return false;
		}
		bitsPerPixel = getShortLittleEndian(a, 26);
		if (bitsPerPixel != 1 && bitsPerPixel != 4 &&
		    bitsPerPixel != 8 && bitsPerPixel != 16 &&
		    bitsPerPixel != 24 && bitsPerPixel != 32) {
		    return false;
		}
		int x = (int)(getIntLittleEndian(a, 36) * 0.0254);
		if (x > 0) {
			setPhysicalWidthDpi(x);
		}
		int y = (int)(getIntLittleEndian(a, 40) * 0.0254);
		if (y > 0) {
			setPhysicalHeightDpi(y);
		}
		format = FORMAT_BMP;
		return true;
	}

	private boolean checkGif() throws IOException {
		final byte[] GIF_MAGIC_87A = {0x46, 0x38, 0x37, 0x61};
		final byte[] GIF_MAGIC_89A = {0x46, 0x38, 0x39, 0x61};
		byte[] a = new byte[11]; // 4 from the GIF signature + 7 from the global header
		if (read(a) != 11) {
			return false;
		}
		if ((!equals(a, 0, GIF_MAGIC_89A, 0, 4)) &&
			(!equals(a, 0, GIF_MAGIC_87A, 0, 4))) {
			return false;
		}
		format = FORMAT_GIF;
		width = getShortLittleEndian(a, 4);
		height = getShortLittleEndian(a, 6);
		int flags = a[8] & 0xff;
		bitsPerPixel = ((flags >> 4) & 0x07) + 1;
		//progressive = (flags & 0x02) != 0;
		if (!determineNumberOfImages) {
			return true;
		}
		// skip global color palette
		if ((flags & 0x80) != 0) {
			int tableSize = (1 << ((flags & 7) + 1)) * 3;
			skip(tableSize);
		}
		numberOfImages = 0;
		int blockType;
		do
		{
			blockType = read();
			switch(blockType)
			{
				case(0x2c): // image separator
				{
					if (read(a, 0, 9) != 9) {
						return false;
					}
					flags = a[8] & 0xff;
					progressive = (flags & 0x40) != 0;
					/*int locWidth = getShortLittleEndian(a, 4);
					int locHeight = getShortLittleEndian(a, 6);
					System.out.println("LOCAL: " + locWidth + " x " + locHeight);*/
					int localBitsPerPixel = (flags & 0x07) + 1;
					if (localBitsPerPixel > bitsPerPixel) {
						bitsPerPixel = localBitsPerPixel;
					}
					if ((flags & 0x80) != 0) {
						skip((1 << localBitsPerPixel) * 3);
					}
					skip(1); // initial code length
					int n;
					do
					{
						n = read();
						if (n > 0) {
							skip(n);
						}
						else
						if (n == -1) {
							return false;
						}
					}
					while (n > 0);
					numberOfImages++;
					break;
				}
				case(0x21): // extension
				{
					int extensionType = read();
					if (collectComments && extensionType == 0xfe) {
						StringBuffer sb = new StringBuffer();
						int n;
						do
						{
							n = read();
							if (n == -1) {
								return false;
							}
							if (n > 0) {
								for (int i = 0; i < n; i++) {
									int ch = read();
									if (ch == -1) {
										return false;
									}
									sb.append((char)ch);
								}
							}
						}
						while (n > 0);
					} else {
						int n;
						do
						{
							n = read();
							if (n > 0) {
								skip(n);
							}
							else
							if (n == -1) {
								return false;
							}
						}
						while (n > 0);
					}
					break;
				}
				case(0x3b): // end of file
				{
					break;
				}
				default:
				{
					return false;
				}
			}
		}
		while (blockType != 0x3b);
		return true;
	}

	private boolean checkIff() throws IOException {
		byte[] a = new byte[10];
		// read remaining 2 bytes of file id, 4 bytes file size 
		// and 4 bytes IFF subformat
		if (read(a, 0, 10) != 10) {
			return false;
		}
		final byte[] IFF_RM = {0x52, 0x4d};
		if (!equals(a, 0, IFF_RM, 0, 2)) {
			return false;
		}
		int type = getIntBigEndian(a, 6);
		if (type != 0x494c424d && // type must be ILBM...
		    type != 0x50424d20) { // ...or PBM
		    return false;
		}
		// loop chunks to find BMHD chunk
		do {
			if (read(a, 0, 8) != 8) {
				return false;
			}
			int chunkId = getIntBigEndian(a, 0);
			int size = getIntBigEndian(a, 4);
			if ((size & 1) == 1) {
				size++;
			}
			if (chunkId == 0x424d4844) { // BMHD chunk
				if (read(a, 0, 9) != 9) {
					return false;
				}
				format = FORMAT_IFF;
				width = getShortBigEndian(a, 0);
				height = getShortBigEndian(a, 2);
				bitsPerPixel = a[8] & 0xff;
				return (width > 0 && height > 0 && bitsPerPixel > 0 && bitsPerPixel < 33);
			} else {
				skip(size);
			}
		} while (true);
	}

	private boolean checkJpeg() throws IOException {
		byte[] data = new byte[12];
		while (true) {
			if (read(data, 0, 4) != 4) {
				return false;
			}
			int marker = getShortBigEndian(data, 0);
			int size = getShortBigEndian(data, 2);
			if ((marker & 0xff00) != 0xff00) {
				return false; // not a valid marker
			}
			if (marker == 0xffe0) { // APPx 
				if (size < 14) {
					// not an APPx header as we know it, skip
					skip(size - 2);
					continue;
				}
				if (read(data, 0, 12) != 12) {
					return false;
				}
				final byte[] APP0_ID = {0x4a, 0x46, 0x49, 0x46, 0x00};
				if (equals(APP0_ID, 0, data, 0, 5)) {
					//System.out.println("data 7=" + data[7]);
					if (data[7] == 1) {
						setPhysicalWidthDpi(getShortBigEndian(data, 8));
						setPhysicalHeightDpi(getShortBigEndian(data, 10));
					}
					else
					if (data[7] == 2) {
						int x = getShortBigEndian(data, 8);
						int y = getShortBigEndian(data, 10);
						setPhysicalWidthDpi((int)(x * 2.54f));
						setPhysicalHeightDpi((int)(y * 2.54f));
					}
				}
				skip(size - 14);
			}
			else
			if (collectComments && size > 2 && marker == 0xfffe) { // comment
				size -= 2;
				byte[] chars = new byte[size];
				if (read(chars, 0, size) != size) {
					return false;
				}
				String comment = new String(chars, "iso-8859-1");
				comment = comment.trim();
				addComment(comment);
			}
			else
			if (marker >= 0xffc0 && marker <= 0xffcf && marker != 0xffc4 && marker != 0xffc8) {
				if (read(data, 0, 6) != 6) {
					return false;
				}
				format = FORMAT_JPEG;
				bitsPerPixel = (data[0] & 0xff) * (data[5] & 0xff);
				progressive = marker == 0xffc2 || marker == 0xffc6 ||
					marker == 0xffca || marker == 0xffce;
				width = getShortBigEndian(data, 3);
				height = getShortBigEndian(data, 1);
				return true;
			} else {
				skip(size - 2);
			}
		}
	}

	private boolean checkPcx() throws IOException {
		byte[] a = new byte[64];
		if (read(a) != a.length) {
			return false;
		}
		if (a[0] != 1) { // encoding, 1=RLE is only valid value
			return false;
		}
		// width / height
		int x1 = getShortLittleEndian(a, 2);
		int y1 = getShortLittleEndian(a, 4);
		int x2 = getShortLittleEndian(a, 6);
		int y2 = getShortLittleEndian(a, 8);
		if (x1 < 0 || x2 < x1 || y1 < 0 || y2 < y1) {
			return false;
		}
		width = x2 - x1 + 1;
		height = y2 - y1 + 1;
		// color depth
		int bits = a[1];
		int planes = a[63];
		if (planes == 1 &&
		    (bits == 1 || bits == 2 || bits == 4 || bits == 8)) {
			// paletted
			bitsPerPixel = bits;
		} else
		if (planes == 3 && bits == 8) {
			// RGB truecolor
			bitsPerPixel = 24;
		} else {
			return false;
		}
		setPhysicalWidthDpi(getShortLittleEndian(a, 10));
		setPhysicalHeightDpi(getShortLittleEndian(a, 10));
		format = FORMAT_PCX;
		return true;
	}

	private boolean checkPng() throws IOException {
		final byte[] PNG_MAGIC = {0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a};
		byte[] a = new byte[27];
		if (read(a) != 27) {
			return false;
		}
		if (!equals(a, 0, PNG_MAGIC, 0, 6)) {
			return false;
		}
		format = FORMAT_PNG;
		width = getIntBigEndian(a, 14);
		height = getIntBigEndian(a, 18);
		bitsPerPixel = a[22] & 0xff;
		int colorType = a[23] & 0xff;
		if (colorType == 2 || colorType == 6) {
			bitsPerPixel *= 3;
		}
		progressive = (a[26] & 0xff) != 0;
		return true;
	}

	private boolean checkPnm(int id) throws IOException {
		if (id < 1 || id > 6) {
			return false;
		}
		final int[] PNM_FORMATS = {FORMAT_PBM, FORMAT_PGM, FORMAT_PPM};
		format = PNM_FORMATS[(id - 1) % 3];
		boolean hasPixelResolution = false;
		String s;
		while (true)
		{
			s = readLine();
			if (s != null) {
				s = s.trim();
			}
			if (s == null || s.length() < 1) {
				continue;
			}
			if (s.charAt(0) == '#') { // comment
				if (collectComments && s.length() > 1) {
					addComment(s.substring(1));
				}
				continue;
			}
			if (!hasPixelResolution) { // split "343 966" into width=343, height=966
				int spaceIndex = s.indexOf(' ');
				if (spaceIndex == -1) {
					return false;
				}
				String widthString = s.substring(0, spaceIndex);
				spaceIndex = s.lastIndexOf(' ');
				if (spaceIndex == -1) {
					return false;
				}
				String heightString = s.substring(spaceIndex + 1);
				try {
					width = Integer.parseInt(widthString);
					height = Integer.parseInt(heightString);
				} catch (NumberFormatException nfe) {
					return false;
				}
				if (width < 1 || height < 1) {
					return false;
				}
				if (format == FORMAT_PBM) {
					bitsPerPixel = 1;
					return true;
				}
				hasPixelResolution = true;
			}
			else
			{
				int maxSample;
				try {
					maxSample = Integer.parseInt(s);
				} catch (NumberFormatException nfe) {
					return false;
				}
				if (maxSample < 0) {
					return false;
				}
				for (int i = 0; i < 25; i++) {
					if (maxSample < (1 << (i + 1))) {
						bitsPerPixel = i + 1;
						if (format == FORMAT_PPM) {
							bitsPerPixel *= 3;
						}
						return true;
					}
				}
				return false;
			}
		}
	}

	private boolean checkPsd() throws IOException {
		byte[] a = new byte[24];
		if (read(a) != a.length) {
			return false;
		}
		final byte[] PSD_MAGIC = {0x50, 0x53};
		if (!equals(a, 0, PSD_MAGIC, 0, 2)) {
			return false;
		}
		format = FORMAT_PSD;
		width = getIntBigEndian(a, 16);
		height = getIntBigEndian(a, 12);
		int channels = getShortBigEndian(a, 10);
		int depth = getShortBigEndian(a, 20);
		bitsPerPixel = channels * depth;
		return (width > 0 && height > 0 && bitsPerPixel > 0 && bitsPerPixel <= 64);
	}

	private boolean checkRas() throws IOException {
		byte[] a = new byte[14];
		if (read(a) != a.length) {
			return false;
		}
		final byte[] RAS_MAGIC = {0x6a, (byte)0x95};
		if (!equals(a, 0, RAS_MAGIC, 0, 2)) {
			return false;
		}
		format = FORMAT_RAS;
		width = getIntBigEndian(a, 2);
		height = getIntBigEndian(a, 6);
		bitsPerPixel = getIntBigEndian(a, 10);
		return (width > 0 && height > 0 && bitsPerPixel > 0 && bitsPerPixel <= 24);
	}

	/**
	 * Run over String list, return false iff at least one of the arguments
	 * equals <code>-c</code>.
	 * @param args string list to check
	 */
	private static boolean determineVerbosity(String[] args) {
		if (args != null && args.length > 0) {
			for (int i = 0; i < args.length; i++) {
				if ("-c".equals(args[i])) {
					return false;
				}
			}
		}
		return true;
	}

	private static boolean equals(byte[] a1, int offs1, byte[] a2, int offs2, int num) {
		while (num-- > 0) {
			if (a1[offs1++] != a2[offs2++]) {
				return false;
			}
		}
		return true;
	}

	/** 
	 * If {@link #check()} was successful, returns the image's number of bits per pixel.
	 * Does not include transparency information like the alpha channel.
	 * @return number of bits per image pixel
	 */
	public int getBitsPerPixel() {
		return bitsPerPixel;
	}

	/**
	 * Returns the index'th comment retrieved from the file.
	 * @param index int index of comment to return
	 * @throws IllegalArgumentException if index is smaller than 0 or larger than or equal
	 * to the number of comments retrieved
	 * @see #getNumberOfComments
	 */
	public String getComment(int index) {
		if (comments == null || index < 0 || index >= comments.size()) {
			throw new IllegalArgumentException("Not a valid comment index: " + index);
		}
		return (String)comments.elementAt(index);
	}

	/**
	 * If {@link #check()} was successful, returns the image format as one
	 * of the FORMAT_xyz constants from this class.
	 * Use {@link #getFormatName()} to get a textual description of the file format.
	 * @return file format as a FORMAT_xyz constant
	 */
	public int getFormat() {
		return format;
	}

	/**
	 * If {@link #check()} was successful, returns the image format's name.
	 * Use {@link #getFormat()} to get a unique number.
	 * @return file format name
	 */
	public String getFormatName() {
		if (format >= 0 && format < FORMAT_NAMES.length) {
			return FORMAT_NAMES[format];
		} else {
			return "?";
		}
	}

	/** 
	 * If {@link #check()} was successful, returns one the image's vertical
	 * resolution in pixels.
	 * @return image height in pixels
	 */
	public int getHeight() {
		return height;
	}

	private static int getIntBigEndian(byte[] a, int offs) {
		return
			(a[offs] & 0xff) << 24 | 
			(a[offs + 1] & 0xff) << 16 | 
			(a[offs + 2] & 0xff) << 8 | 
			a[offs + 3] & 0xff;
	}

	private static int getIntLittleEndian(byte[] a, int offs) {
		return
			(a[offs + 3] & 0xff) << 24 | 
			(a[offs + 2] & 0xff) << 16 | 
			(a[offs + 1] & 0xff) << 8 | 
			a[offs] & 0xff;
	}

	/** 
	 * If {@link #check()} was successful, returns a String with the
	 * MIME type of the format.
	 * @return MIME type, e.g. <code>image/jpeg</code>
	 */
	public String getMimeType() {
		if (format >= 0 && format < MIME_TYPE_STRINGS.length) {
			if (format == FORMAT_JPEG && progressive)
			{
				return "image/pjpeg";
			}
			return MIME_TYPE_STRINGS[format];
		} else {
			return null;
		}
	}

	/**
	 * If {@link #check()} was successful and {@link #setCollectComments(boolean)} was called with
	 * <code>true</code> as argument, returns the number of comments retrieved 
	 * from the input image stream / file.
	 * Any number &gt;= 0 and smaller than this number of comments is then a
	 * valid argument for the {@link #getComment(int)} method.
	 * @return number of comments retrieved from input image
	 */
	public int getNumberOfComments()
	{
		if (comments == null) {
			return 0;
		} else {
			return comments.size();
		}
	}

	/**
	 * Returns the number of images in the examined file.
	 * Assumes that <code>setDetermineImageNumber(true);</code> was called before
	 * a successful call to {@link #check()}.
	 * This value can currently be only different from <code>1</code> for GIF images.
	 * @return number of images in file
	 */
	public int getNumberOfImages()
	{
		return numberOfImages;
	}

	/**
	 * Returns the physical height of this image in dots per inch (dpi).
	 * Assumes that {@link #check()} was successful.
	 * Returns <code>-1</code> on failure.
	 * @return physical height (in dpi)
	 * @see #getPhysicalWidthDpi()
	 * @see #getPhysicalHeightInch()
	 */
	public int getPhysicalHeightDpi() {
		return physicalHeightDpi;
	}

	/**
	 * If {@link #check()} was successful, returns the physical width of this image in dpi (dots per inch)
	 * or -1 if no value could be found.
	 * @return physical height (in dpi)
	 * @see #getPhysicalHeightDpi()
	 * @see #getPhysicalWidthDpi()
	 * @see #getPhysicalWidthInch()
	 */
	public float getPhysicalHeightInch() {
		int h = getHeight();
		int ph = getPhysicalHeightDpi();
		if (h > 0 && ph > 0) {
			return ((float)h) / ((float)ph);
		} else {
			return -1.0f;
		}
	}

	/**
	 * If {@link #check()} was successful, returns the physical width of this image in dpi (dots per inch)
	 * or -1 if no value could be found.
	 * @return physical width (in dpi)
	 * @see #getPhysicalHeightDpi()
	 * @see #getPhysicalWidthInch()
	 * @see #getPhysicalHeightInch()
	 */
	public int getPhysicalWidthDpi() {
		return physicalWidthDpi;
	}

	/**
	 * Returns the physical width of an image in inches, or
	 * <code>-1.0f</code> if width information is not available.
	 * Assumes that {@link #check} has been called successfully.
	 * @return physical width in inches or <code>-1.0f</code> on failure
	 * @see #getPhysicalWidthDpi
	 * @see #getPhysicalHeightInch
	 */
	public float getPhysicalWidthInch() {
		int w = getWidth();
		int pw = getPhysicalWidthDpi();
		if (w > 0 && pw > 0) {
			return ((float)w) / ((float)pw);
		} else {
			return -1.0f;
		}
	}

	private static int getShortBigEndian(byte[] a, int offs) {
		return
			(a[offs] & 0xff) << 8 | 
			(a[offs + 1] & 0xff);
	}

	private static int getShortLittleEndian(byte[] a, int offs) {
		return (a[offs] & 0xff) | (a[offs + 1] & 0xff) << 8;
	}

	/** 
	 * If {@link #check()} was successful, returns one the image's horizontal
	 * resolution in pixels.
	 * @return image width in pixels
	 */
	public int getWidth() {
		return width;
	}

	/**
	 * Returns whether the image is stored in a progressive (also called: interlaced) way.
	 * @return true for progressive/interlaced, false otherwise
	 */
	public boolean isProgressive()
	{
		return progressive;
	}

	/**
	 * To use this class as a command line application, give it either 
	 * some file names as parameters (information on them will be
	 * printed to standard output, one line per file) or call
	 * it with no parameters. It will then check data given to it
	 * via standard input.
	 * @param args the program arguments which must be file names
	 */
	public static void main(String[] args) {
		ImageInfo imageInfo = new ImageInfo();
		imageInfo.setDetermineImageNumber(true);
		boolean verbose = determineVerbosity(args);
		if (args.length == 0) {
			run(null, System.in, imageInfo, verbose);
		} else {
			int index = 0;
			while (index < args.length) {
				InputStream in = null;
				try {
					String name = args[index++];
					System.out.print(name + ";");
					if (name.startsWith("http://")) {
						in = new URL(name).openConnection().getInputStream();
					} else {
						in = new FileInputStream(name);
					}
					run(name, in, imageInfo, verbose);
					in.close();
				} catch (IOException e) {
					System.out.println(e);
					try {
						if (in != null) {
							in.close();
						}
					} catch (IOException ee) {
					}
				}
			}
		}
	}

	private static void print(String sourceName, ImageInfo ii, boolean verbose) {
		if (verbose) {
			printVerbose(sourceName, ii);
		} else {
			printCompact(sourceName, ii);
		}
	}

	private static void printCompact(String sourceName, ImageInfo imageInfo) {
		final String SEP = "\t";
		System.out.println(
			sourceName + SEP + 
			imageInfo.getFormatName() + SEP +
			imageInfo.getMimeType() + SEP +
			imageInfo.getWidth() + SEP +
			imageInfo.getHeight() + SEP +
			imageInfo.getBitsPerPixel() + SEP +
			imageInfo.getNumberOfImages() + SEP +
			imageInfo.getPhysicalWidthDpi() + SEP +
			imageInfo.getPhysicalHeightDpi() + SEP +
			imageInfo.getPhysicalWidthInch() + SEP +
			imageInfo.getPhysicalHeightInch() + SEP +
			imageInfo.isProgressive()
		);
	}

	private static void printLine(int indentLevels, String text, float value, float minValidValue) {
		if (value < minValidValue) {
			return;
		}
		printLine(indentLevels, text, Float.toString(value));
	}

	private static void printLine(int indentLevels, String text, int value, int minValidValue) {
		if (value >= minValidValue) {
			printLine(indentLevels, text, Integer.toString(value));
		}
	}

	private static void printLine(int indentLevels, String text, String value) {
		if (value == null || value.length() == 0) {
			return;
		}
		while (indentLevels-- > 0) {
			System.out.print("\t");
		}
		if (text != null && text.length() > 0) {
			System.out.print(text);
			System.out.print(" ");
		}
		System.out.println(value);
	}

	private static void printVerbose(String sourceName, ImageInfo ii) {
		printLine(0, null, sourceName);
		printLine(1, "File format: ", ii.getFormatName());
		printLine(1, "MIME type: ", ii.getMimeType());
		printLine(1, "Width (pixels): ", ii.getWidth(), 1);
		printLine(1, "Height (pixels): ", ii.getHeight(), 1);
		printLine(1, "Bits per pixel: ", ii.getBitsPerPixel(), 1);
		printLine(1, "Progressive: ", ii.isProgressive() ? "yes" : "no");
		printLine(1, "Number of images: ", ii.getNumberOfImages(), 1);
		printLine(1, "Physical width (dpi): ", ii.getPhysicalWidthDpi(), 1);
		printLine(1, "Physical height (dpi): ", ii.getPhysicalHeightDpi(), 1);
		printLine(1, "Physical width (inches): ", ii.getPhysicalWidthInch(), 1.0f);
		printLine(1, "Physical height (inches): ", ii.getPhysicalHeightInch(), 1.0f);
		int numComments = ii.getNumberOfComments();
		printLine(1, "Number of textual comments: ", numComments, 1);
		if (numComments > 0) {
			for (int i = 0; i < numComments; i++) {
				printLine(2, null, ii.getComment(i));
			}
		}
	}

	private int read() throws IOException {
		if (in != null) {
			return in.read();
		} else {
			return din.readByte();
		}
	}

	private int read(byte[] a) throws IOException {
		if (in != null) {
			return in.read(a);
		} else {
			din.readFully(a);
			return a.length;
		}
	}

	private int read(byte[] a, int offset, int num) throws IOException {
		if (in != null) {
			return in.read(a, offset, num);
		} else {
			din.readFully(a, offset, num);
			return num;
		}
	}

	private String readLine() throws IOException {
		return readLine(new StringBuffer());
	}

	private String readLine(StringBuffer sb) throws IOException {
		boolean finished;
		do {
			int value = read();
			finished = (value == -1 || value == 10);
			if (!finished) {
				sb.append((char)value);
			}
		} while (!finished);
		return sb.toString();
	}

	private static void run(String sourceName, InputStream in, ImageInfo imageInfo, boolean verbose) {
		imageInfo.setInput(in);
		imageInfo.setDetermineImageNumber(true);
		imageInfo.setCollectComments(verbose);
		if (imageInfo.check()) {
			print(sourceName, imageInfo, verbose);
		}
	}

	/**
	 * Specify whether textual comments are supposed to be extracted from input.
	 * Default is <code>false</code>.
	 * If enabled, comments will be added to an internal list.
	 * @param newValue if <code>true</code>, this class will read comments
	 * @see #getNumberOfComments
	 * @see #getComment
	 */
	public void setCollectComments(boolean newValue)
	{
		collectComments = newValue;
	}

	/**
	 * Specify whether the number of images in a file is to be
	 * determined - default is <code>false</code>.
	 * This is a special option because some file formats require running over
	 * the entire file to find out the number of images, a rather time-consuming
	 * task.
	 * Not all file formats support more than one image.
	 * If this method is called with <code>true</code> as argument,
	 * the actual number of images can be queried via 
	 * {@link #getNumberOfImages()} after a successful call to
	 * {@link #check()}.
	 * @param newValue will the number of images be determined?
	 * @see #getNumberOfImages
	 */
	public void setDetermineImageNumber(boolean newValue)
	{
		determineNumberOfImages = newValue;
	}

	/**
	 * Set the input stream to the argument stream (or file). 
	 * Note that {@link java.io.RandomAccessFile} implements
	 * {@link java.io.DataInput}.
	 * @param dataInput the input stream to read from
	 */
	public void setInput(DataInput dataInput) {
		din = dataInput;
		in = null;
	}

	/**
	 * Set the input stream to the argument stream (or file).
	 * @param inputStream the input stream to read from
	 */
	public void setInput(InputStream inputStream) {
		in = inputStream;
		din = null;
	}

	private void setPhysicalHeightDpi(int newValue) {
		physicalWidthDpi = newValue;
	}

	private void setPhysicalWidthDpi(int newValue) {
		physicalHeightDpi = newValue;
	}

    private void skip(int num) throws IOException {
        while (num > 0) {
            long result;
            if (in != null) {
                result = in.skip(num);
            } else {
                result = din.skipBytes(num);
            }
            if (result > 0) {
                num -= result;
            } else {
                if (in != null) {
                    result = in.read();
                } else {
                    result = din.readByte();
                }
                if (result == -1) {
                	throw new IOException("Premature end of input.");
                } else {
                	num--;
                }
            }
        }
    }
}

hi how can i get bit depth for a jpeg image