Check if a file is an image

Question

I am using JAI and create a file with:

PlanarImage img = JAI.create("fileload", myFilename);

I check before that line if the file exists. But how could I check if the file is a .bmp or a .tiff or an image file?

Does anyone know?

Answer 1

The Image Magick project has facilities to identify image and there's a Java wrapper for Image Magick called JMagick which I think you may want to consider instead of reinventing the wheel:

http://www.jmagick.org

I'm using Image Magick all the time, including its "identify" feature from the command line and it never failed once to identify a picture.

Back in the days where I absolutely needed that feature and JMagick didn't exist yet I used to Runtime.exec() ImageMagick's identify command from Java and it worked perfectly.

Nowadays that JMagick exist this is probably not necessary anymore (but I haven't tried JMagick yet).

Note that it gives much more than just the format, for example:

$  identify tmp3.jpg 
tmp3.jpg JPEG 1680x1050 1680x1050+0+0 DirectClass 8-bit 293.582kb 

$  identify tmp.png
tmp.png PNG 1012x900 1012x900+0+0 DirectClass 8-bit 475.119kb

Answer 2

Try using the width of the image:

boolean isImage(String image_path){
  Image image = new ImageIcon(image_path).getImage();
  if(image.getWidth(null) == -1){
        return false;
  }
  else{
        return true;
  }
}

if the width is -1 then is not image.

Answer 3

To tell if something is a png, I've used this below snippet in Android java.

public CompressFormat getCompressFormat(Context context, Uri fileUri) throws IOException {
    // create input stream
    int numRead;
    byte[] signature = new byte[8];
    byte[] pngIdBytes = { -119, 80, 78, 71, 13, 10, 26, 10 };
    InputStream is = null;

    try {
        ContentResolver resolver = context.getContentResolver();
        is = resolver.openInputStream(fileUri);

        // if first 8 bytes are PNG then return PNG reader
        numRead = is.read(signature);

        if (numRead == -1)
            throw new IOException("Trying to reda from 0 byte stream");

    } finally {
        if (is != null)
            is.close();
    }

    if (numRead == 8 && Arrays.equals(signature, pngIdBytes)) {
        return CompressFormat.PNG;
    }

    return null;
}

Answer 4

At the beginning of files, there is an identifying character sequence. For example JPEG files starts with FF D8 FF.

You can check for this sequence in your program but I am not sure whether this works for every file.

For information about identifying characters you can have a look at http://filext.com