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Image file processing

  1. Apr 30, 2005 #1
    I want to write a program in Java that reads RGB information pixel-by-pixel from an image file, processes that information, and then writes it to a text file. I know how to do everything except read from the image file. I'm thinking a Bitmap file might be the best choice for the image file, unless there's a simpler option.

    I am not averse to using a "kludge" like transforming the image file into text using some other application and then working with that, if that would make the processing easier; I only care about the result. I have read that it is easy to do a text dump of a bitmap like that in Unix, but I'm using Windows XP. So, how does one work with image files? Thanks for any help.
     
  2. jcsd
  3. Apr 30, 2005 #2

    robphy

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  4. Apr 30, 2005 #3
    How do I use all this stuff? I can't tell if that's what I want or not. It seems that it was designed as a stand-alone program.

    All I want to do is read RGB triplets from a bitmap file.
     
  5. Apr 30, 2005 #4
    Sun has there own API for accessing and manipulating images It is called the Java Advanced Imaging toolkit (JAI). Documentation can be found here

    An alternative would be to write your own methods to read in the header and map the file to some custom class(I would call it BMPmage or something like that) and perform you processing from there. BMP iis a pretty simple format, unlike say JPEG or even GIF that has compression. Here is a URL I found that documents the BMP format http://www.inversereality.org/tutorials/graphics programming/BitmapLoading.html
    You should be able to google for more.

    ImageJ's functionality doesn't seem easier to use than Sun's JAI, so I wouldn't see much point in using it. If you did go that route, it looks like you would download the source code for the application and use the classes to load your image file into an ImagePlus class, to perform manipulation on them. Browsing the source however, the API does not seem like it was that well designed (classes are too interdependent and not self-contained like they should be)
     
  6. Apr 30, 2005 #5
    Try using perl from the XP DOS command line. If you don't know it, read something about some of the instructions, these problems are nicely dealt with in perl.

    example:

    $_='p0.jpg';
    open inf,$_; binmode inf;

    while (read(inf,$buffer,6))
    { # here you can do whatever with each character of the binary file


    execute from dos as c:\perl thisprogram.pl > result
     
  7. Apr 30, 2005 #6

    chroot

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    Java contains built-in image-processing functions.

    Use java.awt.Toolkit.createImage() or java.awt.Toolkit.getImage() to read a GIF, JPG, or PNG file into a java.awt.Image object.

    Next, use java.awt.image.PixelGrabber to read the pixel data from the Image.

    Whatever you do, don't try to follow oldtobor's horrible advice and try to decode the image yourself, byte-by-byte. Image manipulation libraries exist for Perl, also.

    - Warren
     
  8. Apr 30, 2005 #7
    It sounds like he needs access to BMP, which is not supported by the AWT methods.

    I don't see how reading and parsing an BMP is that bad. Its a pretty simple, uncompressed image format.
     
  9. Apr 30, 2005 #8
    He wants to do it in Java, not Perl.
     
  10. Apr 30, 2005 #9
    I think you can use javax.imageio.ImageIO.read to read BMP files.
     
  11. Apr 30, 2005 #10
    Coda, ImageIO might be the trick. Here is the line I'm going to try:
    BufferedImage input = ImageIO.read(new File(INPUT));
    And then I can use input to get RGB triplets (I hope).
     
  12. Apr 30, 2005 #11
    I don't know, I keep getting a null pointer exception. I'm not sure how I'm supposed to write the filename--my best guess right now is "c:\\javawork\\textpics\\input.bmp", is that right?
     
  13. Apr 30, 2005 #12
    Ah, it was just that it couldn't read a bmp file. It's working with a gif file.
     
  14. Apr 30, 2005 #13
    I know that it supports BMP files in the newest version of Java (1.5 or 5.0, whatever). It might not in the 1.4 version.
     
  15. Apr 30, 2005 #14
    Yeah, I have the 1.4.2 version. That image there was the output of the program when I just ran it (only a couple bugs). There still is a bug though because a line got chopped off the top of that. Hmm.
     
  16. Apr 30, 2005 #15
    Aha, it didn't get chopped off, it's just way over on the right.
     
  17. Apr 30, 2005 #16
    This is strange... I just changed the input file for another one and now it's not working. Maybe variation in the file format?
     
  18. Apr 30, 2005 #17
    It works! Almost! Now that is one strange error, with the right side of his head getting chopped off and put on the next line. I don't know what's causing that...
     
  19. Apr 30, 2005 #18
    (The trick, by the way, I believe lies in first saving it as a 24 bit bitmap before saving it as a gif; I think that ensures that the gif is in the right format)
     
  20. Apr 30, 2005 #19
    NOW it's working! Thanks a lot everyone for your help. Now I can transform a smiley into a text image in a matter of seconds :). If you posted in this thread and you want to see the code so you can do it too then ask me; I don't want to just post it for everyone to see.
     
    Last edited: Apr 30, 2005
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