Re: BufferedImage and bit depth

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 17 Jun 2009 16:48:31 -0700

Message-ID:

<4a3980cf$0$5442$b9f67a60@news.newsdemon.com>

Uli Kunkel wrote:

I'm trying to convert 24bit depth jpg to 16 bit.
I'm using BufferedImage.TYPE_USHORT_565_RGB option to do so.
There are 2 thing that bother me:

1. Anyway when I write the file it always says it is 24 bit in the header.
The photo changes but the bit depth info stays the same.

2. The photo is smaller with 24 bit depth (BufferedImage.TYPE_INT_RGB)
than with 16 bit depth (BufferedImage.TYPE_USHORT_565_RGB) ?!?

Is it even recommendable to have 16bit jpegs?

Thanks in advance for any suggestions.

I don't think that is possible. I'm not an expert but there are two
JPEG file formats, JFIF and Exif. Both of them store the data in a
format according to their color space. The BufferedImage type is not
relevant to the file format other than it determines the color space.

Adjusting the compression of a JPEG written using ImageIO is fairly easy
while not obvious. Below is code I use to write a JPEG image and
control the compression.

You should look at JPEGImageWriteParam class and the docs, "JPEG
Metadata Format Specification and Usage Notes" which you will find near
the top of the JPEGImageWriteParam doc page.

     public static void writeJPEG(RenderedImage image, float quality,
File file)
      throws IOException {
         if (quality < 0.0f || quality > 1.0f)
             throw new IllegalArgumentException("0.0 < Quality < 1.0");
         ImageWriter writer = null;
         Iterator iter = ImageIO.getImageWritersByFormatName("JPEG");
         if (!iter.hasNext())
             throw new IOException("No Writers Available");
         writer = (ImageWriter)iter.next();
         if (file.exists())
             file.delete();
         ImageOutputStream ios = ImageIO.createImageOutputStream(file);
         writer.setOutput(ios);
         JPEGImageWriteParam iwp = new JPEGImageWriteParam(null);
         iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
         iwp.setCompressionQuality(quality);
         writer.write(null,new IIOImage(image,null,null),iwp);
         ios.flush();
         writer.dispose();
         ios.close();
     }

--

Knute Johnson
email s/nospam/knute2009/

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