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From "Gary Lucas (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IMAGING-102) TIFF parser does not support floating-point images
Date Wed, 06 Feb 2013 15:27:16 GMT
Gary Lucas created IMAGING-102:
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             Summary: TIFF parser does not support floating-point images
                 Key: IMAGING-102
                 URL: https://issues.apache.org/jira/browse/IMAGING-102
             Project: Commons Imaging
          Issue Type: Bug
            Reporter: Gary Lucas


The TIFF specification defines a data form for storing pixels as either 32-bit or 64-bit floating
point values given in the IEEE 753 format. The TIFF-6 specification is actually incomplete
in this regard, but typically such values are stored as data in the range [0,1] with 9999
(or other values out of the range zero to one) used to indicate "no-data".   Typically, values
are rendered in gray tones. The TIFF "SampleFormat" tag indicates when data is encoded in
this form.

Commons Imaging does not currently support data that uses the floating-point sample format.
 It does define a constant in the TiffTagConstants.java file which is named SAMPLE_FORMAT_VALUE_IEEE_FLOATING_POINT.
 But this constant is not used in the code.

I propose to at least implement read-support for images in this format. I am working to obtain
permission to post a sample image which I will attach to this tracker item in the future.


Currently, the TIFF parser provides output in the form of a BufferedImage. For the initial
implementation, I recommend staying with that convention and resolving the floating point
values to gray tones. Although this approach has the disadvantage that it will not provide
an API for extracting the original floating-point values, it seems to me the safest tactic
for an initial implementation.

Development will require some caution to avoid degrading parser performance. The BitImageStream.readBits()
method which reads samples (pixels) from the source data, currently returns the Java int type,
which only supports 32 bits.  To support 64 bits, this function would have to return a Java
long.  The development effort will require testing to ensure that making a change of this
type does not degrade performance for the mainstream TIFF data formats (probably this is only
an issue on 32-bit operating systems).

For those of you who are asking why someone would choose to store data using floating-point
values (at the cost of 64 bits per pixel)... I don't really know. Putting aside the fact that
it's in the spec (sort of) and somebody wants me to plot data from such images, I would have
to say the motivation would probably be using TIFF files as a way of storing arbitrary data
in gridded fields.  The proposed changes wouldn't satisfy their requirements, but it is a
first step in that direction.

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