[ImageJ-bugs] [Bug 931] New: Possible error when down-converting from 32- or 16-bit-depth images (to 16- or 8-bit).

[bugzilla at fiji.sc]

http://fiji.sc/bugzilla/show_bug.cgi?id=931

            Bug ID: 931
           Summary: Possible error when down-converting from 32- or
                    16-bit-depth images (to 16- or 8-bit).
           Product: Fiji
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: ImageJ1
          Assignee: imagej-bugs at imagej.net
          Reporter: leonardo.guizzetti at gmail.com

I seem to have a problem down-converting 32-bit to 16- or 8-bit images, or from
16-bit to 8 bit. It appears that even if the image histogram fits neatly inside
an 8-bit image, down-converting causes a re-scaling of all pixel values. My
FIJI and ImageJ1 are up-to-date.


Steps taken to produce the problem:
1) SCIFIO is off.

2) Open Blobs sample (ctrl+shift+b)

3) Measure original image statistics. Pixel values range from 8-248 (originally
8-bit colour image).

4) Convert image to 32-bit, and measure image stats. Pixel values remain the
same.

5) Convert back to 8-bit, and measure image stats. Now, pixel values range from
0-255, and histogram has been stretched to fit entire 8-bit range.

This behaviour seems abnormal to me, as I wouldn't expect the scaling to occur,
and could be destructive for image manipulation.

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