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https://issues.apache.org/jira/browse/IMAGING-267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17200118#comment-17200118
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Jukka Rahkonen commented on IMAGING-267:
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A few comments that hopefully clarify some points
Georeferencing
The image is georeferenced, or perhaps better say oriented with the ESRI world
file system [https://en.wikipedia.org/wiki/World_file]. The .tfw sidecar file
is telling the coordinates of the centre of the top left corner. Same
information seems to be copied into the ModelTiepointTag but there are no
other GeoTIFF tags and normally .tfw file is used with a baseline TIFF without
any GeoTIFF tags.
The coordinate system is unknown because .tfw does not report the coordinate
system. The ESRI way for presenting the CRS is to include another sidecar file
.prj but this sample is missing it. Thus the image should be considered to be
in some engineering coordinate system, the top-left being at coordinates
262846.525725 4464275.
Bit depth and histogram
Data type of the image 32 bit floating point but the data are in the low end of
the full 32 bit range, between 514 and 2410. Because of this very many TIFF
viewers would show this image as totally black to bare eyes (black because of
min-is-black metadata). Viewers which are prepared to meet this kind of imagery
are using the min/max data range and stretch this range to 0-255 range for
viewing. More clever clients are analyzing the histogram and stretch by the 5 -
95% of the full range. Clients can either analyze the image (slow for big
images) or read the statistics from the normal tiff tags
[https://www.awaresystems.be/imaging/tiff/tifftags/baseline.html]
MinSampleValue and MaxSampleValue if they are present. Geo viewers may support
other ways, in this case by reading the sidecar file .aux.xml
<PAMDataset>
<PAMRasterBand band="1">
<Metadata>
<MDI key="STATISTICS_MAXIMUM">2410</MDI>
<MDI key="STATISTICS_MEAN">1410.9055247993</MDI>
<MDI key="STATISTICS_MINIMUM">514</MDI>
<MDI key="STATISTICS_STDDEV">427.16367167723</MDI>
<MDI key="STATISTICS_VALID_PERCENT">100</MDI>
</Metadata>
</PAMRasterBand>
</PAMDataset>
Min-is-black question
The image is indeed min-is-black and the attached sextante.png is rendered as
min-is-white. Either that is a bug in sextante of perhaps sextante has an
option for reversed colors.
> Colorful rendering of b/w Monoband TIF
> --------------------------------------
>
> Key: IMAGING-267
> URL: https://issues.apache.org/jira/browse/IMAGING-267
> Project: Commons Imaging
> Issue Type: Bug
> Reporter: edgar soldin
> Priority: Major
> Attachments: ISSUE_267.JPG, mdt25a-commons.png, mdt25a-sextante.png,
> mdt25a.tfw, mdt25a.tif, mdt25a.tif.aux.xml
>
>
> see attached images.
> mdt25a.tif - the original tif
> mdt25a-commons.png - as rendered/read with Commons Imaging
> mdt25a-sextante.png - as rendered /read properly with ImageIO-Core from
> https://github.com/jai-imageio/jai-imageio-core
> thanks!.. ede
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