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<div class="moz-cite-prefix">Le 02/06/2021 à 22:08, Javier Jimenez
Shaw a écrit :<br>
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<blockquote type="cite"
cite="mid:CADRrdKsRGezL3MnjyYf+CsXyQhL5vaTRREWh-fvhEJ58zB2Xkw@mail.gmail.com">
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<div>Hi Evert,</div>
<div><br>
</div>
<div>As far as I know, TIFF data type is "constant" along the
bands. You cannot have a uint16 band and a byte band in the
same page.</div>
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</blockquote>
Yes, in theory this would be possible since the SampleFormat tag has
as many values as bands
(<a class="moz-txt-link-freetext" href="https://www.awaresystems.be/imaging/tiff/tifftags/sampleformat.html">https://www.awaresystems.be/imaging/tiff/tifftags/sampleformat.html</a>),
but in practice libtiff only handles its value to be same for all
bands (and similarly for BitsPerSample)<br>
<blockquote type="cite"
cite="mid:CADRrdKsRGezL3MnjyYf+CsXyQhL5vaTRREWh-fvhEJ58zB2Xkw@mail.gmail.com">
<div dir="ltr">
<div>If you are worried about space, you can use the "nodata
value", assigning a single value for that purpose (assuming
that you do not want intermediate values, just on and off).
However I do not know if this nodata is only for GDAL -and
widely used-, or in the (Geo)TIFF standard.</div>
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GDAL-only concept. See
<a class="moz-txt-link-freetext" href="https://www.awaresystems.be/imaging/tiff/tifftags/gdal_nodata.html">https://www.awaresystems.be/imaging/tiff/tifftags/gdal_nodata.html</a><br>
<blockquote type="cite"
cite="mid:CADRrdKsRGezL3MnjyYf+CsXyQhL5vaTRREWh-fvhEJ58zB2Xkw@mail.gmail.com">
<div dir="ltr">
<div><br>
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<div>Cheers,</div>
<div>Javier<br>
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<div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">.___ ._ ..._ .. . ._.
.___ .. __ . _. . __.. ... .... ._ .__<br>
Entre dos pensamientos racionales <br>
hay infinitos pensamientos irracionales.<br>
<br>
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<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, 2 Jun 2021 at 21:44,
Evert Etienne (SITEMARK) <<a
href="mailto:evert.etienne@sitemark.com"
moz-do-not-send="true">evert.etienne@sitemark.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote">Dear all,<br>
<br>
I was wondering if there is a best practice or guide for the
data type of alpha channels in geotiffs.<br>
I have many files where the data type is constant over all
bands (UInt16 for example). <br>
I would expect the alpha band to be a byte band or even bit.<br>
<br>
Is it possible to have different types in a single file? If
so, can I change the type of the alpha band alone to see if it
has impact on the file size for example?<br>
<br>
Many thanks<br>
<br>
Evert<br>
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<pre class="moz-signature" cols="72">--
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My software is free, but my time generally not.</pre>
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