<div dir="ltr"><div><div><div><div>Hi,<br></div>While investigating on some rendering
issues we have with java JAI based operations involving interpolations, I
have found the topic of bicubic interpolation introducing values
outside of the input dynamic, as well as negative values and
overshooting.<br><br></div>The problem we had was with a grayscale GeoTIFF with noData=0.<br>For
some very dark area (pixel near to zero) the output of the
interpolation was a negative value being clamped to zero (which is
noData).<br></div>So it was introducing noData in regions where all pixels were valid.<br><br></div>Therefore I did a test with gdal_translate -r cubic and I got same result:<br><br><img src="cid:ii_j0uosug41_15b19199afd1610e" width="462" height="141"><br><div>on the left side: original image<br></div><div>on the right side: cubic interpolation <br></div><div>weird white shapes you see on the top right are zero/nodata pixels.<br></div><div><br></div><div>I got different result once using cubic spline instead.<br></div><div>What is the difference between the two algorithms?<br><br></div><div>Second question:<br></div><div>I did a gdal_translate -outsize 800% 800% from a small pixellated image.<br></div><div>is it expected to have output pixels exceeding the original shape of the valid input pixels?<br></div><div>I was thinking the interpolated image pixels should stay within the original pixel edges.<br><br>Let me provide an image to clarify:<br><img src="cid:ii_j0uos8bz0_15b19192a6d0b3e8" width="462" height="118"><br><br><br></div><div>Left image: original<br>Right image: cubic spline.<br>See
how the 2 edges are different, having the cubic spline producing some
kind of buffering on the edge (note the white-missing pixels on the
borders are nodata).<br></div><div><br></div><div>Please, let me know.<br></div><div>Best Regards,<br></div><div>Daniele<br></div><br><br clear="all"><br>-- <br><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span style="font-size:12.8px">==</span><br></div><div dir="ltr"><span style="font-size:12.8px">GeoServer Professional Services from the experts! Visit</span><br style="font-size:12.8px"><a href="http://goo.gl/it488V" style="color:rgb(17,85,204);font-size:12.8px" target="_blank">http://goo.gl/it488V</a><span style="font-size:12.8px"> for more information.</span><br>
==<br>
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