[gdal-dev] gdal_translate to TIFF -- color mismatch

[mladen-g at distributel.net]

Wow, that was fast.  Thanks!

I see that the fix is in 1.8.2... Do you know will this be a separate  
release or will the fixes be merged into 1.9.0?  I ask because I see  
some recent discussions suggesting that 1.9.0 may be released by the  
end of the year.

Thanks again for the quick response,
Mladen


Quoting Even Rouault <even.rouault at mines-paris.org>:

> Le jeudi 15 décembre 2011 18:08:26, mladen-g at distributel.net a écrit :
>> Hi all,
>>
>> I am trying to use gdal_translate to convert a .grd file
>> (Northwood/VerticalMapper format) to TIFF.  However, the colors in the
>> translated file don't seem to be interpolated correctly based on the
>> color scheme, for values near the end of the range.
>>
>> Here is a link to the original GRD, as well as the exported TIFFs
>> (small download, only 200K):
>> http://dl.dropbox.com/u/53500018/GdalQuestion.zip
>>
>> The GdalTranslateExport.tif file was produced with the command
>> "gdal_translate -b 1 -b 2 -b 3
>> C:\source\Ottawa_east_DEM30m_trim_copy.grd
>> C:\temp\GdalTranslateExport.tif".
>>
>> Notice the top and bottom areas of the image:  they are yellow.  For
>> comparison, take a look at the NativeExport.tif file in the same
>> package.  The top and bottom areas are orange, as they should be.  The
>> NativeExport.tif file was produced by Pitney Bowes MapInfo.
>>
>> Here is the color scheme for the GRD:
>> http://www.smugmug.com/photos/i-bRZ879w/0/X3/i-bRZ879w-X3.jpg
>>
>> Notice that the thresholds are "70" for yellow, and "161" for orange.
>> Well, the values at the top and bottom are in the high 130s/low 140s.
>> So they should be interpolated close to orange, not yellow.  Therefore
>> the NativeExport.tif is correct, and the gdal_translate export is
>> incorrect.
>>
>> I have also tried changing the thresholds, and as soon as I change the
>> orange threshold to be below the maximum actual value in the GRD
>> (let's say 144), the gdal_translate export shows the orange shades.
>
> Good analysis. There was indeed a bug in the way the end of the color palette
> is interpolated if the maximum z value is below a threshold of the color
> scheme. See http://trac.osgeo.org/gdal/ticket/4395 for the fix (a  
> simple typo)
>
>>
>> So, it seems there might be a bug in gdal_translate where color values
>> are not interpolated correctly for thresholds that fall outside of the
>> range of actual values?  Or is there a way to make gdal_translate
>> behave the way that I want with some different command line options?
>>
>> Regards,
>> Mladen Gavrilovic
>>
>> P.S.  For convenience, here is a gallery with the TIFFs converted to
>> JPEG (difference is still obvious), and the color scheme:
>> http://smu.gs/vMEemF
>>
>> P.P.S  Version of GDAL is 1.8.1
>>
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