[gdal-dev] how to convert UInt16 Tiff

[Brent Fraser]

Another alternative is GINA's 
(http://www.gina.alaska.edu/projects/gina-tools/) gdal_contrast_stretch:

Usage: gdal_contrast_stretch.exe <src.tif> <dst.tif>
   { { -linear-stretch <target_avg> <target_stddev> } |
     { -percentile-range <from: 0.0-1.0> <to: 0.0-1.0> } |
     { -histeq <target_stddev> } }
   [ -ndv <no_data_val> ]
Input must be either 8-bit or 16-bit.  Output is 8-bit.

I think the input can be any GDAL supported raster type.

Best Regards,
Brent Fraser


On 4/24/2012 2:53 AM, jr.morreale at enoreth.net wrote:
> On Tue, 24 Apr 2012 09:38:44 +0200, Even Rouault wrote:
>>>
>>> thanks for the reply, I did try with NBITS=8 and 12 with osgeo4w's gdal
>>> and tamas' nightly build but the output results are incorrect
>>>
>>> Here is a sample file (93Mo) :
>>> http://dl.free.fr/iFT4hH3Yj
>>>
>>> I'll try to rebuild gdal on my linux box with the internal libs
>>
>> I haven't looked at your result image, but you cannot just specify 
>> NBITS=8 or
>> 12, if the range of the values in the original file is full 16 bits.
>>
>> You need to rescale the values, otherwise they will get clamped to
>> [0, 255] or
>> [0, 4096].
>>
>> So you can look for the min/max reported by gdalinfo -mm
>> uncompressed_original.tif
>>
>> and then try :
>>
>> gdal_translate -co "COMPRESS=JPEG" uncompressed_original.tif 
>> compressed.tif
>> -scale min max 0 255 -ot Byte
>>
>> or
>>
>> gdal_translate -co "COMPRESS=JPEG" uncompressed_original.tif 
>> compressed.tif
>> -scale min max 0 4095 -co NBITS=12
>
> Thanks, I didn't knew that !
>
> The man says that you can omit the input min max scale so gdal 
> computes it for each source, however I can't find how to write that 
> correctly
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