[gdal-dev] Does gdal_calc.py not calculate arithmetic with in the same file?

[Vincent Schut]

On 07/29/2014 04:04 PM, Cleo Drakos wrote:
> Thanks for your response.
> I tried the followings:
>
> gcalc = 'C:\\Users\\cleo\\Documents\\gdalpys\\gdal_calc.py'
> ##I produced second file (b)as the copy of first(a)
> a = 'D:\\a.tif'
> b = 'D:\\b.tif'
> outfile = 'D:\\result.tif'
> expr = '(A-B)/(A+B)'
> subprocess.call([sys.executable,gcalc,'-A',a,'--A_band','1','-B',b,'--B_band','0','--outfile',outfile,\
> '--calc',expr,'--type','Float32','--format','ENVI'],shell=True)
> a,b,outfile = None, None,None
>
> Unfortunately, resulted file is completely black.
>
> I hope someone can help me.

I don't use gdal_calc myself, but I suppose the problem is the byte 
datatype. I would try to convert the input data to float32 first (use 
gdal_translate -ot Float32) and try again.

Best,
Vincent.

>
>
> On Tue, Jul 29, 2014 at 10:37 PM, Etienne Tourigny 
> <etourigny.dev at gmail.com <mailto:etourigny.dev at gmail.com>> wrote:
>
>     I am not sure, but you can do the following to make sure:
>
>     cp infile infile2
>     gdal_calc.py -A infile --A_band 1 -B infile2 --B_band 0 --outfile
>     outfile --calc "(A-B)/(A+B)"
>
>     Also, perhaps the extra comma in your command might be to blame
>     "-B infile,"
>
>     Etienne
>
>
>     On Tue, Jul 29, 2014 at 3:46 AM, Cleo Drakos
>     <cleo21drakos at gmail.com <mailto:cleo21drakos at gmail.com>> wrote:
>
>         Hi GDAL Developers,
>
>         I have one GeoTIFF file with 2 bands. The data type is Byte. I
>         want to calculate (Band2-Band1)/(Band2+Band1).
>
>         But the following command provided a dark image:
>
>         gdal_calc.py -A infile --A_band 1 -B infile, --B_band 0
>         --outfile outfile --calc "(A-B)/(A+B)"
>
>         Does gdal_calc.py not calculate arithmetic with in the same file?
>
>         Thanks for your time.
>
>         cleo
>
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