Saâd, It is better to have a combined LUT. It will save processing time and data degradation. Be informed that GDAL VRT is not specialized for this work. To get a smooth curve as LUT, use some other graphics application that can handle 16bit rasters.
On Wed, Mar 21, 2012 at 6:00 AM, Saâd HESSANE <[email protected]>wrote: > Thank's all for your answers. > I will use the LUT method, cause is the most right for me. > > Chaitanya said : "Gamma correction is more related to displaying the data > than the data itself". > Not in my case. I have to do this correction. But how to do that? Do i > embed a VRT with a contrast correction LUT, in another VRT with a gamma > correction LUT ? Or there is a method to declare LUTs in order to execute > in the same vrt ? > > Thank's again ! > > > > 2012/3/20 Brent Fraser <[email protected]> > >> I like to use gdal_contrast_stretch from >> http://www.gina.alaska.edu/projects/gina-tools/ >> >> Usage: gdal_contrast_stretch <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. >> >> For example: >> >> gdal_contrast_stretch -percentile-range 0.02 0.98 input16bit.tif >> output8bit.tif >> >> Best Regards, >> Brent Fraser >> >> >> On 3/20/2012 9:55 AM, Saâd HESSANE wrote: >> >> Hi list, >> >> I use gdal_translate to convert 16bits images to 8bits images. The >> gdal_translate have the -scale argument to specify the convertion range >> (source->destination). >> If I change the destination range (dst_min and dst_max), I can do >> manually a brightness correction (also a contrast correction). >> >> But is there any way to do that with a Photoshop like method? >> For example set a brightness to -50, a contrast to +8 and let >> gdal_translate do the job ? >> >> Also can I apply a gamma correction? >> >> I saw the VRT format and there's a way to apply a LUT. But I don't think >> a LUT of 65536 values is the best way to apply the correction. >> >> Also the VRT have the scale ratio and scale offset elements. I think it >> can be useful but I don't understand how use it... >> >> So simply put, my question : can I do a contrast, brightness or gamma >> correction to a raster with gdal? >> >> Thank you ! >> >> PS : I apologize for my broken English ! >> >> >> _______________________________________________ >> gdal-dev mailing >> [email protected]http://lists.osgeo.org/mailman/listinfo/gdal-dev >> >> > > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev > -- Best regards, Chaitanya kumar CH. +91-9494447584 17.2416N 80.1426E
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