Hi, I think the method described by Chaitanya in the VRT : "<LUT>[src value 1]:[dest value 1],[src value 2]:[dest value 2]</LUT>" is equivalent to do "-scale srcMin srcMax dstMin dstMax", right? So why when I do "-scale 0 65535 0 120" the output have pixels values greater than 120 ?
Thank you. 2012/3/20 Chaitanya kumar CH <[email protected]> > Saâd, > > Gamma correction is more related to displaying the data than the data > itself. > You can, however, modify the contrast and brightness of the dataset. > > Using LUT is not hard to learn as long as you know what you want. > A simple method is the stretch the data linearly along the whole range. > For that, your LUT element looks like this: > > <LUT>[src value 1]:[dest value 1],[src value 2]:[dest value 2]</LUT> > > There are only four values. > src value 1: This should be the least value of the pixels in the source > raster band. > src value 2: This should be the greatest value of the pixels in the source > raster band. > dest value 1: This should be the least value the data type of the raster > band can hold. That would usually be zero. > dest value 2: This should be the greatest value the data type of the > raster band can hold. That would be 255, 65535 and 4294967295 for 8bit, > 16bit and 32bit raster bands. > > The VRT driver calculates the intermediate values. The result here would > be similar to using the scale ratio and offset parameters. > > On Tue, Mar 20, 2012 at 9:25 PM, Saâd HESSANE <[email protected]>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 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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