Saâd,<br><br>It is better to have a combined LUT. It will save processing time and data degradation.<br>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.<br>
<br><div class="gmail_quote">On Wed, Mar 21, 2012 at 6:00 AM, Saâd HESSANE <span dir="ltr"><<a href="mailto:saad.hessane@gmail.com">saad.hessane@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Thank's all for your answers.<br>I will use the LUT method, cause is the most right for me.<br><br>Chaitanya said : "Gamma correction is more related to displaying the data than the data itself".<br>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 ? <span lang="en"><span>Or there is</span> <span>a method to</span> <span>declare</span> LUTs <span>in order</span> <span>to</span> <span>execute in the same vrt</span><span> ?</span></span><br>
<br>Thank's again !<div class="HOEnZb"><div class="h5"><br><br><br><div class="gmail_quote">2012/3/20 Brent Fraser <span dir="ltr"><<a href="mailto:bfraser@geoanalytic.com" target="_blank">bfraser@geoanalytic.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
I like to use gdal_contrast_stretch from <a href="http://www.gina.alaska.edu/projects/gina-tools/" target="_blank">http://www.gina.alaska.edu/projects/gina-tools/</a>
<br>
<br>
Usage: gdal_contrast_stretch <src.tif> <dst.tif><br>
{ { -linear-stretch <target_avg> <target_stddev> } |<br>
{ -percentile-range <from: 0.0-1.0> <to: 0.0-1.0> }
|<br>
{ -histeq <target_stddev> } }<br>
[ -ndv <no_data_val> ]<br>
Input must be either 8-bit or 16-bit. Output is 8-bit.<br>
<br>
For example:<br>
<br>
gdal_contrast_stretch -percentile-range 0.02 0.98 input16bit.tif
output8bit.tif
<pre cols="72">Best Regards,
Brent Fraser</pre><div><div>
<br>
On 3/20/2012 9:55 AM, Saâd HESSANE wrote:
</div></div><blockquote type="cite"><div><div>Hi list,<br>
<br>
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).<br>
If I change the destination range (dst_min and dst_max), I can do
manually a brightness correction (also a contrast correction).<br>
<br>
But is there any way to do that with a Photoshop like method?<br>
For example set a brightness to -50, a contrast to +8 and let
gdal_translate do the job ?<br>
<br>
Also can I apply a gamma correction?<br>
<br>
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.<br>
<br>
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...<br>
<br>
So simply put, my question : can I do a contrast, brightness or
gamma correction to a raster with gdal?<br>
<br>
Thank you !<br>
<br>
PS : <span lang="en"><span>I apologize for</span> <span>my</span>
<span>broken English</span><span> !<br>
</span></span>
<br>
<fieldset></fieldset>
<br>
</div></div><div><pre>_______________________________________________
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</div></div><br>_______________________________________________<br>
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<a href="http://lists.osgeo.org/mailman/listinfo/gdal-dev" target="_blank">http://lists.osgeo.org/mailman/listinfo/gdal-dev</a><br></blockquote></div><br><br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>
<br>+91-9494447584<br>17.2416N 80.1426E<br>