Hi,<br><br><span id="result_box" class="short_text" lang="en"><span class="hps">I think the method described by</span> Chaitanya in the VRT : "</span><LUT>[src value 1]:[dest value 1],[src value 2]:[dest value 2]</LUT>" <span id="result_box" class="short_text" lang="en"> <span class="hps">is</span> <span class="hps">equivalent to</span></span> do "-scale srcMin srcMax dstMin dstMax", right?<br>
So why when I do "-scale 0 65535 0 120" the output have pixels values greater than 120 ?<br><br>Thank you.<br><br><br><br><div class="gmail_quote">2012/3/20 Chaitanya kumar CH <span dir="ltr"><<a href="mailto:chaitanya.ch@gmail.com">chaitanya.ch@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Saâd,<br><br>Gamma correction is more related to displaying the data than the data itself.<br>You can, however, modify the contrast and brightness of the dataset.<br>
<br>Using LUT is not hard to learn as long as you know what you want.<br>
A simple method is the stretch the data linearly along the whole range.<br>For that, your LUT element looks like this:<br><pre style="font-family:courier new,monospace"><LUT>[src value 1]:[dest value 1],[src value 2]:[dest value 2]</LUT></pre>
There are only four values.<br>src value 1: This should be the least value of the pixels in the source raster band.<br>src value 2: This should be the greatest value of the pixels in the source raster band.<br>dest value 1: This should be the least value the data type of the raster band can hold. That would usually be zero.<br>
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.<br><br>The VRT driver calculates the intermediate values. The result here would be similar to using the scale ratio and offset parameters.<br>
<br><div class="gmail_quote"><div><div class="h5">On Tue, Mar 20, 2012 at 9:25 PM, Saâd HESSANE <span dir="ltr"><<a href="mailto:saad.hessane@gmail.com" target="_blank">saad.hessane@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
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>
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<br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>
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