[gdal-dev] Contrast, Brightness and Gamma

[Chaitanya kumar CH]

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 <saad.hessane at gmail.com>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 <bfraser at geoanalytic.com>
>
>>  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 !
>>
>>
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>>
>>
>
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-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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